W204 - No Rear Brakes?

[mbe350]

Hi All,

Have an issue with a 2013 C220 Auto which I bought with no rear brakes working, only front brakes work.

This was evident by the surface rust on the rear discs - pads are never coming into contact with the rear discs, plus the reduced braking performance.

What I have checked so far -

1. The rear calipers - pistons move back and forward freely not stuck or seized.
2. Flow of brake fluid to rear calipers - pressure bled the brakes and fluid flowing freely from all 4 calipers, no air in the fluid.
3. No visible leaks around any brake pipes or flexi's - no loss of brake fluid either, level stays the same in the reservoir.
4. Isolated the master cylinder, brake pedal held firm suggesting no issues with seals or leaking.
5. Flow of brake fluid between master cylinder and ABS unit - OK and no air evident.

Is there any common reason either in a W204 or Mercedes generally as to the rear brakes not working? Something I have missed?

Thanks in advance for any help or ideas on this.

 

[colinallcars]

Hi All,

Have an issue with a 2013 C220 Auto which I bought with no rear brakes working, only front brakes work.

This was evident by the surface rust on the rear discs - pads are never coming into contact with the rear discs, plus the reduced braking performance.

What I have checked so far -

1. The rear calipers - pistons move back and forward freely not stuck or seized.
2. Flow of brake fluid to rear calipers - pressure bled the brakes and fluid flowing freely from all 4 calipers, no air in the fluid.
3. No visible leaks around any brake pipes or flexi's - no loss of brake fluid either, level stays the same in the reservoir.
4. Isolated the master cylinder, brake pedal held firm suggesting no issues with seals or leaking.
5. Flow of brake fluid between master cylinder and ABS unit - OK and no air evident.

Is there any common reason either in a W204 or Mercedes generally as to the rear brakes not working? Something I have missed?

Thanks in advance for any help or ideas on this.

Have you checked the slider pins? They could be seized.

 

[mbe350]

Slider pins are fine/moving freely, checked when callipers were removed to inspect movement of the pistons.

 

[Railwayman]

Hi All,

Have an issue with a 2013 C220 Auto which I bought with no rear brakes working, only front brakes work.

This was evident by the surface rust on the rear discs - pads are never coming into contact with the rear discs, plus the reduced braking performance.

What I have checked so far -

1. The rear calipers - pistons move back and forward freely not stuck or seized.
2. Flow of brake fluid to rear calipers - pressure bled the brakes and fluid flowing freely from all 4 calipers, no air in the fluid.
3. No visible leaks around any brake pipes or flexi's - no loss of brake fluid either, level stays the same in the reservoir.
4. Isolated the master cylinder, brake pedal held firm suggesting no issues with seals or leaking.
5. Flow of brake fluid between master cylinder and ABS unit - OK and no air evident.

Is there any common reason either in a W204 or Mercedes generally as to the rear brakes not working? Something I have missed?

Thanks in advance for any help or ideas on this.

You have done mostly all the checks I would, the only thing that springs to mind could be a problem with the ABS unit. I take it the pads are free to move on the rear callipers?

 

[colinallcars]

You have done mostly all the checks I would, the only thing that springs to mind could be a problem with the ABS unit. I take it the pads are free to move on the rear callipers?

Does it have an electric parking brake? If so, might be worth carrying out the piston retraction / reset routine a few times to make sure everything is moving freely.

 

[mbe350]

You have done mostly all the checks I would, the only thing that springs to mind could be a problem with the ABS unit. I take it the pads are free to move on the rear callipers?

Yes, the pads are free to move on the callipers.

I did actually replace the ABS module and pump as well since I had the same thought on it potentially causing an issue - it didn't make a difference however.

 

[mbe350]

Does it have an electric parking brake? If so, might be worth carrying out the piston retraction / reset routine a few times to make sure everything is moving freely.

No, it has the foot operated brake with pull release on the dash so not able to cycle the calliper - though I know they move freely anyway having done this manually.

 

[markjay]

Any warning on the dash? The car should be clever enough to know the rear brakes are not working, and disable the ESP/ABS which will result in a warning.

Have you checked for fault codes using STAR?

