4x4Wire TrailTalk

Custom driveshaft vibrations

Posted By: Ian Sharpe

Custom driveshaft vibrations - 10/08/15 08:23 AM

Hi guys,

When I put the dual transfer cases in my Pajero, I had 2 custom shafts made up, front & rear.

They both had to go back for a rebalance & the front one went back for a rebuild as it had 40thou runout.

The rear shaft has 11 thou runout at the transfer case end & the front one still has 12 thou run out.

I still have vibes when I run the car in 4wd highway mode, no vibes that worry me when I run in 2wd with front axle disconnected.

Heres my theory,

Most sources seem to indicate that 12 thou is 'within spec' for run out tolerance on driveshafts.

If so then why do I have vibes in 4wdh? My theorey is that whilst one shaft with 12 thou runout may not produce vibes, 2 shafts with 12 thou runout each however running at the same time, tip me over the tolerance level & hence I get vibes? What do you guys reckon?

The driveshaft guys say they cant get the tolerance any lower (cheap arses they are), so I am in discussion atm with Tom Wood over in the US to make me a custom front shaft.

I also believe that others who have done this mod, ie dual cases, have used the NP231 which doesnt have the highway 4wd mode, so shaft vibrations may not have reared their head since the NP231 doesnt run in 4wd on the highway. Does this sound reasonable/

cheers


Posted By: 4x4Wire

Re: Custom driveshaft vibrations - 10/08/15 03:06 PM

I'm not sure what you mean by "4wd highway mode". The NP-231 is a dual range t-case with many applications.

As you have a dual t-case setup, I would look into driveline angle for your source of vibration, especially as the vibration occurs in 4wd.

Another possibility would be the vibration coming from within the T-case or the output shaft.

Use the site search at the top of the page to see several 4x4Wire article dealing with driveline angle like the link below...

http://www.4x4wire.com/tech/pinionangle/
Posted By: danz91crx

Re: Custom driveshaft vibrations - 10/08/15 03:27 PM

Whats speeds do you get vibration at?
Posted By: Ian Sharpe

Re: Custom driveshaft vibrations - 10/09/15 12:00 AM

by 4wd highway mode I mean 4wd high range with the centre diff unlocked. I think you guys call it Active Trac. AFAIK the NP231 does not have a centre diff?

The vibes kick in around 80kph

Driveline angles are not excessive, in fact quite mild.

I just need to know if I should get Tom to make a shaft that has less that 12 thou runout
Posted By: 4x4Wire

Re: Custom driveshaft vibrations - 10/09/15 05:41 AM

Okay, got it. There are several variants of the NP-231 and the NP-241 with creative names like Select Trac and Command Trac.

Anyway, your issues is with vibrations when you hit 80 kph (about 45-50 mph is I have the conversion right).

Tom Woods does produce a quality drive shaft. I am sure he can make one that is within tolerances.

As you have mild driveline angles, there are other factors that have could be contributing to you vibrations. I recall some past threads about vibration in the forums. Search for "driveline vibrations".

I have had vibration issues that were resolved by replacing the transfer case mount. I like to look for the simple (cheap) solutions before swapping high cost parts....
Posted By: danz91crx

Re: Custom driveshaft vibrations - 10/09/15 05:51 AM

You could tell the original guys and see if they'll balance them again. I'd check the u joints for any play before they do. Something seems off if the second time you got the shafts back when they balanced them you had less vibration.
Posted By: Ian Sharpe

Re: Custom driveshaft vibrations - 10/09/15 08:08 AM

Tks guys, one thing I didn t make clear was that I am running an NP242 which is very different to the NP231, mine has a centre diff that can be unlocked & run in 4wd mode on the highway.

Sorry I didnt specifically say this.
Posted By: 4x4Wire

Re: Custom driveshaft vibrations - 10/09/15 12:58 PM

Figured that after your clarification of terms. Like I said, the NP-231 and NP-241 are basically similar. There are severel model variants, mostly with internal gear ratios.

The NP-241/2 is known in the Jeep world as Command Trac and is a full time 4x4. The NP-231 is the most common.

