Rear Axle: Is this too much backlash in differential?

[bsrosell]

Hi; after getting cast off, back into the shop to finish differential!! ('57 Golden Hawk, non-TT)
Got the assembly OUT (originally just to clean), and found HORRIBLE spalling and pitting on the bearing races (inner axles). Fortunately the Pinion was ok; original owner must have run it really low on gear lube, and pinion sits lower so it survived, thank goodness (would hate to take those races out and re-set tolerance!)

Speaking of tolerances, have two questions:
1) after COMPLETELY PRESSING on new Timken bearings, (same part number as originals after 60 years!) reassembled into housing, and torqued down the caps. Original shims all EXACTLY same positions, even filed any 'ragged edges' to keep original thickness.. VERY careful about this, AND completely pressing bearings to their stops.

When I rechecked for ring gear run-out, I got ZERO. It turns with some resistance but smoothly (and easier using pinion yolk), so NOT binding...
Before Disassembly, I had 0.003" run-out on the ring gear; max per shop manual (when "just checking" it); NO MINIMUM is stated.
And (see snapshots from manual), when completely rebuilding one, they talk about a "pre-load"; so does this mean I'm OK (maybe 'perfect' :-) as-is?
Again, it states MAXIMUM of 0.003", but NO MINIMUM is stated anywhere for run-out.


2) for backlash, spec is .003-.006". Best I can measure is 0.010. (Also please look at the prussion blue imprints for meshing, which looks good to me but I'm no expert...)
I ONLY pulled the pinion OUT, greased both bearings and cleaned it all up, put the FRONT shims (and new seal) back on, and put it back together, so the INNER race and shims didn't even move. Should be factory minus wear.. Thus, I'm guessing that extra backlash is from wear, and wondering if an .010" vs 0.006" max spec is enough to justify the massive job of trying to pull out pinion races and reset, multiple times... without Stude tools either. Massive also, for me, as I can't lift and carry the differential assembly even; had to roll it over to my bearing press, etc.. on a wheeled chair..... Whadda you think? Not going to be racing, but don't want it grinding on me either...
Thanks!
Barry

[TWChamp]

If the coast side looks good, then I'd say wrap it up and go to the next step in the restoration.

[wittsend]

I've only done this once, and that was over 15 years ago. The order I recall was:

1. Place the carrier in the housing/caps without shims, un-tightened and determine the full side to side movement. If (as an example) it was .030 then the total shim pack should be .038. While this is determined for pre-load it is not necessarily for final placement (see #3). The carrier is removed for step #2.

2. Set the pinion depth, and then properly install pinion.

3. Install the carrier and measure the backlash. IF it is not in spec adjust the shim pack on the carrier bearings side to side until it is the desired value. What this means (as in the example, not necessarily your specific setup) the proper pre-load was set with .038 shims because it is .008 over the side to side movement. It must stay at .038 total. Let's say the end backlash is .010 like you have and the desired is .006. That is a .004 difference. You shift the shims side for side .004 maintaining the .038 total shim value, but shift it .004 to the tighter direction to achieve .006 backlash. Note because of the gear taper .004 may not produce an exact .004 change.

I assume the .010 backlash might be the wear you suspect. The question is..., will you have issues because the backlash is too large..., or would you have issues if you shifted the shim pack to the .006 spec thus altering the initial set-up that caused the teeth to mesh the way that they have??? I wish I could tell you the answer. But I can't because I don't know. Did the rear end make noise prior to taking it apart. If so, was there a discernible reason (like a bad bearing)? I'd think if there was no noise prior to taking it apart and the backlash was .010 then that it could be OK. It looks to me like you have replicated the original wear pattern.

Congratulation on the job. It shows you are very thorough. And, given the physical difficulties, you are to be commended. Whatever you decide my hope is that it turns out well.

[DEEPNHOCK]

Couple of things to consider...
Once you install 'new' bearings, the shims that were in there mean NOTHING.
You need to set the side play for the NEW bearings.
And.. You need to set the pinion depth again if you have NEW bearings.
The old shims mean NOTHING.
All of your shimming is to get the CORRECT tooth pattern.
If you need to add or subtract shims for the carrier bearings, and for the pinion bearings.......DO IT.

Your tooth pattern is paramount.

[swvalcon]

A little trick that my dad told me. Back when no one or few had dial gauges he said they would take a long piece of a wood farmer match stick put some wheel bearing grease on it and set it in the ring gear. Now turn the gears over the match and it should smash it flat but not cut though the wood. I set up a chev 12 boltposi as it should be and then tested his wood trick. It did just what he said it would do.

