Clutch not releasing

[Dearg1275]

I have a problem with a newly built engine and gearbox. Seemingly it is the clutch not releasing. These are the symptoms and what has been tried so far.

Back ground- all hydraulics are new and bled convincingly. Standard pre Verto flywheel and pressure plate. AP clutch plate. Original arms and plunger with some wear but not excessive.

When the engine is not running all gears are easily engaged. If fourth is selected it is possible to turn the engine by rocking the car back and forwards.

With the engine running all gears just grate and will not engage.

We have tried backing off the over throw stop to eliminate this preventing the clutch from moving. We have tried progressively screwing out the adjustment stop from it’s correctly set position.

It seems likely that the clutch plate is either stuck on the primary gear splines or is some how stuck to the flywheel or pressure plate.

Has anyone any other suggestions before we dive in and pull the flywheel assembly?

I’m sure this has been discussed before but can’t find the thread.

Thanks D

[Polarsilver]

Many & including me (on some past occasions ) just add about 1/4inch in length to the Slave Cylinder Push Rod = sorted

[Dearg1275]

Yes, good idea. We will try that trick before going further. It’s not an elegant solution but does point to where the problem might be. If the clutch then works it’s all down to wear in the linkages.

Thanks for jogging the memories.

D

[johnv]

I had that and I think it was down to the plate sticking on the primary gear splines .. I took it back apart and cleaned up the spllnes with 600 grade ( I think) and used red rubber grease .. it solved the problem, so I'm guessing it was the cause!

[Andrew1967]

If the ball on the end of the clutch arm and the plunger has any wear it will greatly reduce the operating effectiveness of the clutch.

Adding extra to the pushrod simply masks this problem.

[Peter Laidler]

Andrew is dead right of course. Like lengthening the push rod, bending the arm '....a bit...' is also a palliative and not a cure

[imack]

Primary gear and idler gear shimmed correctly?
Possibly flywheel going too far up the crank taper and pinching 'C' clip and backing plate and reducing/eliminating primary gear clearance.

[mk1]

All suggestions above are good, is it a lightened or standard flywheel / backplate?

[Dearg1275]

All suggestions above are good, is it a lightened or standard flywheel / backplate?

Standard pre-verto flywheel and back plate.

D

[Dearg1275]

Primary gear and idler gear shimmed correctly?
Possibly flywheel going too far up the crank taper and pinching 'C' clip and backing plate and reducing/eliminating primary gear clearance.

Yes, I always make a point of getting this right and checking the primary gear spins easily.

D

[Dearg1275]

Andrew is dead right of course. Like lengthening the push rod, bending the arm '....a bit...' is also a palliative and not a cure

As I sort of suggested it may not be a good permanent solution but it would indicate if the problem was wear related before taking everything apart. I’m all for avoiding more work than is necessary. One the problem is diagnosed a permanent cure can be effected with new bits.

D

[ricardo]

How was your diaphragm spring and straps when you assembled the clutch? I am just trying to visualize things and thinking thw problem might be related to the spring having just slight pressure against the flywheel and/or the straps pulling the backplate back against the disc.

[AndyPen]

Just to check, has the flywheel been skimmed at all? If so, was the backplate skimmed to match?

[iain1967s]

For the quickest way to determine if it’s a problem with excessive wear in the linkage, get a 7/16” AF Acorn nut and slide it over the end of the slave cylinder pushrod. It’ll space the rod out about 1/4” from the piston without having to faff around with building it up with weld.

[1071 S]

Or even easier.... peel back the rubber boot on the slave, have an attractive assistant floor the clutch pedal.

Does the slave piston run up against the C clip at the outer end of the slave bore??? (You may need a torch and mirror to see properly.)

If it does, you need to bend the lever/add length to the slave rod.... which will allow extra compression of the clutch spring. If there is still travel left in the bore, then such fixes will not make any difference.

Cheers, Ian

[Dearg1275]

Great suggestions as usual from this forum. The problem is on hold while a holiday is taken and hopefully enjoyed without fretting about a clutch back home. Just got to come back refreshed with a clear mind and positive attitude.

All further suggestion will be gratefully received though.

D

[imack]

Primary gear and idler gear shimmed correctly?
Possibly flywheel going too far up the crank taper and pinching 'C' clip and backing plate and reducing/eliminating primary gear clearance.

Yes, I always make a point of getting this right and checking the primary gear spins easily.

D

Did you check that the primary gear spun freely once the flywheel was fitted and torqued?
You say the gearbox was rebuilt, we're the gears able to rotate freely on the mainshaft once fully built and the pinion nut torqued? Not uncommon for baulk rings to be a knats too wide causing the individual gears to bind on them and cause difficult to impossible gear change.
Can you start the car in gear? How does the clutch bite point feel then?

[Dearg1275]

Primary gear and idler gear shimmed correctly?
Possibly flywheel going too far up the crank taper and pinching 'C' clip and backing plate and reducing/eliminating primary gear clearance.

Yes, I always make a point of getting this right and checking the primary gear spins easily.

D

Did you check that the primary gear spun freely once the flywheel was fitted and torqued?
You say the gearbox was rebuilt, we're the gears able to rotate freely on the mainshaft once fully built and the pinion nut torqued? Not uncommon for baulk rings to be a knats too wide causing the individual gears to bind on them and cause difficult to impossible gear change.
Can you start the car in gear? How does the clutch bite point feel then?

The gearbox was built by Guessworks and John has a good reputation for getting things right. Naturally I checked it over and all seemed fine. Fitted up with its remote everything selected easily and all the gears spun freely.

As to the primary gear flywheel interface, I have to say that I didn’t trial fit the flywheel with the primary gear in place. As it was a standard flywheel and had seen previous successful service, I didn’t consider this a possible issue. It’s certainly something I will now make a routine for future builds especially with unknown/non standard flywheels.

Thanks

D

[Dearg1275]

An up date. The problem is now solved but I thought it could be useful to share how we found the problem.

A. We checked that there was enough travel on the hydraulics. Fine
B. Checked the overthrow stop was backed right off and there was a gap at maximum travel.
C. Wound out the adjustment stop
D. Took off the timing mark inspection plate and turned the engine until the corner of the diaphragm spring showed. Fully pressed the pedal and observed. Result no movement at all.

These quick and easy steps showed that the problem is out side the clutch/primary gear set up because there is nothing to stop the pressure plate moving away from the flywheel and clutch plate (unless they had become completely fused together - possible but not likely on a new build).

The clutch arm was duly removed and the ball end was found to be completely bent back although there was little wear on the ball itself. Replaced with a new Minispares arm everything was back to normal.

Thanks for all the suggestions. All things to watch out for on any new build. This time it was an easy fix.

D