MORE BRAKES!

[Poledriver]

I'm also working on my housemates Wedge. Intermittently the brake pedal would travel to the floor!
Today I changed the master cylinder. I bled the brakes until new, clean fluid came out of all of the bleed nipples, with no bubbles. There is no change!
I assumed that, as there are seperate circuits for front rear, even if there is a problem with one circuit the other would work OK!? There are no visible leaks anywhere yet thre appears to be a loss of brake pressure somewhere! I've never had this happen before in 35 years of car maintenance1 Any ideas?

Edited by Poledriver on Sunday 15th March 01:29

[TVR_owner]

Poledriver said:

I'm also working on my housemates Wedge. Intermittently the brake pedal would travel to the floor!
Today I changed the master cylinder. I bled the brakes until new, clean fluid came out of all of the bleed nipples, with no bubbles. There is no change!
I assumed that, as there are seperate circuits for front rear, even if there is a problem with one circuit the other would work OK!? There are no visible leaks anywhere yet thre appears to be a loss of brake pressure somewhere! I've never had this happen before in 35 years of car maintenance1 Any ideas?

Edited by Poledriver on Sunday 15th March 01:29

Have you tried small none return valves in the brake lines. The bigger wedges had a problems from new with pad knock back that resulted in the pedal dissapearing to the floor when apllied after a series of enthusiastically taken corners.

[SubRosa]

The master cylinder centre seal can start to fail which just allows the fluid to pump from one chamber to the other. I had this and ended up changing my M/C and upgraded it to a later Mondeo (IIRC) one. Can check if you like. Meant the servo had to be turned 90 degrees and an adaptor plate made but it also reduces the pedal travel as it's a bigger bore cylinder. Essential in my opinion especially if you are going for bigger 4 pot calipers.

TVR_owner said:

Have you tried small none return valves in the brake lines. The bigger wedges had a problems from new with pad knock back that resulted in the pedal dissapearing to the floor when apllied after a series of enthusiastically taken corners.

Excuse my ignorance here, but how do non-return valves in brake lines work? Surely when you applied the brakes they would stay on?
The only time I've ever really come across pad knock back is on bikes with fully floating discs, normally after a good tank slapper

[TVR_owner]

SubRosa said:

The master cylinder centre seal can start to fail which just allows the fluid to pump from one chamber to the other. I had this and ended up changing my M/C and upgraded it to a later Mondeo (IIRC) one. Can check if you like. Meant the servo had to be turned 90 degrees and an adaptor plate made but it also reduces the pedal travel as it's a bigger bore cylinder. Essential in my opinion especially if you are going for bigger 4 pot calipers.

TVR_owner said:

Have you tried small none return valves in the brake lines. The bigger wedges had a problems from new with pad knock back that resulted in the pedal dissapearing to the floor when apllied after a series of enthusiastically taken corners.

Excuse my ignorance here, but how do non-return valves in brake lines work? Surely when you applied the brakes they would stay on?
The only time I've ever really come across pad knock back is on bikes with fully floating discs, normally after a good tank slapper

NR valve was possibly the wrong description - its like a small shuttle valve thing with a disc that offers fluid flow resistance rather than preventing flow..Mocal or someone of that ilk I'm sure will sell them. Not expensive and easily fitted in line. I came accross knock back on both my 390s.

Floating discs I had on my SP3 Duke. Because they float I would have thought that would prevent the knock back??

Edited by TVR_owner on Sunday 15th March 08:33

[Number 7]

TVR_owner said:

SubRosa said:

The master cylinder centre seal can start to fail which just allows the fluid to pump from one chamber to the other. I had this and ended up changing my M/C and upgraded it to a later Mondeo (IIRC) one. Can check if you like. Meant the servo had to be turned 90 degrees and an adaptor plate made but it also reduces the pedal travel as it's a bigger bore cylinder. Essential in my opinion especially if you are going for bigger 4 pot calipers.

TVR_owner said:

Have you tried small none return valves in the brake lines. The bigger wedges had a problems from new with pad knock back that resulted in the pedal dissapearing to the floor when apllied after a series of enthusiastically taken corners.

Excuse my ignorance here, but how do non-return valves in brake lines work? Surely when you applied the brakes they would stay on?
The only time I've ever really come across pad knock back is on bikes with fully floating discs, normally after a good tank slapper

NR valve was possibly the wrong description - its like a small shuttle valve thing with a disc that offers fluid flow resistance rather than preventing flow..Mocal or someone of that ilk I'm sure will sell them. Not expensive and easily fitted in line. I came accross knock back on both my 390s.

Floating discs I had on my SP3 Duke. Because they float I would have thought that would prevent the knock back??

Edited by TVR_owner on Sunday 15th March 08:33

Its a residual pressure valve - have 2 on my Wedge, and have never suffered pad knock-back.

7.

[TVR_owner]

Hi Paul,
Did you fit them to cure knock-back??

[Number 7]

TVR_owner said:

Hi Paul,
Did you fit them to cure knock-back??

That was the reason, although I'd never experienced it, but it seemed a
good preventative measure.

7.

[Poledriver]

Sorted! Put an E-Z Bleed kit on it at 25psi, and re-bled the rear brakes. There was a small trickle of browny coloured fluid (it was clear when I finished last weekend!) then a sudden splatt of dark coloured solid followed by clean fluid at high-speed. Got brake pressure now! (And yes, I did let it run for a while to clear out all of the crap!)