Limited slip diff's and gearing options

[scottydont]

Considering that I don't even have the "transvair" at my house yet this is probably premature, but what can I say, I have a few minutes of my lunch break to kill.

Anyway, I know that limited slip diff's were an option for corvairs, but I've no idea how common or hard to find LSD transmissions were, if the option was available only on specific cars/transmissions, or wether they're compatible with other non-lsd transmissions...

Also, considering the nature of the vehicle, I'm more worried about low speed characteristics and acceleration than top speed. Were there multiple differential gearing options available for manual transmissions? (I'm thinking of the 3 speed in particular).

I'm just looking for background information here mainly.

Thanks

[bbodie52]

Because of the rear-wheel drive coupled with the engine in the rear, a Corvair needs a limited slip rear end the least of any car ever produced. The weight over the rear wheels and light front end provides good drive traction under most circumstances -- especially when compared with other automobile configurations.

A limited sllp (Positraction) differential can be detected when the rear of the car is off of the ground. When rotating the wheel hub by hand on one axle, the axle on the other side of the vehicle will rotate in the same direction. On a standard, non-limited slip differential, the two axle hubs will rotate in opposite directions.

Corvair Differential Code Numbers

http://corvaircenter.com/phorum/read.php?1,469444

Re: Open VS Limited Slip. Your opinions, please
Posted by: cnicol ()
Date: December 18, 2011 04:50PM

IMO, they're a mixed bag but after you shake it all out, they do add some value. I have them on both my cars and I live in snow country.

While I wouldn't consider driving the Corvairs during the winter (I'm not going to subject them to salt, deicer, or accidents) I do move them around on my hilly property when there's snow and ice on the ground and that's when the posi comes in handy.

Positives:
More traction than a regular Corvair

Negatives:
Reputation for breaking
Howl on slow tight turns (yes I have Posi addititve in both)
Less secure on side slopes

I guess I'd call that a mild recommendation.

Craig N. Coeur d'Alene ID

[azdave]

Experienced owners on many Corvair forums will agree that limited slip is not enough value to worry about looking for and installing unless you have a bad diff already and need a new one. I've read that some people don't like them at all for racing as they don't want the outer tire pushing them wide in the corners. Looks like 62 and up you could get a posi option. The fist few posts at this link are chocked full of posi info.

http://corvaircenter.com/phorum/read.php?1,26761,26764" onclick="window.open(this.href);return false;

[scottydont]

Thanks guys,
I'm an old enough hand at detecting posi's that I'm not worried about that, just trying to find out if they're like hens teeth or not.

I always wanted one in my old vw's but they weren't available at all at the time. I'm assuming I'd want one in the transvair as well. At the minimum it will be helpful on the occasional icy morning. Not a have to have thing, I'm just exploring my options at the moment.

[terribleted]

They are not common. There are 3 stock gearing options(open or posi), 3.27, 3.55, and 3.89. There are alos some after market options like 4.11.

[scottydont]

So are diffs compatible between the older straight axle and IRS transmissions? Not that I plan to build a trans anytime soon, but if I were, I'd probably think about putting a 3.89 in if it would fit....

[terribleted]

No. The swing axle and IRS axles will only work with their matching diffs. If you note from the chart above 3.89 was only available stock in the earlier swing axle transaxles.

[scottydont]

Yep, I noted it. That's why I asked the question.

No worries, like I said, probably not gonna be doing a transmission rebuild anytime soon.

[Bobby65]

couldn't you swap the ring and pinion into a different carrier, for either early or late models?

[coleslaw31]

I am thinking on the idea of adding posi to my diff. what parts do I need to swap to make a standard into a posi? I will do research but just in case I figured I would fire up a old thread and get some pointers.

[Scott V]

There are 3 stock gearing options(open or posi), 3.27, 3.55, and 3.89.

3.08 also but rare - 1 yr only.

-Scott V.

[notched]

Posi side cover (with the appropriate number of bolts to match the ring gear (6 bolt on earlies and 9 bolt on lates)
Posi side gear
Posi side adjuster sleeve
Clutch pack
Clutch pack spacer

[coleslaw31]

I will start searching around, got a guy with a side gear for a late wasnt sure what else was needed and how hard to come by.

[66vairguy]

I appreciate the enthusiasm for something different, BUT --- I found a posi in a pile of parts I bought out of a garage years ago. I used the posi to build a differential for one of my 66 cars. Fortunately I got a real good education from guys familiar with the POSI differential and the first issue is going to be the clutch pack. It is comprised of steel plates, NOT wet clutch material plates and are unobtainable. I was lucky, my clutch pack was, as one fellow told me, "The best used unit I've ever seen". Once the clutch plates are ruined they can't be repaired easily, if at all. The next issue is going to be the internal sun and spyder gears. The sun gear on one side is unique to the POSI and finding a new one, or good used one is difficult. So there you are - POSI's are a challenge to find and and if they need repair you are probably going to have a difficult time finding parts meaning lots of $$$$$$$.

BTW - I'd spend some time looking for a used pinion gear shaft with GOOD inner splines. They are getting hard to find and the new replacement pinion shafts are no longer being made - last I heard. Not counting the 1960 there are three basic pinion shafts 1961- 64 (can be used in the 1965 differential), the "long" 1965 pinion shaft, and the "short" 1966-69 pinion shaft that is REQUIRED to clear the slightly longer shoulder on the "saginaw" 1966-69 transmission output shaft that goes inside the differential pinion gear shaft. NOTE: If you install the longer 65 pinion gear shaft in a 66-69 transaxle it will fit, but binds the bearings and will cause a transaxle failure. I've seen it done.

Also if you replace the pinion gear shaft you may find a shim on the pinion gear. The shim affects the contact area between the ring and pinion gear and a change of the shim might be necessary. Something someone with experience and proper tools should do.

[coleslaw31]

Yeah no need to rush it I figured it wouldn't be easy and may just look for a complete unit somewhere. I shall be happy with my little standard diff until then.

[66vairguy]

Oh - regarding transmission gearing. The early boxes up to 1965 had different gear ratios over the years. When folks go to a "highway" ring and pinion like a 3:27 they try to find a low first gear set from the FC's.

With the 1966-69 "Saginaw" (they were all Saginaw trans, but the name is used for the late unit) there was only one gear ratio set. Some folks have used parts from Saginaw units used in the other small engine GM cars to change gear ratios, BUT it involves cutting and welding the unique Corvair counter gear assembly. $$$$$$$$$

BTW - I would not waste the time looking for a 3:89 axle ratio for more low speed go. Just install a lower profile (small diameter) tire/wheel set up with the stock 3:55 axle. Same result as the lower3:89 axle with stock tires.