# Planning to convert a 1968 Corvair 500



## j4ckcampbe11 (Sep 24, 2018)

About a year ago, I bought a 1968 Corvair 500, thinking it would be a good donor for an EV conversion: 2 speed powerglide transaxle, relatively light weight (2550 lbs) and room for batteries in the 'frunk'. The car only has 14,000 miles, so I have been enjoying it with the ICE until now, but I think I'm ready to get started.

My goal is to have a nice little Chicago commuter vehicle. Work is 10 miles each way. I would like to be able to take it on the highway. So 35 miles/ 70 mph seems like a reasonable target.

I have considered these broad strategies:

Budget: get a refurbished electric motor and some deep-cycle 12v batteries. Pull the ICE, bolt the motor to the existing transaxle, distribute the batteries at various locations around the car. 

Prius: I have a 2006 Prius in good mechanical condition I would be willing to donate to the cause. This has some real benefits in terms of range, modern systems, etc. I know the "Corvarius" would be a major project.

All out: Buy everything from one place and get the latest/ greatest batteries, motor, etc. Maybe even have someone do the conversion. This one is unlikely, but I may win the Powerball, who knows?

I am a decent shade-tree mechanic, but I don't have great work space, or a lift. I have pretty limited fabrication skills and no access to machine tools. 

I would love to hear any "how I'd do it is..." from the experts as a way to clarify my thinking and get further motivated. If you're in Chicago and up for getting together to discuss, beverages are on me...


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## dragonsgate (May 19, 2012)

I think Nader was talking through hisass because I have had some good experiences with Corvairs. 

The Prius in Corvair clothing sounds like an idea worth trying.

While LA's are still doable it would be best to go the extra cost for and get lithium from the start.

Limited knowledge is not necessarily a draw back but limited tools and work space can be a problem in my opinion.


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## nucleus (May 18, 2012)

j4ckcampbe11 said:


> About a year ago, I bought a 1968 Corvair 500, thinking it would be a good donor for an EV conversion: 2 speed powerglide transaxle, relatively light weight (2550 lbs) and room for batteries in the 'frunk'. The car only has 14,000 miles, so I have been enjoying it with the ICE until now, but I think I'm ready to get started.
> 
> My goal is to have a nice little Chicago commuter vehicle. Work is 10 miles each way. I would like to be able to take it on the highway. So 35 miles/ 70 mph seems like a reasonable target.
> 
> ...


Forget the lead acid. You save money using Lithium actually. 

I would figure out where and how to mount your batteries first, then go from there. 

Think used packs, Tesla, Chevy Volt, etc.

Maybe talk to the guy who built the Electrovair and see if he can hook you up with an adapter.

https://www.corvairforum.com/forum/viewtopic.php?t=13925


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## brian_ (Feb 7, 2017)

If you use a Corvair transaxle, you basically have a choice of using a manual, adapting a very expensive converted PowerGlide, or doing your own transmission conversion, since an automatic is unsuitable for an electric motor.

The Corvair transaxle is a weird thing, which can accept drive from the front (which is how some mid-engine V8 conversions have been built). There are possibilities beyond the traditional approach of bolting an electric motor directly in place of the engine, and if you get the motor on or ahead of the axle line you could have a great space for a battery pack in the back.

Whatever you do, keep in mind that the Corvair suspension uses the axle shaft as locating arms, so the final drive (differential) bearings take all of the cornering force on the rear tires, so any change of transaxle requires either maintaining that capability or radically changing the suspension.


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## j4ckcampbe11 (Sep 24, 2018)

brian_ said:


> If you use a Corvair transaxle, you basically have a choice of using a manual, adapting a very expensive converted PowerGlide, or doing your own transmission conversion, since an automatic is unsuitable for an electric motor.
> 
> The Corvair transaxle is a weird thing, which can accept drive from the front (which is how some mid-engine V8 conversions have been built). There are possibilities beyond the traditional approach of bolting an electric motor directly in place of the engine, and if you get the motor on or ahead of the axle line you could have a great space for a battery pack in the back.
> 
> Whatever you do, keep in mind that the Corvair suspension uses the axle shaft as locating arms, so the final drive (differential) bearings take all of the cornering force on the rear tires, so any change of transaxle requires either maintaining that capability or radically changing the suspension.


Thanks for your reply, I know it has been a mighty long time. But I am once again looking to get into this. Your approach outlined above has a lot of appeal. I think it would be awesome to do the 'mid engine' approach and move build storage for batteries on either side of the motor and in the back. I'm fine with losing the back seat forever.

Now for a real newbie question. do I need a transmission at all? Can I just attach a motor to the pinion of the transaxle and do a direct drive, single speed? And just reverse the motor to back up? What components might lend themselves best to this approach? I like it because it seems really simple and preserves the transaxle as you mention above.


