C2 rear end set up

[Steve Daniel (37270)]

Craig Schultz if you are out there.....

In an August 31 thread, you gave some information re: set up tolerances. I would like to clarify a couple of things.

1) Side yoke end wear. You mentioned comparing (old vs new) measurements from the inside of the snap ring to the end of the yoke, but didn't mention what that measurement should be. Is there a spec for that?

2) Is there a spec for the center pin diameter? I guess there shouldn't be any wear on it, but I thought I would ask.

3) If .005" to .008" is spec for new set up, mine is way off. My driver side was .05" and my passenger side was .11". There is no apparent wear in the splines on either yoke, i.e. there is no play between the yoke and the sidegear when the yoke is inserted. Will worn clutches create this much end play?

4) Any suggestions as to where I might find a spring compressor suitable for removing the posi springs?

Steve

[Joe Ciaravino (32899)]

Re: C2 rear end set up

Steve:

It sounds like your "posi" is so badly worn, that it isn't "posi" at all right now.

The wear is caused by a combination of the following:

1. Wear on the thrust surface of the end yokes.
2. Wear on the center pin.
3. Wear on the "C" clips.
4. Wear on the clutches.

I had a similar situation with my 1965 Eaton unit. I do not know the tolerances, but I remember finding everything I needed in the Shop Manual. I ended up reusing the clutches, because they passed muster when examined per Shop Manual. I replaced the 4 springs, because they were mismatched. Replaced the 2 "C" clips. Replaced 1 yoke, because it was the big block type. Clearance is set by shim combinations. I did not use any special spring compressor, just patience and care.

I recommend miking the center pin at a non wear area, then miking across the area that contacts the thrust areas of the yokes-suggest that if more than about .005" wear, then replace the pin. If the yokes show excessive galling on the thrust surface, then the heat treated "case" is worn off, and wear will accelerate. If not badly galled, then clean them up and reinstall. Replace the springs, and the C clips-they are inexpensive. Examine the clutches CAREFULLY, if there is any doubt, then replace them (about $100.00). Shim kits are available. It is not too hard to set up ypur posi unit, but I would send the carrier out to a good shop, and have them set up your gearset.

Set mine up a bit tighter then Shop Manual suggests--about 80 ft-lbs to slip clutches. Car lays down 2 parallel stripes every time.

Good luck,
Joe

[Steve Daniel (37270)]

Re: C2 rear end set up

Joe

"Two parallel stripes" is my goal.

The center pin doesn't show any apparent wear, but I haven't miked it. I will check that tonight. The ends of the yokes are smooth to the touch, but have visible swirls or circles on them. The snap rings aren't visibly thinned, but I will replace them also. This leaves the clutches. I haven't inspected them yet, as I am still wrestling with the second set of springs. I removed the first two springs (pliers and blade), but have not been able to get the spring seat frames in the right position to allow rotation of the gear set 180 degs. to allow access to the second pair of springs. Is there a trick to it, or does it just require a little more patience?

The ring gear looks good; no visible wear pattern. One of the ring gear bolts was twisted off. No metal in the case and no damage to the gears, so I guess it was done during a previous overhaul and someone just put it back together without bothering to remove and replace it.

The pinion looks good also. No play, and no seal leak. I am contemplating just leaving it alone. What do you think?

Steve

[Philip Whitaker Member# 2024]

Re: C2 rear end set up

Steve,

You don't state in your post what year Corvette you're working on, but I read your profile and it indicates that you own a 63. If you are working on the original Borg Warner posi unit (used in 63 & 64 only), you will find that parts are limited, if not impossible to get. There is a special Kent Moore tool for removing and replacing the springs in the posi unit.

I had my diferential rebuilt, and took the advice of those posting on this board, and replaced the whole posi unit with a new Eaton unit.

I could not find any one who had the Kent Moore tool (shown in the service manual), and I could not find anyone willing to work on the Borg Warner unit.

Phil

[Steve Daniel (37270)]

Re: C2 rear end set up

Phil

You're right, it's a 63. I think my unit may have been replaced previously. It looks very much like the one described in the service manual, except the spring seat frames are different. Also, the service manual shows a picture of a ring gear with guide pins in it. My ring gear is attached completely with bolts, no pins. The only markings I've found are a part # and date (67) on the ring gear and a part # on the end of the pinion.

Steve

[Philip Whitaker Member# 2024]

Re: C2 rear end set up

Steve,

On page 4-30 of the 63 Corvette shop manual there is an exploded view of the Borg Warner posi unit. If you have the cages aligning the clutch plates and discs (part #2), then you have the Borg Warner unit. If this is the unit you're working with I don't think you will find parts available. However, if this is not your unit, you probably have an Eaton and parts shoudn't be a problem. The ring gear shown in the manual has guide pins installed for alignment during assembly. It will bolt in like yours.

[Steve Daniel (37270)]

Re: C2 rear end set up

I think I must have the Eaton. I just noticed another difference. In the pictures of the differential case in the manual, there is a large square opening in the front, and 2 vertical rectangular openings in the back, making access to the springs apparently easy. Mine has the large square opening in the front, but only a small opening in the back. This is the reason I'm having a challenge removing the 2 back springs.

Steve

[Joe Ciaravino (32899)]

Re: C2 rear end set up

Steve:

It has been a few years since I did mine, and it was the first and only one for me. I don't remember too many details, but the removal/insertion of the springs/seats required some patience and ingenuity--I think I made up some kind of clamp setup with some flat stock, nuts and threaded rod. I am sure that there will be some experts who can give more specifics.

