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Are rear brakes supposed to be hotter than front brakes? I thought it would be the other way around. Occasionally I get a moderate brake shudder when decelerating. It's only happened around 3-4 times over the last 6 months or so. But this last one was more severe than the previous. I looked at tire temps through the dash board, my car is a 2018 S63 sedan, last time this happened and they all looked in the same range. But this last time I used my digital thermometer. On both rears I saw close to 200 degrees farenheight around the inner edges of the rotor faces, and around 120 on the outer edges. On the front brakes they were at 120 degrees on the inner edges of the rotor and around 90 on the outer edges. Ambient temps were in the low 50's, or high 40's, with light rain. I did a nice 0-100 pull in a tunnel after dropping my wife off at the airport just to hear the exhaust. it was fun! But when braking from that speed down to around 35 is when the shudder happened. I checked the rotor temps within 5 minutes and 3 miles from when it happened.
Need to compare swept area vs wheel load vs rotor mass vs pad area front and rear to make a clear comparison. Rear brakes are generally smaller than fronts and the fr/rr ratio (pad area, swept area, rotor mass, wheel load) could mean higher rear temps.
Collect a dataset over time of brake temps for your car and other cars in the household to sense check what is happening.
Yes, that's not unusual. The rear brakes in modern cars do more than they used to. Old cars used to have a fixed brake bias between front and rear, but these cars have what's known as electronic brakeforce distribution (EBD). The brakeforce going to each wheel is constantly regulated based on multiple factors. Also, as mentioned above, the rear brakes actually engage first nowadays as that reduces the typical nose dive. It settles the chassis before the front brakes engage and increases comfort for the occupants. As said, this mostly happens during moderate braking and when using DISTRONIC. In addition, many performance cars now have torque vectoring, so during cornering the rear brakes are used to slow down the inner wheel and help rotating the car. In AMGs this is in addition to the electronic locking differential, although now that I'm thinking about it, I think the W222 S63 didn't get the locking diff, so the rear brakes have to work that much harder to achieve a similar result. The two systems together are constantly regulating how much torque is going to each driven rear wheel. This is also why the rear brakes often wear out before the front brakes.
Last edited by superswiss; Apr 2, 2025 at 04:31 PM.
At any rate you have one or more warped rotors. Time for some new brake parts.
Rear brake rotors and pads are less than a year old, Zimmerman rotors and Powerstop pads, less than 7K miles, probably only 5K miles on them.
Maybe I'm missing something, but in the past when rotors were warped they didn't "get better" meaning they always felt warped. This has only happened 3-4 times in the last 6 months. What ablut all the other times, even when braking hard or moderately.
Last edited by carlosinseattle; Apr 2, 2025 at 04:59 PM.
Yes, that's not unusual. The rear brakes in modern cars do more than they used to. Old cars used to have a fixed brake bias between front and rear, but these cars have what's known as electronic brakeforce distribution (EBD). The brakeforce going to each wheel is constantly regulated based on multiple factors. Also, as mentioned above, the rear brakes actually engage first nowadays as that reduces the typical nose dive. It settles the chassis before the front brakes engage and increases comfort for the occupants. As said, this mostly happens during moderate braking and when using DISTRONIC. In addition, many performance cars now have torque vectoring, so during cornering the rear brakes are used to slow down the inner wheel and help rotating the car. In AMGs this is in addition to the electronic locking differential, although now that I'm thinking about it, I think the W222 S63 didn't get the locking diff, so the rear brakes have to work that much harder to achieve a similar result. The two systems together are constantly regulating how much torque is going to each driven rear wheel. This is also why the rear brakes often wear out before the front brakes.
Great information especially the electronic brakeforce distribution part.
Warped rotors is actually somewhat of a myth. What's most often diagnosed as warped rotors are actually irregular pad material deposits on the rotors. This can happen when they are hot and you sit on the brakes so the pads imprint, or you suddenly brake hard with cold brakes resulting in uneven heat distribution. The latter can also result in local material expansion potentially causing inconsistent performance. Same as warped rotors, though, once the irregular deposits are there, you would always feel them as a thumb thumb sensation as the pads pass over them until they get scraped off again. Glazing is certainly an option, but again, if the pads are glazed they would consistently not perform well anymore.
For best brake performance, the brakes need to be bedded in properly and re-bedded frequently if you do a lot of daily driving during which the brakes operate in abrasive mode because they are not hot enough and scrape the pad material off the rotors instead of maintaining it. Need to get heat in them regularly. Improperly bedded brakes can have all kinds of issues from noise to inconsistent performance.
Last edited by superswiss; Apr 2, 2025 at 05:49 PM.
The rear pads are half the size of front axle and normally last twice as long ...
Having noticed your rear brakes are working hard under Bosch ESP control:
This is a good time to get them inspected or serviced.
Probably not so much...If this was 25 years ago I might have a shot. Most technicians are taught to replace things. If the computer can't tell them what's wrong, then replace it.
