Model TT

[GJB49]

So I have this 27 TT that I am still trying to get running, and I am wondering if it is possible (or feasible) to change the gears in the differential to something lower than the 7.75:1 ratio so the truck would be more driveable. It has a Ruckstell underdrive.

Thank you

[RajoRacer]

Sure can - 5 & some change is the high speed gear set - not common but they're around. I have them in my TT with a Ruckstell & Warford - I have so many gears, I confuse myself !

[tom_strickling]

There is a TT high speed rear listed in the classifieds Good price

[Hal]

Embrace that low speed rear end! Own it!

I thought that same way when i first got mine, but I wouldn't change it for the world now. I put a triangle on the back and I drive mine to breakfast on Saturdays and around town on occasion. I live 2-3 miles outside of town, but the highway into town is lightly traveled on weekend mornings. Yeah, there's that chance of being rear ended, but I don't remember even having a close call. As for other drivers being held up behind me, it goes so slow, they can readily get around. I seldom ever have to pull over. I have to pull over more often in my Model A doing 45, than I do in my TT doing 22-24. The Model A is fast enough they can't easily just go around, but slow enough they want to real bad.

[Tom Hicks]

I have one TT with 7:1, it has a maximum speed of 15 mph.

I have another with a 5:1 rear and Ruckstell. It will easily go 25 mph. With the 5:1 it needs the Ruckstell on hills.

If you have a Ruckstell, I strongly recommend auxiliary brakes.

I love both my TT's, and I drive them according to their capabilities. That means lots of LED lighting and lots of driving between midnight and 5:00 a.m.! Or anytime Sundays. If there is a bike lane I can crowd into it and drivers can pass me easily.

[Hal]

Engine speed in a 15 MPH TT with a 7.25:1 rear end is the same as doing 28 MPH in a stock T. Both are at 1150 rpm. If you are willing to do 1800 rpm, the TT will do 24 mph, same a stock T doing 44.

[Tom Hicks]

Engine speed in a 15 MPH TT with a 7.25:1 rear end is the same as doing 28 MPH in a stock T. Both are at 1150 rpm. If you are willing to do 1800 rpm, the TT will do 24 mph, same a stock T doing 44.

Yes, but... Ford recommended a top speed of 17mph with the 7:1 rear. The driveshaft is relatively long. I suspect mine is not well balanced. The vibration over 15 mph is terrible, I think caused by "driveshaft whip". Mine has a top speed of 15 mph. I have heard that a "carrier bushing" can be put in the torque tube to control driveshaft whip, and higher speeds can be attained that way.

[Hal]

Tom,

Mine will do the same, but it is only for a very narrow frequency range. It will vibrate about that speed, but I just accelerate through it. It goes away after another couple of MPH. It only does it for a second or two as I pass that speed. After that, it smooths right out.

[tom_strickling]

"""If you have a Ruckstell, I strongly recommend auxiliary brakes."""

Why? A Ruckstel does not make you go faster, it is an underdrive isn't it?

[Tom Hicks]

"""If you have a Ruckstell, I strongly recommend auxiliary brakes."""

Why? A Ruckstel does not make you go faster, it is an underdrive isn't it?

Yes, the Ruckstell is an underdrive and straight drive, it does not give an increase in top speed. But, although it is not supposed to have a neutral, I can put either of mine in neutral.

If your Ruckstell gets stuck in neutral the transmission brake is useless.

[Tom Hicks]

Tom,

Mine will do the same, but it is only for a very narrow frequency range. It will vibrate about that speed, but I just accelerate through it. It goes away after another couple of MPH. It only does it for a second or two as I pass that speed. After that, it smooths right out.

Mine starts vibrating at 17 mph according to GPS, and gets worse as I increase speed up to 20 mph. I am scared to push it any harder due to the vibration, I just keep her 15 and under.

[Burger in Spokane]

Got my TT with an unbalanced/original engine/trans, 7:1 "farm" gears, and Ruckstell.
Would begin shaking badly above 19, smoothed out at about 22, and maxed out a little
under 30, but it was never smooth above 19, even if it was worst in that 19-22 range.

Carefully rebuilt/balanced the engine with the express purpose of eliminating vibration
as a speed limiting factor in the quest for increased speed, leaving a cleaner slate to focus
on performance enhancing measures.

5:1 "express" gears were added during the rebuild. It now cruises comfortably at 35,
can easily do 40, and the engine just simply winds out at 48 on flat ground. Vibration
is limited to the driveshaft and really isn't much of a problem. Engine RPM's are just too
high for comfort and there just isn't any more "poop" to give.

I plan to rebuild a Lincoln over/underdrive, but am stalled there, as wheels were getting
sketchy and that is my current focus. Folding a wheel over at higher speed just seems like
a bad idea and poor care of all previous investment. The math suggests 50 should be a
comfortable cruising speed, with perhaps 60+ top end ? Brakes are already an issue with
T's at stock speeds. Anyone considering speed building a T/TT for in traffic driving really
must take braking into consideration as part of the speed build.