Inliners International Forums General Discussion Drive Train Truckstell Overdrive Unit

Greetings . . .

I think it was integrated_ I_78 that asked for some more info and pics about the Truckstell overdrive unit.

Truckstell was a Cleveland based company that supplied rear ends to OEMs in the big truck business. They also made a dual axle conversion for big Fords (the so called twin screw):
Ford Trucks Site posting
that was capable of over and under driving. So they were no stranger when it came to power transmission and/or gear sets. Ford Trucks so equipped included a fender call out: “Truckstell Conversion”.

Their well-built overdrive units were created after WWII:

and were marketed as a dealer installed add on. I have no idea how much they cost back in the day:

There were two models – the 101 was for 46-48 (but I have read that these have been retrofitted to older cars too) – the 103 was for 49 and up (until the enclosed driveline became obsolete). The difference between the two models is twofold:
1) The 103 has a much longer snout to position the OD unit further back from the ball housing. This places the unit directly between two floor braces under the front seat. The floor has to be cut and a raised panel was supplied by Truckstell to close the hole. It was not removed from the donor car so I had to fabricate a hump to provide an additional 2 ¼” of clearance.
2) The under dash linkage on the 101 is a bit of complicated contraption compared to the more straight forward 103 linkage.
Both of the linkages have a mechanical interaction with the stick shift lever. Engagement of “overdrive range” is via under dash pull knob:

that is located between the steering wheel and the heater controls. From what I have read the internal design of the unit’s semiautomatic engagement sprague-clutch creates and added feature of hill-holding. But at the same time this design means that the unit must NEVER be engaged when the transmission is reversed. So the linkage is designed with a detent in the shaft to hold the knob in the overdrive range (when pulled by the driver) against a return spring mounted on the other end of the cable on the OD unit. When shifting the car into reverse a trip lever raises the detent off the shaft allowing the return spring to pull the unit out of OD. So even if the driver forgets to disengage the OD before reversing – the automatic defeat will do it for them:

This is a bit of an eye chart in the bulletin board – so I suggest that you right-click on the photo and choose View Image – this will render it full size. In terms of the so called tip-toe cable I intend to attach it just to the clutch (but not the accelerator). This cable causes the unit to remain in over-drive range but to step down into 1:1 ratio when the driver engages the clutch or floors the accelerator. OD ratio is re-engaged by backing off the accelerator and allowing the cars to inertia to act against the driveline. This causes the sprauge-clutch and something called a tangent spring to engage OD. Hence the so called semi-automatic operation of these units.

I bought this 103 from a guy who was toying with the idea of trying to fit it to a shoe-box Ford. I guess the differences in the splines, placement of the unit and getting the linkages adapted to the Ford proved to much. The unit came to me well packed but quite greasy and grimy. POR15 Marine Clean made quick work of the grunge:

The only issue I found (while flushing the inside with acetone) was a leaking rear seal:

A few measurements with a micrometer and a specification based search yielded a National that fit the bill. Instead of trying to dig out the old seal I just installed the new one over the top. After flushing I stuck the unit in the sun for an hour to evaporate all the fumes. Then sealed it with POR15 and top coated in red. All in all I think that it cleaned up nicely.

Before putting it back in storage I filled it up with Shaeffer’s:

there was no evidence of leakage when I recovered it in the fall for installation on the car.

Bench testing suggests that it is ready to go. But I won’t really know until the car is on the road with the OD engaged. Hopefully I won’t find it in need of repair as parts are as rare as the units themselves.

Regards,
stock49

There is at least one more thread here and thanks to Rich one came up in a search here. Sadly some of the links no longer work. A Truckstell google search brought up a lot. I think I read somewhere that the business or at least someone who repaired then ended up in Washington or Oregon. Somewhere I have a copy of a manual.

Thanks a lot Stock 49. I was completely unaware something like this even existed. When you get the car on the road the way it will work is it goes back to 1:1 when you push the clutch in and shift from say first to second. Then let off the gas pedal and it shifts back to O.D. Is third correct? Jay

Exactly. And one can also downshift from OD to 1:1 by tapping the clutch pedal (in any gear).

Thanks for explaining it to me. Seeing this makes me want a three speed with an overdrive, in a newer car like a 1964 model with the factory set up. Jay

When I get my roadster running and my inline credentials are safe I'm thinking of replacing the 270/T5 in my pickup with a 331 Cad and a T85 OD. 3 on the tree.

Beater, you might know the answer to this. What 3 speeds were offered by GM with overdrive? We're Saginaw 3 speeds ever used? How about so called "j boxes"? I am talking about cars in the 58-67 year range. Thanks Jay

There were Saginaw 3 speed ODs. Late 60s early 70s I think. That Saginaw used the some case as the 4 speed. They are great units but hard to find now and usually expensive. The 3 speed ODs before that are OK but not synchro into first when down shifting. All the OD units are BW 10 or 11 models. Mostly 10.

Greetings . . . given recent mention of the Truckstell overdrive units I thought I would bump this old thread and provide some updates.

I am several months into testing with the unit installed on my '49 and I must say that the driving experience is nothing like I expected. The Truckstell literature's characterization of it being Tip-Toe-Matic is telling.

In an attempt to monitor what is actually taking place when the OD is engaged I have installed a second speedo:


The main speedo is attached to the transmission. The Stewart Warner 'bike style' gauge is attached the Truckstell unit.

When the primary Truckstell engagement rod is pushed forward the unit disappears with both input and output spinning 1:1. If one accelerates in 1st gear and lifts off the throttle - one immediately applies engine braking with concomitant nose dive. The same happens in 2nd and 3rd gear.

But when the Truckstell engagement rod is pulled and locked into so called "overdrive range" the behavior in all forward gears changes dramatically.

