3spd to 4 spd swap question

[Racerdoc]

I am doing a 3 speed to 4 speed swap on my 1966 Monza. I purchased a 4 speed trans with the trans axle/differential attached so I swapped out the whole 3 speed trans axle/differential unit.

The problem that I have run is an issue with bolting the axles to the transaxle. The original 3 speed bolts that secured the axle/universal joint to the transaxle are larger then the 4 speed transaxle holes.

I have checked the Clarks Corvair catalog and do not see a smaller bolt option.

Should I source the appropriate gauge bolt or do I need to swap the flanges on the transaxles (worried that these may not be "swapable").

Thanks

[bbodie52]

It sounds like the 4-speed transaxle you bought is a 1965 unit with the smaller bolts. The 1966-1969 4-speed used a Saginaw 4-speed transmission mated to a differential that used larger bolts and U-joint clamps. The 1965 transmission was similar to the transmission used on 1964 and earlier Corvairs.

The correct bolt sizes are listed for 1965 or 1966 and later Corvairs. See the Retainers and Bolts listed near the bottom of catalog page 123. However, the retainers are only in-stock for 1966-1969 vehicles. I suspect the smaller bolts that are correct for the 1965 yolks on the differential can be used with 1966 and later retainers, since the small bolts will pass through the large holes in the 1966 retainers.

Other than the Universal joint differential yolk bolt size mismatch you ran into, I don't think you will have any problem using a 1965 transmission and differential in a 1966 vehicle.

http://www.corvair.com/user-cgi/catalog ... d_page=123


Part number C1374: BOLT-65 U-JOINT RETAINER

Weight: 0 lbs 2 oz
Catalog Pages(s): 123(4)
Price: $ 0.85

Part number C1375: 66-69 U-JOINT RETAINER BOLT

Weight: 0 lbs 2 oz
Catalog Pages(s): 123(4)
Price: $ 3.65

Part number CU1446: USED 65 U-JOINT RETAINER(CAP)SMALL HOLES

Notice: Sorry - This part CU1446 is currently out of stock.

Weight: 0 lbs 2 oz
Catalog Pages(s): 123(4),U,17(4)
Price: $ 6.30

Part number C1373: 66-69 U-JOINT TO YOKE RETAINER 65 USES CU1446

Weight: 0 lbs 2 oz
Catalog Pages(s): 123(4)
Price: $ 5.10

http://www.corvair.com/user-cgi/catalog ... ge=TECH-13

[terribleted]

65 units used smaller 1/4" bolts. 66 units used larger 5/16 diameter. The simple way to put it together is use the smaller bolts and and smaller hole universal retainers matching the 65 transaxle you are installing. The other way is to swap the yokes from your current differential into the 65 unit you are using. You could also swap only the transmission retaining your 66 differential. You must in any case use the input shaft that matches the 4 speed transmission.

As Brad (who posted while I was typing this) said above you may be able to use the larger u-joint retainers you have with the smaller bolts (I would think some flat washers would help them sit better). I would prefer to have the larger bolt setup and would therefore either use my existing 66 differential or swap the large bolt yokes onto the 65 unit (not hard to do).

[Racerdoc]

The whole power pack is back in the car, therefore the bolts and washer solution seems to be the easier fix and sounds like it won't affect functionality. Or can I swap out the yokes without pulling the unit back out and if so is it a simple process.... I don't want to risk parts falling out of the differential.

Terribleted regarding the input shaft, when I had the transmissions out the input shafts were identical.

Thanks guys.

[bbodie52]

Terribleted regarding the input shaft, when I had the transmissions out the input shafts were identical.

The chart I posted seems to indicate that the input shafts ARE identical for a 1966 and later 3-speed or 4-speed transmission, but it would have been shorter if you had a 1965 4-speed mounted. Yet the yolk bolt sizes on the differential are small, indicating a 1965 differential. Perhaps you have a 1966 or later Saginaw 4-speed transmission mounted to a 1965 differential! The last Clark's Corvair Parts catalog page I posted describes the differences in appearance between the 1965 and earlier 4-speed and the 1966 and later 4-speed Saginaw unit. You might want to read both transmission descriptions to determine just what configuration you have installed.

You will have to judge if the small bolt heads appear to secure the large bolt retainers adequately. You can also review the procedure in the shop manual for swapping the yolks from one differential to the other, and determine if you want to take that option to permit the use of the large bolts and matching retainers. Or you probably could find some small hole retainers from another source like the Corvair Ranch. http://www.corvairranch.com

[terribleted]

The yokes unbolt. There is a bend over retainer that locks the head of the bolt. Flatten it remove the bolt swap in the matching yoke from the other diff and bend up the retainer to relock. The differential gear is supported by the side carrier bearings, so swapping the yoke should be no big deal.

If you decide to just use the small bolt yokes, it would be best to find the matching U-joint retainers. I likely have some laying around if you want.

[Racerdoc]

Great, thanks guys.

Here's my plan A:
Check to see what trans I have (I did this initially and I am pretty sure that its from a 66 car and the transaxle is a posi, my original was not).
Attempt a yoke extraction and replacement with the power pack as it sits in the car.

My plan B
Source the smaller diameter bolts and matching u joint retainers (Terrbleted I will take you up on the retainers if plan A fails to be an easy solution).

Once my local temp goes above 40F I will be back in my garage.

Thanks again

[Scott V]

My plan B Source the smaller diameter bolts and matching u joint retainers

get gr8 bolts only - dont use gr5.

-Scott V.

[notched]

Post some pictures of both transaxles. We can tell you what you have.