[C1] Identify POSITRACTION
Thread Starter
Instructor
Joined: Jan 2015
Posts: 241
Likes: 9
From: Lynchburg VA
Identify POSITRACTION
I'm confused (which aint hard to do)
The casting number on my differential housing is 3725899 (See photo). As best as I can determine, this is the housing for the 57 - 62 NON-posi.
However, with the rear axle up on jackstands and the car in neutral, when I spin the drivers side tire, the passenger side spins in the same direction which means POSI right?
The casting number on my differential housing is 3725899 (See photo). As best as I can determine, this is the housing for the 57 - 62 NON-posi.
However, with the rear axle up on jackstands and the car in neutral, when I spin the drivers side tire, the passenger side spins in the same direction which means POSI right?
Race Director
Joined: Jun 2006
Posts: 17,901
Likes: 751
From: Inverness FL
St. Jude Donor '07
Tom Parsons says the case can be modified to accept a positraction gear set.
unless the spiders have been welded or spooled, then both tires rotating in the same direction, to me, would indicate positraction.
Bill
unless the spiders have been welded or spooled, then both tires rotating in the same direction, to me, would indicate positraction.
Bill
Race Director
Joined: Mar 2001
Posts: 14,634
Likes: 4,684
From: Mustang OK
2026 Corvette of the Year Finalist - Modified
2025 c1 of the Year - Modified Winner
2024 C1 of the Year Finalist - Modified
2023 C1 of the Year Finalist - Modified
2015 C1 of the Year Finalist
Obviously, not everyone has seen this.
I put this article together a few years ago.
I put this article together a few years ago.
Last edited by DZAUTO; Mar 3, 2018 at 09:40 PM.
Race Director
Joined: Mar 2001
Posts: 14,634
Likes: 4,684
From: Mustang OK
2026 Corvette of the Year Finalist - Modified
2025 c1 of the Year - Modified Winner
2024 C1 of the Year Finalist - Modified
2023 C1 of the Year Finalist - Modified
2015 C1 of the Year Finalist
When posi was first introduced (late Dec 56) there was NO identifier on the case, only the casting number--3743833, which was different from the casting number on the non-posi case--3725899.
Then about Feb 57, the posi cases (same 3743833 casting number) had an X cast next to the casting number. Either of these two posi cases are worth gold!!!!!
Then about Apr 57, the big P was cast on all posi cases and the X was gone. The P cases lasted to 62 on Vettes and 64 on pass cars.
NOW, with all of that said---------ONLY POSI CASES WITH THE THIN P (Detroit Gear and Axle plant) IS CORRECT FOR CORVETTES (and was also used on pass cars). If a thick P (Buffalo, NY plant) is on a posi case---------IT WAS ONLY USED ON PASS CARS.
Here is a thin and thick P.
Oh ya, and if you ever seen one of these (most likely you will not), it came from a Canadian pass car.
Last edited by DZAUTO; Mar 4, 2018 at 10:42 AM.
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
Race Director
Joined: Mar 2001
Posts: 14,634
Likes: 4,684
From: Mustang OK
2026 Corvette of the Year Finalist - Modified
2025 c1 of the Year - Modified Winner
2024 C1 of the Year Finalist - Modified
2023 C1 of the Year Finalist - Modified
2015 C1 of the Year Finalist
That is a 1956 ONLY center section, in a 1957-61 axle housing (I cannot tell what year the car is). ONLY 57-61 cars had a drain plug, 62 cars no longer had a drain plug. That's why I say the axle housing is a 57-61.
Last edited by DZAUTO; Mar 9, 2018 at 10:16 AM.
Team Owner
Joined: Jul 2006
Posts: 22,190
Likes: 4,178
From: Kannapolis NC
