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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: zieg85 on March 26, 2017, 01:25:20 pm

Title: TH400 speedometer gears?
Post by: zieg85 on March 26, 2017, 01:25:20 pm

I can't seem to find a source you can go to for determining the correct gear set needed to have the speedometer read right.

Currently I need to change out my TH400 in my C30 and I am changing the rear end while I am at it.

I will end up with a 3.21 and LT265/75R16 tires.  I know I may have to adjust the driven gear once I see how it is but while the transmission is on the bench I would like to know what drive gear is needed.

Thanks in advance

Title: Re: TH400 speedometer gears?
Post by: bd on March 26, 2017, 01:42:18 pm

Have you seen the attached page from the 85 parts book?

Title: Re: TH400 speedometer gears?
Post by: zieg85 on March 26, 2017, 01:53:42 pm

Awesome Rich, THANK YOU!!!

Title: Re: TH400 speedometer gears?
Post by: Irish_Alley on March 31, 2017, 10:12:49 pm

where did you get that from rich? maybe have a full set for the tech section?

Title: Re: TH400 speedometer gears?
Post by: bd on March 31, 2017, 11:21:05 pm

It's 1 of ~77 pages in the 4.450 parts group for 1985 - 1990 C/K/R/V.  Every year is represented by its own unique set of charts organized by transmission.