Slipping Clutch 1973 2000TC

E

edward1

New Member
Can anyone help with my very baffling problem. Before I replaced the very leaky slave cylinder with a brand new one the clutch performed faultlessly. Now it has the replacement, adjusted in accordance with the w/s manual, the take off from standstill is perfect. A hill start presents no difficulty nor, indeed, driving up ramps to work underneath.
However, when driving at any speed fast or slow a dab on the throttle sees the rev counter surge up the scale with no increase in the vehicle's speed. I have twice checked the adjustment and re-bled three times. In desperation, I have backed off the adjustment to allow more free play to no avail. The clutch actuating arm is not seized and will travel smoothly to disengage. I have checked its movement with the slave disconnected using a length of pipe to give leverage.
Why, oh why, is the clutch slipping when on the move but not when moving away or doing a hill start?
I would be most grateful for any suggestions.


1973 P6 2000TC Lunar Grey RPJ200L
1959 P4 100 Rush Green over Shadow Green XXO837
1986 XJS 5.3 V12 Coupe Burgundy C331CAP
 
If the hydraulics aren't holding the clutch on and causing it to slip, then either the release bearing sleeve isn't coming fully back and that's causing it, (but faults with the release bearing and it's housing are rare, although they do happen), or it's just a case of the pressure plate being weak and not clamping the pressure plate properly. If all of the clutch settings are correct, (pedal height, release arm one spline forward, and the slave piston isn't hitting the circlip) then although I'd want to test it myself to be certain, which in this case probably isn't possible, then you may be looking at the box coming out, and the fact that it's happened after fitting the slave is just coincidence.

It probably won't help in your case, but you won't get the best result by following the WM procedure for all the clutch settings to the letter.
 
Thanks harveyp6 for your prompt response to my question. I would like to raise one query with you. Assuming that I have a problem with the pressure plate, then why does it only occur on the move? Surely starting from rest would give rise to clutch slip and a hill start would also be almost impossible. I am able to do both without any slipping.
I await hearing from you and, meanwhile, many thanks for your interest in my problem.
 
edward1 said:
Assuming that I have a problem with the pressure plate, then why does it only occur on the move? Surely starting from rest would give rise to clutch slip and a hill start would also be almost impossible. I am able to do both without any slipping.
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When clutches wear they often show no signs when pulling away from rest, only when trying to accelerate once on the move. The gearing pulling away in first is far lower than 1:1 in top, plus there's all the momentum in the flywheel that you add to by opening the throttle, which rather than moving the car forward, just overcomes the clutch making it slip. Can you make the clutch slip at a standstill? In other words with the handbrake on and trying to pull away in 4th gear, can you get your foot fully off the clutch without the engine stalling?
 
I have just given it a try, twice. The engine stalls in 4th at both 1,500 and 2,500 rpm. Not a hint of any slipping.
 
Well if that is the case then either it's not slipping when you accelerate, it's just an erratic tacho reading, or something is happening while the car's on the move that isn't happening at a standstill. Is there an increase in engine speed to go with the increased tacho reading, and if you continue with you foot on the throttle when it happens, what is the eventual outcome? Do the revs continue to rise with a loss of speed, or does the roadspeed eventually catch up with the revs?
 
I'm tempted to suggest putting the leaky slave cylinder back on and giving it a test . Possibly he didn't test the clutch so vigorously while the old cylinder was on
 
The engine revs are most definitely rising; it is not a tacho malfunction. If I keep my foot down then the revs keep rising and rising with no corresponding increase in road speed. I do, in fact, lose speed and I have to back off for fear of over-revving.

Turning to the suggestion by DaveHerns, the old cylinder is past redemption! The bore is badly rusted and this has damaged the seal. I am amazed that it ever functioned. (The result of being left unused for a decade and ,yes, all the brake cylinders and master cylinder have been renovated on the bench just in case they were similarly affected.)
When the old cylinder was in service the car was put through its paces with not a trace of clutch slip.
 
edward1 said:
The engine revs are most definitely rising; it is not a tacho malfunction. If I keep my foot down then the revs keep rising and rising with no corresponding increase in road speed. I do, in fact, lose speed and I have to back off for fear of over-revving.
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Well in that case the clutch is slipping as you originally said, and as it will stall out at a standstill there must be enough freeplay on the clutch, so I can only go back to my original thought that the clutch slips under the greater load put on it when asked to transmit the drive under acceleration. I'm at a disadvantage in that I'm not able to drive it, so maybe missing something, but I can't think of anything that would only cause the clutch to slip in those circumstances, but showing no other symptoms elsewhere, other than the clutch itself.
 
