Rebuilt Possi Differential

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Flytofun
Posts: 1
Joined: Thu Dec 28, 2017 7:02 pm

Rebuilt Possi Differential

Unread post by Flytofun » Sun Jan 21, 2018 6:27 pm

Looking for a rebuilt Differential for my '62 Van
I have a '64 110 motor in it
Would like to install a rebuilt Possi 3.27 gear Differential
Would like to also install a rebuilt 4 speed Transmission and Clutch

Would appreciate any west coast sources for the needed parts

Thank You,

Rob
Santa Rosa, CA
707-953-2426

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vairguy63
Posts: 34
Joined: Tue Dec 05, 2017 9:16 pm
Location: Oceanside, CA

Re: Rebuilt Possi Differential

Unread post by vairguy63 » Sun Jan 21, 2018 6:45 pm

Thinking of doing the same 3.27 diff for my van. Any suggestions on if that gearing is too low and should go for 3.55 instead? I'm not pulling anything but do take 4-6 kids and boards on top surfing quite a bit.

I've got a source for you in socal and can get you his info tomorrow. Thanks


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notched
Posts: 659
Joined: Wed Jul 25, 2012 8:13 pm
Location: Southern New Jersey

Re: Rebuilt Possi Differential

Unread post by notched » Mon Jan 22, 2018 10:21 am

I would reconsider the final drive gearing if you have to drive any mountains or carry a heavy loads UNLESS you have a big bore 3.0 liter or larger engine. GM purposely put 3.55 and 3.89 gears in the differential so they would have enough torque multiplication. Putting less gearing in those vehicles can hinder their proper operation.
1966 Corsa turbo
1969 Monza convertible
1987 Buick Grand National

66vairguy
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Re: Rebuilt Possi Differential

Unread post by 66vairguy » Mon Jan 22, 2018 11:17 am

I installed a 3:27 in my 66 for highway use. Nice to lower the RPM on the highway, but first seems a bit high when starting out. On the FC's some had a nice low first gear, depends on year.

Frankly if your planning on going 70MPH I'd stay with a 3:55 since the FC has to push a LOT of air at that speed. The 3:55 puts the engine close to torque peak at 70MPH. Engine may sound busy, but the Corvair engine can run up to 4,000 RPM all day long without issue. Unlike modern engines, the Corvair engine won't tolerate high load, low RPM, use - in the old days it was called "lugging an engine".

Unless you plan on driving in a lot of mud or snow - the POSI differential is not needed. With the rear weight and good tires you won't have a traction issue for most driving conditions. Also on the early POSI units they were not as strong as the standard "open" differential.

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vairguy63
Posts: 34
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Location: Oceanside, CA

Re: Rebuilt Possi Differential

Unread post by vairguy63 » Mon Jan 22, 2018 1:54 pm

My diff guys name is Mike McCrae in south San Diego. Been doing corvair transaxles a long time for all applications and knows his stuff. Was referred to me by an ol time corvair racer. 1 (619) 890-1638


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notched
Posts: 659
Joined: Wed Jul 25, 2012 8:13 pm
Location: Southern New Jersey

Re: Rebuilt Possi Differential

Unread post by notched » Tue Jan 23, 2018 10:36 am

Early 6 bolt posi units are HIGHLY prone to cracking. Jeff at the Corvair Ranch showed me several last time I was there. He said they rarely pass the magaflux testing. If you absolutely have to have a posi in then consider the steel cover Clark's sells or modify a late 9 bolt for use inside the early differential housing
1966 Corsa turbo
1969 Monza convertible
1987 Buick Grand National

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