Again, when you lock it into 4x4, you are fully engaging the front drive. If you get vibrations then, the factors are driveline angle, driveline balance, worn bearings, u-joints, front tire balance and alignment, loose or worn spring hangers. If the runout you measure is within factory specs, I would eliminate all other factors before focusing on the driveline.

I overlooked the question of where (how) are you feeling the vibrations? You said the when. If you feel it in the steering wheel, I would focus on the steering components such as tire balance, ball joints, and steering linkage. If you feel it in the console (at the shift lever) I would focus on mounting issues.

I have experienced vibrations due to driveline balance, worn u-joints, t-case mounting, and tires. Tires can be fine at low speed but cause vibration at high speed due to internal issues where the steel-belt is off center.

Posted By: Ian Sharpe

Re: Custom driveshaft vibrations - 10/09/15 08:11 PM

Thanks mate,

all was fine before the conversion to the NP242, ie I had no vibes from the front or the rear. Thus I can eliminate most of the usual causes.

The only thing I can really put it down to it the front shaft given that it does have 12 thou runout. I guess I am just gonna have to bite the bullet & get Tom to make a shaft for me.
Posted By: TOASTY

Re: Custom driveshaft vibrations - 10/09/15 11:45 PM

I made a rear driveshaft in my garage with .006 runout and I never had it balanced. I didn't notice any vibrations so I just let it ride. I think the shop is giving you the shaft... They possibly cheaped out on the front shaft because they mostly don't turn all the time and they probably don't know you're running AWD.
Posted By: Ian Sharpe

Re: Custom driveshaft vibrations - 10/10/15 01:41 AM

Thanks Toasty, pretty clever machining there by you to get that result.

You could be right.

I think I will just get Tom to make me a shaft & be done with it.

Posted By: ES_97Sport

Re: Custom driveshaft vibrations - 10/23/15 12:43 AM

Originally Posted by Ian Sharpe
all was fine before the conversion to the NP242, ie I had no vibes from the front or the rear. Thus I can eliminate most of the usual causes.

The only thing I can really put it down to it the front shaft given that it does have 12 thou runout. I guess I am just gonna have to bite the bullet & get Tom to make a shaft for me.


Hey, Ian. What kind of shafts are you running? CVs at the t-case outputs with u-joints at the diffs? You're running a solid front DS, correct? Not a two-piece like mine? Is the front DS a slip drive shaft?

What kind exactly and WHEN exactly do you get the vibration in 4WD. On acceleration, deceleration, steady cruise? At what speed? Does it steadily build? Or does it hit 55 and then start up?

"Driveline angles are not excessive, in fact quite mild."

Excessive/mild doesn't necessarily have anything to do with it. Drive line angles change over time.

If you've ruled out everything obvious noted above, its time to check and make sure everything still points where it should. smile When I have fresh springs, everything points exactly where it should, but after a couple years I start getting drive line vibration because the springs eventually sag as does transmission mounts, engine mounts.

Edward
Posted By: Ian Sharpe

Re: Custom driveshaft vibrations - 10/24/15 09:04 AM

hi Ed,

Both shafts have a double cardan at the transfer case & standard unis at the diffs.
Both shafts have a slip joint on the diff end.

Vibes come in around 80kph, seem to be more on deceleration.

I had all my angles assessed by a truck shop & have sent that info to Tom Wood. Interesting that the truck guy assesed the run out at 35thou on the front & 24 thou at the rear.
Thats more than my dial gauge said.



cheers
Posted By: ES_97Sport

Re: Custom driveshaft vibrations - 10/29/15 12:46 AM

Originally Posted by Ian Sharpe
Both shafts have a double cardan at the transfer case & standard unis at the diffs.
Both shafts have a slip joint on the diff end.


Ok, I thought so. I wasn't sure if you'd changed anything.

Quote
Vibes come in around 80kph, seem to be more on deceleration.

I had all my angles assessed by a truck shop & have sent that info to Tom Wood. Interesting that the truck guy assesed the run out at 35thou on the front & 24 thou at the rear.
Thats more than my dial gauge said.


