I do not know if this is correct, but I have been told that '55 TBird's have the smallest transmission tunnel. This makes sense as '57 TBird manual transmission cars had T85s which are much larger than my T86.

A T85 is bigger than a Fordomatic?

There is some good info. on Ford Barn, regarding BW 259, T85, T86 transmissions and 55-57 Tbird transmission tunnels. According to CTCI, the BW 259 transmission (side-loader) was used in 55 Tbirds, not the T86. Tbird tunnels were enlarged to accommodate the T85 in 56. A T85 has the same mounting location as a T86, but the T85 tailshaft is longer. The 56-57 driveshafts are larger in diameter than the 55's. When installing a T85 in a 55 Tbird, the smaller diameter 55 driveshaft needs to be used, and it has to be shortened to accommodate the longer T85 tailshaft. 

I guess the million-dollar question, then, is a T5 bigger/smaller than a T85? 

My '55 TBird has it's original transmission.  My car came from the factory with a manual three speed transmission with O/D.  My transmission is a BW T86 top load three speed with a R10 overdrive unit.  I have owned a number of T85s over the years.  T85s are side load, much larger and much stronger.  They are not larger than an automatic.

The bent gasket reminds me of when I order lots of parts from a Tbird supplier. One of the parts I ordered was a fuel line. They bent it 180 degrees so that it would fit in with the rest of the parts. There was no time to replace it as I had to pack it all and get it to the warehouse for shipping back to Australia before I flew out myself. They did refund me the cost of the fuel line though.

I'm not sure what Ian's post has to do with transmissions.

If the T85 is not larger than the Fordomatic, which was used for all three years of the 55-57 Tbird, why did Ford enlarge the transmission tunnel for 56-57? Was the larger diameter driveshaft required for the additional power of the 312?

Next question for those who have done the swap:  What did you use to adapt the speedometer cable to the T-5 transmission?  The Thunderbird cable adapter has the gears that are cut in opposite direction from the T-5, and will not intermesh.  I have this about ready to start up, and the speedometer cable is no way going to work with the T-5 as is.  Joe-JDC

JDC

The gear and cable for my 3 speed (1961) worked and I have since bought a gear assortment to adjust for different rear gear ratios so a cable and gear that will mesh with the T5 should be pretty easy to find.  The gears are very common.

But I guess that the rotation is opposite for yours?



Lawrenceville, GA

I'll try to post a pic of what the cable end with gear looks like for the T5 I installed in my 64 F100. If this is what you have, those gears, as Charlie stated, are available for numerous ratios. They can be right hand or left hand determined by wether the gear is above or below the output shaft.  NPD used to have a very good assortment of those gears. I believe this style ran from 57 on. Not sure about 55. If your Tbird has the "mushroom" style gear then simply buy a cable for a 57 and that will fit the T5 and your speedometer. The speedometer head connection is the same through the 50's and 60's as far as I can remember. 

64F100 57FAIRLANE500