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Strange one this. I've looked on all sorts of MB forums and not found a similar issue.
2005 SLK350. Steering perfect most of the time, both moving and parking. But occasionally at parking speeds it will go hard. It will turn with a real heft but no assistance yet when you force the wheel it suddenly goes free, just like overcoming an obstruction.


I suspected slipping belt or low fluid but belts are recent, can't hear any slippage or untoward noise. Fluid is correct level so ruling that out.


Also suspected low pump pressure at tickover so tried putting it in park and revving but no improvement so thinking unlikely to be pump.


I gather some models had a speed sensitive solenoid. Do all 350s have this? I have carsoft but away right now so haven't tried it. Would carsoft detect a fault with the sensor?


I guess it might just be a case of replacing bits until I find the fault (I do everything myself) Used racks and pumps are not that expensive but just trying to narrow down which it's likely to be. I guess it has to be one of the three?


Are all 350 racks the same or did they vary a lot?



All advice appreciated.


Thanks
Dave
 

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@frogfoot have you played with yours? :D
:grin:

Not had a issue with the power steering nor heard about it on a slk.....I know it is a issue on merc sprinters and the cure is a new rack as I have changed a fair few due to steering going very heavy in full lock.
As for slk not sure , sorry
 

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Strange one this. I've looked on all sorts of MB forums and not found a similar issue.
2005 SLK350. Steering perfect most of the time, both moving and parking. But occasionally at parking speeds it will go hard. It will turn with a real heft but no assistance yet when you force the wheel it suddenly goes free, just like overcoming an obstruction.


I suspected slipping belt or low fluid but belts are recent, can't hear any slippage or untoward noise. Fluid is correct level so ruling that out.


Also suspected low pump pressure at tickover so tried putting it in park and revving but no improvement so thinking unlikely to be pump.


I gather some models had a speed sensitive solenoid. Do all 350s have this? I have carsoft but away right now so haven't tried it. Would carsoft detect a fault with the sensor?


I guess it might just be a case of replacing bits until I find the fault (I do everything myself) Used racks and pumps are not that expensive but just trying to narrow down which it's likely to be. I guess it has to be one of the three?


Are all 350 racks the same or did they vary a lot?



All advice appreciated.


Thanks
Dave

Not all 350's (or any model btw) have SPS. Check your datacard for option 213.
The electronics that control the SPS solenoid are integrated in the ESP/BAS control unit.
In other posts you mention problems with ESP/BAS, ESP and/or BAS light coming on intermittently, so this that could be related to this problem.
Afaik racks for SPS and non-SPS are different and not interchangable.
 

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Discussion Starter #5
Thanks Pete


Actually the previous ABS/BAS light posts were for my 320, solved by replacing the sensor by the gearstick. No warning light issues on the 350. Looks like I need to find the VIN number and get the datacard.
 

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Discussion Starter #6
Thanks Avel and Frogfoot. Imagine Merc racks are pretty similar. The SPS system if fitted is probably the main difference. I can see how a rack could go hard consistently at full lock. Just seems more of a power assistance issue than the actual rack sticking as most of the time it's fine. Happened twice today and I parked in quite a few places with no issues. Turn the wheel really hard against the resistance around the straight ahead and it breaks free. Fine when I'm driving as I'm strong enough to overcome it, not so good if my wife drives it :)
 

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There were two variations on the speed sensitive steering, one had the actuator on the pump, the other on the rack. A scan would be a good start.
 

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Discussion Starter #8
Right, I've checked the datacard. No option 213 and no other steering related options. So am I right in assuming I don't have the speed sensitive steering? So that means it has to be a mechanical/hydraulical rather than electrical problem? Therefore scan won't reveal anything? Or are there other electrical sensors that could be involved? Thanks again all.
 

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thinking outside the box......could it have a badly worn ball joint , strut top bearing starting to seize up , broken front coil spring .
any of these could also cause stiff steering at a certain position.
worth a look b4 diving into pumps and racks

just a thought
 

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thinking outside the box......could it have a badly worn ball joint , strut top bearing starting to seize up , broken front coil spring .
any of these could also cause stiff steering at a certain position.
worth a look b4 diving into pumps and racks

just a thought

I Agree - an in-the-air inspection is in order here.



It should be easy to confirm there's no electrical solenoid (no electrical connectors) present on steering pump or rack.
 

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Discussion Starter #11
thinking outside the box......could it have a badly worn ball joint , strut top bearing starting to seize up , broken front coil spring .
any of these could also cause stiff steering at a certain position.
worth a look b4 diving into pumps and racks

just a thought

Thanks Frogfoot. Not impossible. However it passed MOT test and also, when the steering is hard it's also smooth, exactly as you'd expect with power steering failure so thinking unlikely.
 

