Do I need Brake Discs changing aswell or is the garage having me over?

EdGasket

Strider590 wrote: »

The discs often used to be on the inside of the wheel hub, requiring the whole upright assembly to be dismantled, even the wheel bearings dismantled in some cases (like the Ford Cortina).

Ah the Ford Cortina, lovely, all that poetry in a motor.

Johno100

molerat wrote: »

It is cheaper to change the disc than to clean them up at £90 an hour labour. If the discs look OK I remove them, clean off the lip and rust, de glaze the braking surface and re fit which would take the best part of an hour all round. A decent set of after market pads (Mintex, Delphi or even EBC) is around £60 - £80 and discs another £150. These garages obviously use the merc owner = deep pockets factor.

I thought they had kit nowadays that allowed discs with sufficient 'meat' on them to be skimmed and 're-surfaced' while still on the hubs?

AdrianC

Johno100 wrote: »

I thought they had kit nowadays that allowed discs with sufficient 'meat' on them to be skimmed and 're-surfaced' while still on the hubs?

That's been around for donkey's. But it's fallen out of use, because it's now cheaper just to put a new pair on.

arcon5

How on earth do we know? We haven't even seen the discs!

Joe_Horner

Contrary to popular belief, scoring of disks makes very little difference to the stopping ability even before the pads are bedded.

That's because of basic physics - the frictional force (ie: the stopping power) depends on two things: The coefficient of friction between the pads and the rotor and the total force pressing them together (ie: the force applied by the caliper).

Within very wide limits it doesn't matter whether that force is a small pressure over a large area (new, flat, disks) or a higher pressure over a smaller area (grooved disks with only partial contact). If contact area made a difference to stopping power then disks like these EBC ones would be a very bad idea because of all that "missing" contact thanks to the holes and grooves:



What wear grooves do make a difference to is heat dissipation. The average ability to get rid of heat won't change much, but the pads will be heated unevenly because they only heat directly where they contact the disks (because that's where the friction happens!)

So badly scored disks can theoretically cause local hotspots on the linings and potentially glaze them, making them less effective until the glaze breaks down.

They'll also cause faster initial wear (until the pads match the grooves), so shorten the life of the pads slightly - if the grooves are 1mm deep then the first 1 mm of the pads will wear away slightly faster.

None of which is likely to be a real-life problem in a car with brakes designed to deal with 100MPH+ (ie: most, if not all current models) while being driven at anything like legal speeds on the road.

On the other hand, letting the scare rumours becoming "common knowledge" is an excellent way to sell extra disks.

straighttalker

Johno100 wrote: »

I thought they had kit nowadays that allowed discs with sufficient 'meat' on them to be skimmed and 're-surfaced' while still on the hubs?

Yes they do but look at the prices charged...

http://www.awesomegti.com/brake-skimming/

Only economically viable for expensive performance discs.

s_b

straighttalker wrote: »

Yes they do but look at the prices charged...

http://www.awesomegti.com/brake-skimming/

Only economically viable for expensive performance discs.

mike brewers mate (the tall one ) had some discs skimmed on a Porsche a few weeks back because the discs were apparently £900

to OP youve already had your pants felt by the local garage when you agreed to £350 for a pad swap so its only right he went for the full movement by saying likely your discs will need doing too:D

get another quote from an independent local operator thats established

Silver-Surfer_2

s_b wrote: »

mike brewers mate (the tall one ) had some discs skimmed on a Porsche a few weeks back because the discs were apparently £900

to OP youve already had your pants felt by the local garage when you agreed to £350 for a pad swap so its only right he went for the full movement by saying likely your discs will need doing too:D

get another quote from an independent local operator thats established

It was a good few weeks ago. That's a 2013 programme.

s_b

Silver-Surfer wrote: »

It was a good few weeks ago. That's a 2013 programme.

im a moneysaver so dont have sky i saw it on quest channel 37 because its free tell you
freeeeeeeeeeeeeeeeeeeeeee:D

AdrianC

s_b wrote: »

mike brewers mate (the tall one ) had some discs skimmed on a Porsche a few weeks back because the discs were apparently £900

You aren't believing daytime TV repeats again, are you...?