I noticed a familiar grinding sound coming from the right rear yesterday on my 240D. I pulled the wheel, ASAP, and found the inner brake pad was 99.9% gone. The outer pad still had better than 75% left on it.

I checked the other wheel and it was not as bad, but still was showing far more wear on the inner pad than the outer pad.

The fronts are wearing about even.

Do I need to rebuild the caliper, or is it better (easier) to buy a re-manufactured unit for the rear brakes? Can these be repaired efficiently. What causes this problem, exactly.

By-the-way, the rotor suffered only minimal scratches... not enough to need resurfacing.

Thanks in advance for info.

------------------
William
76 240D (W115) - 550K miles
78 300D (W123) - 200K+ miles

William,
I experienced the same type of problem on the front calipers of my car. I bought MB kits and repaired them. I found it to be a long painstaking job if you try to do it precisely. If I have caliper problems again, I will probably go to rebuilts. Come to think of it, I don't believe rebuilts were available when I had my problem.

As to what causes it, I don't know for sure, but I suspect that if you don't follow the MB procedure exactly and pull the pads with an impact tool and then press the caliper pistons back with their special tool, you may get the piston "cocked" in the cylinder and it then won't retract when you release the pressure on your brakes. It is like driving with the brakes on all the time.

Another possibility: there is a small rubber rib on the edge of the piston seal that allows the piston to draw back slightly.....it may just wear out.

Hope this helps you somewhat. Good luck.

------------------
Ted
1979 240D
160,000 miles

The best thing to do is replace the caliper with a remanufactured unit. The time involved with rebuilding and the cost of the materials tto do it is more than it's worth. The usual causes for premature caliper failure is not flushing the brake fluid on a yearly basis.

------------------
ASE Master Technician, Lead Technician for Deutsch American Inc. Over 6 years of Import experience-specializing in German Automobiles.

Bad fluid probably killed them. I fully bled the system when I bought her, but they were in bad shape then.

Any ideas on the price for re-man's on this car?

Thanks again,

------------------
William
76 240D (W115) - 550K miles
78 300D (W123) - 200K+ miles

The brake fluid in my car was changed on schedule and according to MB procedures. My failure, at least, was not due to maintenance neglect.

Calipers are available from Performance Products and probably from PartsShop on this site. To give you some idea of cost, rear ATE calipers for the 123 model, not TD, (the only Performance Products Catalog I have) are $91.41 each. The seal kits for ATE are $15.05 each. There is no mention that these are rebuilt units and there is no core charge, so my guess is that they are new. I have no idea what remanufactured units may cost.

Good luck with your project.

------------------
Ted
1979 240D
160,000 miles

For that price, I'd have to guess that those calipers are rebuilt. (no, I am not going to bet $5 bucks on that! ;) )

-Larry

I have rebuilt calipers on the 123 cars with great success. Because I'm the tight fisted, anally retentive person that I am, I would rebuild them rather than replace them every time, unless I found the bore or piston had a problem which would preclude rebuilding. It's really not that much trouble. If I were doing it professionally with the labor costs to consider, rather than only parts costs, that would be a different matter.

And yes, if the system was never flushed and bled, that's probably what killed them. The fluid absorbs moisture, and then the moisture does them in. When I'm evaluating a used car, it's always impressive to see that the brake fluid has been flushed regularly.

Good luck,

------------------
Larry Bible
'84 Euro 240D, 523K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in
Mercedes automobiles

[This message has been edited by LarryBible (edited 08-04-2000).]

This discussion has raised a question in my mind. Since the changing fluid maintenance had been done on my car, I concluded that changing the brake pads in other than the MB manual described manner must have been what caused my problem. I didn't have the special tool, just did my best to press the pistons back squarely without it. May not have succeeded.

Has anyone else had a similar experience and what other thoughts does anyone have about this?

Thanks for any observations and comments.