I strongly doubt very much run out has anything to do with this. That would be a constant and accel/decel wouldn't make any difference.

IMHO, you need to be talking to someone(s) else about drive shafts or have someone else do them for you. This isn't that complicated and from what I've read of your thread, you're having to jump through a lot more hoops than you should.

What's probably the issue is you have one or more CVs that are in need of rebuilding. However, from your description, it sounds to me like you have one that's getting close to needing rebuilt and you have one drive shaft that's either out of align or not aligned properly.

Since you didn't have the problem originally if I remember correctly, its probably going out of align. By 'out of align' I mean that your pinion is shifting enough to throw your drive shaft angle off.

That would explain the decel vibration but no cruise or accel vibration, because when you take your foot off the brake, the pinion is going to try and rotate the opposite direction from what it would normally do.

That means pinion angle wasn't set quite correct originally OR it was set right on the hairy edge and you've had enough wear and tear that the pinion angle is shifting JUST ENOUGH now that you're getting vibration. Over time this can easily happen - its how I know when my leaf springs are close to needing replaced.

A CV just starting to need rebuilding will give you that steady low level almost untraceable constant vibration. Put the two together and that sounds like what you described. Something else, too, if someone didn't rebuild a CV correctly, you'll get the same thing.

Quicky test - pull the front drive shaft, drop it in 4HI, and drive it around and see what happens. Replace the front and drop the rear and repeat. That'll tell you straight up whether I'm right or not and which ones doing what. Obviously, make sure you don't do this in AWD mode. laugh

Edward
Posted By: Ian Sharpe

Re: Custom driveshaft vibrations - 10/29/15 08:29 AM

Tks Ed,

I dont see how the pinion could be out, it was OK before I did the transfer case swap.

I have tried it without the front shaft & its all good. Ive also tried it without the rear & it still gives the vibes.

I have sent all the info to Tom Wood for the angles etc. One of the things to come out of having the angles measured is that that because I had to clock the transfer case upwards a bit to clear the front torsion bar, that has got the front yoke pointing upwards at 5.5 deg. It then meets a downward pointing driveshaft of 3.4 degs, so that operating angle is 8.9 degrees.
Posted By: ES_97Sport

Re: Custom driveshaft vibrations - 11/03/15 12:25 AM

Originally Posted by Ian Sharpe
... others who have done this mod, ie dual cases, have used the NP231 which doesnt have the highway 4wd mode, so shaft vibrations may not have reared their head


Nope, if anyone tells you this that's BS. Even with the crazy angles I'm running with the SAS and the pasted together SYE on the front output of the Mitsu t-case, I could run 55-60 MPH in 4WD on the highway and it was so smooth you couldn't tell it was in 4WD.

Originally Posted by Ian Sharpe
I dont see how the pinion could be out, it was OK before I did the transfer case swap.

I have tried it without the front shaft & its all good. Ive also tried it without the rear & it still gives the vibes.


No worries. It doesn't take much; sometimes all it takes is a bushing or mount sagging a little or loosening up to through everything off. In your case, since you're running IFS in the front, that's unlikely. smile

Ok. That means that the problem is in the front drive line. That narrows it down.

Quote
... One of the things to come out of having the angles measured is that that because I had to clock the transfer case upwards a bit to clear the front torsion bar, that has got the front yoke pointing upwards at 5.5 deg. It then meets a downward pointing drive shaft of 3.4 degs, so that operating angle is 8.9 degrees.


Ok, so ... you did what I got away from by running the split drive shaft. My front output yoke points up, too, but with the split drive shaft, by the time I'm to the CV, its flat with the frame.

5.5 degrees upward at the front output yoke, then downwards 3.4 degrees to the differential pinion. And, you have a CV at the transfer case and a U-joint at the differential. Starts about 80KPH and its an existing problem since the conversion.

