[GoinManta]

Could a sticking caliper cause a intermittent pedal?

Well says it all.. I have rebuilt 3 masters, changed all the lines, fluids, etc... bleed and bleed... and bleed the brakes.

Yet I stil have a pedal that goes to the floor OCCASIONALLY.. Other times and when I am bleeding the brakes the pedal is nice and stiff...

Only thing I can think of is the front brakes sound like they are dragging occsionally as well...

Charles

 

[RallyBob]

Yet I stil have a pedal that goes to the floor OCCASIONALLY.. Other times and when I am bleeding the brakes the pedal is nice and stiff...

Charles, check the M/C booster, and the hard metal lines. This kind of stuff drove me crazy on a few cars I worked on. Intermittant pedal from a faulty brake booster, and 'self-aerating' brake lines due to rust. I'd bleed the brakes and everything would be fine for while, then suddenly the pedal was crap. Turned out to be a 'slight' leak from a rusty metal line that would draw air into the system over time, but not physically leak enough fluid to lower the fluid level.

Bob

 

[GoinManta]

Checked the lines they are good.

Would the booster be "overboosting" ?

When the pedal goes soft and too the floor, the next pump is tight and good usually and this is withouth "pumping up" the brakes.

When I first get into the car and the engine is off, the pedal is tight and firm. With the engine on, intially its still firm.

When I start to drive it thats when it starts going soft, intermittently. The hotter the brakes the more prone to getting soft in stop and go traffic. ON the highway, it stays firm for teh most part.

I am thinking of pulling the entire brake system apart again. Getting new metal lines because "maybe" I am getting iar in the master at the connection. Altough it doesnt seem like I am.

May rebuild the calipers since I have some kits. Pull apart the master again to make sure everything I did before is in good order. Even tempted to replace the new rear wheel cylinders with new ones I have in stock.. just because.

Oh.. one thing I don't think is the problem. But it maybe.. I have a standard bolt going through the eccentric at teh foot pedal and not the speacil bolt with serrated edges on it.. Would that cause it?

Its driving me nuts...

 

[guyopel]

A pressure bleeder would help show a sys. leak.. if you do not have
access to one , take a long screwdriver or block of wood & put between
the dr. seat & brake pedal , to apply to brakes ..leave there for 1 to 2 hours
or as needed , then go back & look for leaks .. then go to next step ..
hope this helps

 

[RallyBob]

Oh.. one thing I don't think is the problem. But it maybe.. I have a standard bolt going through the eccentric at teh foot pedal and not the speacil bolt with serrated edges on it.. Would that cause it?

This won't make the pedal soft, but it will make the pedal variable-height. That serration is to set the pedal height after a brake job. Without it, it may be high, it may be low.....

 

[baz]

hi charles , i've always found an intermittent pedal to be the M/C or a leak
now a leak is obvious but the M/C i've normally found to be a seal in the wrong way or split when fitted
as you have just rebuild it it should be ok so the next thought would be which way are you doing the bleeding of the system

 

[GoinManta]

I have gravity bleed, slowly bleed, bleed with quick pumps, from the front first, from the rear first, its not a matter of how I have bleed the GD brakes, its a matter of how havent I.

That would be vaccum or pressure. But thats because I cant find anything either inexpensive enough or that will fit the master.

I am going to get the bolt for the brake pedal and see if that helps.. if it does then woo hooo... if not I am going to pull the whole damn system off. Replace the booster with a early Manta booster I have, then get a BMW master to fit it that is guaranteed to work. Replace the calipers or rebuild them at minimum since they are sticking.

Replace all the steel lines on the car. etc.. etc..

But right now none of it is happening.. it looks like OMC is out of the picture for me unless something miraculous happens. So no rush on fixing anything. Hope to drive out next year.

I still have my fingers crossed that I can fly out for the show.. minus car.

Charles

 

[bear]

Charles, reading your diagnosis, it appears you have a leak at the MC shaft seal, both at the booster and MC. Here's the reasoning: Engine not running, no problem; Engine running, sometimes; getting hot as in using the brakes a lot, they go to the floor; highway use, not a problem. My reasoning is vacuum from the booster is pulling the fluid out of the MC. Here's why, engine at idle, max vacuum, using the brakes a lot, again, max vacuum. Freeway speeds, minimal vacuum and engine not running, no vacuum. HTH.

 

[GoinManta]

Charles, reading your diagnosis, it appears you have a leak at the MC shaft seal, both at the booster and MC. Here's the reasoning: Engine not running, no problem; Engine running, sometimes; getting hot as in using the brakes a lot, they go to the floor; highway use, not a problem. My reasoning is vacuum from the booster is pulling the fluid out of the MC. Here's why, engine at idle, max vacuum, using the brakes a lot, again, max vacuum. Freeway speeds, minimal vacuum and engine not running, no vacuum. HTH.

Thought about that..

It was the problem on the first master.. but you could tell it was bypassing, etc..

Right now I am not losing fluid, and the master seems to pass the bypass test. Because when I press and hold the master with the engine off the pedal holds.

Here is what I am thinking... I may have a bad seal in the caliper, causing it to stick intermittmentally AND letting a little air in.

What I do know is this:

1) The New Calipers are sticking and were New OLD Remaned calipers (they had been on a shelf a while.. probably long enough for the seals to harden)

2) The bolt for the ecentric in teh foot pedal is wrong.

So I will replace the calipers (Or simply rebuild them), and get the right bolt for the pedal. I will then flush the entire brake line assembly again. If I STILL have the problem.. I will get a 1980 BMW master and put on a 71-72 Manta booster. I may do that anyway since I have 75' brakes and 3/4" rear wheel cylinders. Which at one time I thought might be problem.. but have since ruled out since they work great at times.. and not at other.

Charles