The problem I encountered was that the input shafts are different in length and the pilot bearing area is much shorter on the BB.

Check out toploaderheaven.com or one of the other sites for add'l info.

 

Big block toploaders have the shorter pilot shaft. (the part that fits into the pilot bushing)

The BB unit is only around 3/4" long, while the SB unit is a little over an inch.

You CANNOT use a BB trans behind a SB.

Some BB transmissions that came behind the higher horse engines have the larger 1-3/8" input and 31 spline output shafts.

Good Luck!

 

Just curious. I bought a motor and tranny for my mustang and I drove the car before it was taken out and the toploader is from a 390 and it is on a 289? will I run into any problems? The car ran and drove great with no problem?

 

To gtnrb71: Yes, you may have problems. If the trans still has the original 390 input shaft, the front of the shaft barely starts to enter the pilot bushing so there is very little, if any, support for the front of the shaft. It will actually work this way with maybe a little vibration that you can never figure out where it's coming from. However, if you start to rev that 289 like it was intended, the front bearing retainer (where the throwout bearing resides) will break. I bought a toploader for my 289 Cougar that came out of a '66 289 Mustang. The tag code on the case was for a '67 289 Mustang so in the Cougar it went. Drove it for several years with that slight vibration. Then I started drag racing it. When I got brave enough to shift at over 7,000 it started breaking bearing retainers, about every four or five runs. Finally figured it out and put in a small block input shaft. No more problems. Wide ratio, ten spline input toploaders all use the same gears so you only need to change the input shaft.