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

Mercedes R107 Rear Brake Rotor Replacement

Another very straightforward job on the Mercedes 107 and W123 models is removing and or replacing the brake rotors. If your rotors have enough surface left they can be turned to refinish, or if need be replaced. For this job I am using Zimmermann rotors for the front and back.

Now is also a good time to check brake pads for wear and also the calipers for any leaks. As our cars approach over 40 years, things will need to be replaced and things will begin to leak and obviously brakes are not something to neglect. 

This article will cover removing the rear rotors and calipers and an inspection along the way.

STEP 1
Jack up car and remove rear wheels.

STEP 2
Prepare to remove the rear calipers. Make sure emergency brake is DISENGAGED. Pry open lock tabs with a screwdriver. These will need to be replaced as they will most likely be significantly weakened and will not stand up to reinstallation. They are still available from Mercedes-Benz.

STEP 3
Tap out (remove) the locking pins, and remove spring. If the hardware is in good shape it can easily be cleaned up using a bench top wire wheel. Should it need to be replaced, it is available from Mercedes-Benz and many aftermarket Mercedes parts shops. 

STEP 4
When hardware is removed remove brake pad, depress caliper pistons using channel lock pliers as shown. When pistons are sufficiently depressed, the pad should slide out very easily.

STEP 5
Loosen bolts with a 19mm socket attached to a breaker bar. If car has been exposed to particularly wet or salty conditions a good soaking of penetrating oil the day before would be recommended. Once the two bolts have been removed the caliper will fall off if not held in place. These bolts should not be reused.

STEP 6
Hang caliper so it does not hang from flexible brake line hose. At this stage make sure the hoses are in excellent condition. If there is any cracking or feeling of dryness, REPLACE THEM! Also, check the condition of the pads. If your hoses will need replacing I will be doing an article on brake bleeding shortly.

STEP 7
Check rotors for deep scoring or warping and replace if necessary.

STEP 8
Remove rotors. Begin by lightly tapping all round hub and lightly around rotor surface on front. If that does not release the rotor, tap firmly on back where caliper was located. IF you are replacing the rotors and emergency brake shoes a penetrating oil can be sprayed inside each of the lug bolt holes to help release any rust that may hold the rotor from releasing. REMEMBER any grease will foul the operation of the braking systems.

STEP 9
Inspect emergency brake (each side) for wear, corrosion, and be sure it is fully releasing and engaging. If new emergency brakes are needed they are available through Mercedes-Benz. The kit provides all the necessary hardware and shoes for both sides. A future article will cover emergency brake replacement. In my case I am replacing the e-brakes.

Mercedes R107 Emergency Brake. Appears to be original and never touched. Needs to be replaced.

STEP 10
Installation is in reverse order. Be sure that all braking surfaces are 100% free from any oil or greases before installation. Unfortunately my rear calipers were rusting in the piston cylinders and so I needed new ATE calipers, and discs. ATE calipers are available new from aftermarket Mercedes parts stores or from Mercedes-Benz. If you need just the piston they are available from Mercedes-Benz.

NOTE: When reinstalling caliper hardware, be sure to properly lubricate all components with applicable caliper grease.

Complete and ready for bleeding

COMING UP

• Super Easy One Person Brake Bleeding
• Replacing Emergancy Brake
• Rebuilding ATE Brake Caliper
...and much more

Mercedes R107 Rear Sway Bar Links

If you are getting strange banging noises from the rear of the car when riding on a bumpy road, it is most likely either the shocks or the sway bar links that have failed. Since we covered the shocks in the last post, it is now time to cover the sway bar links.

At least on the earlier R107's such as the 1975 450SL, the sway bar links are very, very easy to replace. 

STEP 1
Jack jack up rear of car and support on jack stands. I personally prefer the flat top jack stands for my European cars.

STEP 2
Remove rear wheels

STEP 3
Unbolt sway bar link from sway bar and back of wheel assembly. Very self explanatory. If your sway bar links have popped apart as mine have, you will only need to remove the lower bolt of the link.

This photo shows the sway bar broken loose from the upper portion of the link. The ball joint is still attached to the sway bar.

