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M.O.T. day

Community Veteran
Posts: 16,834
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Registered: 06-11-2007

M.O.T. day

Today is/was my M.O.T day......  Undecided
I thought I had everything covered..... bought a new tyre to replace a "iffy" one, so had good boots all round..... fixed a rusty bit on the outer skin of the silencer box.... had the rear brake cables renewed together with the brake drums and shoes. thought that the only thing to be worried about was the emissions.  Undecided
  Was a bit shocked to say the least, when  it failed......  Cry  Cry 
one disc pad below recommended thickness, and possible excessive wear on front discs. and of course.... the obligatory fail on a stop light.  Embarrassed
Got my mobile mechanic on the phone, he said get the bits and I`ll do it today.! great !....  Cheesy
I managed to do the stop light myself though. ! total cost for brake bits and labour was £110.00 which was about £50 less than the garage wanted if I left the car for them to do !
Worst thing about it,  the mechanic said he would not have thought it necessary to replace the discs, after comparing them to new ones.....and he did not think they were bad enough to fail the MOT..... But..... unfortunately I have to "play safe" to get them to re-test and pass it..... I won`t be going there next year...
13 REPLIES
Community Veteran
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Registered: 10-08-2007

Re: M.O.T. day

Sorry you got a bum deal at the MOT station

Recently the warning light came on for brake pads in my German car. As these were the original pads from new I thought I would do the whole job properly. So I got some brakes pads for front and rear. When I took the wheels off I couldn't believe the condition of the discs, they so badly worn I had to go and buy discs all round. Remember the car was still on its original pads, it was not like it had three or four sets of pads to wear out the discs. Had some discussions with the $tealer and was quietly informed that they are regularly changing discs at 10,000 miles or less. Same story from the motor factors, he says he sell lots of discs, thank you very much.
So what should be  a relatively inexpensive job, particularly if you do it yourself, turns into an expensive job.
Now I am not an expert but have messed around with cars a lot when I was younger. I remember changing lots of brake pads but never had to change discs.
Is it because the material in the pads is harder now or is it that the steel used in the disc is not as good as it used to be? Maybe its just another way to get the motorist to pay more. Vorsprung durch Technik as they say ...advancement through technology
Also to change the brake light bulb in my car you have to remove the whole rear light cluster from the car.
Angry
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Registered: 13-04-2007

Re: M.O.T. day

My Audi was the same the discs were worn down like nothing on earth and a few thousand miles after having new ones with pads they were very blue as if they were on fire just managed to get them past the MOT. It seems a common fault with them.
The MOT is now a con as if the car leaves the garage you cant get a free retest like you used to. So you can save £50 doing jobs your self but then you have to pay for a retest so you save nothing.
You have to find a good cheap garage that does MOT and tell  them you want any problems fixed before it leaves the garage.
Isnt it funny how bulbs have worked for years but suddenly fail when the do a MOT leave the garage and it comes back on again never to fail ever again
Community Veteran
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Registered: 10-08-2007

Re: M.O.T. day

I have experienced that with some MOT stations, I am lucky now I have a good local guy for the MOT.
I have some links to useful help sheets with pics on bulb changing in the Audi A4, let me know if you want them.
Moderator
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Registered: 11-01-2008

Re: M.O.T. day

What there seems to be is a lack of MOT testing stations that do that and nothing else so have no vested interest in finding anything wrong with your car.
I'm in the fortunate position that my brother in law is a mechanic and does all my servicing and repairs for me sorts out my MOT.
Will Moderate For Thanks
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Re: M.O.T. day

Quote from: Santiago
Now I am not an expert but have messed around with cars a lot when I was younger. I remember changing lots of brake pads but never had to change discs.

Same here, changed many sets of pads on various cars/vans over the years in the dim and distant past. Was very rare to need to change the discs too though.
Having said that, I suppose that cars are getting heavier these days, but then Transit and Courier vans which used to get a fair bit of abuse (agricultural use Wink ) always seemed fine, so perhaps not a weight issue after all?
Perhaps it could be a softer metal to help counteract warping?
Can't remember my physics well enough to be sure, but don't softer metals dissipate heat faster than harder ones?
If so, the increased habit of people sitting at traffic lights/in traffic/etc with their foot on the brake pedal could be the cause.
The contact of the pad on the disc whilst stationary means that part of the disc can't cool as quickly as the exposed part, thus having the potential to cause warping. Maybe softer metal might cool better whilst also being less likely to warp do to decreased rigidity.
Again, no real basis for this idea, but a possible reason for the car makers to use softer metals? (If indeed this is the case.)
Cliff_Jordan
Grafter
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Registered: 01-08-2007

Re: M.O.T. day

Come and live in the London Borough of Waltham Forest Smiley.
The council does MOTs for residents of the Borough at their Transport Depot - no vested interest in finding anything wrong and their fees are less than commercial rivals. The added bonus for me is that they have a massive building (to service all the Council vehicles) so they have no problem in fitting my motorcaravan in, which is a big problem for most commercial operations.
Cliff
Community Veteran
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Registered: 06-11-2007

Re: M.O.T. day

Quote
  from Samurai`s post

The MOT is now a con as if the car leaves the garage you cant get a free retest like you used to.

