I am in the process of a frame off and have my differential out of the car. I removed the front u-joint coupler and replaced the seal on the front of the differential, I did leave the space in between the differential and the seal lip, and put permatex no 2 on the splines. Now I find out I should have marked it to put it back the same. Is there any way I can set this back or am I screwed?

 

Do a search for pinion bearing preload. There will be a used spec and a new one. You can use an inch pound tq wrench (beam type) to make sure it's right. Once you've done a lot of them you can get there by feel..but tq wrench is most accurate. You tighten the nut to achieve the spec for used bearings. There is a crush sleeve inside..so don't go too far. You can't back up at that point. You have to sneak up on it. Should be pretty easy to tell. If you TQ the nut to the spec, hopefully you'll end up in the used spec range.

It's best to use a new nut...or at least put some Loctite on the pinion threads and nut.

Good luck,

JIM

 

MY opinion...You are screwed. This nut is critical to how the ring and pinion mesh. Not saying that you can not get it right...BUT I never replace the pinion seal by itself. ONLY during an overhaul of the differential.

You are dong an off-frame restoration. I would be checking the run-out of your side yokes and the integrity of your clutches in the differential also. Also possibly replacing the pinion shaft due to wear.

You are traveling down a path that you have to ask yourself something. If I leave it alone and get it "kinda" close. If in a year or two you break a tooth off the ring or pinion and have to do it again...would you want to???? I am ALWAYS asking myself that question when I am restoring/repairing a Corvette...then I ask the customer the same question I asked myself and leave it up to them...so if they want to "by-pass" a service operation or a part replacement...it is on them if it goes bad and I have to go back in and replace it. Putting a worn crappy part back on costs the same as installing a new part most of the time.

DUB

 

Torque it to 10 inch pounds for used bearings, 20 for new.

 

Thanks for the advice. I will check the torque tomorrow.
Thanks
Mark

 

That spec is for a pinion gear installed only! If you havent removed your ring gear and it sounds like you havent, you will not be able to use that specification. Probably time for a teardown and rebuild.

 

If you only changed the seal and your differential was working properly prior to the seal change (and not noisy), just put it back together. You aren't changing any other hardware and the new seal does not matter when considering gear clearances.

If you had a Chevrolet Chassis Service Manual, it would have given you all the detailed info you needed to do this job properly. As you mentioned, you should have marked the yoke to index it properly for re-assembly; and you should have checked the pinion preload before removing the nut...so that you could know when you have the nut re-tightend properly as you reassemble.

But, you will have to "make do":

1. Look at the surfaces that contact between the yoke and the pinion. There may be some surface imperfections/wear pattern/etc. that help you get the two parts oriented the same as when they came apart. Do the best job you can with this, then put the yoke back on.

2. Install washer and nut and tighten ONLY to take up slack.

3. Use a torque wrench to apply torque to the pinion nut. WATCH THE TORQUE VALUE INCREASE AS YOU ARE APPLYING TORQUE. It should increase smoothly (you must gradually apply increased force to the torque wrench) until you reach a solid connection between parts...then the torque value will rapidly increase. As soon as you see this 'spike' in increasing torque load, STOP TORQUING THE NUT!! You will have reached the point where the crush ring was 'set' at the prior installation.

Note: The pinion nut will only require a small amount of rotation, once the parts have made solid contact during application of torque.

Be aware that this is a "stop gap" approach to reassembly, since you didn't do the disassembly correctly (sorry...that's just the way it is). But, if this reassembly method seems to go well and leave you will reasonable confidence that it is put back together correctly, it would be worth a try. The alternative is to remove the rear gear and have it rebuild which is a troublesome and expensive proposition when you only needed to fix the seal.

Give it a try. It will let you know if it isn't working well by the whining it emits while driving . If no unusual noises, you may be OK.

P.S. Buy a Service Manual for your model year and an AIM (assembly instruction manual) and read them ahead of any DIY jobs. You will be glad you did....

