Rearend Gear Pattern

[JEFFTATE]

Hey everyone ,
I'm changing the ring and pinion gear set in my 69 Camaro ( GM 12 bolt ) and I'm having the worst time getting the pattern correct..
I'm no expert on rebuilding rearends , but I've rebuilt about 8 rearends over the years ( Both Chevrolet and Ford ) , and I've never had this kind of problem with the set-up .

The problem I'm having is :

No matter what thickness of pinion shim I put in ( that is : no matter what the pinion depth ) , the pattern is always too close to the face ( top ) of the gear tooth.

I've tried .015" , .020 , .024" , .028" ( the original shim from the original GM gear set ) , .033" , and .038" .
Each time I change the pinion depth , I keep re-setting the backlash to around .008" and the pattern is always too high on the tooth .

By moving the pinion closer to the ring gear , ( that is, by using a thicker shim ) , I have moved the drive side pattern from the outside(heel) to the inside(toe) of the ring gear , but the pattern is still too close to the top(face) of the tooth ..
Moving the pinion closer to the ring gear should have moved the pattern deeper into the tooth ( towards the flank ) , but it hasn't changed much ..
I have just managed to move the pattern across the tooth without getting it any deeper on the tooth .




I'll post some pictures later this evening ..

[BuzzKillian]

I had a similar experience... What mfg. gears did you get? I got the Summit brand... I did not end up with a perfect pattern... SO... I may (not really wanting to) get a different set.

[ErikLS2]

I agree with the above post, most likely it's how the gears are ground. When I did my 12 bolt I bought a Motive Performance (more expensive Motive line) and had a nice pattern. I bought the stuff from Drive Train Specialists who've I've bought from before with good luck. They build a lot of rear ends and said they had the best luck with the Motive Performance gearsets.

I would try to see how it looks with a little less backlash, like .006", and then break it in gently and properly. Or, try another brand of gearset. I'm curious what brand this is you're using too.

[JEFFTATE]

The gears are Yukon Gear Brand .

I've used that brand before and never had a problem.

I must be doing something wrong , I just can't put my finger on it ..

Maybe it's the pinion gear trial fit .
I'm putting it in without a crush-sleeve and tightening the pinion nut till I get the required preload (19 in/lbs.)

Or maybe I'm using too much marking compound and not cleaning it off well between adjustments ..
So , I'm getting a similar reading each time..

[CamaroAJ]

when you are checking the pattern do you have a load on the ring gear? i use a pry bar between the case and the ring gear to put some load on it when checking the pattern. it will show a different pattern loaded and unloaded.

this might help you with your patterns.
http://www.differentials.com/install.html

[JEFFTATE]

when you are checking the pattern do you have a load on the ring gear? i use a pry bar between the case and the ring gear to put some load on it when checking the pattern. it will show a different pattern loaded and unloaded.

this might help you with your patterns.
http://www.differentials.com/install.html

Yes , I am loading the ring gear while marking the pattern.. That's a good idea though ..

To make matters worse , I popped the carrier out with a great deal of force the first time , and it flew out and smashed my left shin ..while I was sitting under the car .
And I strained a tendon in my right elbow ..
So , I'm hobbling and holding one arm up.
I look like the Hunchback of Notre Dame
This thing is beating me to death ...

[ErikLS2]

You don't need a crush sleeve for checking the pattern and you're doing the right thing as far as pinion setup. Are you sure you're dial indicator is secure and not moving at all? That obviously would give you more backlash than you measure and cause what you're experiencing. Can't think of anything else you could be doing wrong. Are you placing a little load on the carrier when you check the pattern? I like to wedge a large screwdriver against the back side of the ring gear.

My guess is your two choices are finding a happy medium between backlash and tooth contact and hope it breaks in properly or trying another brand of gearset.

A member on here, Big Gear Head, does a lot of this stuff. You might try contacting him too and see what he thinks. I know he deals with Yukon.

