190e brake hum & pulse?

[Bob 2316]

hi i am experiancing a strange hum after pressing the break pedal followed by a severe and unusual pulse feed backing through the pedal. this happened yesterday after mending my electric window . decided to take my mate for a spin in it. we set off slowly along a road turned up a hill and slowly stopped at the crest (T junction) slowly edged forward releasing my foot from the brake (this is an auto car) and then gentley pressed the brake again where upon a quite loud hum was heard followed by a severe pulsating feeling for a second or two through the pedal. only seems to happen when the car is cold and the rest of the time the brakes when applied are good. break fluid is new. pads are ok for a couple of thousand more miles. ABS warning light did not come on when this happened.

190e 2.3 16 1986 auto

would be grateful for any feedback about this.

Bob

 

[joe bloggs]

Sounds like the ABS working, was the road slippy, did it just happen once??

 

[Bob 2316]

Hi Joe thanx for your reply. its happened a couple of times usually when the car is cold and always when the pedal is pressed very slowly/gently like as described ( edging forward slowly to get on to a main road or in stop start traffic cue.) is it happening because im not giving the pedal enough pressure so then the ABS is `not sure` what to do? if that makes any sense? the rest of the time the brakes are fine aspically at speed no pull or anything.

thanx for yr advice on the window

Rgds

Bob

Ps the road yesterday was dry and not slippery.

 

[joe bloggs]

Could be a poor signal from one of the wheel sensors, take them out (if not jammed) & clean the swarf off them (magnetic) . Possibly a bad connection at the cables to the sensors as the w/lamp is not showing. What can happen is that when braking the front of car dips slightly and moves the cables with bad connection (very common), as you are braking at the time the ABS does'nt pick this up as a fault, but it thinks one wheel has locked up so applies the ABS, if the bad connection was present when not braking then the w/lamp would come on.
Bestway to check leads is with ohmeter connected wiggle/stretch leads while carefully watching meter (plugs are accesible under bonnet on inner wings , it is the sockets you want to test)

 

[white190]

Hi bob
As Joe said you might want to remove the ABS sensor on each front hub (they're only held in by two female hex bolts).
If this improves matters you may want to remove the reluctor ring behind the front hub and remove any loose rust from it......this is more involved.
But sometimes it is sufficent to use a air gun to blow through the hole that the ABS sensor was fitted in whilst turning the wheel to remove any flaking rust from the reluctor ring, then with the wheel still turning spray a light oil into the hole....this will help revent the reluctor ring rusting again and help stop the ABS sensor getting caked in rust again.......

as I'm sure you know be carefull not tot get any oil/grease on the brakes.

 

[Bob 2316]

thanx guys for you help/suggestions.
i have purchased a Haynes manual 190 1983- 1993. i know my particular model isnt featured but it is a help. i am currently reading up on the ABS system, they mention that those bolts if removed should not be replaced and only new bolts re inserted!

can anyone tell me if my car is fitted with ASR (traction control) i understand my car has a Limited Slip Differential, but thats not the same thing is it?

best rgds

Bob

 

[Orlando 300E]

Hello Bob,

The reason why Haynes tell you to use new bolts, is to cover their arse.
If they did not, and you had an accident because of an old bolt being reused, they could be held liable.
In the end, it comes down to you & the condition of the bolts when you remove them. If you think they look in good condition & are happy to re-use them, do so.
If they look bad or you are unsure -pay a visit to your local money depository (sorry, I meant dealer) and get some new ones.

A limited slip diff (LSD) is different from ASR traction control. an LSD reduces wheel spin by (clue in the name) limiting the slippage between both driven wheels. The end result is reduced wheel spin, more traction & hello horizon!

Traction control systems work by sensing a wheel loosing traction -most commonly by using the ABS sensors. As an example, say a driven wheel starts spinning mid corner for instance, what happens next is the car cuts the ignition briefly till the wheel stops spinning and finds grip. Without Traction control you would loose grip, go wide, spin, visit the green stuff Etc.

Hope that makes sense, all above from memory, I am sure someone will correct me if I got it wrong!
Hope you sort your brakes
Orlando

 

[Bob 2316]

Hi Oralando
thanx for your reply, i think where my confusion lay/lies is when trolling through the Mercedes cosworths in auot trader web site for the past 9 months many cars were said to have ASR/ traction control. others advertised stated LSD/Traction control? i guess im gonna have to get under the car to see if there is an additional rear wheel sensor fitted to the final drive unit as mentioned in the haynes manual. it seems to imply that ASR was an option on most 190s and im wondering if it was standard or optional on a 2.3 16?

anyway ill have a go at the sensors and the bolts as the pads will need changing soon. The braking is fine apart from this small problem. im not so worried about driving it now, but it did wory me as it would have scared my partner if she had been driving it when it happened. At least no one came back with the reply` Dont drive the car!`

best rgds

bob

 

[white190]

I drove mine for a couple of days till I got time to clean the sensors and reluctor rings......It's been fine since....So I guess it did it no harm.