Rebuilding and Splitting an ATE Brake Caliper

Debunking the myth of "splitting" an early ATE Mercedes brake caliper

The million dollar question. Can an ATE brake caliper be split in two halves, and rebuilt? The answer is YES!

This article will cover splitting an original ATE front caliper on a 1975 Mercedes-Benz 450SL. If you own a different car or model or caliper, be sure to get the specs for your particular vehicle and chassis number. The rear caliper has a slightly different assembly process.

WARNING: Working on a vehicle braking system is serious business as it involves the safety of yourself and others. If you are not certain of what you are doing, have a professional take care of your brakes!

Unfortunately, the internet can be a very bad place to go for information. In this case, the myth of not splitting an ATE brake caliper. This information could not be farther from the truth. Yes, Mercedes and ATE do warn not to split a caliper, but there is one very simple reason for this, they don't want to be sued! As soon as a company gives the "ok" to do something, they are opening themselves up for serious liability. So, in order for the companies to cover their backs, they state, it can't be done, and I would do the same if it were my company. 

All that said, the ATE calipers can easily be split, and reassembled with ease. Ease in a job however does not mean fast and sloppy. In this particular case, it means no special tools or  back braking labor is required. For this job, absolute cleanliness is critical, and paying excellent attention to detail is of vital importance! YOU WILL NEED caliper o-rings if you are going to split the calipers. These o-rings can be purchased from Performatek in Massachusetts, USA. Phone: 508-655-8079. While their website does not reference Mercedes-Benz, don't forget they are ATE brakes not Mercedes that were used across many makes and models. When ordering, ask for Andrew to make sure you get the correct o-rings for your particular caliper.

Before we move on to the process, I found it ironic that there is such a todo about splitting the caliper, when not properly bleeding a braking system can have devastating results. The worst that will most likely happen with a failed caliper rebuild is a leak which you will discover quickly! How? Because you will be pulling the wheel after a short trip around the neighborhood at slow speeds to check for any seepage.

STEP 1
Jack up the car, remove front wheel, and caliper. To remove a caliper see my article on rear brakes for the Mercedes R107. The removal of the front is identical. Click here to view article.

STEP 2
Once the caliper is removed, inspect it throughly along with the rotor for any abnormal wear. If the caliper appears damaged or worn in any way, or is heavily corroded, it is highly recommended that you purchase a new ATE caliper from an after market Mercedes shop or from Mercedes-Benz. The ATE calipers are available new and rebuilt. 

STEP 3
Once you have determined that all is in excellent condition, the next step will be to remove the two pistons from the caliper. To do this, shop air (compressed air) is the best way as shown in the photo. WARNING: The caliper contains a fair bit of residual brake fluid and will dispense with force during the piston removal process. It is highly recommended to place the caliper in a container and cover it with a rag. This job should also be done away from other vehicles, people, pets and painted surfaces. Brake fluid is very corrosive! Wear eye protection and gloves! 

STEP 4
Place heavy cardboard, cloth or thin piece of wood between caliper halves. Remember how the pistons came out. They must go back exactly the same way. This is critical in order to get proper brake wear.

STEP 5
Inserte shop air nozzle in to brake line hose, and gently inject air. Both pistons should eject with considerable force. DO NOT have fingers in-between pistons when removing—it's painful! If both pistons do not eject the use of a screwdriver will be required. First, remove the dust cover, and heat shield (front calipers only), then gently pry piston out by placing the tip of a flat head screwdriver under the lip of the piston, and working around the entire edge until removed. This may take a few minutes.

As you can see the left piston did not fully release.

Pistons removed from caliper

STEP 6
Remove bleeder nozzel. Blow shop air through nozzle to make sure it is free of any dirt. Again be mindful that brake fluid is in all of these parts. I changed out the original ATE bleeder valves for Speed Bleeder™ valves. The Speed Bleeder valves allow one person to bleed the brake system quickly and with ease. Customer service is excellent, the price is right, and the product is of excellent quality. You can click the link above or reach them by phone at 1.888.879.7016

STEP 7
Remove brake hose. Unless it's only a few years old, replace it.

STEP 8
Split caliper. Using a breaker bar and a 14mm socket, remove the four bolts. REMEMBER, brake fluid may still leak from the caliper when disassembled. You will most likely need to secure the caliper gently in a mounted vice for this process.

STEP 9
Remove cylinder/piston seal on edge of piston wall. A metal dental pick works very well. Once removed, use the dental pick to clean out all the edges where the cylinder seal was fitted. Again a dental pick works great. You will see that a shocking amount of old rubber and dirt will be removed. If this dirt is not removed, the new seal will not fit properly, causing potential sealing problems.

