speedometer/rear end gear ratio
Thread Starter
Heel & Toe
Joined: Mar 2012
Posts: 18
Likes: 0
From: Twentynine Palms CA
speedometer/rear end gear ratio
I'm moving on to the next issue with my 1972 vette. I'm trying to determine if my speedometer or speedometer cable are bad. At 30mph my car reads 50mph and 70mph my car reads 110mph and it progresses at a consistant pace between the 30mph to the 70 mph. I've lubed the speedo cable and the symptoms remain the same, before I spend the money on a new speedometer I was thinking that someone changed out the rear end. The car is an automatic and at 70 mph the tac is reading about 3500rpm. Is that normal/high/low? I'm hoping that all I need to do is replace the transmission driven gear?
Drifting
Joined: Dec 2004
Posts: 1,714
Likes: 42
From: Austin Texas
go here http://tri-5.chevyrides.com/rpm.php
stock tires and a 3.73 rear with a 1:1 end ratio auto puts you at 3300 rpm at 70. If you add a couple hundred rpm for the converter, you are at 3500. Does the car feel like it has 3.73? It would really launch pretty good if so.
This site also helps calculate the driven gear.
stock tires and a 3.73 rear with a 1:1 end ratio auto puts you at 3300 rpm at 70. If you add a couple hundred rpm for the converter, you are at 3500. Does the car feel like it has 3.73? It would really launch pretty good if so.
This site also helps calculate the driven gear.
Last edited by johnt365; Jul 15, 2012 at 12:46 PM.
Thread Starter
Heel & Toe
Joined: Mar 2012
Posts: 18
Likes: 0
From: Twentynine Palms CA
Thanks for the info John. I had a C5 before, so in comparison the 72 seems pretty slow. I really couldn't tell you if she launches good. I don't have all the vacuum hoses connected properly so the transmission shifts pretty early, its hard to tell. I haven't really dogged her out yet as I'm afraid the engine will blow.
Race Director
Joined: Apr 2000
Posts: 17,676
Likes: 201
From: Who says "Nothing is impossible" ? I've been doing nothing for years.
Racer
Joined: Mar 2012
Posts: 476
Likes: 37
From: Lynnwood WA
go here http://tri-5.chevyrides.com/rpm.php
stock tires and a 3.73 rear with a 1:1 end ratio auto puts you at 3300 rpm at 70. If you add a couple hundred rpm for the converter, you are at 3500. Does the car feel like it has 3.73? It would really launch pretty good if so.
This site also helps calculate the driven gear.
stock tires and a 3.73 rear with a 1:1 end ratio auto puts you at 3300 rpm at 70. If you add a couple hundred rpm for the converter, you are at 3500. Does the car feel like it has 3.73? It would really launch pretty good if so.
This site also helps calculate the driven gear.
Nice find on that calculator. Thanks for posting the LINK.
Zorro