Now, I have a question. How does the pinion, u-joint and CV line up? This isn't a u-joint/u-joint setup. The pinion should be in align with the drive shaft. You should be able to draw a straight line through the pinion, u-joint and drive shaft. The angle in a CV setup is handled by the CV, not the u-joint.

If you clocked the t-case either clockwise or counter clockwise from EXACTLY the OEM t-case output location, then the pinion is out of align. That means you would need to do one of two things.

1) Rotate the differential until the pinion is lined up with the drive shaft, OR ...
2) Clock the t-case until the pinion is back in align with the drive shaft

#1 is easier. smile smile

So the question is, what's the angle between your pinion and drive shaft? 'cause in IFS, that should be zero.

<edit> No, actually I think zero is incorrect. I think that should be +1 or MAYBE +2 degrees.

Neither CV or u-joints are too picky, and neither is the CV/u-joint setup. Until you start trying to do what you're doing. IME, 50 MPH is about where things start showing up if things aren't quite in align just right.

Edward
Posted By: Ian Sharpe

Re: Custom driveshaft vibrations - 11/04/15 07:04 AM

Ed,

I cant change the pinion angle & I cant clock up or down, the floor is in the way at the top & the torsion bar is in the way at the bottom. Its clocked in the only position it can go.

The front pinion isnt in line with the case or shaft.

Here are all the angles I had done by a truck shop.

Driveshaft

Speaking to Tom Wood , he has suggested a shaft with a double cardan at the yoke & a double cardan at the diff. I have sent him a Pajero front pinion flange & he is going to make me a shaft.

cheers
Posted By: ES_97Sport

Re: Custom driveshaft vibrations - 11/05/15 01:20 AM

Originally Posted by Ian Sharpe
I cant change the pinion angle & I cant clock up or down, the floor is in the way at the top & the torsion bar is in the way at the bottom. Its clocked in the only position it can go.

The front pinion isnt in line with the case or shaft. ....


The front differential pinion has to be inline with the drive shaft. That's it. Not the case, the shaft. Looking at your diagram - if I'm reading it correctly - you need to rotate the front differential 2.3 degrees counter clockwise when viewed from the driver side.

I don't understand. I know you can't clock the t-case, but that's not where the problem is. You need to rotate the front differential. How can you not do that? There shouldn't be anything in the way that would prevent that. All you should have to do is modify the brackets that hold the front differential or make new ones.

That seems to be Tom's solution to everything. I talked to him several years ago. He wanted to do the same thing to mine. Ended up spending $500 here on the solution you have now - only my stuff is aligned correctly. Did he bother to tell you that that solution is more prone to vibrations than what you have now?

Edward
Posted By: Ian Sharpe

Re: Custom driveshaft vibrations - 11/05/15 08:45 PM

Ed, rotating the front diff would be a big job,

No Tom didnt say that 2 doubles would cause more vibes, can you expand on that. He has a reputation for quality work, you dont seem confident in him.?
Posted By: ES_97Sport

Re: Custom driveshaft vibrations - 11/06/15 01:21 AM

Originally Posted by Ian Sharpe
Ed, rotating the front diff would be a big job,


I'll take a look at the FSMs tonight. I want to see a breakdown of the front axle assembly but from what I remember ...

There are two brackets that bolt the differential housing to the sub-frame. What you need to do is figure out how much you need to rotate the housing to get the 2.3 degrees, pull the front differential assembly, take the brackets off, weld up the original bolt holes and then re-drill new holes in the appropriate locations. And you're not going to be able to do this with a hand drill. smile If the bracket setup is like the Sport with both housing brackets at the housing, you shouldn't need to build anything up. I think I remember some Montero's have the PS bracket at the end of the axle tube rather than at the housing. That one may need to be built up.

OR, you can look at shimming the brackets at the sub frame to get the rotation. Sometimes that's possible depending on how its mounted to the sub-frame.

So, yep, I have a pretty good idea. smile Its not as bad as it sounds, though. I think I'd rather do that then pull the t-case, doubler and transmission. smile smile

Quote
No Tom didn't say that 2 doubles would cause more vibes, can you expand on that. He has a reputation for quality work, you don't seem confident in him.?