That's a lot of crud to have been left behind

STEP 10
Inspect pistons, and cylinders very well. Look for any pitting or rust. Stains may be visible and can be often removed with a soft cloth and brake cleaner. If any light surface dirt remains, a gentle rub with a Scotch Brite pad and brake clean will clean the surface. If any rough or sticky feeling spots remain on the cylinder or piston walls, replace the caliper. According to Mercedes, pistons are no longer sold separately, at least for the 450SL but new calipers are available from Mercedes or after market Mercedes shops.

STEP 11
Throughly clean all parts (exterior and interior) with brake cleaner. Use attached nozzle on can to inject cleaner through brake fluid passage ways. WARNING: cover caliper halves as brake cleaner will begin to spray in unpredictable directions. 

Cylinder and piston should be throughly clean as photo shows.

STEP 12
As with the prior step, use shop air to blow through passage ways in the caliper, to free any debris and throughly dry the caliper parts.

STEP 13
Install new cylinder/piston seal. Make sure it is not twisted and is seated properly (flush with the side walls).

STEP 14
Wipe piston off throughly with a lint free cloth, and  grease with  fresh brake fluid.  Also grease the cylinder walls. I pour a 1/4 teaspoon of brake fluid in the bottom of each caliper cylinder half and distribute it around the cylinder walls, and the remaining on the piston.

STEP 15
Insert the pistons. The pistons must be installed just as they came out! If installing front pistons, the piston must be seated to align with the heat shield that will be fitted over the dust cover. The pistons are not easy to press in, but should slide in with moderate pressure. I use a 24mm socket and a flat steel bar to depress the pistons. Once the pistons get moving, they will seat smoothly. Should the pistons stick, and not enter the cylinder, remove and check to make sure the cylinder sealing ring has not slipped from the groove. 

STEP 16
Install piston dust covers, making sure they are pressed down around the entire lip of the seal area. It should be quite difficult to seat the outer edge of the dust cover. 

STEP 17
Install heat shield (front only) and gently tap flush

STEP 18
Install caliper o-rings (between caliper halves) as shown. Make sure the adjoining caliper halves are perfectly clean before mating. As you will see, my calipers were beginning to seep fluid as is indicated by the dark areas. This is not surprising as they are more than likely the original calipers and are now over 40 years old. It was only a matter of time before they would start to leak more. DO NOT put any type of sealant on o-rings or between caliper halves. 

O-rings marked by read circle

STEP 19
When joining ATE caliper halves, make sure the o-rings do not move from the recess. If for any reason you suspect the o-rings might have moved, double check before securing the two halves. This entire job boils down to whether or not you come to a proper stop.

STEP 20
While holding caliper halves together securely, insert the four bolts, and hand tighten to keep caliper o-rings from moving out of position. Make sure these caliper bolts are free from rust or dirt. These bolts do not require thread lock as indicated by the absence of the product on removal. I simply removed the rust and cleaned up the bolts before reinstallation.

STEP 21
Torque the four ATE caliper bolts to 24.5 foot pounds. (This according to Performatek). This step should be done however in two phases, as with most torquing. First is to torque the four bolts to 12 ft. lbs. then to the final 24.5. 

STEP 22
The caliper is now ready to be installed. Fit new flexible brake line and tighten. Remember to pass the new brake line though the retaining eye on the back side of the wheel, and attach to main brake fluid line. Be sure to also install a new bolt locking tab for the two caliper retaining bolts. It is recommended that new bolts be used. They are available through Mercedes or after market shops

STEP 23
Install brake pads and hardware greased well with appropriate caliper grease. DO NOT get grease on the fronts of the pads or the rotor surface. 

STEP 24
Bleed brakes. If you use the Speed Bleeder system, follow the manufacturers directions. Make sure the fluid is air free before you stop passing fluid through the system!

STEP 25
Take car out on side streets to make sure you are able to stop fully. Brakes will still need to be seated (bedded) according to manufacturer recommendations. 

If you are able to rebuild your calipers, this will save you about $1,000 for all four. In my case this can go toward the many other unexpected expenses on this restoration.

Products I recommend for this job (ATE CALIPERS ONLY)
• Pentosin or ATE DOT 4 brake fluid
• ATE or Mercedes-Benz brake pads
• ATE or Mercedes-Benz brake lines
• ATE or Mercedes-Benz caliper rebuild kit
• Caliper Hardware Kit (I could only locate a quality front kit in England from the SL Shop. The aftermarket hardware I sourced locally in the U.S., was not a good quality at all.)
• Speed Bleeder brake fluid bleeder valves
• Performatek caliper o-rings
• Permatex or Mercedes-Benz brake caliper grease

Thanks to Speed Bleeder and Performatek for making this brake job a great success.

Again, you will find a considerable amount of information on the web about this subject, but if you feel confident on your ability to work carefully and very clean you can easily do this job with perfect results.

COMING UP

Parking Brake rebuild

Brake Disc (rotor) Replacement

Seating or Bedding in New Brakes