Clutch wont bleed up

[red_slr]

Anyone got any advice.

We had a dead clutch pedal on one of our work vehicles. Went out of the office and 2 junctions later clutch was floppy.
So brought it back and the master cylinder reservoir had a lot of black flecks in it so assumed the seal had gone.

Replaced the master cylinder and bleed up but only getting about 25% movement.
Damn. So replaced the slave cylinder and still only getting 25%.
Now back bled the system from the slave and still no better.
Checked the fittings and all seem ok at both ends.

Anyone got any advice - the only thing to change now is the line?!

[red_slr]

Just to clarify we are getting good flow out of the bleed nipple but it seems to go clear then after a few more pumps more air appears.

I am confident we have a good seal on the bleed nipple.

The system holds about 600-700ml of fluid and so far we have put 2.5-3L through it to try and bleed it up.

Edit to add we replaced the return spring too.

[Peanut Gallery]

Good call on the line - how much of it is rubber?

Could a broken bit of seal still have remained in the system, and is now holding the new seal in the master or slave cylinder out of shape?

[red_slr]

Its all rubber.

Getting a new line made up as we speak will report back...

[InitialDave]

If it's an external slave cylinder, moving the actuator arm/rod about a bit with whatever free play there is can sometimes burp out a bit of air that's in an awkward position and not bleeding out.

Sometimes back flushing by putting a tube on the open bleed nipple and squirting brake fluid "backwards" through the system with a syringe does a better job than bleeding the "right" way.

[red_slr]

Back bled it twice using a proper pressure bleeder.
Also tried it the "normal" way 3 or 4 times. Each time we still get air so that's why I think the hose is gone although no visible signs of a leak.

[red_slr]

Spoke to a mechanic that advises we need to actuate the slave through its full motion range to clear out the air. Will try that tomorrow..

[stevieturbo]

And not a single mention of what vehicle...

Chances of it being the hose are almost zero.

There may have been a master or slave problem, if you took either apart ( where it's a normal piston type ) you should be able to see if there was an issue.
Concentric..not so easy to visualise.

[Steve_D]

We often have this issue with the clutch on TVRs
Get your assistant to press the pedal to the floor and hold it there. Then crack the bleed nipple. Quite a dramatic woosh of fluid but seems to work.

Steve

[GreenV8S]

I've seen brake systems which don't fully self-bleed and have dead zones which can trap air pockets. Seems unlikely that your clutch has this problem since there is not so much scope to use clutch components in the wrong orientation, but worth a quick visual check for any potential high spots that could trap an air pocket. If you have one of these the normal solution is either a vacuum bleed, or just unmount the component and tilt it to chase the air out.

[rev-erend]

It could even by the lever fulcrum has punched thru the lever arm or pins broken on an actuator mechanism.

Check it out with a bore scope (about £5 now days..)

[red_slr]

Well we have now discovered we have the wrong master cylinder and our bleeding process is fine!

Externally it looks identical when offered up to the OE part but the recess which the push rod goes into is much deeper thus giving the impression of a dead clutch. Its not actually moving the cylinder other than the last 10mm of travel, which if the spec was the same would be the first 10mm of travel...

Sigh.