[fh4ever]

just a couple of things...check mesh on more than 2 teeth and it wouldn't hurt go all the way around..and coast side too. Also, your .003 ring gear run out...the diagram shows it being checked on a the back side of the gear which is machined...dont use the cast surface for checking. I agree the old shims mean nothing but it is a starting point and you might luck up and the shims be correct.

[Hawkowner]

Your pinion depth should be correct because if I am reading correctly. Sounds like your preload on th carrier is correct ?I would remove the carrier take 1 shim out of the bearing on the toothed side of the ring gear and install it on the back side.
are the shims under the races or under the bearings .
Hawkowner

[altair]

No ring gear is perfect, they are machined perfect when soft, then when hardened will distort .002 - .003 therefore the crown gear is required to be set to the closest position and the rest of it doesn't matter. If it was set to .003 at the closest position, the opposite side could be .006 and you can't do anything about it. On the few that I have done I use a strip .002 paper and find the closest position by inserting it between the gears, at the closest position the paper should just crease and not cut the paper. If the paper is cut it is too close.
This process may take several hours to complete.

[fh4ever]

one more thing to help clarify the .003" ring gear run out...this is how true the ring gear is axially, and it is not the side to side clearance. You need to rotate the ring gear while measuring and this is why you need to measure against a machined surface. Zero runout is perfect and .003" would be max. If you have more than 003" like the manual says there are other issues and this will affect the meshing. Now since you are measuring against the cast surface, I assume you are measuring side to side clearance in which case you dont need to rotate the ring gear and the cast surface is sufficient for that. hope that helps.

[bsrosell]

Shims are under the bearings as originally installed. EVERYTHING is as factory setup, except I had to replace those two Timken bearings on each side. Tried measuring them with Vernier to compare to original and just too much variation, too much variation possible in how bearing sits in cup and where you measure, so I have no comparison, but bearings are so precise compared to all other components I'd hoped they would be within a thousandth or so of original, but can't guarantee that obviously.

Your pinion depth should be correct because if I am reading correctly. Sounds like your preload on th carrier is correct ?I would remove the carrier take 1 shim out of the bearing on the toothed side of the ring gear and install it on the back side.
are the shims under the races or under the bearings .
Hawkowner

[bsrosell]

Good idea; THAT I did not do, and will; I measured in only one place, (well, several attempts so different but always zero "run-out" when stationary, as I simply was looking for runout, side to side.) Good idea to see how consistent it is at the ring gear rotates, will check for the fun of it (machine work IS fun; just wish I had the bearing and race pulling equipment; had to CUT one bearing cone off finally; other side came right off with the heavy-duty farm-quality puller. (I pricked that side with centering punch all the way around the journal/bearing-seat, just to make sure that bearing is more tight when it went back on; that journal DID measure a thousandth less diameter than opposite, difficult side, while the cone ID was same on both bearings...).

one more thing to help clarify the .003" ring gear run out...this is how true the ring gear is axially, and it is not the side to side clearance. You need to rotate the ring gear while measuring and this is why you need to measure against a machined surface. Zero runout is perfect and .003" would be max. If you have more than 003" like the manual says there are other issues and this will affect the meshing. Now since you are measuring against the cast surface, I assume you are measuring side to side clearance in which case you dont need to rotate the ring gear and the cast surface is sufficient for that. hope that helps.

[bsrosell]

Thanks Jeff; that is why I included the mesh pattern with the Prussion Blue. (I did a several-tooth section also but not as distinct and was hard to photograph, but looked like similar to this).
I did NOT do the opposite side, only drive side; honestly didn't know it really mattered (how often do you spend in Reverse?)... but will look at that too.

My thought, besides the large amount of effort involved (I don't know HOW I'd ever get those pinion bearing cups out; THOSE were never removed, they are both exactly where they were and original bearings/shim-packs; pinion 'assembly' is simply cleaned, no changes) is if the tooth-pattern mesh is good now, it will move if I were to try and remove the differential bearings (again) and shift one shim over to the other side. (and, since tooth-pattern looks good now, doesn't it??) which way would I even go?

So to tighten up the backlash by .004" to get to <0.006", I'd throw my tooth mesh pattern out one way or another; seems I'm better having the 'original' tooth pattern with a tad extra backlash, doesn't it? Not arguing, trying to learn. Never set up a rear-end before, just as I never rebuilt an automatic tranny until my Flightomatic (and still anxiously waiting to see how that works! :-) But EVERYTHING got replaced on that, every bushing, band, etc.. and clean as a surgical ward, so I'm hopeful....).

But back to differential, what is more critical to proper, quiet operation, the tooth-pattern mesh I have shown (do you agree it looks right??) or tightening up the backlash a little to get in spec, and shifting the mesh?

