Significantly more wear on rear rotors vs front rotors on new BBK

[LakeTahoeQuattr]

So back in April '16 I did my bbk setup with b6 s4 rear calipers and 310mm a8L rotors (stop tech slotted). Front was 18Z with 350mm Giro discs. Hawk HPS all around.

So I have noticed significantly more wear on the rear rotors than usual after only 6 months. I am able to run my finger along the rotor and feel the lip around the outside edge. Equal wear on both sides. Front rotors have no lip what so ever. Additionally, after a normal drive around the block I touch both rotors to feel the rear rotors significantly hotter than the fronts. Now I know that the fronts will dissipate heat more than the rears but i would not expect them to be so hot under normal conditions

I am thinking that the e-brake cable may be too tight. I have not adjusted it since the b6 rear install. I am able to lock the car on a hill by just pulling the e-brake 4-5 clicks up. This is the same amount of tension required with the old allroad single disc calipers. The car will roll by itself at a mild incline without the e-brake on

I have not adjusted the brake bias in vcds because forum / friend census said it was not necessary. I am not able to lock up the rear under heavy breaking. Biasing feels normal to me.

I have read that vag cars may use the rear brakes more under normal / relaxed driving. Is this true? On our stock c5 4.2, there is always more brake dust on the front wheels that contradicts this claim. Anyone have any thoughts or suggestions on this matter?

Rear w/ only 8k miles:


Front w/ 8k miles:

[G0to60]

You could probably check your ebrake theory by jacking up the rear and hand turning the rear wheels. If the ebrake is dragging you should be able to hear it and maybe feel more drag then what the drivetrain would cause.

It may not be quite the same but on my wife's 20th AE GTI her back brakes tend to wear slightly more then her fronts. Her originals from the factory did this and the next set also is doing this. She has vented both front and rear, similar to your BBK.

[LakeTahoeQuattr]

I have tried this when the car was cold and they spun freely. When the brakes are heated up it seems like it is more hesitant to roll on a mild incline. Rotor expansion maybe..

[julex]

so... what about pads? Were you able to find EXACTLY same pads brand/model to match 18z and new rears? If you mixed and matched and got some really harsh stuff for rear, that would explain difference in wear and dust would not be of any indicator of how hard are brakes working since they would dust differently as well.

When I was looking for 18Z pads, it was hard to find what I liked to match 350mm front to stock pad size for audi (although I have S8 rear calipers, which really means vanilla V8 caliper mounted on S8 carrier bracket and 300mm rotors) and no-dusting at that. My favorite, Akebono doesn't make pads for 330mm/350mm 17/18z at all so that went out of the window. I eventually found that Axxis 45-03400D Deluxe Advanced Premium Ceramic Brake Pad Set for rear and Axxis 45-0977ED Deluxe Advanced Premium Ceramic Brake Pad Set for front was the ticket as I have ZERO dust, I mean zero, like akebonos and even better brake performance than akebonos ever had. Although I believe that they discontinued or renamed themselves since then.

[LakeTahoeQuattr]

I am starting to think that this may be a b6 / b7 rear caliper deal. Maybe not.

I am running Hawk HPS in the rear and Hawk HPS Street 5.0 in the front. No dust from any wheel ever. The car stops as fast as the tires will allow.

After more research the inter web states that people often need to replace rears before fronts. Is this not the case for you? You basically have the same rear setup as I do...

[julex]

I am starting to think that this may be a b6 / b7 rear caliper deal. Maybe not.

I am running Hawk HPS in the rear and Hawk HPS Street 5.0 in the front. No dust from any wheel ever. The car stops as fast as the tires will allow.

After more research the inter web states that people often need to replace rears before fronts. Is this not the case for you? You basically have the same rear setup as I do...

I had Hawk Ceramic before and I didn't like the pad, it is relatively dusty IMHO even though it has "Low dust output" designation HPS doesn't... My baseline comparison is Akebono Euro Ceramics which you can drive on for 1y without a wash and there will be ZERO residue on rims when you swipe your finger over. I mean zero. That's "Dust free" nobody else can match except for select few pads including these Axxis ones.

Anyhow, Since you have different formulations you can safely assume that's the reason. Front is probably weaker bite/torque causing you to use more pedal resulting in overworking rears and the wear you see.

Wear on my rears is in norm, nothing abnormal here and since rear rotors are super cheap I would not worry if it was anything significant either.

[LakeTahoeQuattr]

True, I am glad that my two piece fronts are not getting eaten. So you suggest a slightly lighter compound in the rear? Couldnt a vcds re-code help this bias?

Can you confirm that audis typically are rear brake biased under normal / casual driving to decrease nose dive? Or is this a fable?

Could an improper brake bleed also result in this issue. Such as rear brakes are bled better than fronts for some strange reason?

[ChicagosPhantom]

I am starting to think that this may be a b6 / b7 rear caliper deal. Maybe not.

I am running Hawk HPS in the rear and Hawk HPS Street 5.0 in the front. No dust from any wheel ever. The car stops as fast as the tires will allow.

After more research the inter web states that people often need to replace rears before fronts. Is this not the case for you? You basically have the same rear setup as I do...

I'm installing same setup as you on my A6,just different pads EBC RED all around.We'll see how it goes.

I'm not doubting your work my Taho friend, just going over stuff...did you space out rear caliper/carrier correctly?Discs being eaten from both sides (inner/outer) the same?Pads wearing evenly?Have you rebuild calipers and guide pins before install?Were you able to retract pistons fully before install?

