W204 Hot braking vibration and shuddering (Advice please)

[gibsonk]

I am experiencing a shuddering and Vibration when braking, but seems to be only only when my brakes are hot. And a slight knock on the nearside front.



My first port of call was to replace the control arms, i have done both front upper and lower arms on both sides of the car, this has certainly helped a bit but i am still getting the braking issue and knock when going over speed bumps.



After this i replaced both front discs and pads (brembo) and tried to run them in as best i could without overheating or keeping my foot on the brake when at a junction or lights etc. Initially i didn't notice the issue but i was careful on my brakes for a good 400 miles.



As soon as i felt they had time to bed in once they got hot i experienced the same vibration and juddering.



The best way i can describe is it feels like warped discs but i doubt they are, if braking hard when your almost stopped it feels like the brakes are pulsing on and off there is a distinct change in braking force, this repetition gets slower as the car slows, (its not the ABS firing either).



I also changed my springs about 5 months ago and i am due to swap the dampers out as soon as they arrive.



My drop links have also been done when i did the springs also the front ARB was swapped for one from a 63 all bushings in good condition.



Both front wheel bearings have been done



In summary i have changed the following

• All four springs
• Front upper and lower control arms,both sides
• Front Sway Bar
• Front wheel bearings
• Front Discs & Pads
  
• Drop links both sides

New dampers are incoming with rear wheel bearings





Other than the dampers i am not sure what is left in this equation, any advice would be really good



Thanks in advance

 

[Bellow]

Presumably there are rear (pointing) control arms? It will be those that deal with most of the braking forces, the lower ones especially.

 

[gibsonk]

Presumably there are rear (pointing) control arms? It will be those that deal with most of the braking forces, the lower ones especially.

Indeed, they have been done on both sides

 

[Bellow]

A tricky one for sure!
Are the wheel bearings taper roller - ie, the type that requires tightening only to pre-load (as opposed to ball race types that are tightened to secure)? If so, worth a recheck on the pre-load?
'When hot' may be a clue. To what though I have no idea!

Not sure if this helps or not but.... apparently, the discs are never 100% true and that slight out of true helps in pushing the pads back into the calipers to reduce drag. It can (again apparently) create 'glazing' on the 'high spots' of the disc that repeatedly make contact with the pads. This can lead to an inconsistent disc surface with variable friction and is much much more likely to happen on cars that spend prolonged periods on motorways.

 

[gibsonk]

A tricky one for sure!
Are the wheel bearings taper roller - ie, the type that requires tightening only to pre-load (as opposed to ball race types that are tightened to secure)? If so, worth a recheck on the pre-load?
'When hot' may be a clue. To what though I have no idea!

Not sure if this helps or not but.... apparently, the discs are never 100% true and that slight out of true helps in pushing the pads back into the calipers to reduce drag. It can (again apparently) create 'glazing' on the 'high spots' of the disc that repeatedly make contact with the pads. This can lead to an inconsistent disc surface with variable friction and is much much more likely to happen on cars that spend prolonged periods on motorways.

They are conical taper bearings, I don't have the correct gauge to set the preload so aired on the side of caution and went 1/2 turn after all play was removed.

Interesting comment about the motorway, 90% of my miles are motorway. I had wondered if there is a uneven build up on the rotors thought about taking glass rust removal pad to the surface then bed in again to make sure they are clear.

 

[OneForTheRoad]

Sticky caliper slide pins or piston.??

 

[Bellow]

They are conical taper bearings, I don't have the correct gauge to set the preload so aired on the side of caution and went 1/2 turn after all play was removed.

Worth a quick check that they are neither too tight or slack?

Interesting comment about the motorway, 90% of my miles are motorway. I had wondered if there is a uneven build up on the rotors thought about taking glass rust removal pad to the surface then bed in again to make sure they are clear.

It's something I used to read of years ago - and always attributed to motorway use.
If you cleaned up the disc face such that any high spots were dressed back and got (even brief) respite from the problem, then that would help the diagnosis - yes?

 

[gibsonk]

Worth a quick check that they are neither too tight or slack?



It's something I used to read of years ago - and always attributed to motorway use.
If you cleaned up the disc face such that any high spots were dressed back and got (even brief) respite from the problem, then that would help the diagnosis - yes?

agreed, I will clean up the discs tomorrow, should order a gauge for the bearings really.

Sticky caliper slide pins or piston.??

Pins are good replaced those when I did the discs and pads, I have considered a Calliper service kit. They have done 120k, although feel fine and I did the fluid also when I did the discs and pads.

certainly can’t hurt

 

[Bellow]

agreed, I will clean up the discs tomorrow, should order a gauge for the bearings really.

By 'feel' will be fine.
Let us know if dressing the discs works. If it does point to what is currently suspected, I guess the next thing is a disc and pad combo that may be less prone to this. Maybe someone here with advice - or it's you out stopping every Mercedes on the motorway asking what they use!

 

[gibsonk]

By 'feel' will be fine.
Let us know if dressing the discs works. If it does point to what is currently suspected, I guess the next thing is a disc and pad combo that may be less prone to this. Maybe someone here with advice - or it's you out stopping every Mercedes on the motorway asking what they use!

I have bought Brembo Pads and Discs twice for it now and to be honest am not hugely impressed, i guess they are not the same as the real Brembo brakes i have had previously on a Integra DC5.

