Main.TrailIndexPage | Brake System | Disc Brakes

Disc Brakes

This component is part of Brake System.


This section covers disc brakes. The 230 SL has Girling 17/3 front disc brakes, while the 250 & 280 SL have front and rear disc brakes from ATE sometimes called Teves (Alfred TEves) brakes. The rear disc brakes have a small drum brake on the outside for the handbrake.


Hydraulic pressure in the caliper extends the pistons and brake pads on both sides of the disc, or rotor, which is firmly mounted to the wheel hub. Friction between the pads and disc slow and stop the car. The piston extends the dust cover slightly when the brakes are applied and when the pressure is released, the dust cover retracts and pulls the pads off of the disc.


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Describe common maintenance procedures, and common faults that may occur. Describe how these may be diagnosed and resolved. Again, include diagrams, photographs and explanations. Where possible, include measures, tolerances, weights etc.

  • Symptoms when it faults
  • How to test if it is faulty - what tools to use
  • How to fix / change

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Just took my 230 SL on a very spirited jaunt up and down Mount Hamilton (my local mountain right behind my house). When I came back, the brakes were smoking quite heavily (despite downshifting to use the engine to brake all the time). Does anyone of you know a good and easy way to improve the brake performance? Can something be done with brake pads or the like?

Achim: This is a more common problem with the 230 SL brakes, I guess. Under normal circumstances they should work fine but if you use them hard they get hot and they tend towards fading. The Mercedes Museum prepared an SL last year according to the original Boehringer rally-230 SL from 1963. This 1966 car has the original brakes and they (MB) are having problems with fading as well when using the car in a sportive manner in the hillside. Basically, the 230 SL brakes are identical to the ones from the fintails of the same production years. So, the 230 has the smaller brake discs (brake rotors) from the W110/111 which will fit in 13 inch rims. You can change the rotors to the larger type from the 250/280 SL (for 14 inch rims) but it won't make much difference. The best improvement you can make without changing too much is to use the front disc brakes and calipers from the 450 SE (W116). These are larger in diameter (for 14 inch rims) and have the inner ventilation/cooling system. For these rotors you need to use the wider 450 SE calipers, of course. This should do the job for your case.

Joe Alexander: the 230 SL brake assemblies are smaller than the later SL's and you have drum brakes in the rear instead of discs like the later cars. First of all optimize what you have. Make sure your rubber brake hoses are good. Check the back hoses also. There are a total of five in all. They make a big difference in brake responce, and performance. They can get restricted with age. Some performance brake pads may also help. Lots of metal content will dissipate heat and help prevent fading. Make sure your brake fluid is fresh, the fluid collects moisture with age. It will boil during hard use and your brakes will go away! Flush and add new fluid every two or three years. If you want to get a little radical, I believe the large front ventilated discs and calipers from any 108 series V-8 sedan (280-SE 4.5 or 3.5, 300 SEL 3.5,4.5 and 6.3) will bolt right on!

Pete Lesler: The front calipers (if they are ATE), can accept much higher performance pad material. Performance Friction, Porterfield and Hawke all make higher performance pad material to fit the ATE calipers which use the same pads as 911 Porsches. If your car was equipped with the later 250/280SL front rotors, you could substitute vented rotors and front calipers from a 4.5 sedan which uses the same size pad material as the earlier ATE calipers. I would recommend higher performance brake fluid like DOT 4 or and higher temp wheel bearing grease as well.

Rodd says: I've ordered brake rotors (and other brake parts) for the front of my 230SL. Looking at my service manual, it seems I need to remove the hub to get to the rotor. Questions: Has anyone done this job? Is it difficult? Should I replace the bearings and seals in there while I've got it apart? The manual mentions the following tools required to do this job (job 33-5). Hub Cap Puller 180 589 00 33; Hub Assembly Puller 136 589 15 33; Assembly Fixture (metric) 120 589 03 61; Assembly Fixture (standard) 111 589 13 61; Bearing Play Tester 136 589 04 21; Hub Cap Fixture 180 589 11 39. Are these truly required, or can some other tools be substituted? It also mentions heating a spacer ring (on some versions) to 80 degrees C to remove it if worn. Also, preheat the replacement for installation. Has anyone done this? How would one do that?

