78 Chev 1T - brake fluid disappears?

Doug - Iowa · Jan 3, 2011

I have a mysterious leak on my old ton dump truck. It has the power brakes that operate off the PS pump. Anyway it takes a half quart of brake fluid a week but I can't find a drop on the front calipers or the drums in the back. No wet lines I can see either. Is a little wet around the MC but at this rate it should be leaving a puddle. PS fluid is normal so not gaining there. Got me stumped. Swept out the shop and leaving her set in there maybe something show up. Any ideas?

molinebob · Jan 3, 2011

Tome it sounds like it may be being sucked into your vacuum booster....common problem with them...Bob

Anonymous-0 · Jan 3, 2011

Just a shot in the dark check the booster. Had a ford was doing the same thing and it would smoke only on left turns. The master was leaking fluid into the booster and when I made a left turn it would get sucked into the engine by the vacum hose causing it to smoke. Took ALOT of beer to figure that one out!

Anonymous-0 · Jan 3, 2011

look and see if it is leaking where the master cly. bolts to the hydboost, the part that bolts to the firewall with all the lines that takes the place of the vacuum booster could be leaking there and driping onto the ground, sounds like the master cly.

RandyB(MI) · Jan 3, 2011

Excuse me if I'm missing something here but if it operates off the power steering pump then isn't that where it gets it's boost pressure as apposed to a vacuum booster???

GregCO · Jan 3, 2011

If it has a hydroboost system it can't go into the vacuum booster because it doesn't have one.
It may be leaking out the rear seal of the master cylinder just ahead if the hydroboost and just falling to the ground while you drive so you can't see it making a mess. It could also be following the bottom of the master cylinder and hydroboost and flowing down the inside of the firewall. Try pulling the floor mat back and have a look.

Greg

Doug - Iowa · Jan 3, 2011

Thanks all. Doing a bit of searching and find out the system is called Bendix Hydra-Boost. It does not have a vacuum chamber but an hydrualic piston affair that runs off the power steering pump. Supposedly a good system. I'm guessing it is the master cylinder leaking, they're cheap to replace so best place to start if I can't find the leak elsewhere.

Billy ky · Jan 3, 2011

his truck doesn't have a vacuum booster, it uses the power steering pump for power.. some GM stuff uses that system..

Janicholson · Jan 3, 2011

The hydro Boost system can leak at the joint between the MC and the booster. If it drops onto the ground (possible if the MC is over air) the missing fluid will be gone. Put a piece of cardboard under the MC and see if it needs a new MC. Jim

Ultradog MN · Jan 3, 2011

BTDT
Don't remember on what occasions mine would poof but once in a while man o man would it let out a cloud. I often thought about timing it so I could chase off the tailgaters but replaced the hydrovac and it quit.

78 Chev 1T - brake fluid disappears?

Doug - Iowa

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molinebob

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Anonymous-0

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Anonymous-0

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RandyB(MI)

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GregCO

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Doug - Iowa

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Janicholson

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Ultradog MN

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