The 75 and ZT Owners Club Forums - Bleeding brakes a warning

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- - Bleeding brakes a warning (https://www.the75andztclub.co.uk/forum/showthread.php?t=63314)

This is really interesting I have changed the rear calipers pads and discs on my wifes ZS and have exactly the same problem. Been bled on five occasions now and only ever improved by a very small amount. First application of pedel is poor second you get normal pressure and good effort. I'm off to find someone with a testbook !!!!!

I have played around with my brakes a lot trying to get them to work. Replaced front caliper and ABS but no fluid flowing to any calipers....

In the end I ran out of time and patience so took the car to Corin as he has a T4 to do the job correctly (master cylinder replaced now). Today I held the brake on whilst sitting at lights and noticed NO SPP (pressing the peddle harder then needed to hold the car stationary) .......... Was just a quick thought that went through my mind when I was sitting at the lights.

I will try to remember to do a more thorough check when I next use the car which may be a week or two.:shrug:

Can't imagine where the fluid can be going? 2 thoughts...
1/ Master cylinder is leaking fluid passed the seals (old escort did this before it lost brakes completely):mad:
2/ Air in the ABS secondary cct and fluid is seeping passed the ABS valves letting the peddle fall.

Brake fluid does not compress so it must be going somewhere!:D

I picked the car up this evening and the brakes do not seem to have any sinking pedal problems.
I had always wondered about this but it seemed to be 'normal' from reading various threads. Now I am not so sure.:shrug:

Maybe Corin has a trick? :D

Quote:

Originally Posted by BigRuss (Post 657977)

There are two bleed methods on the menu system on T4 one of which is for use when the ABS modulator has been replaced.

I agree.

The procedure which is suggested after replacing the ABS modulator tells you to bleed a caliper, press continue on the T4, and firmly press the brake pedal, while the ABS modulator starts buzzing and the caliper is bled. The bleed screw can be closed after the buzzing stops. The same procedure for all 4 wheels.

Hi.
I have recently retired from 20 years running a UK company manufacturing power brake bleeders. We supplied Snapon with them at up to 50 per month, and also designed and supplied high performance bleeders to all of the F1 teams, together with companies like Aston Martin, Ferrari, Jaguar, JCB and many others. Many of these bleeders were used in production where systems were first filled from dry on the line, and this problem with ABS systems was a common one.
Obviously a number of different ABS systems were involved, so the solutions were not always the same, but there always was a solution and in the 20 years I was with the company, we never failed to find it.
Having recently had the pleasure of solving this problem on my son's Rover Tomcat, I would expect that as the systems are very similar, the solution should also suit the ZT/R75. (I haven't needed to bleed my ZT as yet!)
The solution on his vehicle, which was initially due to the fitting of a very high specification upgrade, and therefore requiring a new fill from dry, proved also to be just as effective when parts of the system had been changed due to experimentation etc.
We bled it with an electrically powered bleeder, with the vehicle ignition switched on during the process, in order to open the internal ABS valves.
The flow rate of the bleed operation was quite slow because a relatively low bleed pressure was employed (around 20psi.) to help prevent any changes in the ABS valve positions during the operation.
Some vehicles, depending upon the actual ABS system (or manufacturer) require that the engine is actually running during the bleeding operation, but this was not a requirement with the Tomcat.
This procedure is what we advised most garages who encountered the problem, and especially Rover, Honda and BMW, and there were rarely any problems afterwards.
Not every owner will have a power operated bleeder available for use, but the procedure should be effective with manual bleeding and also with vacuum operated bleeders and the likes of a Gunson Easybleed.
Remember that high bleed pressures could change the ABS valve positions and effect the results adversely, and what is required is more a smooth and steady pressure.

I hope this proves helpful and will try to answer any question regarding bleeding either here or by PM.

Quote:

Originally Posted by derek999 (Post 693718)

Sounds very interesting. To be clear are you saying that by using a Gunson Easibleed at a pressure of about 20PSI with the engine running, the ABS system should be effectively purged without the use of a T4? Does the pedal require to be pumped at any stage during this process?

If you're using an easy bleed don't run it off the spacesaver as they are approx 60psi ;)

This is far too high a pressure to do it, as recommended above, a pressure of 20 psi is sufficient.

Deflate a tyre to approx 20 psi (spacesaver or normal wheel) before connecting it.

Russ

I always recommend using the lowest pressure possible but 20 psi. is a good start. Try with just the ignition switched on to position 2, running the engine is only required in certain circumstances and particular ABS types.
Derek

Very intersting read as I have had 2 brand new Ford Transits with ABS and they both suffered from sinking brake but the other 2 I had didn't have ABS and brakes didn't sink. So looks like Ford may not be able to get it right from new, but the good old 75 and 25 before it both with ABS the brakes were as hard as rock. So looks like Rover could get it right more than can be said for ***** Ford (I have never had a good Ford 7 of them all useless).

My only Ford was an XR3i back when they were a fast car... 100K miles and only 2 things ever went wrong. Master cylinder gave up the ghost and the car refused to start once. Was the only year I have ever had the AA and he new exactly what it was. Cleaned two contacts on a relay, fuel pump came back to life.

We all know that fluids don't compress so where is it going? Leaking past the master cylinder seals? Or finding somewhere to hide in the ABS pump?
Mine now seems fine but both my ABS pump and master cylinder have been replaced so no idea which was causing it.