Yes, in some places it seems to be a con  However, I think you will find that there is the following on your failure certificate...
"If this vehicle is removed from the testing station for repair and returned for a retest within 10 working days, then only a partial retest is needed and a partial retest fee may be charged"
This is what I did..... Took it back this morning, and they did a "partial retest" and passed the things that it failed on originally.... no charge....
The "con" is when they tell you.....
"Sorry sir, it failed on xxx xxx xxx and xxx.  If you leave it with us, we will fix it and not charge you for the re-test"..
Oh... Right, then,  So how much will it cost? 
"mMmmm... can`t be sure exactly until we get the bits and do the job..... probably about £XXXX. but you won`t need to worry about booking it in for another test, as we will do that as well."
The inference is that further test expense is inevitable, so you are pressurised into accepting their "offer" to fix it for you....  (of course, you would not want to be caught driving a car without an MOT now would you?)  etc.,
They carefully avoid mentioning the fact that you CAN take the vehicle away, get it repaired (diy) and bring it back within 10 WORKING days... for a "free" or Partial test fee....
Wink

EDIT..... Quite a few council transport depots do the MOT for "joe public".... it just isn`t advertised..... I know that Leicester and Portsmouth definitely do...Plus a couple of others that I have heard of... All you need to do is look in the phone book (yellow pages) and phone up to find out.....

Community Veteran
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Registered: 10-08-2007

Re: M.O.T. day

Quote from: Whiffler
Come and live in the London Borough of Waltham Forest Smiley.

No thank you Grin
Denzil
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Registered: 31-07-2007

Re: M.O.T. day

Quote from: James_H
Can't remember my physics well enough to be sure, but don't softer metals dissipate heat faster than harder ones?
If so, the increased habit of people sitting at traffic lights/in traffic/etc with their foot on the brake pedal could be the cause.
The contact of the pad on the disc whilst stationary means that part of the disc can't cool as quickly as the exposed part, thus having the potential to cause warping. Maybe softer metal might cool better whilst also being less likely to warp do to decreased rigidity.
Again, no real basis for this idea, but a possible reason for the car makers to use softer metals? (If indeed this is the case.)

Heat dissipation has nothing to do with hardness of the metal. I can't see that having your foot on the brake would have that effect IMHO. When your foot is off the brake there is a very small gap between the pads and the disc, so there will be very little airflow through the gap. If there was a big enough gap for airflow there would be a heartstopping and dangerous delay between application of foot to pedal and actual stopping as the pads take up the 'slack'.
Softer (and cheaper) steels may be the cause of the problem as they will wear a lot quicker.
Community Veteran
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Re: M.O.T. day

Not being an expert, but................ When braking, the brake pad(s) bear down on the disc causing friction, which causes heat, in both materials. By keeping your foot on the brake, when stopped (stationary) at a junction/traffic lights, the pad and disc remain in contact.  Assume the disc is being cooled by the surrounding air, the section that is in contact with the disc pads , does not get any cooling effect, but is also having the heat from the disc pads transferred back into the disc.....  (or the heat dissipation is reduced in that specific area..... this can in extreme circumstances cause distortion of the disc itself, due to unequal cooling....
Edit::::::  Also don`t forget that your brake lights will be illuminated too!.... so it could also contribute to premature failure of the brake light...... ( watch out..... plod can stop you and check the rest of the vehicle! !)
Community Veteran
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Re: M.O.T. day

Pads and discs have never been the same since asbestos had to be removed from the compound for pads (and drum shoes) the heat resistance is nothing like what it was, therefore more heat, the more likely discs are going to warp at much lower temps. Don't know whether you've seen night shots of Le Mans 24 hour, with their brakes glowing yellow hot, but these are quite different from domestic brakes, using ceramic materials. There is of course nothing to stop you upgrading your brakes to better materials, if you've got a car that eats discs and pads, it may even pay you to do so. 
PS. @ shutter. prior to my very recent MoT my wife and I went round my car looking for failed bulbs the evening before, from there the car didn't move more than half mile to test station, and guess what....yup you've guessed it, a failed number plate bulb!!
Experience; is something you gain, just after you needed it most.

When faced with two choices, simply toss a coin. It works not because it settles the question for you. But because in that brief moment while the coin is in the air. You suddenly know what you are hoping for.
Denzil
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Re: M.O.T. day

He he, mine did the same recently. All the lights checked the day before, then the number plate lights fail.
@shutter - even if the brake pads were not in contact with the hot discs, the gap between them would be too small to allow much cooling airflow. They would still rely on heat being conducted to the rest of the disc. Besides, cooling when stationary is a slow process. Sitting at lights for a minute or two wouldn't be long enough to make a significant difference to the temperature.
Community Veteran
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Registered: 15-06-2007

Re: M.O.T. day

Bit of history.
I had the same problems of brake disc warping on my Humber Sceptre (not the big bulbous one but the later model) and the cause was the lousy design. I believe that the disks and bearing hubs were machined from a single lump with the discs themselves being quite thin. On a modern car the discs are bolted to the hub and are very much thicker. For this reason warping is much less of a problem but there is a minimum thickness and one they get down to that then it may well be an MOT fail point - certainly the garage will recommend changing them well before that point is reached.