knocking/tugging from steering at low speed

[dan f]

Hi.
I have a 2001 SLK 200K. Just recently, as you turn the steering (typically at low speed whilst parking) it will make a knocking/clonking sort of noise that you can feel through the steering wheel at the same time and it feels like you are rolling over large stones.

Once you have finished the low speed almost full lock manouver, then it doesn't happen again whilst normally driving, or indeed once you get to you destination and try to replicate the problem.

Seems only to do this when the car is cold, and in the weather recently, that has been very cold.

Car has 18" rims with 225/40-18 tyres, and has not done this before it started getting colder (had the car since May and it hasn't done it before last week). Wheels do not rub and all wheel bolts are tight.

Anyone any ideas before I ring the stealer about it?

Cheers,
Dan.

 

[clive williams]

dan,

Could this be a sticking pressure relief valve in the power steering knocking? Its easy to get a very high pressure in the system when cold and on full lock. When warm the system is better lubricated and less viscous. Alternatively, there's no icing on the joints etc? causing resistance when cold.

Clive

500E
E320CDIT210

 

[dan f]

Hi.

Would a sticking valve give a sympathetic sensation down the steering column to the wheel? When the noise occurs, it is also like something is tugging at the steering wheel as well.

I will check for icing, but could the steering linkage be worn or loose?

Cheers,
Dan.

 

[clive williams]

Dan,

The answer to both parts is yes.

If there is a sticking/releasing on the valve then the felt sensation will be like tugging at the wheel. Even on a system that is working perfectly well there is a sensation like a gentle pull at full lock as the system is operating at its max. pressure. Pusle that with a sticky valve and you ought to feel the same result you've got.

If the steering linkage is worn and its icing then there will be knock as the system takes up the slack.

Clive

500E
E320CDIT210

 

[dan f]

Thanks for the info Clive.

I will check it out at the weekend when it is light.

Regards,
Dan.

 

[television]

I think that the speed sensitive valve is sticking You can check with service codes.
C1014 PML solinoid valve
C1501 PML solinoid valve line break or short circuit
C16EF PML valve inspection.

Malcolm

 

[dan f]

Cheers for that. I will see what I can find.

It did it very badly first thing this morning in -3 degrees but disappeared when the car warmed up a bit. Feels a bit like the tyre is going to come off the rim....

Regards,
Dan.

 

[clive williams]

Dan,

I know this may sound stupid but I was thinking about the correlation with cold weather (sad sod ain't I). I once had water in the tubeless tyre on one of my cars - no idea how it got there but it made the wheel almost impossible to remain in balance and the inflation was always changing. But if you have the same then I suppose it could freeze at one point inside and give the same symtoms. In a very short distance it would have warmed up and 'cured' itself.
I've read that bit of advice again and it sounds just as stupid second time around but possible.

Clive

500E
E320CDIT210

 

[jberks]

Another possibility is the serpentine(?) belt. I had a similar problem many years ago, admittedly on an '84 280E but when I went over puddles, the belt got wet, slipped and the symptom was that I lost the power steering. It would come in fits and starts so the wheel jerked and twitched as the power came and went. Lasted a few seconds until it gripped again but given the slow speed of the engine, the temperature issue etc I thought I'd mention it.

 

[dan f]

Thanks for all your replies.

Funnily enough the water inside the tyres thought had crossed my mind as well, as I have heard of funnier things.

Cheers,
Dan.

 

[dan f]

Hi All.
In case it is of interest to anyone, the problem I was describing was simply due to an unusually low level on the power steering fluid!
Once this had been replaced the steering is now lovely and smooth again.
No leaks are evident, so one can only surmise as to where the fluid went.
Cheers,
Dan.