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Old 03-27-2002, 01:12 AM
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Question Bad brake booster?? Please help!

I had great luck with my last posting, and I hope this will yield the same!

Background for problem:

When I was changing my wheel bearings, I didn't clamp the brake hoses because they seemed brittle; instead, I just put a block of wood in between the pistons when I removed the caliper. I went to bleed the brakes. I didn't realize the block had fallen out, and consequently the pistons fell out. I got them back in okay, and the seals seemed fine. Later the same night I managed to break off a bleeder screw another caliper, and ended up replacing the caliper another used one.
I went to bleed the brakes again, pushing the pedal all the way to the floor, which I later found out, you aren't supposed to do. I thought I had ruined the master cylinder, so I replaced it.
My brakes still don't work. I've bled the lines at least three times and there is no air, and there are no leaks. The pedal is quite stiff after bleeding, but as soon as I start the car, the pedal is very soft, and stays soft in subsequent sessions - car running or not. Also, when I tried hitting the brakes while driving (To see if I would make it to a mechanic which I realized it wouldn't) there is an audible and tactile (pedal) rumbling sensation that was never there before, which seems to be originate from the front driver caliper (the one with the pistons that fell out).
The only thing I think is left is the brake booster, but since I'm not sure how they work, I don't know if this is accurate.
Any suggestions or shared knowledge would be most appreciated.


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Old 03-27-2002, 01:43 AM
Registered User
Join Date: Jun 1999
Location: Surrey, Beautiful British Columbia, Canada
Posts: 750
get your car towed to your trusted mechanic pronto.
dont mess with your brakes for your sake and so for
the safety of others!
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Old 03-27-2002, 01:51 AM
MikeTangas's Avatar
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Join Date: Apr 2000
Location: So. Cal
Posts: 4,430
I don't think the booster is the problem here. You've done a lot to the system, including (from your description) bleeding the brakes while the caliper is off the car (????).

The last step in working on brakes is the bleeding.

You need to take a close look at the brake resevoir. The resevoir is designed with a partition, this partition combined with the location of the resevoir makes it hard to discern if the rear chamber is full or dry. Often, when bleeding the brakes, the rear chamber goes dry which defeats the effort.

A good rule of thumb is to top off the resevoir after every third crack of the bleeder valve if bleeding by the two-person method. Might be easier to keep the resevoir full by building your own pressure bleeder. Do a search on "Pressure bleeder" and you'll find directions on constructing your own.

If not comfortable with, or knowledgeable in, the brake system, this might be a job better left to the pro's.
Mike Tangas
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72

'02 CLK320 Cabriolet - wifey's mid-life crisis

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Old 03-27-2002, 03:13 AM
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Allow me to clarify:

The caliper was off the rotor because I was changing the wheel bearings. During the bearing replacement, I hit the brake out of habit when I was getting in the car. The block of wood I had placed between the pads had fallen out and the pistons fell out of the caliper.

I've been bleeding the brakes with a second person while making sure both compartments of the reservoir is full.

I don't plan on driving the car until I get this fixed, but I am really hoping to solve this myself. I've already eliminated the possibility of a bad master cylinder, initial hydraulic pressure (before the car starts), and possible one caliper....
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Old 03-27-2002, 06:40 AM
engatwork's Avatar
Join Date: May 2000
Location: Soperton, Ga. USA
Posts: 13,242
Did you bench bleed the master cylinder prior to installation?
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Old 03-28-2002, 06:02 PM
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Yes, I did bench bleed the master cylinder. I also learned not to buy remanufactured ones, after buying two back to back that had bad seals.
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Old 03-31-2002, 01:28 AM
Senior Member
Join Date: Jun 2001
Location: Northern Calif. (Fairfield Area)
Posts: 2,225

I agree with Joel;have it towed to a professional.If you want to tinker with your valves or change your water pump, go for it.The questions you are asking,however,indicate you have no business fooling with brakes.You run the risk of killing yourself or worse some innocent person.Take it in,man,and I'd be happy to answer any questions you have about any other part of the car.

Good luck,
Auto Zentral Ltd.
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Old 03-31-2002, 09:27 PM
Posts: n/a

I was working on this car at 3am with a friend. I don't know which one of us did this, but I have been kicking myself for days now. One of the pads was in backwards, so the steel side of the pad was on the rotor. I'm not exactly sure why the pedal doesn't travel as far, since the width of the pad is the same, but it fixed the problem. Thank god I didn't have the car towed in. Thank you all for your replies.


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