Chevy & GMC Vans

There seems to be a consensus that the 136 cannot be converted to manual engage in and out transfer case. As I see it this shouldn't be a huge problem as the motor simply actuates an internal cam that operates an arm that applies pressure to a thrust bearing that engages the clutch pack. There should be any number of ways to operate this cam. An arm with a cable attached, a vacuum diaphragm, a cylinder operating on power steering pump pressure, a worm drive servo actuator, etc. Of course it's a simple matter to build a pulse width modulator circuit......... or you can buy one: http://www.eachbuyer.com/pulse-width-mo ... fgodTnEAEg Here's one for $11 capable of 20 amps, complete with a rheostat to control pulse width.

What is clear is that this system was not meant for long term engagement, or it would have a drive system that didn't require power to stay engaged. It's intended to go in and out rapidly as it senses wheel slip, so the motor would probably overheat and fail if you tried to apply it steadily. What is also questionable is weather the actuator arm and bearing assembly would stand up under long term engagement. The bearing is obviously designed for a thrust load, so it should stand up fairly well. How many pounds of force is necessary to apply good front assist? I suspect that in most instances during highway driving, it isn't much. The computer obviously has algorithms that help it decide how much power to apply under various circumstances, and it's probably very good at it under "typical" operation. I doubt that you and I could do better, but there are times when it makes sense to just lock the damn thing in.

It's very unfortunate that they didn't make the front drive primary.............

Howard

Interesting you should bring this up as I have been wondering the same thing in regard to the 236. That would be ideal: manually selectable low, high and AWD. I would just dump the actuator motor and put in a manual shift. I was wondering if the clutch pack would hold up to continuous use?

The 236 encoder motor has a brake that needs to be energized to release the motor shaft. I have read that the brake cannot be energized for very long. Normally it is energized long enough for the motor to make an adjustment, then is de-energized to lock the shaft. That is how it locks itself into 4WD.

I think both the 136 and the 236 can handle the clutch fork locked in forever. You just have to have the right type of motor setup and circuit to get you there.

If you could find a way to fit the 236 motor on the 136, then design a circuit that would operate the brake and motor with your manual switch.

To switch to 4WD, the circuit would energize the brake(release) then energize the motor to turn the shaft fully counter clockwise, then de-energize the brake(lock) just before you de-energize the motor. To switch back to 2WD the circuit could just energize the brake and the fork should spring back to its normal position.

All this in ms(milliseconds). It takes around 72ms for the motor to fully engage the TC and around 50ms for it to fully disengage the TC. I would base the timing around those times. At this point you are making a simple TCCM.

Or you could make up a manual linkage on the 136: viewtopic.php?f=58&t=8913

That's what I was wondering; would it be feasible to manually shift the 236. This could be a great setup for those that want AWD and low range but don't want to deal with a TCCM and a flash of the PCM.