Guru_4_hire

I keep losing my pedal in about 3-5 hours of driving. I have replaced the master cylinder twice and we cant see a leak ANYWHERE.

Could the booster be bad, or is a really miniscule leak in a caliper more likely?

GDaina

you could have a leak, that's easy to spot, and/or air in your lines. I assume you bled the master cyl, and the rear calipers have two bleed screws, both have to be bled.

brookman

With that much time passing I would guess the fluid is boiling. If it hasn't been changed it a while it will absorb water and the boiling point will go down.

Guru_4_hire

the brake fluid has been changed each time I replaced the MC. I am just trying to figure out how air is getting in my lines. I am not losing fluid either.

7vette2

Guru,
Check for wetness or a sheen like Armorall on the inside of the tires. You could have a slight leak on a caliper piston. Difficult to see but possibly there. Been there done that.
Ben :flag

GDaina

You may have air bubbles that never were expunged. How did you bleed the brakes? Air, gravity, or someone pump the pedal? Did you tap the calipers to disloge the air bubbles? Did you attach a vacuum tube to the bleeder and watch the fluid pour into a jar and see the air bubbles in teh jar?

Guru_4_hire

They have been gravity bled, pressure bled, bled into a jar.

The last time our mechanic had me sit in the car and had me pump the brake in sets of 3 till we got a set of 3 pumps without a bubble on each bleeder.

I can do it again I spose....


[Modified by Guru_4_hire, 5:47 PM 9/27/2003]

GDaina

you can do this yourself if you have an air compressor. get a mc cover, drill a hole and screw an air fitting, make sure you seal the hole with gaskets, use low pressure, no more than 5 lbs. Bleed and constantly check the fluid in the MC. Also a tool called Mity Vac, vacuum pump, I understand works very well.

Start by eyeballing and feeling all the fittings in the brake system, see if there are any leaks. If none, bleed the MC, then the calipers

Guru_4_hire

I dont have the facilities to do that. I will have to take it too a mechanics to have them bled again :banghead:

What is really really pissing me off is that 2 different mechanics have inspected the system and found nothing wrong with it, bled the brakes only for them to go bad again and I have no brakes.

GDaina

I wnder if they bled the MC? If the MC is not bled, you will have air in the lines

Guru_4_hire

They bled the MC all three times and replaced it twice. I am beginning to think the trouble may lie elsewhere.

GDaina

Can't...either air is getting in the system, or the system still has air that was never purged. Air is the culprit that will make the system loose peddal

Also, check if any electrical wires are touching the brake lines, or if the lines are close to exhaust pipes

GDaina

One more thing, have the mechanic check for rotor runnout
are the rotors rivited to the axle assy?

Wrecked82

Rotor runout = air in calipers, but what if no air is in calipers when you bleed them. Think he says there is no air.

Guru_4_hire

All kinds of air gets into the lines.

What is rotor run out?

GDaina

calipers sit dead vertical on the rotor, means there is no side to side movement. It doesn't take much side to side movement...if the rotor moves, then it acts as a gigantic air pump, and the pistons are constantly pumping fluid...this may be the case...to avoid this, the rotors have to be true, no warpage, and only way to insure trueness. is to turn them as a trailing arm assembly

GDaina

Also, if the rotors are not rivited to the axle, they sit loose and are held in place by the tire and lugs, again, if there is any movement, as little as .005-008, caliper pistons will start to move.

Constant movement will generate heat, and I'm guessing this is the root of your problem


[Modified by GDaina, 6:47 PM 9/27/2003]

Guru_4_hire

That would explain why it only happens when I drive..... thanks :cheers:

GDaina

A dial indicator will tell just how much runout you have.

Guru_4_hire

It will have to wait till I have some access income to blow on it