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## brian_ (Feb 7, 2017)

j4ckcampbe11 said:


> Can I just attach a motor to the pinion of the transaxle and do a direct drive, single speed? And just reverse the motor to back up? What components might lend themselves best to this approach? I like it because it seems really simple and preserves the transaxle as you mention above.


Yes... with conditions.

The Corvair transaxle does come apart in sections, one of which is the final drive (differential plus ring and pinion gears), so you could probably make an adapter plate to mount the motor and a shaft adapter allow the motor to drive the pinion shaft directly, and still have the feature of being able to handle lateral suspension force through the axle shafts. The input to the pinion comes from the front end (the Powerglide transmission) and the engine is bolted to the back, with a shaft from engine to transmission passing through the differential; it looks like the pinion shaft is hollow, so the input shaft runs inside it (automatic transmissions are generally coaxial, with all shafts running on the same axis). Unfortunately, this would be substantially more custom machining and mechanical work than using a common separate differential in a modern rear suspension.

Nearly all production EVs have only a single-ratio transmission; this works because they have enough battery voltage to make the motor produce sufficient power at high speed, while using a gear ratio that provides enough torque at low speed. But none use just the ring and pinion of a final drive, mostly because the ratio between the motor speed and axle speed is too much for a single stage of gearing; common ratios for EVs are in the range of about 7:1 (e.g. Nissan Leaf) to 10:1 (e.g. Tesla). A 1968 Corvair with Powerglide apparently has a 3.27:1 or 3.55:1 ratio, although some 1960-1963 apparently had 3.89:1.

This plan can work with the single gearing stage, though - you just need a motor which is big enough to provide enough torque at low speed when only multiplied by that one stage of gearing, and the ability to run that motor fast enough for your desired top road speed. GM actually used only one stage of gear reduction (instead of the usual two) in the Chevrolet Spark EV, and it only had something like a 3.5:1 ratio, but they gave the car an abnormally large motor to compensate.

Some DIY EV builders are satisfied with just the final drive gearing even with relatively moderate gear ratios. An example might be Duncan with his "Dubious Device" using the final drive from the rear of a Subaru (4.11:1 ratio?); however, he has an exceptionally large motor for the size of the car (for sufficient torque to the wheels at low speed), and feeds it from exceptionally high voltage battery for a brushed DC motor (to keep it working at high road speed).


Regardless of number of transmission ratios, you can just run the motor in reverse to back up (unless you use the Powerglide, which probably doesn't work that way). While this is easiest with an AC motor (it's just a signal to the controller telling it what direction to make the motor turn), it is even possible with the old brushed DC series-wound motors, using set of contactors (relays) to flip the polarity of the field winding for reverse.


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## brian_ (Feb 7, 2017)

since this thread has been revived, I'll take the opportunity to respond to an earlier comment:


dragonsgate said:


> I think Nader was talking through his ass because I have had some good experiences with Corvairs


Ralph Nader's exercise is self-promotion used the first-generation Corvair as a example of dangerously irresponsible vehicle design, even though that design was essentially the same as the VW Beetle and early Porsches, because his target was GM. That generation did have unsuitable handling characteristics due to the swing-axle rear suspension, compounded by the rear engine placement; however (after a quick fix for 1964) the second generation (starting in 1965) had a very different suspension which fixed the problem.

The 1968 (and any second-generation) Corvair rear suspension is a decent design, without the concerns raised by Nader. It is derived from and similar to the second and third generation (C2 and C3) Corvette, but with coil springs instead of the Corvette's transverse leaf spring. Even the rear suspension of the C4 (introduced in 1984) shares some features, including the use of the axle half shafts as lateral suspension links.


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## brian_ (Feb 7, 2017)

Whatever you do, this lever used to shift the Powerglide in a Corvair looks like a fantastic thing to use to switch the motor between forward and reverse.


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## brian_ (Feb 7, 2017)

For planning purposes, some drawings might help. The first is a plan view of the first generation, so the rear suspension (in orange) is all wrong, but the other components are right. The final drive (diff housing) is in green (with an "X" cast into the top), and the transmission is in purple ahead of it. It might be possible to fit a reasonable motor in place of the transmission and extending wider and longer, but still within a hump that would leave usable rear seating. The fuel tank is in the front (also shown in green), and for balance and to keep the rear weight manageable some of the battery should probably go there.








(from Silodrome:chevrolet-corvair-history; also available in B&W from smcars.net)

A side view might help with component placement as well; again, this is the first generation (and the image is from the same source) but the dimensions and components shown should all still apply for 1968. The brown space behind the rear seat is the parcel shelf, which might not be a great place for battery (because it is pretty high and not very wide) but could hold electronics (controller/inverter, etc), perhaps under a clear plastic cover to show it off if done neatly.


