I’m lazy so looking for advice on new Ring and Pinion shim

[Justasgood]

Changing Ring and pinion to a milder gear. And hoping to minimize mockups.

Current 8.25 suregrip with 3:73 gears has a shim sized at .069.

Can anyone tell me the shim size I would need when using a 3:21 gear?

Thanks,

Kurt

 

[493 Mike]

No. Use the old shim-check the mesh pattern-adjust as needed. The long way is usually the best way.
Mike

 

[Fran Blacker]

Any numbers on pinion gear face on both? You may get close but no numbers see, 493 mike.

 

[steve340]

No shortcuts I know of that work. Every housing/ring and pinion is different.
Start with what you have and go from there.

 

[451Mopar]

You could try to get a calculated pinion depth from the pinion bearing bore in the case to axle centerline and subtract the stack up of the pinion bearing (with cup) width and the distance of the head of the pinion? That might get you in the ballpark if you don't have a starting point. I'm not sure how much to subtract to compensate for the bearing and cup press fit which might make the installed pinion bearing just slightly wider, guessing maybe 0.002"?

 

[RemCharger]

Changing Ring and pinion to a milder gear. And hoping to minimize mockups.

Current 8.25 suregrip with 3:73 gears has a shim sized at .069.

Can anyone tell me the shim size I would need when using a 3:21 gear?

Thanks,

Kurt

If you notice, .373+ .321 = .694. Pretty damn close to your original shim of .069. Basically that shows you start there and work out.

 

[Justasgood]

Any numbers on pinion gear face on both? You may get close but no numbers see, 493 mike.

032

 

[Fran Blacker]

032

That doesn't help. Some gears have center of axle to face of pinion.

 

[Justasgood]

 

[RemCharger]

the shortcut is to use the original shim. As mentioned in almost every post.

 

[Justasgood]

It was tried, thank you. There is a height difference between the pinion of the 3.73 and the 3:21. The 3:73 has a shorter head(teeth) than the elongated 3:21 pinion head.

 

[Rebelrouser]

The shim for pinion depth is usually to shim for machining tolerances in the housing, not the ring and pinion. 99% of the time if the original shim was correct it will be correct for the new gears. If you don't have access to a pinion depth gauge a .020 shim is the starting point for a 8 3/4 with a 1 7/8 pinon diameter I seldom see a pinion depth shim that THICK that is correct. Look at the old pinon gear it the shiny wear pattern in the middle of the teeth?

 

[Justasgood]

 

[Cranky]

Also helps to have a pinion 'dummy' bearing or one that's slip fit honed as a trial bearing. I'll even hone the new bearings if they are too tight. Never had a problem with a bearing spinning even at .0005" tight. Had one years ago that was .005" tight on a Dana 60 and thought the press was going to wreck itself and it was an industrial press. It actually pulled metal from the pinion fit. Anything over .001-.0015 is too tight in my book.

 

[Justasgood]

Anywho, at a stand still until I can source one of these:

 

[Justasgood]

Also helps to have a pinion 'dummy' bearing or one that's slip fit honed as a trial bearing. I'll even hone the new bearings if they are too tight. Never had a problem with a bearing spinning even at .0005" tight. Had one years ago that was .005" tight on a Dana 60 and thought the press was going to wreck itself and it was an industrial press. It actually pulled metal from the pinion fit. Anything over .001-.0015 is too tight in my book.

I have a fitting bearing that we did just that.

 

[Rebelrouser]

View attachment 1557672View attachment 1557673

That looks pretty close, I would set it up with the shim you have, and of course check with gear marking compound when done.

 

[1KoolBee]

Changing Ring and pinion to a milder gear. And hoping to minimize mockups.

Current 8.25 suregrip with 3:73 gears has a shim sized at .069.

Can anyone tell me the shim size I would need when using a 3:21 gear?

Thanks,

Kurt

If I recall correctly, most aftermarket gear sets are marked with a recommended “installed” pinion depth. You need a depth tool to calculate shims. Factory gears on the other hand are marked in paint with a deviation from the “Nominal” desired installed height. So a gear with “-.002” is lapped .002 inches below spec. Therefore it needs an additional .002 shim thickness above what a “ theoretically perfect “ set of gears would need. So if your new gears are marked +.005 (lapped .005 above perfect, .005 thinner shim required) and your old gears are marked -.002 (.002 below perfect, .002 thicker shim required) the math goes : “original shim thicknesses -.002 -.005” or original shim -.007” in this example. I did a 3.91 swap in a 8.25 Dakota and a couple 8-3/4s using this method and the patterns came out perfect. If one or both of the sets is aftermarket it’s use original shim, check pattern, adjust shim, repeat. Or buy the proper pinion depth tools. Good luck!