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Rear braking vibration at speed - not rotors - HELP!
Hopefully someone can shed some light on this frankly exhausting subject that I've been battling with for months.
The car is an 80,000 mile CLS63 (wrong forum but same platform and more E than CLS cars around!). Violent high frequency vibration from the rear wheels only during braking any speed over 80mph. Also, rear wheels feel imbalanced over 90mph and get worse and worse.
Taking a technician out in the car to replicate the fault has been hit and miss. It does it 100 times out of 100 for me. When I drove it up to speed with the tech on board and hit the brakes it was smooth as butter on every run. Typical.
Work so far:
-3 sets of brand new rotors/discs and pads - OE quality, replaced back to back when I assumed it was just bad luck and the new parts were bad
-New Continental tyres
-Wheels balanced up perfectly - checked and re-checked 3 times
Prop bearings checked, no noticeable bush/ball joint wear, gearbox mount seems good.
What am I missing? Any ideas from someone more knowledgable and experienced than I would be greatly appreciated as I'm at my wits end with what is otherwise a spectacular car.
I will just throw this out there:
But are the wheels sitting rush up against the hub?
Could it be your flex disc, the rubber joint between the drive shaft and the rear differential?
Are you wheel properly torqued?
I will just throw this out there:
But are the wheels sitting rush up against the hub?
Could it be your flex disc, the rubber joint between the drive shaft and the rear differential?
Are you wheel properly torqued?
Thanks for that. The hubs have been wire brushed to death and are like new - that crossed my mind too. The wheels are recently refurbished so no oxidisation on the mating surface. Wheels torqued to spec.
WIll double check the flex disc. I assume it'll have fine cracks if it's toast?
Thanks for that. The hubs have been wire brushed to death and are like new - that crossed my mind too. The wheels are recently refurbished so no oxidisation on the mating surface. Wheels torqued to spec.
WIll double check the flex disc. I assume it'll have fine cracks if it's toast?
Yes, yours could have cracks all thru it. And could be falling apart, it could cause vibration issues. There are two flex disc; one between the trans and drive shaft and another between the drive shaft and the rear diff.
I would check both of them, while your down there check your transmission mount. Have you check to ensure that your wheels aren’t bent. I’m just trying to think outside the box to help out. Sometimes we overlook the obvious things. 👍🏽
What does "oe quality" brakes mean? They are either MB parts purchaed from a dealership, or they are not. Refurbished wheels, are these the original oe wheels that came on the car? Have you taken it to a dealership, not an isp?
Last edited by E55Greasemonkey; 05-07-2021 at 06:46 PM.
What does "oe quality" brakes mean? They are either MB parts purchaed from a dealership, or they are not. Refurbished wheels, are these the original oe wheels that came on the car? Have you taken it to a dealership, not an isp?
OE quality means that they meet the same quality standards as the Original Equipment Manufacturer.
You have to understand that Mercedes doesn’t make a lot of their parts, they pay subcontractors to make parts that meet their standards. Take Brembo for example they manufacture brakes for probably 85% of all cars equipped with 4/6/8 piston calipers. This includes all high performance sports cars including AMG.
Refurbished could have multiple definitions. But one could say there OE Wheels that have been refinished or repaired or straightened.
What does "oe quality" brakes mean? They are either MB parts purchaed from a dealership, or they are not. Refurbished wheels, are these the original oe wheels that came on the car? Have you taken it to a dealership, not an isp?
Specifically they are Pagid discs and pads, so no worries about using a budget brand.
The wheels have been refinished and are the original wheels that came with the car from factory. Perhaps swapping the wheels from my SL onto the rear for a quick test drive to see if it cures it might be wise?
I haven't checked the wheels for being out of shape, Would it balance perfectly if it was out of shape? Would I need a road force balancer to show up any wheel damage?
Wheels can still balance out even with a bend in them, sometimes you can feel the bend when driving. Road Force can tell you, but you only need to have the car on a lift and just spin the wheels on the car to get a visual look for yourself.
Any bent wheel is noticeable right away. And wheels can be straightened, but take it to a competent wheel shop. A good price is about $125 +\- per wheel.
