A blast from the past.

Apr 27, 2007 8 Replies
T

I have a need to get an old 1951 GMC 2.5 ton side-dump farm truck running for a few errands. This truck has been parked out behind the barn for about two years now.



My question is about a part in the brake hydraulics system. When I started the project, there was no brake pressure. A several minute search brought me to the master cylinder that is located under the driver's position floorboard. Pulled a plug from the floor and found where the reservior is (it is actually the body of the master cylinder itself).



Following the hydraulic line from the master cylinder brings me to the part in question. This is a large cylindrical device about six inches in diameter with a narrower neck coming off the front of it. The neck feeds into a rubber tube that ends at a breather of some sort mounted on the firewall. There is a bleeder for the brake system in the narrow neck as well, and the brake lines come off of there too.



There is also a feed from this device to the hydraulic pump for the dump bed on this truck, but I don't believe that the system shares the fluid between the brakes and the dump hydraulics.



I got the brakes working well, but I'm still baffled by the purpose of this rather large device in the middle of the system.



Any ideas?


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T

OK, bad form replying to my own post. I know.

Thinking about it, could it a system that is set up to apply pressure to the brakes while the dump bed is in the up or tilted position? Was there such a thing on these old farm trucks?

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C

Sounds like it is a brake booster to me.Look them up on the net. cuhulin

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T

No vacuum lines to it though. My Google searches have been fruitless so far. Have you got any search terms that may find this part?

I've tried 1951 GMC farm truck brake systems and a few other variants. No luck for me yet.

I think it is not a booster, but who knows? I've been wrong before.

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A

From what you describe taht sounds like a good guess. However, with rear dumps they often want to be able to crawl them along as the dump the dirt out so not sure why they would insist that the brakes be applied unless the truck is just to unstable to move when dumping.

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D

Sounds to me like an early version of Bendix's Hydroboost, which became popular when diesels showed up in smaller vehicles. Diesels have no useable manifold vacuum, so the hydroboost used power-steering pump pressure to boost the brake pressure. The Hydrovac used manifold vacuum to boost the brakes.

Dan

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M

Wanna bet someone here will know?

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C

I like that stovebolt.com website,MasterBlaster.Thanks for posting it. cuhulin

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S

Could just be an air vent and filter for both the hydraulic and brake systems, placed high enough that water from off-road work doesn't get into the system.

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