RRC ABS issue. Help please.

[Pacemaker]

Hi Everyone,

I have a 94 softdash with a brake pedal that goes to the floor when it feels like it.

I have bled the brakes following Rave. I used approx 2.5 ltrs of fluid and the brakes were good for about a minute. Mind you the vehicle was not driven at all. Its been on stands since I bought it.

I can start the car up and the pump will run for approx 30 seconds and then shut off. I can hold my foot on the brake pedal for 15 seconds and the pedal will feel good. Then all of a sudden it slowly sinks to the ground. Lift my foot off and straight to the floor again. If I give it a few pumps the pedal goes firm again. It might be firm for a minute or so then the pedal sinks again. It cannot be driven in this state.

When I was bleeding the system the manual says to bleed the lower front 4 nipples at the end of the bleeding process to bleed the master cylinder. What I found was I could bleed the inner nipple and eventually get all the air out. Then bleed the outer nipple. If I re checked the inner nipple the line was full of air again. This happened over and over again. Is it possible the master cylinder is sucking in air somewhere??

Thank you.

[benji]

Within the fluid reseviour there's a partition, and fluid must be on both sides of this.
I've also had blockages at the bottom of the fluid reseviour that's restricted flow into the matter cylinder too...

I can't be of much more help I'm sorry.



Sent from my SM-G900I using AULRO mobile app

[sierrafery]

IMO you need a new master cylinder

[Vern]

Pull the abs unit out, place it in the bin, install vacuum booster and master cylinder😊

[discorevy]

IMO you need a new master cylinder

(X2)

[DoubleChevron]

This could be normal. Try it any modern car with ABS. My wife poogoe 407 brake pedal will slowly go to the floor if you apply constant pressure. Google it, it appears to be normal behaviour across a range of vehicle. Certainly it worried the crap out of me after I did brake work on the car (I'd never noticed it happens prior to that .... and had forgotten until you mentioned it above).

seeya,
Shane L.

[Pacemaker]

Thanks everyone.

So the t piece above the rear diff is now leaking plenty of brake fluid all over the diff. I will fix it this weekend and see if that's where the air was being sucked in.

I hate abs and how it feels during emergency braking and off road but I'm if I can fix what's there without spending much money I will deal with it.

I will check all the filters that can be cleaned as the fluid was very dirty. I will update after I've cleaned the filters, fixed the leak and re bled the system.

Cheers.

[discorevy]

[QUOTE=DoubleChevron;2517988]This could be normal. Try it any modern car with ABS. My wife poogoe 407 brake pedal will slowly go to the floor if you apply constant pressure. Google it, it appears to be normal behaviour across a range of vehicle. Certainly it worried the crap out of me after I did brake work on the car (I'd never noticed it happens prior to that .... and had forgotten until you mentioned it above).



This is not normal , I reckon your wife might want to take her car somewhere to get the brakes repaired , before she comes to grief, Google will probably tell you anything you want to hear depending on how you word it.

[schuy1]

This could be normal. Try it any modern car with ABS. My wife poogoe 407 brake pedal will slowly go to the floor if you apply constant pressure. Google it, it appears to be normal behaviour across a range of vehicle. Certainly it worried the crap out of me after I did brake work on the car (I'd never noticed it happens prior to that .... and had forgotten until you mentioned it above).

seeya,
Shane L.


That behavior is NOT normal. If thats happening there is something wrong. The ABS does not bleed off pressure, it only pulses a particular brake unit in response to slippage input. At all times there should be constant braking available, even without vacuum assist, albeit much more effort required . There may be a faulty ABS unit though.
Cheers Scott

[Pacemaker]

This situation is definitely not normal. I can be sitting at the lights with a good pedal that has efficient stopping power then all of a sudden the pedal goes to the floor and the brakes don't work. The pedal might work well for 2 stops in crawling traffic and the the 3rd stop the pedal goes to the floor and the car barely stops.

As I said earlier I'll update after I've fixed the leak and re bled it.

Cheers.

