Mailbag: Swapping a TH-350 Transmission for a TH-700-R4
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.
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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.