Spongy Brakes after front brake disc Swap - 2009 W221 S63AMG
01-21-2019, 12:18 PM
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Thread Starter
Spongy Brakes after front brake disc Swap - 2009 W221 S63AMG
I just posted this guidance on a thread created in the W204 C-class forum from 2009 as I found the solution to my problem there. But as it seems this issue (caliper over return) pertains to multiple MB platforms i wanted to post it here also in case anyone searches for a solution specific to S-class AMG issues.
The original thread:
https://mbworld.org/forums/c-class-w...placement.html
My issues began after a routine front brake pad change about (didn’t touch the rears and didn’t touch the front rotors) 4 months ago. I’ve performed 20+ brake jobs over the years but never on this car and was pleased at how smoothly everything went (the pistons pushed back in SO effortlessly). I figured brand new pads, even on old rotors, would give me a slightly better brake feel and get me through another couple of years before a full overhaul. I immediately discovered a spongy pedal, but only in the initial grab, and then solid breaking. I KNEW I hadn’t allowed any air into the system as it went completely untouched but for displacing the caliper volumes back into the reservoir.
I found this thread and while I’d NEVER heard of this phenomena it was the only plausible explanation on what could be happening.
So yesterday I set about tackling the issue. I did each of the front sides separately, even doing each piston separately (the S63 has two separate caliper/piston assemblies and thus two full sets of pads on each side). I left one complete set of pads in place on the drivers side as I addressed the first caliper assembly.
Procedure for Caliper#1 of 2 - Drivers Side:
- Remove wheel and secure vehicle on jackstands, leaving jack in place for good measure
- For driver's side assembly, turn the wheel all the way to the right to allow better access to rear of caliper assembly
- Unscrew brake fluid reservoir cap, set aside and place shop rags around the reservoir in case of spillage/overflow
- Remove the caliper dust shield and spring loaded plates (aesthetics only - N/A to all models)
- Remove pin dust caps and caliper pins (two of each per caliper)
- Gently pry the floating section of the caliper upward to clear the main caliper frame (pads may or may not come with the upper assembly)
- Secure the upper assembly (even as a redundancy). The last thing you want to do is let the assembly dangle or accidentally drop it - both can damage the hydraulic lines, flanges and/or fittings
- Remove pads and set aside
- Insert spacer of your choice instead of pads*
Glyn mentioned using old pads or something else to represent the appropriate thickness of the brake pad backing plate. I rummaged through my garage and found (of all things) a wooden 5 gallon paint stirrer from Home Depot that was the EXACT same thickness of both the inner and out pads (they were identical in thickness but i'm not sure this is true of all cars?? These things are free if you buy the paint or can be bought for pennies if you don't. I measured and cut sections down to place as stops for both the piston and the backside of the caliper assembly. This wasn't made explicitly clear in the earlier write-ups but its worth detailing as the last thing you want to do is only insert one filler (to represent one of the two pads) and then pop-out your piston. I positioned one piece of wood between the piston and the inner/car side of the rotor and another between the caliper housing (on the upper/sliding section) and the outside/street side of the rotor. In essence I now had two ~1/4" pieces of pine to represent my brake pads.
- Have a friend get into the car and with the engine OFF, while you monitor both the piston movement/progression and the position of the wooden shims, have your friend slowly press the break pedal down. There was no definitive guidance on how to do this, so I told my friend to push the pedal approximately half way down, release and start again from the top of the pedal stroke. Once the piston and caliper assembly had sinched-up on the wooden blocks and they were being help firmly in place I asked my friend to step out of the car while I prepared the second caliper on the driver's side.
I repeated the exact same process again on the second driver's side caliper and with the second set of wooden pads held firm, asked my friend to again step out. With the engine OFF, I got behind the wheel and slowly pushed the brake pedal all the way down until it wouldn't compress any further (I wanted to make sure the pistons were as deployed as they were ever going to be so I pressed the pedal with a lot of force - but again, smoothly and evenly, then released the pedal back to its resting point. The pedal actually felt solid at this point but I remembered Glyn had made mention of pressing the pedal quickly somewhere (perhaps to snap the seal direction back to the correct position). I did this with quick and deliberate pump of the pedal - mimicking an emergency stop.
My goal yesterday was to not only reverse the caliper over return but also change out the front rotors, so for the purposes of only correcting the caliper over return, I will not describe changing the rotors here, but to say that I think it's best to perform the caliper over return correction while the OLD rotor is installed and not after you've put the new one in place as it will give you further piston extension (the amount will vary based on how much material has been scrubbed off of your existing rotors, but take all you can get as you only want to have to do this once!)