 

7T1vette,

EXCELLENT advice to help this guy out. But I am sure that you would agree. Without the correct procedure of removing the pinion nut. Going back in is a "hit-or-miss" situation....even if you use the torque increase method....as you clearly outlined. I hope he (and anyone else in this similar situation) reads your post and makes the correct decision.

I am NOT directing this to any one specifically:

Anytime I run into a situation where there is a slight chance of something screwing up...due to parts are brought to me all disassembled in a box and I have to re-assemble them...I ...as a rule of thumb...rebuild the item. And if the customer begins to "squawk" on how long it will take or the cost to rebuild it...I tell them..."Here you go"...I give them the parts back to them and wish them the best...because it was their ignorance that created the problem AND assuming that whatever they tore down would be as easy to re-assemble correctly. Even a dentist will go to another dentist for any dental work....I don't know..there may be some who can drill on their own teeth and be fine with it.

A tip for any Do-It-Yourselfer";

You can do EVERYTHING that I can do...just as long as you make sure that you obtain the knowledge, tools and are willing to take it to completion. Which in itself is the costly part in many cases. Because bringing "something" that is 95% completed to me ( or many other mechanics) does not mean anything. What it does is make me question all of what was done to get you to that 95%...and more times than not...it requires me to have to tear it all back apart due to specific processes were not performed. Because...in the past.... sure as shooting...if I didn't rebuild it again correctly...and just finished where he left it at...and something failed....I would hear..."Your the Corvette expert...and I would have paid you to get it right" (hindsight is kinda funny that way)...BUT ...what they forgot ...is that THEY did not want to pay to get it right and were willing to live with what THEY did. That is the main reason I do not just finish a partial repair...especially if it is important mechanical component. I do not possess a "crystal ball" nor a "magic wand"....I have to verify what is going on and work to achieve a quality repair.

DUB

 

I have decided to have it rebuilt. Thanks for all the comments.

 

It certainly can't hurt to go through it...but there are a gazillion seals done every month and I can guarantee you that most are done with an impact. Who knows if it had the proper TQ to start with? I've never marked one in my life....pull it off...change the seal and zip it back up. It's entirely possible the crush sleeve has compressed some over the years from hammering it...so it needs to be torqued to whatever the spec is. Ck to make sure it all turns properly....sleep good.

You're not going to change anything to do with the gear setup. The only thing you can possibly impact is pinion bearing preload. As long as you don't crush the sleeve any more than it is...you're fine. And even if you do a little...as long as it's not preloaded too much it will live a nice and long life.

Just my .02.

JIM

 

DUB: I understand your concerns. But, with a little care, the OP can save himself a lot of grief by buttoning it back up and seeing if it still works OK. I also accept that he has decided to have it rebuilt. I just hope he finds a credible technician to do the work.

 

Ok I'm going to check the runout on my side yolks tomorrow and that will be the deciding factor
Thanks again

 

You can check you clutch packs also to see if they hold up to the torque GM has outlined to check the clutches. If my memory serves me correctly...so do not quote me...I am not at work with my data...but I believe that the new clutches should be able to take 70 lbs/ft torque and not break the clutches loose and spin....and a used differential should be able to handle 40 lbs/ft torque.

Very good idea. If they are worn...I would replace them. Also take a very close look at the long bolt that secures the pinion shaft in the carrier. I have encountered NUMEROUS times that the end of the special bolt ...that fits into a hole in the pinion shaft to secure it...is either bent or cracked. If the tip breaks off...the chance that the pinion shaft can slide out is increased...and if it does fall out...you will create problem...depending on how fast you are driving. Now ...I have NEVER seen a differential that has actually had this shaft slide out...but the though of it just makes me shake in my boots.

DUB

 

If you're opening it up...definitely need to ck the cross shaft as mentioned and inspect the hole it goes through for being oblong or cracked. Definitely a weak area.

JIM