The Stovebolt Site Forums The Shop Area Driveline 3.55 gear set install and shim selection

So I have had good luck installing new NOS bearings correctly installed everywhere on the pinion shaft assembly and nice parts new ring gear installed new carrier bearings, I keep reading mostly the Chevy manual although I’ve looked at several other articles from the various members on the site. Everyone has a different answer. Should I go by the shim selection of the Chevy manual which suggests using one 0.18” shim when installing new ring and pinion or should I short cut to some other shim selection?
What I had in there originally was one 0.15 shim and it was a sloppy mess with huge backlash, at least 0.70

Running in a 54 half ton with a 53 gear carrier

Thanks Todd

I’m going thru this gear swap right now and can’t find a source of pinion shims but I’m working on a 40’s rear. Can you find shims for the 50’s? Think the 0.18 was the stock starting point and adjusted up/down at the factory and marked on the pinion.

There is no "standard" pinion shim thickness. The whole purpose of shimming gears is to correct for manufacturing tolerances that add up and build in errors in tooth contact patterns. OEM pinion gears had depth adjustment information electro-penciled on the back end of the gear, which might be "(+4)"- - - -"(-3)", etc., which indicates the distance in thousandths of an inch from the centerline of the ring gear the pinion gear needs to be positioned. If the markings on the original gearset can still be inspected, a WAG can be made about how to alter the shim pack. Final tooth contact patterns MUST be checked and adjusted as required, using some type of indicator dye such as Prussian Blue or white lead. Somehow, I think it's impossible to get a backlash of nearly 3/4" "(.7)" ?????? Maybe that was intended to be ".070"? Yes, decimal points and place-holder zeros do matter! There's no substitute for an extensive amount of experience in setting up rear ends, except maybe blind luck!
Jerry

The pinion shim will not have any impact on the backlash, it will have an effect on the contact pattern of where the pinion rides on the ring gear, I would start out with shim thickness of .023 since you had a .015 in there originally. You stated .15" but surely you meant .015"
Backlash is adjusted with the side to side nuts on either side of the differential side bearings.

So you are all right with my decimal point being off. Please take a look at these and let me know your thoughts, I think I am close.
The shims I am using are 1 - .018 and 1 - .012 let me know your thoughts.

Thanks

Maybe I should mention backlash is .007"

I think your contact is a little high on the ring gear teeth. You also need to look at the coast side pattern.
Here's a pic I got off the web. It would indicate that you need a little more shim thickness on the pinion. But again, you need to look at both drive and coast patterns.

I see that you're reusing the carrier that the pinion ate into. Hope you at least deburred it and cleaned everything up.

Almost there, If it were me try a little more pinion shim, no more than .003 to start with. Looks like you are working with a deep bore carrier. You are getting there, keep creeping up on it.

Thanks for the help

Be sure to load the gears as hard as possible when turning the pinion to check tooth pattern, and always use the pinion to turn the gears, not the ring when checking. Another really good trick is to take a new pinion bearing and have the center honed out for a slip fit on the pinion gear, use this bearing to set up with, once you are happy with the set up, replace the slip fit bearing with a press fit. If the pinion bearing is tough to get back off, cut some steel shim material to fit behind the race. The races are pretty easy to knock to and put back in.

I tend to agree on the pattern shown, needs to be a bit deeper into the ring gear.

I got you confused with another member who had the pinion bearings go and the pinion contact the differential carrier. Yours isn't as bad as his, but still, I'd be a bit concerned with that much metal running around inside the pumpkin.
Check out the damage on his carrier. Crunched differential

Kevin, the carrier was an extra that I sent him, it had some marks on it but checked out ok.

I think every diff carrier I have ever seen illustrating a repair or replace article had some form of marks on them including the old one I removed from
my truck in no worse condition that the one I show in the picture. It had lots of backlash and run-out but not blown-out.

This Diff has all new bearing sets for the entire rear end, NOS Hyatt and NOS New Departure on the pinion and NOS GMC on the carrier.

Looking forward to the day I get to take it out for the first run.

All I know is that the engineers didn't design them so the pinion hits the differential carrier.
Something has gone wrong on those that are marked up to reduce the clearance between the pinion and carrier. Wear in the pinion bearings, which would increase backlash as well as axial movement of the pinion, could easily account for the interference markings. That metal that used to be on the carrier had to go somewhere, and would increase the wear rate of everything.
If yours was checked out and cleared for use, then that's good.

The most common cause of that damage to a carrier is a badly worn or destroyed front pinion bearing. When the driver lets off the throttle, the pinion gear gets sucked back against the carrier. I've also seen a loose pinion nut cause the same sort of problem.
Jerry