[Tins]

This situation is definitely not normal. I can be sitting at the lights with a good pedal that has efficient stopping power then all of a sudden the pedal goes to the floor and the brakes don't work. The pedal might work well for 2 stops in crawling traffic and the the 3rd stop the pedal goes to the floor and the car barely stops.

As I said earlier I'll update after I've fixed the leak and re bled it.

Cheers.

It's a closed system. If air is getting in then fluid must be getting out, and of course if fluid is getting out then air WILL be getting in. Fluid gets out by passing worn or failed seals in the calipers, burst or damaged hoses, loose connections or cracked or damaged pipes. ABS modules just create more potential for leaks, but all leaks should be obvious if you look close enough. Oh, and the master cylinder can leak of course, but that's visible as well.
Is the level dropping? Brake fluid level should only drop to compensate for pad wear, nothing else, so if it has fallen noticeably then you have a leak.
The pedal can go to the floor without a leak if the main rubbers have worn, but it would be unusual for that to happen without a leak being created as the back seal will struggle to cope as the pedal comes up.
So, fix ALL leaks and bleed it. If it still happens replace the master, as a couple of folk suggest.
As for it being 'normal', I don't claim expert status, but I know that if I was driving a car and the pedal went to the floor I would stop driving it immediately.

[aRRon]

Ditto Johntins comments and adding I too am no brake expert let alone with the deeper mysteries of the Wabco ABS system. I am about to go outside and replace the braided hose between the electric brake pump and the accumulator for the second time in six weeks after the first one burst with brake fluid sprayed everywhere and the second one leaked from new.
I have been through the elaborate total bleed sequence too without any problem, however interestingly one of the rear axle brake hoses developed a leak straight after the above and replaced both, getting away with bleeding just the rear calipers.

I've wondered about the mysterious internals of the master cylinder/booster unit and the mother of all RR classic nightmares - replacement cost of $5K upwards. Yet never in reading these posts for eight years has anyone reported a total failure of the master unit nor has anyone (that I've noticed) ever reproted on its internal construction or reconditioning of same. I've also never read of anyone experiencing a leak of brake fluid into the vehicle interior as you'd expect from the conventional master cylinder rubbers wearing.

My 89 Vogue WABCO unit has done 270k without a problem but I guess yours could be a first. Some speak of replacing everything with the non ABS system which involves replacing brake pipes etc but also contravenes the laws about mods. Suely someone could help with a serviceable second hand unit from a wreck - even to borrow and change it over and test if problem disappears.

Having mused about all the above, is it by any chance possible that the bleeding of the two hydraulic boosters on the side of the master cyl unit has not properly dispelled all the air inside? Is the reservoir to master cylinder port clear so fluid can flow to and return from the master cylinder?

[DoubleChevron]

[QUOTE=DoubleChevron;2517988]This could be normal. Try it any modern car with ABS. My wife poogoe 407 brake pedal will slowly go to the floor if you apply constant pressure. Google it, it appears to be normal behaviour across a range of vehicle. Certainly it worried the crap out of me after I did brake work on the car (I'd never noticed it happens prior to that .... and had forgotten until you mentioned it above).



This is not normal , I reckon your wife might want to take her car somewhere to get the brakes repaired , before she comes to grief, Google will probably tell you anything you want to hear depending on how you word it.

How much money do you want to put on it .........................

[DoubleChevron]

This situation is definitely not normal. I can be sitting at the lights with a good pedal that has efficient stopping power then all of a sudden the pedal goes to the floor and the brakes don't work. The pedal might work well for 2 stops in crawling traffic and the the 3rd stop the pedal goes to the floor and the car barely stops.

As I said earlier I'll update after I've fixed the leak and re bled it.

Cheers.

That's not normal, if there is no evidence of leaking, I'd be checking if the booster is leaking brake fluid back into the motor where it gets burnt (so there is no evidence of leakage). My wife had a ford escort when I met her years ago that did that :)

seeya,
shane L.

[discorevy]

How much money do you want to put on it .........................