[JEFFTATE]

A member on here, Big Gear Head, does a lot of this stuff. You might try contacting him too and see what he thinks. I know he deals with Yukon.

Right , I'm hoping he chimes in ..

[hotrdblder]

Have you tried putting less shim between pinion and pinion bearing, which would move pinion further forward in rear end, and pull it off the top of the ring gear?
generally i get the depth set with the pinion shims, then tighten up backlash with shimming the carrier left or right, depending on what i want to do

[JEFFTATE]

Ok , here's a couple of pics with a .033" pinion shim and .008" backlash.

[JEFFTATE]

Here's 4 pictures with a .028" pinion shim and .007" backlash ..

[CamaroAJ]

the second set looks pretty good to me. i've seen lots of GM's come from the factory with that wear pattern.

[JEFFTATE]

It's wierd , the pattern looks a lot better in the pictures than it does under the car...
It looks like it's coming off the top of the tooth under the car ..
Maybe my eyes are getting bad.
I need glasses to read things up close anyway ..



I think I may try a .029" pinion shim with .006" backlash , and see if I can get the pattern a little deeper in the tooth ..

[ChevelleNV]

Ya , the last couple pics don't look bad.

[big gear head]

The pattern with the .033 shim is too deep and needs less shim. The pictures with the .028 shim look pretty good on the drive side, but not quite deep enough on the coast side. This is one of those gears that isn't going to have a perfect pattern. I hate it when the pattern looks like a paralellagram (probably misspelled). Try something around .030 and play with the backlash somemore. Yukon gears sometimes like more backlash than other brands. Let me know how it goes. I stay in the drivetrain section and I don't check this area.

[MonzaRacer]

The patterns look ok for Yukon gears. I have been running Sierra from West Coast Differentials for last nearly what8 years and near perfect every time.
Here is another thing are you pressing the bearing on ever time or have you had the pinion polished so you can remove the bearing by smacking the pinion on a piece of wood.
Oldest trick I got from long time diff guy many moons ago. take pinion to local machine shop and have the bearing mounting surface crank polished so the bearings will nearly slide on by hand. Then I just have a nice piece of oak or walnut block around and can remove bearing by simply smacking it on the wood. makes adjustment sooooo much easier and have yet to have a rearend fail even running 1000lb ft of torque.
Generally I will disassemble stock rearends and engrave factory shim measured thickness on cover face, and I also put other useful stuff like new specs, parts installed ,etc.
I always set them on tight side as first 50 miles will make more as they burnish in. Also if motive didnt recommend, use a good grade of dino gear oil, appropriate limited slip additive. Then drive for 50 miles and let cool down couple of hours (good time to go to lunch on a weekend with wife/GF/significant other. Then drive back home, drain well, refill with same mix and put about 500 miles on the gears. Avoid cruise control and keep varying speeds and dont beat on them. My favorite breakin gear oil with best results has been Shell Spirax 85W140 and which ever brand limited slip additive you like GMs or Ford works better in my professional opinion.
I also avoid synthetics in anything that will be near or in water, nasty things happen with synth and water in diffs.
I also would put dino oil in for first 5k to 10 k. Of all the synthetics I like Mobile 1 and used to have access to a full synthetic Kendall but also have found out Shell has a great synthetic that has very impressive results from testing I have had done on used oil.
Also some of the current gears are giving similar patterns but patterned after break in look perfect.
Oh and for others who need rearend parts give Mike Maddox at West Coast Differentials 18003099342 ext 110, awesome service and full of help.
I completely rebuilt a 31 spline, 8.8 for a 94 Ford 4x4 with Ford Motorsport posi, new axles,c clips,Sierra gears and install kit for $805 then found out housing was junk and had to buy a core case for $75. Diff still together and in a rock crawler now and that was in like 04 or 05.
Good luck.

