Speedo Gear Question?

Ricks82

Ricks82

Active member
Joined
Jun 30, 2008
Messages
25
Location
Illinois
I just installed a set of 3.73:1 gears in my 82. Somehow, I managed to forget about the speedo until after the fact. Does anyone know which speedo drive gear I need for my 700r4? I am basically running a stock tire, and I think that the tranny is from an 85 or 86 Astro. (My tranny guy selected this tranny to build) So now at highway speeds my 85 MPH speedo is pegged. This leads me to question #2. Does anyone have exeriece good or bad that they could share about the 165 mph speedometer conversions?
 
IF your 82 had a 308 gear, you now have to find a speedo DRIVEN gear with some ~20% more teeth in it....say you had one at 27 teeth, you need one with 31 teeth...that type thing....nice to find one outta a junkyard....

I would not pay particular attention to the speedo gear selection sites, but instead pay attention to a good GPS.....I believe my Garmin above all else with tables and calculations crap....

:crutches:
 
You need to pull your speedo gear out and see how many teeth are on your drive gear. Then you can calculate how many tooth driven gear you need. The bad news is you will probably have to change your drive gear also after changing from a 3.08 to a 3.73.

Here is a link to a good site that has the formulas and calculator.
http://www.tciauto.com/Products/TechInfo/speedo_gears.asp
 
Just go to GM and order a gear set for a 83-85 f-body, they came with the 3.73 and 700r4.

Kind of remember my 84 trans am using a red driven gear but unsure of the drive gear.

good luck
 
JeffP1167 said:
Just go to GM and order a gear set for a 83-85 f-body, they came with the 3.73 and 700r4.

Kind of remember my 84 trans am using a red driven gear but unsure of the drive gear.

good luck
Click to expand...

That may get you close, but won't be figured for the right tire height.
 
Fuelie74 said:
You need to pull your speedo gear out and see how many teeth are on your drive gear. Then you can calculate how many tooth driven gear you need. The bad news is you will probably have to change your drive gear also after changing from a 3.08 to a 3.73.

Here is a link to a good site that has the formulas and calculator.
http://www.tciauto.com/Products/TechInfo/speedo_gears.asp
Click to expand...

The stock ratio was actually 2.87:1 so I agree that it will probably require both gears. Hopefully I can check this out a little closer this weekend. (Currently away for work):crap:

Thanks for all of the input.

Has anyone ever done the 85 mph speedo conversion?
 
Fuelie74 said:
JeffP1167 said:
Just go to GM and order a gear set for a 83-85 f-body, they came with the 3.73 and 700r4.

Kind of remember my 84 trans am using a red driven gear but unsure of the drive gear.

good luck
Click to expand...

That may get you close, but won't be figured for the right tire height.
Click to expand...

My 84 trans am came stock with 215/65r/15's that should be very close to what the stock 82 vette has which would have been 60 series correct?
 
Order by color. I Have a 373 and it's the "green" one or was it brown. Crap.

Call Exotic Muscle in AZ. Those guys are good, they helped me.
 
Get on Bowtie Overdrive's website. They have a speedo gear calculator. I used it and mine is dead on the money. I have a 700R-4, 3.70 rear gears and 255-45/18" tires @ 27.05" diameter.
 
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