Yep, he does. But every time I mention his name here to drive shaft guys they roll their eyes. He had me 98% convinced to do the double Cardan setup you're talking about. When I talked to the local shop that usually does my drive shafts, they rolled their eyes and told me that was ridiculously over the top, expensive and unneeded. I told them the same thing you wrote because that's the impression I had. All they'd say is, yes, he does good work, but its usually ridiculously complicated and expensive.

I'd be maybe willing to doubt the shops here, but I've never had them be wrong and Tom right. And, I've read too many posts on Pirate that all echo the same thing.

I don't remember all the little details. I was addressing this 5-6 years ago. What I do remember is that the shop strongly disagreed with running a double cardan setup on the street at high speeds. That with two joints I would be MORE likely to have high speed vibration. It has to do with having two big floppy joints vs a u-joint and cardan. The u-joint/drive shaft alignment holds the Cardan in place, so to speak. That doesn't happen as well as with a double Cardan.

And there is also the fact that Cardan's wear and are expensive to rebuild. Something to think about.

I know what I'm talking about is a pain, but its cheaper in the long run and based on my experience, I know that won't cause vibrations. I can run my rear drive shaft with a Spicer Cardan and a 1310 up to 5K RPM at 85 MPH and its absolutely glass smooth. I have NEVER talked to anyone with a Jeep and the double setup that can do that. So, YMMV. smile

Edward
Posted By: Ian Sharpe

Re: Custom driveshaft vibrations - 11/06/15 06:51 AM

ok thanks Ed, I've been doing a bit of internet research & most of the opinions out there are against multiple cardans,i think I will just stick to a double at the yoke end & a single at the diff.

I still think my custom shaft I had made here is a dud, the double cardan seems a bit stiff to me & it has too much run out for my liking.

cheers I'll let you know how it all goes
Posted By: ES_97Sport

Re: Custom driveshaft vibrations - 11/07/15 12:06 AM

Originally Posted by Ian Sharpe
ok thanks Ed, I've been doing a bit of internet research & most of the opinions out there are against multiple cardans,i think I will just stick to a double at the yoke end & a single at the diff.


Yea. It finally started coming back to me on the way home last night. smile

There are three different configurations for drive shafts. Two u-joints - one on each end, Cardan and u-joint - one on each end, and a Cardan on each end.

Level of potential for vibration/vibration follows that order with the first being the least likely and the last being the most likely. If at all possible, you ALWAYS want to use the first, followed by the second if the 2 u-joint setup won't work, followed by the last if NOTHING else works.

And, never use a double-Cardan joint setup for high-speed highway use. Such as in a NP242 AWD setup. smile

As explained to me, the u-joint and drive shaft stabilize the Cardan joint. That's what makes this setup work on the highway at high RPM. Its like having a rotating solid shaft attached to the end of the Cardan joint. It minimizes potential vibration through the pinion/u-joint/drive shaft and stabilizes the Cardan joint.

Quote
I still think my custom shaft I had made here is a dud, the double cardan seems a bit stiff to me & it has too much run out for my liking.


Hmmm. Don't know there. I think all your worrying about run-out is for nothing. The tech that works on my Sports at the dealership built his drive shafts at home for his Truggy. He swears he can run it at 60 down the highway and there's not a hit of vibration. I'm pretty sure the 'run-out' on his shafts isn't down to specs you were quoting. smile

If it were me, I'd bite the bullet and align the front diff correctly. If I put that much work into something and then had to live with an unnecessary vibration, I'd go nuts. smile smile

Edward
Posted By: Ian Sharpe

Re: Custom driveshaft vibrations - 11/09/15 11:45 PM

i'll see how Toms shaft goes first.
Posted By: Ian Sharpe

Re: Custom driveshaft vibrations - 11/11/15 02:34 AM

I think this shaft is well & truly F A R K E D.

I have been hiding the front vibes by running the vehicle in 2wd with the front axles disconnected via the vacuum system.

This has allowed me to get around daily without vibes until I can get a new shaft built.

