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Replacing Pinion Seal ...


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How hard is it to replace a leaking pinion seal on a 12-bolt rear?  Does the rear cover and internals need to be removed or can it be done from the front?

Is this kind of thing be left to a repair shop?  I've read that the "car" seals can no longer be found and "truck" ones have to be used with modification.

I'm sure someone out there must have done one.  I have not.

Thanks!!
Mike

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From what I remember it's not a terrible job but you do have to be careful to get the pinoin nut back in the same position. You have to mark it good and when you tighten it back up make sure the mark lines up. It all gets done from the front no need to open it up. I have to do the one on my 10 bolt. Seal for the 10 bolt was available although I don't remember where I got it, I got it along with some other parts maybe from jegs or summit.

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I've changed them in place, no big deal. I was changing the yoke to a different size, plus replacing the axles & bearings on both the Monte & Z/28 recently, so the rear cover was off anyways. Take the yoke nut off, pull the yoke & seal out & replace. Be careful not to over torque the nut when installing because there is a crush sleeve in there that is a critical part of the gear mesh adjustment. As always, put a little gear oil on the rubber seal lip so it doesn't spin dry.

Also recommended to use a new nut, plus I usually blue Loctite it as well. Last, put some good quality RTV along the end of the spline & under the washer and nut to keep the gear oil from weeping out (not much, just use a skim coat). Remember, don't go crazy when you tighten it, do it by hand so you don't crush that sleeve any more.

The seal is readily available, but I got them from Denny's Driveshaft when I picked up the new yokes. Look for a TIMKEN 8460N seal. The new nuts came with the yoke, but I'm sure he has them too. You could also stake & loctite the old nut if you can't find one too. 

Here's the line item for the seal from Denny's:

1 x [8460N] TIMKEN 8460N Pinion Seal fits Chevy 12 Bolt CAR
& TRUCK rear ends

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Thanks guys!! That is a big help.

- what size socket do I need for the nut?

- is it hard to break loose? Wheels on the ground?

- are the threads normal or reverse?

Thanks!

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 - May be 1-1/8" socket according to google.

- I had the car on the lift, probably grabbed the yoke with a big wrench to keep it from spinning. An impact may work to take it off too, just not to install.

- Normal,  7/8"-16 thread

 

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Be sure to inspect the yoke carefully as they can develop a groove over time that will cause the leak to come back quickly. That is what happened with mine which caused me to replace it. 

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I believe they sell a pinion sleeve and seal kit to fix that. Also I believe there is a seal out there that  moves the sealing surface off the worn spot on the yoke. Probably not the best solution but it will work. Same principle as a harmonic balancer and sleeve kit. 

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Replaced mine on jack stands no problem.. except the yoke did have a grove ,as mentioned by these other guys.. thanks Dennis , wish I had known about the special seal earlier... would have done that ...

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The correct and more permanent fix is to replace the yoke. The above was just informational. As it would be to replace the harmonic balancer. 

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Correct me if I’m wrong but I remember from years back, I’m talking the early 1980’s in the Chevrolet garage that the pinion seal was installed with a tool behind it leaving approximately a 1/16 of an inch gap between the housing and the seal. I think they make a repair sleeve for the yoke or you can tap the seal in farther. If I am wrong please correct me but I thought that there was a tool that went between the housing and the seal and it left the gap. It is not a hard job just mark the nut in relation to the yoke and the housing pretty straightforward.
John S

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I think I am going to give it a try. I'm going to remove all the pieces first so I know what condition the yoke is in before I order any new parts.

Thanks for all the great info!!!

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The correct way to do this is to measure the rotating torque prior to and disassembly of the rear end. The way we do it at work (GM dealership) is remove the rear driveshaft, remove both rear tires, if you want to pull the drums off you can too just to take any drag variation away. Use a quarter inch drive rotating torque wrench with adaptors up to the socket that fits the Yoke nut. Rotate the pinion a few times to get an average, you’ll probably have 10-30 inch pounds of rotating torque. Jot that number down. 
 

From here you can remove the yoke nut. If you’re doing it on the ground you can put the u joint straps back on and use a pry bar to hold the yoke in place by rotating it into the ground. Use a large ratchet/breaker bar to remove the yoke nut. Once off clean any debris/silicone from the splines and use a puller to remove the yoke. We use the snap on CJ2001P, but anything similar should work. Even Harbor Freight stuff should be fine for a one time deal. Once the yokes off you can just take a screwdriver and a hammer and tap the seal inwards a bit until you can get the screwdriver under the lip, pry it out and wipe the seal area with a clean rag. Tap the new one in. You can use a big socket or just firm taps around until the seal is seated.
 

Once fully seated you are going to want to clean the splines on the pinion and on the yoke. Just so there’s not a ton of debris. Take and set the yoke back on the pinion and give it a few taps with a deadblow hammer. Once you can get a couple threads on and you’re sure it’s not going to cross thread or pull the threads you can run the nut down, not until tight yet, just until the slack is taken up and the pinion isn’t loose. Now is when I’ll take the nut back off, lightly coat the yoke to nut interface with silicone and reinstall the nut. Here’s the important part!!!!

 

Beneath the nut is the yoke, beneath the yoke is the outer pinion bearing, beneath the pinion bearing is the crush sleeve, from there is the inner pinion bearing and then a few small (thousandths thick) spacers and then finally the pinion gear. When you tighten the nut what you are effectively doing is pushing the bearings both into the crush sleeve and into the bearing races. The idea is that the nut crushes the crush sleeve which sets the preload by controlling how much pressure is put on the bearing races by the bearings. As you tighten the yoke nut down you take up the clearance between the two bearings and the crush sleeve. When you first start to tighten the nut the yoke will flop around and it’ll seem wrong, keep going slowly tightening until there’s no clearance or lash in the pinion. Once you feel no slop you’ll want to grab that rotating torque wrench and measure the rotational torque by turning the pinion with the yoke nut and adaptors. At first it’ll be none or next to none. You slowly tighten the nut, we are talking 1/16ths of a turn at a time, until you reach the number you jotted down or 3-5 inches of torque higher than what you had before. If you leave it with significantly less rotating torque it’ll wear in quickly and become loose, wreaking havoc on your ring and pinion and taking out the rear end. Too tight (20+ Inches higher than originally measured) and you’ll overheat the pinion bearings or have to take the rear end part. It’ll probably also make noise.
 

It may sound daunting but once you get under there and spin the rotating torque wrench the first time it’ll make sense. Good luck and take your time!

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