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  #1  
Old 08-08-2003, 05:28 PM
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Join Date: Nov 2002
Location: Kite, Georgia USA
Posts: 48
Vibration and now locked up front brake W126

Hi, all

A few months ago I was on a long trip in my 88 300 sel and I got a vibration much like an out of balance tire or a tire that was coming apart etc.. As I was about to pull over the vibration slowly went away. So I stoped at the next convenient spot and looked over everything. Didn't see anything wrong just looking at the brakes, tires, suspension, etc..
So I continued on my trip and never had any more trouble out of it.

Yesterday, I made short trip into town, and the vibration started again at 50-60 mph after driving this constant speed for several miles, and just as before it went away within lets say 30 seconds. I drove it pretty hard on the way back trying to rule out a transmission problem, etc.
And when I got home the brake pedal would almost mash to the floor. I got out and could smell something burnt. After checking it out I found that the right wheel was a good bit hotter than the others, you could put your hand on it but it got quite hot.

Jacked it up this morning, front wheels would turn. Got in it and cranked it up pumped the pedal several times. Right front wheel could barely be turned using both hands on the tire.

So obviously there is something wrong with the right front brake caliper now, but what caused the problem and where did the vibration come from? Should I be looking at other sources for the vibration problem? Or was the intermittent vibration the sign of the brake caliper or something else in the braking system going awry?

Any help appreciated.

BMJR
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  #2  
Old 08-08-2003, 08:53 PM
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Join Date: Sep 2002
Location: Kingsport, TN
Posts: 375
Hi BMJR,

I think once you smelled the overheating brakes, it's time to check them thoroughly. Nothing worse than the brake pedal going to the floor and no braking when you need it.

In my case, the sticking brake caliper had overheated enough to ruin the rubber seals inside and rebuilding was in order.
I don't know whether changing the brake fluid every year will prevent this kind of sticking calipers, but some say it does.

Have them checked asap.

Reinhard Kreutzer
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  #3  
Old 08-08-2003, 09:04 PM
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Join Date: Aug 2001
Location: Evansville, Indiana
Posts: 8,150
Pump the brakes up with the wheel off the ground, then open the bleeder valve and see if the brakes release. If they do, replace all four brake hoses (both fronts, both rears). The lining inside can separate from the outer cover and act as a one-way valve -- pressure goes to the caliper, but nothing can go back, so the pads drag, and the hotter they get, the more they drag.

Check the rubber on the dust boot behind the pads -- if it is cracked or brittle, you need to rebuild the caliper, it will stick otherwise.

The dragging brake scenario can also be a result of running new pads on worn out rotors -- if the backing plate on the pads is touching the anit-rattle spring, you need new pads and rotors, the rotors are seriously under thickenss. The causes the pad to hit the spring, and it cocks up on the bottom. This will cause the piston to cock int eh bore, and stick -- roasted brakes.

All my old benzes (and my brother's 300D) were in this condition when purchased.

Peter
__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!
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  #4  
Old 08-08-2003, 09:57 PM
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Join Date: Nov 2002
Location: Kite, Georgia USA
Posts: 48
Thanks for the tips, Reinhard, and Peter.

As soon as I get time, I'll check it out and see what it's going to take. I pulled the rotors off last summer and had them turned, and installed MB pads. The rotors were still above the minimum.

I'll post my findings when available.

Thanks again

BMJR
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  #5  
Old 08-10-2003, 04:37 PM
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Join Date: Nov 2002
Location: Kite, Georgia USA
Posts: 48
Checked it out today

Ruled out the brake line itself as the problem.
So I pulled the caliper and disassembled it. Found rust to be the culprit. Pistons are in good shape (no pits) housing has some pits but should be ok. The dust seals were both still in fair shape not split or stiff. I guess they just didn't seal properly.

I checked the rotor with a dial indicator for warp. Barely had .02 mm runout.

So maybe I'm lucky. Looks like all I need is a caliper rebuild kit.

Bill
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  #6  
Old 08-10-2003, 04:40 PM
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Join Date: Aug 2001
Location: Evansville, Indiana
Posts: 8,150
It doesn't take much dirt in the caliper to cause it to seize. Do the other side while you are at it, it's in the same shape, just not stuck yet, I'd bet!

Peter
__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!
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  #7  
Old 08-10-2003, 04:51 PM
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Join Date: Nov 2002
Location: Kite, Georgia USA
Posts: 48
Yea, thats what I was thinking.
I think the caliper kits are pretty cheap, just as well order two.

Thanks,

Bill
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