checking brake discs
Discussion
Want to put new pads on my car, got an MOT advisory for 'worn, pitted or scored' brake disc on the same axle (it doesn't say near or offside though). Not sure what I should be looking at, only thing I can find is that the discs are 22mm new and replace at 20mm, though not sure how to measure these. Also replacement discs seem to be ~£20 to ~£50 depending brand not sure if it makes a difference, and 'left' and 'right', but one site sells 'left' and 'right' but only lets me buy two (surely you'd want 1x left and 1x right?)
Nearside
Offside
Also offside
Nearside
Offside
Also offside
E-bmw said:
My advice to you would be next time take it elsewhere, there is nothing wrong with them!
I can't comment on the pads obviously, but in discs of that condition I would be surprised if they are badly worn.
Can you see the depth of pad material left?
Well the pad doesn't look great I think? (failed <1.5mm)I can't comment on the pads obviously, but in discs of that condition I would be surprised if they are badly worn.
Can you see the depth of pad material left?
You measure the remaining disc thickness with a micrometer - a vernier caliper will do, but you might need to push a piece of plastic tube over the jaws to get past the lips caused by wear.
If they are at or past the specified minimum thickness then they need to be replaced as do the pads. I've not come across handed discs - yet! - although pads may have physical differences which require them to be fitted so they work on specific sides of the disc.
I've found over the years that I usually get two sets of pads to one set of discs.
Minimum pad thickness is usually also given in factory manuals but for MOT purposes it's 1.5mm:
"Reason for rejection g. a brake lining or pad insecure or less than 1.5 mm thick at any point"
https://www.mot-testing.service.gov.uk/documents/m...
If they are at or past the specified minimum thickness then they need to be replaced as do the pads. I've not come across handed discs - yet! - although pads may have physical differences which require them to be fitted so they work on specific sides of the disc.
I've found over the years that I usually get two sets of pads to one set of discs.
Minimum pad thickness is usually also given in factory manuals but for MOT purposes it's 1.5mm:
"Reason for rejection g. a brake lining or pad insecure or less than 1.5 mm thick at any point"
https://www.mot-testing.service.gov.uk/documents/m...
Edited by paintman on Monday 27th November 19:32
As others say, the outer surface looks to be in great condition...pads not so. And disc thickness could be questioned.
however...sometimes the outer surface can look great and the inner totally different. And with an outer pad down that far, I'd expect the inner to be much worse.
So there's only a part of the story there.
however...sometimes the outer surface can look great and the inner totally different. And with an outer pad down that far, I'd expect the inner to be much worse.
So there's only a part of the story there.
thelawnet1 said:
227bhp said:
The description says 'worn, pitted OR scored' and yes they are worn out, you can see a mm or so of lip on just one side.
is there a loss of efficiency between 22mm (new), 21mm (part-worn) and 20mm (replace)?Don't fall into the trap of thinking an MOT is something to try and get around or a tiresome expense, the attitude should be 'Thanks, you've just highlighted something that will be dangerous given time'.
227bhp said:
Don't fall into the trap of thinking an MOT is something to try and get around or a tiresome expense, the attitude should be 'Thanks, you've just highlighted something that will be dangerous given time'.
Well there's always a balance. On the one hand you might as well do them both as labour is significant part of the cost, on the other I only do 4500 miles a year so it's not really clear they will ever become dangerous as long as I own the vehicle, and then on the other it's only another £60 or whatever (depending on brand).And so on.
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thelawnet1 said:
227bhp said:
Don't fall into the trap of thinking an MOT is something to try and get around or a tiresome expense, the attitude should be 'Thanks, you've just highlighted something that will be dangerous given time'.
Well there's always a balance. On the one hand you might as well do them both as labour is significant part of the cost, on the other I only do 4500 miles a year so it's not really clear they will ever become dangerous as long as I own the vehicle, and then on the other it's only another £60 or whatever (depending on brand).And so on.
I'd say the MOT station have been very fair, basically you've now got all the facts (including those provided by yourself) and can make an informed decision based on those.
I actually ordered some discs, but they came too late and turned out I had some pads kicking around that were supposed to have been fitted previously.
have now been fitted by the axle on which they were fitted is making a sort of squealing noise, just driving along 1 mile or so from garage. Not sure if that is normal and they should settle down or?
have now been fitted by the axle on which they were fitted is making a sort of squealing noise, just driving along 1 mile or so from garage. Not sure if that is normal and they should settle down or?
thelawnet1 said:
I actually ordered some discs, but they came too late and turned out I had some pads kicking around that were supposed to have been fitted previously.
have now been fitted by the axle on which they were fitted is making a sort of squealing noise, just driving along 1 mile or so from garage. Not sure if that is normal and they should settle down or?
It may be the lip catching the old discs. Or the pads are seized into the carrier ; did you have to force the pads in with more than hand pressure and were they free to move on the carrier?have now been fitted by the axle on which they were fitted is making a sort of squealing noise, just driving along 1 mile or so from garage. Not sure if that is normal and they should settle down or?
SebringMan said:
It may be the lip catching the old discs. Or the pads are seized into the carrier ; did you have to force the pads in with more than hand pressure and were they free to move on the carrier?
I dunno I didn't do the pads. However all seems ok now, so it must have just been a newly fitted thing.Gassing Station | Suspension, Brakes & Tyres | Top of Page | What's New | My Stuff