Posi-Trac Differential

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michael johnson
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Joined: Tue Jul 18, 2017 11:21 am

Posi-Trac Differential

Post by michael johnson »

I recently purchased a '65 Monza with a Kelmark V-8 conversion installed. How can I tell if the differential has posi-trac, and what year the transaxle is?
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bbodie52
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Re: Posi-Trac Differential

Post by bbodie52 »

If you jack up the rear of the car and place it on jack stands and then release the parking brake, try manually rotating one of the rear wheels by hand. If the rear wheel on the opposite side of the car rotates in the same direction, you have a Positraction differential. If the rear wheel on the opposite side rotates in the opposite direction from the one you are rotating by hand, you have a standard, non-Positraction differential.

Left-click each image with your mouse to enlarge the image for better viewing…
Differential Code Numbers.jpg
Differential Code Location (1965) [1].jpg
Differential Code Location (1965) [2].jpg
Differential Code Location (1965) [3].jpg
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1965-1969 Corvair Rear Suspension Design...
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1965 is 1/4 x 20 and 1966-1969 use much larger 5/16-24 thread bolts to secure the differential universal joint yoke straps to the differential yoke.

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Brad Bodie
Lake Chatuge, North Carolina
Image 1966 Corvair Corsa Convertible
michael johnson
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Re: Posi-Trac Differential

Post by michael johnson »

Thanks for the info, Brad. Now I need to figure out whether the transmission is a '66 or later.
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bbodie52
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Re: Posi-Trac Differential

Post by bbodie52 »

:link: http://www.corvair.com/user-cgi/catalog ... age=TECH-4
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:link: http://www.corvair.com/user-cgi/catalog ... ge=TECH-13
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cnicol wrote:Re: Manual Transmission ID please
Date: November 05, 2012 05:10PM

The big divide is the number of bolts to the differential.

6 bolts & cast side cover = 66-9 3sp or 4sp
4 bolts = 60-65 3sp or 4sp

sheet metal side cover = 61-65 4sp
sheet metal top cover = 60-65 3sp

Aluminum case = 60 3sp (except for prototype 61 4sp)

12 spline input shaft = 60-63
14 spline input shaft = 64-69

No provision for back up light switch on 61-5 4sp = FC trans

Craig N. Coeur d'Alene ID
.
Brad Bodie
Lake Chatuge, North Carolina
Image 1966 Corvair Corsa Convertible
michael johnson
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Joined: Tue Jul 18, 2017 11:21 am

Re: Posi-Trac Differential

Post by michael johnson »

Thanks again for your input, Brad. BTW, that's one beautiful convertible you've got there.
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caraholic4life
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Re: Posi-Trac Differential

Post by caraholic4life »

More important than if the transaxle is Positraction or not would be... "Does it have the reverse ring and pinion installed?"

I had a Kelmark Mid Engine 1966 Coupe for 16 years and got lots of enjoyment from it. Back then transaxles were very inexpensive and plentiful but that is no longer the case.

Over the years, I replaced the differential several times. Sometimes they didn't last long and other times one would last for a good long while but eventually they all failed for different reasons. Most of the time even when driving the car like I had some sense, the ring and pinion would simply wear out. I tried various gear oils and additives over the years but always the same end result.... a razor sharp pinion gear.

Eventually I purchased a Reverse Ring and Pinion made by Richmond Gear that was produced for the application but never got around to installing it before I sold the car. The buyer didn't want it so I sold it to someone else.

I would strongly suggest you first purchase a spare Input Shaft from someone like Clarks Corvair Parts while you still can, and second, try to locate a reverse ring and pinion if your car doesn't already have one in it because differentials are getting more scarce and expensive.

As far as the Posi or Not, I preferred the Non Positraction differential simply because it did not want to push me straight while accelerating through a curve in the road, but then again....it was simply my preference.

Enjoy the car. :tu:
1962 95 FC Van
1964 Greenbrier Deluxe
1965 Monza Coupe
1965 Monza Convertible
Mid Engine enthusiast &
Prior Kelmark Owner
michael johnson
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Re: Posi-Trac Differential

Post by michael johnson »

I have a feeling the reverse ring and pinion will be difficult if not impossible to find... they don't exactly grow on trees. Tried Summit, tried Jegs, tried Richmond Gear. I'll try the other Corvair websites. Did you ever try a free-flow oiling system with some sort of pump to lubricate the ring and pinion? Did you install four-spider kits in your differentials?

Thanks!
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caraholic4life
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Re: Posi-Trac Differential

Post by caraholic4life »

michael johnson wrote: Wed Aug 02, 2017 10:58 am I have a feeling the reverse ring and pinion will be difficult if not impossible to find... they don't exactly grow on trees. Tried Summit, tried Jegs, tried Richmond Gear. I'll try the other Corvair websites. Did you ever try a free-flow oiling system with some sort of pump to lubricate the ring and pinion? Did you install four-spider kits in your differentials?

Thanks!
I sent you a PM with a possible person to ask about one. :pray:
1962 95 FC Van
1964 Greenbrier Deluxe
1965 Monza Coupe
1965 Monza Convertible
Mid Engine enthusiast &
Prior Kelmark Owner
notched
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Re: Posi-Trac Differential

Post by notched »

Ken Hand had said on the other message board that he had a set. You might want to check with him.
1966 Corsa turbo
1969 Monza convertible
1987 Buick Grand National
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