Welcome to the Corvette Forums at the Corvette Action Center!

Speedometer Correction

S

Steel Half-Shafts

Guest
A friend of mine just recently installed 3:70 rear end gears in his 1987 Corvette with an automatic transmission. Needless to say, his speedometer is now incorrect.
What can he do to correct the problem? ;help
 

Ken

Gone but not forgotten
Joined
Jan 30, 2001
Messages
8,236
Location
Hermosa Beach, CA
Corvette
1987 Z51 Silver Coupe
I've got a chart from Richmond for the manual trans cars Gordy, but I can't help you with an automatic. Sorry.

_ken :w
 

Mad-Mic

Gone but not forgotten
Joined
Feb 12, 2002
Messages
1,853
Location
Annapolis Maryland
Corvette
1987 Redskin Red Coupe
gotta get this......

where the speedo cable goes in you got to change the speedo gear to compensate for it. any tranny shop can help. it is fairly inexpensive. they can even compensate for tire size.
 

vms4evr

Well-known member
Joined
Jul 18, 2001
Messages
466
Location
Durham, NC
Corvette
2002 Flat Black Z06
send me an email and i'll reply with the speedo gear cross reference chart. it shows all gears for auto and manual trans for all years of C4s.
when i bumped the 2.59 to 3.54 gears in my92 i went through this. it was a PITA. if you search for my gear post you'll see the ones i used. you need a slight adjustment to that,
Graham
 

vms4evr

Well-known member
Joined
Jul 18, 2001
Messages
466
Location
Durham, NC
Corvette
2002 Flat Black Z06
oops i messed that up. with the email in the forum you can't send an enclosure. use it to give me your real email address or post it here. i have the info in a Word doc in tables. so i need to send it that way. it won't post properly in here as a response.
graham
 
S

Steel Half-Shafts

Guest
Thanks Guys, :D
I'll let my friend know what he needs to do to correct the problem.
vms4evr you have mail! :beer
 
E

Eagle85C4

Guest
How much hassle is it when you change from 16" to 17" rims?
 

Mad-Mic

Gone but not forgotten
Joined
Feb 12, 2002
Messages
1,853
Location
Annapolis Maryland
Corvette
1987 Redskin Red Coupe
not much....

my 87 came with 17's but i dont' think they changed the gearing but it's not noticable as when i'm driving seems like it's very close or right on. Remember it's not the size of the rim but the diameter of the overall tire size that changes it. Anyone know what the difference is from 255.50.16's to 245.40.17's? i think thats the sizes that is on mine from stock.

vms can you send me that reference chart?

madmic@cablespeed.com

Thanks!
 

vms4evr

Well-known member
Joined
Jul 18, 2001
Messages
466
Location
Durham, NC
Corvette
2002 Flat Black Z06
madmic,
your 255/50-16 are 26.1" dia.
a 245/45-17 are also 26.1" dia.
so if that is what you swapped then it's dead even.
the 275/40-17 on my92 are 25.7" dia.

with an auto trans at 65mph using 25.7 and 26.1 in tires you get 2167 and 2200rpms respectively with 1.0 final drive. so it would be hardly noticeable. in OD it's about 25rpms difference.

the doc is on the way, check your email
same for you steel half-shafts. just sent it.

Graham
 

Corvette Forums

Not a member of the Corvette Action Center?  Join now!  It's free!

Help support the Corvette Action Center!

Supporting Vendors

Dealers:

MacMulkin Chevrolet - The Second Largest Corvette Dealer in the Country!

Parts/Accessories:

Vetteskins

Advertise with the Corvette Action Center!

Double Your Chances!

Partners

Top Bottom