Brake issues...need direction......
Elder User
Joined: Nov 2006
Posts: 973
Likes: 2
From: Texas
We had a problem similar to this with a 99 suburban. We replaced vacuum booster, and master several times. the peddle was soft and squishy, If you rolled up to a stop light slowly, it would stop then begin creeping forward again, no matter how hard you pushed. And sometimes you would hit the brakes and nothing would happen. It was scary and we ended up selling the truck at action because the brakes were so weak it wasn't safe
I dont mean to discourage you, but thats my story and i hope yours turns out diffrently, haha.
Good Luck!!!
I dont mean to discourage you, but thats my story and i hope yours turns out diffrently, haha.
Good Luck!!!
Thread Starter
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Junior User
Joined: Feb 2006
Posts: 76
Likes: 0
Revived thread from the dead......
OK guys. I need your thoughts on this issue. I want to rule out the MC (master cylinder) being the issue. Now this the issue: When the engine is running, vehicle not moving, I press down on the pedal it slowly goes to the floor. Did it 3 times, same results.
Now with the vehicle not running engine off, I press on the pedal, its rock hard. No drop in pressure. Did it a second time, same results. My thoughts is this: If the MC is bad, it should leak without the engine running (pedal going down to the floor). If so, the MC is not bad.
Now I mentioned that with the engine running, I hear a "shhhhhhhhhhhh" when the brakes are pressed down. Brake booster being bad? So I was going to replace the MC and brake lines. But if the booster is bad, it needs to be replaced. Not the MC and brake lines.
So I need to figure out this issue. Tomorrow, I will replace all pads and resurface the drums. And re bled the system. So any thoughts would be greatly appreciated. Thanks.
Now with the vehicle not running engine off, I press on the pedal, its rock hard. No drop in pressure. Did it a second time, same results. My thoughts is this: If the MC is bad, it should leak without the engine running (pedal going down to the floor). If so, the MC is not bad.
Now I mentioned that with the engine running, I hear a "shhhhhhhhhhhh" when the brakes are pressed down. Brake booster being bad? So I was going to replace the MC and brake lines. But if the booster is bad, it needs to be replaced. Not the MC and brake lines.
So I need to figure out this issue. Tomorrow, I will replace all pads and resurface the drums. And re bled the system. So any thoughts would be greatly appreciated. Thanks.
Fleet Mechanic
Joined: Mar 2005
Posts: 1,603
Likes: 1
From: St Louis
You should replace that master cylinder: either the brake booster is pulling the fluid out of the master, or the booster is aiding with enough pressure for the fluid to leak past the seals in the master and go back into the reservoir. You can replace the booster at the same time, but that master should be replace no matter what. Just because it is rock hard with the vacuum off just means it requires more force than you can apply to get the master to leak (that is why it is called a vacuum assist brakes).
Elder User
Joined: Nov 2006
Posts: 973
Likes: 2
From: Texas
I agree with Alxsnmr. The vac boost will put much more pressure and cause it to leak much more quickly. I would bet that if you push hard enough, for long enough with the engine off, you would probably get the same result.
Good Luck
Good Luck
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