I had issue with HPs pads before on my very first A6 that I recently sold.Front's were dusty,had a squeal in front left (that could be something else),rears were OK on stock brake setup...they had even wear on all four corners,but on solid rear discs they were kinda harsh.Those rotors were 10mm thick (WTH Audi?).

[LakeTahoeQuattr]

I'm installing same setup as you on my A6,just different pads EBC RED all around.We'll see how it goes.

I'm not doubting your work my Taho friend, just going over stuff...did you space out rear caliper/carrier correctly?Discs being eaten from both sides (inner/outer) the same?Pads wearing evenly?Have you rebuild calipers and guide pins before install?Were you able to retract pistons fully before install?

I had issue with HPs pads before on my very first A6 that I recently sold.Front's were dusty,had a squeal in front left (that could be something else),rears were OK on stock brake setup...they had even wear on all four corners,but on solid rear discs they were kinda harsh.Those rotors were 10mm thick (WTH Audi?).

I guess I should just be happy since there is little dust, no squeal, no vibrations, fade, or anything for that matter.

Yea those 10mm rear single disc rotors were not the business. I just went and checked and can confirm that the rotor wear is on both sides of the rear rotors, not just the outsides. I guess in all actuality after 8Kmiles only .5mm of wear is normal. With spirited driving I think 25 - 30K out of the rears will be ok.

I did not rebuild the rears, but I did clean and lube the guide pins and confirmed that they did slide smoothly when I got them in the mail. Everything checked out. I am starting to believe what Julex said about my rear ceramic pads being a little hard on the rear rotors. Funny thing is that the pads still appear to be a half inch think "new" in the rear so they must be winning the battle.

Nominal thickness is 22
Minimum Thickness is 20

So at this rate I should expect over 20K which I guess is more or less normal...

[glennda5id]

You can not adjust brake bias with VCDS. The braking system is purely mechanical and the only way to adjust bias is to change the size of the brakes.

I highly doubt you have worn .5mm of the rotor. Have you used calipers to check?

I plan to run S4 rear calipers and find it annoying that Hawk doesn't make the HPS 5.0 it. All I can say, is that may be an issue but I sort of doubt it.

Why not adjust the parking brake so it is very loose and do some rotor heat tests. Do you have an IR temp gun?

[LakeTahoeQuattr]

But you can code what brake setup you have in vcds so it modulates the abs correct?

Good idea, I will grab some calipers and go check in a few minutes. I have an IR gun, I will also try your suggestion.

[glennda5id]

The ABS coding doesn't change your bias, but it can impact how the module works when the abs is used. It isn't in use most of the time though so that isn't your issue.

[LakeTahoeQuattr]

I measured the surface to surface to be 21.90mm. Top of lip to lip is 22mm so maybe it just visually looks worse than it is and I am over reacting. Just in comparison to the front there is more wear.

[glennda5id]

yeah, so I would loosen the parking brake cable to make sure to rule that out. Is it even wear on both sides?

[LakeTahoeQuattr]

OK I will try that. Yes it is even on both sides thankfully

[julex]

I looked at my rears very closely yesterday since I was replacing RL caliper with a brand new TRW unit. Rotors show like ZERO wear. I cannot detect any lip between pad friction ring and rest of rotor. They are probably 10k/1y rotors.

BTW, after looking at the caliper I replaced for TRW, there are stark differences in quality. My previous caliper was about 3y old "quality" rebuild unit from Nastra. Bascially same stuff as centric. Nastra developed frozen hand brake actuator symptom where it would remain locked after releasing the hand brake until I would duck under the car and help it by pushing it out. It is a typical rusting problem of shaft, obviously they used some crap parts in there. So I learned not to use hand brake but leave in gear instead . Few weeks ago I got a mysterious brake fluid loss which after quick glance around was that caliper. Lots of fluid seeping out from around that shaft.

I got the TRW caliper and found out that parts where is matters are definitely better. Shaft and arm and definitely stainless steel, nastra was some painted crap. Bottom part of bracket is either less shiny stainless or galvanized steel too. So nothing that can rust, unlike rebuilds.

And the price difference was very little too.

[LakeTahoeQuattr]

BTW, after looking at the caliper I replaced for TRW, there are stark differences in quality. My previous caliper was about 3y old "quality" rebuild unit from Nastra. Bascially same stuff as centric. Nastra developed frozen hand brake actuator symptom where it would remain locked after releasing the hand brake until I would duck under the car and help it by pushing it out. It is a typical rusting problem of shaft, obviously they used some crap parts in there. So I learned not to use hand brake but leave in gear instead . Few weeks ago I got a mysterious brake fluid loss which after quick glance around was that caliper. Lots of fluid seeping out from around that shaft.

I got the TRW caliper and found out that parts where is matters are definitely better. Shaft and arm and definitely stainless steel, nastra was some painted crap. Bottom part of bracket is either less shiny stainless or galvanized steel too. So nothing that can rust, unlike rebuilds.

And the price difference was very little too.

I think I am going to rebuild / replace my rear left caliper as it is producing more rotor lip than the passenger side. I thinking it is sticking as well as you had encountered. Additionally, after beating on the car I can barely pull the brake one click because I think of the rotor expansion or something. I will probably loosen up the ebrake cable a little bit and then try and rebuild the caliper afterwards.

If this all fails I will go with the TRW like you did.