[JEFFTATE]

The pattern with the .033 shim is too deep and needs less shim. The pictures with the .028 shim look pretty good on the drive side, but not quite deep enough on the coast side. This is one of those gears that isn't going to have a perfect pattern. I hate it when the pattern looks like a paralellagram (probably misspelled). Try something around .030 and play with the backlash somemore. Yukon gears sometimes like more backlash than other brands. Let me know how it goes. I stay in the drivetrain section and I don't check this area.

Ok , thanks .
I'm gonna move this over to the Drivetrain Section later .
I just started it here ..

I'm trying to get the car together for the trip to California next week ..

[JEFFTATE]

The patterns look ok for Yukon gears. I have been running Sierra from West Coast Differentials for last nearly what8 years and near perfect every time.
Here is another thing are you pressing the bearing on ever time or have you had the pinion polished so you can remove the bearing by smacking the pinion on a piece of wood.
Oldest trick I got from long time diff guy many moons ago. take pinion to local machine shop and have the bearing mounting surface crank polished so the bearings will nearly slide on by hand. Then I just have a nice piece of oak or walnut block around and can remove bearing by simply smacking it on the wood. makes adjustment sooooo much easier and have yet to have a rearend fail even running 1000lb ft of torque.
Generally I will disassemble stock rearends and engrave factory shim measured thickness on cover face, and I also put other useful stuff like new specs, parts installed ,etc.
I always set them on tight side as first 50 miles will make more as they burnish in. Also if motive didnt recommend, use a good grade of dino gear oil, appropriate limited slip additive. Then drive for 50 miles and let cool down couple of hours (good time to go to lunch on a weekend with wife/GF/significant other. Then drive back home, drain well, refill with same mix and put about 500 miles on the gears. Avoid cruise control and keep varying speeds and dont beat on them. My favorite breakin gear oil with best results has been Shell Spirax 85W140 and which ever brand limited slip additive you like GMs or Ford works better in my professional opinion.
I also avoid synthetics in anything that will be near or in water, nasty things happen with synth and water in diffs.
I also would put dino oil in for first 5k to 10 k. Of all the synthetics I like Mobile 1 and used to have access to a full synthetic Kendall but also have found out Shell has a great synthetic that has very impressive results from testing I have had done on used oil.
Also some of the current gears are giving similar patterns but patterned after break in look perfect.
Oh and for others who need rearend parts give Mike Maddox at West Coast Differentials 18003099342 ext 110, awesome service and full of help.
I completely rebuilt a 31 spline, 8.8 for a 94 Ford 4x4 with Ford Motorsport posi, new axles,c clips,Sierra gears and install kit for $805 then found out housing was junk and had to buy a core case for $75. Diff still together and in a rock crawler now and that was in like 04 or 05.
Good luck.

Thanks Lee ,
I have a hydraulic press and some necessary tools (and attachments) that make pressing the pinion bearing on-and-off pretty easy .
I think I may be on the right track , finally , with the advice and second opinions from you guys..

I was gonna break it in with 75/90 petroleum lube and a bottle of GM limited slip additive.
Then switch over to Torco petroleum RGO Racing Gear Oil with a bottle of Torco limited slip additive later ..

[ErikLS2]

I took the old pinion bearing to my lathe and bored out the inside so it just slid onto the pinion easily and then setup the gears. Once it was setup I pressed the new bearing onto the pinion and when I checked the pattern it was exactly the same with the new bearing. This made it much easier and I'll save that bearing for future jobs.

[JEFFTATE]

I took the old pinion bearing to my lathe and bored out the inside so it just slid onto the pinion easily and then setup the gears. Once it was setup I pressed the new bearing onto the pinion and when I checked the pattern it was exactly the same with the new bearing. This made it much easier and I'll save that bearing for future jobs.

Companies sell " setup" bearings that are made like that.
You kinda made your own , that's cool .
It's probably a good thing to have , it would make the task easier ..