Spongy brakes after rear pad change. - Mercedes-Benz Forum
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#1 (permalink) Old 12-23-2007, 12:40 PM
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Spongy brakes after rear pad change.

After changing the rear pads and spark plugs last night, my brakes are now spongy with a long travel.
I also noticed above the odometer it says "lim" in very faint red, with no other warning lights.
The rear pad change was a simple operation and did a few in the past. I also installed a missing emission hose that ran from the valve cover to an intake neck that sits under the Maf and in the process I pulled out a sensor in the Maf to allow for more room.

It feels that my brakes are fine until I do 5mph or above then they fail, any thoughts on this are appreciated. The car is a 98 s420.
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#2 (permalink) Old 12-23-2007, 02:11 PM
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by chance did you maybe not tighten one of the bleeders enough? have you noticed any fluid around the area?

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#3 (permalink) Old 12-23-2007, 02:18 PM
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I didnt come in contact with brake fluid at all, pulled out the old pads and slipped in the new.
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#4 (permalink) Old 12-24-2007, 12:46 AM
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Sounds like you got some air in the system somewhere. When is the last time you changed the brake fluid? Personally, I'd bleed em' a bit and see how they feel.

"It's not about how fast you can go, but how well you can go fast."

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#5 (permalink) Old 12-24-2007, 02:54 PM
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Took the car to a local mechanic this morning. He thinks I damaged the master cylinder by not opening up the bleeder valve, allowing fluid to flow back up to the master cylinder during decompression of the piston. This is something that was mentioned to me before on this forum but totaly forgot while doing the job.
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#6 (permalink) Old 12-25-2007, 07:23 AM
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Sounds like your mechanic is trying to make lots of money off you. Every time you let off the break pedal fluid from all 4 calipers is forced back into the master cylinder!! Anti-lock or not. When the pedal is at rest there is a bypass port which allows any pressure in the lines to bleed directly into the fluid reservoir. Or there may be a small one way valve in the master cylinder piston cup to do the same thing. Every vehicle I have owned has worked the same way. Think about using large Channellocks or a C-clamp to compress the front pads so you can remove them and take he front end apart--to put on new rotors or such. All that fluid is just pushed up into the reservoir. The only problem I have ever had is a little too much fluid up there and a little overflow.
I agree with Bobs--bleed the system.
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#7 (permalink) Old 12-25-2007, 08:31 AM
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We bled the system at the shop, no air what so ever. Theres a few posts on here that you can damage the master if you dont crack the bleed valve, Ive done this job in the past and agree I never had any problems. I think on rare occassions it can go the way it did on mine, going to the dealer for testing and see what they say.
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#8 (permalink) Old 12-27-2007, 08:54 AM
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brake lines

Look at the rubber brake lines - any bulging under pressure? If your lines are old and swelling under pressure that is going to impact brake feel.

If the brake fluid is old (dark colored), then you can expect more brake fade (brake pedal travel) after a lot of driving as water in the line (it's hygroscopic) will boil to vapor (which will compress unlike fluid) near the hot calipers. Granted this is extreme (shouldn't happen when cold) - but a reason why you need to bleed the brakes with pad / rotor changes.
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#9 (permalink) Old 12-27-2007, 01:09 PM
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I appreciate all the responses, my only fear is this problem did not exist before I changed my rear pads. I will do a complete flush this weekend with all new fluid and maybe Ill get lucky. I found a few articles for ABS brake jobs and I hope I dont fall into this catergory, I never had a problem in the past doing it the old fashion way and hope I dont now.

Ryder Fleet Products - ABS Brake System - Common Problem Prevention
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#10 (permalink) Old 12-27-2007, 06:51 PM
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Bass,
I would not discount the "emision hose" issue you mentioned. As you said, you didn't physically touch the hydraulic system. Perhaps you agitated a vacuum leak related to the brake booster??? This could manifest itself into "feeling" like air in the system.
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