Issues with a long, mushy brake pedal after rotor/pad swap...

Went and replaced the brake rotors and pads on my '03 Audi Allroad this past Friday. Installed new two piece rotors and a good, used set of pads (70% left on them at least) to match up with the Alcon Mono 4 calipers that were on the car. Didn't crack the brake hoses, so I didn't bother to bleed.

The brake pedal throw was long and mushy, not much bite on the pads. I expected the lack of bite until the pads/rotors bedded in, but not the long pedal throw, particularly with pads that were much thicker than what I removed.

Tonight I did a full brake flush using my Motive Power Bleeder. Used ATE TYP200 fluid, pushed 2/3's of a quart through. Got some air bubbles out and cleared out all the old dirty fluid.

Brake pedal feel has improved marginally. Throw is still long, feel is still mushy. I've driven the car ~50 miles so far. In looking at the front rotors it looks like the pads are beginning to bed in and sweep all of the rotor. I'm sure the pads will begin to bite more as they bed in, but the pedal feel is still horrible.

If the engine is off, 2-3 pumps on the brake pedal result in a good feeling pedal.

WTF is going on here? I've done tons of rotor/pad swaps and never had an issue like this...

Adding insult to injury I noticed that I need to replace my rear brake pads AND there's a nail in my left rear tire. Wicked awesome!

Air or bad bearings or caliper/pad misalignment.

Just so everybody knows- When you shut the car off and pump the brake pedal, you are just exhausting the supply of vacuum in the booster. You are not fixing anything. If you were to pump the pedal 3 times, and restart the engine without taking your foot off the pedal, it would drop to wherever it was before.

And the lower radiator hose will ALWAYS be cool, so quit saying that too.

Caliper/pad misalignment? Like the pads are in crooked? Not possible on these 4 pots, they literally click into place and are held in with a spring. Caliper positioning didn't change with the rotor swap...

Something is binding somehow or there is a brake hose that's swelling. On a 4 piston caliper, I vote that one piston is stuck in the bore. Try this (takes two people): remove 1 caliper and take the pads out. Have helper push the brake pedal as you watch the pistons, they should all move equally. If the first side is okay, reinstall it and repeat for the other side. If it's OK too reinstall it and have helper stand on the pedal hard as you check the brake hoses for swelling. FWIW, the front hoses on my XS650 would swell to the point that the front brake was useless. Oh, and worn rear pads may have some effect as well. The nail in the tire is innocent.

Sigh. Having to rebuild these Alcons would be icing on the cake. I hate these calipers. I'd much rather have a set of StopTech st40's instead. I had to have custom built rotors made as Stasis went out of business, then pads cost a metric ton. If these calipers are bad I may pull all this stuff off the car and do a 17Z caliper setup instead

What condition were the pads in ?

I can't understand the mating of new rotors to used pads. If the rotors needed replacing then most likely the pads are not in the best condition.

Guess you missed the part in the 1st paragraph where I said the pads I put in had 70% left on them. The pads I removed were finished, they got thrown away.

Why wouldn't I use a good set of pads that I had laying around? They have plenty of meat on them. Pads for this caliper fitment are obscenely expensive. The pads I installed will last easily for 30-40k miles.

Did you bleed both sides of each caliper? My 4 pots have double bleeders.
Are the new rotors centered? Seems silly but they are custom.
Conversely, are the pads of equal thickness per caliper?
Is there any chance you installed a single pad backwards? Yeah its silly, but i did it once and had the same symptoms.
OR
Through chance and happen stance, the extra travel you feel is all coming from the rears.
I totally hate mushing brakes myself.

Yep, bled both sides of each caliper. Pretty sure the rotors are centered. Measurements said I'd need a 1mm shim on the caliper carriers and that's what I installed.

Pads are close to the same thickness, but not the exact same per caliper.

It's always possible I put a pad in backwards. Pretty sure I double checked that before I assembled them. I'll pull them apart tonight and check.

That's also possible that since my rear pads are almost gone they're causing the issue....

docwyte wrote: That's also possible that since my rear pads are almost gone they're causing the issue....

This could be the case - especially if you added aftermarket calipers with larger volume to the system. Moving larger pistons equals more effort and travel given the same master cylinder size. I made issues like this for myself with a less than well thought out upgrade to an E36 once. The difference between 1.75" 4 pots and 1.38" is HUGE to both performance and feel. I ended up with a car that could barely be heel-toe'd when the fronts were less than 50% and the F/R bias was all out of whack.

