WAKING THE SLEEPING GIANT ...........
Thread Starter
Racer
Joined: Feb 2001
Posts: 315
Likes: 0
From: Pensacola Florida
WAKING THE SLEEPING GIANT ...........
I have decided to go with 3:70 gears for my '77 TH-350. In fact they are being installed right now. I have also just replaced my rear tires with 255/60/15 SS20 Firestone Firehawks.
What type of errors will this cause for my speedometer and/or tach?
Thanks
Larry :seeya
What type of errors will this cause for my speedometer and/or tach?
Thanks
Larry :seeya
Drifting
Joined: Sep 2000
Posts: 1,616
Likes: 2
From: Round Rock, Texas, USA Texas
Re: WAKING THE SLEEPING GIANT ........... (vettecor)
Shouldn't change your tach - be it mechaincal or electric - its engine driven.
When I got the "nothing fancy"'77 - had had the 2.something:1 rear changed to a 3.55:1 - my speed showed much faster than I was going - speedo=65MPH car actually moving 50MPH or so. I changed out the gears in the tranny a couple of times - find a good Chevy counter guy and he can (or at least mine was able to) tell you the percentage the different gears will change and you just have to figure the percentage your gauge is off.
good luck
Ronnie
When I got the "nothing fancy"'77 - had had the 2.something:1 rear changed to a 3.55:1 - my speed showed much faster than I was going - speedo=65MPH car actually moving 50MPH or so. I changed out the gears in the tranny a couple of times - find a good Chevy counter guy and he can (or at least mine was able to) tell you the percentage the different gears will change and you just have to figure the percentage your gauge is off.
good luck
Ronnie
Melting Slicks
Joined: Apr 2000
Posts: 3,286
Likes: 8
From: San Jose California
Re: WAKING THE SLEEPING GIANT ........... (vettecor)
Your tires are the correct diameter, but you didn't say what gears you are changing from. Divide your old gear ratio by 3.70. i.e. 3.08/3.70=83% If your speedometer reads 70mph, you are going 83% of that speed, ~58mph.
Chuck
Chuck
