Clutch drag when hot

J

johnsimister

Active Member
My last P6, a 1967 2000 SC, could be difficult to get into gear when the engine and gearbox were well warmed up after a long run. The symptom was of the clutch not disengaging fully, although the pedal felt normal. Now my recently-acquired 1965 example is doing the same thing, despite a new clutch fitted shortly before I bought it. It's fine when cold and on short journeys. Sometimes the release mechanism squeals a bit when the pedal is depressed, although the previous P6 never did that.

Any ideas? Should I increase the clutch pedal stroke? I haven't yet measured it to compare with the dimensions given in the manual, and it does seem a bit short, but why should it be a problem only when hot?

Thanks very much

John
 
Make sure the gearbox has oil in it.
Make sure the idle speed isn't too high.

Set the clutch as follows:

Pull back the carpet and underlay and set the brake pedal height between the bottom of the pedal and the floor to 6 & 7/8"
Set the clutch pedal level with the brake. This is done on the threaded rod into the master cylinder.
Push the clutch operating arm rearward until the release bearing touches the pressure plate and make sure the arm is one spline forward from vertical. Remove the arm and move it on the splines if it's not, and take care not to drop the nut in the bellhousing.
Pull back the slave cylinder boot. Adjust the pushrod so that the piston is about 1" away from the circlip. (Pedal at rest)
Wind the stop bolt all the way in. (Thats the one in the footwell.)
Then get someone to slowly depress the pedal as you look at the piston in the slave. What you need to get is the piston just touching the circlip when the pedal is on the stop, and you achieve this by adjusting the pushrod each time just before the pedal is depressed.
Once you get to the point that putting your foot on the clutch down to the stop makes the piston touch the circlip in the slave, lock the nut on the pushrod.
Then wind the stop bolt up one turn, and lock it with the nut.
Depress the pedal again and make sure there is at least 25thou clearance between the piston and the circlip in the slave.
If not wind the stop bolt up some more a turn at a time.

If it still has the problem it could be the spigot bearing running clearance too tight, in which case you either remove the gearbox to set that, or try filling the gearbox with EP90.

Noises are unusual, but you can get a mismatch between pressure plates and release bearing sleeves, which I would imagine could be noisy. If that is the case, it's gearbox out again.
 
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Remove the gearbox... those are the words I didn't want to hear! I'll set everything up as you suggest, and try EP90 if the problem persists. Failing which, out it comes. Thanks very much for your sage advice.

Meanwhile, I think there's a broken diff mount to attend to and the bar at the back of the gearbox is snagging the snub rubber. I think I need to spend some time underneath and go through everything.

John
 
Hi,

Might be worth trying some new brake/clutch fluid, old fluid can behave strangly to a bit of heat.

Tim
 
Very productive day in and under ELT 44C.

First off, thank you Harvey for your how-to guide, which was extremely useful.

Pedal heights were too low, so I fixed that. Then I discovered that the clutch pedal was reaching the end of its rather short travel well before the stop bolt on the floor. Next, the release bearing's actuating arm wasn't angled as it was supposed to be, but vertical. So off it came, managing to avoid dropping the nut in the bellhousing. I epoxied the nut to the arm to prevent disaster on refitting, and refitted the arm one spline round from where it was.

Time to enlist the help of Mrs S. Even with the pushrod held in by just two threads it still wasn't possible to get the pedal to touch the stop bolt before the slave piston touched the circlip. Master cylinder fault, allowing insufficient travel? No - I pushed the slave piston right into the cylinder, pressed the pedal and there was full travel to the stop bolt. And, in doing so, got air in the system. Mrs S was cajoled away from trimming the rain forest that our garden seems to have become and back onto clutch-pressing duties while I bled the system.

Still not right. Conclusion? The pushrod was too short. Why that should be, I don't know. So I made up a longer one from a spare bolt, tapping a longer thread and rounding the end, and tried that. Success! All now seems to work perfectly - nice biting point, no drag, no funny noises, lovely snickety gearchange. And much relief all round.

While under there I also realigned the engine and gearbox so the spring at the back of the gearbox is vertical instead of leaning at a drunken angle, and the snub rubber is as central around the bar as I can get it. I'd like the back of the gearbox to go up another 1/4in but I don't see how it can. The tie rod at the front of the engine was loose as I repositioned the engine slightly on its mountings, so that's not forcing the gearbox down. Anyway it's as good as I can make it.

I also think I might have discovered the source of a bang at the back when taking up drive smartly, which might be tied in with a slight tremor (not quite a judder) when reversing slowly with the clutch slipping - the tremor seems to cycle with the slow rotation of the propshaft. Should it be possible to heave the diff extension, where the propshaft enters, up and down quite easily against the mounting? Or has the mounting come to bits? It does seem to be very softly mounted at the moment.

John
 
Sounds like your pinion mounting has had it. The inner sleeve comes unbonded from the rubber allowing the pinion housing to move up and down, which can cause the prop bolts to hit the crossmember. Leaking pinion seals often wreck the mounting.

As for the pushrod, who knows what people have done in the past.
 
That makes perfect sense re the pinion mounting. I shall order a new one. It's quite oily round there so it probably needs a seal as well.

The pushrod? Yes, lots can happen in half a century plus a year.
 
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