I am going to have to have my differential pulled and serviced this week. When my mechanic was replacing the rear brake lines and hoses, he noticed that he could move the splined yoke on the passenger side slightly in and out of the differential by moving the tire. His diagnosis is that the C-Clip is missing from the yoke, inside the differential. While the diff is down and open, he recommends new bushings, seals, etc. Also, since it will be apart, he recommends new yokes (not knowing yet whether the old yokes are damaged) and halfshaft U-Joints. This will cost me $680 in labor and $480 in parts. I must get this repaired to make my car safe to drive. But, once this is done, will having replacement parts hurt my car when I take it for Flight Judging later this year? -Clark
-
-
Re: Rebuilt Diff using Repro Parts
Some noticeable yoke end play is normal on a used axle. Though there is no OE maximum specification up at least 1/32" is considered "normal", and many have been run with much more and no ill-issues. Normal forces on the wheel/suspension will keep the yoke pushed inboard unless you get it airborne!
I recommend you hold off on overhauling the axle. I doubt if a c-clip is missing, and I doubt if it is unsafe to drive. I also doubt that your "mechanic" understands the axle and rear suspension design at an engineering level, which would include the various forces and reactions.
About three years ago I co-authored a detailed article on Corvette axle diagnosis and overhaul, and I expect it is on the current Corvette Restorer CD, but I'm not sure. You should read it before you progress further on the axle.
Yoke end play increase on Positraction axles is normal as the clutch pack wears. Also, yoke end wear can increase end play, but this is not typical of C2 yokes - just later built yokes used on C3s. The axle end play on my Cosworth Vega must be at least an eighth-inch. I don't like it, but it's normal! I guess your mechanic would want to overhaul it, but the large play is part of the design and cannot be fixed without redesigning the axle.
Meanwhile, check Positraction preload, make an accurate measurement of yoke end play, and keep you ear out for clunks and other axle noises that may indicate it needs an overhaul.
From what you have provided so far, I see not need to overhaul it.
Duke -
Re: Rebuilt Diff using Repro Parts
Duke, the mechanic showed me that the yoke pulls out of the diff about 1/4" or so, changing the toe-in/toe-out on just that rear wheel. He moved the tire/wheel and I saw the yoke's splined shaft move in and out. I wonder if that is the reason my car is so "rear-end happy" over slippery surfaces? I saw no yoke "play" on the left side. So, you still recommend no service?
Also, he showed me where someone used "star washers" on the rear suspension instead of the correct "French Locks". -ClarkComment
-
Re: Rebuilt Diff using Repro Parts
A quarter inch is significant and could cause toe changes, which can produce rear wander. I still don't think it is unsafe to drive (at a moderate pace), but that amount of end play should eventually be addressed.
Axle overhaul is not difficult, but is a precision task. Once it's opened up/apart a judgment has to be made on what parts to replace, and that's a tough call for anyone here unless they can inspect the parts and get a feel for the axle's history You should still test Positraction preload before the axle is removed.
Given that the excess end play is only on one side it may well be yoke end wear. Clutch pack wear usually increases end play about the same amount on both sides.
I don't think new yokes are commonly available, so you are left with good used or rebuilt yokes. Search the archives on the availability of rebuilt yokes before you proceed. I know this has been discussed in the past, and I think it was Joe Lucia who provided most of the information.
DukeComment
-
Re: Rebuilt Diff using Repro Parts
I had a similar situation on my 1970 several years ago, and although given my use of the car it would not have created much of an issue -- I did decide to have the trailing arm bearings and differential rebuilt.
There was substantial wear on the stub axle, and we replaced both both of them. The positraction plates were also replaced, although they really didn't need it. That decision was one of those "while we were in there" sorts of choices.
We replaced the trailing arm bearings without removing the trailing arms. That made the job more difficult, but I didn't want to disturb the original fasteners or shims. The condition and your use of your car should dictate how you proceed.
I very much doubt a judge would detect the new stub axle if the car were judged on the ground, but it would be obvious if judged on a hoist. Had we removed the trailing arms I am sure we would have had to destroy the original toe shims and possibly the through bolt at the front of the trailing arm. Replacing all those certainly would be obvious to the judges. On the other hand, my car is past being judged and is mostly used for Bowtie display these days. NCRS members can be more discerning than the judges, and I wouldn't want them to see a lot of replacement parts on the car. That is not what they come to see. So we went out of our way to preserve what was there. Your decisions may be different, but I suggest the thought process ought to be the same.TerryComment
-
Re: Rebuilt Diff using Repro Parts
Clark,
As earlier stated, your guy is either real hungry or really does not understand whats going on. Although his prices are not way out of line.
