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Brakes: Lift and rear brakes. Proportioning valve after rear life. #262349 12/05/01 09:50 PM
Got a look under my Pajero today and I've discovered a thing that looks like a rear brake limiter (well, I've installed personally my new coils some months ago and I haven't noticed that thing); I mean, a valve on the brake circuit actuated by the droop of the rear axle.<P>Ok, I think that with the 2" of lift the valve is partially closed even if I'm not braking and there is no weight transfer to the front. And I think that while I'm braking the valve is completly closed, so rear brakes don't work. And so I always have locked front tyres and rearend wagging (without rear locked tyres) on hard braking.<P>Well, now the question: what about a fix?<P>Thank you guys.<P>Disma

Last edited by DougH; 12/29/04 03:03 AM.
Re: Lift and rear brakes #262350 12/05/01 11:42 PM
Disma,<P>What you're looking at is called a Load Sensing Proportioning Valve (LSPV). To correct for the lift, you need to bend or modify the mechanical linkage so the linkage is on the same angle as it was before the lift. If you don't know the prior measurement, you'll have to guess.<P>Not attending to this will produce the exact result you are describing, soon followed by front brake rotors that are warped from being constantly overheated.<P>DougM

Re: Lift and rear brakes #262351 12/06/01 11:37 AM
Wow! This got me worried [img]images/icons/confused.gif" border="0[/img] - have I been driving for the last year with bad rear wheels breaking ability? I haven't looked under my Pajero yet (99 GLX, 2.8TDI, LWB) so I don't know if it has this gudget.<P>Do you have more information? Pictures?<P>Dror [img]images/icons/confused.gif" border="0[/img]

Re: Lift and rear brakes #262352 12/06/01 01:19 PM
I would like to know more info too. I just lifted my Montero and would like to know how to fix this. Does anyone else out there know about this problem?

Re: Lift and rear brakes #262353 12/06/01 03:43 PM
Joined: Oct 2001
Posts: 3,169
mrGUY Offline
Roll Me Over
Doug, I haven't looked this up, so my homework isn't done- [img]images/icons/frown.gif" border="0[/img] But is this on newer models only? Or has this been a standard part of the braking system right along? I've never experienced a braking problem on any of my gen1s.<BR>Guy

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Re: Lift and rear brakes #262354 12/06/01 04:23 PM
Whoops, don't mean to start a panic on this but it is definitely an issue if you have one and lifted your truck without modifying it.<P>As for Gen 1's, I cannot recall if mine had one or not. It's pretty easy to tell if you have one. Simply lay under the rear axle and look at where the brake line comes from the front of the vehicle. Before the brake line splits to each rear wheel, look for a valve that is physically connected to a rear suspension arm or the axle housing itself by a metal link. <P>What it does is quite simple. The metal link changes angle as the rear of the vehicle is loaded more and more heavily - such as when you're packed for a trip. This tells the valve to proportion more and more braking force to the rear wheels. The default position when the truck is empty sends the minimum amount of braking force to the rear, which prevents rear wheel lockup.<P>If you lift the truck, the LSPV is sending the minimum amount of braking force to the rears. If you then load the lifted truck with 1200lbs of gear and people, the LSPV's sensing arm still says the truck is empty and the front brakes are getting an incredible heat load trying to stop the truck and added load essentially by themselves. Symptoms include front brake lockup or fade, warped front rotors, and rear brakes that won't lock up on gravel in extreme cases.<P>The cure is to look at the valve and understand how the linkage moves as the truck goes up and down. Then modify the valve's link so that when your truck is empty, the valve "sees" the axle as being located where it would be if the suspension were stock. For instance, on my 80 series the link is modified by bending it slightly with a pair of pliers. On others, you must extend the arm, and on still others you shorten the arm - study yours to see what needs to be done.<P>Remember simple geometry when doing this. For instance, on the 80 a 2 inch lift means something like a 1/8 inch change in the arm link location, not a 2 inch change. This is simply due to the angle of the sensing arm vs the axle. Study the way your particular model works to determine what should be done so your LSPV valve "sees" an axle in the stock position when your truck is empty.

