Accuracy of an MOT brake test - garage having it on?
Discussion
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.
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
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...
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
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.
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
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.
What's to say that "your" mechanic is correct to have passed it? 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
blueovercream said:
I'm suspecting this is just a way to fleece money from more naive customers. Happy to be convinced otherwise.
Some of the new ones do facial recognition and pass your details to every branch so they know when you walk in
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.
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.
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. 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.
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):Some of the new ones do facial recognition and pass your details to every branch so they know when you walk in
https://www.youtube.com/watch?v=t5NjcZRbPrk
Chris
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