If one accelerates from a light in 1st and then lifts off the throttle there is no engine braking - no nose dive. Instead the RPM on the Tach drops off quickly and the main speedo (attached to the gear box) follows: dropping off as if the car is slowing. But the auxiliary speedo (attached to the OD) remains firm reading true rolling speed.

If one floors the accelerator (after a lift throttle drop off) the behavior is equally surprising. The tach jumps (as if the transmission/clutch is slipping) meanwhile the main speedo seems to glide upward to eventually match the auxiliary speedo reading.

In 2nd and 3rd gear the effect of the Truckstell's so called sprag-clutch is less pronounced. But the behavior is identical. Any lifting off throttle will cause the OD to engage. But re-applying the throttle causes the OD clutch to enforce the OD ratio less and less - as in approaching a hill in 3rd OD. The further the gas pedal is pressed the higher the RPM climbs and the main speedo slowly climbs to match the auxiliary speedo. There is no need to downshift. It is as if the OD just fades away on a grade.

The Truckstell unit also includes a secondary linkage that is attached to the clutch fork:

When the clutch pedal is pushed the OD immediately 'ducks' allowing engine breaking in whatever gear is selected.

Very interesting piece of engineering. And before I forget - it's a hill holder too!

Not at all what I was expecting from an overdrive.

regards,
stock49

Thanks for posting this. You are the only one I've ever heard describe how these actually feel while driving. Much of it sounds very similar to the Borg/Warner ODs. I have never seen anyone use two speedos before but that is interesting to show what is happening before and after the OD.
Does it have a solenoid and governor system like the BW? It sounds like the "kick down" is more progressive than the BW which just takes the car out of OD when the accelerator in floored and back in when you let up. Studebakers had a hill holder that was a ball seal unit connected to the brake master cylinder and the clutch linkage.
When I looked under the pickup here with the Truckstell it looked to have several connections through linkage. This is cool old tech stuff.

Hi Beater . . . there is nothing electrical on a Truckstell - no solenoid. And I hear you on the 'kick-down' concept from the BW units. It is what I was expecting from the Truckstell.

But the functioning is completely different. The Truckstell concept of being in "over-drive range" means that the planetary gear-set CAN affect Input versus Output shaft speed. But it doesn't behave in a way that is as if it is "in" or "out".

The unit I have was purported to be in good running condition (by the previous owner) - so I did not tear it down. This is in keeping with the old car guys adage "don't fix what ain't broke." Especially on something with few or no repair parts available!

In studying the various diagrams and threads on these Truckstell units it appears that they are both mechanical (planetary gears) providing an over-drive ratio and hydro-static (fluid pump and clutch) providing smooth transition between 1:1 and over-drive.

And this makes the whole 'kick down' concept something other than an on/off proposition - hence the Tip-Toe-Matic marketing.

So let's review to be clear. When the main OD engagement knob is pushed toward the firewall:

the OD is invisible - as if it was not installed.

When this same engagement knob is pulled toward the driver and locked on its detent the OD is now in the so called "over-drive range". This is the Tip-Toe-Matic place I am attempting to describe here.

When the unit is in "overdrive range" it is as if the unit has a mind of it's own. The car seems to coast along and the RPM on the tach drops off with lift throttle. Conversely, adding throttle is sort of a lazy affair - especially in 2nd and 3rd gear. But as the throttle (alone) is advanced - there is no perceptible down shift. It is as if the OD ratio just fades away with the engine just climbing back up onto the ratio selected in the gear box.

But there is a true kick down:

though it doesn't feel like an automatic transmission downshift. This is because it is controlled by separate OD 'defeat' cable attached to the clutch throw-out fork.

When this defeat cable is pulled the OD immediately returns to 1:1 on the input/output shafts allowing direct gear engine breaking or acceleration. BTW when the kick down linkage is fully in installed to Truckstell specs - it is attached to both the clutch fork and to the accelerator pedal - allowing either a clutch pedal action or WOT to cause the OD to step down.

I have yet to bother with adding the accelerator linkage to the mix.

As for the hill-holding feature it appears to be part-and-parcel with the unit's design. When in "over-drive range" the sprag-clutch interface with the planetary gear-set prevents reverse rotation. But this comes with a big caveat. The transmission can never be reversed when the Trucksell is in "over-drive range". To do so will ruin the innards.

The stock linkage includes an over-drive dis-engagement tab that attaches to the gear-shift rod. I have yet to fit this particular feature since it appears that my Heater Controls are installed to close to the steering column. Both Heater Control and the Truckstell engagement knob need to move to the left before this auto-disengage-on-reverse-gear-select can be fitted.

regards,
stock49

The "Tip-Toe Matic" name makes me wonder if once in motion the trans cane shifted without using the clutch like the MOPAR "Fluid Drive" transmissions.

The BW (at least later ones) had a reverse kick out to override the overdrive when the trans was put into reverse. The planatary gears do not like being turned backwards. I've thought some of making a stand alone unit from one of these by machining a front cover and a yoke.

The Truckstell seems to be a much more mechanical unit with several more linkages than the BW which only has one main engagement cable and a few wires. The hydro part is interesting. When I looked at the one mentioned before looked very comlitcated but I didn't have time to really think it out. I'd hate to get one without all the pieces and I'd want a lot of pictures. That it fitted into the torque tube is really cool.
I agree with not fixing stuff that works. Sometimes it is hard not to look inside something just to "check it out". I find it too easy to keep looking until I'm left with a basket case that worked until I got.

There is a great thread over at Chevy Talk that reveals the Truckstell internals in detail:
chevytalk.org circa '17

The thread's author managed to get a basket-case back on the road with no expert input. He even had to fabricate some broken parts from scratch.

He's a better man than I am!