Re: Lift and rear brakes #262355 12/06/01 07:45 PM
Valve location: in my Paj is on the left side, in front of the rear axle. You can see a spring linking axle and frame.<P>I think I'll give it a better look next week. Maybe there is a register on it.<P>Bye<P>Disma<p>[ 06 December 2001: Message edited by: dsmdsm ]

Re: Lift and rear brakes #262356 12/07/01 05:55 PM
Is this probelm for the older Montys or newer ones? mine is a 1996 (obviously, signature) I understand the concept I just think it would be nice I everyone new witch trucks to look under.

Re: Lift and rear brakes #262357 12/08/01 06:03 AM
VMAX,<P>I don't know what years have them for certain, but I suspect all Gen2's have an LSPV. It would not surprise me to find that Gen1's do also, but I can't remember if mine did. Anyone got a few minutes and a clean garage floor to take a look using my description above?<P>DougM

Re: Lift and rear brakes #262358 12/08/01 01:19 AM
Joined: Dec 1999
Posts: 2,329
Augie Offline
Body Damage is Cool
My manual specify 224-228 mm between the spring ends with the LSPV lever pushed all the way forward and vehicle empty.<P>I did play with mine when I lift mine but notice no big difference. The biggest difference I got is when I flush all the flud with DOT 4 brake fluid <P>BTW: I use russell 7mm speed bleeder to bleed my brakes and by far is the best and easiest way to do it.

Re: Lift and rear brakes [Re: Anonymous] #1103235 03/25/17 06:35 PM
Joined: May 2016
Posts: 41
MMeadows Offline
Getting the Wheeling Fever
I recently did a 2in lift and stared to have symptoms including noticed poor gas mileage and a rear rear right dragging caliper. I replaced the rear pads rotors and right caliper the problem is gone. Then my rear left caliper starts is stuck in the closed position. Im going to replace my rear left caliper.... but would a LSPV cause the symptoms I'm having? My front right brakes seem to be fine.

Also, I'm not the sharpest tool in the shed but i dont fully understand how a body lift would effect the LSPV if the spring is connected to the axle and the frame, the body lift is between the body and frame and would seem to have no effect on axle and frame distance?

97 Montero SR: 2in body lift. 33" KM2

Re: Lift and rear brakes [Re: Anonymous] #1103236 03/25/17 09:10 PM
Joined: Feb 2000
Posts: 6,246
4x4Wire Offline
Trail Leader
Perhaps this will help explain:

Load sensing proportioning valves usually are adjustable, and must be adjusted correctly if they are to properly balance the rear brakes to the vehicle's load. The valve linkage is adjusted with the suspension at its normal height (wheels on the ground) and the vehicle unloaded. The adjustment bracket or linkage is then adjusted according to the vehicle manufacturer's instructions, which typically involves adjusting the linkage to a certain position or height.

Load-sensing proportioning valves are also calibrated to work with stock springs. Any suspension modifications that increase the load-carrying capability (installing helper springs, or overload or air-assist shocks, for example) may adversely affect the operation of this type of proportioning valve. Modifications that make the suspension stiffer reduce the amount of deflection in the suspension when the vehicle is loaded, which prevents the proportioning valve from increasing rear brake effort as much as it normally would. A defective proportioning valve, or one that is not properly adjusted, can also upset brake balance. If the rear brakes on a vehicle seem to be overly aggressive (too much pressure to the rear brakes), or the vehicle seems to take too long to stop (not enough pressure to the rear brakes), the problem may be a bad proportioning valve. Proportioning valves can be tested by installing a pair of hydraulic gauges (one on each side of the valve) to see if the valve reduces pressure as it should.

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