Thankfully, it’s not an “oh sh*t” type of thing. After about a second or two the brakes grab and stop the car. As I lift my foot off the pedal I can hear a mechanical type sound as the pedal returns to the extended position. I can avoid the situation and the car stops fine if I tap the pedal then fully apply the brakes. The problem started last week so this past weekend I flushed the fluid and installed my track rotors and pads. The problem still remains. Thoughts?
TIA
Air in the master cylinder is my guess, or a squished seal in the main bore of the master cylinder. When you flushed them, did you push in on the pedal at all? The reason I ask is you can overextend the piston in there and it’ll tear the seal, leading to a sound like you hear when the pedal returns to rest position. How many track events do you do before you clean and lube the sliders on the calipers? I rebuild mine every two events and my car is quite a bit lighter that yours. This could lead to sticking a bit (on brake application or release) but does not make a sound in the cabin.
Prior to the bleed on Sunday I had not bled the system since April. I always use a power bleeder and I usually clean/lube the sliders every other month. I agree with the idea there might be air in the system. I don’t see any leaks and everything was tight so I’m not sure how air could get in there. I guess I can try another bleed tonight.
you may have pushed a bubble into the master itself with the power bleeder.
I would think air in the system caused by the bleed in April would have caused problems sooner than last week. Nevertheless, trying another bleed might make sense before I start digging deeper.
All it takes sometimes is a bubble getting into the MC from the reservoir side. Power bleeders are known for that, actually. It certainly is not from the April bleeding. I got in the habit of using different colored fluids every time I bleed, since MOTUL 600 can be had in blue and gold. That way I’m sure I’m pushing everything that is old out, and doing sufficient cycles to be sure that there is no cavitation or bubbles anywhere.
Blue Motul RBF 600? I’ve only seen/used the gold and I’ve been using it for years. Where do you buy the blue?
Are you sure the mechanical sound isn’t just the sound of the brake switch? Most likely you would be listening closer and hearing it engage/disengage?
save your money on motul. pentosin makes a dot 4 grade brake fluid that is 6 bucks for a full liter as opposed to the 15 for a 1/2 liter motul sells for. specs on the pentosin are a bit lower than motul, yet i doubt you will have a problem. have yet to see anyone fade out w/ that fluid.
If you really wanne go overboard, pentosin’s all out race fluid is like 18 bucks bucks for a liter, as opposed to motuls 15 for 1/2 liter. as you would expect, dry and wet boiling points are higher in the pentosin race.
only fluid id say stick away from is ate super blue. not that it dont work, but all you are doing is buying blue shit that stains everything… for same money you can get better.
as for the brake issue itself–
possible you have air in the system. but seeing this was happening before you tossed the track stuff on, i’d be looking more toward abs issue, which is what im thinking the mechanical noise you are hearing is. any lights on?
try this-- you have key off, and pump the brakes a few times to kill the built up boost on the brakes, then hit the brakes and hold the pedal down. keep holding the pedal down, after a while, does the peddle drop further?
save your money on motul. pentosin makes a dot 4 grade brake fluid that is 6 bucks for a full liter as opposed to the 15 for a 1/2 liter motul sells for. specs on the pentosin are a bit lower than motul, yet i doubt you will have a problem. have yet to see anyone fade out w/ that fluid.
If you really wanne go overboard, pentosin’s all out race fluid is like 18 bucks bucks for a liter, as opposed to motuls 15 for 1/2 liter. as you would expect, dry and wet boiling points are higher in the pentosin race.
only fluid id say stick away from is ate super blue. not that it dont work, but all you are doing is buying blue shit that stains everything… for same money you can get better.
as for the brake issue itself–
possible you have air in the system. but seeing this was happening before you tossed the track stuff on, i’d be looking more toward abs issue, which is what im thinking the mechanical noise you are hearing is. any lights on?
try this-- you have key off, and pump the brakes a few times to kill the built up boost on the brakes, then hit the brakes and hold the pedal down. keep holding the pedal down, after a while, does the peddle drop further?
Zero codes and no lights. I used the VAG-COM last night.
I pumped the brakes like you said and the pedal is rock hard.
after pumping the pedal and it is rock hard, keep your foot on it applying steady pressure. may take a minute or two. if the peddle doesnt fade, then that would tell me hydraulic side is intact. if the pedal drops then there is air in the system or it is open. i’d then be looking toward a booster issue.
if thats the case, check the line from the booster to the engine. pinhole or possible bad check valve-- especially look around where the line runs through the firewall. these plastic lines are prone to breaking w/ age. it is like 70 bucks new iirc. or you can get a check valve and rubber line/clamps and make your own.
I would not rule out the booster, yet that would be last on my list.
I just finished another bleed, including cycling the ABS with the VAG-COM, and the problem remains.
I did this and the pedal is still firm.
I repaired leak in the booster line a few months ago. I found it while pressure testing for a boost leak. I did another leak test tonight and everything seems fine.
Funny you mention the ABS because its been in the back of my mind as the possible cause. The sound made while the pedal returns to the extended position is very similar to sound the ABS system makes when its cycled with the VAG-COM.
just for the hell of it, try pulling the fuse for the abs. lets try some good ol’ process of elimination. pull all 3 fuses Lh side of dash
abs fuses are–
small fuses-- fuse 7 (10amp) fuse 16 (5 amp)
big fuse-- fuse 41 (25 amp)
what happens w/ abs disconnected?
i’ve had sticky caliper pistons present this kinda problem before…
I will pull the fuses during lunch and report back. Thank you!
I wanted to cross this off the list as a possible cause so I made sure to check and clean the pistons last Sunday while I did the rotor/pad change and bleed. The pistons looked pretty good from the start plus I could easily push them in by hand when installing the track pads.
It looks the ABS (module) is the problem. I pulled the fuses and the brakes worked perfectly. Good call! Now I just need to get the module rebuilt.
It looks like the ABS (module) is the problem. I pulled the fuses and the brakes worked perfectly. Good call! Now I just need to get the module rebuilt.
i just recently had this problem with my elantra minus the mechanical sounding noise…
same situation just bled the fluid and replaced with dot 4. replaced pads and rotors for the auto-x at north park i ended up bleeding the brakes a good 10 to 15 times on sunday. i then broke in the pads for like an hour and was having the problem with a spongy pedal so i continued to drive it until monday night thinking the pedal would return as i expected it did not. i then bled the brakes 2 more times and even bled the mastercylinder for the hell of it. took it for a spin around the block and all was good…
you really may just need to bleed the mc and brakes again!?!?!
Are you the white S4 going down McKnight every morning at 815AM-ish? I’ll be sur to stay away from your car 
well disregard my last post it seems we posted at the same time!?!