W124 Rear Brake mystery

craigfza

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Hi all

Looking for some help on my 1992 200e A/T.

It failed it's local roadworthy test (MOT) today due to the rear brakes not working properly. All seems fine when driving and reversing as the brakes stop the car with no shudder, judder or any other "udder" :), the pedal does not feel spongy and there is no apparent fade. Fluid reservoir is good. But doing a couple of tests myself, I have come up with the following:

1. Put car in D, release foot brake and parking brake on - car does not move :)
2. Put car in R, release foot brake and parking brake on - car does move :shock:

I have taken the rear wheels off and examined the rear brake pads on both sides. The pads look fine with about 4mm on each pad - but I could be wrong about the "fine" part! :).

I need help as I need to get this sorted asap. Where, or what, could the problem lie? (Hopefully it is not an expensive problem!)

Thanks in advance.

Craig
 

Bolide

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The handbrake uses a set of shoes inside the rear discs. I suggest you look there for your problem...

Nick Froome
 
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craigfza

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The handbrake uses a set of shoes inside the rear discs. I suggest you look there for your problem...

Nick Froome

Hi Nick

Thanks for the tip. I am aware of the shoes inside the rear discs for the parking brake. Is there a similar set up inside the front discs? Just wondering as the car did not move forward when put in D.

Also, the MOT failure was when the foot brake was applied while on the motorised rollers.

Just call me :confused:
 

brandwooddixon

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There're two shoes inside the rear brake discs that are used by the parking brake.

By their geometry one will act more strongly with the wheel trying to rotate in one direction rather than the other.

I would jack the car up, remove the wheel, undo the adjuster as far as it will go (flat blade screw driver through a hole in the rear) and remove the rear disc.

Inspection will show whether the shoes are worn down; the mechanism requires replacement; or more likely a small amount of copperslip is required on the backplate wear points. Remember to readjust the brakes once put back together.
 

syncropaddy

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4mm on the pads is a little too close to replacement for me! I would be looking at the parking brake for adjustment or replacement. Those shoes are a horrible thing to replace!
 

teddycatkin

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w124 rear brakes

As Nick has said the thandbrake iny inner shoes are on the inside of the brake drum --only around £8 for a set from Euro Car Parts.
Remove drums and replace ---may as well do rear pads too for what they cost (£12) assuming the discs are good ?----also check with the mot tester what did it fail on -Hand or Footbrake -cables can stretch or break altogether on the handbrake ---should be an easy repair and always pass the mot break test machine easily ?





Hi all

Looking for some help on my 1992 200e A/T.

It failed it's local roadworthy test (MOT) today due to the rear brakes not working properly. All seems fine when driving and reversing as the brakes stop the car with no shudder, judder or any other "udder" :), the pedal does not feel spongy and there is no apparent fade. Fluid reservoir is good. But doing a couple of tests myself, I have come up with the following:

1. Put car in D, release foot brake and parking brake on - car does not move :)
2. Put car in R, release foot brake and parking brake on - car does move :shock:

I have taken the rear wheels off and examined the rear brake pads on both sides. The pads look fine with about 4mm on each pad - but I could be wrong about the "fine" part! :).

I need help as I need to get this sorted asap. Where, or what, could the problem lie? (Hopefully it is not an expensive problem!)

Thanks in advance.

Craig
 

hotrodder

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the MOT failure was when the foot brake was applied while on the motorised rollers.

Just call me :confused:

Craig, what was the actual reason given for failure? The tester will (or should have) been more specific than...
It failed it's local roadworthy test (MOT) today due to the rear brakes not working properly
Could it be 'imbalance' across the rear service (foot) brakes i.e. one caliper isn't doing it's fair share? Specific reason should be written on the failure sheet

The rollers measure braking forces which is calculated out to efficiency (braking effort/weight x 100). Brakes have to be pretty appalling to fail on efficiency (pass is something like 50% efficiency for service brake and 16% for parking brake) but can fail on balance more easily i.e. even if the car feels like it stops 'straight and true' the brakes can be imbalanced enough to fail, especially rear brakes as they contribute relatively little compared to the fronts
 

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television

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The OP has clearly said that it failed on the foot brake on the rolling road.

This can only mean one thing, a seized caliper on the wheel or side, and nothing to do with the parking brake, and yes there will be a slight movement of the car if the parking brake is on and you go from D to R, it will also hold the car better in one direction than the other due to the self binding action of the shoes
 

NW_Merc

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Hi all

Looking for some help on my 1992 200e A/T.

It failed it's local roadworthy test (MOT) today due to the rear brakes not working properly. All seems fine when driving and reversing as the brakes stop the car with no shudder, judder or any other "udder" :), the pedal does not feel spongy and there is no apparent fade. Fluid reservoir is good. But doing a couple of tests myself, I have come up with the following:

1. Put car in D, release foot brake and parking brake on - car does not move :)
2. Put car in R, release foot brake and parking brake on - car does move :shock:

I have taken the rear wheels off and examined the rear brake pads on both sides. The pads look fine with about 4mm on each pad - but I could be wrong about the "fine" part! :).

I need help as I need to get this sorted asap. Where, or what, could the problem lie? (Hopefully it is not an expensive problem!)

