Clutch slipping on full load

[paydase]

Hi everybody,

Recently I noticed that the engine revs suddenly surged at WOT in 2nd or 3rd gears from around 3000 rpms (so at max torque).

Could it be a clutch slipping and an indication of it needing to be replaced? (I know that the clutch was serviced in the past, as part of a full rebuild of the engine and gearbox about 25 years and 10.000 km ago).

Or possibly an indication of oil contamination through a shaft seal (I recently changed the oil of my gearbox with synthetic Redline MTL that is known to have low vixcosity and I had not noticed the surge before)?

If a replacement of the clutch needs to be performed (would be done by my mechanics), how costly could it be (pieces and number of hours)?

Thanks for your help.
Serge

[mgcjag]

Hi Serge...you can test your clutch....engine running foot on brake......put in 3rd gear let clutch out......you should feel if clutch is slipping.......cost?....engine/gearbox out.....seperate. .fit clutch....replace.....Steve

[paydase]

Thank you Steve.

I did the test today.
Not sure it's conclusive...

First, I did not notice any strange behaviour when engaging the clutch at idle (no vibrations, no undue hard pedal, no modification of the pedal travel), also when driving at low speed and changing gears.

Then I drove the car during 15 mins to warm the mechanics and avoid the engine stalling when testing the clutch because of cold.
Car stopped, a couple of times, on 3rd gear, handbrake on, I slowly let the clutch out while trying to keep about 1500 rpm with foot on accelerator.
Result: twice the engine stalled!

So I am now confused...
I thought (and still think) that the behaviour of the engine/clutch slipping at full load on 2nd and 3rd (didn't try 4th) is a sign of a worn clutch.
Could it be that it is just the first signs of a clutch on its way out, still behaving correctly when doing the test as you said?

Now, I understand that on a 3.8 with Moss box, if I have to replace the clutch, I need a 10" clutch kit, coil spring type, such as offered by SNGB, including pressure plate, driven plate and release bearing. Could you confirm?
Also could you provide an indicative list of additional items that I shall also better replace in addition, once the drive train is out: oil seals, bearings, engine/gearbox mounts, etc.?
And finally, if possible, an estimate of the number of man-hours for the job to be done by my mechanic, I understand that it may be substantial as the whole drivetrain (engine and gearbox) has to be put out after disassembling peripherals, and put back in?

Thank you for your help,
Serge

[mgcjag]

Hi Serge...yes as you say re the clutch.....but i would wait till its dismantled to see what you actually have installed now...you never know whats been fitted in the past. .....a new spigot bearing in the end of the crankshaft would be reccomended......any other work should be assessed once dismantled....as per cost and time thats really up to you work out.........Steve

[Turnip]

It might be worth checking the gap on the clutch operating rod, in case it's is too small.
I had this problem, although the slippage started at around 4000 pm WOT, in 3rd & top.

Simon

[PeterCrespin]

Correct. First thing is check for movement at the fork before the release bearing presses hard against the pressure plate.

Then try flooring it in 4th or up a hill in third. The higher the gear the easier to provoke slip.

If correct adjustment doesn’t fix it then wait until gearbox is off and you can see whether m the flywheel is drilled for 10” & 9.5” before deciding what to buy.

[paydase]

Thank you for the advices.
I'll make the WOT test in 4th or uphill in 3rd.
Could the check of movement of the fork be done before engine/gearbox out?
And isn't the 3.8 engine normally mounted with a bell housing hosting a 10" flywheel and hence this normally drilled for 10" (although I understand that work on the engine may have replaced pieces) ?

[PeterCrespin]

Checking clutch adjustment is in the manual and should be a service routine item. Nothing difficult.

Yours is a late 3.8 and after 50-60 years you never know what has been fitted.

[Turnip]

Could the check of movement of the fork be done before engine/gearbox out?

If you're happy to put the car on axle stands and wriggle under it then it's not too difficult.
As Peter says, it's described in the manual.

If you find measuring the gap tricky then try just opening it up by one turn. That might make the difference if the problem is the rod adjustment.

Simon

[paydase]

Thank you again, sirs, I'll do that.