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Discussion Starter #12
Just scanned it with my icarsoft. Getting 9352 steering angle sensor speed too high, 9353 steering angle sensor has overflow and voltage at terminal 30 too low. Actual value is 12.2 volts (also noticed voltage to electronic ignition too low)



Not sure though if steering angle sensor has any input to power steering? Is this not more related to esp/abs system?

Dave
 

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Discussion Starter #13
Also just noticed that with ignition on/engine off I don't have BAS/ESP light showing. Only have SRS and ABS lights plus brake shoe symbol and (!) in triangle. Should I have BAS/ESP lighting up too? Suspecting warning light disconnected.
Dave
 

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Discussion Starter #14
I haven't had a chance to do anything about this yet. I'm now thinking about replacing the steering column lower knuckle or UJ. I've ordered the used part (£15 on ebay) and just wondering how easy it will be to swap. Has anybody done this?


Further to the symptoms previously mentioned I have found that when it goes hard you can either fight it round until it frees or if you just back off slightly the other way then push again it instantly frees up. It could feasably be the knuckle joint. I can't see how the rack could behave in this way.


If the knuckle is really tricky to change without removing the rack then maybe it's worth swapping the rack at the same time. Recon ones are about £220 and used from £50 so not too costly and it looks easy to access.


Any thoughts?.
 

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Steering perfect most of the time, both moving and parking. But occasionally at parking speeds it will go hard. It will turn with a real heft but no assistance yet when you force the wheel it suddenly goes free, just like overcoming an obstruction.


I suspected slipping belt or low fluid but belts are recent, can't hear any slippage or untoward noise. Fluid is correct level so ruling that out.


Also suspected low pump pressure at tickover so tried putting it in park and revving but no improvement so thinking unlikely to be pump.


All advice appreciated.


Thanks
Dave
My 55 had similar symptoms before losing the power steering altogether. Turned out to be the pump had failed. Mechanic suspected that a damaged pulley had set up a vibration that over time caused the bearing to fail. Once it had failed, only a very faint ticking noise could be heard coming from the pump when the engine was idling so it wasn't obvious it was the problem.
 

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Discussion Starter #16
Finally solved it. It wasn't getting any worse but needed fixing. Looking at replacing bits, the rack seemed the simplest and cheapest and also I had a hunch this was the problem. £30 bought a used rack delivered from an e bay breaker. Came from a w203 C class. They are identical hence why so cheap. I fitted it today and now have perfect steering.


For anybody considering this it's a pretty easy job. I did it on ramps.



I did the worst bit last week, getting the diagonal braces off. Mercedes in their wisdom used Torx bolts. I managed the front four by soaking with penetrating oil, heating with blowlamp , tapping with hammer etc. The ones into the sills were another matter, siezed solid. Resorted to angle grinder and drilled out. Will need to use some sort of expanding bind bolt here on reassembly. My brace bars were both rusted right through so some good used ones from ebay will be going on later. £40 for the pair.


Now the rack: Locked steering wheel central. I left the track rod ends connected at the wheels, just undid the tracking adjusters until they popped out. , the wheels just turned out a few degrees on the ramps. Getting the two mounting bolts out was easy, would have been much easier if they were the other way up with nuts at bottom. I left the lower pinch bolt in place and reached up by the exhaust to the upper bolt under the heat shield (captive nut) pulled the bolt out and the column came free (the way the loose column waggles around in the bulkhead is quite disconcerting). I left all hoses connected, just undid the torx bolt holding the metal pipes to the rack. Do this last as it helps to pull the rack out to get to this. Should have put new O rings on but didn't have any. Rack lifted out. New one slotted in and reversal of disassembly.


Now the crunch. Filled with fluid (CHF Green, less than 1 litre needed). Started up, rolled off ramps and turned from lock to lock to bleed. There was a horrendous screeching sound as I moved the wheel. Thought this might clear as fluid circulated so quickly went from lock to lock but by this time getting a burning smell too so shut down. Rather worrying! Topped up fluid and tried again. This time perfect! Test drive revealed much lighter, smoother steering and the problem has gone.


The screeching? Can only conclude perhaps the lock to lock needs to be done with engine off first? If doing again I would loosen the pipes off and let the fluid run through before starting. This would have given a better flush too. The burning was the belt slipping I think.
 

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Did your rack have the electrical connection for the proportioning valve? Or was it just hydraulic and mechanical connections?
 

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Discussion Starter #18
Did your rack have the electrical connection for the proportioning valve? Or was it just hydraulic and mechanical connections?
No electrics on mine, just two hydraulic pipes. The ones with electrics may also have a w203 C class equivalent rack.
 
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