I have heard a rumor that Brembo switched supplier for their aftermarket stuff recently and since the quality has suffered (some say) shame i heard this after buying discs and pads.

I guess genuine mercedes is the way to go

Will dress the discs tomorrow and report back

 

[Silver350machine]

Has all the symptoms of a warped disc. New Brembos fitted to my old Audi warped within a short time (who knows they might have been a Chinese knock off) but once replaced with Pagid were faultless for the next 30,000 miles.

 

[Wolfie1]

What you are describing is an abs issue, but dont worry its an easy fix, check your abs rings as 1 may have cracked and this its whats giving you the pulsing pedal when your almost at a stop as the gap between the teeth has changed but is only significant enough to notice when your doing slower braking.
To me it sounds like that is what your describing.

 

[gibsonk]

What you are describing is an abs issue, but dont worry its an easy fix, check your abs rings as 1 may have cracked and this its whats giving you the pulsing pedal when your almost at a stop as the gap between the teeth has changed but is only significant enough to notice when your doing slower braking.
To me it sounds like that is what your describing.

They use a magnetic pulse ring on the back of the Hub, i don't recall these being damaged when i did the wheel bearings, however for the sake of £6 each it will be worth getting a pair

I may be going nuts, but i can only find the impulse ring for the rear hubs and nothing for the front??

Even ASRA isn't showing me much

 

[Wolfie1]

It could be a rear ring any ring will cause the issue, if you have access to a diagnostic tester go into live data and the value will jump on the faulty ring if you cannot see the actual ring

 

[Bellow]

They use a magnetic pulse ring on the back of the Hub, i don't recall these being damaged when i did the wheel bearings, however for the sake of £6 each it will be worth getting a pair

I thought you were confident it wasn't the ABS 'firing'. It isn't easily missed when it happens!

I may be going nuts, but i can only find the impulse ring for the rear hubs and nothing for the front??

Embedded within the bearing on some MBs I think.

 

[gibsonk]

I thought you were confident it wasn't the ABS 'firing'. It isn't easily missed when it happens!



Embedded within the bearing on some MBs I think.

I am pretty confident, it doesn't feel anything like ABS kicking in, but that's not to say its not a weird issue that causes sensation i am getting.

Also i am starting to clutch at straws a little, especially if dressing the discs today doesn't work, i can check the ABS data output and find out pretty quickly

 

[Bellow]

I am pretty confident, it doesn't feel anything like ABS kicking in, but that's not to say its not a weird issue that causes sensation i am getting.

Also i am starting to clutch at straws a little, especially if dressing the discs today doesn't work, i can check the ABS data output and find out pretty quickly

Wheel bearings replaced - and if the reluctor ring is embedded - then there should be a sensor on the upright. Refitted correctly?
Recall ABS start up check only checks for presence of sensor and ABS in operation doesn't illuminate dash lamps - unlike ESP.

When you check the discs, scrutinise the pads for any marking. Any rubbed high spots should be visible and point to contact points on the disc.

 

[gibsonk]

Wheel bearings replaced - and if the reluctor ring is embedded - then there should be a sensor on the upright. Refitted correctly?
Recall ABS start up check only checks for presence of sensor and ABS in operation doesn't illuminate dash lamps - unlike ESP.

When you check the discs, scrutinise the pads for any marking. Any rubbed high spots should be visible and point to contact points on the disc.

The sensor is there on both sides, it doesn't have to come out to change the bearing, its on the rear of the steering knuckle. They must be magnetic impulse rings as there was no reluctor ring on the rear of the Hub, and the ABS sensor looks like a hall sensor

 

[gibsonk]

Wheel bearings replaced - and if the reluctor ring is embedded - then there should be a sensor on the upright. Refitted correctly?
Recall ABS start up check only checks for presence of sensor and ABS in operation doesn't illuminate dash lamps - unlike ESP.

When you check the discs, scrutinise the pads for any marking. Any rubbed high spots should be visible and point to contact points on the disc.

A quick update here.

Looks like this is Disc and Pad related, i pulled them off both sides this morning to dress them.

When looking at the rotor they looked to have blue heat marks on them which i presumed came form yesterday when i gave them a bit of abuse after replacing my control arms.

However, it turns out this is some kind of residue buildup on the discs, when i skimmed them with the glass fibre pad it almost smudged, certainly not blued metal.

I cleaned up both rotors and noticed i have pitting already, they are pretty much brand new only maybe a month or so old. Surely this is not correct i have never seen a rotor pitted that quickly and its on both sides.

I also cleaned off the pad surface and dressed it to make sure everything was clean and good to go, all parts wiped down with solvent, pads, sliders caliper carriers greased.

Behold my vibration issue has gone, I have not given them much grif at the moment as they will require bedding in again, but under moderate braking you could just feel it previously, now there is nothing.

I can see said residue seems to be building up already on the nearside rotor, this was the worst side before i dressed them.

Think it may be time to go have a chat to the motor factors about these discs and pads.

 

[Bellow]

Result!
Yes, a chat with supplier is in order - not least as you may not be the only one who has suffered this. Hint: ask if you are the only one!

Slightly aside - I'm not sold on the idea of bedding in brakes, or not beyond being kindish to them for 10 minutes. My way of driving will see the brakes seldom used but when they are they are used with some force. This works for me! (When I used to return my father's car after borrowing it, he'd often remark how much better the brakes worked - after I'd busted his glazing that was).
Anyone have a view on bedding brakes - good or bad?