Brakes Unusual brake issues

Northwest_stang · May 7, 2019

2000 GT, brake pedal on soft side of normal when cold but becomes very firm after driving some. Also found noticeable drag at time. As in I let off gas and slow down quicker then one would normally coast. It does not drag every time it’s hot that’s just when it happens more often. My thoughts is that there is back pressure in the lines almost as if there is a bad one way valve not letting pressure return to MC. You can attach a line to a bleeder and it will slowly push fluid up it

Front pads and rotors done 5 months ago, Front left caliper 4 months ago, front right 1 month ago, master cylinder done 4 months ago. Both front flex brake lines done 1 week ago.

Rears are untouched because I still have to buy caliper push back tool. Also brake booster/hydro boost is untouched because it’s 200 for a new unit and didn’t want to replace unless I knew it was bad(or on its way lol)

1990 5.0 LX · May 7, 2019

If the brakes are dragging the brake booster could be bad. You can disconnect the vacuum line to the booster and see if the brakes release. If so, the booster is bad.

Obviously plug the vacuum line when it's disconnected and don't try driving the car at any speed as you won't have power brakes when the vacuum is disconnected.

Northwest_stang · May 8, 2019

well i hope it is bad because I found a deal I couldnt pass up. found a used power booster at a local yard I deal with because they offer warranty's on all there stuff for only $60 better than 200 for a new one

Mustang5L5 · May 9, 2019

1990 5.0 LX said:
If the brakes are dragging the brake booster could be bad. You can disconnect the vacuum line to the booster and see if the brakes release. If so, the booster is bad.

Obviously plug the vacuum line when it's disconnected and don't try driving the car at any speed as you won't have power brakes when the vacuum is disconnected.

It's hydroboost, so none of that really applies here. No vacuum booster.

1990 5.0 LX · May 9, 2019

OK. Is it worth checking the hydroboost to make sure it's functioning correctly?

And a dumb question, why do they call it hydroboost? Why not pneumo-boost? Hydro sounds so much like water...

Northwest_stang · May 9, 2019

Mustang5L5 said:
It's hydroboost, so none of that really applies here. No vacuum booster.

There is still a vacuum line attached to the hydroboost unit... not exactly sure how it works because it’s new to me but you still have one

Northwest_stang · May 9, 2019

1990 5.0 LX said:
OK. Is it worth checking the hydroboost to make sure it's functioning correctly?

And a dumb question, why do they call it hydroboost? Why not pneumo-boost? Hydro sounds so much like water...

Too my understanding it’s a mix of vaccum pressure and transmission fluid. I just don’t know the specifics of how

Mustang5L5 · May 9, 2019

Northwest_stang said:
There is still a vacuum line attached to the hydroboost unit... not exactly sure how it works because it’s new to me but you still have one

I think you are mistaking one of the Power steering lines as a vac line. The system works solely on power steering system pressure.

There's a nitrogen filled accumulator on the side. During operation the pump compresses and internal piston with PS fluid. If the engine stalls, it gives you 2-3 pumps by the pressure of the nitrogen fill in the accumulator similar to how a vacuum booster has reserve vac inside if the engine stalls

Northwest_stang · May 11, 2019

Then I’m super confused because that’s the top of the hydroboost unit. That’s definitely a vacuum line I’ll try to get a better picture once I take it out

Northwest_stang · May 14, 2019

ok i bow to the superior knowledge of Mustang5L5

because what I swore was a vacuum line was actually a fluid line. im not sure why it needs 3 lines.. 2 hard and 1 flex hose but what ever lol..... so the brake booster was definitely bad once I got it off the brake pedal hook thats susposed to freely move was very clunky

Brakes Unusual brake issues

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