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Brake pedal hitting the floor


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Hi All.

 I’m posting on behalf of a friend who has a TR6, he’s chanced his front callipers for 4 pots and now after a couple of days the brake pedal disappears to the floor. If you rebleed it it comes back, no leaks of fluid. I’ve given him another master cylinder I had and it’s still happening. Any ideas ?

 Cheers Mark

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When you bleed it does more air come out? Logic says that if air is getting in then fluid is getting out. The system has a fixed volume so it can’t be otherwise.

Any smoke, maybe the fluid is getting past the seals and into the servo. 

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It can be either the MC, where air is sucking in via the outer seal, or the same thing at the new 4-pot callipers (I think the latter is not very likely).

If during bleeding a MC is pressed in further than normal (where it has been operating for many years) this can damage the seals.

Waldi

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If the problem is still there with the second master cylinder then (assuming that is ok) it must be something related to the new wheel cylinders. Check that the brake pipes are secured properly to the wheel cylinders. Bleed the cylinders but push the pistons right back so less chance of air being trapped inside. Make sure the bleed screws are tight. My guess is that one of the connections or a bleed screw is allowing air back into the system when the brake pedal is released. It is easier for air to leak into the system than fluid to leak out so you may not see a fluid leak. I use an Eezibleed rather than having someone pumping the foot pedal to bleed the brakes.

Keith

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