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Old 11-09-2003, 06:50 PM
Greg in Oz Greg in Oz is offline
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Join Date: Jan 2003
Location: Sydney, Australia
Posts: 627
Clutch master cylinder question W201 & 124.

This is a question for those who really know the clutch master cylinder setup on a W201 and W124 well. My Haynes manual (for both W201 & 124) describes an adjustment for the master cylinder pushrod. The adjustment allows the piston in the master cylinder to return just far enough to uncover the port for the connection to to fluid reservoir when the pedal returns to its stop.

Problem is my 1990 190E has no such adjustment. It appears there is no stop for the pedal and that the piston returning to the circlip at the end of the master cylinder forms the stop. Other diagrams in the Haynes manuals also tend to agree with this setup.

I ask this as I'm still having a problem that I posted about previously where my clutch pedal take-up point gets progressively higher with increasing temperature, to the point where I can get some clutch slip. Once cooled there is no slip. The clutch plate is not worn out (according to the measuring tool) and I get no slip until everything gets plenty of time to heat up (ater maybe 1 hour driving in heat).

My diagnosis is that the fluid inlet port in the master cylinder is remaining covered by the piston. This prevents excess fluid returning to the reservoir when the fluid expands due to a temperature increase. The result is that pressure remaining in the system prevents the slave cylinder from fully retracting the clutch release lever. In the absence of any push rod adjustment it suggests that possibly the master cylinder piston seal is swollen. It appears my best option is to fit a master cylinder kit or replace the master cylinder.

Can anyone confirm that:
1. the '90 models had no pushrod adjustment.
2. my diagnosis seems reasonable.
3. that the piston seals can swell thereby blocking the master cylinder port.
107.023: 350SLC, 3-speed auto, icon gold, parchment MBtex (sold 2012 after 29 years ownership).
107.026: 500SLC, 4-speed auto, thistle green, green velour.
124.090: 300TE, 4-speed auto, arctic white, cream-beige MBtex.
201.028: 190E 2.3 Sportline, 5-speed manual, arctic white, blue leather.
201.028: 190E 2.3, 4-speed auto, blue-black, grey MBtex.
201.034: 190E 2.3-16, 5-speed manual, blue-black, black leather.
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