W221 parking brake efficiency mot failure :(

alex_78

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hi me again with another problem

just fail my mot today by :

Parking break: efficiency below requirements
i was advised minimum is 16% (im not familliar with this at all) also i was advised my parking brake is:
n/s 70
o/s 80
again not sure what unit etc it is

service brake passed (recently done pads)

i want to clarify few things if someone can help:

1 when i drive and once stop press brake twice i go to HOLD function (i can release brake pedal but car will be still till i press brake or acceleration again) is this function use service or parking brake?

2 i almost not use my parking brake maybe few times last year (car is park on flat surface so i just leave on P (gearbox) is any chance that something just need wd40 etc? when i try now my parking break works i mean stop car on hill etc also if on D (drive and press it hold car)
last year i passed mot ok so i guess if HOLD function works on service brake i don't expect my brake shoes for handbrake are worn etc

is any way to adjust it like some regulator ?

i was wondering what i can do before i start strip car again :)
 

bembo449

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I think the hand brake shoes are inboard so whip a wheel off , find the adjuster and make sure the shoes are nipped up to the drum pal
 

jimc230

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I had a similar problem over the last few years of the MOT with the parking brake (just) passing. My mechanic advised me that it was down to lack of use and corrosion on the drums...he suggested I drive about half a mile with the parking brake on BUT BY ONLY ONE OR TWO 'CLICKS' (to avoid them overheating) I did this a few times and at the next MOT the measurements were greatly increased.....worth a try..??
 
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alex_78

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Thanks for reply

In case of w221 is not possible to drive with handbrake on coz is electronic and once you start driving is going off itself

But lack of use make perfect sense i will strip it off tomorrow and clean it

I only wondering is HOLD function use service brake or hand brake?

Once i will be cleaning i will check is any option for refulation

Is anyone aware how this 16% efficiency to pass mot isnreflected with this 70/80 strenght which was readed during mot?
How i can convert it
Sorry for silly question im ok diy with my car however never have proble like this before and this theory part is a bit mysterius...

Thanks
 

EmilysDad

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Hold is via the discs. The handbrake is via a drum incorporated within the rear discs ...... or at least mine is & my Vauxhalls before it.
 

alexanderfoti

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Thanks for reply

In case of w221 is not possible to drive with handbrake on coz is electronic and once you start driving is going off itself

But lack of use make perfect sense i will strip it off tomorrow and clean it

I only wondering is HOLD function use service brake or hand brake?

Once i will be cleaning i will check is any option for refulation

Is anyone aware how this 16% efficiency to pass mot isnreflected with this 70/80 strenght which was readed during mot?
How i can convert it
Sorry for silly question im ok diy with my car however never have proble like this before and this theory part is a bit mysterius...

Thanks

Ask them what the value is, if its 80% then I cant see how its failed.

You can actuate the handbrake whilst moving by pressing and holding the handbrake button, its quite aggressive and I wouldn't recommend it, but it will stop the car in an emergency.
 
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alex_78

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UPDATE:

thanks you all for your help

as was mentioned above parking brake should be used ;)
mine was used only few times last year so i was following patch described above that they are weak coz of lack of use

i remove brake callipers and discs clean drums and brake shoes (which looks like nearly new and are genuine merc parts) then use my friend wd40 then use regulator between brake shoes and adjust it slightly

comeback to mot station and success :) happy days mot passed :)
 
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