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  #1  
Old 04-03-2003, 02:27 PM
glenmore's Avatar
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Brake Pad Wear Light W124

Couple questions for the forum:

My brake pad wear light is flickering occassionally but not when applying the brakes going forward, only when applying the brakes while backing up. Does this indicate new pads are needed or something else?

All my rotors have lips on them but seem to be within wear limits as suggested by the "3 coin rule" mentioned in another thread.

Do these lips need to be removed before putting in new pads? How does a DIYer do this? Take all the rotors off and take them to a shop?

Thanks,

glenmore
1991 300CE
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  #2  
Old 04-03-2003, 02:56 PM
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The pad wear sensor resides on one side of the pad. Going in reverse probably orients the portion of the pad with the sensor a bit closer to the disc...this is a miniscule dimension, but regardless, you are due for replacement.

MB does not recommend "turning" for any reson other than slight abberations on fairly-new ones.

Most of us have a different "3-coin" rule...replace the rotors on the "third" brake pad replacement interval.

Relative to the cost of pads, the rotors are inexpensive.

Rotor replacement is a DIY...just make sure you use Loctite on the bolts when you reinstall...
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  #3  
Old 04-03-2003, 03:07 PM
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It appears one of the pads has worn down to the sensor... (time for new brake pads). The difference in response between forward and reverse may simply be a servo effect of the system.

Unless the rotors have deep scoring or ridging, I'd leave them as is, assuming the average thickness is comfortably above minimum spec. If you have the patience and really want to remove the ridge, you may try filing it off with a crosscut roughing file.

The difference in thickness between new and discard is not a whole (25 mm vs 23 mm) for my car. Most posters here report that it's better to buy new rotors than turn old ones.
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Old 04-03-2003, 03:40 PM
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i have the same thing happening to my car and have already bought new rotors, just waiting for the new pads to arrive. i found www.alloemvolvoparts.com
to have the best prices on rotors after you factor in the free shipping. car parts to go is slightly cheaper per rotor but with the shipping it more expensive. ken
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  #5  
Old 04-03-2003, 04:21 PM
LarryBible
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You don't have to go into total panic mode about this. There is A LOT of pad thickness left after the sensors are exposed. Most people could probably go 5 or 10 thousand miles on them before getting metal to metal contact.

Unless the brake pedal is pulsating when you are applying the brakes, don't even worry about replacing the rotors unless they are very thin. Just replace the pads and make sure you have some new sensors handy when you do it so you can replace the ones that are worn. There are plenty of rotors that are unnecessarily replaced.

As far as the "lip" goes, it will be no problem getting the pads in and out. Make SURE that you remove only one pad at a time. Remove a pad, press that piston all the way back into the bore, put the new pad in place, THEN do the other pad. If you remove both at the same time, the pressure from one piston can push the opposing piston out past the seal which will require disassembling the caliper.

This would be a great time to thoroughly flush the entire brake system and the clutch system if it is a manual transmission.

Good luck,
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  #6  
Old 04-03-2003, 06:51 PM
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Thanks for all the advice.

I was studying the DIY brake change article and the method he used to free the pads was to use a big screwdriver and pry against the rotor. I remember reading in another post "never pry against the rotor". I see in my repair manual, the use of a special tool. Is it OK to "gently" pry? Any other suggested methods to free the pads?

Thanks,

glenmore
1991 300CE
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  #7  
Old 04-08-2003, 02:11 PM
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I checked the pads on all my brakes, trying to size up the situation before plunging ahead. Learned that the rear brakes do not have sensors. Although the brake wear light comes on more often now, I can see, as Larry said, there is still pad wear left. In looking at the front pads, there appear to be thin metal shims between the caliper and the back of the pads. I assume just reassemble everything in the same way with the new pads? The service history I have is new front rotors, pads and rear pads at 94m. New front pads again at 104m and the odometer is now 119m. Rear rotors are barely worn. The brakes work perfectly now, but in looking at one of the front rotors, there is an "alley-oop" going from the edge to the center of the disc. Sort of a high spot then dropping lower, definitely not flat. I would guess if this alley-oop was in the other direction, then you would get shimmy and pulsating brakes. The wear on the rotor is modest overall but would new pads work on this rotor or should the rotor be turned or replaced also?

Should I check the front bearings also while I am doing this? What is the best way to pull off the grease cap?

Thanks all,

glenmore


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  #8  
Old 04-08-2003, 02:41 PM
I told you so!
 
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You're averaging 13,000 miles between front pad changes. This is rather low life for pads, but it may be normal if you drive in a hilly urban environment. For my car new pads are 11 mm thick. It contacts the sensors at 2.5 mm.

As you said, with pad replacement you simply reverse the disassembly procedure with new pads. Like Larry said, do one wheel at a time -- you might find yourself in trouble when you push back the caliper piston with the other calipers unmounted.

The scored rotor is worrisome. You shouldn't put new pads with badly gouged rotors. Replace the rotors in pairs (both fronts).

Ditto on flushing the brake fluid afterwards.

How do you plan on checking the wheel bearings? If you're only checking for axial play, be very careful not to let any grit into the grease cavity. Anything more will require you to completely clean the old grease, regrease with proper amount of new grease, replace the grease seals, and properly set the axial clearance. Sometimes it's better to just leave it alone.

The center bearing cap can be coaxed off with a blunt wedge - such as a cold chisel - and gentle hammering, then pried off with a screwdriver.
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  #9  
Old 04-08-2003, 08:29 PM
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[QUOTE]Originally posted by Kestas
[B]You're averaging 13,000 miles between front pad changes. This is rather low life for pads, but it may be normal if you drive in a hilly urban environment.

I've only had the car since 111m, but the pad wear is not encouraging. Hopefully I can do better with this set of pads.


>How do you plan on checking the wheel bearings? If you're only checking for axial play, be very careful not to let any grit into the grease cavity. Anything more will require you to completely clean the old grease, regrease with proper amount of new grease, replace the grease seals, and properly set the axial clearance. Sometimes it's better to just leave it alone.

Don't laugh, but all I was going to do was pop off the cap and make sure there was fresh grease there!

Thanks,

glenmore
1991 300CE
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  #10  
Old 04-08-2003, 08:36 PM
I told you so!
 
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The only way to lose grease is by leakage past the seal on the inboard side. It would be obvious from all the greasy mess around that area.

I forgot to mention that a sticky caliper may cause poor pad life. Make sure the wear on all pads of an axle are even with no funny wear patterns.
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