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.




Here is a shot of what is in the repair kit.
Two O-Rings, Two dust covers, and two heat shields.




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.




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.




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.






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1983 123.133 California
- GreaseCar Veg System

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.



I inserted Brian Carlton's procedure on removing a piston that is still stuck after using compressed air.

Photo showing a split caliper.



Use a pick and pry the old O-Ring out of the cylinder.




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.






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__________________
1983 123.133 California
- GreaseCar Veg System

Poured fresh brake fluid in the cylinder and installed the new O-ring.




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.




Coat piston with brake fluid and install in caliper by press down with your both sets of fingers.




Once the pistons are almost down, you can press the rubber dust shield into place on the body of the caliper.




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.




Rear calipers are basically the same process. Hope this helps somebody save a bit of money!


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1983 123.133 California
- GreaseCar Veg System

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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'82 300D (project)
'46 Willys (project)
"Nothing seems to be the way it should in this garage." -jt20
"Smarter than an engine, dumber than a hoodlatch..." -jt20
"Start jumping up and down to smoosh down those engine mounts" -DeliveryValve
"no" -kerry
"At this rate, you may have it done by winter" -layback40

Thanks! Great tip on the 1X4 piece of wood.

__________________
1983 123.133 California
- GreaseCar Veg System

Thank you for posting this. It's very much appreciated.

You've got some problems with this procedure.

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........

According to MB, splitting the calipers is never in order. At least not at the field level.


The use of petroleum-based products on brake components is also never in order.

Agreed........clean and degrease with Acetone.

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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Good to be corrected. I've done separation before with no problems, but would like to retract the statement if it is a possible detriment to the members.


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.




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__________________
1983 123.133 California
- GreaseCar Veg System

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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1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

Hopefully you were also taught that new rubber parts should not be installed until after the cleaning process has been completed. Or perhaps that concept was perceived to be so self-evident that it wasn't a line item in the lesson plan.

Aircraft brake systems generally don't use glycol ether brake fluid, so the caution against the use of petroleum-based cleaners does not apply.

Sorry I wasn't specific enough - there are situations, much like when cleaning a W123 / W126 brake caliper where you may not take the component completely apart (so in the case of a W123 / W126 caliper if you do not separate the two halves of the assembly). In those situations because you know there is a rubber seal in there somewhere you should not be cleaning with acetone or trichloroethane.

__________________
1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

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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-SpecialDelivery
1985 300CD Silver/Blue H&R Suspension (Sold, still cryin over that)
1982 300SD Silver/Blue '85 OM617 (Sold)
1982 300D - Blue/Blue (Sold)