South Bay Driveline's "Extreme Slip" Driveline
Built For The Serious Rock Crawlers Short Cuts
by: Ron Hollatz - 5/2000
Twisted up on Upper Buzzworm
Twisted up on Upper Buzzworm during the 1999 Dakota Territory Challenge. Photo by Laurie Hollatz.
Trailside driveline repair
Trailside driveline repair. Photo by Laurie Hollatz.
Extreme Slip Driveline
South Bay Driveline's "Extreme Slip" driveline. Photo by author.
Greasy Extreme Slip Driveline
Freshly greased and installed driveline. Photo by author.
Moab Rim
Moab Rim Trail during Moab Easter Jeep Safari 2000. Photo by Vance Anderson.

One thing I've learned during the buildup of Project Money Pit is what seems like an easy modification isn't. I try to plan projects out well in advance so I can make sure all the pieces work together, but sometimes things don't work out the way they were planned. I hate to hold people up on the trail for something as avoidable as a pulled apart driveline.

While I was planning for the Dakota Territory Challenge last summer, I decided I needed to get some more articulation out of my suspension. The front of my YJ has 4" Pro-Comp lift springs and a Warrior shackle reversal. The weight of my 4.0L and my Warn winch had softened the springs up nicely, but to crawl over big rocks in South Dakota I needed all the flex I could get. The easiest way to achieve that goal was to add a set of Revolver Shackles by Metal Made Rite. The Revolvers gave me a huge increase in flex and I thought I was all set for the rocks.

My trail choice the first day was the 5+ rated Upper Buzzworm. This trail travels up a dry river bed filled with rocks. As I approached the first obstacle I tried out some of the rocks along the side and was really impressed with the articulation I had gained. As I climbed up the dry waterfall everything seemed to be working until I heard the sound of metal hitting rock and someone yelled STOP. I crawled under my YJ and saw that my driveline had pulled apart at the slip spline. Luckily I was able to disconnect the driveline from the front axle and put it back together. Unfortunately I had to do that eight times on the trail. Once we got back to camp I pulled off the Revolvers and put my regular shackles back on. The rest of the weekend was uneventful and my YJ performed as well as expected.

Just how much spline do you really need

There are both good and bad points about a shackle reversal. It does give better on-road manners and an improved ride, but it also allows the axle to move in some strange ways. When I hit a rock with a front tire my axle moves backwards like you would expect. When the tire crawls over the rock the Revolver Shackles allow the front axle to crawl ahead which can pull apart the driveline if slip splines are not long enough. When I put in my Atlas transfer case I had installed a front CV driveline with 8+ inches of travel. This was plenty of travel for most situations, but I was pushing the envelope.

I was convinced of the Revolver Shackles performance so I gave Steve Johnson at South Bay Driveline a call. He decided one of their "Extreme Slip" drivelines would be perfect for the Money Pit. Most drivelines are built with two U-joints (or 1 U-joint and 1 CV joint) welded to tubing connected with a short slip spline. The "Extreme Slip" driveline has equal amounts of tubing and spline. The tubing is welded to the CV joint while the splined shaft is welded to the front U-joint yoke. The slip spline is super-long and beefy allowing an incredible amount of travel. Steve asked me to ramp the Money Pit and find the minimum and maximum operating lengths. Since I was in the middle of swapping in a 700R4 transmission, this proved to be difficult. Finally just days before we were to leave for Moab I was able to get the measurements and South Bay Driveline, living up to their reputation, was able to get me the driveline in time for our departure.

Care and feeding of the "Extreme Slip" driveline

A driveline of this type needs some special care. As Steve Johnson puts it "grease grease grease". The splines are expensive and they can never have too much grease. Steve puts in two grease zerks which should be used to fill the cavity frequently. The zerks will keep it lubed unless the shaft gets in the water. Then the shaft should be disassembled and the grease replaced. I use a synthetic waterproof grease to combat this, but I still plan to disassemble it regularly.

A shaft of this type is built for off-road use, the components are much heavier than a standard driveline so it can't be balanced as well. With the hubs locked I start to get vibration at 45 mph or so. I don't drive my YJ on the road during the winter anymore and I hate mud so that doesn't bother me. I can still put in my old shaft if I have to be in the mud or snow without the need for a lot of articulation.

Conclusions

With the memories of last summer still fresh in my mind, I was a bit apprehensive about twisting up the Money Pit during the Easter Jeep Safari. As the week progressed and I got the feel of the new setup, I became impressed with the way the driveline worked with the suspension modifications. On our Moab Rim run I took every opportunity to put a tire on a rock and see how far I could get. I never had any bind on the driveline, even at the most extreme angles. The South Bay Driveline "Extreme Slip" driveline is a must have for the serious rock crawler.


Contacts: Related Links:
  • South Bay Driveline
    Dept. ORN
    573 W. Julian St.
    San Jose, Ca 95110 USA
    Phone 408-995-6000
    Fax 408-995-6513
    Email: Steve Johnson
  • Metal Made Rite
    Dept. ORN
    781 Foster Road
    Casper, WY 82601 USA
    Phone 307-234-7430