Tin worm attack ...
AO Gold Member
Join Date: Jan 2003
Location: United Kingdom
Re: Clutch loses adjustment when hot
I've not taken an 156 master cylinder apart, but frequently changed seals on older cars (eg MG Midget) so assume they work in similar ways.
Normally you have a metal "plunger" with a sealing ring fitted to it (possibly two). This fits tightly into the cylinder body. In front of that will be a spring to return the plunger to the normal position when you take the pressure off. Or there may be a spring on the actual clutch pedal that pulls the piston back. Often both!. Inside the "open" end of the cylinder will be a circlip to stop the plunger from coming out. Sometimes there is a second spring held in by this circlip holding the piston in the middle of the cylinder. On the end of the cylinder will be the sealing cap, and through this runs the operating rod, which is attached to the clutch pedal. Into the side of the cylinder will be two pipes: one is the feedpipe from the reservoir (note the 156 uses the brake master cylinder reservoir not a separate one), and the other runs to the slave cylinder.
When you push down on the pedal you "squeeze" the fluid which only has one place it can go, so it travels down the pipe to the "Slave". The slave (which is a similar setup to the master, just the other way around inside) then pushes on the clutch operating arm and "opens" the clutch, disconnecting the drive from the flywheel to the gearbox.
Do you know when the fluid was last changed? Non-synthetic Dot 4 brake/clutch fluid attracts moisture (hygroscopic) and needs to be replaced about every two years. The water means the boiling point is lower and this might be why you only get the problem when the engine is hot. As the water evaporates, the clutch has to travel further to take up the gap. If there are two springs then the one pushing the piston into the clyinder could "pull" the clutch pedal in depending on how the operating rod is fitted .... and a small movement here would be translated into the pedal moving a larger amount due to the pedal length (remember any physics from school??).
Chris was right when he said there's a How-To about bleeding the clutch on my website. I put it together with the help of BlackBeauty when I changed my discs/pads and replaced the brake fluid. It's not the same as the brakes as on the TSpark there isn't the normal type of bleed nippple that you unscrew to open like you get on the brakes (and most other cars). You have to pull the feedpipe out a small amount to open the hole to release the fluid.
Remember that brake fluid is the world's best paint stripper. And once it gets onto the metal it is almost impossible to respray the area.
HIS: 1998 156 2.0 TSpark with Sport Pack 2, sunroof and hi-level spoiler in Alfa Rosso. V6 intake mod, clear side repeaters and Zeatek undertray.
HERS: 2009 MiTo 1.4 95bhp Turismo arrived 21st November in Techno Grey with colour-coded headlight surrounds.
"If you're driving on the edge ... you're leaving too much room!"
My Alfa156 Web Site - how-to's, piccies, links, useful stuff, etc.
Last edited by gazza82; 24-04-06 at 10:49.