Wheels can still balance out even with a bend in them, sometimes you can feel the bend when driving. Road Force can tell you, but you only need to have the car on a lift and just spin the wheels on the car to get a visual look for yourself.
Any bent wheel is noticeable right away. And wheels can be straightened, but take it to a competent wheel shop. A good price is about $125 +\- per wheel.
Update:
Used the best wheel shop in the area and only one rim had a microscopic imperfection. Made no difference to the vibration. I've swapped the wheels with known good rims off an SL600 I have and the vibration is still identical. Stumped.
Just think about this logically, what is it in the drive line that could be causing this vibration issue? engine mounts, transmission mounts, flex disc, rear subframe mounts, rear differential mounts, wheel bearings, rotors, wheels
Think about everything from the engine to the wheels. Honestly, I really can't think of anything else it could be.
If I understand, occurs while braking at high speeds which implies rotor/pad heat and weight shift when braking. Also occurs at higher speeds when not braking so no weight shift involved unless road undulations cause weight shift aggravated by speed. Hypothesis, root cause is there and aggravated when braking but will occur without braking at higher speeds.
-Possibly temperature related? If so, Yuille36 pointer towards the hub bearings would bear investigation. Suggest removing the rear wheel center caps and invest in an IR temperature gun. Check hub temps after normal drive and again after an occurrence of the violent high-speed vibration. Does outside air temperature affect occurrence? e.g. occurs more often in temperatures above 70 degrees F versus below that temperature. (FWIW, I once had a failure mode that would *always* occur below 36 degrees F and never above.)
-Were the rotors and pads identical to the previous set? Or did you try a different combination of rotors and pads? This one I assign a low probability.
-Confirmed that there is nothing inside the tires? (Unlikely but possible. When balancing I have no idea what the equivalent road speed is. Balance at 40 mph but problem shows up at 90 mph?) Just brainstorming here and again a low probability.
-Rear control arms inner and outer bushings? FWIW, the outer bushings on my rear control arms were extremely loose and had some slack in them at only 100,000 miles. I would assign a higher probability.
-Like Yuille36 suggested, I would investigate subframe and differential mounts and would add, check the bolts. Possibly a broken bolt or two in one or the other. This I would assign a higher probability.
Edit: The more I think about it, the more I lean towards something related to the drive shaft. That would imply the transmission tail bushing, the center support bracket and bearing, or the rear pinion bearing. The issue seems to arrive at high rotations of the drive shaft and unloading of the drive shaft. When under acceleration or steady load it is stable, as soon as the load is removed the drive shaft begins vibrating. Something to consider.
If I understand, occurs while braking at high speeds which implies rotor/pad heat and weight shift when braking. Also occurs at higher speeds when not braking so no weight shift involved unless road undulations cause weight shift aggravated by speed. Hypothesis, root cause is there and aggravated when braking but will occur without braking at higher speeds.
-Possibly temperature related? If so, Yuille36 pointer towards the hub bearings would bear investigation. Suggest removing the rear wheel center caps and invest in an IR temperature gun. Check hub temps after normal drive and again after an occurrence of the violent high-speed vibration. Does outside air temperature affect occurrence? e.g. occurs more often in temperatures above 70 degrees F versus below that temperature. (FWIW, I once had a failure mode that would *always* occur below 36 degrees F and never above.)
-Were the rotors and pads identical to the previous set? Or did you try a different combination of rotors and pads? This one I assign a low probability.
-Confirmed that there is nothing inside the tires? (Unlikely but possible. When balancing I have no idea what the equivalent road speed is. Balance at 40 mph but problem shows up at 90 mph?) Just brainstorming here and again a low probability.
-Rear control arms inner and outer bushings? FWIW, the outer bushings on my rear control arms were extremely loose and had some slack in them at only 100,000 miles. I would assign a higher probability.
-Like Yuille36 suggested, I would investigate subframe and differential mounts and would add, check the bolts. Possibly a broken bolt or two in one or the other. This I would assign a higher probability.
Edit: The more I think about it, the more I lean towards something related to the drive shaft. That would imply the transmission tail bushing, the center support bracket and bearing, or the rear pinion bearing. The issue seems to arrive at high rotations of the drive shaft and unloading of the drive shaft. When under acceleration or steady load it is stable, as soon as the load is removed the drive shaft begins vibrating. Something to consider.
