Why are my discs warping?

[falkster]

My workhorse is a 2006 C class avantgarde se with the sport pack (only gave the full Sunday name as its got the 330mm drilled discs as standard).
I've had the car 18 months, done roughly 40k in it and I've replaced the discs once and had a set skimmed too but they are now ready for doing again.
I bought Pagid discs and pads so thought the quality would be pretty good - I don't understand why they're constantly warping. I drive like I'm driving miss daisy, I do 100 miles a day all on the motorway and rarely use my brakes. I push it into N when at the lights but still the warping occurs.
Any ideas?

[mk2 24v]

You put it in N, but do you sit there with your foot on the brake still?
usually the main cause of disc warp in my experience

[falkster]

mk2 24v said:

You put it in N, but do you sit there with your foot on the brake still?
usually the main cause of disc warp in my experience

Unless I absolutely have to I just sit without the brake applied.

[gavsdavs]

http://www.stoptech.com/technical-support/technica...

[lanan]

^ What he says. Discs don't warp, common misconception.
I was with the OP and fitted Pagid discs to my car and they were dreadful after just 100 miles. Pagid pads are great, but not had good experience with their discs. Amazingly in desperation I fitted a set of EBC discs and they were spot on

[Mr2Mike]

lanan said:

^ What he says. Discs don't warp, common misconception.

Discs certainly can and do warp, but the majority of brake judder problems are caused by other issues such as uneven pad transfer.

[falkster]

Mr2Mike said:

lanan said:

^ What he says. Discs don't warp, common misconception.

Discs certainly can and do warp, but the majority of brake judder problems are caused by other issues such as uneven pad transfer.

Id agree if I hadn't replaced all the suspension arms, shocks and wheel bearings in the search for the most enjoyable silent drive to work.
I think I'll try a different type of disc, I chose pagid because they've always been good - might try textar

[blank]

falkster said:

I do 100 miles a day all on the motorway and rarely use my brakes.

This is probably your cause.

Driving without using the brakes generates DTV (disk thickness variation) which causes judder.

Check:
Wheel bearings for play
Hub faces for runout
Disks for runout (ideally when properly bolted up on the car)
Disks for DTV


You could also try giving the brakes a work out now and again to 'clean up' the DTV.

Edit:
You might find genuine Mercedes parts the best bet. They will have tested them for susceptibility to DTV generation and vibration during development. Pagid et al won't have.

Edited by blank on Wednesday 24th June 21:28

[With these feet]

Are the calipers themselves clean and move freely?
How about the stub axle? if the surface the disc mounts to flat and corrosion free? Had a Porsche in that had a damaged mounting flange and when the wheel was bolted on it deformed the disc.

Also check the wheels are seated properly and if required the centralizing spacers are there.
Friend had very similar issues with a Merc people carrier. Turned out the wheels were the cause as they were moving slightly which caused judder under braking which felt like an out of true disc.

[Dave Brand]

blank said:

You could also try giving the brakes a work out now and again to 'clean up' the DTV.

Edit:You might find genuine Mercedes parts the best bet. They will have tested them for susceptibility to DTV generation and vibration during development. Pagid et al won't have.

Giving the brakes a good workout has cured rumble for me on a couple of cars!

As for testing, vehicle manufacturers work with brake & friction material manufacturers when developing new vehicles, so the friction material manufacturer will be aware of any problems. Testing does, however, tend to concentrate on the higher end of the performance spectrum & is not done on vehicles which are a few years old . . . no point in testing the old model!

Mercedes OE pads are probably made by Pagid.

[CrutyRammers]

blank said:

This is probably your cause.

Driving without using the brakes generates DTV (disk thickness variation) which causes judder.

I may be being thick here, but how does not using the brakes cause the disks to change thickness

[fatjon]

It doesn't, it's cobblers.

Having had a dial gauge on either side of several warped disks and seen the needles moving in unison I can tell you for sure that they do warp.

[blank]

CrutyRammers said:

blank said:

This is probably your cause.

Driving without using the brakes generates DTV (disk thickness variation) which causes judder.

I may be being thick here, but how does not using the brakes cause the disks to change thickness

If the disc has runout, then when the wheel turns one part of the disk will catch the pads more than the rest. Doing this over extended periods of time without using the brakes causes DTV.

It's certainly not cobblers. If it is then lots of car manufacturers are wasting huge amounts of money on testing.

[blank]

http://www.bendix.com.au/news/disc-thickness-varia...

That about sums it up.

[fatjon]

blank said:

CrutyRammers said:

blank said:

This is probably your cause.

Driving without using the brakes generates DTV (disk thickness variation) which causes judder.

I may be being thick here, but how does not using the brakes cause the disks to change thickness

If the disc has runout, then when the wheel turns one part of the disk will catch the pads more than the rest. Doing this over extended periods of time without using the brakes causes DTV.

It's certainly not cobblers. If it is then lots of car manufacturers are wasting huge amounts of money on testing.

So you justify this theory by changing the statement to include an additional parameter, that the disks must have runout for it to not be bks. In either case it's still cobblers as the runout will push back the pads by design until they no longer touch the disks, that is how disk brakes work and why you end up with a long pedal when you have warped disks and/or failing wheel bearings, the pads get pushed back further. If the disk has runout then one cirumferential strip will be closer to the pad and wear in preference to the rest of the disk until such a time as the pads wear to take up the runout. Unless of course the "runout" is variable around the circumference of the disk, AKA it's warped.

[blank]

Sorry, you clearly know more than me about it.

I'll contact all of the manufacturers I have done DTV generation tests and investigations for, refund their money and give them your contact details.



A perfectly flat and uniform disc can still have runout when installed.

[aka_kerrly]

falkster said:

I chose pagid because they've always been good - might try textar

I don't know why you would think Textar are any better given they are the same company as Pagid and Pagid provide Mercedes parts.

[Mr2Mike]

fatjon said:

If the disk has runout then one cirumferential strip will be closer to the pad and wear in preference to the rest of the disk until such a time as the pads wear to take up the runout.

Read that back and see how daft it sounds. Pads can not possibly "take up" disc runout because the angle between the pads and disks is constantly changing as the disc turns. The pads will likely wear unevenly, as will the discs, but the wear can not compensate for the run out

[andyiley]

He seems to think his pads are working like a lathe tool!

[ch427]

Maybe you had eicher discs in a pagid box as they are made of chocolate!