.......................you suddenly brake hard with cold brakes resulting in uneven heat distribution. The latter can also result in local material expansion potentially causing inconsistent performance. Same as warped rotors, though, once the irregular deposits are there, you would always feel them as a thumb thumb sensation as the pads pass over them until they get scraped off again. Glazing is certainly an option, but again, if the pads are glazed they would consistently not perform well anymore.
To your point, it ONLY happens under these circumstances.
I'm pretty sure I bedded the pads properly. I changed the rear pads before I changed the front pads. Is it possible that I caused a problem for the rear pads when I replaced and bedded the fronts a few weeks, maybe 3, later?
Unlikely you can simply try to rebed but with those temps check for a dragging caliper.
Also check the mating surfaces. Hub to disc and disc to wheel, must be completely clean and free of paint or rust.
Unlikely you can simply try to rebed but with those temps check for a dragging caliper.
Also check the mating surfaces. Hub to disc and disc to wheel, must be completely clean and free of paint or rust.
Thanks for the ideas. I just removed the rear passenger side hub a few weeks ago to inspect it, that one seemed to be slightly worse than the driver's side. It looked great, and no binding on the caliper, pins looked fine. But maybe I'll look again since it's relativey easy. The odd part is that it only happens when the car is cold, like the first 10 minutes of driving. I live close to the airport so it was a short trip to drop off the wife prior to this happening. And I distinctly remember the first time it happened was on a cold morning heading to a meeting, it was at the highway exit, and again I was going at least 90 prior to braking for the exit, shudder/vibrations from the rear. Felt just like old school warped rotors when it happened, but car drove fine for months before it happened again.
The rear pads are half the size of front axle and normally last twice as long ...
Having noticed your rear brakes are working hard under Bosch ESP control:
This is a good time to get them inspected or serviced.
That was once upon a time when cars had a fix rear to front brake bias as I explained above. With today's electronic brakeforce distribution that's no longer the case. In many scenarios it engages the rear brakes first and they generally wear out before the front. It's been like that for my cars for the last 10 years or so. Always get less miles out of the rear. Reasons for that as said are things like torque vectoring and engaging the rears first to minimize nose diving and keep the chassis flat during braking.
Originally Posted by carlosinseattle
To your point, it ONLY happens under these circumstances.
I'm pretty sure I bedded the pads properly. I changed the rear pads before I changed the front pads. Is it possible that I caused a problem for the rear pads when I replaced and bedded the fronts a few weeks, maybe 3, later?
You can bed your brakes as often as you want. Another option if this only happens intermittently is debris or dirt that might get caught by the brakes. You definitely wanna make sure that the hubs are clean and the rotors installed properly so they don't have any runout. Runout is when the installed rotor deviates from the zero degree axis due to rust, dirt or something on the hub or improper torquing of the wheel bolts. Runout can be measured, so you may wanna take it to a competent shop that can fully inspect your brakes and measure everything. Dealerships don't do this. They just replace.
Last edited by superswiss; Apr 2, 2025 at 09:00 PM.
Yes, that's not unusual. The rear brakes in modern cars do more than they used to. Old cars used to have a fixed brake bias between front and rear, but these cars have what's known as electronic brakeforce distribution (EBD). The brakeforce going to each wheel is constantly regulated based on multiple factors. Also, as mentioned above, the rear brakes actually engage first nowadays as that reduces the typical nose dive. It settles the chassis before the front brakes engage and increases comfort for the occupants. As said, this mostly happens during moderate braking and when using DISTRONIC. In addition, many performance cars now have torque vectoring, so during cornering the rear brakes are used to slow down the inner wheel and help rotating the car. In AMGs this is in addition to the electronic locking differential, although now that I'm thinking about it, I think the W222 S63 didn't get the locking diff, so the rear brakes have to work that much harder to achieve a similar result. The two systems together are constantly regulating how much torque is going to each driven rear wheel. This is also why the rear brakes often wear out before the front brakes.
“Electronic brake force distribution” happens with 211 and 240 chassis cars that are equipped with what I refer to as ‘Brake by Disney.’ It really was ‘brake by wire.’ The driver applies brakes and the electronics apply brake pressure; made via electric pump to wheels as it sees fit. If it was all that all our cars would be still equipped with it and MB wouldn’t have got to settle a class action lawsuit for lifetime warranty of that junk.
Our 222 cars; same as all cars which use a brake master cylinder + ABS for braking have a baked in percentage of front/rear brake bias based on boresize in the brake master cylinder, sizes of pistons in calipers, rotors and brake pads. When the car sees a need to intervene due to a driver applying brakes such that one or more wheels may lock, is being a savage and induces wheelspin or a skid the electronics will then intervene via releasing and re-applying brakes for ABS or applying brakes at one or more wheels to slow a spinning wheel or to intervene with a skid. Clever system. Much better done than EBC(?) in 211 and 240 cars, and when a brake master fails you will still have two wheels that get brake pressure VS the joke MB did with the 211 when EBC failed for no brakes with a red warning (maybe!) that reads BRAKE. Suffice to say that was not fun.
99% or more of braking happens without any electronic intervention. Pure application of hydraulic pressure made via your foot with help from the brake booster.