Also, in the olden days there used to be a mechanical pressure distribution valve that regulated the braking force between the front and the rear brakes (applying more pressure to the front brakes), which is different to having two braking circuits (that are typically crossed diagonally). But maybe in modern cars this is managed electronically by the ABS module, I don't know.

EDIT: since the brakes are meant to work even without the involvement of the ABS module, I'd expect that the mechanical pressure distribution valve will still be there somewhere? Though it might be mechanically incorporated into the electronic ABS module....

 

[Bellow]

Having suffered complete loss of rear brakes recently (not MB) due to a burst pipe (3 channel ABS), if your pedal isn't getting perilously close to the floor, then your hydraulic circuits are intact.

 

[colinallcars]

Brake bias valve stuck?

 

[Railwayman]

Just another thought thou unlikely, internal collapsed brake hoses on the rear.

 

[mbe350]

Thanks for all the suggestions from everyone. Just an update having spoken to a couple of people RE an ABS bleed procedure.

I checked both my diagnostic units, neither had an 'ABS Bleed Procedure' on them, but one was able to actuate the ABS pump.

So I hooked up my pressure bleeder to the reservoir, got someone to sit in the car and continually actuate the ABS pump whilst pumping the pedal - while I went to each corner to bleed the callipers.

As usual, never get any air from the fronts - but I got lots and lots of air out from the rears with the ABS pump running and the pedal being pressured. Continued with this until no more air would come out. Wheels back on, jumped in and started - pedal instantly felt 100%. Took it for a test drive, rear brakes working again and the pedal now good.

Decided to complete the intake valves and separation valves calibration for the ABS module, since still had a couple of lights on after replacing ABS unit. During previous failed attempts (which I now know to have been from air stuck in the ABS unit) this went very quick compared to previous attempts. However, on the final step on the intake valves calibration got a brake fluid warning light appear on the dash, got out checked the reservoir and sure enough it had dropped from max to below minimum. Looked under the car and brake fluid pouring out. Stripped off the undertrays to reveal the hidden brake lines and sure enough there was a rusted section which had given way under the new increased pressure from the brakes now working properly. Removed the arch linings front & rear and pulled out the corroded brake line and dropped off with a brake specialist to make me a new copper line to replace with. Hopefully pick that up today and get it on over the weekend, re-bleed the brakes, re-run the calibration and fingers crossed that sorts everything.

 

[markjay]

Good news! Well Done.

Just to point out that the community here was unable to assist on this occasion, in part due to the initial fault description:

4. Isolated the master cylinder, brake pedal held firm suggesting no issues with seals or leaking.

But now it seems that:

Wheels back on, jumped in and started - pedal instantly felt 100%.

The reason that air in the system wasn't suggested, because it would have to result in a softer brake pedal feel, and this was not consistent with the initial description.

In any event, very good result

And the lesson is that the correct procedure for bleeing the braking system on ABS-equppied cars (all of them, these days) must be flllowed.

 

[BlackC55]

I wish I had commented on this.

We have had this issue a few times. We juts cant get a good pedal. What we do is use the pressure bleeder set at 2 bar. Then we operate the brake pedal (pump) slowly but fully a good few times. Eventually the air lock goes.

All the brake pipes must be in very good order before this is done. That's all the pipes that are covered up too.

 

[mbe350]

Good news! Well Done.

Just to point out that the community here was unable to assist on this occasion, in part due to the initial fault description:

4. Isolated the master cylinder, brake pedal held firm suggesting no issues with seals or leaking.

But now it seems that:

Wheels back on, jumped in and started - pedal instantly felt 100%.

The reason that air in the system wasn't suggested, because it would have to result in a softer brake pedal feel, and this was not consistent with the initial description.

In any event, very good result

And the lesson is that the correct procedure for bleeing the braking system on ABS-equppied cars (all of them, these days) must be flllowed.

Apologies if my description was misleading - the comment in point 4 about the firm brake pedal was in relation to a test of the Master Cylinder, i.e. removing the 2 pipes to the ABS unit and capping the MC to ensure it wasn't leaking/able to hold pressure (firm pedal/not sinking) - I was not describing a firm brake pedal in normal braking during this test.

In hindsight, stating the pedal had some extra travel rather than just stating 'reduced braking performance' might have been better.

pads are never coming into contact with the rear discs, plus the reduced braking performance.