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[Olympia5776]

I did a search on this and found a couple of threads relating to it but there was never a definative answer.
I bled the system through last year replacing the old brake fluid . I noticed after the bleeding process that when engine off the pedal was rock hard within 1/2 inch travel , however when engine was strted the pedal became progressivly softer and if pressed HARD it could be made to travel almost to the floor.
Now it has to be said that the brakes still operated fine arresting and stopping the car way before the pedal got anywhere near the floor it also passed it's annual NCT ( MOT) test with an efficiency of 70%.
I've just went through a bleeding excercise again to try and eliminate the travel but the issue still persists with the same symptoms .
All calipers are free ,pads and discs are  well within spec ( Haynes manual ) . and the fluid is correct and new. Normally I'd suspect the MC but due to the fact that the pedal is solid when engine off casts doubt on that diagnosis.
I've bled the brakes in the correct orientation with an Eezibleed and the normal two person method and have used a considerable anount of fluid to try and ensure that there is no air in the system.
It has definatly only occured since I replaced the fluid and was not like that before.
I have no problem replacing the MC on my manual car but I'm wondering if anyone has experienced this and has a definative answer to it. Could it be air in the ABS pump or flexis balooning ?

[Bigron]

Increased pedal travel after starting the engine is normal; if iy did not do that, there would be something wrong with the power assistance system!
However, continued creep, almost to the floor, is not. I would suspect tired seals in the master cylinder, allowing brake fluid to creep back when you apply pressure.
As you seem to have done everything else, it's well worth getting a repair kit and refurbishing the master cylinder. Check the bore for scoring, though, because if there's significant scoring, the master cylinder will need to be replaced.

Ron.

[Olympia5776]

No kit availble for the B series Omega Ron , new cylinder only.
I'm still not convinced that it is the MC as the pedal is solid when engine off ,I've had faulty MC seals before on other cars and rebuilt many an MC. E Bay items are available for circa £50 .
Don

[Doctor Gollum]

I wouldn't worry about it tbh... there's constant vacuum assistance all the while the engine is running. It is actually the vacuum drawing the partially pressed pedal from under your foot rather than fluid leakage... as bourn out by the fact that the pedal stays firm if pressed and held with the engine off

[cam.in.head]

if the pedal travels slowly down to the floor and there are no leaks / no drop in level AT ALL then its got to be the master cylinder.any other symptom causing a level drop would be a leak somewhere.either visible from anywhere external or out of the back of the master cyl into the servo cavity.
omega brakes when functioning correctly are not the most solid of pedals and due to the slight retraction of all the pistons to provide a running clearance this can create a fair bit of initial pedal movement before anything happens.

[Kevin Wood]

Yep, pedal movement = master cylinder movement, so fluid is being displaced somewhere. If it's not leaking elsewhere in the system, then it's getting past the master cylinder piston seals which doesn't result in a leak because it just leaks back to the reservoir side of the piston.

[BazaJT]

Sounds similar to the problem I had on mine.I bought a couple of hose clamps from Halfords[£6-ish each]and clamped off the brakes at the rear then tried the pedal,then clamped off the front brakes and tried the pedal.I found that the problem was with the rear brakes[if I'm remembering rightly]although I overhauled the fronts as well to be on the safe side and the pedal is now firm.I too had suspected the master cylinder to be at fault but that wasn't the case in this instance.

[robson]

So you must have had a leak of fluid at the back?

[BazaJT]

No no leak anywhere it was the rear calipers/pads .Best way I can describe it that pedal was pushed piston pushed brake pad and "bent" the disc towards the other pad.Removing the pads,cleaning up the calipers and ensuring all parts moved as intended restored the pedal performance.

[cam.in.head]

this would indeed cause an increase of travel but not a steady drop to the floor. if the op is definately having a steady drop to the floor but no fluid leaks anywhere then it must be master cylinder .

[Bigron]

Ahem, see reply No. !.....

Ron.

[Olympia5776]

I'm still sceptical about it being the mc .
Engine off the pedal is solid with no discernible travel , only when the engine is running does the issue occur. Seals in the mc would pass in both cases as all a servo does is assist the piston within .
I should say that the pedal never actually reaches the floor it. firms up maybe just under midway.
I feels like it is over servoing .
No leaks anywhere and I have checked that all pistons are free by removing pads and substituting plywood sections slightly  thinner than the pads to witness the movement.
Ì'm going to isolate the front and rear brakes by clamping the flexibles to see if that throws up anything and eezibleed a couple of ĺitres through it ..........
Many thanks for all your input , so far !
Don

[cam.in.head]

ah . in that case i would say there is nothing wrong. i was under the impression the pedal kept going down. if you are sure all your caliper pistons are free and retract slightly as they should and that the front slider pins are free then i would not worry. the first part of movement of the pedal has to take up these clearances first before even gripping the discs and omega pedals will never be solid with little movement because of this(or other cars for that matter)in fact if you drive a car with a very solid feeling brake pedal with little movement i would expect there to be a piston or two seized
other things that could increase the initial travel are
air still in system
brake fluid u/s
swelling hoses under pressure
brake pad lining lifting off of backing pad or very corroded or uneven/bent shims
loose bolts or other mounting issues between servo and /or bulkhead(unlikely)

you could try clamping off sections as you were going to and if you clamp off all 4 then you would expect the pedal travel to be very little.this will eliminate any thoughts of air in the system right up to where you have clamped .then unclamp a carner at a time and see if any section has more travel than each other.if so you will know where to look or re bleed but i suspect everything will give balanced results.
cheers hope this helps

[Olympia5776]

Juat a little post script to this thread .

As I said earlier I was never convinced that the problem was being caused by the master cylinder as the pedal was firm when engine off.
So the problem, or symptom really , was being caused by expansion somewhere in the system when the additional servo assistance was being applied when engine running . The only items that would account for this would be the soft walls of the flexible hoses .
So this morning I fitted two new flexibles to the front brakes and the creep has been eliminated and a firm assisted pedal reinstated . The pedal is what I would describe as normal now ,ie the same as the other cars in the fleet.
I guess after 20 years there was just enough "give " to require more movement of fluid hence the pedal creep.
I've just ordered two rear flexibles to complete the system overhaul  .
Worth considering when these cars are as old now and not expensive either .
Don

[BazaJT]

Glad you've got it sorted and it's always good to hear how problems have been overcome so that others can learn of fixes