GTR1999 posted this great rebuild differential thread

[grumpyvette]

Ok I know a lot of you have followed my threads on diff's over the years and a question I get a lot is " Why are your's different then any of the others out there"

That is a very good question, so here I present something for those of you who want to play along. Let me know if you see anything odd here. I'll go over what I was told before I opened it up. I won't mention the owner or the well known rebuilder. I will say the shop is South of the Mason/Dixon.

Some may know and Mike Dyer can't play! He's got an unfair advantage over most of you and this is not his work but he does know who it is. There is a fellow in Europe who probably would know too.

Ok this was "rebuilt" recently and has only 800 miles on it. The gears were whining from day one and the pinion seal leaking like an open tap.

What you can't see, 020" backlash, 030 pinion endplay.

So anyone want to take a shot? Win a no-prize!

The main purpose is to use this as a tool to inform and educate the average vette owner. Anyone in the rebuilding business would or should know this.

You guys are sharp but no cracks seen yet. The posi is a loaded Eaton. I want to mention I like and use Eaton posi's. They are my first choice, I just mod them somewhat for my own taste.

Ok here's what I found.
First look at the carrier( housing) and you see it's a 1965, stamped for a 65 396 in fact. NCRS guys might want it,but I already ground off the ears. Then look at the bearing caps, not correct for this year,they're 71-79 with cast in tab. What's that mean? They were not fit to the carrier, the caps originally were line bored so the caps are matched to each carrier. I was able to loosen them by hand with a 3/8 ratchet. The case came out without any resistance and NO preload- Not good.

The Ring gear bolts are std grade 8's,they're ok but I only use them in very mild applications. They are part of the common master kits sold many of which include the cheap side yoke bearings which I also don't use.
I use ARP RG bolts.

The back lash was way off and the wrong shims used. The 63-68 housings are narrow and no one sells a master kit with the correct shims in it. The kits use shims for the wider 69-79 housing- vendors please note. I grind shims to size when rebuilding these.

I've made my feelings known about using certain posi parts. This is just my opinion, only the way I do them, others think otherwise - generally motivated by money.
Here are the fiber coated clutches.

HD springs with less clutches per side and once the springs were removed there was 030" endplay in the side gears- also not good.

The diff leaked from lousy setup - 030 endplay in the pinion yoke and CHEAP parts, in this case the pinion seal used. Also no sealant on the splines - only under the washer completely useless and shows complete lack of experience with this work.

Other things, the crush sleeve was over crushed,the cross shaft had wear on it already- I use HD shafts, I didn't care for the R&P set, the pattern was all over the place.

So I hope this helps answer some questions, if you need a diff make up your own mind and ask questions before you decide.
You all passed!!

I'm still working on this diff and everything I check is bad. This one caught me by surprise at just how bad this was. Many times I'm asked about fitting the bearing caps or a steel cap. This job is getting a fit steel cap on the LH side. I set them to 001-0015 rock,meaning the cap acts like a seasaw. Press on one end the other goes up and you measure the gap between the cap and housing pad. Then you divide it in 1/2 to get your parallel gap for correct cap fit and torque. The stock caps are bored and most times are in this range, +001" and work fine.
The steel cap here is set to 001 and done. When I installed the supplied cast RH cap it had 032" gap or 016 parallel !!! This is why I found the cap bolt hand tight, they must have just grabbed a set of caps from a late C3 and bolted them in and shipped it. I really thought I wouldn't be surprised with this job, I was wrong. I have to fit a RH stock cap. If the cap was torqued down at 016 parallel it would have distorted the race and caused bearing failure. I hope the guys that asked me this week about building cost read this, they went with a similar builder due to lower cost, good luck!


Here is the cap, you can see the "builder" marked them. Too bad he didn't know what he was doing.

Rock in the stock cap

Fit steel cap

Ok for those following along with this build, it's done and on the way back to be installed and broken in.

Here are some more pictures, kind of redundant from my Diff post but these are from this build.

Correct side shims used and ground to size by me. This one isn't ground yet.

This is what they used

My Pattern

Billet 1330 pinion yoke

Solid Sleeve ready to be ground to size.

correctly setting the preload on the bearings with the solid sleeve

Setting up the endplay in the 30 spline axles.

So I took this

And turned it into this, just a bit different.

