1966 vs 1965 4 speed input shaft interchange?

[ChelanV8]

The input shift shaft internal to my 1966 four speed transmission was cracked where the drift pin hole is. I removed the side cover and removed the shift shaft. Having a spare 1965 four speed, I removed the shift shaft and installed it in the 1966 transmission. They appeared identical. On test drive, I had reverse and 1-2 ok. I could not get into 3rd or 4th. The shift linkage was not altered so the issue seems to be with this replaced part.

Believing I could have replaced the side cover improperly, I dropped the trans and opened it up. Everything appeared OK. Being super careful, I replaced the side cover. I've rebuilt this transmission and others so I'm confident the side cover was installed correctly. On test drive, again I couldn't shift into 3rd or 4th. I removed the transmission again and opened it up. Nothing seems wrong and everything is moving freely.

Is it possible there is a difference between the 1965 input shift shaft and the 1966? Has anyone experienced anything similar?

I'm going to install a different transmission but it seems crazy this won't work properly and I hate to not use a transmission with a fresh rebuild a couple thousand miles ago. Thanks for ideas!

[Frank DuVal]

Did you try adjusting the shift coupler? Rotationally I mean. I know, it is keyed to the shaft, but, there is enough play in the key to make it hard to rotate the shifter into 3/4 or vice versa, not getting into reverse!

[66vairguy]

After I install the side cover off a 66-69 transmission I always install a tool on the shift rod and make sure I can engage all the gears and I turn the input shaft to confirm. If you did this and the shifter in the car can't engage 3rd or 4th then Frank D. makes a good point. Maybe the shift coupler hole in the 65 shifter shaft isn't in the same plane as the 66.

[joelsplace]

According to Clark's they are not the same. Not surprising since the transmissions are totally different.

[Phil Dally]

FYI: For all from left to right.

Kelmark
1966-69
1964-65
1961-3?
1960?

First three I'm sure, last two...??

[Phil Dally]

Oops...I read input not shifter!!

Good information no matter what.

[Frank DuVal]

Only if you explain the weld marks on the one second from the left!

[Phil Dally]

Don't know as it was from a random post on CCF.

[markplucenik]

I just went through allot of trans work on my 66. I had to pull it apart a couple times because the 3rd / 4th gear shifter fork dropped while putting on the cover plate. This is a real pain to get right. You need to use real heavy grease to hold them up in place during assembly. I also put my grease in the freezer to stiffen it up. I also used 2 input shaft seals on the assembly to help with possible leaks. My little adaptation worked great. I put the first seal in as usual. the 2ed seal now is loose because it does not have the slight step inside the housing. I modified the 2ed seal by using a thin slice of brass shim stock wrapped around the OD of the seal. I found .002 shim stock was the best fit. I used a very little gel crazy glue to attach the shim stock to the metal OD of the seal. Fit like a champ , and also used the special washer. Plenty of room for both seals. My problem sounds like yours, I had reverse , 1st and 2ed. It felt like I had 3rd and 4th but I did not.

[bbodie52]

[Frank DuVal]

OP question is shift shaft (shift selector shaft) not input shaft (clutch shaft).

[ChelanV8]

Thanks for the help.
The specific question was about the shift input shaft internal to the transmission housing not the drive input shaft that engages the clutch.

After working on this challenge once more, I have taken the differential top cover off and confirmed the side cover was installed correctly. Each gear was checked for full rotational ability and I confirmed gear ratios.

From that I confirm the shift input shaft on my 1965 transmission is exactly the same functionally as my 1966. I know Clark's Corvair said they are different. They are not. Laying them side by side and visually checking, they appear identical. Measuring them with a micrometer they measure exactly the same. The drift pin hole is in the same plane in relation to the mounting bolts for the detent bar inside the transmission. This is not to say that the input shift shaft removed from my 1965 transmission had not been changed out sometime in the past. But functionally, the two shafts are interchangeable in my application.

I found some issues with the shifting tube that I believe has been creating the problem of shifting into 3rd and 4th. I resolved that but won't be able to confirm until I go out for a test drive.

Thanks again for your comments!

[azdave]

I also used 2 input shaft seals on the assembly to help with possible leaks.

This never made sense to me but I see it mentioned a lot. The first seal is all that is needed and some years down the road, the second seal would be starved of lubricant after the initial assembly grease did its job. Two seals (one starved of fresh lubricant most of its life) don't seem to add much value in my opinion. Seals do fail with heat and age. I will agree that there is likely no harm if you install two seals, except for time and money to add another.

The split ring adjacent to the seal is quite important to protect the seal from any input shaft misalignment when joining the engine to the diff. Some people say that split ring is also there to limit input shaft wobble at high RPMs but I've never seen evidence that the ring or shaft were ever touching when splitting old engines and diffs. I just parted a 180 turbo engine from the diff last weekend and the input shaft did not have a single witness mark that you think would be there if the shaft ever wobbled enough to hit that split ring.

[66vairguy]

I also used 2 input shaft seals on the assembly to help with possible leaks.

This never made sense to me but I see it mentioned a lot. The first seal is all that is needed and some years down the road, the second seal would be starved of lubricant after the initial assembly grease did its job. Two seals (one starved of fresh lubricant most of its life) don't seem to add much value in my opinion. Seals do fail with heat and age. I will agree that there is likely no harm if you install two seals, except for time and money to add another.

The split ring adjacent to the seal is quite important to protect the seal from any input shaft misalignment when joining the engine to the diff. Some people say that split ring is also there to limit input shaft wobble at high RPMs but I've never seen evidence that the ring or shaft were ever touching when splitting old engines and diffs. I just parted a 180 turbo engine from the diff last weekend and the input shaft did not have a single witness mark that you think would be there if the shaft ever wobbled enough to hit that split ring.

Dave - I agree. I've never seen "witness marks" on an input shaft in the area of the split ring, even with one shaft that was BENT! The split ring's only function is to keep the shaft from moving too far to damage the seal during transaxle assembly.