700R4 Speedo Gears
Thread Starter
Le Mans Master
Joined: Feb 2000
Posts: 7,032
Likes: 2
From: Newburgh NY
700R4 Speedo Gears
I've got a 700R4 goint back to a 3.55 rear. I'm running 255/60-15 tires. Could someone suggest which speedo gears to use? Currently I'm reading about 100mph when only doing about 60.
I pulled the speedo gear out and it looks like a 38T. Do I need to go larger or smaller (I have an 18T lying around) and do I need to change just the one gear?
Thanks
I pulled the speedo gear out and it looks like a 38T. Do I need to go larger or smaller (I have an 18T lying around) and do I need to change just the one gear?
Thanks
Team Owner
Joined: Jul 1999
Posts: 65,492
Likes: 230
From: Orange Park Florida
Re: 700R4 Speedo Gears (78Vette-SA)
From what you say it seems you will need to change the drive gear on the output shaft also, I don't htink you can get 55-60 tooth driven gears....which is about the range you would need with that drive gear.....
sounds like the rear ratio that tranny came with originally must have been like a 2.73 assuming fairly similar tire diameter....
GENE
sounds like the rear ratio that tranny came with originally must have been like a 2.73 assuming fairly similar tire diameter....
GENE
Pro
Joined: Sep 2002
Posts: 690
Likes: 1
From: near Memphis TN
Re: 700R4 Speedo Gears (78Vette-SA)
Should answer your questions:
http://www.transmissioncenter.net/sp...n_______va.htm
http://www.transmissioncenter.net/sp...n_______va.htm
Racer
Joined: Apr 2004
Posts: 401
Likes: 0
From: IL
Re: 700R4 Speedo Gears (78Vette-SA)
You need to check the color and teeth number of the drive gear in the transmission. I believe you may have a 15 tooth gear which is grey in color. If so, based on your 255/60/15 (27.1" tall tire), 3.55 gear, you'll need a 40 tooth black driven gear. GM part# 1362048 which is still a good number and cost about $5.50 list.
Good luck.
Good luck.
Thread Starter
Le Mans Master
Joined: Feb 2000
Posts: 7,032
Likes: 2
From: Newburgh NY
Re: 700R4 Speedo Gears (GasketDude)
Thanks for the help and suggestions guys.
Question though. If I currently have a 38T (Blue) driven gear and am hitting 100mph at about 60, is 2 teeth going to be enough of a change (to a 40)?
Question though. If I currently have a 38T (Blue) driven gear and am hitting 100mph at about 60, is 2 teeth going to be enough of a change (to a 40)?
Intermediate
Joined: Mar 2002
Posts: 31
Likes: 0
From: Benton IL
Re: 700R4 Speedo Gears (78Vette-SA)
I have same set up on my car and BTO sent me a 17T shaft gear and a 45T speedo gear to make my speedo read correctly. They said both gears must be changed to make a large adjustment to calibrate speedo. Have not installed because I installed digital instructments and being electronic they have a built in calibrating function.
Racer
Joined: Apr 2004
Posts: 401
Likes: 0
From: IL
Re: 700R4 Speedo Gears (78Vette-SA)
You may have a different color drive gear in the transmission. Find this out, and repost this color/tooth count.
A 15t drive/ 40t driven calculates the same as a 17t drive/ 45t driven. Most people try to change only the driven gear because it's the easiest to get to. So bottom line is find out the drive tooth count and go from there.
A 15t drive/ 40t driven calculates the same as a 17t drive/ 45t driven. Most people try to change only the driven gear because it's the easiest to get to. So bottom line is find out the drive tooth count and go from there.
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