70 4 speed driveshaft

[Dennis D.]

Is the 4 speed driveshaft a different length than the auto driveshaft? Checking a vibration issue. Would running an auto shaft in a 4 speed cause any problems?

I was told a long time ago that is was common place in racing since the auto was a stronger piece.

[Joe L.]

Re: 70 4 speed driveshaft

Dennis-----

For a 1970 Corvette, the 4 speed driveshaft is slightly longer than the automatic (THM-400) driveshaft. Also, the automatic (THM-400) driveshaft uses different u-joints. You cannot interchange a 4 speed and automatic driveshaft for a 1970.

For a 1971-74, the 4 speed and automatic driveshaft are exactly the same and are also the same as the 68-70 automatic (THM-400) driveshaft.

[Mark #28455]

Joe, can you swap the later TH350 shaft

The later 1970's TH350 had the smaller output shaft like the older Muncies and the driveshaft used the larger size U-joints. Was the shaft correct length to swap into the 1960's vintage cars (if the differential had the appropriate sized yoke)?
Thanks,
Mark

[Joe L.]

Re: Joe, can you swap the later TH350 shaft

Mark-----

Actually, the THM-350 used in Corvettes was the same length as the THM-400 used in Corvettes and uses the same length driveshaft as the THM-400. There might have been an EXTREMELY slight actual difference in length, but that's accomodated in the yoke insertion.

The 68+ auto driveshaft (or, 71+ manual trans driveshaft) cannot be used in 63-70 Corvettes with manual transmission or 63-67 Corvettes with automatic transmission.

[Dennis D.]

Re: Joe, can you swap the later TH350 shaft

Actually, I had a 70 auto shaft in a 4 speed. Had to use a front universal joint that had 2 sizes. 1 for the 70 trans output shaft and the other for the front driveshaft.

[Joe L.]

Re: Joe, can you swap the later TH350 shaft

Dennis-----

I can see how it might fit with a conversion u-joint. However, the 68+ automatic driveshaft is about 3/4" shorter than the 63-70 manual trans driveshaft. Consequently, you're "giving up" about 3/4" of engagement of the yoke on the output shaft splines. I really don't recommend do this.

[Dennis D.]

Re: Joe, can you swap the later TH350 shaft

Sounds like it might have been the cause of my vibration issue.

[Joe L.]

Re: Joe, can you swap the later TH350 shaft

Dennis-----

VERY, VERY possible.