W115: Clutch/ Master/ Slave Cylinder Rebuild Needed?

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Screwdriver

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Oct 20, 2008
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420
Greetings!

As I drove home today, my clutch pedal didn't rise up to where it normally would be. The sinking feeling soon subsided and the ol' girl got me home safely (God bless Classic Mercs!).

That said, there is one other symptom: A rattling noise at idle. No, it's not the diesel idle clatter. It's a slightly louder, harsher sounding rattle that only occurs at idle. A light touch of the accelerator pedal or engaging the clutch pedal fully and the noise disappears, only to reappear when all feet are off all pedals again.

Perhaps its the thrust bearing?

At this stage, given the likely need to replace the master and slave cylinder, would it be prudent to replace the clutch (doesn't slip - car has plenty of pep) and bearing as well? If so, would the MB dealer be the best place to source the replacement components? Listing the time worn parts you believe are prudent to replace with the transmission dropped out of the car (with numbers if you have them handy) would be incredibly helpful and I would owe you one!

Cheers!
_________
 
It sounds hydraulic, all external to the 'box.
There is a MB measuring tool that's applied to the clutch slave rod to indicate the extent of clutch wear.
I have a copy tool that I've yet to use. The dimensions required are in most manuals.

If you're paying for a 'box removal and reinstatement, it would make sense to replace the lot: plate, disc, release baring and fork.
And so it would make sense to use OEM parts from MB.
 
Sound advice. Before I touch the gearbox, my plan was to start with replacing hydraulic components like the Master + Slave Cylinder and the hose that connects them to start with. Am I missing anything else? Another hose perhaps? I didn't know if dealer parts were just ATE with a dealer sticker on them so thought I'd ask..
 
That said, there is one other symptom: A rattling noise at idle. No, it's not the diesel idle clatter. It's a slightly louder, harsher sounding rattle that only occurs at idle. A light touch of the accelerator pedal or engaging the clutch pedal fully and the noise disappears, only to reappear when all feet are off all pedals again.

Perhaps its the thrust bearing?

_________

A failed or failing thrust bearing should just about be felt through the pedal and heard just as the free play in the pedal is taken up. One or the other.

As for the noise, I'd get under the bonnet and try and pin point its source. Sometimes a cable or hydraulic line can be rattling until it stiffens up by being tensioned/pressurised. Idle speed vibration being low frequency can set some quite heavy components slapping.
 
Definitely can't feel anything through the pedal. It definitely sounds like a rattle.

Anything else I should change along with the Master/ Slave?
 
Greetings!

As I drove home today, my clutch pedal didn't rise up to where it normally would be. The sinking feeling soon subsided and the ol' girl got me home safely (God bless Classic Mercs!).

That said, there is one other symptom: A rattling noise at idle. No, it's not the diesel idle clatter. It's a slightly louder, harsher sounding rattle that only occurs at idle. A light touch of the accelerator pedal or engaging the clutch pedal fully and the noise disappears, only to reappear when all feet are off all pedals again.

_________

Did these two symptoms arrive simultaneously?
Does the clutch allow you to engage gears when stationary with the engine running?
 
No, the rattle has existed for a while. It exists till the clutch pedal is fully depressed or the very slightest application of throttle is applied.

Yes, it allows me to engage gears without issue even now. It is rising back to position (for now) but it has not done so on a couple occasions.
 
Yes, it allows me to engage gears without issue even now. It is rising back to position (for now) but it has not done so on a couple occasions.

If it permits that after the pedal has been held down for a while ie, you not selecting the gear immediately, then I doubt that the master or slave cyls are anything but fine. Another test is if once the gear is selected the clutch self engages with the pedal still fully depressed. It almost certainly will with a leaking master or slave cyl.

No, the rattle has existed for a while. It exists till the clutch pedal is fully depressed or the very slightest application of throttle is applied.

Track that down as a separate issue but, pay close attention to any return springs in the clutch mechanism.
A rattle I had at idle transpired to be nothing more sinister than the warning triangle rattling in its plastic box aggravated by the rocking couple inherent in 3cyl motors and most intrusive at idle.
 
The rattle sounds like the release thrust bearing--the slow pedal return/ sticking may be down to a corroded slave cylinder. Owners neglect to change the hydraulic fluid often enough [ every 2 years like the brakes] and the cylinder suffers internal corrosion. Perhaps a full hydraulic system rebuild master/slave / piping would be an idea?
 
Perhaps a full hydraulic system rebuild master/slave / piping would be an idea?

Yes, both rubber hoses and cylinders on order from Mercedes. The rattle is the real worry but I'm hoping it's something less sinister
 

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