What can move around in a diff under load?

[SUX2BU99]

I was doing some reading about rear end gear installation and saw something about movement when under load and deflection of the ring gear, away from the pinion. What kind of movement can occur when under large loads? As some of you are aware I've been having lots of troubles with my rear end gears. They've been redone 3 times now by the same shop and the same thing seems to keep happening: when I stomp on it and do a full-throttle 1-2 shift at high rpm (above 5000), I get gear noise, like they've been in hard contact with each other.

Before they ever touched it, no issues from the 3.40 ratio junkyard 12 bolt I put in last summer. After putting in a rebuilt Eaton and TORCHING out the Gov-lok, the 3.40 failed 4 days later. Then putting in a 3.73 'thick' Yukon R&P, they failed, again getting noisy after putting it through full-throttle 1-2 shifts. Then again, putting in the same 3.73 'thick' Yukon set and them doing an intitial break-in and me putting on over 350 miles of gentle break-in time, the first time I do a 5000+ rpm 1-2 shift, I get some noise. Not a ton, but more than before. 1-2 at WOT, at 3500 rpm was fine.

I just had the gear oil changed Friday. Put in Castrol Hypoy-C and a bottle of Motorcraft friction modifier.  Was hoping to quiet things down. Sorta did, sorta didn't. I feel better though that it's not their oil in there anymore, although they say they put in GM fluid which is the best according to them.

So anyways, it seems like the high-rpm 1-2 shifts are wreaking some kind of havoc. My tranny shifts really hard. It must have a 'stage 2' shift kit in it or something. Obviously the torque spike that occurs during the shift is doing something, I just don't know what. And I don't know why it would cause these kinds of problems. Would something in my housing be tweaked? When they torched out the Gov-lok could it possibly have warped something?

[Chevalade]

Depending on how much power you are putting to the ground, you may want to brace the rear. Your housing may be distorting causing chatter on the shift where there is a bit of slack then tightening.

[zieg85]

I would look into the driveshaft angle.  Looks like your truck is lowered a little and with that much power may be really flexing the leaf springs causing a bind.  My $.02

[VileZambonie]

I would be very wary of their installation at this point. The differential has nothing to do with it when you're driving in a straight ahead and are getting vibrations or noises. DO a gear tooth contact pattern analysis. It's easy to do and will reveal if there's a problem with their installation.

[SUX2BU99]

Thanks very much guys. Here is a post about my pinion angle and asking if it needs shims or not:
http://forum.73-87chevytrucks.com/smforum/index.php?topic=13213.0

There's a pic of my angle in there. Capt said it looks normal and yeah it does look pretty minor. I'm going to get my driveshaft rebalanced hopefully this week. $40 if I take it in out of the truck. Is there anything special needed to get the front u-joint off? I know the back just had I think 2 bolts on a strap and it was off. Front the same?

I could also go to a local shop and they will check out my diff for free. I just have to either bring or pay for new fluid when they take the cover off to inspect. So if my wear pattern is showing burnt teeth already, then what? That's what happened last time and when I picked it up this time they said absolutely nothing about why that happened or if anything was found wrong with my diff or housing. Of course, if they warped it when they torched out the gov-lok they won't own up to that I'm sure. Man that would BITE big time if they screwed up my housing.  Then I'd be at square 1 all over again with nothing but newer bearings and rebuilt LSD to show for it.

Seems to me that something is happening at the 1-2 shift at high RPM (lower RPM was okay) that the R&P really isn't liking and is seeming to cause bad contact, causing howl. It's interesting that flex was mentioned. Perhaps it is, but this is the same motor, with the same power that my original 2.76 open 12 bolt and the replacement 3.40 12 bolt lived fine behind until the shop touched it.

[SUX2BU99]

I've asked some manufacturers about this and one suggested that perhaps the crush sleeve is moving a little, which is messing around with the bearing pre-load. Perhaps my pre-load is progressively lessening everytime I do a WOT 1-2 shift, until there is no pre-load at all.

I found this very interesting how-to on adjusting pre-load at home. I can't believe this worked for the guy but it did. Pretty smart IMO, if his gears have lasted after this.

http://www.bernardembden.com/xjs/diff/index.htm

[malibu795]

what is your back lash set to?
what does your contact patch look like?
what is running torque on the pinon nut?
which side are you checking contact patch coast or driven?