------------------
Ted
1979 240D
160,000 miles

Ted,

Maybe I've just been lucky, but I've done brake pads probably a half dozen times on my 240D. I'd have to look in my logbook to know for sure. I've also put brake pads in a number of other vehicles belonging to myself. I've always used a set of jumbo channel locks, carefully, to push the piston(s) back. I've never experienced any problems like you describe.

Good luck,

------------------
Larry Bible
'84 Euro 240D, 523K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in
Mercedes automobiles

Thanks for the response, Larry,

Your methodology is the same that I used. Perhaps the calipers were just like so many other things on my car that failed without any particular explanation.

P.S. If you have changed pads only a half dozen times in 523,000 miles, you have gotten about 87,000 miles use from each set. From the time my car was new, a set of front brake pads would only last about 30,000 miles and neither my wife nor I are aggressive drivers. Have you always used your car on a long commute? Thanks again.
------------------
Ted
1979 240D
160,000 miles

[This message has been edited by Ted2222 (edited 08-04-2000).]

Larry and Ted,

My father was a mechanic for 40+ years. I learned about cars from him.

Even though there was a special tool in the tool box for pressing caliper pistons, the 'jumbo channel-locks' have always been the tool of choice for easy compression. I too have never had problems arise from the use of channel locks for brake work. Between my father and I, we have been doing it for almost 70 years in total!

Three things my tool box will never be without... big channel locks, a big hammer, and a long screwdriver. If the 'special tools' do not work, one of these will.

Back to the main question, do I need to replace both rear calipers or can I get away with one for now and the other later? Would it be a good idea to replace all four? Sort of preventative maint. before the front ones fail. Could the previous owners lack of maintenance have damaged the master cylinder?
I have had this car for 5 years and only flushed the system three times myself, the last one was almost 2 years ago. I have learned my lesson, the brake system starts regular, anual flushing starting now!

Thanks again,

------------------
William
76 240D (W115) - 550K miles
78 300D (W123) - 200K+ miles

You would want to replace both rear calipers at the same time. The new one could have different characteristics than the old one, and next thing you know your 240 is wanting to jerk to the side for a moment while the other caliper catches up.
(the only time I ever replaced just one caliper, was on a '76 Malibu with 148k miles, and I didn't expect it to last much longer...plus I was young and dumb (now I am no longer that young)).

-Larry

William,
My father was a mechanic, also. I began working on cars when I was in Junior High, nearly 60 years ago. It would be interesting to know how many of the people participating in this forum had fathers who were mechanics.

Larry (Delor) is right, of course. The calipers should be replaced in pairs. Whether you want to replace all four is a matter only you can decide. How long do you plan to keep the car? How much do you use it? Would a failure at some unforeseen time in the future likely cause you a lot of inconvenience? Etc.?

My guess would be that the master cylinder has sustained some damage from maintenance neglect. You may want to dismantle it, check it out and put a repair kit in it if you find it is not too bad. I had to rebuild mine(right after the car got out of its one year warranty :() and found it very easy to do. It has now lasted about 20 years without further trouble.

Good luck with whatever you decide.



------------------
Ted
1979 240D
160,000 miles

Thanks Ted and Larry,

Checking parts shop for the calipers now.

Interesting thought on our fathers, Ted... Makes you think.

I figured the master cylinder would need service, but you never know... I also should have known better than to ask about the replacement of just one side. I guess I should stop being so miserly, but I just spent out a small fortune on the wife's car and my Mustang's front end. My 240 deserves the best, and I'll make sure she gets it.

I'll be making the repairs this next week if I can get the parts by then. I'll let you all know if I run into any problems with the master cylinder rebuild.

Wish me luck, and thanks for the help.

------------------
William
76 240D (W115) - 550K miles
78 300D (W123) - 200K+ miles

Ted,

Yes, certainly at least 95% of my miles are road miles. What will accelerate wear of disk brakes drastically is driving with your foot touching the brake pedal. When disk brakes came along, some of the people who always drove automatics would be touching the brake pedal while driving, didn't hurt anything with drums, but with disks, keeping your foot on the pedal ever so slightly would kill them quick.

