Possible brake master cylinder problem

[solarman216]

Dave (kitchenman) no it is not surprising that you cannot produce pedal sinking with no vacuum, you should try stopping your car with no vacuum, and compare that with when you have it, you can get nowhere near the same braking effort even if you are a big strong guy, hence the low effort imparted on the master cylinder is not enough to cause sinking/creep, but that is no guide to the integrity of your master cyl, to do this it needs to be operated under normal conditions ie with vacuum, even if you have ABS, on your model as opposed to Rayf you still have a servo, more modern ABS does not, it uses the ABS pump instead, Rick

 

[solarman216]

Ian (ogri) still nonsense I am afraid, max vacuum that can be achieved down here on earth is around 29hg (inches) or 14.6 something in -psi none of which will be available on a petrol (inlet manifold) or diesel (vac pump) just sticking with inches max on average on a petrol engine is around 27 a vac pump is unlikely to get much higher, but even if it got to 29 the difference is so small that this idea of "over assist" is not worth mentioning, Rick

 

[solarman216]

Ian, just read your link, mixed up people, ""The interesting results are the ones with the engine running. With a normal effort exerted on the system the pedal kept creeping virtually to the floor increasing in pressure until it reached 2800 psi. The pedal creep is often mistaken for a master cylinder problem, which it obviously is not, as witnessed by the 800 psi pressure increase!!""

now if the pedal is going down on a normal T2 system the pressure has to reduce not increase especially with "normal pressure" what is happening here is the ABS pump is taking over and producing confusing results, there is no way the pressure can increase under normal T2 conditions, so I stand by what I have said all along, on an older T2 system if your pedal sinks you have a problem, best regards Rick

 

[rayf3262]

Throwing another variable into the mix:
Many assisted braking systems use a "reactor plate" this is included to enhance pedal feel.
The reactor plate is often made from compressible rubber.
Maybe this is the element that is accomading the additional pedal travel under extended pressure?.......

 

[solarman216]

Throwing another variable into the mix:
Many assisted braking systems use a "reactor plate" this is included to enhance pedal feel.
The reactor plate is often made from compressible rubber.
Maybe this is the element that is accomading the additional pedal travel under extended pressure?.......

Mmmmm doubt it, for the pedal to sink the fluid has to be going some place/recirculated, your reactor plate resembles a rubber ball that you squeeze in your hand but it does not stay small/compressed when you let go, Rick

 

[AlexD333]

I don't know if this is at all relevant but I have noticed when I stop at junctions and traffic lights with foot on brake the pedal will push back after a few seconds :nenau. I have a 2004 abs model... :nenau

I have never noticed this "creep" on mine.

 

[kitchenman]

Ouch

Local factor price of Master Cylinder £130 plus
Local Ford main agent if available £214 inc vat
As the car is stopping well and pedal takes around a minute to get to the floor I am going to put things on hold until I hear more from Rick as many other members report similar 'creep'
In the meantime I will be checking the price at Milners

 

[kitchenman]

Update

Milners price £132 inc vat
Seal kits do not seem to be available
Local Ford spares suggested a firm called Past Parts they say Master may be available if so around £150

 

[micktheshed]

Just a thought...
Had this 'sinking peddle' symtom (as opposed to 'spungy peddle' which usually indicates air in fluid or deflecting servo mount/cracked bulkhead) on 2 prievious cars (1 petrol & 1 diesel) & was, finaly (doh!) told by mecky that it was most likely a vaccuum leak in the pipeline (porosity?), one-way valve, or faulty servo. In the case of diesel it could also be the vacuum pump.
Re- built the master cylinders on both (& caliper piston seals on the petrol) but, unfortunately, I never got to the bottom of it, However, the petrol 1 did improve a lot after, as a last resort, pressure-bleading the brakes. It can be quite difficult to remove all traces of air or old fluid (which may be contaminated with water) compleatly from the front pot areas. I always use a full Litre of fluid to give the system a good flush-out.

If the peddle stays firm with engine off this surely eliminates master cylinder seals leaking?

Best of luck with it.

 

[solarman216]

J

If the peddle stays firm with engine off this surely eliminates master cylinder seals leaking?

Best of luck with it.

Fluid pressure (I have not measured it but otheres have) with no vac seems to be around 800 psi, with vac 2000 plus, as to the nature of the seals and the valve disk behind (as my post) lower pressure with no servo does not seem to be enough to leak past the point on the seal that is on the piston, but clearly high pressure can, as said the roughness of the machining at this point means it cannot be designed to seal here but at the steel valve washer that after 100k has scored and so now cannot seat correctly, hope that explains it a bit better, as said I will rebuild the cylinder in the pics but without the disks and test, but I have to say the seals are near perfect, the only sign of wear is the disks, report later, Rick