Accuracy of an MOT brake test - garage having it on?

Accuracy of an MOT brake test - garage having it on?

Author
Discussion

blueovercream

Original Poster:

155 posts

54 months

Tuesday 23rd February
quotequote all
I took my van to my local Kwik Fit for its MOT last week and it failed based on "excessively fluctuating" front brakes (major defect).

The discs and pads were new in June last year and have covered less than 5000 miles. After the test, I took the van to my usual mechanic (very good reputation, a bit more of a faff to get to) who cleaned off some winter grime and confirmed that the discs were in good shape. Repeat test at Kwik Fit, still fluctuating. The guy showed me the test being done - van on rollers, needles on the gauges bouncing as brake pressure applied. He said that with the grime now cleaned off, this can only mean warped discs. He refused to issue an MOT pass.

Took the van back to my my mechanic who MOT'd it with no problem.

My thoughts:
- Would relatively new official VW discs really be defective?
- Surely I would feel MOT failure-worthy brake fluctuation through the pedal
- How reliable is the test described above anyway?

I'm suspecting this is just a way to fleece money from more naive customers. Happy to be convinced otherwise.

Edited by blueovercream on Tuesday 23 February 15:33

SuperPav

764 posts

88 months

Tuesday 23rd February
quotequote all
When you changed your discs/pads, did you check your caliper pins/sliders? Sticky calipers are quite common, and result in all sorts of bad things happening as it applies uneven pressure from just one side and essentially bends the disc under braking.

If they calipers are greased and sliding well with all pistons and pins moving freely, and you have new VW discs, then the chances of warped discs bad enough to "fail an MOT" are near non-existent. The only way to check would be to go to another roller and see if it gives the same results unfortunately...

Edited by SuperPav on Tuesday 23 February 15:39

Deranged Rover

898 posts

37 months

Tuesday 23rd February
quotequote all
As I understand it, this is a relatively common issue. I’m pretty sure the problem is...

blueovercream said:
Kwik Fit
wink

blueovercream

Original Poster:

155 posts

54 months

Tuesday 23rd February
quotequote all
SuperPav said:
When you changed your discs/pads, did you check your caliper pins/sliders?
I didn't change the discs and pads myself so I'm afraid I don't know if this was done, though I think the mechanic would have checked when he cleaned the brakes up after the first test.

sparkyhx

3,685 posts

167 months

Tuesday 23rd February
quotequote all
flexible pipes bulging or collapsed

An often-misdiagnosed cause of pull is a collapsed brake hose. The hose will look OK on the outside, but the inner liner will cause a restriction on the inside. A brake hose problem like this can take two forms. First, it can act like a restrictor in the line. Second, it can act like a check valve.

In the “check valve” situation, fluid will freely flow into the caliper, but will not return to the master cylinder. This can mimic a stuck piston, as the caliper will fail to fully release.

Edited by sparkyhx on Tuesday 23 February 18:37

PH User

16,417 posts

71 months

Tuesday 23rd February
quotequote all
blueovercream said:
I took my van to my local Kwik Fit for its MOT last week and it failed based on "excessively fluctuating" front brakes (major defect).

The discs and pads were new in June last year and have covered less than 5000 miles. After the test, I took the van to my usual mechanic (very good reputation, a bit more of a faff to get to) who cleaned off some winter grime and confirmed that the discs were in good shape. Repeat test at Kwik Fit, still fluctuating. The guy showed me the test being done - van on rollers, needles on the gauges bouncing as brake pressure applied. He said that with the grime now cleaned off, this can only mean warped discs. He refused to issue an MOT pass.

Took the van back to my my mechanic who MOT'd it with no problem.

My thoughts:
- Would relatively new official VW discs really be defective?
- Surely I would feel MOT failure-worthy brake fluctuation through the pedal
- How reliable is the test described above anyway?

I'm suspecting this is just a way to fleece money from more naive customers. Happy to be convinced otherwise.

