GM 8.5" Differential Leak Between Flange and Pinion

[Guest]

My differential shop is working on my '73 Impala with the 8.5" differential (Buick-Olds type w/o the axle retaining clips) and can't stop a leak between the flange and pinion.  The Impala is all stock and has about 268,000+ miles.  All of the differential and wheel bearings were replaced about 75,000 miles ago, with the wheel bearings replaced one more, about 10,000 miles ago.  About 5,000 miles ago, the pinion seal was replaced due to leakage between the seal lip and the flange, and it was noted that the pinion nut was looser than expected.  After that pinion seal replacement, about every two months, gear oil starts leaking out between the pinion and flange, leaving a very small puddle when parked.

 

After the last repair attempt (number 3 or 4), a humming/whirring noise from roughly 30 mph down to a stop while coasting has surfaced.  The shop says that this is the ring and pinion wearing, not anything abnormal with any of the the bearings.  Though I wonder if, in the process of taking the flange off and retorquing the nut multiple times, the preload on the pinion bearing has been affected, causing the humming/whirring noise.

 

The shop uses a new nut on the pinion shaft every time and has checked the vent to be sure it's not plugged or restricted.  They've tried RTV and PTFE paste (not at the same time) on the splines, with no success.  They did lightly sandblast the splines to clean and check them, and to give the sealant a bit more "bite".  The splines on both the flange and pinion shaft have been closely examined, and there is no apparent damage and the fit is what is expected, with no looseness.  For the first two or three attempts at stopping the leak, the work was done while I waited.  One theory was that the sealant wasn't fully setting up (PTFE wouldn't anyway, as it's non-hardening), so on the last attempt the repair was made and allowed to sit overnight before the differential was refilled and the car was driven.

 

The Impala will be going in for one more try at stopping the leak before the shop refunds my money, they don't want to see it anymore.  Seems like a pretty straightforward problem, fluid leakage between a splined shaft and a mating part.  What are we missing here?

 

Thanks.

 

 

[F&J]

13 hours ago, Writer Jon said:

(Buick-Olds type w/o the axle retaining clips)

 

13 hours ago, Writer Jon said:

After the last repair attempt (number 3 or 4), a humming/whirring noise from roughly 30 mph down to a stop while coasting has surfaced.  The shop says that this is the ring and pinion wearing,

 

 

If there are no C-clips, I don't think I'd have a service book for that.

 

The gear noise that has now appeared, is most likely due to the constant loosening of the flange, and that causes alignment problem to the ring gear and causes rapid wear on gear tooth faces.  The noise will not likely go away now, even if the nut problem is solved.

 

A constant loosening of the flange:   Some pinion designs use a crush sleeve to maintain the bearing preloads and also gives the nut something to "torque/tighten" to.    If a crush sleeve is worn down from a loose flange, you cannot get the nut to "torque" properly without binding the bearings.  You should use a new crush sleeve, or in a "backyarder" situation, you could add pinion shims to act like a longer crush sleeve. 

 

Other pinion designs use stacked shims in place of a crush sleeve.  The proper thickness of the total shims in the pack must keep the proper bearing preload, as well as giving a solid way to torque the nut.  If shims are too thin, the nut cannot be torqued without binding the bearings.

 

What I am getting at:  The 2 normal types of pinion designs, do not rely on a locking type nut or locking washer to keep the nut from loosening.  The nut needs something solid to tighten TO, without binding the bearings.

 

secondly, a loose flange/nut will always weep/leak oil.

 

 

[F&J]

I should add a few things:

 

We cannot condemn the shop at this point, as we were not there to see what they did, and how they did it.

 

As I said, I don't know if it is a crush sleeve system to adjust the pinion bearing(s) preload, but I suspect it is... You should be able to web search an exploded view of that differential to see.  Also web search "differential crush sleeve" to know what they look like, before you look for the exploded view.  It looks like a pipe with a raised bump or ring around one end of the pipe.  A pinion design that does not use a crush sleeve will have a straight pipe type sleeve without a bump, and will show several thin shims at one end to set preloads.

 

A crush sleeve system leaves more room for error to some technicians.  If the old sleeve was reused when they installed new pinion bearings, that is a huge problem.  If it was replaced, but improperly crushed, like crushed too far and then had the nut backed off a bit to loosen a stiff bearing preload, that is also a big problem. 

 

on the noise: It is tough to describe rear end noises in some cases, over the internet.  There is a slight possibility that it could be a failing pinion bearing, rather than gear noise.  A gear "pattern" noise is more like a moaning or howling.  A bearing race that is failing, usually has one bearing "race" that is disintegrating/pitting/peeling surface. This should sound more like a rumbling or growling.

 

  Some mechanics can hear a bad pinion bearing with a stethoscope, as an initial diagnosis. At any rate, the first step is to see if the pinion nut is still presently torqued properly, or not.

