But at first glance without getting a micrometer out, it's the best indication we're going to get with minimal faff.
But at first glance without getting a micrometer out, it's the best indication we're going to get with minimal faff.
I doubt many average garages have a micrometer handy these days, and TBH, given discs for most cars are cheap, you could just replace then if they look at all suspect.
I remember my Vespa recommending clutchless changes. But it had a spring drive in the transmission to reduce the impact on the dogs. There are springs in most clutch plates which have a similar effect - but aren't going to stop wear on the synchro.
******************************************************************Well my method is (was) to match the revs in neutral whilst pushing lightly on the gear lever. When they are perfectly matched the gear lever just slides in gently with no jolt or grind at all.
Just like magic, hence the smug grin ensuing. If it doesn't go in smoothly, then it just doesn't go in at all.
I first learnt to do this in my parents' Triumph Herald, which didn't have synchromesh on first gear. I was able to get it up the steep driveway without stopping, and the gearbox never fell out once.
But perhaps I won't do that much any more on my Focus.
Gareth.
On many cars changing the disks is only a little longer than changing the pads - two bolts and the caliper and carrier lift off, one retaining screw (if any) and the disk pulls off. Quick clean of the surface of the hub, new one on. Temporarily clamp in place with the wheel nuts and check for run-out with a dial-test indicator. Caliper and carrier back on, carrier bolts back in.
SteveW
Yeah, about as reliable as squinting at a tyre and deciding it's at the correct pressure.
Chris
That's not a good analogy, unless disc can get pumped up and look like new?
A better analogy is to look at the tread of a tyre and make a guess how many more miles it will last.
I'm struggling here with why so many people seem to think micing a disc is such a big deal? It only takes (literally) a minute or less.
It's not the micing of disc. It's the micing of disc DURING an MOT. It may be grounds for a "incorrect test procedure" V17. Access to mic a disc with the wheel on is very limited and MOT tester is not allowed to remove parts for access.
Of course if you do the idiot thing and use a place that does "MOT + service" then during the service they can measure the disc.
Equally how do you mic a disc when inspecting a prospective purchase? It's not going to happen at a dealer or auction. You might get a private vendor to let you do this but it may cost you as they will be less inclined to reduce the price for your messing around unless you can show them the disc is worn below the limit.
In the context of an MOT, no dismantling of the vehicle is permitted.
In addition to removal of the wheel, every car I've owned has required calliper or pad carrier removal in order to make room to get a micrometer on the disc.
If you could safely raise and support a car, remove a wheel, remove a calliper, and take a measurement of the disc thickness in less than a minute, would you please come and work for my local garage? Because their labour charges would be the lowest in the land.
Chris
Either way, it makes a nonsense of using disc lip appearance as a guide to remaining life.
Chris
Mate, if you have to do all that just to mic a disc then either you've owned some very peculiar cars or you've used a very peculiar micrometer.
I know someone who was taught long ago to find the clutch biting point by the sound of the engine slightly dropping.
With her aged related hearing issues, she can't now really hear the engine to do that, unless she gives it a bit of gas almost flooring the
1 litre engine. That well maintained Polo from new has done 15,000 miles in 14 years, I hope the clutch should reliably out-scream the rest of the life of the vehicle.
Are you saying an MOT can be refused due to disc wear? If so, that wear needs defining. Tyre tread depths are already covered.
You look at the service history. If none, expect other servicing to have been neglected too - and price accordingly.
+1 The clutch in my car lasted 75K miles but much of that was in rush hour(s) commuting traffic where a 14 mile journey could take between 30 to 45 minutes (and quite often 60 minutes).
In 130k miles 3 sets of front brake pads and one replacement set of disks.
It's much like petrol consumption where a full tank in the above driving conditions would get me 330 miles. On a recent holiday with 400+ miles of fast motorway driving and 1000+ miles of fast driving on near empty A roads and winding country roads I was averaging 450 miles per tank.
And possibly with rust as well
But on some cars replacing the disk at the same time as the pads only takes around 10 minutes extra.
The MoT Inspection Manual from DVSA for Classes 3, 4, 5 & 7 includes reason for rejection 3.5.i "a brake disc or drum in such a condition that it is seriously weakened or insecure"
Isn't this why they give the advisory? You then have the thickness of the disk checked.
Be interesting how they know a brake drum is seriously weakened without removing it?
I'm not your mate.
I've owned a couple of versions of the Ford Focus, possible the most common car on the road. Explain to me how you would measure the disc thickness with a micrometer.
Chris
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