The GMC CCKW

Hi, finally got the Hydrovac unit off (topmost outer nut was inaccessible!!) and now stating to strip it down. 2 issues thus far: How do you separate the Slave Cyl. from the 'Tank' and secondly, the 2 'air pipes from the tank go into what I assume is the vacuum control unit are stuck in very firmly. Are these pipes soldered in ??? I hope I can get new parts, seals, diaphragm etc !
Thank you, Roland

Hi RolandRat,

Throughout its service life, several types of Hydrovacs were used on the CCKW. Do you know which type you have ? TM9-8651 lists ID and service information for all types. I found it online someplace awhile back.

The most common replacement Hydrovac unit seems to be the Type 3 - PN 374750. Rebuilt units are actually still available from NAPA, although they are a little pricey.

https://www.napaonline.com/en/p/MBIRV37 ... erchange=1

When I rebuilt the brake system on my truck, I was going to rebuild my existing unit, as I thought that it was a Type 3. However, I did not have much luck trying to find parts. Then, I found out that the unit on the truck was not a 374750. It looked like one, but was actually shorter, and had less slave cylinder capacity than the correct unit, so I had to go the NAPA rebuilt route. NAPA, BTW, also sells master cylinder kits, and cups for the wheel cylinders, as well.

There are a number of threads on this site such as this one that details some of the procedures for CCKW brake service.

viewtopic.php?f=1&t=5435

BTW, if you need to sleeve any of your wheel cylinders or your master cylinder, I would highly recommend these guys. They do excellent work:

http://brakeandequipment.com/portfolio- ... -calipers/

They actually have a pretty cool video that shows all of there machine shop services - (sleeving wheel cylinders is @ 3:22)

http://brakeandequipment.com/machine-shop/

Best Regard.....

Thanks for that. It is a type 2. I have now stripped the Hydrovac (advice given by Rex Ward, thx). Now, to rebuild it of have Rex do it ?

Hi RolandRat,

Rex is The Man. If I lived on his side of the pond, I would seriously consider having him do it. From over here in "The Colonies", however, shipping would be prohibitive.

Does he have serviceable Type 2 parts? If anyone does it would be him. I have purchased hard to find parts from him in the past. Just surprised that there are actually still Type 2 parts out there that are not past their useful life.

Best Regards....

Hi Mudflap, Got the parts from Rex. A lot of money for little bits of rubber !! But can't live without them. I am a little concerned about the age of these rubber parts, but they look ok. (I am looking ok too at my age !!)
Rebuild is going ok. fingers crossed.