With new rotor in place and the wooden shims reinserted (you don't want the caliper piston or clamp to touch the face of your rotor at any point):
- Using a medium sized C clamp I VERY slowly began depressing the upper caliper piston back into it's chamber - one side of the clamp was set against the inner side of the caliper assembly and the other end was set onto the wooden shim (between the clamp and the outer/street rotor face). I cannot quote a rate of compression, only to offer that I would turn the clamp handle 90 degrees, slowly, take a 1 second pause to allow the pressure in the line to normalize and then turn another 90 degrees. To echo Glyn and other's points, the goal is NOT to push the piston all the way back into the caliper housing as far as it will go (as I had done the last time I changed my break pads and as I had with EVERY other brake job i've ever done), but only to push it back far enough to be able to insert/reinsert your pads. I had the upper caliper section still unbolted at this point so as I compressed the piston more and more I would pause, remove the clamp, lift the floating caliper section, insert the pads, and test to see if I had created enough clearance to insert the assembly down over the rotor. Once I had enough space I removed the inner shim and placed the inner pad into position so that all I had to do at that point was gauge the opening i was creating between the out caliper face and the outer/street face of the rotor. When I saw that I was getting close to making enough space to drop the outer pad in I removed the clamp and caliper section and tested to see if it would go in. Trial and error here, adjust a little and test - too small, put the clamp back on and depress the piston a little further and try the pad again. When I was finely able to get the pad in place it was SNUG, so much so that the rotor and pads were fully binding as I spun the rotor in place.
- Bolt everything back up to the appropriate torque spec
- Straighten the wheels to center
- Install wheel
I repeated this process to the passenger side, stopping often as I was compressing the pistons to check the fluid level in the reservoir and make sure it wasn't about to overflow (there was no issues on this project). Once I was done with the passenger side and I'd torqued both wheels-up (110 lb/ft or 150Nm on the W221 S63) I started the car and pumped the brakes slowly until I got a firm pedal, then took the car for a short test drive through the neighborhood. I am pleased to report that the breaks felt and feel (after my 40 mile commute this morning) absolutely perfect, and with the new front rotors fitted, the bite is as crisp and clean as it ever was. Gone is any trace of the spongy feel at initial depression. And if anyone is wondering if the about change is possibly due to the rotor swap the answer is a definitive no as even after I created the caliper over return issue the brakes worked perfectly - from a strength perspective. The issue wasn't the braking power, but the fact that there was a travel period on the pedal before the brakes really dig-in. This feel on the pedal was really doughy and mushy and at slow speeds felt awful. That is completely gone now, the first bite is right at pedal inception and once again the car stops like an AMG should, absent the sponge cake in the lines!!
Thanks again to all who shared their time and knowledge on this subject - as I couldn't find ANYTHING else on the topic (except for Glyn's postings on a Jaguar forum for the same issue).
The original thread:
https://mbworld.org/forums/c-class-w...placement.html
My issues began after a routine front brake pad change about (didn’t touch the rears and didn’t touch the front rotors) 4 months ago. I’ve performed 20+ brake jobs over the years but never on this car and was pleased at how smoothly everything went (the pistons pushed back in SO effortlessly). I figured brand new pads, even on old rotors, would give me a slightly better brake feel and get me through another couple of years before a full overhaul. I immediately discovered a spongy pedal, but only in the initial grab, and then solid breaking. I KNEW I hadn’t allowed any air into the system as it went completely untouched but for displacing the caliper volumes back into the reservoir.
I found this thread and while I’d NEVER heard of this phenomena it was the only plausible explanation on what could be happening.
So yesterday I set about tackling the issue. I did each of the front sides separately, even doing each piston separately (the S63 has two separate caliper/piston assemblies and thus two full sets of pads on each side). I left one complete set of pads in place on the drivers side as I addressed the first caliper assembly.
Procedure for Caliper#1 of 2 - Drivers Side:
- Remove wheel and secure vehicle on jackstands, leaving jack in place for good measure
- For driver's side assembly, turn the wheel all the way to the right to allow better access to rear of caliper assembly
- Unscrew brake fluid reservoir cap, set aside and place shop rags around the reservoir in case of spillage/overflow
- Remove the caliper dust shield and spring loaded plates (aesthetics only - N/A to all models)
- Remove pin dust caps and caliper pins (two of each per caliper)
- Gently pry the floating section of the caliper upward to clear the main caliper frame (pads may or may not come with the upper assembly)
- Secure the upper assembly (even as a redundancy). The last thing you want to do is let the assembly dangle or accidentally drop it - both can damage the hydraulic lines, flanges and/or fittings
- Remove pads and set aside
- Insert spacer of your choice instead of pads*
Glyn mentioned using old pads or something else to represent the appropriate thickness of the brake pad backing plate. I rummaged through my garage and found (of all things) a wooden 5 gallon paint stirrer from Home Depot that was the EXACT same thickness of both the inner and out pads (they were identical in thickness but i'm not sure this is true of all cars?? These things are free if you buy the paint or can be bought for pennies if you don't. I measured and cut sections down to place as stops for both the piston and the backside of the caliper assembly. This wasn't made explicitly clear in the earlier write-ups but its worth detailing as the last thing you want to do is only insert one filler (to represent one of the two pads) and then pop-out your piston. I positioned one piece of wood between the piston and the inner/car side of the rotor and another between the caliper housing (on the upper/sliding section) and the outside/street side of the rotor. In essence I now had two ~1/4" pieces of pine to represent my brake pads.
