Rear Caliper is Leaking, rebuild or replace?
 

I was wondering why I was getting low fluid and found out the left rear is a leaker. How do you know whether it's time to replace vs just to rebuild?

Also what tools do you need to do the rebuild? I was surprised to see the Mercedes star on it, that must mean it is original right?

The only time they're not rebuildable is if the piston or bore are pitted from corrosion. Rebuilding calipers is always much cheaper than replace.

All you need is new piston seals and dust boots. A pair of good hands, and some caliper assembly lube. A cheapo 12v tire pump is handy for pushing the pistons out.

Flush / change your brake fluid every 2 years like Mercedes recommends and the brake hydraulic components will last nearly forever.

I respectfully disagree with Torsionbar. I used to rebuild calipers, but concluded it just was not worth it when you can get a rebuilt one for about $65.

You never know what you are going to find when you tear them down, so you might need a rebuilt one anyway. Polishing tarnished pistons (I've found) is a waste of time. They seem to freeze again eventually.

Since it's just a leak and not a seizure, you may be OK just by replacing the rubber. Or you may not.

Agree completely about flushing the system every couple of years. I think Mercedes actually recommended doing it every Spring.

If you buy rebuilt calipers get them from a local source as people have been having issues with the quality of rebuilt ones.

As in post 5 rebuildablity depends on if you can get the calipers out (if they are rusted in place), the piston bore and the lip area that the boot attaches to.

It is typical for there to be some pitting in the caliper bore towards the back of the piston area but not in the area where the piston seal operates.

From reading reports on the internet, I concluded that my "rebuilds" must be a lot better than the ones that parts stores sell. My success rate is 100%; the parts stores seem to be batting around 50%.

If an tired seal is causing a leak, a new seal ought to fix it.

I'll check to see if the piston is cocked or stuck, it it's normal/in good condition, rebuild kit it is.

You will need a cylinder hone of the correct size. I have several but haven't used them in years.

Kits used to be a few dollars. Calipers required several hours labor to earn enough to purchase. Times have changed.

I'd use a power bleeder to flush and change the fluid. Install new hoses unless yours are relatively new.

Replace in axle pairs.

That's a good point, while you have things apart already is the perfect time to replace those old cracking rubber hoses. If they are over 10 years old, or have visible cracks in the rubber, time to replace.

Just did this job...
 

My latest SDL had one stuck rear caliper and the other rear would drag. I replaced both calipers with rebuilt units and also replaced the lines. The lines were 85% of the problem. They had collapsed internally and wouldn’t allow enough fluid to pass through. I installed the rebuilt calipers and while I waited on the brake lines to arrive I built myself a pressure brake bleeder. That was some of the best money I’ve spent on homemade equipment. It took less than 30 minutes to bleed the rears and change out all the fluid in the system with the pressure bleeder.

I have never used any sort of hone on the inside of a caliper. There is lots of clearance between the piston and the bore so that is not the issue.

A wire brush on a drill motor can be used on the back of the caliper to remove the rust.

Any rust can be smoothed out and away buy using some wet/dry sand paper so that the sealing area is smooth.

You did not say if you have bendix or ATE caliper.

O-rings for splitting brake calipers http://www.peachparts.com/shopforum/diesel-discussion/273570-splitting-brake-calipers.html
The above has the Centric Kits that has the O-ring that goes between the Caliper Housings.
This site worked 3 years ago CALIPERS - Centric Parts

Splitting Brake Calipers
http://www.peachparts.com/shopforum/diesel-discussion/273570-splitting-brake-calipers.html

It just has the Mercedes star on it, doesn't say Bendix or ATE

Easy to tell. Are the anti-rattle clips flat or like coat hanger wire?

I've had rebuilt calipers from the parts store that still dragged and I had to rebuild them again myself (the part store didn't have another one in stock).

I get some seals before I take calipers off just to have them if needed. Rock auto has the seals AND clips dirt cheap, like $4 vs $100 to fix one side. In the mean time just keep topping off system - brake fluid is also dirt cheap.

When you take the caliper off pop out the piston using the brake pedal and have a look at it.If it's not pitted badly, smooth it out with some fine sandpaper and water.
Lube it up with brake fluid and put it back together with a new seal. In most cases that works, unless water has been built up in the old brake fluid for years on end from not being changed.

You still have to do most of the work anyway, wrenching and bleeding (the brakes). I you need to you can always go to your local parts store for a caliper.

Another thing, get a turkey baster from the dollar store and clean out the old DIRTY brake fluid in the master cylinder. Just suck it out, replace, repeat... it won't put any air in the system and will get a lot of junk out. You can do this today.