[joe_padavano]

2 hours ago, F&J said:

 

 

 

If there are no C-clips, I don't think I'd have a service book for that.

 

 

The Oldsmobile style 8.5" axle used from 1971-up is the same as the Chevy axle except for the change from the C-clip axle retention to the pressed-on bearings and retainers for axle retention.  The actual differential, gears, pinion bearings, and pinion flange are exactly the same.  Only the axle shafts and wheel bearings are different, and this has nothing to do with the OP's pinion seal leak.  Yes, this axle uses a crush sleeve.  There's a high probability that the crush sleeve is now over-crushed, which means that pinion bearing preload is wrong.  Unfortunately, fixing this requires taking the axle completely apart.

[Guest]

Thanks for the feedback.

 

Joe, I agree that there's likely more to this than resealing the flange-to-pinion splines, since that hasn't been a permanent fix.  Since there's a decent amount of mileage on the axle, I don't have a problem with having another shop go in and doing a complete rebuild.

 

Your thoughts on the fix, in particular any areas to focus on in terms of inspection?

 

I'd hate to have some part not typically replaced reused, only to have other problems later.  For example, the possibility that there may be a problem with the flange and pinion splines since they were run with the pinion nut looser than spec.  Seems like that might mean replacing both the flange and pinion (of course, the ring gear gets replaced too, since they're a matched set.) 

[TerryB]

268,000 miles on a 1973 Impala!  That's amazing in itself.  I gave up on my 1973 Chevelle SS with 60,000 miles on it in 1977 when I couldn't stop the body rot around the wheel wells.  You must live in a dry climate.

Terry

[Janousek]

Good call on the crush sleeve.  In a perfect world it would be replaced everytime the yoke is pulled from the pinion gear.    If they reused the old one with new pinion bearings then it would over preload the pinion bearings.

 

Now that it is making noise the ring and pinion might always make that noise even with new bearings.  You'll have to rebuild it with new bearings and shoot for .006" backlash and hope it's quite.  Otherwise a new ring and pinion is needed.  

[Guest]

A quick update...  Had another shop ("Shop B") look at this.  They found the apparent problem.  The pinion flange had significant wear on the side facing the pinion gear.  This wear was caused by the normal motion of the front pinion bearing, and was pronounced enough to leave a sharp edge/ridge on the flange where a chamfer is normally located.  The flange, along with the ring & pinion and related bearings were all replaced.  The R&P backlash was out of spec, which Shop B believes was the cause of the humming/whirring noise.  The flange problem was obvious, even to me.  I should have asked to see the flange when things were disassmembled at Shop A (the one that worked on this problem four times), but figured they knew what they were doing.  The funny thing here is that the sole proprietor owner of Shop B was trained at and used to work at Shop A, but branched out on his own after the original owner of Shop A sold it.  I let Shop B have the old flange, he still deals with Shop A and is going to have some fun with them, by taking the part over there and ask them how they missed the problem.

 

The cause of another issue was also located by Shop B.  Since the rear axle bearing replacement about 10k miles ago, I've been trying to locate a driveline vibration that's most pronounced on acceleration.  Shop B noticed the axial play on both axle shafts was about 0.125", way too much.  Shop C did the rear axle bearing and seal replacement, and installed the wrong axle seals, which were too narrow.  This axle (Buick/Olds type) does not have the c-clips in the differential housing to retain the axles, it uses the pressed-on bearing/wheel seal/flange design to keep the axle from moving axially.  So, if the metal housing of the seal is too narrow, the bearing and shaft can move axially more than intended.

 

Will be doing the break-in mileage and checking for leaks now, will update this after the 500 mile oil change and inspection.

 

 

 

[Larry Schramm]

Sounds like you are making good progress.

[Guest]

Just a brief update, I put the break-in miles on the differential and Shop "B" that did the work changed the differential oil and did an inspection at about 1,000 miles.  Everything looked fine.  About 3,000 miles have elapsed since the repair, no issues, everything is as it should be.

[Roger Zimmermann]

Is the shop "A" still in business? How could they miss what you wrote in your post #8?

[Guest]

Shop "A" is still in business.  I don't use or recommend them to anyone now.  How they missed the flange issue, that's a good question, it was plain as day when the pinion flange was removed and I saw it.

 

I guess the moral of the story is that the quality of repair shops need to be monitored, even if the shop name doesn't change.  Even if the shop name hasn't changed, but the ownership and/or techs doing the work have changed, beware.

 

One way to keep up on these changes in the car community is by staying in touch with members of a local car club that's of interest.  At a recent local show, I introduced a fellow club member that has a '31 with a leaking radiator to another member that owns a radiator shop that still does full-service repairs on the older cars.