OT- Dodge grain truck brakes

b.jones · Oct 31, 2009

We have an old 1971 Dodge 10 wheeler with vacuum booster brakes. About 3 years ago we put on a rebuilt vacuum booster and the brakes worked fine until just a few months ago. Usually the first push the brakes work fine and we have a good pedal. If you let up just a little and come down on the brakes again the pedal is very hard and the brakes just barely work even if you push VERY hard on the pedal. When this happens the pedal does not go down much at all and feels very hard, bad part is you have very little stopping power. Any ideas or do we need a new vacuum booster? Thanks

CCer · Oct 31, 2009

could be a bad hose in the system. Brake hoses may get a hole in the inner lining, fluid pressure goes in that hole and expands the inner lining enough to cause a blocked passage. This sometimes acts like a one-way check valve.
If brakes are OK on first application, I suspect that problem. On my old truck, a wheel would lock up and hold after a time, it would drain off and be Ok for one application. Let us know what you find.

Owen Aaland · Oct 31, 2009

First try adjusting the linings.

I believe the problem you are having is that you are running out of stroke on the booster cylinder before the brakes are fully applied. At that point pumping the brakes will raise the pedal height but you will have no assist from the booster. It is possible that an internal leak in the booster is the cause of the problem but you need to make sure that it is not caused by poorly adjusted brakes that require more fluid to apply than can be supplied by the booster cylinder.

John B. · Oct 31, 2009

Yes your vacum assist has gone out again. Before removing anything disconnect the vacum hose at the booster to see if you have vacum at the hose with the engine running. If so then hook it up to the booster. If you don't have any vacum at the hose while disconnectd I would suspect a bad hose especially on a vehicle that old. Let us know what you find.

Anonymous-0 · Nov 1, 2009

I had good brakes on my truck but it would not stop.. the brake drums were worn and the shoes would not reach.. worth a look.

danofarming · Nov 1, 2009

Check your vaccum line from the engine to the booster. My uncle had the same problem with his Chevy some years back, spenta a lot of money trying to find the problem. The hose had collapsed on the inside.

b.jones · Nov 1, 2009

Update on my 71 dodge brakes. I took off the vacuum hose at the booster and it had lots of vacuum. If the pedal goes about half way to the floor on the first push and is just a little bit soft then you have great brakes and will slide the tires. If the first push only goes about a third of the way and is pretty hard then you will have trouble sliding the empty truck on loose gravel, ie pretty poor brakes. You just never know for sure what that first pedal is like. If the first pump isn't good and you decide to pump the brakes , then the pedal is hard as a rock and the brakes are awful. I think we're going to order a new booster tomorrow. Everything else seems to check out ok. When they do work great the pedal is always just a little bit soft but great brakes. Thanks everyone for your help. Never has the pedal gone more than half way to the floor the first pump. Anytime it feels a little soft then I know I'm going to have good brakes.

danofarming · Nov 1, 2009

Sounds like air in the lines to me?

trucker40 · Nov 1, 2009

I agree with the bad hose or booster.Also if you didnt already do this you should adjust the brakes by jacking up the wheel,adjust up tight,loosen until it spins easy,hit the brakes a few times and adjust again.If its not low on fluid or loosing fluid somewhere and you still have trouble after adjusting them,I still think its the booster or the vacuum hose or somewhere in that part of the brake system its not getting the boost it needs.

Owen Aaland · Nov 1, 2009

(quoted from post at 09:55:55 11/01/09) Check your vaccum line from the engine to the booster. My uncle had the same problem with his Chevy some years back, spenta a lot of money trying to find the problem. The hose had collapsed on the inside.

After rereading about the problem you are having, a collapsed hose will act just like you describe. It can allow a little air to pass so that a vacuum can be built up in the booster. That accounts for the brakes being Okay on the first pedal stroke. When you try to pump the pedal, the vacuum is too slow to recover so you get little or no assist.

Check the hose first before replacing the booster again. If you replace it make sure it is with a hose designed for vacuum use. Other types of hose can separate internally or collapse in use.

T_Bone · Nov 1, 2009

Hi jones,

Sounds like a classic bad master cylinder too me. If in deed the MC, then the wheel cylinders will soon follow.

T_Bone

OT- Dodge grain truck brakes

b.jones

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CCer

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Owen Aaland

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John B.

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Anonymous-0

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danofarming

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b.jones

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danofarming

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trucker40

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Owen Aaland

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T_Bone

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