Tech discussion, rear end usage

[mike cobine]

Since there is a good variety of engineers, mechanics, restorers, ex-racers, and so on here, I thought I'd ask a question on a rear end. I'd like to see what everyone thinks of these two ideas.

1. Run a rear end upside down. Basically, grab the snout and flip it up and over to point backwards. Obviously, the vent would have to be changed. Input spin would still be normal rotation.

2. Turn a rear end around and run it reverse rotation.

[Joe R.]

Re: Tech discussion, rear end usage

Hi Mike:

These are strange questions! Care to tell us why you are asking? Sounds like you have an unusual project in mind (or too much time on your hands!).

Anyway, regarding your second question about running the rear end backwards, I can provide some hearsay if you will first allow me to explain the source.

Back in 1975, I built a mid-engine 1967 Corvair using a 327/350. Okay, laugh if you want, but it sure was a blast to drive (only 2900 pounds, and cornered like it was on rails).

There were two competing kits sold for doing this conversion. The first was from a company named Crown. Crown's approach left the Corvair transaxle in place, dropped the Corvair engine off the back, and simply bolted the 327 to the front side. This resulted in the engine being pretty far forward, with the harmonic balancer just behind the driver's hip. I used the Crown kit.

Another company, named Kenmark I think, had a different approach. They bolted the 327 right where the (rear mounted) Corvair engine had been, then turned the entire engine/transaxle assembly around 180 degrees. This put the engine about 10 inches farther back than the Crown kit, but it had the disadvantage that the transmission and differential ran backward.

As I recall, Kenmark (?) claimed that running the differential backward would make slightly more noise and would make it wear out slightly faster, but they felt the difference was tolerable. Apparently their customers agreed.

So, there's a case where someone actually did run a differential backward, and I think it worked out okay. Maybe someone else can comment on running the differential upside down....

Now that I think about it, I'm beginning to suspect what you are after here. If you have some scheme in mind where the differential would end up running backward, you can "fix" that by flipping it over so that it runs forward but is upside down. Maybe you are trying to figure out which option is best.

[Mike McKown]

Re: Tech discussion, rear end usage

I have a KelMark V-8 '66 Corvair. Hopped up 350 engine. The differential in this car is flipped UPSIDE DOWN and BACKWARDS as are the other Kelmark Corvairs.

Flipping the differential in this manner causes the pinion gear to drive on the the "coast" side of the ring gear. Yes you do get a little gear noise but not bad. I haven't had any gear failure but did lose a pinion bearing once. It is said that when the gears turn backwards the pinion bearings do not get the oil bath they normally would. There is a way to divert oil on the bearing but I couldn't tell you what it is. I'll wait until the next time I have to get in there to make a fix.

[Joe R.]

Re: Tech discussion, rear end usage

Hi Mike:

I'm glad to hear that someone is still running one of those V-8 Corvair conversions. Of all the cars I have ever built and then sold, my V-8 Corvair is the one I miss the most.

Since you own a KelMark conversion, I am reluctant to question your description of the "upside down and backward" differential, but please bear with me a moment.

As I recall, the original Corvair engine rotated the opposite way of a small block V-8. So, if you simply bolted a V-8 to the transaxle where the Corvair engine had been (in the back of the car), the car would run backward in first gear. You could "fix" this by rotating the entire engine/transaxle assembly 180 degrees so that the engine was in the middle of the car and the wheel that had been on the left side moved to the right side. I thought this was what KelMark did.

If you did this AND you flipped the transaxle upside down, the effective rotation would be reversed again, and first gear would move the car backward. It seems to me that the "upside down and backward" combination would bring you right back to where you started in terms of the direction of wheel rotation.

Have I missed something here? It's kind of confusing to try and visualize the effects of each change.

Anyway, keep driving that V-8 Corvair!

[Mike McKown]

Re: Tech discussion, rear end usage

Let's see if I can explain this:

Yes, the Corvair engine rotates backwards from a Chevy V-8.
Joe:

Visualize the Corvair engine and transaxle in the car. If you did a back flip of the engine and transaxle and put the engine in the back seat instead of the trunk, the car would still go forward even though the engine is upside down. So since the V-8 would have reverse rotation from the flat six, you now have to roll the transaxle right/left 180 degrees, or upside down to make the rotation come out right.

Roll a pencil between your fingers for a little while and it will come to you.

Yeah, the thing is a lot of fun. It's funny sometimes at cruises when young people come up and look at it, they are very puzzled when they can't find the engine. They look under the hood. Nope, not there! They look in the trunk. Nope, nuthin' but a radiator in there. Wait a minute! What's the radiator doing back here!

[mike cobine]

You guys are sharp

Yes, a mid engine project is what I am considering. Of course, I have considered it for quite some time, but a Corvair transaxle on ebay recently sparked my thoughts on this again.

Since you guys actually ran a small block with a Corvair transaxle, maybe you could elaborate on how they stood up. How hard did you run them? How much power did you make. Weight of car? How high did you rev and shift at?

