Resealing w123/126 calipers
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I haven’t seen a write-up with pictures on this topic, so I figured I’d do one since I recently did this on my w123.
When you are faced with a leaking brake caliper or perhaps a stuck brake caliper, there two options you can do to fix the problem. One option is to buy a rebuilt caliper. The other option is to reseal or rebuild your existing calipers with a caliper repair kit if your caliper is not too corroded or physically damaged. While the former is over 100 dollars for each of the front calipers. The latter is 20 bucks per ATE Caliper repair kit. http://catalog.peachparts.com/item.wws?sku=W0133-1633803&itempk=76449&mfr=FAG&weight=0.25 I feel a much better choice if you have the time and ability to do so. Also, do both sides to avoid braking unevenness and for the reason if this one is leaking, the other would most likely follow. The first thing I did was to remove the caliper from the car. The process is just like with any other brake job with the added step of disconnecting it from the brake line. Since I am replacing the rubber brake lines, I loosened the old line first at the base of the caliper and then I cut it right off leaving a bit of rubber hose near connector. (I’ll explain a bit later). Here is a shot of the leaking caliper with the Caliper Repair Kit. http://www.peachparts.com/shopforum/...1&d=1283812220 Here is a shot of what is in the repair kit. Two O-Rings, Two dust covers, and two heat shields. http://www.peachparts.com/shopforum/...1&d=1283812232 To remove the pistons from the caliper, first make a note of each of the pistons position. I then placed my adjustable wrench with a rubber covered handled in between the two pistons (you can use what ever works for you) as a stop guard. Next I use compressed air (source from an air compressor or a bicycle pump with an adapter) to pop the pistons out by placing my air gun in the cut brake line and shooting compressed air into the caliper. http://www.peachparts.com/shopforum/...1&d=1283812242 The pistons will come out with a lot of force, so be careful of not having fingers in the way. Also, Make sure you have a catch pan to capture any brake fluid coming out of the pistons and having gloves to protect your skin is helpful. http://www.peachparts.com/shopforum/...1&d=1283812254 After the pistons are positioned towards the middle of the caliper, you can use a pry bar on the ridge of the piston to the pry them out. Work it in a way where you don’t bind them. Any slight binding would get them stuck. You might have to push one piston back in a bit to get the other out. http://www.peachparts.com/shopforum/...1&d=1283812264 . |
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If you get one out and the other is stuck, you can pop out the rubber dust cover from the cylinder you removed and place the piston back in. Hold that piston down (easier with an assistant) and shoot compressed air again. It should pop out.
http://www.peachparts.com/shopforum/...1&d=1283812604 I inserted Brian Carlton's procedure on removing a piston that is still stuck after using compressed air. Quote:
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Use a pick and pry the old O-Ring out of the cylinder. http://www.peachparts.com/shopforum/...1&d=1283812629 I originally scrub clean the calipers and pistons with mineral spirits and stiff plastic brush. Some would argue not to use petroleum based solvents in the braking system if not flushed out properly. So using acetone would be a safer choice. Inspect the piston for damage or abnormalities. If the piston surface is corroded, use an emery cloth to remove the corrosion. If deeply pitted, then a replacement piston maybe needed. Also check on the cylinder bores for corrosion or damage or abnormalities. If corrosion or damage is bad then a new caliper body may be needed. I then finish cleaning the assembly with spraying acetone based brake cleaner to degrease the insides the cylinders, passages and pistons, and the outer caliper body. http://www.peachparts.com/shopforum/...1&d=1283812639 http://www.peachparts.com/shopforum/...1&d=1283812648 . |
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Poured fresh brake fluid in the cylinder and installed the new O-ring.
http://www.peachparts.com/shopforum/...1&d=1283812844 I like to assemble the piston with the dust shield and heat shield before installing into the caliper. Main reason is it is easier to get the piston in the correct position with the heat shield on. http://www.peachparts.com/shopforum/...1&d=1283812857 Coat piston with brake fluid and install in caliper by press down with your both sets of fingers. http://www.peachparts.com/shopforum/...1&d=1283812867 Once the pistons are almost down, you can press the rubber dust shield into place on the body of the caliper. http://www.peachparts.com/shopforum/...1&d=1283812877 Caliper is ready to go. Install on the car and bleed the brake lines. Look for leaks. If leaking, then you’ll need to do the process over again and figure out why it leaked. http://www.peachparts.com/shopforum/...1&d=1283812897 Rear calipers are basically the same process. Hope this helps somebody save a bit of money! . |
Great writeup!!!
I always like it when I have an option of rebuilding a part rather than just replacing it. It saves money and it teaches one about how the system functions. When I "blow" the pistons out, I use a piece of 1" x 4" (its actually 3/4" think so plenty of space) between the pistons so they hit the board instead of each other. |
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Thank you for posting this. It's very much appreciated.
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Firstly, if you're going to get into the fine art of rebuilding a caliper, odds are that one of the pistons is frozen quite solid in the bore. You're not getting it out with 100 psi. Furthermore, when you apply 100 psi, the opposite piston immediately and promptly eject itself from the bore, leaving you with a stuck piston and an open hydraulic system. The thing to do is to ascertain your condition prior to disengaging the free piston. Apply about 30 psi.........if one piston moves and the other does not............STOP. Get a C-clamp and clamp the free piston so that it won't move. Install the caliper back on the vehicle and connect the brake hose. Press on the pedal and apply full hydraulic pressure to the stuck piston. This will amount to over 500 psi and the piston will eject itself. Now, you've got the issue of an open bore and one engaged piston. You'll need a sheet of rubber and a wooden block that covers the bore. Clamp the block against the rubber.........over the bore. Now, use your air pressure...........40 psi will do it........to free the remaining piston. DO NOT separate the caliper halves........ |
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Chuck Norris does not rebuild his brakes. Chuck Norris just stares at his brakes and they rebuild themselves. No acetone, no mineral oil, no compressed air.
If Chuck Norris actually needed to rebuild his brakes, he would simply roundhouse kick them until they worked |
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As far as the mineral spirits is concerned. I thoroughly cleaned it off a second time with acetone based Brake Cleaner. I am confident all of the petroleum based cleaner is removed. But as far as this thread is concerned, I'd like to retract using mineral spirits also. . . |
Having done this recently too I'd like to add the following comments:-
1) If you split the caliper you will have trouble finding new o rings 2) I was taught (as an aircraft mechanic) to never clean any rubber parts with Acetone as this has the same effect as trichloroethane - it deteriorates rubber parts (Don't believe me? Do an internet search for "acetone rubber") 3) I think the most important aspect of resealing hydraulic components has been over looked:- ASSESSMENT OF CORROSION AND WEAR - you need to work out whether it is really worth your while putting in new set of seals and trying to bleed calipers that really could do with machine work... |
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Aircraft brake systems generally don't use glycol ether brake fluid, so the caution against the use of petroleum-based cleaners does not apply. |
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Whats the trouble with finding replacement orings for the halves...seems to me like not doing these would only be half a rebuild no?
I've got a leaking rear caliper and its got to go...pedal is way too soft and it's pissing fluid when parked. I'm teetering on rebuilding vs buying remans. I'd like to paint the calipers too while I do this job. Any thoughts? |
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