S320 cdi brakes slamming on

[Mark worsley]

Help guys. Im encountering a dangerous problem when braking in my 2004 s320 cdi. Recently had a new wheel bearing and a front right wheel sensor replaced as the abs/esp/bas was flashing on the dash. Had these done and all great till a couple of weeks ago when I was braking at about 30mph. I gently touched the brakes but instead of slowing as normal the car slammed on nearly putting me through the windscreen and nearly being hit by the car following me. A couple of seconds after it happens the seatbelts retract with a loud whirring noise causing the pasdenger bet to jam tightly requiring heavy tugging to release it. This has happened a couple more times since. Any help really appreciated guys

 

[Wighty]

Hi Mark , can't help with most of it , but the seat belt slamming on is because the car has expected to be involved in an accident . best get to an Indy or Main dealer to get the Star computer codes read . What area do you live in so members can recommend a good Indy nearby

 

[Botus]

as Wighty says, somehow you have a std safety feature cutting in when it shouldn't

it could be a simple as faulty a switch on the pedals... the system is activated when it notices the speed you go from throttle to brakes exceeds a certain level... i.e. u did it quickly coz you decided you want to stop - then it "helps out by giving full braking regardless how much force you are applying"

didn't know you had it on the w220 but the seatbelt tensioning is linked "pre safe brake" in the hand book

 

[John Laidlaw]

Sounds like collision prevention assist , but I didn’t know that was available in 2004 cars?

 

[Mark worsley]

as Wighty says, somehow you have a std safety feature cutting in when it shouldn't

it could be a simple as faulty a switch on the pedals... the system is activated when it notices the speed you go from throttle to brakes exceeds a certain level... i.e. u did it quickly coz you decided you want to stop - then it "hel

 

[Mark worsley]

Hi guys and thanks for the advice. It' the s320 I have though

 

[John Laidlaw]

Hi guys and thanks for the advice. It' the s320 I have though

W220 is the internal Mercedes reference for your model of S Class Mark

 

[Mark worsley]

Oh god Sorry, had a blonde moment as out on an Xmas do lol. Just thought as well, I've noticed the brake pedal also feels softer at times as well as if not up to pressure

 

[Wighty]

Oh god Sorry, had a blonde moment as out on an Xmas do lol. Just thought as well, I've noticed the brake pedal also feels softer at times as well as if not up to pressure

Sounds like the Indy (when you find one ) will have even more work

 

[LostKiwi]

Ah.... Brake assist is detecting the rate at which the brake pedal is going down and thinking 'You're braking for an emergency so I'll help and put the brakes on really hard for you'.
I had a similar issue on my Smart (uses the same system) where the rear brakes were seriously out of adjustment (not the problem you have) and as a result initial pedal travel was quite fast meaning unless you were careful the Brake assist would kick in. I suspect you find the reason for the soft pedal you'll fix the other issue.

 

[Mark worsley]

The soft pedal doesnt happen all the time, only when on start off etc and seems to build up in a few seconds. Sorry to sound thick

 

[alexanderfoti]

Pre safe is the system thats kicking in.

I suspect you have an issue with the BAS travel sensor, but would reccomend a mechanic to look over the lot as its not something common.

 

[om613]

Is there a module or 5 for BAS?

Probably a STAR sesh by a good indy would tell you what's gone wrong.

 

[om613]

The soft pedal doesnt happen all the time, only when on start off etc and seems to build up in a few seconds. Sorry to sound thick

Another bleed might be worth doing. It was on mine, residual air was there.

Soft pedal could be causal: one hits the pedal faster, then BAS happens?

 

[Botus]

check wheel bearing adjustment.... too much slop will mean pads need to move more... (giving longer pedal travel)

 

[Mark worsley]

Guys, thanks for all your help. Problem resolved, it was the wheel bearing that had destroyed itself. My mechanics took wheel off and when he flicked the bearing cover off out dropped a the bearings etc. Refund issued as obviously faulty and a higher quality one fitted in its place. Same old story, use decent parts in the first place

 

[Mark worsley]

Next issue. Can anyone tell me if headlight adjusters are available separately, or does anyone refurbish the lights as mine won't adjust at all. The dip beam is just pointing at the floor making it dangerous in low light

 

[ernieh]

I

Next issue. Can anyone tell me if headlight adjusters are available separately, or does anyone refurbish the lights as mine won't adjust at all. The dip beam is just pointing at the floor making it dangerous in low light

If yours has xenon lights, it might be the automatic levelling system that has become disconnected or corroded. I think there is a link under one of the wheel arches that adjusts both lamps.

Ernie

 

[Naraic]

Are your lights self levelling? If they are then it is likely one of the sensors on the front or back axle is broken causing the lights to point fully down (or fully up).

 

[Mark worsley]

Not self levelling no as no switch inside car. My mechanics tried adjusting the screws but they just turn and do nothing