cruiser54

I know how that works. I had to rebuild that stuff. An air operated valve, triggered by the trans shifter position whether in Forward or Reverse, flipped a sprag clutch so that if there was a difference of about 100 RPM between the front and rear driveshafts, would engage the driveshaft to the front axle.

DFlintstone

Aw, just S-can that air stuff and lock it in full time. Then it will work when you need it!

Just bs'n there Cruiser. Sounds like neat stuff. I just saw the sliding trailer toung hooked up to a hydraulic brake "master" for the first time this spring. Neat setup that, that applies the brakes to the trailer when it pushes the towing vehicle. With more time and energy, I'd like to fab one!

cruiser54

Airstream? I worked on one of those once. Looks like a Ford master cylinder.

1976gmc20

Well, at least on the little 2.5 ton, there is an air flip switch under the dash like some semis use for parking brakes, to engage the front axle. But I have no idea how that works mechanically. I just assumed that it engaged something in the transfer case, and it was either locked in solid or not like a typical part time 4wd.


I honestly don't remember right now how the 5 ton front axle engagement works, whether it's a lever or an air control. I have driven it a lot but of course not much during the winter. Time for a spring refresher training, I guess Anyway I almost never use the "4wd" because the eight wheels on the back are usually enough.


Both trucks are made by AMC General, which used to be owned by Jeep


DFlintstone, none of those big truck have front lock-out hubs. Everything up front is turning all the time when driving, just not under power unless front axle is engaged.

cruiser54

On the 5 t0n, listen for an air solenoid switching when you shift from 1st to Reverse.

1976gmc20

The 5-ton is an Allison automatic


The little 6x6 is a five speed with the weird shift pattern (4th and 5th are reversed from the usual places):


R 2 5
1 3 4

cruiser54

And the 5 ton is full time AWD.

1976gmc20

I will have to look at this at training this week

cruiser54

If it happens to have a CAD by chance, use some of this on it.

DFlintstone

Yep, it did indeed look like the pre 67 Ford single cylinder master. Waz on a much newer car carrier trailer though.

What a slick idea there, using the trailers own push, to apply it's own brakes! (I wanna make one!)

DFlintstone

OK, much thanks for clarifying that! It seems that somehow I have three Transfer cases installed backwards, with the chain driving only the front axle! Do you have a writeup on how I go about turning them around ? Fyi, the two with a disco are fine, it's just the 242 (with no disco) (which the PO had replaced) that is a problem.

cruiser54

Yeah you do have them in wrong!!

My mistake. I was thinking chain turning, not driving.

Then, according to your logical deduction based on your vast experience with ownership of both transfer cases, ALL 242s are bad and suffer early failure due to the front axle not being disco...

Same with every 231 from 91 on I would assume. Excellent study using tons of good data.....

1976gmc20

Surge brakes work great going forward, assuming you have enough brakes on your tow vehicle to activate them.

Not so good if you have to back down a steep hill ...




Edit: I'm going to look at the VFD 5-ton this evening; will report back on the front axle system. I'm pretty sure that there is a separate control for engaging the front axle but I can't say for sure since I am somewhat confused between the two trucks (5t vs 2.5t).

1976gmc20

Okay, the 5 ton 6x6 has an air switch on the dash to engage the front axle, so it's not full time "4wd".


Low/hi range is an up/down lever between the seats. Basically it's just like the M35.

cruiser54

Hmmmm. So they went BACK to basics, eh?

Got rid of a troublesome system, eh?

Why do I hear bells ringing?