Ford Concentric Clutch Slave

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Ford Concentric Clutch Slave

Postby XKV8R on Mon Jul 28, 2014 6:30 pm

Hi all,

After trying to bleed the clutch and suffering an epic fail, I removed the engine and tried to check if it had been damaged because I thought it had popped. There was DOT4 leaking out the bellhousing every time I pressed the pedal.

This is a ford mondeo CSC mounted on a Birkin supplied spacer and nose for a short shaft T9. The bellhousing is a Birkin item as well.

The clutch is an AP racing clutch mounted on a lightweight flywheel bolted to a 2.0 l Duratec.

I measured the distance of the fingers from the back of the engine block and that is 70mm. The face of the thrust bearing fully extended from the front of the bell housing (or the back of the engine block, if you prefer) is 60mm. This tells me that when gearbox and bellhousing are mated to engine the fingers of the clutch would compress the slave cylinder by 70-60= 10mm. This does not sound anywhere near enough to actuate the clutch before the slave cylinder is at full travel. I would think 20mm of travel would be nearer the mark.

Ideally for the given clutch set up, what should the clutch slave be set back to? This would mean a thicker spacer, I should think.
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Re: Ford Concentric Clutch Slave

Postby BradW on Tue Jul 29, 2014 8:38 am

Hi

A 'normal' clutch only needs about 7 or 8mm travel to operate.

Don't know the Birkin setup but we usually end up having to fit a clutch pedal stop to stop the pedal travel, and prevent the piston 'popping' out of it's cylinder.

My guess with fluid in the bell housing you've already 'popped' the cylinder, you can normally get away by putting the piston back in the cylinder as long as the seals aren't damaged, but you'll generally only get away with this once or twice, and do you risk a complete reassembly without knowing if it will leak or not.
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Re: Ford Concentric Clutch Slave

Postby wattywat on Wed Jul 30, 2014 10:52 am

Hey

If it's popped then Brad has the answer, if it hasn't then it might be the o-ring at the back of the slave. I have a clutch stop behind my clutch pedal to stop it from popping out.

I've just recently replaced my Ford Mondeo CSC from Ford (~R1,300 incl. vat). There's an O-ring at the back of the cylinder that perished on mine and it started to leak... Pretty frustrating when I'd put the motor in, did all the plumbing and the thing didn't work when I tried to bleed it... I replaced mine because the silicone boot was buggered as well, but I could definitely have fixed mine.

If its an old slave, it could be that O-ring that's making it leak. I have my old slave that I can take pics to help show you what went wrong on mine. You should be able to replace the o-ring pretty easily. It's a square 2mmx2mm o-ring, just make sure that you get an o-ring rated for hydraulic fluid, normal o-rings get eaten by it.

Cheers
Bryce
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Re: Ford Concentric Clutch Slave

Postby XKV8R on Wed Jul 30, 2014 7:48 pm

Bryce & Brad

This CSC was new. The engine is out, I am waiting on some feedback from Birkin to see if my setup is correct. I've done some research and my view is that the fingers of the clutch should compress the piston to about 15mm off of it's fully compressed position. This will give you a full 15 mm of "wear" that the fingers can move towards the gearbox and compress the piston as the friction plate wears. The stroke of the master cylinder should only move the piston out from this compressed position about 6-8mm, which is the actuation stroke of the clutch pressure plate. This means the piston should never reach it's fully extended position, and hence never pop. The system by it's very nature is self adjusting and strictly speaking should not require a mechanical stop

I suspect mine popped because it was compressed about 10mm from it's fully extended position, and the stroke of the master piston pushed it to the limit. This being a direct result of using a thin non standard flywheel and race clutch, which reduces the compression of the CSC.

Of course your only way to fix this is to adjust the thickness of the backing plate to put you in the sweet spot, ie you cannot pop the CSC and you have room to accommodate the wear factor.

It took my 2 hours to take the engine out what a PITA
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Re: Ford Concentric Clutch Slave

Postby BuzzFuzz on Thu Jul 31, 2014 8:53 am

Brake fluid is a Glycol based hydraulic fluid (DOT 3, DOT 4 and DOT 5.1) don't use DOT 5 (this is silicon based and not very common)

DOT 4 for the Locost's should be more than sufficient, but 5.1 is just better and for some added bragging rights 8)

Using DOT 4, you will need o-rings made of either EPDM or Silicone (I would lean toward EPDM), don't use o-rings made of Nitrile or Viton as these are sure to swell and fail in a short time frame.
Jethro

1) Scratch build - 20V blacktop & T50 box (done... but always tweaking)
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Re: Ford Concentric Clutch Slave

Postby wattywat on Thu Jul 31, 2014 9:29 am

Good luck with it! You'll get faster at taking the motor out, trust me! Hahaha :lol:

BuzzFuzz, I've used DOT 5 for my hydraulics, why do you recommend not using it?
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Re: Ford Concentric Clutch Slave

Postby BuzzFuzz on Fri Aug 01, 2014 2:17 pm

There are three big pluses to using DOT 5 (silicone) fluids.
1. It is compatible with pretty much any rubber seal and life expectancy of those seals are generally increased (I have read some comments that seals sometimes swell a little more than normal, I'm not 100% sure on that info though)
2. It is paint friendly (glycol is not) (great for old classics that don't really get driven and spend their time on a showroom floor)
3. Silicon is hydrophobic and thus has a superior life span (glycol is hydroscopic) (Due to Silicon not absorbing water, if water condenses or somehow gets into the system, water will bead up and can cause localized corrosion)

The two big problems
1. It does not mix with anything really (brake pistons and calipers sometimes come with some sort of anti-corrosion oil or glycol break fluid so if the system is flushed properly and only ever DOT 5 used this should not be an issue)
2. Air Entrainment can be a problem and this leads to the biggest complaint about Silicon fluids... The result is compressibility is more than glycol based fluids and at higher temperatures the problem is exaggerated. So longer pedal movement required.

I suppose I should not have said don't use it... Guess that was more my opinion than fact. I think for a 7 silicon brake fluid is not a bad thing. Even in race conditions I think the brakes are normally so over the top for such light cars that the compresibility issues at temperatures may still be acceptable. It last a longggg time but the price and availability can be an issue.
DOT 3,4 & 5.1 are more available and if one cant remember what they used, topping up with the wrong fluid will not be a problem... as long as one does not throw DOT 5 in :lol:
Jethro

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Re: Ford Concentric Clutch Slave

Postby wattywat on Fri Aug 01, 2014 3:12 pm

XKV8R, sorry for hijacking your post! :lol:

I'll stick with DOT 5 for now and see what happens, if it's an issue I'll change to DOT 5.1 with a good flush of all of the lines.

Cheers
Bryce
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