I am putting some brake pads on the front of a 1998 C230. I have the caliper off and removed the old rusty backed pads. Because the new pads are aso much thicker they won't go back in. Is there a special trick to getting them in? Also do i have to adjust the piston on the caliper since there is more pad material and a new rotor?

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John


1998 C230 for the wife
1986 Porsche 944 Turbo for me in the summer
1993 Audi 90 for me in the winter

Yes, there is a trick. You have to push the pistons back into the calipers. I usually do this with my hands (you can use a tool). Grab both pistons inside with the tips of your fingers, hold onto the outside of the caliper with your thunbs, and squeeze like hell. Might take a few moments - and the pistons will move SLOWLY. You may want to take the cap off of yoru brake fluid reservior and place a rag around the outside - brake fluid can sometimes come back out of the reservoir.

Good luck.

Troy
1995 E420 94k

The best way is with a C clamp. Slowly push the piston back down into the caliper housing. After. you''re finished, make sure and pump the pedal a few times to take up any extra slack you've created, before you try to put it in gear.

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1983 380SL
1995 C280
1995 S500 coupe
1990 Mazda Miata
2004 Suzuki Hayabusa

Thanks. i will give it another shot.

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John


1998 C230 for the wife
1986 Porsche 944 Turbo for me in the summer
1993 Audi 90 for me in the winter

Also - spread brake pad paste on the back of the pads to keep the rust away, reduce sqeualing, and ensure that the pads come out easily next time.

Just to clarify a post above - don't pump the brakes until AFTER you have installed the pads. If you do otherwise, the pistons could leave the caliper and ruin your evening.

when you push back the piston into the caliper, you'll have to open the brake reservior cap first, make sure fluid dosen't spill over the top.

also be aware of the rubber gasket at the base of the piston and caliper, make sure it dosen't bind up as you push the piston back in.

I know quite a few people, my dad included, who feel you have to open the reservoir cap first before compressing the calipers with a C clamp. I never understood this - why??? The system is sealed, it's not like air or fluid needs to escape or anything. So I never did it. Every time I've done my brakes I compress the calipers without popping the cap and have never had a problem.

Just my $.02.

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08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280

When you force the pistons back into the caliper bores, you move fluid back into the master cylinder reservoir. The air that was in the reservoir has to go somewhere or the fluid won't move. The reservoir has a tiny hole in the center of the cap for air to flow into the reservoir during normal operation of the system, as the pads wear.

You are now trying to force the air out through this small hole. It's a hell of a lot easier if you crack the cap and give the air more capability to escape. You probably don't need to force the piston so hard with the C-clamp.

OK, makes sense. I guess since I use the C clamp I never notice if compressing the piston is hard or not. In any event, I always compress extremely slowly because I realize the whole process involves moving fluid through tiny channels the reverse of the way it normally travels. So I never force it; I usually take about 2 minutes to S-L-O-W-L-Y compress the piston.

I'll try cracking the cap next time and see if it makes any noticeable difference. Thanks for the explanation.

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08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280

With the cap open (or cracked) you can force the piston in as fast as you want. The brake lines have more than enough capacity to handle the fluid as fast as you can turn the thread on the C-clamp.

When I do it, I compress the piston in 20 seconds or so.

I've been reading lately where some say when pushing the piston back in you should open the bleeder hose at the caliper to let the brake fluid escape at that point.
Otherwise you are pushing dirty fluid back near or into the ABS module.

I do my brake fluid every year so I am not that concerned about dirty fluid and just open the cap when I do a brake job.

I used to loosen the bleeder, but since I change my fluid when I change my pads I don't do that anymore. Your fluid should be changed every year. Also another trick is to keep the old pads in place and then use the c-clamp on then, this reduces the risk of damaging the pistons and seals in the calipers. Be sure to apply pressure from the C clap to the most center position of the pad while compressing. This is what I do.

1. Open hood and remove cap from resovoir
2. place a towel around the resevoir hole to catch any extra fluid
3. jack the car up at the jack point.
4. place a jcak stand under the rubber stopper (right near the jack point)
5 remove wheel
6. unplug sensors
7. Use a c-clamp to compress the calipers with the pads in place
8. remove the retaining pins
9. slide the pads up and out.
10. insert new sensors in the brake pads.
11. push pads into caliper and lock in pins.
12. connect sensors.
13. repeat for all wheels.
14. bleed fluid completely out until clear.

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Brian W. Heitman

www.MBCA.org/northtexas

Join MBCA!!!

Recently did the pads on a 1990 126 chassis. Without a doubt, the easiest brake pad setup I've ever seen. Not sure how different your model would be from mine, but I did end up with a bit of a project.

On the last (RF) caliper, while pushing the piston back into the caliper, I noticed a very small amolunt of moisture. Uh-oh. Yup, brake fluid began seeping past the piston seal. Ordered a new (not rebuilt) unit from AutoZone and was very pleased to find it not only was the correct Bendix unit, but also had the Mercedes emblem on the casting. Biggest problem I had was bleeding the system. My power bleeder wouldn't work because there are two breathers on the top of the master cylinder reservoir that prevented enough pressure to effectively bleed. I always suck out all the fluid I can from the reservoir before replacing pads since it's 'old' fluid anyway, and insures fluid won't overfill.

Have fun!

I tried pressure bleeding my W126 once too. All it did was blow the fluid out of the seals between the resevoir and the master cylinder. Maybe this is what you saw too.

I jack up all 4 corners and open all 4 bleeders and let them gravity drain.......I drain the entire system and then I fill the master cylinder with synthetic brake fluid......while the old fluid is draining I install the new pads....I let some of the new fluid drain and then I close off the bleeders....I close them in the reverse order that I will bleed them.....it works for me....the reason that fluid can try to go out the master cylinder when using a c-clamp is because the piston is moved beyond its normal position(116-123-126) and it forces more fluid into the lines than normal operations will....

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James A. Harris