Toploader 4-speed Applications

[dbdragracing]

I found a toploader 4-speed with the Tag ID# RUG-AD. In my ID numbers book it list that this transmission came out of a 1968 Mustang w/390 V8. Will this transmission work in my 1970 Mach 1 with a 351C-4V ? Thanks for any info.

 

[dennis112]

I found a toploader 4-speed with the Tag ID# RUG-AD. In my ID numbers book it list that this transmission came out of a 1968 Mustang w/390 V8. Will this transmission work in my 1970 Mach 1 with a 351C-4V ? Thanks for any info.

A 390 toploader will have an input shaft that is too short for usage behind a SBF. The input shaft can be swapped though for one from a SBF. Otherwise the tranny is the same, both externally and internally.

Here is a that shows the difference in the input shaft:

View attachment 352495

 

[ratio411]

I have heard of extra deep crank bushings as well.
They stick further out of the crank to grab the shorter nose.
This is probably a 'band aid' fix compared to swapping to the correct shaft, or better yet, getting the right tranny.

Using the short nose FE unit on a small block will work for a while, but the lack of support will ruin the front bearing and eventually the gears.

Check your numbers too and find out if that is a close or wide ratio.
Wide ratios are better on the street...
Personally, I would never use a close ratio.