In the forums a question keeps appearing asking about the feasibility of swapping a later model transmission into an older truck. While it is possible, it sure isn’t practical. EVERYTHING is possible given enough time and money.
If you have the time and money I can put ANY engine and transmission in ANY truck. I get to set the price and schedule, though. Oh, yeah, I don’t offer any warranty!
In the old days, before computer controls, if the trans would bolt to the engine it would work. If it wouldn’t bolt to the engine it wasn’t very hard to buy or make an adapter so that it would bolt up. While computers have made vehicles MUCH better (I’ll save the why that’s true for another article) it has made swapping engines and transmissions much, much harder.
Transmissions are now shifted by computer. The 5R110 wouldn’t be possible without computer controls. The shifting is too complicated for hydraulic controls.
The 4R100 is an all non-synchronous design. This means that for each upshift all that happens is a clutch is applied. All you need to do is control the pressure to the oncoming clutch and you’re all set.
The TorqShift is MUCH more complicated. The 1-2 and 5-6 shifts are the same as the 4R100, they are non-synchronous and all you need to do is control the pressure of the OD clutch. The other shifts are the problem.
The 2-3 is a swap shift. This is a special category of difficult shift. I believe Ford was the last trans maker in the world to produce a swap shift transmission. Others have put swap shift transmissions in production and then replaced them within a few years.
To make a swap shift the TorqShift needs to release the OD clutch to downshift the OD gearset while applying the intermediate clutch to upshift the Simpson planetary gearset. This is an upshift and a downshift occurring at the same time in the same trans.
From my experience these two shifts MUST complete within 30 milliseconds of each other or it’s going to feel awful. If the OD releases too soon the engine speed will flare. The amount of flare is dependent on how much sooner it completes. If it completes before the intermediate has enough capacity the trans goes back to first gear! Then it has to make a 1-3 shift.
A few WOT 1-3 shifts means the trans comes out to replace the intermediate clutch. Been there, done that. If the OD releases after the intermediate comes on you end up in 4th gear (1.09:1 ratio) then downshift back to third gear (1.54:1 ratio.) Either way it’s really bad.
Now if you made it through that you need to make a 3-5 shift. 4th gear is the 1.09:1 ratio that is only used in special circumstances. The 3-5 is a synchronous shift. It’s timing requirements are about the same as the swap shift, but there is no downshift. To make the shift the intermediate clutch has to release while the direct clutch applies.
If the intermediate releases too soon you get an engine speed flare. If the intermediate releases too late you get a tie up. A tie up is when all three pieces of the planetary gear set are held from turning. This means the output shaft of the trans STOPS. That’s not a pleasant thing to have happen when you have the go pedal on the floor making a 3-5 shift. You can lock the wheels on an upshift! I’ve done this, too. You can also break expen$ive parts doing a tie up. Been there, done that, too.
Now start thinking of the combination shifts that can happen. How about cruising at 55 mph behind some slow poke on a two lane road? A passing zone opens and you floor it. Now you may want to go from 6th to 3rd gear. You need to release both the overdrive and direct clutches and apply the intermediate. That’s a synchronous shift in reverse.
As you can see from just these few examples it isn’t a trivial task to make one of these transmissions shift. It’s what I did at Ford for quite a few years, three of them working on the TorqShift. I’d be really surprised if anyone makes a controller for the TorqShift that works really well. I think someone could make one that does some basic shifting, but getting one so that it shifts at least as well as a stock trans is going to be a HUGE task.
