w124 coupe, 'sort of jerky feedback of late' upon braking, vacumn issue?

[BillyW124]

hello guys,

i thought id raise this with you.

Recently ive been getting a jerky feel to my braking when slowing down (but a smooth refined jerk )..if that makes sense.

Its just began to happen in the last couple of weeks.

Could it be my discs are warped causing this jerk, or could it be an engine thing?

Discs and pads look ok, but will need changing in the next service in November. Brakes have been bled in the last service and was fine then.

Are the brakes connected to some sort of hydaulic/vacumn servo system that would cause this? I say this as when im rolling say in a traffic jam with your foot slightly depressed i also get this slight jerky feeling. I do keep an eye on the rev counter when i brake and it doesnt drop (like its going to cut out) but it does bounce below the norm for a spilt second and returns back to normal.

When i let go of the brake and let it roll the car seems to feel like it BREATHES better again like it should, Put my foot back on it and the jerkyness comes back every so slightly.

its not bad at all not just how it was...

any ideas?

 

[BillyW124]

no one?

 

[Sp!ke]

Does it still do it if you slip the gearbox in neutral?

 

[BillyW124]

Does it still do it if you slip the gearbox in neutral?

cheers spike i will try that .

what would that mean if it didnt do that when it was in neutral?

 

[Sp!ke]

It means it is related to your transmission rather than brakes.

 

[BillyW124]

Oh great lets hope it does it then!

gear box gear changes up and down are smooth however and does have poke when it gets booted..

 

[Sp!ke]

I'm not saying it is a transmission issue, rather ruling out the braking system.

 

[BillyW124]

yea cool, ill report back

 

[BlackC55]

It does sound very much like warped discs.

 

[Stratman]

Give the brakes an Italian tune up.

Find somewhere safe and drive at 60 or 70, then do a hard stop. Repeat.

Over time the discs can get coated with various contaminants. If you're normally fairly gentle on the brakes this can build up and cause the symptoms you describe.

 

[BillyW124]

olly..lets hope so,

Stratman..yes im gentle! i brake softly,

funny you should say that, ive had these brakes and pads on for around two years, and have been subject of soft braking, next service will be 3. Monday to Friday the car is sitting on my drive, when i reverse off it, i hear a grinding sound on a saturday morning. The sound you would hear as if they were bone dry, basically signalling that yes you have parked me up too long.

i did a hard stop the other day and was very surprised how well it did stop. I usually soft brake or pulse at the pedal i.e. say comming off a motorway junction, so by the time i near the stoped car in front i roll up to it.

i'll try these things and report back..

 

[GP801]

Like you I am very gentle on the brakes. Had similar on our s124 and a few hard stops sorted it.

 

[BillyW124]

..so you reckon we should rule out any vacumn type issue?

 

[trapperjohn]

..so you reckon we should rule out any vacumn type issue?

Go out give it some wellie, slap the anchors on (check ye ole mirror first) a few times and come back to us.

Hard to judge anything from the written word (says he) when you have not driven the vehicle.

On my 300D Saloon (as per avatar) the diff has always been a "wrong un"
Recently Ian at 124 Works had a spare so that was fitted and the ABS was re connected. Previous owner (scallywag) had changed the diff and chopped the ABS wire (took the bulb out on the dash too) So ABS all connected up and now. Guess what? At less than walking pace as I apply the breaks I can feel a gentle pulsing back through the pedal. Its fine once I get up to more than walking pace (about half an hour in my old girl)
So you are not alone. As my old Dad used to say "LID it" Let It Develope. If the Italian Tune up, breaks wise does not work.

Good Luck with it.

 

[BillyW124]

Go out give it some wellie, slap the anchors on (check ye ole mirror first) a few times and come back to us.

Hard to judge anything from the written word (says he) when you have not driven the vehicle.

On my 300D Saloon (as per avatar) the diff has always been a "wrong un"
Recently Ian at 124 Works had a spare so that was fitted and the ABS was re connected. Previous owner (scallywag) had changed the diff and chopped the ABS wire (took the bulb out on the dash too) So ABS all connected up and now. Guess what? At less than walking pace as I apply the breaks I can feel a gentle pulsing back through the pedal. Its fine once I get up to more than walking pace (about half an hour in my old girl)
So you are not alone. As my old Dad used to say "LID it" Let It Develope. If the Italian Tune up, breaks wise does not work.

Good Luck with it.

Hi John, hows the silver 124, fixed yet?

that sounds familiar, once the car is in full motion ie not at low speed it doesnt happen, its when as you say like walking pace i get this jerk or as you put it a pulse back, but slight.

p.s. ive recieved the keys and the bits in the postage last week so thanks, when you see Ian next please tell him i said thank you..i'll drop him a Pm too. i can get my IR lock retrofit underway!

 

[trapperjohn]

Hi John, hows the silver 124, fixed yet?

that sounds familiar, once the car is in full motion ie not at low speed it doesnt happen, its when as you say like walking pace i get this jerk or as you put it a pulse back, but slight.

p.s. ive recieved the keys and the bits in the postage last week so thanks, when you see Ian next please tell him i said thank you..i'll drop him a Pm too. i can get my IR lock retrofit underway!

Will pass on the news to Ian.

Silver one not sorted yet. Going to be a mamouth task through a mares nest of wiring. But as Ian says it is not going to die.

I have driven at least two other 124s that have this odd pulsing thing through the break pedal at walking pace or less. I tend to think its a little foilble of the 124.

Other may prove me wrong though.

 

[BillyW124]

good luck with that one John!

so i took the girl out for a spin, couldn't manage to do the italian job on the dual carriage way, but i was slipping the box into neutral foot of the gas and then braking as i would nearing traffic or the lights....

it was still happening. so i guess i can rule out the gear box or is it.....?

somthing interesting, sometimes when the car is about to come to a full stop the rev counter as mentioned in my early post dips for a split second then goes back to the norm. when i was braking to a full stop with the box in neutral it was smooth as a baby's bum. No dip in rev counter solid as you like.

my rev counter when idle is always bang on point and doesn't bounce about or start hunting up and down, just at the point of braking to a stop it would skip a beat a split second then it will be fine. Not as bad like its going to cut out but i know its not supposed to do that.

the only other way i could explain this dip that comes close (others may experience this) is like a drop of electrical power......when the car is idle hit all four of your power window switches and then see the needle drop and the lights go dim for a split second....

thats another thing that happens on my car. The battery is near enough a year old... alternator issue?

These issues aren't major but these little niggles get on my T$%s. i like it to be perfect! I know these cars are getting on now and you cant expect it to be 100%.

..the thing is you can make it 100% and 100% i shall! there will be a strongbow waiting for me at the end of the day!!

 

[BillyW124]

 

[Sp!ke]

If it still does it in neutral then it is nothng to do with engine or transmission or vacuum leaks.

It is a simple break problem - probably slightly warped disks. If its disturbing you you can measure the runout with a dial guage to confirm/establish how bad it is.