Complete brake failure - urgent advice needed
Discussion
Got into the car this evening having not driven her for 2 weeks and experienced the following problem:
1. Engine off - good brake pressure on the pedal - handbrake works, good fluid level etc;
2. Switch engine on - brake pedal goes to the floor, no brakes at all !!
I suspect it is an electrical problem - maybe the servo. Can anyone advise - I am meant to be having have a meeting with the MOT man tommorrow morning.
Many thanks in advance.
1. Engine off - good brake pressure on the pedal - handbrake works, good fluid level etc;
2. Switch engine on - brake pedal goes to the floor, no brakes at all !!
I suspect it is an electrical problem - maybe the servo. Can anyone advise - I am meant to be having have a meeting with the MOT man tommorrow morning.
Many thanks in advance.
GOd that's pretty alarming. Definately NOT electrical, system is hydraulic and vacuum operated, no essential (to operation) electrical components in the braking system. Are you loosing fluid, any puddles on the floor indicating fractured brake line, mosy likley around wheels (hose gone or caliper seals gone). If no leakage and reservoir full, most likley master cylinder seals. With the engine off and the servo not functioning the pressures you generate in the system when pressing the pedal are quite low (ever tried driving with a failed servo ..?!)and maybe insufficient to reveal a leak past dodgy seals or force fluid through small defects, might explain reasonable pedal feel with engine off. Cant really think of anything less serious to explain the symptoms i'm afraid. Anyone got any other ideas? Let us know what you find.Master Cylinder seal failure? Servo leaking big time?
Check the hose from the inlet plenum to the servo hasn't perished - they can do this. Check it's attached at the servo end.
Does sound like a master cylinder prob to me though. is there any fluid leaking around the pedal box srea (probably onto the footwell carpet).
Whether it's the servo or the master cylinder, they're both a sod to get at.
Check the hose from the inlet plenum to the servo hasn't perished - they can do this. Check it's attached at the servo end.
Does sound like a master cylinder prob to me though. is there any fluid leaking around the pedal box srea (probably onto the footwell carpet).
Whether it's the servo or the master cylinder, they're both a sod to get at.
Many thanks. No fluid leaks that I can see but then again if its the master cylinder/servo its not that easy to see. Can the master cylinder be working one day and then complete failure the next? Good job it did'nt let go whilst I was driving!
Its booked in to Dave Batty for a service on Monday - so I will post the diagnosis on Monday night. Looks like its going to be another trip on the low loader - but I still wound'nt swap her.
>> Edited by tadpole on Saturday 24th July 09:25
Its booked in to Dave Batty for a service on Monday - so I will post the diagnosis on Monday night. Looks like its going to be another trip on the low loader - but I still wound'nt swap her.
>> Edited by tadpole on Saturday 24th July 09:25
If fluid has leaked from the master cylinder, (or anywhere else )there will have been loss of fluid from the reservoir. Even if the seals are leaking you will usually only tend to get a slowly sinking pedal on firm pressure (with the brakes working - until you run out of pedal travel)for some time before complete loss of resistance. Pedal going straight to floor means, either: No fluid in reservoir and master cylinder empty (pretty easy to diagnose), or a catastrophic leak somewhere, which again should be fairly obvious and again a rapidly emptying reservoir.
You said your fluid level was ok and I presume that means you haven't been having to top it up recently. With an integrated servo / master-cylinder it is quite true that fluid leaking from the push-rod end of the servo will end up in the servo body (and in extreme cases can fill this up and end up being sucked into the inlet manifold and burnt, with lots of white smoke !). This means there may not be any obvious leak externally, but the reservoir will still tell the tale of lost fluid.
The only explanation i can think of is where (with a dual circuit master cylinder) one or other of the main seals (on either the primary or secondary piston) has failed and fluid, which should be being forced into the respective braking circuit, instead leaks past the seal and then escapes, not by leaking but by being contained by the secondary seal and simply pushed back into the reservoir, creating a flow of fluid in a closed loop instead of pressure to that set of brakes. In that case the pedal will sink until either: the primary and secondary piston contact each other (if the primary main seal has failed) or (vice-versa) the secondary piston meets the end of the cylinder bore. The resistance in the brake pedal which is then met, isn't the end of travel, but pressure being generated in the intact circuit (hence the whole point of dual-circuit brakes).
I assume, without having checked, that the Chimaera / Griffith have front / rear split brakes (would have to really since only one piston at each corner). I would expect (without actually suggesting that you should try it..) that pressing the brake pedal as far as it goes, will in fact operate either the front or rear brakes in isolation, although it will feel as if there are no brakes initially since the pedal travel will be very long.
I've had this exact thing happen on my XJS years ago - (master cylinder overhaul, with new seals and honing the bore - to get rid of the locallised pitting responsible for the failure - and hey presto still going strong 13y later and cost about £10 and some time).
>> Edited by tahiti450 on Sunday 25th July 20:11
You said your fluid level was ok and I presume that means you haven't been having to top it up recently. With an integrated servo / master-cylinder it is quite true that fluid leaking from the push-rod end of the servo will end up in the servo body (and in extreme cases can fill this up and end up being sucked into the inlet manifold and burnt, with lots of white smoke !). This means there may not be any obvious leak externally, but the reservoir will still tell the tale of lost fluid.
The only explanation i can think of is where (with a dual circuit master cylinder) one or other of the main seals (on either the primary or secondary piston) has failed and fluid, which should be being forced into the respective braking circuit, instead leaks past the seal and then escapes, not by leaking but by being contained by the secondary seal and simply pushed back into the reservoir, creating a flow of fluid in a closed loop instead of pressure to that set of brakes. In that case the pedal will sink until either: the primary and secondary piston contact each other (if the primary main seal has failed) or (vice-versa) the secondary piston meets the end of the cylinder bore. The resistance in the brake pedal which is then met, isn't the end of travel, but pressure being generated in the intact circuit (hence the whole point of dual-circuit brakes).
I assume, without having checked, that the Chimaera / Griffith have front / rear split brakes (would have to really since only one piston at each corner). I would expect (without actually suggesting that you should try it..) that pressing the brake pedal as far as it goes, will in fact operate either the front or rear brakes in isolation, although it will feel as if there are no brakes initially since the pedal travel will be very long.
I've had this exact thing happen on my XJS years ago - (master cylinder overhaul, with new seals and honing the bore - to get rid of the locallised pitting responsible for the failure - and hey presto still going strong 13y later and cost about £10 and some time).
>> Edited by tahiti450 on Sunday 25th July 20:11
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