brake discs - how do you tell when they're worn out?

[bella]

mine need replacing at the next service (in 4,500 miles) but i'm about to do a silly cross europe trip and was wondering whether there was any way i could tell whether they were in desperate need of replacing without doing anything daft like removing bits of the car?

/girly

[Dave Brand]

I assume that it's the garage which does your servicing that has told you the discs need replacing? If so, their advice that they need replacing at the next service means that it isn't urgent. Their advice will be based on the condition of the discs, their thickness.......and the fact that they want your money! Can you see the discs through the wheels? If so, do they look smooth & shiny, or are they rusty, grooved & generally scabby-looking? That's really the only check you can make - it's not easy to check thickness without the proper measuring equipment.

If the brakes are performing satisfactorily & the pads are not worn very close to their wear limit, I can't see any cause for worry. Pad wear is more of a concern if you're going on a long trip - when the pad wear warning light comes on (assuming your car has one!) you need to change the pads fairly quickly, not always convenient when you're away from home. (Note that the pad wear warning only operates on the front pads - if you've got discs on the rear, the only way to check is by visual inspection.)

[bella]

the pads are fine, they were replaced at the last service. the only thing that worried me slightly is that the abs kicked in twice yesterday in slightly unnecessary places. i *am* the last of the late brakers, especially where the car has had most of it's use, but we're going on an autobahn trek so it shouldn't be too bad.

i had a set of front pads completely wear down without the warning light coming on once, so that's been and done

the discs look fine, and the car's done this sort of mileage (1,400 miles in 3 days) before without issues, so i'm fairly relaxed (read : still in denial).

thanks for the advice

[275 GTB-4]

Originally Posted by bella

the pads are fine, they were replaced at the last service. the only thing that worried me slightly is that the abs kicked in twice yesterday in slightly unnecessary places. i *am* the last of the late brakers, especially where the car has had most of it's use, but we're going on an autobahn trek so it shouldn't be too bad.

i had a set of front pads completely wear down without the warning light coming on once, so that's been and done

the discs look fine, and the car's done this sort of mileage (1,400 miles in 3 days) before without issues, so i'm fairly relaxed (read : still in denial).

thanks for the advice

The machine is telling you something Bella....even new pads will be useless if the Disk Rotors are undersize. It just ain't worth the grief and worry if you are setting off on a long journey...especially...especially if you are the last of the late brakers!!!

Get a few quotes to replace the rotors...you may consider something like EBC Green Stuff pads...or maybe even Black in your case

[Dave Brand]

Originally Posted by 275 GTB-4

even new pads will be useless if the Disk Rotors are undersize.

New pads will work fine with discs which are below the specified minimum thickness; thin discs are more of a problem with worn pads, as they may allow the pads & pistons to move past their design limits. Of course, there are other issues with worn discs, such as loss of mechanical strength, etc., but limits are, & must be, set very conservatively.

[Dave Brand]

Originally Posted by bella

the pads are fine, they were replaced at the last service.

Hmmm, curious. The pads were replaced at the last service & they are telling you the discs will need replacing at the next service? When new discs are fitted new pads should also be fitted; looks like they are putting you to unnecessary expense...........

[bella]

nah, from the way we've always done it (parents have a car storage company, i get my cars through that and get cheap servicing from the local bmw garage where we take the fleet blahblah), i don't think i've ever replaced the discs and the pads at the same time. actually, come to think of it i've never had to replace the discs on a car before. it would make sense that they didn't need to be replaced at the same time though, because these things rarely synchronise like that?

[StuiE]

I've seen a disc totally worn, as in, all metal on one side gone and just rubbing on the vents, and the other side was pretty near to that too

[thebear]

I would ask the garage for specific a reason that necessitates replacement of the disc. A friend had over 150,000 miles on the original discs on his late 80's BMW 5 series. He bought replacements and returned them as they were not necessary.

Onr thing that may have initiated the ABS activity is a warped disc. There is no way to true them on a lathe as the warp will reappear in another place. Baring that, there is no logical eason to replace a disc unless it is under the minimum thickness which is usually stamped into the outer edge of the disc.

Many garages routinely remove the discs and turn them on a lathe when replacing pads. This is not necessary if there are no grooves in the discs from the backing plates of the pads or the `noisemaking' shims that signal time for replacement. Most minor grooves from stones that get circulated a few revs and discarded can be ignored.

[ss_collins]

I did a pretty intense rally a coupl of years ago and destroyed the brakes on the golf - the pads on one side crumbled away as they just cooked... still finished the rally. Didn't win though

[richard_sykes]

Anybody use Green stuff, are they worth the extra money.

My brakes fade so badly.

[graham bahr]

yes in a word,

they are also cheaper and work better from cold than a lot of uprated pads such as 1144's,
do let them bed in though before giving them extreme abuse

why not give the EBC technical guys bob and bart a call on 01604 593403
they might cut you a deal, race licence holders and marshalls get a good deal so give it a go

[richard_sykes]

Will do, cheers.

[graham bahr]

Originally Posted by thebear

Many garages routinely remove the discs and turn them on a lathe when replacing pads.

mabye in the US but not here in the UK