Pete Lesler: this is typical Teutonic overkill. To remove the wheel bearing hub cap, simply use a screwdriver and gently tap outward around the flage. It will come off with a little persuasion. The rotor assembly is held onto the hub by a threaded nut assembly which can be first released by loosening a 5 or 6 mm allen bolt. It then can be unsrewed in typical counter clockwise fashion. Then remove the large washer and gently pull the entire rotor and bearing assembly off the hub, being careful not to drop any bearings onto the ground. The bearing seals should be replaced at this time. They can be removed by carefully prying them off. MB makes a bearing seal puller, but you can carefully remove it yourself. You may not need to replace the bearing and races. You can see if the balls in the bearing assemblies are loose by looking at the balls and their surrounding holes. If the holes are elongated or appear to puckered outward, the bearings wil need replaced. Also if the races are no longer smooth and appear to be galled or eaten away, then the bearings need to be replaced. The bearings come right out. the races are more difficult. You may wish to bring the bearing hub assembly into a machine shop to have old races removed and new ones pressed in. Then you can repack the bearings yourself. Use MB bearing grease and do not overpack. The new seals can be gently tapped into place. Then the reassembly is the reverse procedure. If you decide to replace your rotors, you will need a large metric allen socket, 8mm I believe, plus breaker, to remove the rotor assembly from the hub. In order to adjust the bearings, start by tightening the outer nut with the allen nut assembly until the assembly is tight. Then back off about 1/4 turn and insert a screwdriver behind the large washer to see if their is any play. If there is none and the rotor assembly rotates freely, your bearings should be about right. You can do a further check by torquing the wheel back on and pull the wheel outward in different directions to see if the play is excessive. Be careful not to confuse bearing play with king pin and idler arm play.

Mike Heaney: I have done this exact job a few years ago on my 1966 230SL Euro model. Forget all the tools... ok, some may disagree with me... but it's too simple of a job to require all that. Take off the wheel, remove the caliper, cap off brake line to prevent dripping. (might be able to tie it back without opening line). Pop the dust cap, loosen the bolt on the side of the hub nut, remove the hub nut, grab the rotor and pull... it should come off easily. Then unbolt the rotor from the hub, put the new one on, repack wheel bearings and put her all back together... careful not to overtighten wheel bearings, but it was easy enough on mine. One note: apparently there are two sets of calipers used on the 230SL's, and they are different sizes, so if you're replacing those too make sure you order the correct pads for the calipers you chose. From what I've heard the larger three piston calipers (Girling) are not as good as the newer two piston ones... which oddly, use smaller pads.

Cees adds: that is exactly how I replaced the front rotors (the old ones were slightly warped, so the car 'shuddered' on braking) on my 1969 280 SL last year without prior experience or any special tools, just the Haynes manual. It cost me two hours, the results were great and I've driven about 7,000 miles since. Separating the hubs from the rotors did take quite some effort, though.

Rodd again: I'm not replacing the calipers themselves, just the parts within them that come in a rebuild kit (rubber and seals?). Also replacing rotors, pads, and flex brake lines. I do have Girling calipers and, according to my MB shop manual, there were three versions of the Girling caliper used by MB on various cars, of which I have the third version. What would make the outer brake pad (two small caliper pistons) wear down to the metal backing and grove the rotor when the inner brake pad (one large caliper piston) still had about 2mm of material left? Obviously, more pressure on the outer pad, but why? I have not been able to remove my calipers yet because the two bolts that hold it on are being very stubborn. Perhaps they were last turned at the factory during their original installation. Once removed, I'll disassemble and examine for obvious signs of wear. Is there any trick to doing this? Do the inner parts come right out? Everyone - Thanks for your input!!! I wouldn't have the nerve to try some of these things without your help.

Bernt: The bolts are locked with metal tabs that you need to straighten first. You will probably find that the pistons of the calipers have corroded through the chrome and are pitted to the extend that they need to be replaced or re-chromed. I had new pistons made from stainless steel in the past. This is especially evident when you install new pads and find that now the brakes leak. The reason is that the pistons get pushed back in and the corroded parts are then moved right into the rubber seals. This old stuff does not always come out easily either and you may very well have to remove the caliper from the disc and the re-connect it to the brake hose, bleed it a little and use hydraulic brake pressure to press out the pistons. You will have to try and get them all 3 loose and moving out by holding the ones that move first in place with some clamp, wood or anything that will fit. Mind any paint in the vicinity! The trick is to get them all loosened simultaneously because once one pops out, there is no more pressure to push the others. Oh, for some reason, it is not allowed to take the calipers apart. MB mentions this a a larger warning and the reason they give is a special torque rate. I did once take some apart anyway (yes, they still work) and the only problem I had was that I could not find a special replacement seal that seals the 2 halves together. Best is not to strip them apart. Once everything is out, you can strip out the old rubbers and clean everything nicely with methilated sprits. Make extra sure that the grooves for the rubber rings and the thin groove for the dust cover are 100% clear.Soak the new rubber rings in brake fluid for some 20 minutes and then fit them in place. Keep everything clean and lubricate the piston and rings with more brakefluid. Fit the dust covers in place. Carefully insert the pistons through the dust covers and into the cylinders. This is sometimes tricky as the dust covers come out or get stuck in wrong places. When done, push the pistons in all the way and make sure that the dust covers' other edge slip into place into the grooves in the pistons. That's it.