Thanks in advance.

Craig

The OP has clearly said that it failed on the foot brake on the rolling road.

This can only mean one thing, a seized caliper on the wheel or side, and nothing to do with the parking brake, and yes there will be a slight movement of the car if the parking brake is on and you go from D to R, it will also hold the car better in one direction than the other due to the self binding action of the shoes

I believe the OP said that the REAR brakes were causing the problem :rolleyes:
 

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I believe the OP said that the REAR brakes were causing the problem :rolleyes:

Are you trying to mess up this thread :D for who has said that it was not the rear brakes
 

Naraic

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The OP has clearly said that it failed on the foot brake on the rolling road.

This can only mean one thing, a seized caliper on the wheel or side, and nothing to do with the parking brake, and yes there will be a slight movement of the car if the parking brake is on and you go from D to R, it will also hold the car better in one direction than the other due to the self binding action of the shoes

Read it again...he says it's the parking brake that will not hold the car in reverse. I think you owe someone an apology.

If there is any confusion it's because in post 3 the OP mentions the MOT fail being the foot brake on the rolling road. I think he is confusing the foot operated parking brakes and the normal brakes. If this is the case...you are wrong. If this is not the case, then we are all wrong and the OP could be clearer...no need for you to be so ungentlemanly to another member. You came late to the thread...and everyone else thinks he is talking about the parking brake...and yet you choose to berate just one member.

Is it time to close yet another thread?
 
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Read it again...he says it's the parking brake that will not hold the car in reverse. I think you owe someone an apology.

If there is any confusion it's because in post 3 the OP mentions the MOT fail being the foot brake on the rolling road. I think he is confusing the foot operated parking brakes and the normal brakes. If this is the case...you are wrong. If this is not the case, then we are all wrong and the OP could be clearer...no need for you to be so ungentlemanly to another member. You came late to the thread...and everyone else thinks he is talking about the parking brake...and yet you choose to berate just one member.

Is it time to close yet another thread?

Thats up to you, but at no time here have I mentioned a front brake as NWmerc implied, I have only been talking about the rear, both parking brake and footbrake, so what was the point in his post
 

Naraic

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Thats up to you, but at no time here have I mentioned a front brake as NWmerc implied, I have only been talking about the rear, both parking brake and footbrake, so what was the point in his post

He meant parking brakes...as everyone else did. Only you suggested a problem with a caliper. What he said did not warrant an attack.

NW_Merc has proved himself helpful in the last couple of weeks...and has an interesting project going on which interests many on here.
 
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Alex Crow

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For me, it is not clear exactly what this car has failed on, and so it is hard to advise.

Craig, please clear up the confusion and tell us exactly what it says on the fail sheet.
 

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He meant parking brakes...as everyone else did. Only you suggested a problem with a caliper. What he said did not warrant an attack.

NW_Merc has proved himself helpful in the last couple of weeks...and has an interesting project going on which interests many on here.

If he meant parking brake as everyone else, then still no point in his post for I am on that list that did not mention anything else, I talked about the caliper when the op said foot brake failed on the rolling road, and if that was the case then my answer was correct.

Sure the OP is none to clear, but my post should not have been picked out as being wrong, for I said nothing wrong
 

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In that case, we will, as gentlemen, agree to disagree.
 

d215yq

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The OP said the footbrake (i.e. proper brakes), not the parking brake. The parking brake on mine does not hold the car in D or in R, it won't even hold it in N on a very moderate incline, it is totally useless but passed the MOT without advisory, so i doubt the OP is talking about the parking brake.

My old W124 failed the front brake efficiency test once and new pads solved the problem (even though the old ones had 4-5mm and weren't properly warn). Something to do with the adjustment being wrong and new pads solving this, according to mechanic??... but it cost £50 and worked! Before the MOT fail for efficiency I never found any judder, shudder, noise or deficiency in braking, but then I generally drive in a manner where good brakes aren't necessary.
 
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television

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The OP said the footbrake (i.e. proper brakes), not the parking brake. The parking brake on mine does not hold the car in D or in R, it won't even hold it in N on a very moderate incline, it is totally useless but passed the MOT without advisory, so i doubt the OP is talking about the parking brake.

My old W124 failed the front brake efficiency test once and new pads solved the problem (even though the old ones had 4-5mm and weren't properly warn). Something to do with the adjustment being wrong and new pads solving this, according to mechanic??... but it cost £50 and worked! Before the MOT fail for efficiency I never found any judder, shudder, noise or deficiency in braking, but then I generally drive in a manner where good brakes aren't necessary.

Thanks that why I mentioned a seized piston, could there be some limit as to how far the pistons come out, the other thing is if the disc are well worn, then add this to the worn pads and it could just be as you say worn pads too low to function properly
 

d215yq

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Thanks that why I mentioned a seized piston, could there be some limit as to how far the pistons come out, the other thing is if the disc are well worn, then add this to the worn pads and it could just be as you say worn pads too low to function properly

I'm not technically minded to know why but 40k miles and 2 more MOTs were done with the new pads and without replacing discs or anything else and there were no further problems/fails with the front brakes.
 

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