Brake problem

[pipelayer]

I have a brake peddle problem, it is sticking to the floor and wont come up only when the motor is running.
The brakes are bled great and the brakes worked for almost a year then a couple weeks back I jumped in the bronco and started to drive out my road when I got to the end to stop it stopped great but acted like a line lock and the peddle stuck down, I got my foot under it and puled it back up to release the brakes.
I was told it was the vacuum booster so I got a new one and it is still doing it. I checked my vacuum its around 16-17 at idle. I dont have a return spring on the peddle and not sure if broncos have them? its a manual trans and when I push in the clutch peddle the brake peddle wants to stay down even more. Im stuck can somebody please help a brotha out?

Brian

[GREMLIN]

Re: Brake problem

did you check pedal bushings?

[pipelayer]

Re: Brake problem

Yep all the linkage is great I'm going to look at the rear drums and see if a return spring broke or something tomorrow. Brakes aren't a priority until you need them!

[Bronco Brian]

Re: Brake problem

Yep all the linkage is great I'm going to look at the rear drums and see if a return spring broke or something tomorrow. Brakes aren't a priority until you need them!

I would check the push rod in the M/C first (sticking?)

[JimGo]

Re: Brake problem

It has to be booster related I think. One side should vent to atmosphere, I would check it to see if clogged???

Jim

[twisted 66]

Re: Brake problem

A vacuum leak at the master cylinder/booster or maybe engine line or something and/or air getting in lines???

[pipelayer]

Re: Brake problem

New booster dident fix it. I took apart the master cylinder and the return spring looks ok and it moves free. I ordered a new master cylinder anyway and it won't be here for a couple days. Is the vacuum low at 16/17? Because I get the same reading without the booster or with. I would think low vacuum would make it stiffer not want to stay on the flore.

[DirtDonk]

Re: Brake problem

I would have to agree with that too. And I'd say that 16/17 inches of vacuum is very decent. Pretty much the minimum expected for a stock-ish engine, but right up there.
Pretty sure 20 to 21 is about as high as you'd normally see on a stock motor. But as soon as you change a cam, or carb or heads, or even ignition timing, you could alter that considerably.

So yeah, less would make for a stiffer pedal, and longer recovery time between applications. And I'm not sure anything to do with vacuum would stick the pedal to the floor anyway.
Neither would a bad return spring or two in the drum brakes. Nor would sticking calipers.
To me it seems like it's got to be on the booster side of the master. There is no rigid connection between the pedal rod and the master cylinder. The rod floats between the booster and master, so even if the master or something downstream stuck, the pedal would be free to come back up.
So it's got to be something that the pedal is rigidly attached to. And I would think then, that this could only be upstream of the master.

Paul

[JimGo]

Re: Brake problem

I can't think of anything other than the booster that could be affected by whether the engine is running or not, the only thing that changes is vacuum supply to booster. Have you tried pulling the one way check valve with hose off the booster (while running) to see if this changes anything? This way you will not have any kind of vacuum charge applied and it should mimic non power brake. The booster usually vents to atmosphere out the back where the pushrod goes in, I suppose it is possible to foul it up with spider crap/webs, ect. I get EVAP tubes clogged on cars at work every once in a while with spider nest inside them!

Jim

[JimGo]

Re: Brake problem

Also, check the integrity of the hose from engine to booster. Sometimes they can collapse and cause brake problems.

Jim

[pipelayer]

Re: Brake problem

It's all new and yes I took off the tube and it acted like manual brakes very stiff. This isent a stock motor it has a mild cam alum. Heads headers forged pistons

[TBS-POPS]

Re: Brake problem

I had similar problem, rod from pedal to booster bell crank would hang on sheet metal at hole in firewall at full compression. just a thought.

[pipelayer]

Re: Brake problem

D you know if a master cylinder has a check valve of sorts like a return that could be closing off under power not letting the fluid to return back to reservoir?

[pipelayer]

Re: Brake problem

I wish but it has lots of room

[JimGo]

Re: Brake problem

It's all new and yes I took off the tube and it acted like manual brakes very stiff. This isent a stock motor it has a mild cam alum. Heads headers forged pistons

So did the pedal continue to stick to the floor when you did this?