Afternoon all,

Im a bit lost and somewhat disheartened, over the weekend I rebuilt my Dads Brake Master Cylinder (Girling, Non ABS) type with new seals etc etc, BMS was perfect, Re installed and started bleeding brakes, first of all I did all 4 corners with the engine off, old skool method of open valve, press pedal, lock valve , release pedal and repeat, The pedal operator (Mom) reported the pedal to feel nice n firm after plenty of bleeding, no air bubbles in pipes etc etc,

Excellent thinks me.

Sadly not.

Told mom to start the engine,

Down to the floor goes the pedal.............

I then opened the bleed nipple on the drivers front and re bled , no bubbles seen in bleed tube.

Mom reported the pedal felt good.

I then went on to do the other 3 calipers, just because........ again, no air bubbles seen in bleed pipe.

I went to move the car off the ramps today, an lo and behold the bloody pedal would depress straight to the floor with the engine running.

Brake fluid level has not dropped.

Thoughts anybody, at the moment im erring towards a 5.3 litre bbq.

Can anybody confirm the specifics of the bleed process and procedure.

What is the best method of bleeding. i.e right hoof, vaccum, or pressure bleed kit.

Can anybody hazzard a guess as to what may be wrong.

After 3 days graft, the pos is worse than when I started.

 

I think that the fluid is getting past the M/C seals. If so, you must have them incorrectly orientated.

 

I did wonder that,

Does anybody here have a definitive guide for rebuild of a BMS, Girling type, Pre HE, 1980 non ABS, I did look in the manual and the ones pictured all had a double seal on the piston nearest the to the Servo, Dads only had 1 seal when taken apart, and was "okay" before strip down, Dad just wanted a belt and braces rebuild of the BMS just incase. Dads piston is only machined for 1 seal in that location.

 

I would start at the beginning and (no disrespect to your Mum!) verify the pedal feel yourself so you have an absolute reference point.

Engine off, slowly press the brake pedal. At what point does it go hard, rock hard? Hold it there, does it slowly start to fall or does it stay firm?

Press teh brake pedal slowly and then press it quickly again. Does it go firm higher up?

Release and press the brake pedal quickly. Does it stop at the same point, or earlier?

If you've got any variance at all in terms of when the pedal goes hard, start again and bleed all 4 wheel circuits again.

Once you've got a consistent pedal stop point whether pressed quickly or slowly. Turn on the engine and press the pedal slowly. It should go down further but eventually find a stop point. Is the stop point at the same position whether pressed quickly or slowly? After finding the stop point, does it start to fall away if you continue to press the pedal?

If you have no leaks, it's one of 3 things:

1. you still have air in the system - varying stop points when pressed with engine off might signify this.
2. you have failing seals in the m/c. A gradual fall of the pedal to the floor when held down. Or possibly a quicker stop of the pedal when pressed quickly as the seal flares out and catches
3. a problem with the servo. You could have a failing poppet valve o check valve, but the pedal won't go fully to the floor unless you have a problem at 1. or 2.

Good luck

Paul

 

Adding to the above.

Whenever I do the master cylinder rebuild/replace, I ALWAYS bleed the pipes AT the Master Cylinder.

OK, messy, gooey, fiddly, but the amount of air that CAN be trapped in cylinder itself is significant at times.
PLENTY of rags etc to protect the paintwork, and many bottles of water to wash it down often.

Always engine OFF, never had issues.

 

Thankyou all that have kindly responded.

Does anybody have an exploded diagram of the BMS pistons showing the seal orientation ?

Does anybody have a definitive sequence for bleeding ?

Thanks

 

No to the 1st, I just followed working sense. Piston travels DOWN, so lips must face the end of teh barrel.

From my time learning in Mid 60's:

Start bleeding at the nipple the greatest distance from the Master Cylinder, then work back in decreasing lengths.

RHD XJS = LHR/RHR/LHF/RHF, simple and has worked for me since the MK VII days.

My current "pretend Jag", the X Type, is RHD, BUT the Master Cylinder is on the LH side, so:
RHR/LHR/RHF/LHF, still simple.

 

Hi, the attached picture shows the pistons before I removed anything to start the rebuild process, the black piston goes nearest to the Servo, the seals are oriented differently on each piston, this is why I really need a drawing to verify, or somebody that knows, to confirm.

Thanks