Huge brake issues. ABS pump at fault?

[Mats]

Hi all,

I'm in big distress as my garage cannot help me.

My FR offsite and RR nearside brake don't get any brake fluid.
My garage says it might be the ABS pump but they don't want to touch it.

Obviously a major fault.
Is it likely to be the pump? How could I check it?
What replacement part would I need a d how much work is it to change it?
Any T4 required?

I'm driving a CDTi without traction control.

Thank you very much for any help!


Cheers

[SD1too]

Originally Posted by Mats

My FR offsite and RR nearside brake don't get any brake fluid.

Hi Mats,

How has this theory been reached?

If you haven't seen the ABS warning illuminating on your instrument panel then the ABS modulator (it's not a "pump", quite the opposite in fact) won't have operated.

Simon

[SteveThackery]

Originally Posted by SD1too

Hi Mats,

(it's not a "pump", quite the opposite in fact) won't have operated.

Simon

Hey, Simon, could you expand on that a little? I've been reading about ABS and it seems that a pump is used to restore the brake pressure after it was released by the anti-lock function.

[SD1too]

Originally Posted by SteveThackery

I've been reading about ABS and it seems that a pump is used to restore the brake pressure after it was released by the anti-lock function.

Hi Steve,

Thanks for questioning me on this. The ABS modulator, amongst other things, does indeed contain a pump to relieve pressure in the caliper when the supply from the master cylinder has been cut off by a solenoid valve.

The reason for my earlier post is that I feel that it's potentially misleading to refer to the modulator as a pump because that's just one of many internal components which work together to control and maintain a suitable pressure whilst the brake pedal is depressed. RAVE's description is basic and doesn't explain the rôle of the restrictor, damper and accumulator in detail.

Another reason why I don't believe that "pump" is suitable as a generic description is that in traction control mode the internal pump does indeed draw fluid from the master cylinder and supplies it to the brakes to arrest wheelspin. This would be more appropriate use of the term "pump" but as I understand it, this does not occur in purely ABS modulators.

I hope to hear back from Mats soon. If there is air rather than brake fluid in the lines to the front offside and rear nearside the first thing I would do is to bleed the brakes following the order given by MG Rover. I wouldn't suspect the modulator at this stage as those symptoms would mean a simultaneous failure of both inlet solenoid valves on that circuit which seems rather unlikely. I'd look at the master cylinder instead since the secondary chamber feeds both those wheels.

Simon

[Mats]

Hello,

I've been going to the same garage for a while. Generally good service.

I seem to have had quite a few brake issues lately. Mainly sticky brake caliper. Garage freed them.
Last visit I had to change the FR O/S caliper as it was beyond freeing up.
Garage told me that the brake fluid seemed OFF and asked me whether I filled it up with wrong fluid. All brakes worked OK in my opinion, no funny pedal and good stopping.

I had a really bad squeak during driving on N/S (don't know if FR or RR) the other day. Disappeared the next day. Booked in for a check and brake fluid change as suggested by the garage.

Was then told that there is no bleeding possible at FR O/S and RR N/S. Completely dry pipes apparently. Garage said that symptoms point to ABS module/pump due to FR O/S and RR N/S both not working simultaneously.
Brake pedal goes almost straight to the floor. Minimal breaking, non-drivable.

I have no ABS lamp on the dash, have not since ABS sensor went last year. That was replaced. Only lamp currently on is the dreadful airbag. Need to change the plug under driver's seat.


Thanks a lot for any help!

[Briodyjl01]

Before you start digging into the abs pump have you confirmed that the flexi pipes are not old and perished? As sometimes the pipes swell and this would cause blocking. Just like your arteries…

As a quick check. Remove the flexi brake pipe and see if there’s any fluid getting to the end of the hard lines. If yes replace the flexi and you are on your way. (I have had this happen)

If no then look further. If it works it would be a cheaper option than an ABS pump.

Also if you don’t check it replace your pump and still find this you have wasted the time and money on the pump.

[SD1too]

Originally Posted by Mats

Was then told that there is no bleeding possible at FR O/S and RR N/S. Completely dry pipes apparently. Garage said that symptoms point to ABS module/pump due to FR O/S and RR N/S both not working simultaneously.
Brake pedal goes almost straight to the floor. Minimal breaking, non-drivable.

Thanks for the extra information Mats.

As you probably know there are two brake circuits and the OSF & NSR are on one of them. This makes it unlikely to be a pipework problem.

Looking at the ABS modulator hydraulic diagram in RAVE, the only component in the normal braking circuit is a solenoid valve which the modulator closes when ABS is activated. There is one of these valves supplying each wheel.

So, the garage's suggestion that the ABS modulator is blocking the passage of fluid would mean that:

1. Two solenoid valves (OSF & NSR) would have simultaneously failed in the activated position. Is this likely?
2. An ABS modulator fault would be detected each time the ignition is switched on and the ABS warning lamp would remain illuminated. You have said that this isn't the case. How does the garage explain this?
3. When ABS braking is inactive, the solenoid valves I mentioned are in their relaxed, default position which is open, allowing the normal passage of brake fluid. This suggests that the fault does not lie with the ABS modulator.

Originally Posted by Mats

Garage said that symptoms point to ABS module/pump due to FR O/S and RR N/S both not working simultaneously.

The OSF & NSR both not working simultaneously points to a lack of fluid or pedal pressure in the secondary chamber of the master cylinder (see my previous post). Your garage does not appear to have considered that. Unfortunately it's quite common to focus on the most misunderstood component when looking for blame; I've fallen into that trap myself recently.

I recall that another member had brake problems after his garage used 40 psi of bleeding pressure! There are warnings that this can displace seals in the master cylinder.

Simon

[Mats]

Simon,
Thanks a lot for the detailed explanation.

The correct bleeding sequence seems to be:
1. Select brake to be bled on screen menu after fitting bleed tube to bleed nipple.
2. Open bleed nipple and depress pedal to expell air until it runs clear ensuring resevoir is topped up.
3. Next press continue on the T4 menu to bleed the secondary circuit with the ABS pump until clear.
4. Finally tighten bleed nipple while pedal is depressed.

My garage does not have a T4. So this cannot be done?

I think I heard the mechanic saying that they used air pressure to try to get fluid moving.


Should I be buying a new master cylinder and ask them to simply change it?
Would this not result in issues due to not having a T4 avaliable?


Cheers

[Arctic]

Hi Matt.
Seeing where you live and we all know whom lives in the same area, if he was still live on the club, i am sure he would have sorted this out for for you without any doubt. MB

Might be worth trying to contact him some how? but right at the moment Josh idea sounds good, maybe the garage have flipped the seal if so they need to check and put it right surely.

[Jamiewelch]

Originally Posted by Mats

Simon,
Thanks a lot for the detailed explanation.

The correct bleeding sequence seems to be:
1. Select brake to be bled on screen menu after fitting bleed tube to bleed nipple.
2. Open bleed nipple and depress pedal to expell air until it runs clear ensuring resevoir is topped up.
3. Next press continue on the T4 menu to bleed the secondary circuit with the ABS pump until clear.
4. Finally tighten bleed nipple while pedal is depressed.

My garage does not have a T4. So this cannot be done?

I think I heard the mechanic saying that they used air pressure to try to get fluid moving.


Should I be buying a new master cylinder and ask them to simply change it?
Would this not result in issues due to not having a T4 avaliable?


Cheers

A T4 is not required, any decent generic diagnostic system (Snapon, Autel etc) will have an option to bleed the brakes. The ABS module can also be talked to by telling the diagnostic system that it is an E46. If they are saying they don't have a machine to do it then they don't trust their diagnosis.