Mike Heaney: Bernt is right about the warning on splitting open the calipers... I made that mistake and it cost me a new set of them... they are a can of worms you don't want to open just for the heck of it...

Dick Krivy adds: I don't know anything about a shrink spacer ring on the front axle. I've had the front disk's off a couple of times and didn't run into anything like that. Re: the Taper Roller Bearings (Cup (outer race in the hub) and cone (inner bearing on the spindle)). You will see a lightly frosted surface where the rollers run. This is normal. If you see any pits or wear lines on any of the components, replace them. The bearing cups can be romoved from the hub with a long punch, working around the exposed edge. If you decide to install the new cup this way, use a soft punch, as you don't want to chip the new bearing. If you find a palce to press them in, its better. Be sure they're completely seated. Always replace the seals; you can't remove them without distorting them. Mike covered all the disc removal, etc. The only thing I'd like to emphasize is wheel bearing adjustment. Too loose is worse than a little tight, especially with disk brakes. I always tighten the nut until the wheel hub and disk are difficult to turn. (Do this before you reinstall the brake caliper, so there'll be no brake drag.) This seats the bearings. Then I back it off loose and tighten it only finger tight (thats right, no tools, only fingers). IE; when the nut touches the bearing washer. Rotate the hub and disk again and loosen and tighten finger tight again. It may be in a slightly looser position. The wheel should now turn freely. Tighten the socket bolt on the split nut. This system is much more precise than the slotted nut and cotter used on most US automobiles. You can cleck clearance between the hub and spindle with a dial indicator, if you want, but a half thousands is difficult to read. The Hayes manual reccomends 1/3 turn back, after tightening, but I find it difficult to tell where this tightening stops. I like the finger tight method.

When you are going through the (massive) effort of dismantling your front wheel/brake assemblies, I would not even CONSIDER putting back anything but new "wear parts". Any bushing, bearing, seal, etc. should be replaced. Anything rubber or plastic should be replaced. Anything not a stamping or casting should be replaced. So before you start, you should have on hand all these parts. Relative to the cost and frustration of doing it all again, the parts you need to change are all pretty inexpensive.

Pete Lesler: I never compromise braking efficiency; i.e. I always replace with new calipers when the situation dictates, however there are some good rebuilts out there. Expect to pay around $70 for the fronts and $60 for the rears. Always replace the flex hoses at this time and renew all brake fluid. Use Castrol LMA DOT 4.

As far as I remember, 280SE 3.5 front calipers and rotors are straight bolt in and should provide more braking power and less fading.

Pete Lesler: 4.5 rotors and calipers are the same, however, the effective brake area remains the same, only the rotors are vented. Also, you will need to replace or remove the backing plates, as they will interfere with the new calipers and rotors. I di this on my vintage race car and upgraded to Carbon Kevlar pads and racing brake fluid. It stops better, but more importantly, no brake fade or overheating.

I am sure you can get the (stuck) pistons out of the calipers. It is tricky but can be done. Looks like you already found why one pad is thinner than the other. It is mostly because the pistons get stuck due to corrosion and then they do not move as easy as they should and therefor the side with the easiest moving piston(s) will wear faster. If you still want to DIY, try this:

  1. Push the piston you have out back in. Use large waterpump pliers for this or a larger screwdriver. If it has corrosion on its sides, take that off with a wire brush or emery cloth. The piston is in this case shot anyway. The objective here is to get it to move easily.
  2. Force all the pistons in all the way.
  3. Put the caliper back onto the car but back to front. This means that instead of onto the disk, next to the disc but upside down. That allows you to re-connect the metal brake line to it. You need to hold the caliper it in place there so that the line does not break or bend.
  4. Get an assistant to fill up with fluid and carefully pump the brake pedal. You might have to open the bleed nipple for a short while.
  5. Observe which piston moves when the brake is pushed. (MIND YOUR FINGERS !!). Stop and hold that one in place with anything suitable.
  6. Observe which one moves next and hold it too.
  7. When they all move, allow them to evenly come out bit by bit.
  8. When they are close to the middle , remove all tools and let on pop out.
  9. Catch the fluid , unscrew the line and let the fluid go into a clean container for re-use on the other caliper.

That is it and the other 2 pistons can be pryed out but grabbing them carefully with a rag and pliers. Some use compressed air to do this but that all depends what equipment you have available. You can only do one caliper at a time so you have to rebuild one first, fir it back and then do the other one because there is no pressure on the other side while one side's line is disconnected.
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