Everyone forgets to replace the Emergency Brake Shoes inside the Rotor make sure to adjust tensioner and replace spring hardware if possible...After several trial and errors in past many parts replaced to no avail new e brake shoes and adjustment did the trick both instances different cars same symptoms be sure to brake clean inside center of hub and rotor before reassembly good luck hope this helps
Everyone forgets to replace the Emergency Brake Shoes inside the Rotor make sure to adjust tensioner and replace spring hardware if possible...After several trial and errors in past many parts replaced to no avail new e brake shoes and adjustment did the trick both instances different cars same symptoms be sure to brake clean inside center of hub and rotor before reassembly good luck hope this helps
An excellent suggestion. I could see where the slightest drag could cause heat expansion at higher speeds and thus the interference between drum and shoes.
This one slipped my mind even though I had to replace the brake shoes on my car during rotor replacement. One of the brake shoes had no friction material on it and I have no idea where or when it occurred over the years. Could easily have been with one of the two previous owners but I like to think I would have noticed it if it occurred while I was driving the car.
Also I tried my parking brake on my way home from work. I actually engaged it at like 30 mph just because I felt like it. It seemed like it started engaging immediately rather than go down part way. Does this mean my shoes are also too tight? Is there a way to back off the adjustment?
I had pretty much the exact issue you are having ... The root cause was actually front wheels not in balance and the front wheel bearings needed recalibration. For what ever reason the vibration feels like its coming from the rear. I never felt any vibration from the steering and the vibration felt like is was coming from middle rear of car.
Get all wheels road force balanced and re-calibrate front wheel bearings. I am back to smooth as butter again.
Does this mean my shoes are also too tight? Is there a way to back off the adjustment?
You have remove the rear wheels, then the rear calipers, then the rotors. In the wheel hub, there is a access hole, where you can get at the slack adjuster.
Actually according to WIS, if you have steel wheels, you don't even need to take the wheel off. You just remove 1 lug bolt and do it through the hole. With alloys they say to remove the wheel to prevent damage. But again it appears you do it through any lug bolt hole. Kinda cool. I will check it out later this weekend. Definitely NOT interested in removing the rear calipers if I don't have to.
So I did half of the instructions. I didn't touch the slack adjuster (or even locate it).
But I did jack up and I do think there was some light drag from the shoes which may have also been causing some light vibes at 75+. Pulled the wheels and very clearly you can see the star wheel through the lug bolt holes. It's around 2:30 on the clock on the driver's side and around 9:30 on the passenger side. Very easy to see. In fact you can even see the wheel while you are turning it with the screw driver. Nicely thought out system for adjustments. I don't think I got to the first click on the pedal before the adjustment which sort of confirms it was too tight. Tightened them until they stopped and I couldn't turn the rotor. Backed them off 10 clicks. It doesn't really click so just try to watch the wheel while turning relative to the spring that is supposed to catch it. After that the wheels seem to rotate with no brake shoe noise and the pedal goes down 1 click and seems to be about the 30 lbs of force they specify. I'd call this a success and very easy.
I might mention that adding some Copper Anti Seize Grease to the back side of the Brake Pads are a good solution for any noisy brakes. As for vibration at high speed, I would suspect warped rotors, but you said you are one several new sets since this issue flared up. I had a new set of Zimmerman Rear Rotors from FCP Euro, and sure enough, one of the was making a racket at slow speed against my new brake pads. When I got it back off the ground with the wheel off, I started it up, put it in gear and got my head right above the rotor and could see the rotor was warped slightly. I ordered another from FCP Euro and the one I had back, but still am awaiting a refund!! But at high speed like your talking about is a real head scratcher! BTW, it’s never a good ideas to hit the E-brake while moving! The only thing securing those e-brakes are 2 little spring/lock thingys per side! And sure, everything mentioned could possibly be a cause and I’m just glad to have tackled most things mentioned and then some as I’ve been working on my ride since May 2020! Check out some PICS!
05-07-2021, 12:17 PM