Ok Mark, I'm waiting to hear from you on your build!

http://dazed.home.bresnan.net/narrowinga9.html

http://www.crankshaftcoalition.com/wiki ... _a_rearend

http://www.bhjproducts.com/bhj_content/ ... ng/dnk.php

 

[grumpyvette]

Fred Mann posted this related info

failure to use quality components, and assembly tech, will eventually result in something similar to this, if you apply serious power to a corvette rear differential with slicks
The 3.70 differential that is the subject of this post is mine. I bought it from Duntov Motors.

A friend of mine found the Duntov website and contacted me about it shortly after he bought a 3.08 rear from them. One of the reasons I bought from Duntov Motors was that I didn't have to send a core to them. I didn't want to lose the 3.08 and 3.36 rears that I had, so that no-core idea appealed to me. I hadn't done a lot of investigating with other sources (big mistake), but I hadn't seen an Eaton posi-carrier upgrade either, except on Duntov's site. I was aware of Gary (gtr1999)from other posts on trailing arms, differentials and steering boxes, but hadn't spoken to him prior to purchasing the differential from Duntov. I wish I had.

When I got the 3.70 rear from Duntov, I used the Royal Purple synthetic gear oil that Duntov Motors recommended. I was told that no special posi additive was needed with the Royal Purple and the carbon fiber clutches that came with the "big window" Eaton carrier. I don't know what all caused the carbon fiber material to come off the clutch plates, as Gary's pictures show, but the differential did not chatter at all going around corners.

The Duntov rear arrived in a plywood-lined cardboard box. There were no break-in instructions. I filled the case with the Royal Purple oil with the differential out of the car. I had the case cocked a little to make it easier to stick a funnel in it and I accidentally overfilled it, by how much I'm not sure, but I still had some left in the last bottle. I was filling the case before putting it in the car because I have the rear dual-mount spring, which makes getting at the fill plug more difficult. When I returned from the first 25 minute ride, I noticed a fluid leak as I backed the car unto my garage lift. The rear had gotten hot to the point that some fluid had leaked out around the stub axles and some from the vent. There was fluid on the rear cover and on the spring. There was a small amount at the pinion seal. I called Duntov and they told me that they expected the diff to get hot initially and that I had put too much gear oil in it. After the call, I got under the car and pulled the fill plug out and let it drain down to the edge of the hole. I don't think this overfilling affected anything other than my ego a little, but since I'm trying to be accurate about Duntov's performance and Gary's rebuild, I'm including my own screw up too.

During the brief initial drive, I noticed that the rear was making a noticable whine that I didn't have with the 3.08 that I'd just had in it. The noise was there at all times when I was giving it gas, even when just crusing at the same speed. If I let off and coasted, the noise disappearred. When I called Duntov about the fluid overfill, I asked about the noise I was hearing. The various people at Duntov I had spoken to, before and when I placed the order, had warned me about the noise I definitely could expect if I went with the 3.90 Richmond gear set. Since I had chosen the 3.70 gears, I didn't expect any appreciable noise or none that lasted as the unit broke in. I'd previously had 4.11s in another Vette that was quiet. I asked about the noise during the call and there was a little surprise on the other end of the line when I described how loud the noise was. I was told that it was normal to have some noise and it should get less noticable as the gears broke in.

I asked about how to break the rear in and was told to drive it easy for the first 500 miles as I would a new car. That and no hard launches was about it. They didn't give a specific break-in procedure. I'm not a clutch-popper and pretty-much bog the engine from a start. I do get on it pretty hard at times once the car it moving, but I behaved myself until at least 500 miles had gone by, probably 30 minutes at a time. The noise level stayed about the same during the 800 miles I put on the rear before pulling it.

At some point over the 500 mile mark, I saw a thread on DC about a Duntov rebuild that had catistrophically failed. In addition to whatever had happened to the internals, the exterior "pumpkin" case had cracked in half. In that thread, I learned that the person that had built rears for Duntov's race car(s) and their customer's cars for the bulk of their 30 year history had left the company four years earlier. Based on the doubts I had about the noise I had in the rear I'd bought, some reading of other posts on another Vette site and the fact that I was going to be upgrading my car with a healthier engine, I decided that I needed the Duntov Motors rear rebuilt, at 800 miles, by someone other than Duntov. I never contacted them again and don't know how they would have handled my problem differential, but I decided that they didn't have the expertise to do the job.

