Found out in angle grinder shocker! - Clanger
A couple of days ago I took Mrs H's C3 for its second MoT. I go to a local independent where I can chat to the tester and look under the car. On examining the front discs, he exclaimed, "Someone's been at these with an angle grinder!". I confessed my crime and he asked if I had any vibration when braking from high speed. The answer was no. The braking efficiency on the brake meter was found to be good. Now I know that discs are not expensive but it was an interesting experiment occasioned by having the car in pieces on the Sunday before a Bank Holiday. When I asked the tester how he knew, I got a passable imitation of Ham in Toy Story 2, "I can tell."

If you are of a sensitive disposition, look away now. My method was to jack the car up, jam one wheel with a screwdriver in the disc ventilation slots, engage second gear and take off the inner and outer ridges with an angle grinder. No attmpt was made to polish or flatten the main contact area; it seemed in good enough nick. New pads went in, followed by some extensive testing before I let Mrs H loose on the car. I first got the idea from a poster on this very forum. Next time I will be a jolly sight cleaner if I put new discs on and bin the old ones; the amount of rusty filth penetrated nearly every orifice.
Hawkeye
-----------------------------
Stranger in a strange land
Found out in angle grinder shocker! - Dynamic Dave
It is worth noting that you take Hawkeye's suggestion at your own risk. It is also worth mentioning that you should never rely on a jack alone to support the vehicle. Jack up, then place on axle stands, making sure the car is secure before carrying out any work. There was no mention of this above, but I am *sure* it was a mistaken omission.

Whilst I've been typing this, I've also been doing a forum search in the background. The closest discussion I could find on a similar subject to this has previously been covered by our ex-moderator Mark, and I think that what he advised still stands.

www.honestjohn.co.uk/forum/post/index.htm?t=12910&...e

DD.

::EDIT::

I previously locked this thread, but on reflection have changed my mind. I have also moved the postings that were added to the above link to here. Please bear in mind though what was said in the above link, that being for those too lazy to bother clicking on it:-

"No more on that particular approach please.

A spinning disc and a file (or grinder) which could shatter or be snatched out of your hand seems a silly combination and should not be recommended.

Further notes on that line will be removed.


Found out in angle grinder shocker! - martint123
My local rural garage has a disk grinding machine. Fit disk, adjust grinding wheels, start machine, finished in about 5 minutes per disk.
He charges a couple of quid a disk. No point in messing about.

Martin
Found out in angle grinder shocker! - bell boy
do you mean he does the discs in situ on the car or you take the discs off the car and hand them over ala lathe ie?
Found out in angle grinder shocker! - martint123
do you mean he does the discs in situ on the car or you take the discs off the car and hand them over ala lathe ie?

Take discs off car, ride motorbike to garage, put discs on machine, drink coffee.
It's not a lathe, more a dedicated disk grinder. A pair of fast spinning grinding wheels make their way down the slowly spinning disk along a worm drive. It does it all on it's own.
Found out in angle grinder shocker! - Bill Payer
My neighbour has a Porche Boxter which he doesn't use very much, and there's never a mark on the disks - they're still shiny even when the cars been stood for 2 weeks.

Mine look horrendous when left overnight.
Found out in angle grinder shocker! - Hamsafar
" My neighbour has a Porche Boxter which he doesn't use very much, and there's never a mark on the disks -"

At £400 a pair, I should damn well hope not! :o
Found out in angle grinder shocker! - bell boy
yes the porsche ones are paved in gold................
actually i thought they corroded like all the others and were the cause of endless disputes with owners and the dealers?
Found out in angle grinder shocker! - Craig_1969
It is not unusual for boxster disks to last 2k before the dealer tells you they need replacing. I had to replace the disks on the rear of my phase iv espace recently, wish i had hung onto the old ones now and had them ground down.
Found out in angle grinder shocker! - Hamsafar
I remember reading about 5 years ago, of Porsche number 911 with ceramic disks which cracked after a few thousand miles landing the owners with a £6,000 bill!! Thankfully, they seem to be able to get pattern parts for £2,000 these days!

tinyurl.com/rgv9o

Found out in angle grinder shocker! - yorkiebar
With the price of most discs for most ordianry cars now a days it is cheaper and better to just replace discs and pads when needed rather than even attempt to grind/lathe them smooth?

