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Very important before replacing pinion seals!

Started by Chopper1942, March 06, 2023, 01:57:45 PM

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Chopper1942

I have seen several posts about pinion seals.  Any one planning to replace a pinion seal or removing the pinion flange please read this. I replied this to the 1952 pinion seal post.

Unless you are replacing the pinion bearings please follow this to avoid having a diff that now makes noise or other more major issues.  When you overhaul a rear diff there is a set up proceedure for the pinion  bearing preload. Pinion bearing preload is very important for the diff set up. This is what I wrote:     

Before you remove the pinion flange from the pinion, remove the rear wheels and rear brake drums. Use an in.lb. torque wrench to measure how much it takes to rotate the pinion. Then remove the pinion nut, flange and seal.  Clean all the gear oil off the diff housing where the OD of the seal goes, the pinion, and pinion flange splines.  Coat the outside of the seal with Permatex and the rubber of the seal with some grease.  Install the seal in the housing being careful not to dent the seal or you may still have a leak.  Coat the pinion splines and pinion flange splines with pipe sealer and install the pinion flange.  Put some locktite on the pinion threads and install the nut and washer.  Tighten the pinion nut until the pinion rotation torque is the same as before disassembly.  Do not over tighten.  If to loose or tight, it can cause bearing failure or diff whine.  Hope this helps.  Good luck!


Scott Nellis

  Thank you Larry for this and other detailed and informative posts that you have taken the time to write. The only thing I would add to your procedure would be to mark the position of the pinion nut before removing it just as a reference point so when you put everything back together you know when you are in the ball park. I have done this in the past and it gave me a bit of comfort. Of course if the differential was not set up right in the first place and things in there weren't behaving as they should this reference point would be redundant and unnecessary. I have only done it on differentials that were working properly and simply needed a pinion seal.
1957 Eureka Hearse
1965 Miller-Meteor Hearse
1968 Miller-Meteor Hearse
1968 Fleetwood Brougham
1970 Superior Hearse

TJ Hopland

Isn't an important thing to know what style of a rear end are you working with?  I'm not expert but thought there were styles that are set up with shims so in theory all you have to do is get it tight again and it should be fine but another common design uses a crush sleeve.

If that is what you are dealing with that is where all the tricks and a little luck is involved of you are not going to do it right with a new sleeve and the proper setup process. 
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

Chopper1942

If you measure the pinion turning torque before taking the nut loose, you will not have change the preload on the pinion bearings when tighten the pinion nut until the pinion turning torque is the same as before disassembly.  This applies to both diffs with crush sleeves (most GM diffs) as well as diffs that use shims.  It just from possibly inducing a problem in the diff that wasn't there before.  Do you have to do it?  No. It's just like wheel nuts. They have a torque spec to ensure that the wheel is not going to come loose, not so tight as to damage the wheel, and to keep from distorting the hub and drum or rotor. Does it always damage the parts or cause shimmy or pulsations?  No, but it usually can and does. Uneven torque causes lateral runout issues.  If you overtighten the pinion nut with a diff using a crush sleeve, you have changed pinion bearing preload.  If diff using shims to set pinion bearing preload has the nut over tightened, the threads on the pinion and/or nut can fail and the nut come loose. Actually most pinion nuts are one time use and should be replaced with new after removal.