Again, I don't think I have the capability or tools to mess with the Pinion bearing cups, to "shift the tooth-pattern back into place" if I were to try and tighten up the backlash by shifting a Differential/carrier bearing shim. I can't get my whole differential into my bearing press. (not anymore anyway; it gets moved around, very slowly :-), with my cherry picker).

Couple of things to consider...
Once you install 'new' bearings, the shims that were in there mean NOTHING.
You need to set the side play for the NEW bearings.
And.. You need to set the pinion depth again if you have NEW bearings.
The old shims mean NOTHING.
All of your shimming is to get the CORRECT tooth pattern.
If you need to add or subtract shims for the carrier bearings, and for the pinion bearings.......DO IT.

Your tooth pattern is paramount.

[bsrosell]

Thanks; unfortunately when I bought the Hawk, it was undrivable (for some years), and have no idea. I've rebuilt every single piece of it from engine to tranny to now rear end, and frame is painted and waiting to start reversing the process FINALLY after starting this in 2010 ! :-( Five kids and now my sudden "can't walk" kind of put a dent in 'speed', but keep plugging away. Somewhat fitting for a Stude, in a poetic sense? :-)

Anyway nothing to go by from "what was it like" except it HAD worn the carrier bearings enough to get the max (0.003") run-out (end-play?) back and forth, vs pre-loaded and ZERO... (which I now have with the new bearings). So you are right, "that is the question"... "will you have issues because the backlash is too large..., or would you have issues if you shifted the shim pack to the .006 spec thus altering the initial set-up that caused the teeth to mesh the way that they have???"
If it's a coin-toss, I'm going with "leave it alone", vs try and remove those super tight bearings without damaging, reassemble everything, and find the tooth pattern looks obviously bad, and have to do it all again. But I don't have any feel for what 0.004" worth of extra backlash means (maybe EVERY old Stude has that or more and you never notice, or maybe that is enormous? That's why I'm posting! :-) Thanks again.

I've only done this once, and that was over 15 years ago. The order I recall was:

1. Place the carrier in the housing/caps without shims, un-tightened and determine the full side to side movement. If (as an example) it was .030 then the total shim pack should be .038. While this is determined for pre-load it is not necessarily for final placement (see #3). The carrier is removed for step #2.

2. Set the pinion depth, and then properly install pinion.

3. Install the carrier and measure the backlash. IF it is not in spec adjust the shim pack on the carrier bearings side to side until it is the desired value. What this means (as in the example, not necessarily your specific setup) the proper pre-load was set with .038 shims because it is .008 over the side to side movement. It must stay at .038 total. Let's say the end backlash is .010 like you have and the desired is .006. That is a .004 difference. You shift the shims side for side .004 maintaining the .038 total shim value, but shift it .004 to the tighter direction to achieve .006 backlash. Note because of the gear taper .004 may not produce an exact .004 change.

I assume the .010 backlash might be the wear you suspect. The question is..., will you have issues because the backlash is too large..., or would you have issues if you shifted the shim pack to the .006 spec thus altering the initial set-up that caused the teeth to mesh the way that they have??? I wish I could tell you the answer. But I can't because I don't know. Did the rear end make noise prior to taking it apart. If so, was there a discernible reason (like a bad bearing)? I'd think if there was no noise prior to taking it apart and the backlash was .010 then that it could be OK. It looks to me like you have replicated the original wear pattern.

Congratulation on the job. It shows you are very thorough. And, given the physical difficulties, you are to be commended. Whatever you decide my hope is that it turns out well.

[TWChamp]

It's not so much how long you are using reverse, but each time you let off the gas you are engine braking, which means running the coast side. That's why I like to check that also. I brush the marker on all the teeth and spin it all the way around, then spin it all the way around in reverse to check the coast side. I still stand by my original thought that I wouldn't worry about a hair extra clearance as long as the pattern looks good on drive and coast.

Talk about extra clearance, you should have seen the MoPars in the 70's and 80's when I worked at the MoPar dealership. They had more clearance when new than car with worn out rear ends. Clunking was part of the game with them.

[bsrosell]

Thanks TW; I'm heading out to "check her both ways" now (and the run-out, on machined service, curiousity mainly as SHOULD be zero all the way around.....??)

Your comments make me feel better about 'leaving well enough alone" unless I see something strange here on 'one last check'; will post photos if questionable to me, not 'dead' center' on both sides....

Say, noticed your avatar, 50 Champ? exact same car as my father-in-law (all original, no rust; just had it painted finally after having it 20 years...) but his is a 4-door, yellow with white top. Love those bullet-nose cars (50-51 only , right?). Maybe I've seen yours at the North Star shows at Lady Slipper or Menomonie? See you list "Minneapolis"; I'm by Stillwater...