MTFCA Forum

I am putting a Muncie 3 speed gearbox in my Model TT Truck. The drive shaft I have, that I am getting cut down to put the auxiliary gearbox in, has 0.035 inch run out in it. I was wondering is this too much for this drive shaft? I would like to know what your experience is in this matter is.

In modern vehicles, that run at higher speeds, 50-100 thou runout is considered the acceptable threshold.
Of course the real test is the vibration you feel at speed.

.005" -.010"
5 to 10 thousandths
Max

Steven
How much wear do you have where the bushings run?
So you are going to remove about a foot of it and likely from the front end. If you chuck it in your lathe 3 jaw grabbing it where you will cut it off with the pinion end supported by a centre by the tail stock , how much runout do you have then?

Les Schubert wrote: ↑

Thu Oct 01, 2020 8:16 pm

Steven
How much wear do you have where the bushings run?
So you are going to remove about a foot of it and likely from the front end. If you chuck it in your lathe 3 jaw grabbing it where you will cut it off with the pinion end supported by a centre by the tail stock , how much runout do you have then?

Les,

The plan is to get 13 1/4 inches cut off the front of the driveshaft (then machine a new front end) to make room for the length of the Muncie gear box. I am having a machine shop do the work since I do not have the equipment to do that type of work. They said there was 35 thousands of runout and are holding up on the work until I find out if that is too much runout for a Model TT drive shaft. The shaft is unfinished in the middle and do not know how they measured it for runout. I have a shorting kit for the torque tub and radius rods so there is no problem there. The driveshaft came out of a running truck and the bushing looks great, as well as the driveshaft where the bushing runs. There is very little play between the drive shaft and bushing. The worm gear bearings were also in great shape as well as the U-joint. I see no signs of a out of balance drive shaft, which make me think the runout is OK at that level of 35 thousands, and really the mass of the driveshaft on the center line is balanced. The truck looks like it was redone in the 1970s, but do not know how many miles were put on it. The rear end had to be rebuilt and I did that(see other posting on the Hall Scott rear end I posted it was pretty bad in the gear ball).

What I mean about the drive shaft is not finished in the middle, it was not turned smooth at the Ford factory (there is a Ford stamp)

Les,

I will ask the machine shop to recheck the runout by clamping up 13 1/4 inches from the end to be cut.

A large press and nudge the shaft back to straight?

My TT has a shortened drive shaft as well. We did much as you are having done, shorten the shaft and cut down the torque tube too.

All the best (it will make the TT much more 'driveable' in todays traffic - but maybe not that much )

to bad your not closer, I have 2 TT driveshafts and tubes cut down already. Might be cut to the right length already. I can check tomorrow after the Orange County Model T club Swap Meet.
scott