The GMC CCKW

I don't mean bleeding as in *&&^%$@!? brakes but actually meaning to get the air out of them.

Ok here it is the situation, manifold done! UJ done! Brush Guard bolted back on! Lets go for a road run I say to Jess (Jack Junior) fire the beast up, pull out of the drive......can't stop, no brakes

So what has happened there?

I have replaced the brake switch as the last one was worn out and when I undone the switch a small amount of brake fluid ran out. Is this the problem?

Is this the sump plug to the Master Cylinder and the little bit of oil that did run out was the last drops left?

The breaks up to this point where fine and well balanced.

Can someone please HELP.

Cheers.

Bleeding Boosted Brake Systems as the Army taught me.


1. Fill the master Cylinder, and keep it full

2. Bleed the Booster (Hydrovac in your case) first

3.Start at the extreme rear Axle and work toward the front axle, (RH or LH first is not important)

4. Finish by bleeding the Booster again,as this will give you the optimum effect in bleeding.

It is not necessary to monkey with draining the opening for the stop light switch, or remove the various plugs at the front of the CCKW Master Cylinder. It helps to have an assistant that is 100% aware of the need to coordinate "pumping" and "holding" with the guy with the bleeder wrench. The truck need not be running. I have a professional pressure bleeder that I connect to the master cylinder , and the process can take as little as 10 minutes. It also helps to adjust your brakes. If this does not work, it is advised to pull all six wheels and service the wheel cylinders.

Do not be tempted to start playing with the adjustment at the rear of the Master Cylinder, one must assume that the brakes were previously up to spec. It is realistic to realize that time has taken a toll on your brake components, as parts do go bad.
Joel

Nice work Joel, thank you.

seeing as it is looking like I don't need a manual as I have an 'online manual' .....thanks guys

What nut/valve am I looking for on the Hydrovac to bleed that one fist?

............and use DOT 3 brake fluid?

It does say so on the nut.

You can make a nice pressure bleeder from the extension pipe and cap from the M211/M135 master cylinder. They use an extension about 4 inches long that screws into the CCKW and Chevy master and the cap they have has a brass fitting on it for underwater operation. For about $14 you can go to Agway or Blue Seal and get a small plastic insecticide sprayer and with a short piece of hose connect the two. You remove the cover from the sprayer and add brake fluid, reinstall the cover and pump it up with the pump on the cover of the sprayer.

It works quite well and allows you to bleed them yourself w/o (most of) the risk of running the master dry and having to start all over again!


Steve AKA Dr Deuce

You will see two brake bleeder fittings on the outlet end of the Hydrovac, do the upper one farthest from end first, your on line manual illustrates the procedure, but always do the Hydrovac a second time.
Joel

"but always do the Hydrovac a second time. "

Is that in the manuals....


Steve AKA Dr Deuce

Not in the CCKW Manual but a procedure used on M-Series Trucks that I was taught in the Army and have practiced for 45 years. It is good procedure. It gives the optimum in bleeding. The M-Series has Air Over Hydraulic, but the hydraulics follow the same path. (you are talking to a very experienced Army truck mechanic.)
Joel

Thanks Joel. It is a helpless feeling when that pedal goes all the way to the floor.

How close your pedal gets to the floor is directly proportional to your bank account and mechanical ability.
Joel

That is not true. You could be driving down the street and run over a piece of metal dropped by another vehicle and rip off one of the brake hoses. The CCKW has a valve under the floor on the passengers side to shut off the front brakes if you might be encountering wire, barbed or otherwise. GMC did a major redesign of the brake plumbing to try and prevent this type of problem. It was carried through to the M211 and M35 in the rears where the hoses run down the upper torque rods instead of flying through the air between the frame and the wheel.

The have fire drills at schools for children

Pilots learn what to do if the engine fails on take off and practice it

Why do they do these things? BECAUSE if and when the time comes that you have that particular problem, it is not the time to try and figure out what to do. You must have thought about this and maybe even (as in pilots) trained in simulators what to do.

Don't they maintain schools? Don't they maintain planes much better than HMVs?


Remember what I told you about how to stop should you have a failure. You don't need to practice it, you need to remember it! Steve Workman did and it saved him from running over a cruiser!


Steve AKA Dr Deuce with over 50,000 miles in a CCKW!

All that is really needed is a crash course on how not to crash your CCKW.
Joel

Do the same techniques apply to a 1942 Chevy G506, ie., bleeding the hydrovac 1st and last?