My thoughts were along the line of taking a Corvette rear, mounting an engine to the front and a transmission to the rear, and tie them all together with a shaft between engine and transmission, and a gear transfer on the transmission output with a shaft back to the rear end. While there would be expense on machining special parts, use of a production rear end and transmission would have to be a lot cheaper than a $10,000 or more Hewland. The ability to plug a 5 speed or 6 speed into the back would also be very nice.

This was because while I know the Corvair was used in Manta Mirage and Coyote cars, I wasn't sure how they would function under high horsepower and heavier loads (racing loads). Also, the Corvair parts are rather old now.

[mike cobine]

Good shot of Transaxle

And a non-iron big block

[Mike McKown]

Re: You guys are sharp

My engine is built similar to a 350/350. It has wide 50 series BFG Trans AM tires. I've beat it zero to 100 on numerous onccasions but never really hammered it off the line. It gets such a good bite I am afraid something will fail. Based on my experience, I can't tell you what the weak link is except for maybe the pinion bearings. The '66 and later four speed is a Saginaw design and I've been told it is on par, strengthwise with the pass car Saginaw. The input shaft from the clutch to the transmission passes through the pinion gear, on through the differential and into the transmission. Due to the fact that this shaft is so close to the ring gear the one on my car can only about 1/2" in diameter. Still, I don't believe this to be a weak link. My differential is a posi-traction with a four spider conversion.

Like I said, I haven't torn anything up except for the set of pinion bearings but I don't ****** and grab every time I change gears.

Something that was popular a few years ago that would hold up was to use the Olds Toronado FWD Hydra-Matic transaxle and mate the Corvair axles to it in a rear drive set-up.

My opinion? If your just gonna' cruise with this set up, fine. If you're gonna' hammer it, I think you could make a better choice of transaxle.

If you're still interested do a Google for Clark's Corvair. I think they are in New Jersey. They bought up a lot of the leftover/surplus KelMark and Crown conversion pieces.

[Joe R.]

Re: You guys are sharp

Hi Mike:

My 327 Corvair used a fairly stock 327/350 with an Edelbrock Torker intake. The car weighed 2900 pounds.

I put about 40,000 miles on the car. I didn't beat on it, but I enjoyed running it up through the gears on a regular basis, shifting at about 6000 RPM. I did manage to break the ring and pinion once, when I was shifting particularly hard at 6000 RPM. After that I was a little more careful.

The Corvair transmission guts were basically the medium-duty Saginaw 4-speed. I never had a problem with the transmission, even though I thought I might.

I think you could readily use a Corvair transaxle if the weight of the car stays below 3000 pounds and/or you don't beat on it too much. If you do decide to use a Corvair transaxle, there are two different methods as I mentioned in my earlier description of the Crown kit compared to the Kelmark kit. I can provide more details if you want.

Used Corvair parts are readily available, and one good source is Clark's Corvair parts that Mike mentioned. They are located near me in Massachusetts, and they sell used transaxles. In fact, just last year I sold them a spare transaxle that I still had lying around.

As someone mentioned, another popular transaxle is the one from the front wheel drive Toronado. I have a friend who has done swaps with these, in case you want more info. Also, didn't Cadillac use a front wheel drive transaxle with their Northstar engine for a few years? Maybe that would be a candidate.

I'm not sure I fully understood the description of your proposed scheme that used Corvette parts, but I would advise caution in creating something too bizzarre. Keep in mind that the structural integrity and the geometry of the rear suspension are affected by whatever design you use. I think it is probably better to stick with a pre-engineered transaxle assembly from a car whose suspension setup you can readily duplicate.

One nice thing about the Corvair setup is that aside from the fact that the differential is actually a transaxle, the rear suspension is very similar to a C2 Corvette. Another advantage is that if you want a 4-speed, the shifter arrangement has already been worked out by GM.

[Joe R.]

Re: Tech discussion, rear end usage

Hi Mike:

You explanation still has me confused. If I followed the sequence you describe, the car would have four forward gears but the engine would end up back in the trunk. Let me try this visualization to describe why it seems that simply running the transaxle backward would do the trick:

Imagine that you bolt a Chevy V-8 to the Corvair transaxle right where the Corvair engine was, which is what the Kelmark kit did. Now you have a V-8 in the trunk, and all four forward gears make the car go backward, due to the reverse rotation of the engine. To fix this, you keep the whole engine/transaxle assembly right side up, and simply rotate it 180 degrees so that the left and right wheels swap sides. Now the engine is in the back seat, you have four forward gears, and the differential is still right side up.

Another way to visualize this is to start with the Chevy V-8 in the trunk again (with the four forward gears making the car go backward). Then you simply pick up the body and turn it around, so that the front of the body faces the other way. Now the problem is fixed and the transaxle is still right side up.

As I recall, the Corvair differential had a stamped steel, vented lid bolted to the top, which was the access point to put in the ring and pinion. I thought the bottom of the differential casting had the mounting points for the bracket that held the inboard ends of the strut rods (very similar to a C2 Corvette). If you turn the differential casting upside down, you have to re-engineer a big part of the rear suspension.

Are you sure that your differential is upside down?