[Healeys] Clutch Master Cylinder/Clutch Slip Saga

[Michael Salter]

Well Simon, that explanation, although a bit weird, is possibly correct.
With a master cylinder, when the piston reaches the top of its stroke, a
"valve" opens to connect the fluid in the bore of the cylinder to the
reservoir.
This ensures that the system is filled with fluid before the pedal is
pressed to operate the clutch or brake and that any expansion of the fluid
in the system can be relieved with the fluid being returned to the
reservoir.
If an incorrect push rod is used which is too long the pedal can reach the
top of its travel (limited by a some mechanical stop other than the circlip
in the master cylinder) such that the piston of the master cylinder does
not reach the top end of its stroke thus preventing the "valve" from
opening.
This scenario results in the fluid in the system remaining under pressure
and, probably in your case, holding the clutch in a partially released
condition.
As the fluid warms up it expands and, having nowhere else to go, this
effectively depresses the clutch release bearing further which eventually
causes the clutch to slip.
This scenario is actually more common in braking systems.
In the case of the master cylinder of the 100 for example the length of the
brake master cylinder is adjustable and incorrect adjustment can result in
the brakes eventually locking up completely.
The same applies in the BJ8 where the master cylinder push rod is also
"adjustable".
A more common and very similar situation with BJ8's is caused when the
brake servo does not return fully to its "rest" position resulting in the
"valve" within the servo not opening.

M



On Sun, Jun 23, 2024 at 8:57 AM Simon Lachlan via Healeys <
healeys at autox.team.net> wrote:

> With reference to the slipping clutch &/or overdrive, I do believe that it is
> fixed. Said that before and it let me down again. But, this time, I had it
> done professionally by a local team that I’d never used before.
>
> Anyhow, after my wasting a lot of time and some money checking everything
> and getting nowhere, these guys said that the rod in the clutch master
> cylinder was too long and they’d had to reduce it’s length. (Non-standard
> rod. Long story). So, apparently the pressure wasn’t being allowed to
> bleed back/out and the slave cylinder remained pressurized etcetc.
>
> Now, if that sounds like a muddle, it is and that’s because I’ve never
> delved into or fully understood the workings of the clutch master cylinder.
> (Which is why I never thought of it during the whole affair. But nor did
> anyone else). I know it’s not just a simple pusher, like a bicycle pump,
> but that’s really all. I googled it and looked into my years’ worth of
> collected files of advice and wisdom. But nothing found.
>
> Can someone just explain how the thing works so I can understand what was
> going on? I should like to close the whole chapter and move on………..
>
> Thanks,
>
> Simon
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