Well today I went on a long drive 70k & back to town & the vibes were really bad. So I stopped off at the local tool shop & bought the spanners I needed to take the front shaft off. I'm getting good at taking it off now!. Took it off & what do you know , vibes gone.

So I reckon the unis may be stuffed which is not very good considering its all supposed to be NEW. So it may be a case of dodgy parts rather than anything else.

Anyway , hope Tom can come good for me with a new shaft.


Posted By: Ian Sharpe

Re: Custom driveshaft vibrations - 01/07/16 06:10 AM

Originally Posted by ES_97Sport
[quote=Ian Sharpe]
The front differential pinion has to be inline with the drive shaft. That's it. Not the case, the shaft. Looking at your diagram - if I'm reading it correctly - you need to rotate the front differential 2.3 degrees counter clockwise when viewed from the driver side.

Edward


Hey ed, looks like I spoke too soon on the driveshaft problem. The shaft Tom made for me has certainly improved the problem but I still have a vibe (annoying vibe) between 85-95 kph. Its more noticeable on deceleration or coasting & produces a hum as well. I didnt notice it before as I hadnt really taken it for a long run only a short one.

So now I am back to chasing the problem. Can you elaborate on your suggestion above to rotate the front diff. When you say 2.3 degrees I am assuming you mean rotate the diff upwards 2.3 degrees. How did you come to that figure?

I am now wondering if I have something out of alignment in the front end, maybe bad bearing or cv??

My plan would be to swap over the entire front end with one in my spare car that I know is good. It has to be the entire front end as you cant mix & match cv shafts between 97 & 99 as they had different lengths. Plus I need to redo the ball joints as well as all the bushes as I have a bad squeek & groan from the left side. If I have everything out , I can move the diff upwards & re weld the brackets, but need more info on this, thanks

Posted By: ES_97Sport

Re: Custom driveshaft vibrations - 01/08/16 10:06 PM

Originally Posted by Ian Sharpe
Hey ed, looks like I spoke too soon on the driveshaft problem.


Dang. frown Sorry to hear that Ian. I was hoping from your last post that the new DS had taken care of that. frown

Quote
The shaft Tom made for me has certainly improved the problem but I still have a vibe (annoying vibe) between 85-95 kph. Its more noticeable on deceleration or coasting & produces a hum as well. I didnt notice it before as I hadnt really taken it for a long run only a short one.



Quote
So now I am back to chasing the problem. Can you elaborate on your suggestion above to rotate the front diff. When you say 2.3 degrees I am assuming you mean rotate the diff upwards 2.3 degrees. How did you come to that figure?


I took your numbers for pinion angle on the front diff, drive shaft and so on and did the math to figure out how much you'd have to rotate the front differential to get the pinion to point directly inline with the drive shaft.

Quote
... because I had to clock the transfer case upwards a bit to clear the front torsion bar, that has got the front yoke pointing upwards at 5.5 deg. It then meets a downward pointing driveshaft of 3.4 degs, so that operating angle is 8.9 degrees.


But, now I can't figure out how I came up with that number either! confused laugh

A perfectly horizontal pinion is 0 degrees. Rotated down would be negative and rotated up from 0 would be positive.

The 8.9 degree operating angle doesn't make any difference if you're running a CV at the t-case. And that's where you want the CV, BTW.

The front drive shaft is at -3.4 degrees. As I pointed out before, the CV/U-joint drive shaft needs the pinion-u-joint-drive shaft in line. The diff would have to rotate the pinion enough to make that happen.

I don't know what the front differential pinion angle is now, but it you assume it is 0 degrees, you'd need to rotate the pinion up 3.4 degrees to get it in line with the drive shaft.

If the pinion is +1 degree, then you'd need to rotate it +2.4 degrees - the difference between 3.4 degrees and 1 degree.

+2.4 = 3.4 - 1

Now, this is just the static math. Usually there is a degree 'off-set' figured in, to take into account torque rotation under power. When you apply force to a differential it tries to rotate one direction or the other depending on whether the gear box is in forward or reverse which changes pinion angle.

