Power glide to 4 speed conversion

[steptoe]

I'm trying to convert my 1964 Monza from a power glide to a 4 speed transmission. I bought a 1964 convertible for the necessary parts. Well what a surprise, the 4 speed won't fit. Can't find enough clearance for the transmission. It is bottoming out on the rear sub frame. I measured the power glide case and it is about 1 1/2 inches shorter than my 4 speed setup. How does anyone perform this conversion on an early model? I am totally confused. The powertrain fit in the convertible but won't fit in my coupe. Can someone please offer any assistance? Thanks, Steptoe

[Frank DuVal]

Two ways:

1. Change the rear crossmember.

2. Cut the rear crossmember and weld the piece back in with clearance.

Don't forget all the other little pieces.

I hope you have both cars side by side. Swap everything that is different.

I always advise people to buy the right car, sell the wrong one, cheaper in the long run. Ha!

[Dennis66]

Wow! Didn't realize there was a different crossmember for the automatics in the EMs. I've converted a LM, as well as a number of other makes of vehicles. At least you did right in getting a complete donor vehicle. I take it the convertible isn't worth saving? Dennis

[Frank DuVal]

Actually a different crossmember for the four speed transmission. The three speed manual and the automatic share the same crossmember. So when GM decided to put in the four speed they had to accommodate the slightly longer 4 speed case by making a crossmember with a depression in it. Many people cut out out rewelded the crossmember when putting a 4 speed into a three speed car. Starting in 1966 the 3 and 4 speed transmission cases are the same size. Called the Saginaw, but of course all of them were made by Saginaw...

[bbodie52]

https://ssl.corvair.com/user-cgi/catalo ... w_page=359

Part number CU258: USED FT TRANS CROSSMEMBER 61-64 CAR 4SPD

Weight: 4 lbs 0 oz
Catalog Page(s): 359
Price: $ 25.00

Part number CU259: USED FT TRANS CROSSMEMBER 61-64 CAR-PG

Weight: 4 lbs 0 oz
Catalog Page(s): 359
Price: $ 10.00


I would think that your donor car would be able to provide all of the components to make a successful transition — including the mounting bracket, shift linkage, clutch cables, pedals, etc. There are a lot of bits and pieces, from the clutch pressure plate, flywheel, throw-out bearing, bell housing, differential, transmission, backup light switch and wiring harness, etc. — not to mention the shift and clutch linkage and hardware from the passenger compartment and tunnel. You have to strip a lot of pieces and small parts from the source vehicle to move them to the target vehicle. It helps to have the donor car next to the target car so that you can work from one to the other, piece by piece, front to rear, to get it all done. When you are finished there won't be much left of the stripped car to make it useful for anything except a parts car.

A 1964 Corvair Assembly Manual might be a good supplement for your shop manual. The Chevrolet Assembly Manuals often show details not found in the 1961 Shop Manual or the 1964 Shop Manual Supplement. I have attached some sections from my 1965 Corvair Assembly Manual to give you an idea of what you would find in the 1964 book.


https://ssl.corvair.com/user-cgi/catalo ... _page=243B

Part number C7314: ASSEMBLY MANUAL-64 CARS

Weight: 2 lbs 0 oz
Catalog Page(s): 243B
Price: $ 16.40

I was stationed at Keesler AFB in Biloxi in 1973 — a long, long, time ago — in a state not so far away (from my current home in western North Carolina). Let us know how your project car finishes up!

When you finish, perhaps you could tell us about your conversion project, and the planning and work involved, so that others who might be considering a similar conversion for their Corvair can learn from your effort.

[Dennis66]

Got the picture now. TRANSMISSION CROSSMEMBER. I was thinking rear subframe crossmember (I've seen some here mention the front "crossmember" referring to front suspension.) Yeah, I could easily see that. When I converted the LMs, I simply dropped the transaxle bracket (crossmember) and all and put the whole thing back in. I think the first one was a 3 speed and the second was definitely a 4 speed. Dennis

[Frank DuVal]

"There are a lot of bits and pieces, from the clutch pressure plate, flywheel, throw-out bearing, bell housing, differential, transmission, backup light switch and wiring harness, etc. — not to mention the shift and clutch linkage and hardware from the passenger compartment and tunnel. " and instrument cluster!

While the transmission support (or bracket) is different between Powerglide/three speed and the four speed, I am talking about the rear crossmember!. That part is also the same between the three speed and Powerglide, but different for four speed from 1960 to 1965. And it weighs a lot more than 4 pounds!

Unless one has both cars sitting side by side to transfer parts that are different, it is going to be very hard job to find all those different parts, hence why I suggest buying the right car. I am jaded, because I LOST a 67/68 clutch pedal assembly (yes, they are different than 65/55 and 69), because a "friend" was getting paid to convert a 67 Powerglide to a 4 speed and the owner never thought the pedals were different. Well, that was over 10 years ago and the owner and my "friend" have been arguing who owes me the correct set of pedals back. So my '68 sits pedal less for 10 years in the yard... So when people want to "borrow" parts any more, you know my answer! And now I hear the owner needs to change it back because due to knee/leg issues he cannot drive a clutch anymore... In just 10 years! You never know what your body will do to defeat you....

[steptoe]

I looked up the 4 speed transmission for the 1965 model and the pic shows the backup switch location in the tunnel about midway. All though I have a 1964 model I thought only the 3 speed had that setup. Anyway I had a powerglide and the switch is on the shifter. I could jump the connection but that would require a manual switch to control the backup lights. I would really like it to happen automatically but cannot find a switch on the 4 speed transmission. My doner car is a 1964 Monza Convertible which did have backup lights. Any help? Thanks, David PS. I retired from Keesler AFB in 1982 as a Technical Writer (I wrote the CDC's for my career field).