[SUX2BU99]

^ All of those questions would have to be answered by the shop that put it in, and they don't want to talk to me anymore.

I've put some more miles on it and it's running fine, except when I do a high RPM 1-2 shift. I've done one and I'm literally afraid to do anymore. I'm convinced something is moving around in there when the torque spikes on the shift, and I can't see how looking at a tooth contact pattern is going to determine this. It's when I drive it hard that it seems to do funny things. If I'm wrong about looking at the teeth, please educate me.

When the 3.73s were replaced last time, I saw the R&P and the drive side of the teeth were wiped out. He said the surface was worn off and it got into the softer metal which ate them up. No explanation was offered 'why' this was happening. I, and probably them, thought it had something to do with break-in and heat.

[malibu795]

back lash and gear mesh go hand in hand.
ideally you want to have majority of the gear mesh in the center of the tooth.
this is adjusted by shims between the pinion and bearing moving then pinion in and out of the ring gear (usually refered to as high adn low) and shiming the carrier left to right this is refered to as heel and toe.

80% of it is controled by the pinion depth.

from you discription of the last R&P that was replaced.. sounds like the pinion was set too deep on the ring. and then back lash was on the tight side..  thus when going down then highway everything heats up and binds causing you to wipe out then set..

honestly i would do it myself next time. that way you would know how they were wearing and be able to adjust then new set accordingly.

i knwo summit and jegs sell a hot to vid on R&P installs

[SUX2BU99]

So I did a WOT 1-2 on Friday and then a WOT 1-2-3 on Sunday. Yep, more noise.


Talked to shop today, they figure it's the carrier I originally bought from them, which is an old 30+ year old Eaton. Same style as the Top Spec but thinner case, steel clutches. They figure it's distorting somehow on the shifts and they want to upgrade it to a Top Spec, put in new R&P again, and even change my housing. Not sure about the housing part but they will pay for all labor and new R&P and credit towards new Eaton. Thinking about it. Something has to be done though.

[SUX2BU99]

I proposed to the shop that they refund all of my money and the shop owner accepted my refund proposal! All I have to do is remove the carrier and gears. Who wants to give me some pointers  It's an Eaton limited slip. Do I remove it like a gov-lok or like an open carrier? My Haynes manual describes but not in great detail. Any tips?

I bought a replacement rear diff today. Stock 77 12 bolt with a 3.40 and gov-lok. 5 years ago new gears and a new gov-lok were put in the truck, it was used for a year and then the motor blew up so it was sitting for 4 years. Internals looked fine. It's going to go in my truck after I clean it, paint it and swap over the new brakes I put on my current diff last year. I'll run it like that until early spring and do the 3.73s and new Eaton. My truck hibernates for most of the winter anyway.

[team39763]

Removal wasn't bad.  It's pretty much just like they describe in the books.  Just drain the oil, pull out the shaft thingy(has a bolt in the side of the carrier to unscrew), push one axle in(with wheels and brake drums off), pull out the c-clip, pull that axle back out and do the same with the other axle, remove the bearing caps and be careful not to let that heavy mamma-jamma fall on you.  I think that's about it.  Good luck man.

[SUX2BU99]

Right on, thanks. So the carrier can come out without the R&P being removed? I have to get those out as well. I presume I'll have to undo the pinion nut. Is there anything about the R&P and carrier removal that isn't basically just unbolting stuff?

[team39763]

I'm not sure about the pinion.  I just know the carrier and ring gear are pretty easy to remove.  The c-clips are the only odd thing that I ran into...you need a magnet pen or a screwdriver to get them out if they don't fall out on their own.

[SUX2BU99]

So it's coming along. I thought I could remove the pinion nut by having the wheels on the ground and using my breaker bar with the socket on the nut. It wouldn't crack. The truck would just try to move. So I guess I have to get a long monkey wrench, put it on the pinion flange to wedge it against the garage floor, and try the breaker bar that way.

I moved on to the carrier itself. That is going smoothly enough. It's just now the carrier itself out. Seems to be stuck in there. The bearing caps are off, axles and c-clips are out so now it's getting the carrier out. Any tips? I have a short prybar but it hasn't really budged it yet.