Clutch master cylinder - whats going on?

**gromit** · 27th February 2013, 05:41 PM

I've posted this picture before but here goes.

This is from a Ford Territory, 2 maybe 3 years since last fluid change used Super Dot 4 as specified.
Nobody can explain it, flushed and brakes work OK.

Same thing 2 years later......

With the Defender master cylinder you have a steel piston in an aluminium body, the fluid is often black from the aluminium wearing.
I didn't have too many problems with my original, resealed it and got another 6 years or so then replaced with a st/st sleeved one.
Slave was resealed 10 or more years ago but I replaced it when I changed the master cylinder. As it's a steel piston in a cast iron bore there seems to be less issues.

The Toyota is an odd one. Dot 3 OK, Dot 4 or higher causes problems. Switching back to Dot 3 shouldn't cause problems because from memory it's only the max temperature that increases with the Dot numbers (except 5 which is silicon).

Colin

**460cixy** · 28th February 2013, 01:34 PM

Originally Posted by rick130

What the hell is the deal with this ?

They're both glycol ether fluids, but I've heard old Series Landy blokes say the same thing

I can't answer that. But it only seems to be a real problem in the brake masters that have the abs and booster built in to it like 100 series some supra s Lexus ect Mitsubishi have them as well but I haven't seen one with a problem. We now use a Penrite fluid that they assure us covers both and so far so good.

Penrite super dot4. As1969.1-2005 grade3 sae 71703/j1704 This explains a little about seal swell http://www.penriteoil.com.au/tech_pd...%20DOT%204.pdf

**steveG** · 28th February 2013, 03:22 PM

Thanks for that article.
On mine the small cup seal that closes off the reservoir appears to be quite soft, and is sticking in the small plastic cup that it moves in and no longer seals.
By comparison the main pressure seal on the piston still feels "normal".

Seems like the seal swell referred to in that document is whats happened to mine.

Steve

**Bushie** · 28th February 2013, 04:57 PM

Sleeved cylinder if done correctly should last for ages. Mine failed after a couple of months, then failed again a couple of months later, when I had a real close look they had creased the sleeve when it was pressed in, so each time the clutch pedal was pressed it would chew a bit more of the seal away, my clutch fluid looked the same.

Martyn

**460cixy** · 1st March 2013, 06:55 AM

Originally Posted by steveG

Thanks for that article.
On mine the small cup seal that closes off the reservoir appears to be quite soft, and is sticking in the small plastic cup that it moves in and no longer seals.
By comparison the main pressure seal on the piston still feels "normal".

Seems like the seal swell referred to in that document is whats happened to mine.

Steve

That's the centre valve common failure point on that style of master

**steveG** · 1st March 2013, 11:38 PM

I fitted the new master tonight, adjusted the pedal height - but even with the locknut wound fully down the shaft towards the cylinder I still can't get the 1.5mm free play between pushrod and piston like you're meant to have. The piston is always partially depressed (maybe 3mm or so).

I've bled it and its working fine, so is it OK to leave like it is, or is it critical to have that free play?
If it is critical, then it looks like I'm going to have to either run a die down the pushrod a bit to extend the thread, or space the M/C flange out a bit.

Steve

**yt110** · 2nd March 2013, 12:59 AM

Does your's have a spacer plate?Mine has one ,about 2mm.

Jim

**460cixy** · 2nd March 2013, 07:57 AM

Yes it has to have the free play otherwise you may find the clutch not fully engaging

**steveG** · 2nd March 2013, 11:55 AM

Originally Posted by yt110

Does your's have a spacer plate?Mine has one ,about 2mm.

Jim

Nope - no spacer plate. Are they meant to have one, or is yours a mod?

Steve

**Johnno1969** · 2nd March 2013, 12:26 PM

Originally Posted by steveG

From reading the many posts on the subject I know that Defender clutch master cylinders only last on average about 3.768 months before failure

I don't want to tempt fate, but I've had my twenty-one year old Defender for nearly ten years, and my master cylinder has always been fine. Mind you, I haven't driven it since 2009. But that's another story...

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