I got a brake math edumacation from angrycorvair's article in GRM back a few million years ago that helped me size everything correctly. I wish I still had that copy laying around.

can anyone point out which issue had that article ?

I'd be surprised if the rear brake pads were the issue tho, as this brake kit has been on the car a LONG time and I haven't had any problems until I did the front rotor/pad swap last Friday.

I just picked up a new set of rear brake pads, plus I ordered a brand new set of front pads. Might as well install all of them, as I need the rear ones and putting new pads in up front gets rid of that variable.

Then I'll do a two man brake bleed and see what happens...

Could be the curvature of the used pads aren't making 100% contact on the new rotors. So I would lean towards new pads too.

Does this have the 4 pads per caliper setup? If the pads aren't completely seated in the caliper the little alignment dowels in the pads could be setting them at an angle against the rotor.

I had this same issue when my master cylinder started going bad. It allowed fluid past the piston, but it ended up going back into the reservoir past the shaft of the master cylinder. hard to explain, hard to diagnose. However, I am not sure why that would have happened at the saem time as the pad / rotor change.

Rob R.

Two pads per caliper. Plan is to install the new rear brake pads tonight after my son goes to bed.

Once I get the new front pads I'll put those in and see what happens...

wvumtnbkr wrote: I had this same issue when my master cylinder started going bad. It allowed fluid past the piston, but it ended up going back into the reservoir past the shaft of the master cylinder. hard to explain, hard to diagnose. However, I am not sure why that would have happened at the saem time as the pad / rotor change. Rob R.

It's a long shot - but I did actually have an issue like this on an older car. I did a 2 man bleed and pushed the seals up over crap/wear at the edge of it's usual travel and it damaged the seal. The pedal had never gone that far before, apparently or, if it had... not in a long while.

I don't think that is likely here as IIRC from other threads doc is a fellow DE instructor and so his brakes see full bleeds and lots of pedal travel often enough. It could just be a coincidence though that the MC was starting to go bad and paying attention a little more to the brakes after touching them brought a gradual degredation to the immediate forefront.

Like how I suddenly had to buy my oldest son new pants and realized that - holy E36 M3 - he is taller than me by quite a bit now... that had to have been going on for a while, right?

It's possible I somehow screwed up the caliper piston seals when I retracted them. They were pretty much all the way out (pads were toast!) and then I pushed them all the way back in...

I am gonna go out on a limb and say the piston seals are fine in the calipers.
I further prognosticate that
A) the new pads fix everything
2) APRacing/Alcon could make a hammer complicated (did I mention that I also HATE these things with a burning purple passion)

You might still have bubbles...I have a Motive Power Bleeder and it pushes bubbles into the system every single time. There hasn't been one occasion I've used it that didn't still require a manual bleed afterward. Sucks, feels like a waste of $50; not sure what I'm doing wrong but IIRC others here have had the same issue with them.

I gave up using mine a long time ago … since there isn't a air tight cap for Honda applications, it was just too much of a PITA to use

Yeah, I hate this Alcon kit too. It was on the car when I bought it, I never would've bought it myself. I've been having serious issues finding replacement consumable parts for this kit. I had to have a shop custom make me a set of hats/rotors and now there's only 1 place that sells the brake pads and of course they're out of stock of the ones I want.

I'm a whisker away from taking all this crap off my car, selling it and going with a Porsche caliper based brake kit instead...

SlickDizzy wrote: You might still have bubbles...I have a Motive Power Bleeder and it pushes bubbles into the system every single time. There hasn't been one occasion I've used it that didn't still require a manual bleed afterward. Sucks, feels like a waste of $50; not sure what I'm doing wrong but IIRC others here have had the same issue with them.

I cut a thicker rubber gasket from a piece of bicycle tubing to use under the cap.

Then, pump it up to 18lbs or so and let it sit 5 minutes to let the bubbles rise away from the valve body. Give the reservoir a rap on the side w/ a screwdriver to loosen them so they come up. Since I've been doing that it's been fine.

wbjones wrote: can anyone point out which issue had that article ?

june 2008

In reply to docwyte:

My Evolution has this same phenomenon with used parts. Lets say I just remove the pads, caliper, rotor to service whatever. Then I put them back on and it has a long and mushy pedal.

After a week or so it comes back to normal. I have to drive with a cautious mode of leaving space to the cars ahead in the period. I do some medium hard braking through the week and then one day they are fine again. IDK why that is. Not a problem though.