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1985 300D Turbo
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Discussion Starter #1
So, I changed my front brake pads yesterday. I had plenty of confidence because I've done this job on a number of different cars and I had lots of advice from the benzworld forums. So, changing out the pads was no big deal.

However, after taking the 300D out for a test drive around the block the brakes never "came back". I know that after changing pads that it can take a few pumps of the brake pedal to get the pressure back up. Well this time they never came back. And by the time I got back to the house there was a trail of brake fluid the whole way around the block...and more on the street this morning. Took a look under the car this morning and it looks like the inside of the wheel/tire is covered in brake fluid. What happened? Where do I start trouble shooting this? Did I blow a brake line? Did I pump the brakes too much?

--Dan
 

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280SE 280CE 560SEL
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978 Posts
Dan, it could be a hose, but it is probably more likely that it's a caliper seal - when you push the piston back that's when the piston seal is most vulnerable to damage. Pull the wheel & check it out - you may be lucky and it's a hose problem, with no hydraulic fluid on the pads, but if they are contaminated they're history, there is no way contaminated pads can be safely cleaned up. If it is the caliper, just replace it, it isn't worth trying to rebuild it with new seals as the chances are that the piston is rusty and was the cause of the seal problem in the first place. Best of luck.
 

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1985 300D Turbo
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Discussion Starter #3
If I were to try to replace the piston seal on my own, do you know of a resource that shows/discusses how to do it. I've searched the benzworld forums...can't find anything.
 

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I found this thread here:

http://www.benzworld.org/forums/forums/thread-view.asp?tid=1204469

I believe it is covered in the Haynes manual - you could also try a google on 'caliper seal rebuild' or similar - I found a bunch of useful sites, though none for a w123.

Anyway, it might be worth confirming exactly where your leak is coming from first - is it the caliper or the hose?
 

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1985 300D Turbo
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Discussion Starter #5
Yep. The leak is coming from the piston seal...and the pads are fouled.

So, here it goes. I'll be attempting a caliper rebuild. Remove calipers. Clean them up. Install new piston seals. New brake pads. New brake sensors. I think that covers it.

I think I'll do the rotors too while I'm at it. Any advice on getting the rotors off?

--Dan
 

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stumptown_dan - 4/30/2005 6:01 PM

Yep. The leak is coming from the piston seal...and the pads are fouled.

So, here it goes. I'll be attempting a caliper rebuild. Remove calipers. Clean them up. Install new piston seals. New brake pads. New brake sensors. I think that covers it.

I think I'll do the rotors too while I'm at it. Any advice on getting the rotors off?

--Dan
Just remove the caliper (block off the brake hose), remove the hub and rotor as a unit (undo the hub nut inside the grease cap to release) and unbolt the rotor from the hub (bolting the wheel back on to the hub/rotor assembly helps give more leverage). At least that's how I remember it from last time!
 

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1985 300D Turbo
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Discussion Starter #7
Ok, everything was going well until I got to the caliper bolts. The ones that hold the caliper in place. I can't make them budge. Any advice on how to loosen these bolts would be helpful. Wrench and wd40 aren't doing it.

--Dan
 

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1985 300D Turbo
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Discussion Starter #8
Ok, finally got the calipers off. It's all about the leverage.

I'm trying to photo document the entire process for other novices like me. Hope to post some pics at some point.

Next I'll be cleaning up the calipers with a wire brush, and brake cleaner after popping out the cylinders. As far as popping out the cylinders goes...I've read a number of times that I should use compressed air or a bicycle pump. Well, how does one attach a bicycle pump to a caliper???

--Dan
 

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2005 SLK350, 91 300SL with Pano Top, 04 S500, 2015 Tesla Model S
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No need to use air pressure if they are not seized. I just pulled them with a twisting motion.
 
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im just going to pop mine out, with someone pressing the brake pedal slowly, in the car...and i will grab them, etc......then unscrew the last caliper bolt.........i think that me disconnecting the old hose would be a bad idea, i should just leave it on there.....maybe it would break or something....
 
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