Rearend gear question
Pro
Joined: Sep 2017
Posts: 516
Likes: 72
From: Modesto California
Set it on safety stands, put it in NEUTRAL, crawl under it, turn your drive shaft while counting how many turns it takes to make the tire turn one revolution. It's best to put a chalk mark or a little piece of masking tape on the bottom of the tire before turning the drive shaft so you have a good reference point. If you have an automatic transmission it'll take about 3.36 turns of the drive shaft to equal one tire revolution.
Drifting
Joined: Aug 2009
Posts: 1,346
Likes: 160
From: new iberia la
exactly.. a lot happens in 4 decades .. I would not trust that its the original...spin the tire, count revs..... then you know for sure
Last edited by fishslayer143; Oct 6, 2017 at 06:25 PM. Reason: spilled my beer
Thread Starter
Instructor
Joined: Sep 2017
Posts: 207
Likes: 53
I was hoping someone knew how to check vin to see what came oem .Or where this stamp is located .I know previous owner never did anything to it 
Last edited by IronMaidens2.0; Oct 6, 2017 at 06:47 PM.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Pro
Joined: Sep 2017
Posts: 516
Likes: 72
From: Modesto California
Drifting
Joined: Dec 2004
Posts: 1,714
Likes: 42
From: Austin Texas
Le Mans Master
Joined: Oct 2007
Posts: 7,453
Likes: 976
From: RI, Now Franklin/Nashville TN
Just an FYI on my 78 L-82 3.70 4 speed. I have verified that the speedo is spot on for mph...60 GPS is 59-60 on the speedo. However, my L-82 GM OEM tach is not.....it reads 300-400 RPM higher revs than it should...verified 2X-once on a dyno machine and the other with a handheld tach/dwell meter..both times the tach shows 300-400 RPM more than actual revs.
The official GM speed/Tach calculations from 1978 magazine tests were for the L-82 4 speed cars with 3.70 gears:
60 mph @ 2,860 revs
I would think you should be showing about 2,600 RPMS @ 60 mph with 3.55 gears and the auto if everything is correct....around 3,000 RPMs @ 70 mph?
The official GM speed/Tach calculations from 1978 magazine tests were for the L-82 4 speed cars with 3.70 gears:
60 mph @ 2,860 revs
I would think you should be showing about 2,600 RPMS @ 60 mph with 3.55 gears and the auto if everything is correct....around 3,000 RPMs @ 70 mph?
Last edited by jb78L-82; Oct 8, 2017 at 02:54 PM.
Melting Slicks
Joined: Nov 2005
Posts: 2,143
Likes: 488
From: Leonardtown Maryland
If the speedometer has been accurate what about pulling the speedometer cable off of the transmission and checking the color of the drive gear shaft? I think you can see it in there. After comparing what is available in most vendor catalogs wouldn't that put you in the ball park?
Le Mans Master
Joined: Oct 2007
Posts: 7,453
Likes: 976
From: RI, Now Franklin/Nashville TN
Here you go for 1978^^^^^
Almost all L-82's with a 4 speed had the close ratio gears and 3.70 gears. The wide ratio 4 speed which I have never been able to document how many were made were very rare and COULD come with a 3.36 rear gear.
All L-82's and the auto had to have only the 3.55 gear....
L-48 4 speeds came only with 3.36 gears
L-48 autos could have a 3.08 or 3.55's
Last edited by jb78L-82; Oct 8, 2017 at 05:02 PM.
Burning Brakes
Joined: Jul 2017
Posts: 1,114
Likes: 149
From: Frisco TX
Just an FYI on my 78 L-82 3.70 4 speed. I have verified that the speedo is spot on for mph...60 GPS is 59-60 on the speedo. However, my L-82 GM OEM tach is not.....it reads 300-400 RPM higher revs than it should...verified 2X-once on a dyno machine and the other with a handheld tach/dwell meter..both times the tach shows 300-400 RPM more than actual revs.
The official GM speed/Tach calculations from 1978 magazine tests were for the L-82 4 speed cars with 3.70 gears:
60 mph @ 2,860 revs
I would think you should be showing about 2,600 RPMS @ 60 mph with 3.55 gears and the auto if everything is correct....around 3,000 RPMs @ 70 mph?
The official GM speed/Tach calculations from 1978 magazine tests were for the L-82 4 speed cars with 3.70 gears:
60 mph @ 2,860 revs
I would think you should be showing about 2,600 RPMS @ 60 mph with 3.55 gears and the auto if everything is correct....around 3,000 RPMs @ 70 mph?
But I think all auto L82 had the 3:55 gear?
Last edited by LenWoodruff; Oct 11, 2017 at 07:55 AM.
Le Mans Master
Joined: Oct 2007
Posts: 7,453
Likes: 976
From: RI, Now Franklin/Nashville TN
If you are getting 3,000 RPM @ 60 mph with 3.55 gears, then yes your tach is off as well since the 3.70 geared cars were @ 2,860 RPM at 60 mph. You should be no more than 2,600 RPM with 3.55 gears..@ 60 MPH.
