23 replies to this topic

[buxvan]

just fit them & start using the brakes. they will soon get rid of the rust. how many new cars do you see with rusty discs when they have not been used for a week or so in wet weather ?

[mini93]

most shot which people have access to wont damage the disk in any way. Where iv previously worked, we shot blasted some inner components of turbo's delicate parts... all part of the reconditioning process... there isnt any damage noticable

[MRA]

However for the price of new discs... I would simply replace them if they are that bad or drive it to "clean" them up, after all look at most cars after a rainy day and the discs are rusting almost immediatly..

[dow62]

Unless you are getting your discs shotblasted/skimmed for free, why not just fit new ones, not a fortune to buy ( 8.4's )

[tiger99]

Well, at least four different basic opinions, and all of them have a point, but it depends on the depth of the rusting. If there is an unrusted patch under the pads, you will forever have brake judder if something is not done to get rid of it, and that means a lathe, or replace them. It might even be cheaper replacing them than paying for someone who actually knows what he is doing with a lathe.

But if it was simple rusting all over, I would try something different, the electrolytic treatment, using sodium bicarbonate, as has been shown working on various steel bits in at least one build thread, followed by careful use of the brakes until the pads finished the job.

I seriously doubt that blasting would damage the disks, unless overdone, but it can't get them flat and parallel if there is a non-uniformity caused by the pads.

[benspickup2011]

Just blast them, this will enable you to see the true condition of the discs. I have found that they do not wear out your pads any faster really. They clean up quickly once in use. If someone thinks they can warp 10mm thick brake discs just by blasting them? Whatever next.

[TopCatCustom]

I would put money on shot blasting in a home type cabinet not damaging the discs, in fact I'd put £500 on it straight up.

I had a body shell shot blasted a while ago by a company with massive industrial blasters, and not a single part was warped (I did not have the roof or quarters done) but what they did was approx 1.5mm thick and no warping so how anyone can say some sand coming out at 80psi will warp a 10mm thick lump of steel is beyond me, and as Martin said any pitting will be done by the rust not the blasting (apart from a tiny amount of surface dulling which is minute pitting).

Personally I would wire brush them to get the loose off, then give them a going over with some glass bead or fine sand, followed by a good clean. Once they have warmed up and been used a few times they will be as good as any other, unless they are rusted majorly!

[redhotminilewis]

I would put money on shot blasting in a home type cabinet not damaging the discs, in fact I'd put £500 on it straight up.

I had a body shell shot blasted a while ago by a company with massive industrial blasters, and not a single part was warped (I did not have the roof or quarters done) but what they did was approx 1.5mm thick and no warping so how anyone can say some sand coming out at 80psi will warp a 10mm thick lump of steel is beyond me, and as Martin said any pitting will be done by the rust not the blasting (apart from a tiny amount of surface dulling which is minute pitting).

Personally I would wire brush them to get the loose off, then give them a going over with some glass bead or fine sand, followed by a good clean. Once they have warmed up and been used a few times they will be as good as any other, unless they are rusted majorly!

When I say warped, It is meant in the sense that the brake rotor surface is not even, Not warping as in bending the rotor, otherwise i would have stated that, and which you said, would be very very unlikely.

The "warping" I am talking about is where you have uneven transfer of the brake pad material on the disk. The cause of this is having "high spots" on the rotor itself. if you hand shot blast them, you will not get an even surface as some areas of the disk may have more shot treatment than other (even if you try your hardest not too) and will leave high spots. High spots can then cause this "warping" and in some serious cases, case cracking of the rotor itself, see picture:



Machine shot blasting with a shot blasting line will reduce the likelihood of this happening but again, it can still happen. Obviously there are other causes for heat cracks in rotors but this is one cause.

As i stated before, to make sure your disks are true and free of "high spots", the lathe is one of the best ways to go! Or, buy new rotors and pads.

Lewis

[benspickup2011]

The shot blasting only removes rust, so it will not warp a un warped disc.