M38A1CDN2 Questions

[Mike Baker]

Two questions from a Sunday of tinkering with the truck:

1) How does one pull a rear axle shaft without the tool called for in the manual?

and 2) Can someone confirm that the master cylinder being vented into the air filter only matters if you want to ford the vehicle (and hence that it doesn't matter if I don't reconnect that vent when I change the master cyclinder out)?

Thanks in advance!

Mike

[rob love]

I'm pretty sure we talked about axle shaft removal in just the past few weeks. Unbolt the backing plates and the brake line, and remove the whole assembly as a unit.

The brake master cylinder question is a good one. You cannot simply block off that line and get away with it. The vent allows for contraction and expansion of the cylinder fluid. If you were to block the vent all together, as the cylinder heats up the brakes will either drag or lock on. Nor can you leave that big gaping hole there either, as it will allow water and dirt to enter the master cylinder. There must be some form of venting to the reservoir.

You can replace the cap with the civilian version that comes with a new master cylinder.

I remember a guy who filled a master cylinder from the vent line at the air cleaner. This is also a mistake, as you must leave some room in the master cylinder for expansion. Never fill the cylinder right to the top.

[Mike Baker]

Originally Posted by rob love

I'm pretty sure we talked about axle shaft removal in just the past few weeks. Unbolt the backing plates and the brake line, and remove the whole assembly as a unit.

Indeed we did, but more in the context of getting hubs off. After reading that thread I went ahead and bought an OTC hub puller, and removed the hubs that way. Then I did as you said in the other post, and removed the line to the brake cylinder, all of the brake bits, the backing plate, the outer (dust) seal, another plate and a shim. Now what I am left with is the axle shaft itself sticking out, with the bearings visible around the edges. I pulled on the shaft a little bit, but it didn't want to move and I didn't want to really reef on it until I had consulted the brain trust here.

Originally Posted by rob love

The brake master cylinder question is a good one. You cannot simply block off that line and get away with it. The vent allows for contraction and expansion of the cylinder fluid. If you were to block the vent all together, as the cylinder heats up the brakes will either drag or lock on. Nor can you leave that big gaping hole there either, as it will allow water and dirt to enter the master cylinder. There must be some form of venting to the reservoir.

You can replace the cap with the civilian version that comes with a new master cylinder.

I think I ended up with a new civilian one, as it has only a very small vent hole in the cap. I think I will try to put the old cap on the new cylinder, as there doesn't appear to be anything wrong with the cap itself.

Thanks!

Mike

[rob love]

OK, understood.

The bearing race is in there as a bit of a snug fit. Hook a slide hammer to the axle somehow and the axle will come out with a few taps. You could reinstall the hub to the axle (reasonably tight), put your OTC puller back on without the center screw, and hook a slide hammer to the center of your puller.

My money says you will need new bearings as they have not likely been serviced in close to 35 years.

The caps between the civilian cylinders and the military cylinders are normally the same threads. I take it you are going to re-install the vent line?

Something that was often done was the ventline would get cut back about 3", a short stub of line would come off the cap, and a piece of fuel line would be installed in between. This was done by others mind you: I always put the proper ventline back on the cylinder.

BIG WARNING: make sure you have some measure of free play on your beake pedal rod. It should not be pushing on the cylinder when at rest. If it does, you will find that the fluid cannot return to the cylinder and the brakes will lock on.