I wouldn't want to take your money.......your going to need it to fix your wife's brakes, it is quite common for the cup seals in a master cylinder to bypass fluid back in to the reservoir when they are worn, leaving no external trace of fluid, I guess Google would confirm that for you, but I was actually sharing my own experiences as a mechanic as I have seen this several times over the years. Also common for said seals to give up after brake work when bleeding, as the seals have to travel through a stroke that they normally don't have to and that part of the cylinder can have accumulated crap or pitting that will finish the seal off if the fluid hasn't been replaced on a regular basis.

[discorevy]

That's not normal, if there is no evidence of leaking, I'd be checking if the booster is leaking brake fluid back into the motor where it gets burnt (so there is no evidence of leakage). My wife had a ford escort when I met her years ago that did that :)

seeya,
shane L.

??? Op has said a couple of times that he does have a leak

[DoubleChevron]

I wouldn't want to take your money.......your going to need it to fix your wife's brakes, it is quite common for the cup seals in a master cylinder to bypass fluid back in to the reservoir when they are worn, leaving no external trace of fluid, I guess Google would confirm that for you, but I was actually sharing my own experiences as a mechanic as I have seen this several times over the years. Also common for said seals to give up after brake work when bleeding, as the seals have to travel through a stroke that they normally don't have to and that part of the cylinder can have accumulated crap or pitting that will finish the seal off if the fluid hasn't been replaced on a regular basis.

You could be right. The brakes work 100% .... There is no sign of this ever happening under any circumstances unless the engine is off ... and you hold constant firm pressure on the pedal for 30+seconds. I looked into at the time and it appears to be normal behavior that 99.99999999999% of people never notice. Those that do when there new are told it's normal behavior from the service people.

If you google it there is quite a few cars that do it ... though most would never notice. I reckon its to do with leakage through the ABS without the engine running :confused:

Certainly the brakes in it are the typical crap over-assisted, way to grabby brakes fitted to all modern cars, and work staggeringly well under all circumstances.

Anyway, were off topic here.

seeya,
Shane L.

[Tins]

I wouldn't want to take your money.......your going to need it to fix your wife's brakes, it is quite common for the cup seals in a master cylinder to bypass fluid back in to the reservoir when they are worn, leaving no external trace of fluid, I guess Google would confirm that for you, but I was actually sharing my own experiences as a mechanic as I have seen this several times over the years. Also common for said seals to give up after brake work when bleeding, as the seals have to travel through a stroke that they normally don't have to and that part of the cylinder can have accumulated crap or pitting that will finish the seal off if the fluid hasn't been replaced on a regular basis.

I've seen it as well, especially in cylinders that are only alloy, and have been neglected. The old type brake fluid was hygroscopic, so the cast iron ones could rust as well. Usually, though, this would become evident by leakage at the push rod end of the cylinder. Non boosted cars would wind up with wet carpet. Boosted cars were harder to diagnose, but eventually the paint on the booster would give it away.

[aRRon]

That's not normal, if there is no evidence of leaking, I'd be checking if the booster is leaking brake fluid back into the motor where it gets burnt (so there is no evidence of leakage). My wife had a ford escort when I met her years ago that did that :)

seeya,
shane L.

There's no way the WABCO ABS can leak fluid back to the motor as there's no vacuum pipe involved - the boost pressure comes from an electric pump.

[Tins]

There's no way the WABCO ABS can leak fluid back to the motor as there's no vacuum pipe involved - the boost pressure comes from an electric pump.

Yeah, we were straying a bit off topic.

[Pacemaker]

Thanks aRRon you beat me to it mentioning there is no vacuum booster or hose from the engine.

So last night I jumped under and got 1 whole turn of the fitting to tighten the hose. I ran the engine for a few mins with my foot on the brake and it hasn't leaked. Hopefully that's all good now. I'll bleed the system again this weekend. I also have a stuffed swivel hub bearing on one side and a collapsed wheel bearing on the other so I'll try replace all those this weekend too.

Cheers.