Twin-High TT Transmission

[BUSHMIKE]

I just bought another TT project which comes with this Twin-High Hi-Lo rear mounted transmission. I am anxious to take delivery to examine it closely in person. In all the forum archives, there are only a few posts about this transmission. I am wondering if any new info has surfaced or if anyone has any experience with these units.

[BUSHMIKE]

I found this in another thread.

[mtntee20]

Mike,

I have never seen a drive line/axle Twin High transmission. I have two engine mount Twin High transmissions. From what I have seen and have been told, the Twin High transmissions are built like a tank. It appears they were designed and built by aircraft engineers. The biggest problem seems to be the bearings. If you need to replace them, they are very expensive and may be hard to find. Otherwise, with proper lubrication and regular maintenance they will last forever.

I'm looking forward to your reports on what it looks like when you get your hands on it.

Good Luck,
Terry

[Dallas Landers]

Thats interesting.

[26modeltt]

I have a Twin-High Hi-Lo in my '26 TT and thoroughly enjoy the operation and performance of this transmission. The Twin-High Hi-Lo transmission allows my TT to stay up with T's on road tours. The engineered design of the rear axle mounting of the Twin-High Hi-Lo transmission allows the Ford drive line to operate at its designed speed. Auxiliary transmissions that mount to the Ford transmission increase the drive shaft speed (rpm's). The TT drive shaft is quite stout/heavy, as a result, if there is an imbalance or bend in the driveshaft, this will result in pronounced driveline vibration. Further, you can "shift on the fly" easily and the weight of the Twin-High Hi-Lo is placed on the rear axle assembly.

[BUSHMIKE]

Thanx guys! Im excited to get it and take a peek inside. I sure like what I am hearing!

[JTT3]

I have very little experience with TT’s on a personal level but have helped in rebuilding the rear axle with & without a ruckstell. Those rebuilds both had the high speed gears. So the question I have is as you increase the speed to the worm gear how much extra pressure & wear is put on the bronze gear? Those high speed gears are getting to be unobtainium.
What type speeds to you achieve? Thanks.

[BUSHMIKE]

In an unloaded condition, which is where you would likely be in high-high, I would think the gear loading would be minute as opposed to fully loaded in low-low, where common sense says a much gear strains would be expected. My expectation is a very comfortable 20-25mph on graded Forest Service roads. Knowing the limitations of safe braking, I have no interest in higher speeds….even on asphalt.

[Dallas Landers]

John, my TT has high speed gears and a Chicago 3 speed. Rebuilt engine with cast pistons " stock" as it can be. I had mine up to 42 on the flat just to see where it could run. Phone booth style wood cab and 9ft heavy wood grain bed and two people. Its much happier at 25 mph and 15 to 20 people going for icecream.

[Dallas Landers]

John, my TT has high speed gears and a Chicago 3 speed. Rebuilt engine with cast pistons " stock" as it can be. I had mine up to 42 on the flat just to see where it could run. Phone booth style wood cab and 9ft heavy wood grain bed and two people. Its much happier at 25 mph and 15 to 20 people going for icecream.

[JTT3]

Thanks guys very interesting. Dallas I’ve heard nothing but good things about the Chicago auxiliary transmission with the exception of it being heavy. When I attended the hundred year anniversary in Richmond, there was a cream color TT with a flat bed, I believe the owner was Mr. Cordes from Texas and they drove it from there to Richmond, Indiana.! What I was told it ran at speeds in the 50’s. I do know it had multiple auxiliary transmissions & I think one that was butted up to the rear axle. I found all that info to be fascinating but did not hear it from the actual owner. Now I may be lying about this next part but I think it also had ac in the cab which ran off a very small compressor. The engine was a model T engine but I never found time to get back to talk with the owner because my youngest daughter was about to go flying in a Curtis Wright biplane that was part of the event we were at. Thanks again I’ll be following this thread with continued interest. Best John

[Dallas Landers]

If I get really brave, I have a Rocky Mountian 6 speed that goes on the rear axle much like Mikes Twin High-lo. It came with the chassis and Dave Stroud had planned on installing it when he had the chassis. I need to install the Rocky Mtn rear brakes before that.

[BUSHMIKE]

John,
Thank you for the info and pic! Ive had an ember glowing about building a tractor/trailer rig for a while now. Your pic just fanned that fire. This pic has been my inspiration.

[Dallas Landers]

Well now you have another chassis ? I see a big rig in your future.