I agree with Harvey. Most unusual. I can't think of anything more that can be done from outside the car, so I'm afraid it looks like drop the box time. My own guess is that you'll find the linings OK but a defect in the pressure plate (broken spring/diaphragm, cracked etc). Clearly with the box down it is pointless not to replace both driven and pressure plates. If it was a normal car I'd also replace the release bearing, but I seem to recall the 4 pot is a little odd in that respect? Harvey?

Chris
 
Hi Chris. Thanks for your input. I am new to P6s having had only this one and since last November at that. Can you give me more info on the release bearing which I would have replaced as a matter of routine while the box is out.
 
Hello Harvey. I fear that you are right and it is the clutch itself. One last thought though. When the car is already under way and doing say 30mph would the extra revs not be transmitted through the clutch more easily than trying to start off in 4th against the handbrake.
 
chrisyork said:
If it was a normal car I'd also replace the release bearing, but I seem to recall the 4 pot is a little odd in that respect? Chris
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I'd check that the release bearing moves freely in the housing, and if it did then I wouldn't replace it just as a matter of course. As the bearing is in a housing with a good oil supply from the gearbox they don't tend to give many problems.
 
edward1 said:
Hello Harvey. I fear that you are right and it is the clutch itself. One last thought though. When the car is already under way and doing say 30mph would the extra revs not be transmitted through the clutch more easily than trying to start off in 4th against the handbrake.
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I'd say yes, and TBH my thought is that you really haven't given it quite enough welly when trying to slip it out at a standstill.
But regardless of that, and it's not really worthwhile giving it more stick just to prove a point, if it's slipping at all, and it's not caused by a lack of free play, then the clutch is going to have to come out.
 
Harvey, Chris and Dave. A big thankyou to each of you for your time and trouble in helping me.
I will post the outcome in due course.
Do any of you have any last minute tips on taking the box out? I have the use of a Clarke hoist,a very substantial bit of kit which has been used to take an xk 150 engine and g/b out. Regards, edward1 (Peter)
 
Make sure you have the Rover workshop and spares manuals to hand! Readily available off Ebay. Harvey will no doubt correct me but I seem to recall the 4 pot appreciates the nose of the car being raised to assist with the angle you need to get the engine and box at. But then, I would have thought you'd only want to drop the box? I seem to remember the sump is bolted through to the box as well and the sump/crankcase/gearbox is intended to form a single unit for crankcase rigidity.

Get the manual! I will assist with scans if you get stuck.

Chris
 
Personally I'd remove the gearbox from underneath, leaving the engine where it is. The worst bit of the job is often the manifold to front pipe joint, and that has to be split whichever way you decide to do the job. If you intend lifting the engine/box out as one unit it's best to do it with the rear of the car jacked up and supported on stands. Alternatively you could just remove the engine leaving the gearbox in place, but refitting can be awkward lining up the 1st motion shaft into the clutch. But as I said before, it's gearbox out from underneath every time for me.
 
Would anyone care to post a quick list of parts to have ready prior to removing the gearbox from underneath?
I really need to do the job too, though in my case it's to swap the noisy 'box, rather than just to do the clutch.
It'll obviously make sense to renew any appropriate bushes, etc at the same time.

I'm pretty sure the manual only talks about removing the gearbox complete with the engine, so it's good to hear that it's feasible from below.
 
You could check the selector striker lever that fits into the selector rods from underneath before you remove the box and order one up if needed. There are also rubbers that mount the remote to the top of the box, but they rarely perish, but for the small cost involved it may be worthwhile getting those. (Series 2) Also the snub bush that the rear mounting goes through can often deteriorate through oil contamination so that can be checked beforehand as well.
 
I had to replace the gearbox in my car from underneath and it wasn't exactly easy, especially when you don't have the practice that Harvey has. :D
But i did not had another option as i don't have an engine hoist. To proceed you need to remove the propshaft, mid exhaust section, radiator fan, starter motor, gear lever fron inside the car, gearbox mounting, engine front tie rod and tilt the engine/box backwards as far as it will go. In my case (LHD car) i had limited space because the rear carb hit the brake fluid reservoir. I guess you won't have an issue with this. Disconnect speedo cable and reverse lights switch and after you remove all the bellhousing bolts (note their position first, they are not all the same) rotate the gearbox to bring the hump for the starter motor in the bellhousing up. At this point it is (realtively) easy if the car is over a pit or on a lift and you have someone to help you manipulate the box out of the car. If the car is just on stands and you are alone, maybe with a trolley jack like i did, it is a bit of a struggle. Refitting is the reverse procedure, but more of a struggle to align the box properly in position without letting it hang from the input shaft. I don't have fond memories of this.

You can look out for details in relevant posts in the gearbox section in this forum.
 
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