The GMC CCKW

I pulled the hydrovac from my truck thinking it was history. I based this on the previous owner's comments and the fact the air intake hose had been disconnected.

I figured I would open it up since it was toast and just have a look inside. Well the main cylinder is spotless. The sides have a thin coat of grease and there is a ring of grease at the bottom. The person who rebuilt this hydrovac previously was very liberal with the grease and the grease looks new. The bottom was clean and I mean spotless. The central rod is spotless too. The main spring has the slightest amount of surface rust, probably due to it not being given a light coat of oil. The rod plunges forward without sticking.

I haven't taken the small cylinder apart since it is probably ok. None of the bolts were difficult to remove. The only odd thing was the inside of the drum between the top of the big plunger and the top of the cylinder, was a fair amount of a yellow powdery substance. It looked more like pollen than anything else.

Do you think I should just degrease it, put some new grease in and put it back together?

Neil G.

Neil
this job is best left to the professionals.
It would appear that you have a GOOD rebuildable core
Is it an early 2 diaphram model or the later/modern single diaphram type ?
Coming up with a correct kit for the early style might prove to be the hardest part.

John

John

It is nearly identical to the one one this page:

http://www.stovebolt.com/techtips/bendix/erickson/

His is marked "3-3 and mine is marked "2-3" otherwise they are the same.

Neil

That's looks like a single diaphram type
Modern units ,new avail from several vendors

John

Is a good rebuildable core worth anything?

Neil G.

Go to Vehicles of Victory. He has the complete new booster and mounting brackets as a kit

I’ve rebuilt 4 cckw hydrovacs in my collector life. The first is now about 15years old and is still working well. I remove them from the trucks every 5 years or so to clean them and put some new grease.
Here are some pics of the last one I’ve rebuild for my 1943 cckw352 (comments are in French, sorry):

http://thierry.becker.free.fr/HydrovacTypeII.htm

and here the same model as yours (restored but in need of new cups + new central rod ) :

http://thierry.becker.free.fr/HydrovacIV.htm

It is very important that all hydraulic cylinders and pistons are clean and not pitted. If so, you can rebuild those using new cups. The problem is that they are hard to find. You can found complete rebuilding kits but not the cups only. I still need some, so if somebody knows of a source

Thierry.

Yes that is the same one as mine. Mine is in much better shape to start with so I am encouraged. The only part on mine that is in bad shape is the rubber diaphragm. Mind you it is one of the critical parts.

Any suggestions on where I can get a rebuild kit? I have emailed BSC Parts warehouse but no response yet.

Neil G.

Hello Neil,

Unfortunately I haven’t found a kit for this model . Kits for early and late US WWII hydrovacs are available here in France, but I haven’t found one for the after war hydrovacs yet. That’s why I still need some parts for mine too. But if this type of booster is still being available in the US, the kits may be available too, I believe

Thierry.

I spoke to BSC Parts warehouse (www.bscparts.com) this morning. They are sending me a rebuild kit for $105. It doesn't include the leather because mine looks new.

I realize once you add labour to the $105 for parts, VoV's rebuilt ones are a very reasonable price, but I have always been one to do the work myself unless it is a licencing issue. If the hydrovac wasn't in such great shape already, I would just get the rebuilt one.

My truck will be a radio van and will never even approach fully loaded. So the handbrake alone will be enough to stop it.

Neil G.

SpookyDad wrote:...My truck will be a radio van and will never even approach fully loaded. So the handbrake alone will be enough to stop it.

Neil G.

I wouldn’t trust in the hand brake (even in new condition) to Stop a cckw. I’ve tried to stop my truck this way at a speed of about 30MPH just to see if it would work in an emergency case. On a “flate road” it worked but tooks a few seconds to stop and a hard “gear play”. Driving down a Hill it didn’t work!!! So I’m really taking care about my footbrakes, check the fluid level prior to drive a long distance and test the brakes at the fist slope.
On the other side, if there is no vaccum on the hydrovac or a problem on the air valve, but no leaks on the hydraulic side, you can stop the truck (if it is unloaded) in any situation.

Thierry.

The ONLY way a hand/parking brake will stop a CCKW is as follows:

Pull up on the lever till it starts to engage, then pull for all it is worth. The band area on the parking brake is too small to stop the truck playing nice nice. It will instantly heat up and become useless. Coming up on the brake till you feel some stopping resistance will prevent shock to the mounting and drive train. Once you have accomplished that, your only hope is to lock the wheels. Remember the situation you are in here (desperate!!!!). Oh on the way over to the brake handle engage the front axle too.