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2006 Scudo hdi
I had a soft pedal and osr and nsf wheels had locked up
So I have replaced the master cylinder
I bled the cylinder then bled the brakes
For the first couple of miles they're fine but then the fronts begin to bind
If I loosen the front most brake line in the cylinder they free off but lock up again in a mile or so
I think I've read that the rod going into the back of the cylinder may not be retracting or needs adjusting?
I'm not sure and I am a bit stuck now
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Not sure of pipe routing on these, but if it's locking both fronts surely you've got a master cylinder fault because of split? How many pistons in front caliper? Silly thought, you've not flattened a brake pipe accidentally?
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It'll most likely be that the pedal pushrod is too long or the stop on the pedal is holding it slightly down.
In short, the inlet port to the cylinder is being covered by the non-return valve/rubber so you have a captive amount of fluid. As you drive the slight drag on the pads and any further braking heats the captive fluid that now has no room to expand back to the reservoir, so the brakes drag more, creating more heat and it's a vicious cycle until every gets do hot and bound that the car might not even drive. Let it cool and all fee's off.
If you can shorten the pushrod slightly or adjust the pedal stop to give a very little free play in the linkage it should sort it. Likewise checking the spring is well worthwhile too.
I'd bet the rears might be suffering too, just that they're not as efficient brakes so won't be as effective or create as much heat into the fluid, also the longer pipe run (fluid volume) will act like a spring and reduce the effect at the rear.
I had this issue on my imp years ago and it was a mis-matched radius on the end of the push-rod and master cylinder, the linkage was free, but when assembled the slight angle of the push-rod would be effectively depressing the master cylinder piston and closing off the fluid inlet port.
I re-rpofiled the end of the pushrod with it mounted in a pillar drill spinning a shaped it with a file.
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Rich
Club Retro Rides Member
Posts: 6,237
Club RR Member Number: 160
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Not sure of pipe routing on these, but if it's locking both fronts surely you've got a master cylinder fault because of split? How many pistons in front caliper? Silly thought, you've not flattened a brake pipe accidentally? Dual circuit brakes generally don't work like that. Modern circuits are a front linked diagonally to a rear so you if you have a failure on one circuit you retain a front and an oppositely linked rear to help keep the car stable. I know some older dual circuits were split up oddly, but the general rule is a front and a rear. I think Good Scrap is on the money here with the fault relating to all the brakes.
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Not sure of pipe routing on these, but if it's locking both fronts surely you've got a master cylinder fault because of split? How many pistons in front caliper? Silly thought, you've not flattened a brake pipe accidentally? Dual circuit brakes generally don't work like that. Modern circuits are a front linked diagonally to a rear so you if you have a failure on one circuit you retain a front and an oppositely linked rear to help keep the car stable. I know some older dual circuits were split up oddly, but the general rule is a front and a rear. I think Good Scrap is on the money here with the fault relating to all the brakes. In a roundabout way that's what I was trying to say, my experience is with 4 pot front calipers, hence the confusion in it being both fronts
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Aug 17, 2019 22:04:12 GMT
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I've been thinking about my next move
We isolated the problem to too much pressure in the master cylinder, we think caused by the pin not retracting fully
To get to the pivot points the engine needs lowering and this is where I've run out of time and interest. Quite a few other things need sorting for the MOT so this is where the van meets its end
Thanks for your help & suggestions
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Know that feeling, I've just dumped a focus for similar reasons, makes a change for me, I usually plough on getting further and further into it, spending more money and time for no results. Maybe we're all getting better at cutting our losses?
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