- Have a friend get into the car and with the engine OFF, while you monitor both the piston movement/progression and the position of the wooden shims, have your friend slowly press the break pedal down. There was no definitive guidance on how to do this, so I told my friend to push the pedal approximately half way down, release and start again from the top of the pedal stroke. Once the piston and caliper assembly had sinched-up on the wooden blocks and they were being help firmly in place I asked my friend to step out of the car while I prepared the second caliper on the driver's side.
I repeated the exact same process again on the second driver's side caliper and with the second set of wooden pads held firm, asked my friend to again step out. With the engine OFF, I got behind the wheel and slowly pushed the brake pedal all the way down until it wouldn't compress any further (I wanted to make sure the pistons were as deployed as they were ever going to be so I pressed the pedal with a lot of force - but again, smoothly and evenly, then released the pedal back to its resting point. The pedal actually felt solid at this point but I remembered Glyn had made mention of pressing the pedal quickly somewhere (perhaps to snap the seal direction back to the correct position). I did this with quick and deliberate pump of the pedal - mimicking an emergency stop.
My goal yesterday was to not only reverse the caliper over return but also change out the front rotors, so for the purposes of only correcting the caliper over return, I will not describe changing the rotors here, but to say that I think it's best to perform the caliper over return correction while the OLD rotor is installed and not after you've put the new one in place as it will give you further piston extension (the amount will vary based on how much material has been scrubbed off of your existing rotors, but take all you can get as you only want to have to do this once!)
With new rotor in place and the wooden shims reinserted (you don't want the caliper piston or clamp to touch the face of your rotor at any point):
- Using a medium sized C clamp I VERY slowly began depressing the upper caliper piston back into it's chamber - one side of the clamp was set against the inner side of the caliper assembly and the other end was set onto the wooden shim (between the clamp and the outer/street rotor face). I cannot quote a rate of compression, only to offer that I would turn the clamp handle 90 degrees, slowly, take a 1 second pause to allow the pressure in the line to normalize and then turn another 90 degrees. To echo Glyn and other's points, the goal is NOT to push the piston all the way back into the caliper housing as far as it will go (as I had done the last time I changed my break pads and as I had with EVERY other brake job i've ever done), but only to push it back far enough to be able to insert/reinsert your pads. I had the upper caliper section still unbolted at this point so as I compressed the piston more and more I would pause, remove the clamp, lift the floating caliper section, insert the pads, and test to see if I had created enough clearance to insert the assembly down over the rotor. Once I had enough space I removed the inner shim and placed the inner pad into position so that all I had to do at that point was gauge the opening i was creating between the out caliper face and the outer/street face of the rotor. When I saw that I was getting close to making enough space to drop the outer pad in I removed the clamp and caliper section and tested to see if it would go in. Trial and error here, adjust a little and test - too small, put the clamp back on and depress the piston a little further and try the pad again. When I was finely able to get the pad in place it was SNUG, so much so that the rotor and pads were fully binding as I spun the rotor in place.
- Bolt everything back up to the appropriate torque spec
- Straighten the wheels to center
- Install wheel
I repeated this process to the passenger side, stopping often as I was compressing the pistons to check the fluid level in the reservoir and make sure it wasn't about to overflow (there was no issues on this project). Once I was done with the passenger side and I'd torqued both wheels-up (110 lb/ft or 150Nm on the W221 S63) I started the car and pumped the brakes slowly until I got a firm pedal, then took the car for a short test drive through the neighborhood. I am pleased to report that the breaks felt and feel (after my 40 mile commute this morning) absolutely perfect, and with the new front rotors fitted, the bite is as crisp and clean as it ever was. Gone is any trace of the spongy feel at initial depression. And if anyone is wondering if the about change is possibly due to the rotor swap the answer is a definitive no as even after I created the caliper over return issue the brakes worked perfectly - from a strength perspective. The issue wasn't the braking power, but the fact that there was a travel period on the pedal before the brakes really dig-in. This feel on the pedal was really doughy and mushy and at slow speeds felt awful. That is completely gone now, the first bite is right at pedal inception and once again the car stops like an AMG should, absent the sponge cake in the lines!!
Thanks again to all who shared their time and knowledge on this subject - as I couldn't find ANYTHING else on the topic (except for Glyn's postings on a Jaguar forum for the same issue).
