Member
I'm just wondering if the series 40-50 manual transmissions will interechange with the series 70 manual transmissions. I know they are internally different but are they the same length? input shaft length? same tooth count and size on the torque tube shaft? Only reason I'm asking is because the 47 special I just bought came with a trailer load of roadmaster parts too including a trans and motor.
Senior Member
Sort of, but the swap isn't a bolt-in. Overall length, splines and release bearing support are the same, but the front bolt pattern is different between the 5 bolt (number of top cover bolts) and 6 bolt transmissions. The upper two bolts are in the same location on both transmissions, but the lower two on the 5 bolt are closer to the upper bolts than they are on the 6 bolt. You also have to watch out for year differences because the rear mount changed between 47 and 48.Originally Posted by 48buickkid
I actually have a 5 bolt transmission in my 52 Roadmaster. I did this because I wanted to get rid of the Dynaflow and 48 was the last year a manual was available in the Series 70. This was a fairly easy swap because I only needed to drill and tap two new holes in the 320 bell housing and use Series 50 shift linkage. Going the other way could present more of a problem because the lower two bolts will be very close to the bottom edge of the bellhousing and you might not have enough "meat" there to drill and tap.
The 6 bolt is a better transmission than the 5 bolt, so if you want to use it, I think it would be well worth the effort to try fitting it onto the 248/263 bellhousing. Just put in the upper two bolts and see how close the lower two holes are to the edge. If you try this, please let us know what you find out.
Sorry for taking so long to answer, but I unavoidably had been away from the internet for a couple of months and am just now trying to get caught up on what I missed.
Ray
Last edited by raycow; 03-13-2013 at 10:41 AM.
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