Hitman's Pontiac Trans Am Forum
Trans Am Information => Trans Am Tech => Suspension => Topic started by: Jhensche@hotmail.com on April 13, 2017, 12:31:58 AM
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I have a 79 t/a with front disc and rear drum brakes. My brake pedal is firm and normal until I start the engine then the pedal will go to the floor.
What have I done so far:
- 2 new caliper in front
- rebuilt rear drum breaks, and adjusted properly
- new master cylinder (bench bled prior to install)
- drained and filled system with new fluid
- bled the system traditionally and with a OTC brake bleeder (no air)
Is it the issue I am having due to a bad brake booster or possibly a bad rubber brake line in the front flexing under pressure? I'm not sure what else could be wrong? Help please
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or it could be that you are comparing a 1970's car to a current car. Is there any resistance at all with the pedal when running? It should still spring back but be extra light to press compared to most cars .
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Well, it's possible that I've some penchant for newer braking systems. However, that being said I've owned this particular car for 25 yrs. And the situation I'm describing isn't normal for a 70's car or for that matter any car with hydraulic brakes. The pedal is firm when the engine is off, the pedal is soft when the engine is operating. The brakes do function "properly". Meaning the brakes will stop the car and do so in a straight line without steering input. But this only happens when pumping the pedal. Again it's a new master cylinder, new fluid, new calipers in the front, new drums in the rear, new pads and shoes, new rotors, fully rebuilt rear braking system. The only thing I haven't replaced is the booster and the rubber lines up front.
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Could be a booster thats not holding vacuum then. The pedal should be hard when engine off and softer when running but shouldn't have to pump it to build up pressure. Luckily they aren't that expensive and easy to swap without bleeding anything, mainly just accessing the nuts on the firewall. If you get that far be sure to get the correct 2nd fen F body type with loop on the end rod. Gold cad plated is original if looking to keep it stock looking.