There isn't a hard and fast rule here for how much (in degrees, or fractions of a degree) you add or subtract because it totally depends on how much stuff rotates when the vehicle is in motion. For instance, I get a lot of pinion shift in the back axle because I have a heavy vehicle and run leaf springs with big tires and a LOT of gearing. The amount of pinion shift would be much less with a link suspension where differential rotation is strictly controled. So, you can't just say, "Do the math and add 1 degree and you're good." smile

Obviously, you don't have front housing rotation because that's IFS. You DO, however, have engine/transmission/t-case rotation. This is kind of a sucky configuration from a math standpoint because normally the differential would rotate up when the t-case rotated up as gas was applied and things would kind of stay in the same line, but you have one moving point and one static point.

I know how to calculate this, but I don't know how to get the data. What you need to know is how much the DS angle increases when the vehicle is under steady state cruise, with the vehicle at its average loaded weight and the tire pressure set where you normally run it (with the tires you normally run). On mine that would be, say, 115 KPH. About 70 MPH. That's where mine spends 95% of its time on the highway and where the most gas pedal is applied to maintain that speed.

So, if the t-cases rotates up and increases the DS angle from -3.4 degrees to -4 degrees, again assuming the pinion is at +1 degrees already ....

+3 = 4 - 1

The front differential would have to be rotated +3 degrees.

The techs can't guess this accurately, and they have a LOT more experience than I do so I'm not even gonna try giving you a number. I drive a M/T so I COULD measure the rotation using the M/T gear shift lever, figure the distance from the drive train center line to the top of the gear shift, measure DS center line to the center line of the t-case output and get the front DS angle increase that way. Being that we run the same DS assembly the static math would be relatively accurate - but all this depends on how much flex and opposing force is involved and that would be where the math totally falls apart.

We're talking about very small numbers so if the drive train is pretty stable and you don't have much movement of the t-case, you MAY well be able to do the simple math - line the DS and pinion straight up - and call it a day. Maybe.

I think if I were doing this I'd put your vehicle on a pad, put a jack under the output end of the t-case and jack it up 1". Simulate t-case rotation. Measure the front DS angle. I would guess that the DS angle @ 1" would be what you'd want to use as your DS angle for the math to figure out how much the differential needs to be rotated. But, if you think the t-case shifs up more than 1" - say, 1.5" - then jack it up that far. You have a one piece drive shaft and that's pretty long so the change in DS angle shouldn't be that much (in degrees).

Quote
I am now wondering if I have something out of alignment in the front end, maybe bad bearing or cv??

My plan would be to swap over the entire front end with one in my spare car that I know is good. It has to be the entire front end as you cant mix & match cv shafts between 97 & 99 as they had different lengths. Plus I need to redo the ball joints as well as all the bushes as I have a bad squeek & groan from the left side. If I have everything out , I can move the diff upwards & re weld the brackets, but need more info on this, thanks


Maybe. I wouldn't rule it out, but what you've described sounds like drive line. You could pull the front DS and try it again, but the last time you said that when you did that the vibration went away.

Edward


Posted By: Ian Sharpe

Re: Custom driveshaft vibrations - 01/09/16 12:52 AM

thanks Ed,

having another look at the angles

Drive angles

it would appear that 2.3 degree up tilt of the front diff would bring the diff onto the same aligment of the shaft, so maybe thats how you calulated it/

But using that theorey , then shouldnt my rear shaft be vibrating as well as it has a difference of 1.8 degrees alignemnt. the rear shaft does not vibrate.

maybe there is some problem in the front end after all.
Posted By: Ian Sharpe

Re: Custom driveshaft vibrations - 01/11/16 10:32 AM

Originally Posted by ES_97Sport

The front pinion isnt in line with the case or shaft.

The front differential pinion has to be inline with the drive shaft. That's it. Not the case, the shaft. Looking at your diagram - if I'm reading it correctly - you need to rotate the front differential 2.3 degrees counter clockwise when viewed from the driver side.
Edward


Ed,

Ive been thinking hard about this. The pinion points up at 1.1 degrees & the driveshaft then goes up 3.4 degrees from that.

