Turbo 350 speedometer gears

G

gbodysupreme

Not-quite-so-new-guy
Jun 26, 2015
13
1
1
Pittsburgh, PA
#1
So I upgraded the 7.5" axle in my 85 Cutlass Supreme with a 3.73 limited-slip gearset, and am now having a hard time figuring out how to get my speedometer to read properly. It has an 18-tooth drive gear, and no one seems to sell a driven gear to get the speedometer close. I just want to be able to go over 65mph without breaking stuff (not that 85 is much better)
 
MrSony

MrSony

Comic Book Super Hero
Nov 15, 2014
4,902
2,977
113
Des Moines, Iowa
#3
I have 3.42s, 26.1" tires (235/60/15), and put a 17/45 set in. Dead on. Those calculators above will certainly help though.
 
Drkuhar

Drkuhar

Greasemonkey
Sep 27, 2018
173
135
43
#4
I just went through this. take the tailshaft off and change the drive gear. Its very easy You will not get close enough changing the driven gear alone. . I got my drive gear, 5 driven gears, and new bullet carrier for 28.00 on ebay.
 
Drkuhar

Drkuhar

Greasemonkey
Sep 27, 2018
173
135
43
#5
Here is some pics. 4 bolts take tailshaft off. Push clip down swap drive gears and put tail shaft pack on. Used gear calculator to pic closest driven gear. My th350 with 26.6 with 3.42 gears was a 7 drive 18 driven gear.
 

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