Any comments on parking brake figures?

[Stuart W]

The beast had its taxi test with the council last week, and the parking brake Maximum Force figures were as follows:

N/S 196 kgf
O/S 220 kgf

(Service:
N/S 218 kgf
O/S 261 kgf)

Test Summary

Pass value: 16% TW
Test value: 25%
Result: Passed :approve:


However, I had it MOTd by my VW dealer a few days earlier, and although it passed the Advisory Notice included the following:

Brake Advisories : RBT Park Brake Efficiency 16%

Your vehicle has only just met the required parking brake efficiency. It would appear that the braking system requires adjustment or repair.

Clearly there's a big discrepancy between the council's figures and the dealer's.

So can anyone suggest why the discrepancy might arise and comment on the council's maximum force figures?

Apart from the difference the reason I'm curious about this is that although the dealer included other advisory items on the invoice they didn't include the parking brake info, which is why I didn't notice it at the time. And since they replaced one of my rear calipers only a few weeks ago - and the other one at the last MOT - then they should be aware that it's maybe a sensitive subject for me, so I'm wondering if I should be smelling a rat, particularly with the supply issue for the replacement calipers.

Unfortunately I don't have the NS/OS breakdown for the dealer's figures.

[martin1810]

If those figures are for an epb, they are terrible. 25% is cr*p for an epb. You have something seriously wrong with the epb.

[kenney]

Correct me if i'am wrong,but from what i can make out of the test result is that the council's test, resulted in a 10% difference,and the service test resulted in a 16% difference,the allowed difference is 25%,so either way you are within the test value.The maximum braking values can differ depending on the settings of the brake tester

[Stuart W]

If those figures are for an epb, they are terrible. 25% is cr*p for an epb. You have something seriously wrong with the epb.

Thanks Martin. Any idea of what the figures should be on a Passat with the EPB working efficiently?



Correct me if i'am wrong,but from what i can make out of the test result is that the council's test, resulted in a 10% difference,and the service test resulted in a 16% difference,the allowed difference is 25%,so either way you are within the test value.The maximum braking values can differ depending on the settings of the brake tester

Not sure if I understand your argument Kenney. I'm just kind of guessing, but I think the percentage figure is the total braking force compared to the car's weight, which is quoted as 1,690 kg.

Thus 196 + 220 = 416 kg.

416 is 25% of 1,690, rounded up. What you are on about is maybe what they call 'imbalance', which doesn't seem to be an issue.

But the dealers figures were presumably around 270 kg (16% of 1,690 kg).

And Martin thinks even the 416kg/25% figure is poor for an EPB!!

[martin1810]

I haven't got any figures handy but the epb is nearly as effective as the hydraulic system. So if you assume the hydraulics do 100% then you will get figures like 70% for the EPB.
It is hard to imagine how your car ever produced such low figures, the system won't allow it without bringing up a fault. The only obvious thing would be very very groved/worn discs or pads.

[kenney]

yes it was imbalance i was refering to,but can someone explain,as i'am not familiar with the procedure,is 16% pass value the value which the vehicle will be approved with???????

[Quatrelle]

fwiw, my French MoTs are: efficiency of handbrake: 21% for the Passat, 20% Laguna and MGB 23%! Clear as mud.

That was three different MoT stations though.

[DSG4ME]

Those figures, are they pedal figures of just the PB? the 196 etc ones, iirc that would swing the needle on the tester over to about 3 o'clock, which should indicate they are ok.

[martin1810]

My apologies for my earlier post which did not help. I should have read the figures more closely rather than just look at the percentage.:o

I'll try again. Wheel brake action is given in kg per wheel. Tester usually tests 2 at a time.
Brake efficiency is total wheel (kg) results divided by weight of car and expressed as a percentage.
So if each wheel records 250 kg and the car has 4 wheels, the total is 1000kg. If the car weighs 1690 kg, the brake efficiency total is 1000/1690 x100%. which is 59%. The MOT limit is 50%, so 59% is a pass.
Using the same figures the rear brakes would supply 250 + 250 = 500kg.
500/1690 x 100% is about 30%. A typical cable handbrake may struggle to beat 20%
but only needs to beat 16% to pass the MOT. So a good cable park brake on a 1690 kg car needs to beat 270 kg. (135 kg per wheel).
Stuarts figures of 261 kg service and 220 park brake, show the park brake producing 84% of what the service brake can. A cable brake would not do this.
So the park brake is functioning fine compared to the service brake. Without seeing figures for all 4 wheels it is impossible to comment further.
God I hate long winded replies.:D

[DSG4ME]

Yeah, but they're a better read though :D

[Stuart W]

The full figures are:

Weight: 1,690 kg

Front 'service brake' (which I assume means footbrake!) maximum force:

N/S 349 kgf
O/S 338 kgf

Rear 'service brake'

N/S 218 kgf
O/S 261 kgf

This gives total footbrake force of 1,166 kgf.

As a percentage of the car's weight this is 69%. The pass rate is 50%

The parking brake figures are:

N/S 196 kgf
O/S 220 kgf

This gives a total parking brake force of 416 kgf.

This is 25% of the car's total weight. The pass rate is 16%. But I think Martin is now saying that 25% is adequate for an electronic parking brake.

These are the council's figures.

However, and to get back to the original question, when the VW dealer tested the car a few days earlier for an MOT the advisory said that the parking brake just met the 16% requirement.

Although the dealer didn't provide a breakdown of the figures, 16% of the car's weight (1,690 kg) is 270 kg, thus roughly 135 kg per wheel.

Martin, I'm still on the original discs at the back, but when the pads were changed at around 90,000 I was told they were OK, and since I've done about 37,000 on the replacement pads then they should be OK. So I don't think they will be hyper efficient, but they should be adequate.

And my two newish calipers should be working efficiently :approve:

[Stuart W]

fwiw, my French MoTs are: efficiency of handbrake: 21% for the Passat,

Well that's better than my MOT figure, but worse than my council test figure.

[martin1810]

My guess is the MOT guy made a mistake as obviously your epb is up to 25%. The NS rear brake seems a bit below par compared to the OS.

[Stuart W]

My guess is the MOT guy made a mistake as obviously your epb is up to 25%.

Thanks Martin; indeed perhaps that's why it wasn't mentioned on the invoice with the other advisory items, but I'll ask next time I'm in.

I probably have the previous years' figures lying around somewhere, so it'll be interesting to compare them, but finding them will be a different matter.

But at least I know a bit more about MOT brake testing than I did a week ago, as I suspect is the case for most of those reading this thread ;)