7.5 Ring and Pinion Pattern

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Not-quite-so-new-guy
Nov 4, 2017
23
5
3
Nebraska
#1
Hi all!,
I just installed a Detroit Truetrack and Summit 3:73 gears in my rearend. It's a Gm 7.5. Goodbye 1 wheel wonder!
What do you guys think of the gear pattern? I wanted it closer to the peak, not the root. I have taken all pinion shims out, to help get that patter to the top. Now, no shims to help the pattern. Will you run it the way it is? Backlash is .007", in spec according to my research.

Thanks!
 

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Bonnewagon

Bonnewagon

Geezer
Sep 18, 2009
5,492
894
113
Queens, NY
#2
No. That looks totally wrong. Do you have a factory manual? They all show the correct tooth contact pattern. Try this link: https://www.gmforum.com/howto/1998SM/gear tooth contact patterns.pdf Or this: https://www.drivetrain.com/parts_ca...ing_and_pinion_installation_instructions.html Or this: http://www.alloyusa.com/gear-patterns Have you done this before? Because you may ruin those parts if you don't understand the concept behind ring and pinion sets. Please find a GM factory manual for any rear wheel drive car and read the gear section until your head hurts. That is the only way to learn the proper procedure. I should know- I got less than 15 feet before my gears crunched themselves. THEN I read the book. (DOH!)
 
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Rocket Powered

Rocket Powered

Not-quite-so-new-guy
Nov 4, 2017
23
5
3
Nebraska
#3
No. That looks totally wrong. Do you have a factory manual? They all show the correct tooth contact pattern. Try this link: https://www.gmforum.com/howto/1998SM/gear tooth contact patterns.pdf Or this: https://www.drivetrain.com/parts_ca...ing_and_pinion_installation_instructions.html Or this: http://www.alloyusa.com/gear-patterns Have you done this before? Because you may ruin those parts if you don't understand the concept behind ring and pinion sets. Please find a GM factory manual for any rear wheel drive car and read the gear section until your head hurts. That is the only way to learn the proper procedure. I should know- I got less than 15 feet before my gears crunched themselves. THEN I read the book. (DOH!)
Yes, this is my 1st time at a rearend. I have researched for weeks. Cannot understand my pattern. That' why I'm asking for advise and other points of view. How can I bring my pattern out more with no shims to remove. Adding pinion shims only drives only worse, closer to the root. And at $500-650 invested, want it done right the first time.
 
Bonnewagon

Bonnewagon

Geezer
Sep 18, 2009
5,492
894
113
Queens, NY
#4
What thickness was the original pinion gear shim? I have used a pinion depth tool many times and have found that the correct shim is almost never more than .001" from the original. If it is not destroyed- put it back in. If it is shot- get a new one the same thickness. Did you get an installation kit? There should be pinion shims in it. Once that is in, re-check preload and backlash. Gear tooth pattern is the LAST thing to check.
 
64nailhead

64nailhead

G-Body Guru
Dec 1, 2014
762
459
63
Upstate NY
#5
As a general rule, you should need some pinion shim. But from where you are at I would increase the backlash to .010-.012 and recheck.

What the original pinion shim? Also, you could use a little less marker (yellow stuff).

Setting up a rear takes patience. I've had a several apart and together 15 times to get it right. Are you using a setup bearing on the inner pinion bearing?
 
bob64

bob64

G-Body Guru
Mar 30, 2017
585
317
63
Niagara Falls, Canada
#6
Your pics aren't great or my eyes are bad, but you need more contact on the ring gear, in the center stretch of the tooth and not on the shoulder. You are going to need shims.

As already mention read, read and find some good visual pics of correct.
 
Rocket Powered

Rocket Powered

Not-quite-so-new-guy
Nov 4, 2017
23
5
3
Nebraska
#7
Yes, I did get a install kit. Shims and all bearings. I did make up dummy bearings. If I shim the pinion, my contact is more toward the root f the tooth. Yes, a little excessive but that' from several adjustments. Assembled and disassembled several times. Original pinion shim. 032"
 
pontiacgp

pontiacgp

Canadian Prime Minister
Mar 31, 2006
23,480
4,222
113
Kitchener, Ontario
#8
how many lbs did you use to crush the sleeve?
 
64nailhead

64nailhead

G-Body Guru
Dec 1, 2014
762
459
63
Upstate NY
#9
.032 is a thick pinion shim, usually in the mid to upper .020's.

Here my recommendation. Put the original pinion shim in. install the pinion with the inner setup bearing and no crush sleeve. Tighten the pinion nut until there is slight rotational torque required - 20 in/lbs or so and be sure there is no movement in and out. Then install the carrier and ring gear and set the back lash to .010-.012 and check with paste. Get those pics back to us.

Also, you need to setup the carrier (carrier and ring gear) preload to .000-.002" for setting up. Be sure you are not loading it to more than .000". If you don't understand what I mean or know how to do this then say so and I or someone else can explain how to get this done.

Basically, I cannot give a good recommendation based on your pics because your setup is so far off.
 
Bonnewagon

Bonnewagon

Geezer
Sep 18, 2009
5,492
894
113
Queens, NY
#10
I agree with 64nailhead. Use the old shim or a new one the same thickness. Look at the pinion gear. If there is a + or - number then add or remove that to the shim thickness. It means the gear was made with a slight variation and the manufacturer wants you to know that and adjust the pinion depth accordingly. This where a pinion depth tool is used. Lacking that- use the old shim as a beginning. Mock it up without the crush sleeve. Lightly oil the pinion bearings. Set the torque at the spec for "new" bearings since that is what you are using. Then install the carrier to .000". Proceed to measure for backlash and adjust the side shims to get what is speced for "new" gears. Once that is done you can adjust for pre-load. Let me explain pre-load. The pinion gear and ring gear carrier need to be held in suspension by pre-loading the bearings. This is because when they are held tightly in the proper relationship to each other- then the drive torque from the motor can't cause them to move out of position- causing incorrect tooth engagement. So if you put it together with no pre-load, as you drive the gears would be forced out of position and get noisy or break. The crush collar is there so that as you slowly tighten the pinion nut, the collar crushes and acts like an adjustable washer. Once you reach the inch pound torque spec to turn the pinion gear, the collar is "set". Now you can take it apart and put it back together and by knowing the torque spec it can go back exactly as it should be. ( You will appreciate this when the pinion seal leaks. You can change the seal and get the pinion pre-load exactly as it was before). The carrier is similar. You install shims on either side of the carrier bearings so that the clearance is .000". That means you cannot add even .001" more shim without forcing it in. Then you adjust the backlash by adding and removing shims which move the ring gear closer or farther from the pinion gear. What you remove on one side must be added to the other side to maintain the .000". Once the backlash is correct for "new" gears- you set pre-load. On GM it is usually .008". That means you must add .004" of shim to either side. You simply remove a shim from each side and replace it with a shim .004" thicker. It will need to be gently tapped in to place. NOW you can paint the gears with a little dye and look at the contact pattern. If it looks good, take it all apart and reset the pinion with the crush sleeve. Re-check everything. If it is still whacky then adjustments can be made. I'm betting it will be fine. Again- get a factory manual, read it, and use those specs.
 
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