Couple of braking issues

[SumonesBungled]

Purchased my S210 (2001) with 102k miles on the clock 6 days ago and have been merrily coming to terms with the size of the beast etc. It rained today so very pleased (startled) by the auto windscreen wipe (I wasn't expecting it !). Anyway last night I had an 'eventful' drive 20 miles out of town and 20 miles back and I wonder whether any one has encountered the same / has any idea what the issue is / suggest a solution.

First issue on the way out approaching a roundabout under light braking I eased up on the brake but the pedal didn't come up with my foot. Continued driving, braked again lifted my foot car continued to brake so I 'flipped' the pedal up with my left foot. Under hard braking pedal comes back, light braking it would need assistance. On reaching destination pumped the brake and it reacted like it should. Drove the car home two hours later no problem with the pedal (and again this morning no problem).

Could it be a spring or something more worrying ?

Second problem while watching the braking on the way home and on a dead straight road and not under braking (and pedal fully returned) the ABS / ESP / BAS warning light came on. Pulled over car seemed to be fine braked ok. Drove on a little further and applied brakes hard and car reacted as I would expect ABS working as expected. Switched off engine, restarted - no warning lights and fifteen minutes later back home and no further incidents.

Looked up the ABS issue on the internet and keep coming across 'Brake Light Switch' as an issue. Does this sound like the same ? and how easy is it for a non mechanical minded old fart to changed said switch ?

Any help would be appreciated in these exciting times !

 

[Hartzpartz]

I would certainly check to see if the switch is fitted correctly as perhaps this could affect correct pedal operation. Easy to remove for inspection. Only about a tenner from MB and a very common fault with these, causing the BAS light to come on. Search this forum and you will find many others who have had the same fault and details of how to fit a new one.

 

[SumonesBungled]

A quick update. The ABS/ESP/BAS issue was the Brake Light Switch all fitted and working as expected.

The brake pedal issue is not resolved - InAutos had the car and checked for an likely issue and, of course, while with them the car behaved itself and they were unable to replicate the issue. Could it be the Brake Light Switch here too ?

No. From the garage I drove 20+ miles without any issue. Parked up left the car for an hour and half and then set off back home (another 20 miles). Almost straight away under light braking the brake didn't come back when I took my foot off. Under heavy braking no problem.

Drove to work this morning.... again no issue. Seems to be intermittent any ideas ?

 

[Hartzpartz]

So the brake pedal is physically sticking in a 'down' position?

 

[Hartzpartz]

Sorry, you described this fault in your original post. I wonder if the pedal is binding on the shaft or if there is any wear in the bushes? Have you tried any lube (being careful not to get any on the pedal rubber pad!).

 

[SumonesBungled]

The pedal is only down an inch / inch and a half, enough to leave the brakes engaged. Have used WD40 on the spring and connections at the top of the pedal but it makes no difference.

Strangely this never happens in the mornings when the weather is chilled. I leave the car in open sunshine (well the little we've been getting) and the pedal is 'sticky'. Later in the evening i.e, in darkness it seems to be ok. Could it be heat related ?

Sorry not sure what shaft you are referring to, but thanks for your help.

 

[Hartzpartz]

I was trying to remember from memory what the pedal pivot arrangement it. Thought the pedal pivots on a shaft but could be wrong. I suppose there could also be an issue with the brake servo. Hopefully someone will come along soon who has experienced this kind of fault.

 

[Hartzpartz]

I found the following on another forum. This was on a W202 and the OP didn't post a final solution. May help with ideas though.....


"I assume that this model is fitted with a normal vacuum servo booster and master cylinder + ABS2 set up, here's what I can think of as possible faults:-

There could be as suggested a return spring fault, the force that lifts the pedal comes partly from this and partly from the servo's operating rod.
There should be a little free play between the pedal and operating rod when in the rest position. lack of this might cause funny intermittent behaviour.

There may be a wear problem in the servo's control valve, it is in the centre of the servo, buried inside it. The control valve admits air into the back side of the servo to assist in pushing the master cylinder, the amount of air admitted depends on the pedal pressure applied to the operating rod. The air is admitted via the operating rod aperture which is normally from he inside of the car some where adjacent to the rubber belows that covers the servo operating rod, a restriction or blockage could cuase the behaviour you describe, but failure of the valve mechanism is I feel more likely than a blockage.
The booster is not a serviceable item a complete unit will be required if its gone duff.
I don't feel that your problem will lie here.

The ABS is passive under normal conditions and unless you are feeling the pulsation from its pump thru the pedal I dont think its here either.

But I think its most likely to be here:-

The master cylinder seals if badly degraded (at 12 years they are old enough to be) can become swollen and roll over in their seats and jam or fail to seal, often when this is the case the seals assume their normal position on release of and will behave normally until they make up their mind to roll over again and cause trouble. Your master cylinder is according to the advise given by brake hydraulics makers overdue replacement by 2 years. If there is any blackness in the fluid reservoir you should seriously look to changing the M/C.

The M/C is not an expensive part and not difficult to change. Changing the brake flexi hoses would also be a worthwhile safety measure, again not expensive."

 

[SumonesBungled]

Solved

Turned out to be the pedal shaft at fault. Purchased a new one for £1.45 struggled to fit it but now no pedal issue !

Thank you Hartzpartz your advice was excellent.

 

[Hartzpartz]

Glad that you got it sorted, and cheaply too!