Air shift for Warn Overdrive

So I built a 51 3A a couple of years ago with 4.88 gears in it. It's a really fun Jeep to run around in, but really needed an overdrive. We put a SM420 4 speed trans behind a 151 4 cylinder with a model 18 tc. The floor cover over the new trans came out really nice and the owner didn't want to cut it up to put in a od shifter. So he says "Why not just shift it with air, it would be just like an old two speed rear-end." This is the part that I use my line "If you have the money, I have the time." We bought an ARB compressor and made a small reservoir that tucked up nicely under the back. I then made a bracket to hold the cylinder. I was able to find a really nice stainless cylinder with a 1" stroke that bottoms the cylinder instead of putting to much pressure on the shift fork. Throw in a small regulator and a 12v solenoid directional block and put it all together with a small push pull switch on the shifter. It turned out really nice and makes it much easier to shift without having to go between shift levers. So the shifter ended up costing him more then the OD, but the customer is always right as long as the bill gets paid.

 

I like it. Used to work for a fertilizer/chemical company years ago and drove an International tank truck every day that had the 2 speed axle with the push/pull switch on the shifter. Got pretty proficient at split shifting through all the gears. Got me to thinking about doing the same thing on my '57' with 538 gears and overdrive.

 

Looks like an interesting idea. The only reservation I would have is slamming the shift fork into the synchro with the air cylinder, might be hard on the synchro ring. Don't get me wrong, I like the engineering you did on this.

When I shift mine I usually slack throttle, slip it out of engagement, rev up or down as needed, then clutch and slip it into engagement. If I just clutch and jam the shifter, I invariably hear a 'crunch' as the OD synchro can't quite slow down/speed up the whole transmission rotating assembly enough. This is a fresh Herm rebuilt unit, and I don't want to abuse it. It does help if the transmission is in neutral, as then there is only the back half of the transmission for the OD synchro to speed up/slow down.

Don

 

I'm with butler, cool idea, but I'd be carefully slamming it into gear with an air ram if everything isn't lined up. That air ram can't feel it pop it gear like you can with a shifter.

 

The speed of shifting was the reservation that I had also. Running the air at about 25 lbs. and this thing shifts really nice. It's seems that the quick shift might actually be letting the gears mesh faster as there is less time to "grind" as you go with the manual shift. You do have to clutch it before shifting and the pause is about the same as a normal trans shift. You do not shift this like a rear-end, as you have to shift after the clutch is engaged. Time will tell about the life of the od. That's one nice thing about it being on a customer's rig is that I make more money replacing it if it does blow up.

 

That's all well and good, unless your customer, or customer base is reading this.......

 

So what's the worst that happens, you wear out the synchro or bend the shift fork? Sounds like the owner has the money to play so why not. Did you use a truck switch on the shifter? I had a T18 with an over-drive and having to shift both the trans and OD at the same time was just a pain. Really cool idea and nice execution.

 

You can buy mufflers/ "chokes" that install on the exhaust side of the control valve that will slow down the speed of operation. Allowing for more time for the syncros to line up

http://www.grainger.com/Grainger/SPEEDAIRE-Speed-Control-Muffler-1EJU5?Pid=search

 

I went both ways while setting it up. With an adjustable muffler on it seemed to slow the shift too much. So I am just running less pressure and it is working very well. The most important, and hardest part, is making sure that you pause with the clutch depressed before shifting it to allow for the rotating assembly to match speeds. It is easy to think of it as a browny rear axle and want to shift too soon.