New clutch drags when hot

[jerry]

fitted a new clutch to the S4 its fine when engine cool but after half an hour it drags very badly so gear changes are a nightmare , have bled the slave silly and its new as well , adjusted the levers and pivots but nothing helps, as soon as the bike cools down all is well until it hots up again,

plates and dixcs are all in correct order ans stack is within limits so I am now not sure what to try next. also fittrd an new clutch throwout bearing .

[analogue_rogue]

has your clutch slave cylinder totallly compressed? i had a nightmare bleeding mine in the end i had to compress it with a small g clamp or it kept pushing out and causing clutch drag.

[Starter Sprag]

There is usually a small 'breather-hole' on both, the slave and top reservoir

If either or both are blocked due to dirt / crap, air will be trapped, the heat from youe engine will cause the air to expand, causing clutch drag

[Capo]

If there was any air in they system and it expanded, surely it would cause the clutch to slip rather than drag. However given any increase in volume/pressure due to the temperature change experienced, I doubt this would be sufficient to cause any significant displacement of the slave piston.

Jerry I'm at a loss to offer a solution. Rendering it down, the slave is not moving enough when it gets hot, the question is why. Lemme think some more.

[jerry]

I will dismantle the entire clutcch tommorow and check willl also replace clutch hydraulic fluid with fresh again , etc etc

[gary tompkins]

My money would be on air still trapped somewhere. Air compesses more than fluid so the slave may not be lifting the push rod properly, causing the dragging. Some kind of force bleeding system usually helps get it out. There isn't much fluid in there to start with, so even a tiny amount of air makes a big difference.

[analogue_rogue]

try clamping the slave with a g clamp. and use a syringe to push the fluid up to the master cylinder banjo bolt. hen bleed normally with it still clamped until no air comes out at all. this is what i had to resort to.....

[utopia]

My money would be on air still trapped somewhere. Air compesses more than fluid so the slave may not be lifting the push rod properly, causing the dragging.

This seems logical,... but the air is present in hot AND cold conditions, so why the difference? Maybe the hot air expands, effectively increasing the ratio of air (volume) to fluid in the system when its hot. Or maybe the hot air is more easily taken into solution by the hot fluid, and this somehow makes things worse, though I can't quite see why this should be.
The fluid itself is virtually incompressible.
Does the feel/free play at the lever remain the same whether hot or cold. If so, maybe the problem is mechanical rather than hydraulic, though the latter would be my first guess.
Just thinking out loud mind you.....can't say I've had much experience.

[jerry]

I have a reverse bleeder , I have left it clamped at the bar for 2 days now and have reassembled the clutch again all is ok so will try tommorow to see if it works Ok ?????

[analogue_rogue]

is it a new slave cylinder?

[Starter Sprag]

When cold, and operating the lever, the entrapped air is allowing the clutch plates to separate, sufficient to change gear

However, as the engine heats up, the entrapped air expands, then full operation of the lever is not able to fully separate clutch plates, hence difficulty in changing gear

Take your time, and fully bleed system, removing ALL air

[Capo]

When cold, and operating the lever, the entrapped air is allowing the clutch plates to separate, sufficient to change gear

However, as the engine heats up, the entrapped air expands, then full operation of the lever is not able to fully separate clutch plates, hence difficulty in changing gear

Take your time, and fully bleed system, removing ALL air

Indeed your point is valid:thumbsup:

[utopia]

Seconded.

Thats kinda what I was getting at......(amongst the waffle).

[jerry]

Slave cyliner was new last year and so was master ,, went for a 50 mile ride today and all seems fine now but dont know wether it was the bleeding all night again or the shims on the basket bolts that cured it or both.

clutch seems sweet now

next job check TPS as slow running a bit off

[animaluk]

Slave cyliner was new last year and so was master ,, went for a 50 mile ride today and all seems fine now but dont know wether it was the bleeding all night again or the shims on the basket bolts that cured it or both.

clutch seems sweet now

next job check TPS as slow running a bit off i had drag and it was down to a worn pushrod