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Renault 6 sticky front brake

Messages
5
Location
Dorset
#1
So. I have fitted a brand new brake cylinder in the (front) wheel. Bled the system and the brake works but does not release. The handbrake has been disconnected where the cables meet under the bonnet (pivot pin out).
Also the brake does release if I crack the bleed nipple off which leaves me to believe fluid may not be returning to the master cylinder.
Should I be thinking it's a master cylinder issue or something else?
Just in case anyone is wondering I have backed off both adjusters and the wheel spins freely (until I hit and release the brake pedal).
I have ruled out the new brake cylinder pistons seizing up on the basis the brakes let go when I crack off the bleed nipple. So I'm assuming the (Bosch) cylinder is okay.

Any thoughts gratefully received. Thanks in advance.
 

mojobaby

Enthusiast
Messages
1,170
#2
Hello Cosmik, it's difficult to know what would be the cause because it's never happened to me before.
The first question I would ask, is if both front brakes are affected.
Secondly, when you release the bleed nipple, does the brake fluid come out in a squirt, like it's under pressure?

Check that your flexible brake hose is not damaged or kinked, which would prevent the brake fluid returning to the master cylinder.
It could also be that the master cylinder piston is not returning. Perhaps the push rod from the brake pedal needs adjusting. At rest, there should be a little play between the pedal and the push rod.
Have you lubricated the contact points under the brake shoes where it touches the back plate?
I presume the springs have been reconnected correctly.
And that you have the correct brake cylinder. Bosch?
 
Last edited:
Messages
272
#3
As said above-my thoughts revolve around a damaged flexible hose, particularly as you've isolated the problem to ONE wheel, and not a generic problem with the brakes as a whole. It's this which is making me go for a problem at or near the wheel.
 
Messages
5
Location
Dorset
#4
Come to think of it. When I was re assembling the brakes and after fitting the brake cylinder I opened the bleed nipple to let fluid through before attempting to properly bleed the system but nothing happened. In all other cars I've worked on the fluid flows through by gravity after a few seconds. It wasn't until I applied the brake that fluid started flowing. That would be consistent with a blocked (or partially blocked) hose. I'll take it off and have a look.

Thanks for the input.
 
Messages
5
Location
Dorset
#6
so... Having removed the hose and applied 150psi up the end with my air compressor, with little or nothing coming out of the other end. I think it's pretty fair to assume the hose is fecked.
eBay are turning up some very contradictory results so I've contacted someone who makes brake hoses. I'd assumed the threads were metric 10mm X 1mm but my thread gauges seem to think not. Does anyone know what the threads are? They seem to be 3/8" X 24 UNF (though I can't easily check the thread angle).
 
Messages
272
#7
Be careful.... Brake hoses are a vital part of the braking system and not an area where one should compromise or use guesswork! If I may quote an "old school" garage manager at the V.W. dealership where I learnt my trade all those years ago in the late 1970s..."if you fit the wrong part to the engine, the car stops. If you fit a wrong part to the brakes.......it doesn't!" I'd suggest removing the old hose & taking it to a decent motor factor shop to match it exactly, for length and threads. There's nothing like seeing the REAL thing in the flesh!
 
Messages
5
Location
Dorset
#8
It's okay. I wasn't thinking of winding any old thing in with a bit of PTFE and bowstring tight so it pulled out on a sharp left hander.

I've found a pair of R4 ones on eBay that should fit just fine. Same length and as the wheel cylinders are the same it's pretty reasonable to suggest the threads will match.
 
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