There is never any outward pulling side load placed on the side yoke in the remove direction. The c-clip would NEVER be suitable to hold any load, its just a little clip! In normal use and driving the side yoke should never be moving in and out, it should be loaded towards the center always right thru the full available arc of suspension travel. If all other components are in good shape camber should stay within an acceptable level, the end play will not give you any loose feelings at all back there and is not a concern unless the yoke is worn beyond tolerance that can be adjusted out with the strut rod camber adjusters. I have seen many cars, especially 76 and later cars where the side yoke wore out enough were the clip fell off inside and they were still driving around with no issues. The only time a missing clip may be an issue is if the car is put on a lift with frame lifting points, allowing the rear wheels to hang unatuarally loose, the yokes will come out farther than one might like, potentially cocking the yoke and pinching the side seal. I remember the first time my alignment shop saw one of my cars that way and he called me to tell me something was bad wrong. I assured him there was not. On my own cars, when I rebuild the differential I do not even put those clips back on, no worries. Top flight cars. No one knows, and the involved replacement parts would never be seen by any judge if you do choose to get it done one day, but based on your description, you presently have no worries!Comment
-
Re: Rebuilt Diff using Repro Parts
Clark-----
If the stub axle is moving in and out 1/4", I'd say that very likely represents extreme wear on the axle end. I would definitely get the differential overhauled. I can almost guarantee you that what you're going to find is wear on the ends of both axles, with extreme wear on the side with the 1/4" play. These axles are case hardened. This means that the hardening is not very deep. Once the hardening is worn away, which is virtually certain on the axle with the 1/4" play, further wear proceeds very rapidly. At tear down, I recommend that if there is ANY wear on the end of the axles, they be replaced. There will almost always be some wear. The differential center pin should also be inspected since this is the component the axles wear against. It's manufactured with a Rockwell hardness greater than the axles, but it will often show wear. If any is found, replace it. It might not be absolutely necessary, but it's not that expensive.
As far as axle replacements go, there are many options. New GM axles are not an option since they were all discontinued quite some time ago. Here are some ways to go:
1) rebuilt axles. These are original axles that have had the ends ground off and replaced by THROUGH-HARDENED sections about 1/2 to 3/4" long. In this manner, no strength is lost since the section replaced is, when installed, external to the spider gears. In addition, the through-hardened section is virtually wear-proof, making the axles effectively "immortal". These axles should appear externally identical to your present axles. So, whether they can be observed by a judge, or not, it won't make any difference;
2) new axles from International Axle. In my opinion, these are the best and strongest axle out there. However, their finish and appearance otherwise is different than original. Also, I don't know if they are available in the u-bolt configuration your small block application uses. Of course, you could always convert to the "HD" cap style. Although also discernably non-original, I like these the best;
3) other new reproduction axles. The ones I've seen look very similar to originals and are available in both u-bolt and "HD" cap-style versions. Some may be of foreign manufacture, though.
ALWAYS replace the u-joints with new, HIGH QUALITY u-joints.In Appreciation of John HinckleyComment
-
Re: Rebuilt Diff using Repro Parts
good information for you, here's some more to think about.
If you have .250 play in the yokes then the snap ring not c clip has to be off. The snap ring groove is .185-.190 from the end of the yoke to the ring. You're beyond that now. If you have an original 65 diff then I would be interested in checking the posi case. I just blueprinted 2 67 BB diff's over the past month. The original Eaton posi cases were both cracked and once they crack they're done. You should have the first design posi case with the sm square window.
Now if the posi and/or diff have been worked on in the past the spider backlash may not be set correctly. I find a lot of 63-79 posi's incorrectly rebuilt, mostly to save time during the job. The spiders in your case should be 10-18's not the best, but will work. The clutches should be solid steels unless someone installed the snowflake clutches in the past.
There are several ways to make these units stronger, not sure if your guy knows these units or not. His price for a base line rebuild is high. You're getting into blueprint cost.
As Joe pointed out international axle make very good parts but I think Toms custom axles are stronger. They come in 17 or 30 spline. The 30 will require new spiders and case machine work but they have C clips which are fit. Once the posi is tuned and correctly setup the endplay in the yokes has to be machine fit. The 67 I just did I set for a true 005-007 endplay. You will not get that with a stock rebuild with the springs in most cases.
good luckComment
Comment