Thread: Spongy brake pedal

Hi Tom

I believe that new master cylinder of yours is faulty, try and get hold of another known good one, swap them over and then go through the bleed procedure's once more. My old cylinder in 'Fred' was leaking internally between the primary and secondary brake circuits chambers back into the reservoir. After changing it out with a spare ABS master cylinder and then purging the brake lines of air, I am happy with 'Fred's' brakes once more and the pedal doesn't sink to the floor when vacuum is available.

Bleed off the worst of the air in the lines at the point where the brake lines go into the top of the ABS modulator ( I undid the easy to get to wiring plug going into the modulator, didn't undo the battery), then after bleeding at the modular, I bled each wheel in turn.

I decided that the bleeding tool / pipe from Super Creep Aue-toes was good enough for my purpose and I didn't need to vacuum bleed. This tool works best with the end kept under some brake fluid in a glass jar, so you can then keep a eye open on the air coming through.

a comparison between 'Daisy' a non-ABS model and 'Fred' ABS model, shows that the braking performance is back to how both vehicles were when they were first purchased. 'Daisy' has a firm pedal with excellent brakes and 'Fred' has that slightly vague feel as do all ABS models have and on a loose gravel surface pulls up well, with the ABS modulator jabbing back through the brake pedal.
.

Hi Arthur, it has had two new master cylinders on it. I have my little box of trick which allows me to close/open each valve in the ABS module and when I close off the inlet valves (badly named as these are the valves that open/close the main lines from the ABS module to each wheel) the pedal comes up hard. Cycled the valves whilst holding the pedal down, operated the pump etc in the way described by wabco. No difference. opened pipes at the top of the ABS module and no air. I know there is air there somewhere, but just cannot get it out. Very, very frustrated and disappointed by this.

It has been to a "professional" workshop that originally rang me and recommended that I buy another car and put my drive train into it, then told me it was fixed, when it wasn't. That cost me $836. I keep thinking I must be missing something basic, but I cannot find it. All the pipes are in the right place and it has been manually bled, vacuum bled, pressure bled and reverse pressure bled to no avail. It can stay in the driveway. If I go near it at present, I would probably tqke an axe to it or something like that (swearing doesn't make it work - tried that - lots!).


Tom ,

(swearing doesn't make it work - tried that - lots!).

It's ok my son you can tell me ----- It is after all, early Sunday!!!

It's time we ( The AULRO'ers ) formed a brains trust to drop around and have a look at this recalcitrant Disco of yours. Heck mate! I would come as well but I'm having enough trouble getting funds out of the Mummybank to go to town ( maybe I shouldn't be telling her that I'm going to Super Creep ), so to get up to your place might end up being a one way trip.

I have found that a Brains trust needs at least a number of two, as one only ends up talking to themselves and the replies don't make any sense at all.

Getting back to the master cylinder, two new cylinders did both the same have the same fault or did the air in the line cloud the situation?

I did find that I had a misalignment once on my Defender, when offering up the master cylinder to the booster and it's possible to get the parts together without seeing this. The sideways pressure was enough to still allow some action but I had some weird faults, so I went over my work and gave myself a proper kicking afterwards.

Be nice to have some new glasses to be able to see close up, as I have always been shortsighted and now to find I have short arms as well is a bit disconcerting!
.

I will try one more thing, a combination of technical skill and basic "mechanicing". I will attach my box of tricks to the abs module and do one or two things. Both will involve opening the outlet valves. These are the valves in the abs module that stay closed during normal operation. When the ABS pump kicks open they open and the inlet valve closes, hence releasing pressure to the calipers. I will leave them open overnight to let any air rise to the top. I will then reverse pressure bleed from the wheels and try release the bulk of the auir by cracking open the pipes at the top of the abs module.

I am absolutely certain that the problem is in the ABS module. So one last try.


Tom.

Hoo bl00dy ray!!! Brakes fixed!!!

In the meantime I bought a 97 300tdi auto Discovery that hasn't missed a beat. That gave me the opportunity to look at the brake problem whilst I had the Disco in my driveway. One workshop that had a go at fixing it mentioned that they had to reverse the Proportioning valve as it was on backwards. They said it was fixed. Crap it was. Same problem. Manually bled the brakes until a nice firm pedal, but when started the pedal would sink to the floor. With this in mind, I used the old front brake lines to bypass the proportioning valve and voila! Problem identified.

Purchased new proportioning valve, manually bled the brakes and used my box of tricks to bleed the ABS module and then started it. Good firm pedal!!! Just tidfying up a few things on it for rego. Once it is registered, I will sell the 97 Disco.

Cheers,
Tom.

P.S. I actually fixed this on Christmas Day as a present to myself. A happy camper!

I'm pleased as well, as that problem led all of us on a merry chase.

A well deserved Christmas present for you.

.

P.S. I actually fixed this on Christmas Day as a present to myself. A happy camper!

In celebration did you stand by the disco and fist pump or run around the yard screaming like a maniac.

That's good to hear. I've been trying to get the brakes on mine right and it's come down the proportioning valve being the only thing it could be.

It's got rebuilt calipers, discs are good, new pads, new master cylinder, servo and braided lines and been bled multiple times. It's driveable and passed a rwc but you have to drive within the limitations of the stopping power it's got.

Got a new proportioning valve sitting there waiting to be fitted. Hopefully it will fix my problems as well.