[joelsplace]

The switch sticks straight down off the bottom of the transmission. It is usually damaged because of the location.

[66vairguy]

I looked up the 4 speed transmission for the 1965 model and the pic shows the backup switch location in the tunnel about midway. All though I have a 1964 model I thought only the 3 speed had that setup. Anyway I had a powerglide and the switch is on the shifter. I could jump the connection but that would require a manual switch to control the backup lights. I would really like it to happen automatically but cannot find a switch on the 4 speed transmission. My doner car is a 1964 Monza Convertible which did have backup lights. Any help? Thanks, David PS. I retired from Keesler AFB in 1982 as a Technical Writer (I wrote the CDC's for my career field).

Maybe you are referring to the wiring diagram. It shows the switch midway, but the wiring comes out of the tunnel and goes to the bottom of the 4 speed transmission to the switch as Joel said.

Yes have to modify (or replace) the wiring harness when changing from a PG car to a manual transmission car.

[Frank DuVal]

Yes have to modify (or replace) the wiring harness when changing from a PG car to a manual transmission car.

Just another one of the many many parts you need from the donor car. Easier to buy a 4 speed car to drive...

64 4 speed convertibles are a blast tor drive! Even though the acceleration time of the stock 4 speed (3.27 gears) and the stock Powerglide (3.55 gears) cars is almost the same. Just rowing the gears seems faster. Call it seat feel.

3 speed transmission had the backup lamp switch on the tunnel 1960 to 1965. The four speed had the backup lamp switch screwed into the 1/2-13 threaded hole on the bottom next to the shifter input shaft. FCs had a plug in there, since no factory backup lamps. To use the same body harness as the three speeds, GM put a six foot (or so) cable onto the switch and then ran it into the tunnel to plug into the connector for the three speed switch.

1966 to 1969 3 and 4 speeds, since they are the same case casting, had the backup lamp switch screwed into the driver's side of the transmission.

[belaraphon]

I converted a 1965 PG car to a 4 speed and wrote a short list of things I had to do to get it to work. I have included it below if it is helpful to you.


1. Transmission, pressure plate, flywheel, bell housing, clutch disk, clutch to "Z" bar linkage and return spring, flywheel bushing, maybe a new throw out bearing. (Get the service and assembly manuals for your car. I think some people have posted them in digital format on the forum).
2. "Z" bar and mounting plate. It screws onto the bottom of the rear seat and the nuts should already be there.
3. Clutch cable, shift tube, shift coupler, shifter, shifter base shims and plastic spacer, shifter lever and base. (A nice thing to do when putting in the shift tube assembly it to replace the plastic bearing ends with new ones, or a bronze sleeve kit for better shifting.)
4. Clutch and brake pedal assembly. Clutch cable pulleys.
5. Jumper the neutral start switch in the automatic trans wiring harness to start the car. See factory wiring diagram. It will be attached to the auto trans gear selector switch.
6. Jumper (or replace the body and dash wiring harness) to get the back up lights to work. There is a switch on bottom of the front part of the trans to turn on the reverse lights. A wire will normally run to the body harness in the tunnel from the switch in a 4 speed car.
7. Recurve the distributor for best power. PG cars have a different advance curve than manual cars. 140 is initial advance at 18 and all in at 2800. PG cars don't come all in until 4,000 (at least in 1965).
8. You will need a new front top engine shroud to block off the excess power glide holes so junk doesn't get into the engine compartment. Also, there is a specific hole in the manual shroud for the differential dip stick. Alternatively you could block off and drill out the needed holes.
You will need new rubber sleeves for the shift cable at the rear of the bottom cable tunnel and for the new front shroud.

My advice is that if you go to through this kind of trouble is to replace parts that can wear out with new stuff to save you trouble later and make the car nicer to drive. Parts to replace/refurbish include:
1: throw out bearing, crank snout bushing
2: clean and re-grease "Z" bar pivots balls and put in new fiber seals
3: Install bronze sleeve bearings on shift tube, Replace shift coupler as the rubber on yours is probably hard as a rock and can introduce vibrations on the shifter and make it hard to hit the gears.
4: Get new plastic shift and brake pedal bushings, and probably new cable pulleys (and grease them up when installing)
5. Grease the shift lever and properly shim the mount bracket so it is snug but will slide forward and backward as the factory intended as the drive train moves. Shimming thickness will vary based on the thickness of the cars flooring sheet metal. You just need to remove a block off plate in the floor to install the shifter lever.

Follow the service manual for clutch and shifter adjustments. There are a few parts suppliers for Corvairs on the internet. Avoid new parts from ebay as they are often incorrect unless it is from one of those suppliers. I use Clark's a lot as they are the most complete supplier (corvair.com). Also check out California Corvairs, Corvair Ranch etc. I think there is a listing on the forum someplace. Sorry if I forgot anything. The service manual will be your best friend and the knowledgeable folks on the forum of course.

[joelsplace]

I'm confused on #8. The way I've always seen it is 64 and 65 all have the differential dip stick. The '66 has a flat where the hole was. I am not aware of any difference in the actual dip stick, tube or where it goes through the '65 shroud.
My knowledge could be lacking in this area. I've only converted a 63 from auto to manual and of course they don't have the dip stick. I was amazed at how easy it was except for cutting and welding the crossmember and that really wasn't difficult. I also added the dipstick to at least 1 LM.

[Frank DuVal]

Right, Joel, all 64s and 65s had a differential dipstick, transmission does not matter. And the 64 and 65 tubes/dipsticks seem to measure the same.

Also #5 in the second set is only for late model cars. The early shifter bolts to the floor and does not move.