Edited by blueovercream on Tuesday 23 February 15:33
What's to say that "your" mechanic is correct to have passed it?

stevemcs

5,285 posts

56 months

Tuesday 23rd February
quotequote all
Strip and clean the front brakes, warped discs are not going to show on the brake tester. Or just go elsewhere for another MOT.

sparkyhx

3,685 posts

167 months

Tuesday 23rd February
quotequote all
blueovercream said:


I'm suspecting this is just a way to fleece money from more naive customers. Happy to be convinced otherwise.
did u not know the brake testing machines costing tens of thousands have a switch for gullible and non gullible customers.

Some of the new ones do facial recognition and pass your details to every branch so they know when you walk in


PhillipM

5,739 posts

152 months

Tuesday 23rd February
quotequote all
Given how they're driven fluctuations are way more likely to be out of round tyres or one with a bulge somewhere.

blueovercream

Original Poster:

155 posts

54 months

Tuesday 23rd February
quotequote all
PH User said:
What's to say that "your" mechanic is correct to have passed it?
He looks after my Elise, I've known him for years and he's highly regarded in the Lotus community. Granted this is a van, not a Lotus, but I trust him a lot more than I do Kwik Fit.

blueovercream

Original Poster:

155 posts

54 months

Tuesday 23rd February
quotequote all
PhillipM said:
Given how they're driven fluctuations are way more likely to be out of round tyres or one with a bulge somewhere.
Possibly but then I'd have thought an MOT test should be able to make this distinction? Plus it would have been noticeable when driving...

stevemcs

5,285 posts

56 months

Tuesday 23rd February
quotequote all
If it was a bulge then it would have failed as a dangerous defect do not drive.

Little Pete

854 posts

57 months

Tuesday 23rd February
quotequote all
Did you notice how much they were fluctuating, ie what the actual readings were?

SteveR1979

289 posts

104 months

Tuesday 23rd February
quotequote all
I've had cars in the past with fluctuating brakes, and it was just brake deposit on the disks.

Couple of hard stops from a reasonable speed cleaned it off.

buggalugs

8,864 posts

200 months

Tuesday 23rd February
quotequote all
If they were that bad you’d be able to feel it when braking from 60-70

Can also be discs not flush with hub i.e. hub surface not clean or a bit of rust stuck in there etc.

Hol

5,968 posts

163 months

Wednesday 24th February
quotequote all
https://www.pistonheads.com/gassing/topic.asp?h=0&...

There's an MOT tester, who could probably confirm if he has witnessed it himself.


Personally, I think you would have felt it through the pedal or steering wheel, , if there was a significant problem.

PH User

16,417 posts

71 months

Wednesday 24th February
quotequote all
blueovercream said:
PH User said:
What's to say that "your" mechanic is correct to have passed it?
He looks after my Elise, I've known him for years and he's highly regarded in the Lotus community. Granted this is a van, not a Lotus, but I trust him a lot more than I do Kwik Fit.
Maybe, but that doesn't automatically mean that he's correct.

Speed Badger

1,395 posts

80 months

Wednesday 24th February
quotequote all
We had a similar thing happen when we took our FN2 Civic Type R to Mr Clutch for an MOT. It had just had new front pads, discs and callipers a week before and they failed it due to excessive fluctuation and also brake binding. We kept asking how is this possible, and they kept saying that's what the tester had said. We took it to another MOT place and it passed no issues. Funny that.

steveo3002

7,991 posts

137 months

Wednesday 24th February
quotequote all
if you trust your mechanic what on earth were you doing letting those monkeys have your money ?

ScoobyChris

900 posts

165 months

Wednesday 24th February
quotequote all
sparkyhx said:
did u not know the brake testing machines costing tens of thousands have a switch for gullible and non gullible customers.

Some of the new ones do facial recognition and pass your details to every branch so they know when you walk in
Reminded me of this sketch (contains some colourful language):

https://www.youtube.com/watch?v=t5NjcZRbPrk

Chris