You said rotate the pinio up by 23. degrees , but dont forget that as the pinion goes up then the shaft angle also decreases as they are joined together. So I reckon I only need to rotate the pinion up by 1.1 degrees , so that the pinion goes up to 2.2 & the shaft comes down to 2.3 (nearly identical).

How does that sound?
Posted By: ES_97Sport

Re: Custom driveshaft vibrations - 01/11/16 09:14 PM

Originally Posted by Ian Sharpe
[quote=ES_97Sport]
The front pinion isnt in line with the case or shaft.


Correct. Right now its close to horizontal - +1.1 as you have noted below.

Quote
The front differential pinion has to be inline with the drive shaft. That's it. Not the case, the shaft.


Correct. For a CV/u-joint drive shaft setup, the pinion is inline with the drive shaft. In other words, you'd be able to draw a straight line along the center line of the drive shaft and pinion, straight through both.

Quote
Looking at your diagram - if I'm reading it correctly - you need to rotate the front differential 2.3 degrees counter clockwise when viewed from the driver side.

Ive been thinking hard about this. The pinion points up at 1.1 degrees & the driveshaft then goes up 3.4 degrees from that.

You said rotate the pinio up by 23. degrees , but dont forget that as the pinion goes up then the shaft angle also decreases as they are joined together. So I reckon I only need to rotate the pinion up by 1.1 degrees , so that the pinion goes up to 2.2 & the shaft comes down to 2.3 (nearly identical).

How does that sound?


You're putting to much into the math. I am trying to keep this REALLY basic for the sake if illustration. That 2.3 degree number isn't accurate. If you really need to figure the rotation mathematically, you need ...

1) The length of the "pinion". This is the distance measured from the center line of the axle shafts to the exact center of the u-joint along the center line of the pinion.

2) The distance from the axle shaft center line to the "pinion" center line and whether the measurement is from above the axle center line or below (+/-).

3) You need the length of the drive shaft measured from the center of the pinion u-joint to the center of the Double Cardan u-joint connected to the drive shaft.

And then you need to do a lot more math than I've shown. smile And it the answer still wont' be exact. I don't know what any of these measurements are so I can't begin to give you an exact number of degrees.

This is one of those things where figuring out all the math ahead of time takes more work than fixing the issue. smile smile

Edward
Posted By: Ian Sharpe

Re: Custom driveshaft vibrations - 01/15/16 11:20 PM

Ed,
well after a lot of trial & error I finally got it balanced by myself.

The first thing I did was take apart the slip joint & moved the splines to 4 different spots at 90 degrees apart until I felt the least vibration. Funny but the least vibes were not in the original position but rather 90 degrees off.

Next step was to strap on a 35 gram weight to the front in 4 different spots until the vibes improved. they did at one spot but still some there.

So I strapped on a 35 gram weight at the transfer case end in 4 different spots but didnt get any joy from that. Then finally as a last resort I machined up a 50gram weight & strapped that on at one spot. Voila ! No more vibes, I couldnt believe it after all the mucking around. So I fine tuned it a bit by moving it a couple of centrimetres either way of that spot , & finally settled on one spot .


SO thats it , although I am sure that the shaft was balanced 'on the lathe' once it was fitted it vibrated , so now I have 2 hose clamps on both ends with weights under them.

I now need to make up new weights with the weight of the clamp screw added which was 14 grams. & then weld them on.

I cant believe I fluked this finally. I guess there are some inbalances in either the transfer case or front diff ,but I finally got it!
Posted By: ES_97Sport

Re: Custom driveshaft vibrations - 01/18/16 07:49 PM

Originally Posted by Ian Sharpe
... I cant believe I fluked this finally. I guess there are some inbalances in either the transfer case or front diff ,but I finally got it!


Cool! Glad you finally got it! That's interesting. I've never had a drive shaft off by that much. I'm on set #3 and they've always balanced out perfectly.

Edward
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