8.5 10 Bolt Build

  • Thread starter Michael Bennett
  • Start date
M

Michael Bennett

Not-quite-so-new-guy
Jun 7, 2018
46
14
8
#12
Well, I think I'n going to put it together as is to see if I like the 3:73 or not. I also have a 2.93 gear set that is in better shape. I'm wanting to stick with the TH350 so that may be a good option. Then i'll have all winter to mess with it. A big part of me playing with this rear end is me learning so I'm not concerned about taking it apart a bunch of times as long as I learn along the way.
 
64nailhead

64nailhead

G-Body Guru
Dec 1, 2014
756
451
63
Upstate NY
#13
You can't use 2.93 gears on a 3.73 diff or a 3.73 gear on a 2.93 diff. You need a 2 series diff for 2.93 gears and a 3 series diff for 3.73.

You'll need this https://www.amazon.com/dp/B001G7END6/?tag=gbody-20 to put the 3.73 gears on the 2 series diff.



My86R3gal - what '81 Cutlass described is spot on. Once the gear is broke it is a matter of time until a catastrophic failure occurs. If you need replacement gears, then Motive gear is what I prefer, but others will say Richmond, Strange, etc. I've had excellent service from Motive gears.
 
M

Michael Bennett

Not-quite-so-new-guy
Jun 7, 2018
46
14
8
#14
Everything I can find and even in the motive gear catalog it lists one carrier break for GM 8.5. 2.56 and down/2.73 and up. Going by that, the carrier from the caprice that currently has the 2.93 gear set should work with the 3.73's, right?

Also, i get it about the chipped gear. It's living on borrowed time, but I don't think it's ready to explode tomorrow.
 
Last edited:
My86R3gal

My86R3gal

Greasemonkey
Jan 12, 2015
158
162
43
South of Chicago
#15
My86R3gal - what '81 Cutlass described is spot on. Once the gear is broke it is a matter of time until a catastrophic failure occurs. If you need replacement gears, then Motive gear is what I prefer, but others will say Richmond, Strange, etc. I've had excellent service from Motive gears.
Thanks for clearing it up, I thought he was saying the 30 spline moser axels were trash. I may have misread it. But good info on the gear I was looking up the Richmond 373 gear.
 
64nailhead

64nailhead

G-Body Guru
Dec 1, 2014
756
451
63
Upstate NY
#16
Thanks for clearing it up, I thought he was saying the 30 spline moser axels were trash. I may have misread it. But good info on the gear I was looking up the Richmond 373 gear.

Sorry about that, no issues with Moser axles as we are running a set without issue.
 
8

81cutlass

Royal Smart Person
Feb 16, 2009
1,234
1,094
113
Western MN
#17
Thanks for clearing it up, I thought he was saying the 30 spline moser axels were trash. I may have misread it. But good info on the gear I was looking up the Richmond 373 gear.
Yeah I might have worded it a bit poorly

30 spine axles are good

Already broken gears are trash

quick performance has the cheapest diff parts I know of. I have read there is only like 3 people that cut aftermarket gears, so if you buy a US standard gear, richmond, motive, or any of the other places good chance you are getting 1 gear from about 2 or 3 total suppliers.
 
olds307 and 403

olds307 and 403

Comic Book Super Hero
Oct 14, 2008
3,396
784
113
Melville,Saskatchewan
#18
Use the Caprice carrier and gears. What is the rest of your combo, engine, compression, cam and stall? Do you drive on the highway much? How tall are your tires? I run at 2700 rpm at 70 mph with a 2.78 gear and 26" tall tires.
 
pontiac guy

pontiac guy

Apprentice
Oct 28, 2016
90
47
18
Royse City, TX
#19
If you are on a budget I'd run those gears. I've used worse. You should see the countershaft in the T5 I just cobbled together for my GP. Use a stone, as on a whetstone or machinist stone to knock off any burrs or highs on the chipped edge and go for it. It may be a bit noisy on acceleration. Hum most likely. Maybe at cruise too.
 
M

Michael Bennett

Not-quite-so-new-guy
Jun 7, 2018
46
14
8
#20
Combo is a 408" small bock. Zero decked, 5.7 rods 10.7:1, Performer RPM 195CC heads, Performer RPM intake, Lunati Voodoo flat tappet cam Duration @ .050 (Int/Exh): 233/24, Lift (Int/Exh): .504/.525. Flowtech 1 5/8" full length headers, 3" pypes exhaust with race pro mufflers, 28" 275/15/60 Cooper Cobras, and a TH350 with stock stall. Surprisingly enough it actually runs very strong with the current 2.41 gears and no posi so I'm pretty excited to get some gears in it. My plan was to try the 3:73's out right now to see if I can live with the gearing.
 

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