Strange brakes??

[JIM 2B]

Its a strange one for sure, has anyone any ideas??  800miles ago i have replaced the master cylinder all the brake pipes / slave cylinders with new items and fitted stainless flexi pipes.  :)

 Bleed the system no problems.... then used on the road for 600 miles no problems then when decending a hill one day and braking to stop from 40mph at about 30mph when i depress the brake peddle a little more it seems to be solid and has not reached full travel as though some thing is wedged under the peddle.

I press even harder  with no affect so i lift my foot thinking to pump the brake! and again it starts to brake again and then becomes solid again with both feet on the pedal pressing hard and a fast heart beat it eventualy stops..  :shock: scary for sure... the brakes where deffinatly not slowing me down 

I have looked at the peddle addjustment and it is correct there is no fluid leaking from anywhere and the slave cylinders and shoes are all ok.. i have bleed the system again no air in system.. :?

This has only happened on two occasions going down a hill and the brakes work perfectly fine at all aother times even locking the wheels up :lol: in fact i would say they work better than i expected.

But im worried that this may happen again in the wrong place at the wrong time when i need them most

I have had the brakes tested on a rolling road at my mates truck depot and they are perfect :? no problems and they appear to still be working as good as ever...

Has anyone ever heard of or had an intermitant falt on a master cylinder piston jamming :? as this is the only thing i can think of???????????? :|

[electricbluebadger]

Are they servo assisted??

Cheers Steve

[JIM 2B]

Hi yes its servo assisted it is a remote servo and the servo has also been fully serviced with new seals etc  :)

umm could it be the remote piston sticking?????

[Singlefin]

Could it be the butterfly in the air intake not closing? That'd mean there's not enough vacuum for the servo to work.

[JIM 2B]

Hi, i take it you mean the butterfluy in the carb.. the carb definatly shuts off ok and i thought when the butterfly was closed it would increase the vacume for the servo as it has no where else to get air from

its as though the peddle has reached its full travel and is solid but the brakes are only half on :? but after stoping and then re trying the brakes they are fine until it randomly happens again its quite frightening

[Singlefin]

Hi, i thought when the butterfly was closed it would increase the vacume for the servo as it has no where else to get air from

Exactly, so if it's not closing for whatever reason, that'd do it. I discovered this when I used the hand throttle to keep the engine at a *fast* idle when it was cold - butterfly stayed open, brakes didn't work. Cue excitement!

[JIM 2B]

Thanks i take your point, its hard to say if it was stuck open at the time i was panicing so much  trying to stop it has the six cylinder engine with an su carb on it definatly closes ok as it has huge spring on the linkage at the carb! and would i not notice the engine revving if stuck open..

[JIM 2B]

Hey Singlefin ...... :D :D i think you have it  :-k

i just remembered that the servo hose sometimes has appeared to have slightly colapsed under the vacume on tick over....... i now think that this could be the problem :D

when im brakeing and the butterfly has closed the vacum must be increaseing so much it is colapsing the pipe and the servo is only working for a short time until it runs out of vacume...due to the colapsed pipe... :-k
 this would be why it is unnoticable on the rolling road test as there is no engine braking and the vacume created is not enough to colapse the hose and shut off the vacume to the servo .....

Thanks for your help  :clap: :lol:

[Range Rover Blues]

Either the servo isn't working or, if you are correct that it's reached it's full travel then you have either loose wheel bearings (not sure if it has the same effect on your drums as on disks) or a collapsing adjuster somewhere.