Q: I have a 1941 Ford sedan with a small block Chevy. I would like to replace the TH-350 transmission with a TH-700-R4. How much difference is there in the physical size of the transmissions? Will I need to change the transmission mount? Would the driveshaft need modification?
A: The TH-350 is 27¾ inches in total length and 20¾ inches long from the front of the transmission to the mounting pad. The TH-700-R4 is 30 inches in total length and 22¼ inches from the front to the mounting pad. To use the TH-700, you will have to move the transmission mount crossmember back 1¼ inches, and the driveshaft will have to be shortened 2¼ inches. The driveshaft yokes are the same on both transmissions.
I thought because the 700 is longer the drive shaft would be shorter
if the 700r is longer, would the transmission not have to be shortened?
I think you might mean the driveshsft would need shortened if the yokes are the same and the transmission is longer.
I had to cut 3 1/4 inches off of my driveshaft
Correct, the driveshaft should be shortened. We apologize for the typo and have made the correction!
do NOT use a tranny out of a c-4 vette , they don’t have a crossmember mounting pad.
Use a 200-4R and you’ll have better ratios and not have to cut the driveshaft.
^ 200-4r is the same size as the th350, just have to make new mounts. Put one in my 79 Trans Am, use a servo from a grand national.
I’m going to do that to my 78 trans am. Did you have to move the crossmember back any?
Summit racing offers a cross member that will allow the use of the 700R4, it can be found here… http://www.summitracing.com/parts/sum-770318/overview/year/1978/make/pontiac/model/firebird
You will also need to shorten your driveshaft or we can help you with a custom made driveshaft built to your dimensions.
is a turbo 400 with a gearvenders od better that the 4l80?
No one on staff here has installed Gear Vendors Overdrive before. Unfortunately, we’ll have to withhold judgment.
Not sure about thise measurements pist here unless there are different dimensions because I took a 700r4 out out of my 3rd gen. Camaro and put a turbo 350 in they did say it had 9” tailshaft I used factory cross member and the stick driveshaft was the same length
What all needs changing for swapping a turbo 400 w 9 inch tail, To a 700r4? It’s going in a 1987 gmc 1/2 ton w a 305.