Time taken to strip off for work needed is same as replacing, cost of machining them etc probably same as new discs? Not worth the effort to get smooth worn down discs?
Found out in angle grinder shocker! - martint123
cheaper and better to just replace discs and pads w

I've just checked and just over £100 for new discs and pads all round for MX5 - they're just run of the mill, nothing special.
Found out in angle grinder shocker! - yorkiebar
Ok, but how much would it be to skim discs and renew pads?
Found out in angle grinder shocker! - martint123
Ok, but how much would it be to skim discs and renew pads?

Like I said earlier, £5 to skim the discs - full surface.

New bits:-

What's In My Basket?
Kevlar Rear Pads £18.79
Brake Discs Front £28.80
Brake Discs Rear £25.50
Kevlar Front Pads £23.03


Found out in angle grinder shocker! - yorkiebar
But you have then got discs that are even thinner? Front and rear discs for 53 quid, you would need pads anyway whether changing discs or not. Replace discs for 53 or skim for 10? I Know which I would choose and if I was doing it for a customer the time involved would equal more expense than just replacing them.
Found out in angle grinder shocker! - martint123
Replace discs for 53 or skim for 10? Pardon? I said £5 for skim. Discs are well within min thickness stamped on them and as usual the lip on the edge is raised rust clinker rather than a wear lip so the amount of material taken off the braking surface. For me, why throw 50 quid away. If you're doing it for a customer, then maybe fair enough. The garage says that the machine was well worth it and no doubt their normal servicing customers appreciate not having to pay for new discs when it isn't necessary.
Found out in angle grinder shocker! - JH
A
oh, that's ok then, only £2,000. !!!
JH
Found out in angle grinder shocker! - Pete M
Here in New Zealand discs often last the life of the car because there is no salt on the roads. There are mobile disc grinding operators who mount the machine to the hub and grind both sides of the disc without removing it from the car. I did replace the front discs on my Mitsubishi Galant Estate as they were worn below limits and shuddering. I suspect they had been used hard in Japan before it was imported here. That was at about 100,000 km (62K miles), and they were not rust-affected at all, just worn out.
Found out in angle grinder shocker! - Cliff Pope
I think there is a big distinction between simply grinding off a thin bead of outstanding metal around the rim, and a major refacing of the contact surface itself. The latter I would definitely leave to a professional, if indeed worth doing at all.
But I have sometimes removed a disk that had a thin bead around the edge and ground it down on the workbench until I had got the protruding metal down to the level of the rest of the disc. It is then worth going round with sandpaper on a block, in a circular movement, to polish it smooth. Carefully done there are no grinding marks on the disc and it looks like new. Obviously you have to be aware of the permitted minumum thickness.
Sometimes pads don't have quite enough area to fully cover all the disk surface, so some kind of grinding becomes necessary at some point, particularly before fitting new pads, or they won't contact properly.
Minor scours can also sometimes be polished out with sandpaper..
Found out in angle grinder shocker! - cheddar
Discs have a minimum thickness, so grinding not always applicable, 22mm as it happens on the Mondeo fronts, I recently measured them as 22.6mm with a micrometer so need doing soon. They were last changed at 65k and now on 109k, also the dealer highlighted them as an forthcoming job at the last service at 104k. The pads have a little life in them so as usual I have bought the parts in advance so I can do the job at my leisure. So for new discs and pads I got a nice discount from the Ford dealer, a benefit of being a good customer, under £90-00 all in, list price around £150.
 

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