Regearing the Jeep 8.25
How to set back lash and pinon pre load on the Jeep 8.25
I recently put 4.10 gears in Jenny’s XJ. Her Jeep has a Chrysler 8.25 rear end. There seems to be very little info available on the 8.25 compared to what is on the web for the Dana 35 and Dana 44. So here is how I did it.
I began by removing the rear end from the Jeep and replacing it with our spare 8.25. That gave me the opportunity to take my time and not be in a rush to find parts. We got parts from our Crown Distributor as well as Advance Auto and Ebay.
With the axle out and mounted on my work stand, I removed the cover. Since this cover will be replaced with a Blue Torch Fabworks Kryptonite cover, I set the original aside.
Next, I disassembled her Lock Right locker so I could remove the axle shafts. The 8.25 uses the same length axle shafts on both sides so I did not have to keep track of where they went.
Next, I used a punch to mark the bearing caps so I could keep track of where they went. I could not see any factory marks like the Danas have. I removed the two small bolts that hold the keepers and then removed the keepers. I then removed the bearing cap bolts and the caps. I set all the parts in a box in order so that I could easily put them back where they came from.
Next, I slipped out the threaded preload plates and set them in the box. Then I was able to lift out the carrier.
I then rolled the axle over and drained all the oil out. I then removed the pinion nut and the yoke. I used a soft hammer to tap the pinion out. I then pried out the front seal.
I made a drift out of a piece of soft steel pipe and drove out the pinion bearing races. I set the races and crush sleeve aside to be replaced.
The gear set came from Ebay. It was slightly used but in perfect condition. The first odd thing I noticed about he 8.25 is that the bolts that hold the gear to the carrier are reversed threads. I was sure glad I read that before I tried to get one loose. They are marked with a big “L” on the heads as a reminder. I had to clamp the carrier in my vise to get them loose as they were very tight.
With all the bolts out, I used my heat gun to warm the ring and gently tapped it off with a soft hammer. I set the old ring gear aside to be sold.
Removing the carrier bearings was a bit of a challenge. I used a bearing separator and a two jaw puller to get them loose. I also warmed the bearing with the heat gun to help reduce the force needed. Due to the shape, I could not fit it in my press. I made a plug out of an old ball joint for the puller to press on while pulling the bearing off.
I installed the new bearings by warming them with the heat gun and chilling the carrier in ice water. I tapped them with my soft hammer to make sure they seated.
I chilled the carrier and warmed the new ring to slip it in place. I then snugged the bolts down to make sure it was seated properly.
Next, I removed the lower pinion bearing from the old gear set to retrieve the shim under it. I used the bearing separator in my press this time. I also had to heat the bearing with a torch to get it to release. With the shim retrieved, I set the old pinion aside and put the shim on the replacement pinion.
I then used my die grinder to open up the inner race of the pinion bearing until it slipped easily on the pinion shaft. This became my “set up bearing.”
I used my bearing driver set to press new races into the housing. I did chill the races in ice water before installing them. However, I did not attempt to heat the housing. There was a noticeable difference in the sound of the hammer on the driver when the races seated.
I assembled the new pinion with the old bearings and yoke but no crush sleeve or seal in to the housing and snugged the pinion nut just enough to take out any end play. I then set the carrier into place with the new bearings and races installed.
I fabricated a tool to turn the back lash adjusters using a nut from a Ford fan clutch, a length of ¾” pipe and an old ½ inch drive socket. I welded the nut to one end and the socket to the other end. The back lash adjusters are 36mm hex. A Dana 30 axle nut will work as well as any other 36mm nut. You can also use the miller tool C-4164.
I set the adjusters in place beside the bearings and set the caps on. I tightened them finger tight at first. I then used the tool to turn the adjusters to take out all the back lash but not put any extra pressure on the gear.
I made sure that all the end play was eliminated from the carrier bearings. I had to rotate the assembly a few times to get the bearings seated in the cones. I then set the back lash to about .003 inches using about 10 ft lbs of torque on the adjusters.
I then tightened the cap bolts to 70 ft lbs. I then tightened the right side adjuster to 75 ft lbs. or until I got a back lash of between .006 and .008 inches. I then checked the left side and found it to be close to 75 ft lbs as well.
I then coated the ring gear teeth with yellow marking compound. I rotated the assembly to get a gear wipe pattern. I was very happy when the pattern showed the pinion depth to be correct since the shim I had from the old gear was the only one I had. The Timken rebuild kit we got did not come with pinion shims.
Since I was happy with the pattern, I removed the carrier and pinion. If I had needed to change shims, I would have slipped off the set up bearing and tried a new shim using the same procedure.
Next, I installed the new pinion bearing by heating it and pressing it on the pinion shaft. I then installed the new crush sleeve, outer bearing, seal and yoke using the new nut from the kit.
I repeated the back lash adjustment procedure to get a back lash of .006 inches with the adjusters at 75 ft lbs. I rechecked the torque on the ring gear to carrier bolts. I then compressed the crush sleeve to get a pre load of 20 inch pounds. I noticed that then nut turned a long way with no change in preload and then suddenly the preload went up as I made the last 1/8 of a turn on the nut.
The torque needed to compress the crush sleeve was significant. I had to use a long breaker bar to turn the nut and a large pipe wrench to hold the yoke. With the preload and back lash set, I installed the keepers on the adjuster plates.
Since the adjuster tool had made numerous trips across the axle seals, I replaced them before installing the axle shafts. I reinstalled the Lock Right locker and secured the axles with the c clips.
I then put a bead of RTV on the gasket surface and installed the new Differential cover. I tightened the bolts finger tight and then let the RTV set up. I then tightened them the rest of the way down.
I waited until the axle was back in the Jeep to add the gear oil. The new cover held almost a quart more than the stock cover did.
The result was a smooth running rear end with no noise. I expect it to last a long time.
Timken 8.25 rebuild kit
Carrier bearings and races
Pinion bearing and races
Gear marking compound
RTV for the cover seal
4.10 ring and pinion set
Blue Torch Fabworks cover
Technical info came from this source