I've been having an issue with my clutch lately, I seem to intermittently lose the pedal as the car warms up. I start off with a full pedal at the beginning of a trip but it quickly reduces to a point where i have some grinding when changing down gear. I have recently changed the fluid (dot 4) however it hasn't helped the problem. Any advice before I try and tackle this problem will be greatly appreciated.

what you want to do is work out whether it's hydraulics, or inside the gearbox.... it may just be that the seals in your slave or master cylinders are cactus and are letting fluid past, then the fluid is getting back to the right place when left (somehow :S)

find a helper - when the pedal is good, get your helper to push the clutch all the way to the floor and you measure how far the slave cylinder pushrod is moving, then when the pedal is bad, do the same check. If the amount of movement changes, then be happy, and move on to finding which part is at fault. If the measurement is the same, be sad, because something is wrong

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If the pedal comes and goes and you're not loosing fluid, it's almost a certainty is a dud m/c and /or m/c seals. If it was the slave you'd have fluid leaking out it.

Might need to adjust your clutch arm. To start, take off the big nuts at the bottom end of the clutch plunger (at the centre of the wok cover).

Now, about 1/3 of the way up the clutch arm there is a stop bolt that prevents the arm from going back too far when the clutch isn't engaged. Ensure that there is a little gap between the bolt head and the arm - perhaps half a mm. Have a look at the image here: the little bolt stops the arm from going too far to the right. You can also see the two big nuts on the left which should now be removed.



Now see if that solves the problem - I have seen the big bolts work their way back in towards the plunger so that they don't allow enough travel - that's most likely your problem. If that fixes it you can put the bolts back on - get and attractive assistance to push the pedal in as far as it goes, and wind the bolts on - give just a little clearance before ther hit the end, and tighten them against each other. Or you can just leave them off.

If that's not your problem, you might be up for a new clutch or master cylinder.

Slave cylinder seals can leak air in on the upstroke when worn, without leaking fluid out.
See my thread on clutch slave cylinder- cup spreader.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Thanks for the advice, ill check it out on the weekend

Also might be worth checking the clutch hose
when the engine bay warms up , the hose may be getting softer and expanding

Mark

Get a helper, watch the slave cyl arm and get yr helper to push the clutch pedal fully to the floor...and gold it in. Watch the clutch arm closely. If if slowly drifts backwards then you have a slave cyl or master cylinder bypassing. Replace them both. Job done..

An oddball one I had was a small hole in the inner of the hose. If I held the clutch in at a set of lights then it would start dragging, let it off and after a while it would be ok. Drove me nuts trying to figure out the problem as I couldn't see the hose swelling...

Cheers

Dan

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Mafs waz not my strong subgeckt at skkol

Yeah, nice story but this might confuse the situation.