Clutch hydraulic problem

[peterdeane]

I have a 1964 S Type where the clutch hydraulics fail when the engine gets hot (ie. after a long drive or sitting in traffic). No fluid leaks so that made me think it couldn't be the slave cylinder. I have replaced seals in the master cylinder, and of course the fluid, but the problem persists (old seals were definitely a bit soft and questionable but cylinder itself looked in good condition).
Could it be the fluid is boiling ? Would it be worth replacing the Dot 4 with Dot 5.1 type ? Any other ideas would be appreciated !

[PPV]

Although DOT 5.1 has a higher boiling point and may help it will not cure the source of the problem. Most of our Mk2's do not have a problem so could it be the routing of the pipe to the slave cylinder, issues with soft rubbers in the slave. When you say it fails do you mean that the clutch will not disengage ot that the pedal goes to the floor with nothing happening or something else?
Regards,

[peterdeane]

Thanks for your thoughts. When I said the clutch hydraulics fail when engine gets hot, I mean clutch does not disengage fully when pedal is pressed to floor - as if there is air in the system (?). So result is gear crunching when trying to engage or change gear. The routing of the pipe to the slave cylinder hasn't been changed from original, and the problem is fairly recent.
Maybe I need to replace seals in the slave cylinder - though I would have thought poor seals would have shown up as a fluid leak at the slave ? Or maybe I need to re-bleed in case I missed some air when I bled the system after changing out master seals.

[3.8etypephil]

For the sake of what they cost, I'd be inclined to replace the slave cylinder seals in any case, also the flexible hydraulic hose; this could be expanding as it gets warm, or closing up. I have found both scenarios to give apparently random brake and clutch operation faults. The only other thing I can think of is excessive crankshaft end float; I hope for the sake of your sanity, and wallet, that this is not the case.

[Tintin]

I'm not intimate with the S type clutch but are you sure it is the hydraulics? Binding or wear in the linkage may also cause drag.

Robbie

[peterdeane]

Thanks again for your thoughts !
I've just bled the clutch hydraulics again today and seemed to get some air out (not sure how it got there as previous bleeding was pretty thorough). Just waiting for the roads to dry up before I take it on a test run (I don't like getting my S-Type wet !).
If all is well - great ! If not, I'll replace slave cylinder seals as the next stage. By the way the only flexible hose is a couple of inches at the plastic reservoir outlet, which seems fine.

[340jag]

The problem is down to bad designs of hydraulic systems that need bleeding , when you think about it !
Air rises in fluid , so what bright spark thought it would be a good idea to put a bleed nipple at the bottom of a system .
On my Motorbikes I tie back the leavers over night , as the air rises it all comes out in the master cylinder's .

Saying that my clutch is fine on my MK2 !

[3.8etypephil]

Thanks again for your thoughts !
I've just bled the clutch hydraulics again today and seemed to get some air out (not sure how it got there as previous bleeding was pretty thorough). Just waiting for the roads to dry up before I take it on a test run (I don't like getting my S-Type wet !).
If all is well - great ! If not, I'll replace slave cylinder seals as the next stage. By the way the only flexible hose is a couple of inches at the plastic reservoir outlet, which seems fine.

There should be a flexible hose between the body and the slave cylinder. Part no C11603

[340jag]

The hose C11603 is around 300mm long !

[piman]

Hello Peter,

your symptoms are common in the Triumph 2000 world, when hot the clutch doesn't clear. The fault being the plastic pipe that supplies the slave ballooning when softened by heat. Now I know the MK 2 line is mostly steel but do wonder if the heat is affecting the flexible hose? These hoses do deteriorate with time.

Alec

[peterdeane]

Thanks to all for your helpful comments and suggestions.
I took my S-Type for a long run yesterday after thoroughly re-bleeding the clutch circuit a few days ago. It now seems to work pretty well as it should although I have not tested it yet in lengthy stop/start(ie hot) M25 traffic which is where the problem became worse after my initial replacement of master cylinder seals. Hopefully problem is now solved.

By the way, there is no flexible hose between clutch master cylinder and slave - any movement presumably is just taken up by the length of the copper hydraulic pipe in my S-Type. Not sure this is normal, but It has been that way for years !

[oldtimer]

Peter,
If there is no rubber hose pipe in the line somebody has done a bodge job. There is no need to change from Dot 4.
The clutch hydraulics don't get any more basic. The recuperating seal in the bottom of the master cylinder can leak allowing pressure to escape back into the reservoir. When servicing the system all the seals in both the master cylinder and slave cylinder should be replaced

[340jag]

Diagram is the S-type lay out !

[broughworld]

Hi, is getting the air out of the clutch hydraulic system a known problem? I've recently replaced the master and slave seals and bled the system but the clutch still does not disengage properly. Pumping the pedal makes crunchless gear change possible. I've been pondering trying to reverse bleed ie via the nipple on the slave cylinder to see if that would expel any air present. Has anyone ever tried this?

[B87UL]

Broughworld

Have you clamped the slave cylinder in the fully retracted position before bleeding?

Also can you say whether we are talking about the later hydrostatic cylinder here which is "supposed" to have a 19mm maximum travel?