Carlos you have warped rear rotors. It happens. Difference in temperature front VS rear is nothing. I’d be concerned if rear brakes were 900 degrees and fronts were 120 but what you measured is a nothing-burger. Not even a Dick’s Deluxe. There is a break-in procedure for rotors that Brembo suggests. It never worked for me with my 221 S-65. I just accepted that being a savage I would (and did) always have warped brakes. CCB does not do that.
To your point, it ONLY happens under these circumstances.
I'm pretty sure I bedded the pads properly. I changed the rear pads before I changed the front pads. Is it possible that I caused a problem for the rear pads when I replaced and bedded the fronts a few weeks, maybe 3, later?
Nope. No fault of yours. Some pull rotors and use a sanding block to remove pad material that collects on rotors and swear by it. That has never worked for me with iron brakes. I would chuck them up in the brake lathe and take off .003-.005” of iron and re-apply a cross-hatch finish. But that didn’t work worth a damn on the 221 car either.
If you are working rear brakes super hard with applying power you may wish to consider installing a Quaife differential.
“Electronic brake force distribution” happens with 211 and 240 chassis cars that are equipped with what I refer to as ‘Brake by Disney.’ It really was ‘brake by wire.’ The driver applies brakes and the electronics apply brake pressure; made via electric pump to wheels as it sees fit. If it was all that all our cars would be still equipped with it and MB wouldn’t have got to settle a class action lawsuit for lifetime warranty of that junk.
Our 222 cars; same as all cars which use a brake master cylinder + ABS for braking have a baked in percentage of front/rear brake bias based on boresize in the brake master cylinder, sizes of pistons in calipers, rotors and brake pads. When the car sees a need to intervene due to a driver applying brakes such that one or more wheels may lock, is being a savage and induces wheelspin or a skid the electronics will then intervene via releasing and re-applying brakes for ABS or applying brakes at one or more wheels to slow a spinning wheel or to intervene with a skid. Clever system. Much better done than EBC(?) in 211 and 240 cars, and when a brake master fails you will still have two wheels that get brake pressure VS the joke MB did with the 211 when EBC failed for no brakes with a red warning (maybe!) that reads BRAKE. Suffice to say that was not fun.
99% or more of braking happens without any electronic intervention. Pure application of hydraulic pressure made via your foot with help from the brake booster.
Carlos you have warped rear rotors. It happens. Difference in temperature front VS rear is nothing. I’d be concerned if rear brakes were 900 degrees and fronts were 120 but what you measured is a nothing-burger. Not even a Dick’s Deluxe. There is a break-in procedure for rotors that Brembo suggests. It never worked for me with my 221 S-65. I just accepted that being a savage I would (and did) always have warped brakes. CCB does not do that.
I'm not sure what you are talking about here, but you are talking about something else. None of this is brake by wire. EBD is an actual thing. It monitors and controls brake pressure to the rear wheels and is separate from ABS, but integrated with it. It's even mentioned in the owner's manual. Here's an example for the GLC. That's just the first one that came up in Google, so don't read too much into the GLC part. It's not pulsing the brakes like ABS. It's reducing brake pressure as necessary.
Brake by wire was in the 211 and 240 chassis. That is why there is none-zero-zip-nadda brake feel in ‘03-06 211. No-one will ever drive a 240 hard enough to gripe about brake feel.
You guys say measure runout. How do you do that on an AWD car??? Or are you suggesting removing the rotors and taking them in to be measured? I will double check for over-tightened lugs on the rear passenger side, that is the one I messed with last time. I bought a new impact gun and it's possible that I overtightened the lugs.
You guys say measure runout. How do you do that on an AWD car??? Or are you suggesting removing the rotors and taking them in to be measured? I will double check for over-tightened lugs on the rear passenger side, that is the one I messed with last time. I bought a new impact gun and it's possible that I overtightened the lugs.
Nope, runout is measured with the rotors mounted and wheels off using a dial indicator mounted to a fixed point.
Another option is that the sliding mechanism is stuck on one or both rear calipers. AMG uses sliding calipers in the rear, so they can move laterally as the rotor experiences thermal expansion and center over the rotor to always make optimal contact with both pads. The front calipers are fixed, so they can't slide. Instead some of us, including myself have replaced the front rotors with full-floating rotors. These types of rotors have springs between the rotor disc and the hat, so the disc can move laterally and center itself naturally between the pads. This improves braking performance, consistency and wear. They also look cool.
When they did the brakes, did they also do the brake hoses in the back? I know some people will say you don't need to do the hoses. Whatever.
I have owned cars from the 60's till now. Replace the brake hoses every so often. Dirt and rubber gets into the hoses and they impede the flow of brake fluid.
I have 100% fixed sticky brake calipers with new hoses. Friend was arguing with me, he wanted to get new calipers as his was locking up and overheating the brakes.
I said, lets do the hoses first, its cheap. It worked. Replace the hoses and flush the brake fluid. Its cheap and easy to do. Hoses are $15 or so each and they do go bad over time.
Last edited by waterzap99; Apr 12, 2025 at 05:24 PM.
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