Clutch master cylinder - replace or not?
 

New DMF, clutch and slave cylinder already fitted. Is it worth changing the master cylinder as well or should I leave well alone? :shrug:

I've read the horror stories about accessing, removing & refitting a master. cylinder.

Someone (it might have been Trikey) suggested it should be cleaned out.

If it aint broke don't fix it!;) A flush of the fluid may be a good idea though as it has been suggested that contamination of the fluid can cause premature wear of the seals.:}

Flushed mine at around 60K, now 101K still fine.

What's the correct procedure for flushing it chaps?

RAVE isn't much help - it only covers removal & refit, it doesn't cover flushing the fluid through. (p692 / repairs section 33-4)

You can either bleed it from the master to the bleed valve or some do it in reverse using a large syringe full of fluid back to the master via the bleed valve. Either way,empty the master of old fluid using a tube on a syringe and put something under the master to catch spillage as it gets messy!

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Either way bleed it before connecting the new slave cylinder up - you don't want to contaminate the new slave.

I would certainly consider it. There has been many people have premature slave cylinder failure on fairly new clutch / slaves. Some have had repeated failures. It is thought the master cylinder breaks down inside and contaminates the new slave.

The LandRover Freelander TD4 has exactly the same concentric slave cylinder as the 75, yet the Freelander seems to have far less issues with new slave cylinders failing. Same engine, gearbox, and slave as the 75, so whats the difference? Different master cylinder on the Freelander - more like the one fitted to the Rover 45 actually. That and LandRover dealers change the master cylinder any time a new clutch slave is being fitted.

Sorry for the delay in answering chaps - I'm bogged down on something else at the moment (ABS brackets). Anyway, back to the master cylinder plot.


RE BLEEDING THE MASTER

I don't understand Mike. When you say 'bleed it from the master to the bleed valve', presumably that means all the fluid in the master is forced out at the bleed valve end - in which case why does the master still have to be emptied with a syringe?

Ok, I'll remember to bleed it before the slave is connected (assuming I manage to suss out how to bleed it).


RE REPLACING THE MASTER

That's one vote in favour of not changing it and one in favour of changing it. Now I really don't know what to do.

Ashley: what would you change it for - a metal one or a plastic one?

Rimmers have a pre-filled one with ready-made pipe for £122 (STC100146) or a kit version with an unmade pipe for £87 (STC100146T). The pre-filled one appears to be plastic and the kit one is metal.

Then DMGRS have an AP branded plastic master with no pipe for £50 (link) - and just to add to the confusion here's an Luk pre-filled plastic one with ready-made pipe for £165 (link).

There are probably more but I'm confused enough already!

There is a quick release coupling in the hydraulic pipe, which self seals to avoid having to bleed it. Part the coupling and defeat the self sealing, that will allow the fluid to run out with the master cylinder cap removed, plus diaphragm under it. Refill and pump it out with the pedal unit it runs clear.

The other way is to pump fluid up from the slave bleed nipple, with a syringe, with master cap removed. Master does not have a bleed nipple, it will just overflow (see below).

Replace the master and which one, I have no opinion on? Swapping the master for the plastic one is quite an easy task, even at the road side - so if you have doubts, carry replacement plastic master as a spare, plus the tools to do it.

Swapping is a matter of undoing two fixing nuts to the bulkhead, taking out the clevis pin fixing it to pedal, then pulling it out far enough that you can push a roll pin out, which retains the pipe. Then reassembling with replacement master and bleeding through. I could do it in 30 minutes, but when I broke down in south Wales with no spare, a break down garage charged me £460 and two days, to get me back on the road [1].

A new master arrives with the plastic pipe and quick release joint already attached at the far end. Getting that through the bulkhead into the engine compartment is a nightmare task and mostly unnecessary, if you don't mind bleeding it and in retaining the original pipe.

Bleed method is one of attaching a large medical syringe, filled with brake fluid, via a short bit of plastic pipe onto the (released) bleed nipple below the battery. Remove the master cap and diaphragm, add plenty of newspaper under it and pump fluid in, until it flows out perfectly clear of discolouration.

[1] I bought the fancy Polish billet alloy master cylinder, as a replacement for my plastic original. All of the billet alloy ones had an issue with a weak seal failing in use, so it was a complete waste of money. It had though felt better in use, until it eventually failed. This is not the same metal master as the one you mention.

I meant to empty the master first to avoid taking any contaminated fluid from the master through the system, then only fresh fluid is pushed through. A bit belt and braces really. The fluid in the master just shuffles backwards and forwards in normal use. It does not travel the whole length of the pipe (ie circulate like water in a central heating system) unless you are draining or bleeding the system.