Bad Spedometer
Racer
Joined: Mar 2005
Posts: 487
Likes: 0
From: Jacksonville FL
what tires are you running on? are you sure that they are the exact same tire as what it came with back in 1979?
you will probably have to change the speedometer driven gear down in the transmission.
i had to change my driven gear becasue i was reading about 10 mph too high. it's a pretty easy job on a manual transmission. i suppose its probably easy on an auto trans also.
there are web sites with calculators to help you figure out which gear you need, but i am at work and do not remember any of them off of the top of my head. if nobody else helps out, i'll try to post a link when i get home.
hope this helps,
Mike.
you will probably have to change the speedometer driven gear down in the transmission.
i had to change my driven gear becasue i was reading about 10 mph too high. it's a pretty easy job on a manual transmission. i suppose its probably easy on an auto trans also.
there are web sites with calculators to help you figure out which gear you need, but i am at work and do not remember any of them off of the top of my head. if nobody else helps out, i'll try to post a link when i get home.
hope this helps,
Mike.
Safety Car
Joined: Nov 2004
Posts: 4,359
Likes: 57
From: Mundelein Illinois
what tires are you running on? are you sure that they are the exact same tire as what it came with back in 1979?
you will probably have to change the speedometer driven gear down in the transmission.
i had to change my driven gear becasue i was reading about 10 mph too high. it's a pretty easy job on a manual transmission. i suppose its probably easy on an auto trans also.
there are web sites with calculators to help you figure out which gear you need, but i am at work and do not remember any of them off of the top of my head. if nobody else helps out, i'll try to post a link when i get home.
hope this helps,
Mike.
you will probably have to change the speedometer driven gear down in the transmission.
i had to change my driven gear becasue i was reading about 10 mph too high. it's a pretty easy job on a manual transmission. i suppose its probably easy on an auto trans also.
there are web sites with calculators to help you figure out which gear you need, but i am at work and do not remember any of them off of the top of my head. if nobody else helps out, i'll try to post a link when i get home.
hope this helps,
Mike.
Speed calculator
http://www.keislerauto.com/tools/gm_analyzer_5sp.html
Sorry that won't help you.
If you call Corvette Cental, Eklers, Paragon etc. They will sell you the right gear you need for the factory Trans. You need to tell them how far off you are in speed and they will sell you the right gear.
Last edited by spedaleden; Jun 20, 2007 at 05:18 PM.
Thread Starter
Instructor
Joined: Mar 2006
Posts: 108
Likes: 0
From: Lansing MI
Tires are the same size as the original.
I'll note how much it's off, and the RPM's at highway speeds tonight.
One calculator said with 27.4" tires, 3.55 rear end, at 70MPH I should get about 3129 RPMS.
I'll note how much it's off, and the RPM's at highway speeds tonight.
One calculator said with 27.4" tires, 3.55 rear end, at 70MPH I should get about 3129 RPMS.
Instructor
Joined: May 2006
Posts: 221
Likes: 1
From: Albuquerque New Mexico
If your speedometer reads too high, a driven gear with one more tooth will slow it down approximately 5 MPH.
http://www.parts123.com/parts123/yb.dll?parta~partsort
http://www.parts123.com/parts123/yb.dll?parta~partsort
Racer
Joined: Mar 2005
Posts: 487
Likes: 0
From: Jacksonville FL
here are a couple of good links that helped me fix my fast speedo reading problem:
http://www.tciauto.com/Products/Tech...eedo_gears.asp
http://www.novaresource.org/speedo.htm
by the way, the large speedo gears are for the automatics and the small gears are for the manuals.
the AIM should tell you how many teeth you have on the drive gear inside the transmission.
good luck,
Mike.
http://www.tciauto.com/Products/Tech...eedo_gears.asp
http://www.novaresource.org/speedo.htm
by the way, the large speedo gears are for the automatics and the small gears are for the manuals.
the AIM should tell you how many teeth you have on the drive gear inside the transmission.
good luck,
Mike.
