Attached are pics of the pattern on a new 3.73 R & P from Toms.
Struggled to get 22 inch lbs pre-load with seal using a "crush sleeve eliminator".
Instructions sheet for US Gear from Toms's suggests 25 in lb on new pinion bearings and 15 for used.
Backlash was .008, again US Gear recommends .008 - .012 for street, .006 - .008 for track.
Set up with a slip fit pinion bearing (made from bearing I took out)
Drove the car 12 miles per instructions and let cool in addition to running a 2-3 minutes on the stands
Little noisy. Thinking as the gears seat, they will quiet down.
or I need to get the contact patch on the drive side more to the center away from the toe by changing shims.
PO had new axles, carrier, 3.08 R/P, yoke, bearings etc, only about 500 miles on this setup.
Reused carrier bearings, replaced pinion bearing/races with new 3.73 R/P

Comments? thanks in advance Mark

 

Did you use a pinion depth gauge? That pattern looks like the pinion is not correct.

 

No, trial and error with set up pinion bearing

 

Noise doesn't seem to ever go away if the pattern or lash is off. I had a 4.11 that sang on coast for 20 years and now a4.11 that sings under load while in 4th and 5th gears

 

Hi Mark,
Your pattern is deep. One thing you that you mentioned to me in a pm was this is for a Pontiac 12 bolt. I believe that Pontiacs came with a 10 bolt posi. The 455's could get a 12 bolt but it was a Chevy 12 bolt. So setting up new gears in a solid diff like this Pontiac is usually done on a lift in the car. I don't know if you pulled the diff or did it in the car. It only makes a difference in the ease of work. I would rather do it out of the car. To those out there that refer to the 10 or 12 by the number of diff cover bolts it should be by the number of posi ring gear bolts. The vette rear cover has 8 bolt but it's not an 8 bolt there is a 10 bolt in every 63-79 diff made. The 12 bolts were never offered in a vette to do the tight housing, of course Tom's offered them for 45 years and still sell a 12 bolt kit today.

So on to your diff. As mentioned look at the pattern on both the coast and drive side. The length of the pattern is longer in the root of the tooth then the crown on both sides. This is a bad pattern setup and it will never wear in or quiet down. You need to start over and get the pattern equal on both sides of the gear. Text book would be equal and center on the tooth. The US Gear vette gears have been center to toe on the drive and center or center to toe on the coast. The 12 bolt gears are the same only larger. Those gears should set up center to toe on the drive and center on the coast. You need to go to a thinner shim, however if I was doing that I would start with a fresh rebuild kit with USA Timken bearings. Yes I know your case bearings are newer and you can use them, again I would replace them all going back into it.

You setup the pattern well before you go to the crush sleeve or solid sleeve and the seal. That may mean 4-8 times of setup and break down to dial it in. I don't know if you did that first or not. That is one reason doing a vette diff is actually easier to work on. Now I have read more then once that vette diff's are harder to setup and this is Total BS. The 12 bolt and the vette diff use the same bearings and clutches, the procedures are the same it's just the 12 is physically larger then the vette 10.

Once you get the pattern dialed in, then you go to final and if you're using a solid sleeve kit they have to be fit. Many are made by Ratech and they are good but the shims supplied with them are no where close to dialing them in, as it sounds like you found out. I parallel grind them and then dial them in. The preload should be 15 -20 in/lbs on new pinion bearings only. It is important to understand the final measured preload has to include the preload on the case bearings and that adds 8-10 more. If you are not drag racing or going to launch the car hard you can use a crush sleeve. I use a solid sleeve in all my super 10's (not the knock off type builds) and my 12's. Trying to dial them in using the supplied shim kit will drive you crazy. The preload is measured once the solid sleeve has been torqued to 125 ft/lbs then the drag measured. It takes time to do this and on the car makes it much more difficult.

With new bearings go 15 -20 in/lb, add 8-10 for total. With used good bearings 5-7 total. The gears should be heat cycled and I tell guys to drive the car 20-30 minutes- normal street driving- no racing or highway use. Stop and let the diff cool for at least 1 hour. Do this cycling 10 times, change the oil at 500 miles and then I change again at 8-10k miles for high quality maintenance. I am not going to get into oil types, seems everyone has their favorite brand. I use 2 bottles of GM additive and Lucas 85-140 gear oil, no synthetics or high priced oils. Also I have read some say Lucas turns to a water consistency. I have not seen this nor have I heard back from anyone I worked with that used it that had a problem. Given the source of that comment I suspect it might be biased. Lucas is not a fly by night company and I think they would be the first to know if their products were not performing to high standards, there are just too many out there using it.

So recap, I would get a new master kit and go through it again. Pulling a pressed on bearing several times is not recommended. At a minimum you need a new seal. I think you should be able to reset the gears as you don't have a lot of miles on them.

Good luck, I'll be watching for your progress.

 

Gary thanks for your comments. Yes I have a 4 post lift and I changed out the diff in the car. Going on 67 so it beats laying on a slab of concrete!!
12 bolt diffs were avail thru 1970 on GM F bodies.
I had a Corvette vendor do my last diif in my 72 Vette. Took it out and had it rebuilt, change ring and pinion from a 3.08 to a 3.55 installed and was noisy on coast. Took it back and then reinstalled again, same thing. It was a Motive gear.
I have a decent amount of mechanical skills sooo I thought I would give it a try.
I had a rebuild kit from Tom's (all bearings are Timken USA) and I used a set up bearing to save the pinion bearing to one press. So I need to determine if I need new pinion bearings.
Wondering If I can reuse the pinion nut (new with only 1 install) ?
So I am going to re do the pinion depth with less shim
thanks to all who commented Mark

 

Mark you can do it. Sounds like you have the time, place, and tools to do it. Even a new master kit costs a lot less then having a shop do it and do it again. Don't get me wrong, things happen, yours was a setup issue but you don't do this all the time so really not bad, a learning curve. If you did diff's and sent out that pattern then I would suspect some issues with build quality. You have the best gears to use, US Gear is all I use. I would not use the other brands if you have a choice. A shop will use the gears they get the best price on and then there are still issues as you found out.

If you decide to go back at it and want to discuss the procedure you can call me. It is always better to run over things with someone if you can especially on stressful things like setting up a diff. One big thing you have going for you is you know what is being done and can control it. Sometimes guys are told one thing and get another based on potential profits for the builder.

 

I agree... deep for my liking and what we say here is once a singer always a singer.... Look at the pattern in Gary's avatar.... that's what you want it to look like.


Ernie

 

I nominate this for post of the week......well said and to the point.

Jebby

 

I agree,
Gary is a great guy.
He has been a huge contributor to this and other forums for years!!
Not too many people are willing to share their time and knowledge today.

 

So I tore into the diff on Thursday. Gary R was gracious enough and called me with help and support. Also diagnosed my many pattern changes along the way. So after several setups with reducing pinion shim from .045 to .033 to .036 to .041 than back to .040. I think this is it: .040 shim with .006 backlash. Haven't gone to final setup yet. I used an old pinion nut and a setup bearing.

Struggled with getting a clean pattern. Added oil to the paint, tried WD 40 and so on. Maybe because I put 12 miles on the gears and the gray coating was wearing off???

Coast and drive appear to be centered between the root and crown and the coast is the center to toe as is the drive side