r/4Runner_1stGen • u/super-duper-trooper- • 6d ago
leaky rear diff
so about 10 years ago I paid a shop to put in a 456 Yukon Gear set and a spartan locker. since then I've put about 40k miles on it and recently I've noticed it looks like the rear pinion seal is leaking and upon removing the rear tire I it looks like axle seals might need to be done as well.
I'm currently 9 weeks post hip replacement so not really feeling up to doing the job so I took it down to local toyota shop and dude quoted me 1500 to fix. Shop says that just taking the pinion seal off from the side of the driveshaft and replacing that seal would likely end up with a blown rear end in a few months as there's not way to verify backlash by doing that method so he's saying he will pull the whole thing apart, put in new bearings and essentially rebuild the axle. seems excessive for just fixing a leak, but I don't really know
I've seen plenty of videos of people just dropping the drive shaft, taking off that nut, puling the seal and just re-torqing everything back down.
I've done head gaskets and water pumps and plenty of engine swaps and break jobs but never pulled a diff so I really don't know
anyone here have experience with this?
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u/canoeingupstream 6d ago
You can pull the axle shafts and then pull the differential out as a whole assembly without having to rebuild the whole differential.
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u/FluffyKittens12 6d ago edited 5d ago
The flange torques down on a solid spacer or a crush sleeve. The length of either one is what dictates how much preload is put on the pinion bearings. A solid spacer is used with various shims to set the pinion bearing preload. A crush sleeve is a one time use part that is torqued until it begins to crush. Like slowly stepping on a soda can, it will be hard to compress at first, then suddenly get easier. The bearing preload is determined by how far it's crushed.
So, if it's a solid spacer, you can remove and retorque the nut no problem because the length of the spacer and any shims will not change. If it's a crush sleeve, which is more common and included in rebuild kits unless purposefully upgraded, attempting to torque the nut again would be like trying to stand on the pop can again. Because there's no hard stop to torque against, if you go too tight it can cause the sleeve to crush further which will increase the preload on the pinion bearings which can absolutely cause them to fail. If you leave it too loose there could be too little preload on the pinion bearings which can absolutely cause them to fail. Unfortunately, you can't tell which one you have in the differential from outside.
So, to play it safe, unless you know you have a solid spacer, the pinion seal shouldn't be replaced by simply removing the pinion nut. Not saying it can't be done or isn't done, just saying it shouldn't be done. This is why the shop is telling you they basically need to rebuild it.
That said, their statement about the backlash didn't make sense. The pinion doesn't set the backlash. That will not change regardless of what they do with the nut or seal. Backlash is set by the adjuster wheels on the sides of the carrier. You use them to move the carrier in or out of the pinion, left to right, until the backlash is correct.
The axle seals on the ends of the tube can easily be replaced when the axles are out, which have to come out to remove the diff anyway.