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Suspension & Braking Forum by BimmerWorld
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Old 08-30-2008, 11:57 PM   #1
sgtfury40
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Brake Questions (general)

Replaced all the pads a couple days ago and tried to make sure I did not get any air in the calipers. I was by myself so it was a little tough to do and I think a couple air bubbles made into the system through the calipers. My question is: once air is in the brake system, will it work its way to the calipers or the master cylinder? I'm going to bleed the system tomorrow, but I've been driving for a couple of days. (Brake pedal is still pretty firm, but the brake light [yellow] came on today).
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Old 08-31-2008, 12:09 AM   #2
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If you changed your pads, how would you get air in the system?
I change my rear pads the other day and I didn't bleed a thing. I just pumped it and rode the brakes for a mile of so to re-set the calpier pistons, and that was it, brakes have only felt better since because of the new pads.
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Old 08-31-2008, 12:16 AM   #3
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I've changed my brakes recently, and after I changed rear pads and rotors, pedal was firm and everything was fine. after changing front pads and rotors though brake pedal became soft and even bedding didn't help. I flushed my lines afterwards, followed with several bleeding attempts but my pedal is still softer than it used to be and braking power is noticeably reduced. I'm still looking for solution. would re-bedding them help?
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Old 08-31-2008, 12:17 AM   #4
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When you compress the brake cylinder back into the caliper, to get the new pads to clear the rotor, you have to loosen the bleeder on the caliper to relieve the pressure, otherwise you can't press the cylinder back. When you do that brake fluid will, of course, come out of the caliper, and if you are not careful it will suck air back in through the bleeder.
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Old 08-31-2008, 12:19 AM   #5
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Thatsonlyme. It sounds like you do need to re-bleed the system. That would account for the soft pedal. Make sure you have someone to help, b/c it's really a two person job.
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Old 08-31-2008, 12:24 AM   #6
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I had a bmw tech sit right beside me and help me do it. We did not touch the bleeder nipple except to remove the sensor line.
We used a flathead screwdriver looking thing and wedged it in and pushed the pads apart. Then proceeded from there. No brake fluid at all.

Iirc, we removed the clip. Then pried the inner pad apart by sticking the screwdriver like tool in there, and pushing the piston side pad into the caliper. Then removed the caliper bracket screws.
Then removed the caliper, cleaned, applied the wurth good stuff to the new pad, and put it back together.
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Old 08-31-2008, 12:46 AM   #7
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I didn't touch bleeder nipple either. I replaced about 1 1/2 liter of brake fluid, first with pressure bleeder, then I had helper pump the pedal and then push it while I'm opening bleeder nipple, and we did it several times, no air was coming out. maybe soft pedal is not correct explanation, it's more like brake pedal engages lower than it should. I can still brake hard and even lock my wheels, just don't have braking power when I touch the pedal. sorry for posting in this thread, but I think it's related.
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Old 08-31-2008, 12:55 AM   #8
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Go to autozone and spend $40 on a mightyvac bleeder kit. It makes bleeding a whole lot easier. I've only used it on my bike tho. But it made a HUGE difference. Quicker, cleaner, 10x more effecient.
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Old 08-31-2008, 12:55 AM   #9
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i had the same ^, but it went away after a week or so. pedal feels good now.

just had my mechanic do a full flush with ATE blue, and don't notice a difference really
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Old 08-31-2008, 01:24 AM   #10
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I flushed my system with ATE blue too. it's been already a week and I have 500 miles on my new brakes. should I try bedding them again? it's kinda hard to find enough open road for that in the city and cops are all over. I'm wondering how shops do bedding procedure? I don't believe they drive around in customer's car 60 mp/h and then slamming on brakes multiple times, especially in the city.
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Old 08-31-2008, 01:32 AM   #11
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I think they just drive and drag the brakes for a few miles.
If your pedal is soft that's not bedding. Lack of bedding makes for "greasy" feeling brakes, like u press all day and it just can't grip enough to stop.
A soft pedal is something hydraulic.
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Old 08-31-2008, 01:50 AM   #12
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Quote:
Originally Posted by sgtfury40 View Post
When you compress the brake cylinder back into the caliper, to get the new pads to clear the rotor, you have to loosen the bleeder on the caliper to relieve the pressure, otherwise you can't press the cylinder back. When you do that brake fluid will, of course, come out of the caliper, and if you are not careful it will suck air back in through the bleeder.
NO, you never release the bleeder valve to compress the piston into the caliper....you use the proper tool or a large channel lock wrench to compress it...

Yes, it is likely you have air in the system since you opened it - bleed properly, in fact have someone else do it if you opened the system to compress the piston....NONONONONONO

good luck
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Old 08-31-2008, 05:49 AM   #13
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I just tried re-bedding my pads on the way home tonight. expressway was empty, so I tried with some dragging brakes, then few times hard braking, then cooling off brakes by coasting on expressway, then again... my pedal feels firmer now, I still don't have that initial bite though. I'll try with some moderate braking next few days to see what happens.
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Old 08-31-2008, 06:31 AM   #14
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good to hear, an old trick with my motorcycles pads is to rub some sandpaper on em before mounting them, and on the rotor to remove the glaze. but my BMW tech buddy looked at me like i was crazy when i asked him if they do that at the dealership.

EDIT: my 5000th post yay for me
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Old 08-31-2008, 08:40 AM   #15
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There are a couple of different bed-in theories...but nobody recommends doing ALL of them. Pick one and stick to it. Doing them all repeatedly isn't going to do a thing to properly bed them, and is probably doing more harm then good.

For the soft pedal - bleed again, and make sure you're adding enough back in quickly so that the fluid level never drops below the minimum. If its still poor, you may have a cylinder issue.
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Old 08-31-2008, 03:17 PM   #16
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I'm sure that bleeding part I've done properly. brake fluid never dropped below minimum, only clear fluid was coming out of nipple, no air bubbles whatsoever. still I kept bleeding few more times, just in case. anyway I had the issue from the moment I installed new pads and rotors, before any bleeding or opening the system. I.m pretty sure that I messed up the bedding part. especially because a friend of mine has the same issue, and we replaced our brakes together in the same time. his brake pads were bmw oem, mine are akebono euro. I guess if re-bedding attempt shows useless, I'll just have to either live with that or have shop check my brakes.
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Old 08-31-2008, 03:19 PM   #17
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snikwad, congrats on 5000th post how the hell you people have so much time to spend on this board?
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Old 09-01-2008, 11:01 PM   #18
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update: it seems that after second bedding my brake pedal improved and today I can already feel more grip from my brakes. it's not as good as oem bite, but it's still improving, and I could definitely live with this. hopefully over time it will get even better.
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Old 09-02-2008, 01:03 AM   #19
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Take a bit of sandpaper slip it between the pad and rotor, and rub that thing down.
Do the rotors lightly too. Those pads sound hella greasy.
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