Brake master cylinder woes Options

[jmargush]

I put a new 19mm master cylinder from PMB on my car within the last two years.

The pedal had been getting a little more travel in it over the past week or two.

Yesterday at the Autox the pedal got enough travel that it tripped the warning light on.

Does this point to a failed master cylinder?

If I pump the pedal it will build pressure and reduce travel. after this is done it doesn't seem to drift to the floor with continued pressure.

I bought from PMB because I learned form Eric that the ones you by at FLAPS don't have the correct material in the seals and that a new one should last years.

[Dave_Darling]

It means you have air getting into your system. Could be from the master cylinder, could be from the calipers, could be from the lines. Time to start going over the system carefully, looking for leaks.

--DD

[screenguy914]

Discounting any external leakage, increased pedal travel during braking usually indicates an internal leak in the MC.

However, increased pedal travel during heavy braking (autoX use) usually points to boiling fluid and thus increasing pedal travel and softness.

Sherwood

[worn]

I put a new 19mm master cylinder from PMB on my car within the last two years.

The pedal had been getting a little more travel in it over the past week or two.

Yesterday at the Autox the pedal got enough travel that it tripped the warning light on.

Does this point to a failed master cylinder?

If I pump the pedal it will build pressure and reduce travel. after this is done it doesn't seem to drift to the floor with continued pressure.

I bought from PMB because I learned form Eric that the ones you by at FLAPS don't have the correct material in the seals and that a new one should last years.

The warning light is activated by a shuttle that moves towards the side of low pressure, generally a leak in front or rear of the system. As Dave says it could also be that the fluid got low enough to entrain air in the front or rear causing the low pressure, but a leaking fitting or caliper would be my bet. Check the inside of each tire for signs of fluid. Fix it before driving it more, but you probably have already reached the same conclusion. IMHO the master is the last place I would look other than perhaps to find out which side is low, front or back. Not that Eric is infallible. No wait, not certain about that.

[jmargush]

I am always fearful when I have installed the MC that he feed lines don't go in all the way. I have felt the little snap or pop as if falls into the seat int he grommet but I always wonder if it is fully seated.

Does anyone have a recommended installation that they feel makes sure the feed lines are seated?

Has there ever been a modification to use lines with threaded ends in that application? I know you would have to have the MC be able to accept the threaded fittings.

[dlee6204]

I am always fearful when I have installed the MC that he feed lines don't go in all the way. I have felt the little snap or pop as if falls into the seat int he grommet but I always wonder if it is fully seated.

Does anyone have a recommended installation that they feel makes sure the feed lines are seated?

Has there ever been a modification to use lines with threaded ends in that application? I know you would have to have the MC be able to accept the threaded fittings.

Anytime I install a MC I remove the clamp holding the reservoir allowing the lines to be pulled further down. Then I can get good access and leverage to fully seat the lines.

With that being said, The last time I messed with the MC on my driver I tapped the two inlets on my master cylinder and put threaded fittings on eliminating the grommets. (IMG:style_emoticons/default/smile.gif)

[914werke]

With that being said, The last time I messed with the MC on my driver I tapped the two inlets on my master cylinder and put threaded fittings on eliminating the grommets. (IMG:style_emoticons/default/smile.gif)

Id like to see that. Do you have a pic or two of that setup?

[dlee6204]

This is the only picture I have at the moment.

[jmargush]

Starting the process of trying to find where the brake system might be drawing air in.

If the bleed screws on the calipers were leaking wouldn't they be pushing fluid out or am I not thinking about this correctly?

[76-914]

Starting the process of trying to find where the brake system might be drawing air in.

If the bleed screws on the calipers were leaking wouldn't they be pushing fluid out or am I not thinking about this correctly?

Yes. they would bleed out not in.

[worn]

Starting the process of trying to find where the brake system might be drawing air in.

If the bleed screws on the calipers were leaking wouldn't they be pushing fluid out or am I not thinking about this correctly?

I should think they would bleed fluid out and air back in. No leaking fluid at all anywhere I take it? Both reservoirs showed full when the warning light came on? Shouldn't have but that is theory.

[jmargush]

Yeah, no fluid showing up any where and reservoir is full to the top.

Would it be feasible that I am drawing air in at the grommets for the feed lines to the MC and not see fluid leaking out?

[jmargush]

Should I start by rebleeding the whole system?
or pull the MC down and pull the feed lines out and re install or even get new grommets?

[914Mels]

How old are your calipers? If they have not been touched in years the piston seals may be sticking to the pistons keeping them from self adjusting out as the pads wear. By pumping the pedal and getting a good pedal that way it sounds like the pads aren't close enough to the rotors so you're having to pump them out to take up the excess clearance. If indeed you have a hard pedal after pumping them, you probably do not have a internal leak. A internal leak would still have the pedal fade after you pump up some pressure. Don't for get about the rear calipers adjustment process either. If that gap is too big you'll end up with a low pedal.

[jmargush]

All the calipers were rebuilt about 12 yrs ago

I'll have to get back in the car and see exactly what the pedal is doing after pumping
I'll also run through rear brake adjustment procedure again