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## j4ckcampbe11 (Sep 24, 2018)

Thanks for all the excellent feedback and ideas. I had the same idea of creating a battery pack that would fit where the gas tank went. I also agree, the PG shift on the dash is ready-made for a Forward/Reverse rework. Wouldn't it be amazing if I find out there's a motor that will fit on the front side of the transaxle that will be compact enough to use without a lot of cutting and still be able to retain a second seat. Even if I had to have a hump for the motor, I bet Camaro or Nova back seats would be adaptable for that purpose. 

I have a buddy in Chicago who is a leading Corvair expert - he will be able to supply me with parts. The diff comes in 3.27:1 and 3.55:1. I can get my hands on either. Once I zero in on a motor, I can look at what it would take to connect, and look at whether it is possible, or preferable to have the motor in front, or trailing the transaxle/diff.

Regarding a gas tank/ battery pack - I can find out dimensions for a replacement gas tank and work on creating a battery tank that will fit. I'm getting ready to take a welding course that offers free shop time to graduates. 

Another fun idea - since the batteries will be in front, I can locate the charging system in the frunk, and use the gas tank filler door for my port.

I'm going to continue lurking/ reading to try and identify what kind of motor/ controller/ battery systems would work best with this approach. Anyone reading along, feel free to chime in.


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## j4ckcampbe11 (Sep 24, 2018)

I confess I do not know exactly what "keep in mind that the Corvair suspension uses the axle shaft as locating arms, so the final drive (differential) bearings take all of the cornering force on the rear tires, so any change of transaxle requires either maintaining that capability or radically changing the suspension." means, or how that is different from other designs. I found my way to a Tesla refurbisher that sells the smaller Tesla 3 type motor/ transaxles. They can even make axle shafts in custom lengths. Would that work?


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## brian_ (Feb 7, 2017)

j4ckcampbe11 said:


> I confess I do not know exactly what "keep in mind that the Corvair suspension uses the axle shaft as locating arms, so the final drive (differential) bearings take all of the cornering force on the rear tires, so any change of transaxle requires either maintaining that capability or radically changing the suspension." means, or how that is different from other designs.


Axle shafts and suspension links have fundamentally different purposes, and normally they are completely separate things. The axle shafts need to transmit power, and the suspension links need to locate the hubs and take all of the forces in every direction to guide the vehicle and push it around corners.

When they are separate as they should be, you could remove the axles and the final drive (including the differential) completely and it wouldn't make any difference to the suspension - the car would still be drivable if there was something pulling it down the road. Similarly, you could remove all of the suspension and the engine would still be able to turn the wheels through the axles (although the wheels would be flopping around!).

The second-generation Corvair is one of those unfortunate vehicles in which the same shafts (one to each wheel) are used as both axles (turned to make the wheels turn) and suspension links (connecting the hubs to the structure of the car). When the car turns a corner, something has to push the car toward the direction of the turn - that's the tires, which push the wheels, which push the hubs, which push on suspension links, which push the car. The two suspension links that do this in a late Corvair (or the second through fourth generations of Corvette) are a rod under the axle shaft, and the axle shaft itself. So when you are turning left (for example), the left side axle shaft is trying to pull the gears out of the differential, and the right side axle shaft is trying to push the gears into the differential. The bearings on the gears are then pushing the car side to side, and they wear out. More importantly, with a differential not suitable for these forces the axle shafts might just pull right out, or destroy the differential.

This is not rare in older cars. No one makes cars with swing-axle suspensions any more, but they all (including most VW Beetles and my Triumph Spitfire) used the axle shafts as suspension arms. One of the best known early independent rear suspensions in front-engine rear-drive cars was the Jaguar system, which is still used by some street rod builders - it is very similar to the Corvette/Corvair design, with U-jointed axle shafts as suspension arms. They work, but you can't just change the differential to any other design and get away with it.



j4ckcampbe11 said:


> I found my way to a Tesla refurbisher that sells the smaller Tesla 3 type motor/ transaxles. They can even make axle shafts in custom lengths. Would that work?


Like all modern cars, the axle shafts in a Tesla Model 3 are not used as part of the suspension, and will not work that way. The Model 3 drive unit won't work properly with axles that push and pull on it, even if you make axle shafts that connect to both the Corvair hubs and the Model 3 transaxle outputs.


There is a way around this if you don't want to use the Corvair transaxle or a similar differential: you could probably modify the suspension to include an extra link above the axle, so the axle shaft would no longer be part of the suspension. This is sometimes done on Corvettes, although it is not a common modification.


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