[BUSHMIKE]

Off topic a bit. Here is a pic of my Grandfathers 1937 Chevy. He bought it new and sent it to Fisher Body to have a sleeper cab built. It is rumored to be the first sleeper in the state of Michigan. Gramps was hauling potato's from Belding Michigan to Louisville, Kentucky. He and another driver would tag-team continuous runs. The truck disappeared sometime in the 50’s in Belding. Being a Yooper, cool part to me is this rig probably spent a lot of time up in the Keweenaw Copper Country hauling spuds downstate. If I do build a rig, it would have Gramps logo on the doors.

[JTT3]

Dallas, bingo that’s what he had at the rear axle, Rocky Mountain 6 speed I remember that the logo was cast into the case. Before then I had no idea that the company made anything else other that auxiliary brakes, I’m not sure what was off the forth main area but do recall it had a combination of gear selections north of 15 or so. That may be wrong though.

[BUSHMIKE]

Well, I am now in a very small subset of TT owners…..that being TWIN-HIGH HI-LO TT twins! I found another Unicorn. I just purchased another TT truck that to my astonishment sports yet another TWIN-HIGH HI-LO transmission. The truck appears to be a time capsule. Ill know in a couple of weeks when I pick it up. Im so excited that I can hardly stand myself.

[Scott_Conger]

Mike

I think this now confers "expert" moniker to you

congratulations and have fun

[Dallas Landers]

Would that be a Twin Twin hi hi lo lo ?

[BUSHMIKE]

I pulled the cover off the Time Machines’s Twin-High shift detent and got a nice surprise, clean, no rust and sharp teeth faces! It looks to be in excellent internal condition and, I hope, low use. Yee-haw!

[BUSHMIKE]

Over a foot of new snow and as much still forecast for today and tonite. A good day to work in the shop.

Ive now been on many short drives tying to figure out the shift pattern for the Twin-High. Repeated frustration finally made me tackle it in the garage. Figuring out the shift pattern sounds like a really easy thing to do….right? High and low, how hard can that be? Well when detent positions are so far off that they allowed cross- shifting, it was not something I wanted to experiment with. I jacked up a rear tire and pulled the plugs on the engine to start recording tire vs. crank revolutions in an attempt to start somewhere. Since I am alone, everything had to be done with the TT in std. high. With nearly two hours of frustration getting nowhere and a sore crank arm, it finally dawned on me that it could NEVER have worked as intended in the current configuration. The adjustment yokes on the shift rods are there for a reason……duh! I adjusted both yokes to put the heavily loaded spring detents in the proper locations for the neutral lockout on the shift gate to be functional. Resolution was fairly quick after this. I had wrongly made the assumption that it must have worked as is. I have attached a sketch showing the intended shift pattern if it helps anyone out. I am very anxious to get out on some dry level roads and test everything out.

[BUSHMIKE]

To clarify….with the yokes not adjusted correctly, the shift gate allowed this configuration and is what led to my confusion and reluctance to “trust” any setting.

[26modeltt]

Mike,

Your first sketch is correct, which the exception the N is DIRECT DRIVE (NOT NEUTRAL,UNDER or OVERDRIVE).

Good luck,

Jack

[BUSHMIKE]

Jack,
Do you have a TT with Twin-High Hi-Lo? If so, I have some questions.

[26modeltt]

Mike,

Yes I do.

Jack

[BUSHMIKE]

Jack,
Do you know if the detent springs on the Hi-Lo are original? All (4) of my springs appear identical on both my transmissions. The compression springs seem excessive to me in regard to their intended purpose. At the height of its travel and just before the detent snaps down, the spring is very nearly solid height. This is bad spring design and drastically shortens their life(30 year diemaker speaking here). Does your Hi-Lo shift easily? Its a bit of a push or pull to activate mine….more than I feel should be normal. I could understand the excessive pressure if it were helping to hold a helical pitch gear in place under load, but its not. I believe the internal gears and associated splines are all straight cut as I see no indication of anything rotating during the shift.

[26modeltt]

Mike,

I believe the Twin-High Hi-Lo shifts correct for that period --- with that said, when shifting from Under to Direct it shifts a tad harder. I have over 13,000 miles on my TT since restoration. I've disassembled and reassembled the transmission and saw no abnormalities.

Next few days, I'll take photos of transmission with the top cover removed and send to you, so you can see the fork and springs.

Jack