I doubt that this is your problem though. If you drive strictly in the city and drive hard, 30,000 miles might not be too bad. But someone else will have to confirm that.

Yes, my Father was/is a mechanic. He did car work for awhile then was in the Fork Truck business. He retired in '83 and is now 79 years old and still does a good bit of car work. He buys Hondas at the dealer auction, fixes them up and sells them. Still works in the heat and everything. He also has always been a real analyst and great troubleshooter.

William,

Ditto on the tools, but I have to add one, a BIG, Big hammer. I think you were talking about the big screwdriver for a prybar. I have a couple of those. I have a SnapOn screwdriver that's so big it looks like there probably isn't a screw anywhere that it would be small enough to fit. When you first said big screwdriver, my extra long SnapOn screwdriver came to mind. I found it on the road about fifteen years ago. What a find, a SnapOn screwdriver! It's probably about 3 feet long. I would never have bought one, but I've been surprised how handy it is sometimes.

Have a great day,

------------------
Larry Bible
'84 Euro 240D, 523K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in
Mercedes automobiles

Lots of good advise here but let me add something to explain what actually happens during caliper application that explains why you get dissimilar wear.

When you apply the brakes, what causes them to unapply???? Its not the spring clips. They are there to keep the pads from rattling and to dampen vibrations...........

The answer is the resilience of the square cut piston rubber seal. When the brakes are pushed the seal FLEXES to allow the pad to come in contact. Overall the piston eventually slips through the seal(with pad wear) but not with each braking. During normal operation the seal flexes out with the pad and something like a rubber band it springs back pulling the piston back also, after the event. Over the years the seals get hard and the piston moves through the seal (eventually leaking) and in this case they aren't pulled back properly. This causes the pad to stay partially engaged with the disc and accelerates wear. Any dirt or corrosion that holds the piston of course causes the brake pads to stick also, but this is usually much worse than just differences in pad wear.

We charge an hour labor to rebuild a caliper. With rebuild kit this is much cheaper than rebuilts and I am sure of the quality.

PS: My father was an administrator for United Air Lines for 40 years before his retirement. He lets me (my shop) do all his work now, but during my childhood he did almost all his own car repairs. Some of my most memerable moments as a child were hanging around the one gas station that he would go to when things were beyond his capabilities.

------------------
Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician



[This message has been edited by stevebfl (edited 08-06-2000).]

Steve,

Thanks for your explanation. I thought it was just me, doing my own work as economically as possible, that saw rebuilding calipers as preferrable. However, when I think about it, if I were trying to turn some profit AND see that the customer didn't have to bring the car back, rebuilding them myself would provide much better quality control. If you see that a caliper is not rebuildable, then you get what you need. I guess it gets back to the old "if you want something done right, do it yourself" motto.

Thanks again for the insight,
Larry

Larry,

Thanks for the input about riding the brake pedal. That is one habit I have assiduously avoided. Can't speak for my wife, however; anyhow, I do better than 90% of our driving and as stated earlier, neither of us drives hard. Perhaps Steve's point about the difference in wear patterns holds here. I discovered my caliper problem while driving between Baton Rouge and Houston. The car was pulling severely to the right. When I checked, I found the outside brake pad was tightly locked against the disc :(

Steve,

Thanks for the clarification. In a previous post I referred to a "rib" on the seal that pulled back the piston. I didn't realize that it was only the basic seal itself.

As to ease of rebuilding calipers, it has been a long time, but I seem to recall that the exterior of the piston has a cutout that has to be installed at a specific angle in order to prevent squeal. I believe my biggest problem was that I could not get the precise angle. I made a template to be used to check the angle. Once the piston was installed, it could not be turned and had to be extracted, repositioned and reinstalled. I don't know how many of these cycles I went through before giving up and just saying, "That's going to have to be close enough." It has worked all right, so I guess it was "close enough". :)

Thanks to all for the input.


------------------
Ted
1979 240D
160,000 miles

Sometimes those rubber sealing rings in the caliper body get put in the wrong way. They've got a bevel that's not particularly noticeable.
Harvey