I would absolutely, tear down the carrier to replace the pinion bearing and seal. Also the side bearings and seals. I would replace ALL of the ring gear bolts, especially since you said that one had sheared off. Make sure you have an expert set up your ring-and-pinion. They should deliver it with the white lapping compound on the gearset, so that you can verify the tooth contact pattern for yourself.

Joe

[Joe Ciaravino (32899)]

Re: C2 rear end set up

Steve:

I didn't realize that you had a '63, I normally check the profile, but for some reason I was thinking 1965. Anyway, if, in fact yours is a Borg Warner unit, then all bets are off.....parts are hard to get, and most folks won't touch that unit.

Check the casting info and stampings on the case. Chances are, that it is not the original diff., and so, that is why it has the Eaton posi unit.

Joe

[Craig Schultz (29385)]

Re: C2 rear end set up

Hi Steve - sorry I didn't see your post sooner, but you have received lots of good information already I see. Some of the information I quoted is not specifications from GM, rather, input from Charlie Smith from a couple of rear end classes I took at Bloomington.

1. On the dimension from the INBOARD side of the snap ring to the face of the yoke end, I recall the dimension is right around 0.250 - 0.251, but I would have to check to be sure. On reasonably decent quick check is to look for the bevel on the end of the face...if it appears to be square or gone, you probably have some wear. Your dimensions are way out of range....the 0.005-0.008 AFTER clutch pack break in is what Charlie likes to reach on setup. If you get 0.001-0.004 or so when assembling, it breaks in to the dimension stated. Usually, with the current Eaton posi packs, typical cases use a 0.028-0.030 shim on the clutch packs on each side, the way most are machined. This should give you a setup where the cross gears will fit just about right, and you can barely slide in the cupped washers behind each to assemble the unit.

2. The pin dimension I am not sure either, but it is very hard on the rockwell scale. I change mine out frequently, but only since they are about $8-10 or so. You should be able to easily tell if there is wear on the pin where the yoke ends press. The pin is designed to be harder than the yoke ends.

3. If you do have wear on the yokes, get either the refurbished yokes from Lonestar Caliper (they are a wholesaler but sell at shows to the public) as they have hardened through inserts on the ends which is better than original, or go to Tom at International axle and buy his yokes...they are extremely well made of superior steel forgings held to very close tolerances and case hardened carefully. The recent GM stub axles apparently have inferior and thin case hardening on the tips of the yokes and are prone to wear through easily.

4. If you reatain your originals, DON'T discard the original circlips that are 0.064" thick. They fit far better in the grooves machined in the yoke ends. The current GM circlips sold in packs of 10 are the standard fare that you buy through hardware stores etc and are 0.055" thick, which actually causes some slop in the end play and doesn't allow setup to be controlled as well as with the originals no longer available. This was a tip from Charlie as well.

5. I made my own posi spring compresser out of steel bar stock and grade 8 bolts. It works perfectly to compress the pack and allow it to slide in. Charlie does it with his hands and chin, and years of experience, he can pop them right in. It sure didn't work for me, I like my clamp compressor better.

6. GM posi packs recently had "ears" on each disk, and they tend to break off in Charlies experience. The EATON brand from DTS are like the original GM packs....maybe they are all this style now.

While you are in there, make sure and replace your bearings, seals etc. Set up the rotational torque on the pinion to 16-18 inch pounds for new bearing for rotational torque once the breakaway torque is reached, or about half that for used bearings. Usually the shim thickness behind the pinion bearing is 0.028 - 0.032 to obtain the correct pinion depth setting for most cases the way they are machined. GM has an elaborate tool to measure the pinion depth from the centerline of side bearing mounts, but generally you don't need to go to that trouble, and using the shim that was there with new bearings almost always works. If you are installing a different ring and pinion, a little experimentation may be required. 66 and back carriers were cut differently than 67 up so GM could use cast iron shims to more quickly assemble in the factory, the older ones just used steel shims on the sides. With the cast iron shims, the shim on each side is in the 0.235" or so range, while the 66 back is in the 0.074-0.090 range. All of this will vary on setup to get the correct 0.008" or so backlash. Make sure you use the yellow grease dye to check the mating pattern to insure it is centered and uniform width. Most used ring/pinions will show a full tooth mating pattern unlike a new set, and check for the pattern running off the pinion gear to insure it is centered correcty or the pinion depth shim may need adjustment. You don't need a case spreader to obtain a correct preload on the side bearings, you need 0.002-0.003 preload on each side. You can tap in the shims with a brass hammer in the 8-10 oz range.

Good luck....Craig

[Steve Daniel (37270)]

Re: C2 rear end set up

Craig

Thanks. In describing your spring compressor, you mentioned that it compresses the pack. Does that mean that you assemble the 4 springs between the 2 spring seats and compress and insert as a "pack" ? Does that mean that you remove it as a pack also? If so, I may be on the wrong track. I have removed the 2 springs accessible through the window, and have been attempting to rotate the gear set to get access to the other two springs. So far, I haven't been able to get the spring seats in a position that will allow the gear set to be rotated. I am beginnig to think that the the dimensions of the spring seats are such that they cannot be rotated within the case. Do I need to start working on Plan B ?

Steve

[Steve Daniel (37270)]

Re: C2 rear end set up

Craig

I got the other springs out and all is well. My previous efforts to rotate the gear set were obviously misguided.

I will not be able to install the springs the way I removed them, so if you would be so kind as to describe the tool you fashioned or perhaps post or e-mail a picture of it, I would be most obliged to you.

Steve