I'm not going to try to repeat all of Gary's findings here on the teardown, when you can look up above for the details, but basically it appeared that the Duntov rear had been thrown together in a hurry by someone who didn't know what they were doing, didn't care what they sent out or both. When I saw the cheap parts, sloppy set-up (3 times and more over what the various tolerances should have been, in some cases much more), ruined brand-new (foreign-made) gears, worn cross-shaft (either from being a used part or just damaged from the bad set-up) and bolting hardware that was practically hand-tight, I knew I had made the right choice not to deal with Duntov Motors on any kind of repair. It wasn't as though there was one main error in the Duntov rear, it was filled with one problem after another. Crappy gear pattern, excessive lash, mis-matched ill-fitting caps. I had paid about $1800 for that rear.

I contacted Gary through DC, discussed the problem I was having and the fact that I was going with a new engine with at least 100 more horsepower than I currently had. We decided on a "Super 10 Bolt" build. Currently, the "Gary Special" is on its way here and should arrive in 2 days. Gary has been great during all of my dealings with him. Straight-forward, up-front, and any other superlatives that you can name. I am a mechanical engineer by trade and by nature. Gary is one of those guys that you immediately know is on top of what he is doing and an expert. His attention to detail and the amount of "fit-up" time, where he is getting things perfect, is great to see. He continuously sent photographs of the whole rebuild, from the initial teardown to the packaging as it went out the door. He answered anything I asked him and we had a pretty steady e-mail string going as he sent me about 100 photographs with a running report on what he found and what he was doing. I'm getting the new rear back about 2 weeks earlier than I expected, thanks to Gary's hard work. The proof of the pudding will be when I get the rear installed and broken in. I will post about that when it occurs. Based on everything so far, I couldn't be more pleased.

Fred Mann

 

[northrnyankee]

Since it was a recent rebuild you probably didn't bother checking the thrust washers for the pinion gears but I think it should be noted that brass thrust washers were used in older units which tended to wear out rather quickly. GM did replace those brass washers for metal ones at some point but the 67 rear end I have with an Eaton had the brass thrust washers that were worn paper thin on it's edges.

 

[grumpyvette]

http://www.dennysdriveshaft.com/c34_dri ... hafts.html

http://www.corvettemagazine.com/transmi ... ement.html

http://www.lgmotorsports.com/Corvette-Half-Shafts

http://www.dennysdriveshaft.com/c29_corvette.html

http://www.markwilliams.com/axleHalfSha ... nQodcV3zVg





"In regard to some Spicers joints, they are now merging with Mexico. Some boxes clearly print Mexican and USA parts. I haven't seen it on the 1350's...yet. I'm going to stock a few sets while I can still get the USA made ones.

Also on another forum there was a question on wall thickness of 1/2 shafts, both new and original. Many think the 2.5" shafts were thin walled but they were not. I had to order a new set of shafts for a buddy and the new 2.5" come in 083 or 095 tubes. I got the 095's for a st car, no real abuse.
Then I cut in 1/2 one of the old worn out shafts, .132" wall tubes from GM 40 years ago. I don't have any junk 3" shafts to cut and compare. IF anyone does post up what you find.
For HP use I only go to Tom's and his 3.5" .134 steel tubes, no aluminum, fiber, or thin walls."

To follow up on the new solid spicer install.
The body appears to be the same as the earlier 799x body, the black rings replaced with the white,and what appears to be red grease, maybe mobil1 is used to lube them. Remember do not mix up the caps, keep them with the cross end they came off of.

I had in a near mint set of 3" shafts from my buddy Tom. These have no pitting on them at all and really came out nice. I didn't have to radius the yokes but did have to cut the flanges a little to get the cross to fit.

These come with 3 sets of clips, 060", 061" and 0635". I didn't like any of them. I tried the copper 060" ones but it was too tight on the caps so I went back to the old ones I still have. These are new and what came with the 799 joints. They were 0585" and fit perfect. This may be a problem for those who don't have them, I could have ground them down but the 058's worked fine. Keep in mind if you have a tight clip in a flange it usually means the flange is bent. If a needle fell in the cap you wouldn't get it near the clip groove.

I seat & then witness mark them and finally test them in my fixture. These came out great. I found they actually install better then the old 799's because the white rings don't break like the black ones did, but they also don't snap in and lock like the black ones. I would use either. These are cold formed joints too so you don't have to treat them to any special deals as some advertise. The white rings are not available yet but I'll see if I can get some to have, like I did with the black ones.