The GMC CCKW

Used the same power booster system that CCKWs prior to Serial 41189 used.

I talked to a WW2 vet who started out as British then came to America and the army. He drove both Studes and CCKW and he said that they stopped about the same.

Empty.

What was the main thing that went wrong with this power booster system and can they be rebuilt? Who works on this type of brake booster set-up?

In the number of moving parts, it is similiar to the CCKW.

The linkage is more complex, but hydraulically there is less to go wrong with it as everything works off of the master cylinder. It had a vacume chamber like that on a Hydrovac and an inline valve (in the brake to master pedal linkage) that controls the vacume and air to the vac chamber. You can also run a trailer off of it (which Studes did) easily using the output from the valve.

Unlike a hudrovac, there is no way the engine can eat brake fluid. That is a failure mode in a hydrovac. That is also why I don't run silicone fluid. A chemist explained to me one time that the silicone when burned forms a grit which in your engine cylinders....

Many of the European CCKWs that are recent Surplus have Silicone Brake fluid. When Hydrovacs go bad and the fluid starts disappearing from the Master Cylinder overnight, the culprit is normally the Relay Rod seal, and the fluid goes into the chamber of the Hydrovac which will hold a couple of gallons. When this happens, it is time to replace the Hydrovac. Many owners are driving their CCKWs around with a can of Brake Fluid under the seat,-not a good idea in the interest of safety.

You can inspect the check valve at the manifold to see if the hydrovac is leaking regular brake fluid.

When I redid Annie the cckw crane, the hydrovac was junk. Because I was putting in a new hydrovac, I checked out the whole system and replaced the vac hoses. The check valve was all gummed up inside from the brake fluid being 'eaten' by the engine to the point, it was more or less open all the time.

What did you use for vacuum hose, as the correct hose is over $10.00/ft, and not many stock it?

Reinforced airbrake hose

You didn't use Vacuum Brake Hose?

No

That is what the old guy at my parts place said to use. It has been on my cargo truck for over 10 years now.

It may work, but was designed for positive air pressure and not designed for vacuum, it could under some circumstances collapse under vacuum. Problem is, should you have a serious accident with your MV, you may have to answer some serious questions, as a sharp insurance investigator would look for details such as that, and they do look for flaws. Many States issue Antique or Historic Vehicle registrations, and exempt the vehicle from the vehicle inspection requirements on the premise that the vehicle is restored to good original operating order and used solely for the purpose of Parades and Car Shows. The fun begins after a property damage or personal injury type of accident. Example, My CCKW is covered by Antique Vehicle insurance, but the policy states that my vehicle insurance is for parades and shows, and does not cover the CCKW during operation of the winch. I have 4 Antique Vehicle insurance policies thru State Farm.

I think on Annie, I used hydraulic suction hose.

I have insurance thru Hagerty for mine with basically no limit on what I can do. Sunday drive OK with them and they cover you for liability when towing a trailer. You can even insure the trailers for F-T-C with them too!

I dumped JC Taylor because they would not cover me/you when towing a trailer.

They would not do Annie though....

Sorry to rehash old posts but Im rebuilding a US6 and would like to know more about this system. I need to find the larger booster for my truck. AS mine really needs some help

Ken

Do you have a CCKW or Stude?

If you have a CCKW and thereis not enough "boost" for your pleasure, you have something wrong. With a good working system, you can easily lock the wheels.

I have a 1942 US6 Studebaker and we are working on the brakes and need all the help I can get

Ken

Ross Prince in Australia has all these parts NOS complete or as repair kits. He has complete vacuum booster assemblies, pedal control valves, vacuum check valve, or kits. In fact, he has the world's largest inventory of NOS Studebaker US6 parts.