Old and new sway bar link. Photo shows how the ball joint separated after many years of service.

STEP 4
Fit new link and you are done! It's almost as easy as 1-2-3.

This is what the final job should look like.

Mercedes R107 450SL Rear Suspension

R107 Rear Shock Absorber Replacement

If your convertible 107 is clunking around over bumps, it is more than likely bad shocks, and or broken sway bar links. Sway bar link replacement will be covered in an up coming post.

The good side of all this, if broken things have a good side, is that the replacement of these two components is probably one of the easier jobs on the Mercedes-Benz R107. From start to finish this job should not take more than 2 hours for both. There is one caveat, if your car has grown up in a wet or particularly snowy area, it will require the bolts to be well soaked in penetrating oil such as BP Blaster. My recommendation is to do this the day before, and spray it three times several hours apart should the corrosion be heavy. 

Let's get started:

STEP 1
Remove hard top if installed or lower convertible top. If soft top is already down and the hard top is off, open the soft top deck lid cover.

STEP 2
Provided you do not have rear seats, remove the luggage shelf from behind the seats. If fitted with a rear seat, remove those.

STEP 3
Remove hard/soft top locking crank on driver side. First gently pry out trim insert on handle and remove handle.

STEP
Remove the 3 small Phillips screws which retain the side paneling trim on each side

Location 1

Location 2

Location 3

STEP 4
Remove the two 10mm bolts, and two Phillips screws from the chrome trim on each side and remove the trim piece.

STEP 5
Remove paneling. Gently remove by pushing downward to release from upper retention lip.

STEP 6
Remove upper shock retaining bolt, washer and rubber bumper on each side. This will require pliers or vice grips to hold the center rod in place while loosening the nut.

STEP 7
Jack up car. I use wheel cribs with the hydraulic floor jack in place. ALWAYS use extreme caution when jacking a car and aways chock applicable wheels. Always check for rust or damage before jacking up the car.

STEP 8
Remove shock retaining bolts. When bolts are removed, shock will release and fall through to the ground. You can always leave the upper nut in place and remove after the lower bolts have been removed. I find it easier to just catch the shock on the way out.

STEP 9
Install new shocks in revers order and you are ready to go! Always make sure all nuts and bolts are securely tightened an always double check.

COMING UP
Replacing the rear sway bar links. Another very easy job.

Mercedes 450SL Muffler Comparison

Not all things are created equal and often times, you get what you pay for and hindsight is generally 20/20, and this is what I discovered about aftermarket mufflers for the Mercedes-Benz 450SL.

After having done considerable research on the Bosal and Ansa 450SL mufflers, I felt reassured that the Bosal would provide the best OEM exhaust note according to the representative I spoke with. It should be noted that in no way am I criticizing either manufacturers quality, durability, materials, craftsmanship etc. The issue at hand is simply based on tailpipe sound or "note", both at idle and under exhilaration. In fact, both manufactures seemed to have very well made products in both fit and finish.

When the Bosal muffler was installed however, I was extremely disappointed at how loud and throaty the car sounded, far from the OEM note I was reassured to get. Interior noise was excessive, and at speeds between 40-55 mph, a very unpleasant drone resonated throughout the cabin.

With this discovery, I contacted Ansa and discussed the current dissatisfaction, and was told I would receive an OEM note from their muffler. In short that was not the case either. Indeed a different note was delivered, but that much closer to an American muscle car on steroids and again generating a very unpleasant tone in the cabin. While I have no problem at all with the exhaust note of a muscle car, I want my Mercedes to sound as it should, and as the manufacture intended.  

Photo shows underside of 1975 450SL with aftermarket muffler

This takes us back to the drawing board with one last option, the $500 OEM muffler from Mercedes-Benz. Yes, in the end it would have been much less expensive to do this from the beginning, but some of us need to learn the hard way. 

All this said, if you are looking to ramp up your exhaust note on your 450SL, either the Bosal or Ansa would be the way to go, and does indeed offer a good price point. If however, original is what you are looking for, the Mercedes OEM muffler is the only option.