Clutch Release Geometry

[BarryS]

My 1992 Torslanda M47 5-speed gearbox has been swapped out for a good salvaged M47 5-speed which works perfectly. Unfortunately, I now have a clutch issue which seemed strange because the clutch was not disturbed during the gearbox swap. My original clutch release fork was reused, no damage or deformation. Clutch action was perfect prior to gearbox swap. There is no appreciable wear at the clutch pedal pivot and the clutch master cylinder is also perfect.

After a considerable time diagnosing the problem, I have concluded that it is due to the clutch release bearing fork geometry versus clutch slave cylinder stroke because the slave cylinder is being actuated beyond its proper stroke, thereby allowing hydraulic fluid past the seal. The slave cylinder has now been replaced with a new one but the same problem persists.

As a temporary fix, I made a clutch pedal stop to limit pedal travel and restrict the slave cylinder stroke which means the car is driveable, gear shifts are ok and slave cylinder doesn’t leak.

However, I pulled the clutch release fork out of the hole in the side of the bellhousing and discovered that the Ball Pivot in the replacement box is shorter than the original. Original is 30mm long and the replacement gearbox version is 24mm.

I managed to unscrew/remove the short ball pivot working through the bellhousing aperture but although screwing the original longer ball pivot into position was possible, it then seems to be impossible to get the release fork back into position.

Putting the release fork in place before attempting to screw the longer ball pivot onto its stud also proves to be impossible. So, short ball pivot back in and now considering what to do next. I don’t want to have the gearbox taken out again just to swap the ball pivots.

I assume that the shorter pivot was meant to have the plastic seat that clips over the ball with lugs clipping into the release fork in lieu of the spring clip that my release fork uses.

Now, it occurs to me that it may be possible to get a plastic seat (part no. 9163851) onto the short ball pivot and clipped into the release fork via the bellhousing aperture but would the plastic seat work with my release fork? This would obviously affect the geometry moving the slave cylinder push rod end of the release fork closer to the slave cylinder and would presumeably return my setup to standard hopefully curing the problem with the slave cylinder.

Now, although they look identical, there appear to be different part numbers for the release fork when paired with the metal spring clip or the plastic seat, so I am wondering whether the alternative version release fork has a larger dimple to accept the increased size of plastic seat on the short ball pivot or will the plastic seat still fit the dimple of my release fork? Anybody know for sure?

Additionally, other threads talk about making a longer slave cylinder push rod which sounds a simple fix but can someone confirm whether this will actually result in the slave cylinder piston sitting deeper into the slave cylinder when not actuated thereby allowing adequate stroke to prevent the piston seal popping out of the end of the cylinder when actuated?

Advice would be much appreciated – thanks.

[Bugjam1999]

Hi- an interesting problem, not one I have heard of before.

I have an adjustable actuator rod on my car, made for me by a friend. I put it on as the clutch biting point was right down at the floor, which some time later turned out to be caused by a very worn clutch pedal pivot point...

The detail you’ll be interested in is that the action of the slave cylinder remains the same however long/short the rod is adjusted to, the piston moves in and out the same distance depending on the clutch pedal movement no later what it’s starting point. Of course there are limits to this, the slave cylinder isn’t infinitely deep so in theory if the actuator rod was adjusted to a length that was too long, it wouldn’t be possible to fit it as the slave cylinder piston would be at the back of the bore.

All of which is a long winded way of getting to saying that I think an adjustable rod will solve your problem, and it’s a simple solution too as you say. If you have access to a lathe or a friend with one, I suggest you get one made up and try it.

Cheers

[Clifford Pope]

As far as I can recall, there are indeed several variants:

There are two kinds of operating fork/pivot set up. One just has the ball, the other has a plastic cushion. I don't know whether you can omit the plastic, allowing for the different geometry. I don't see why not.

There were also as you say two different lengths of actuating rod. I'm sure I've come across one that was adjustable. As bugjam says, the length of rod doesn't change the clutch operation itself, but it does determine the range of piston movement in the slave cylider, which is what you seem to need.

Other thoughts are:
There is a dished washer on the end of the push-rod where it engages with the fork. Has this been lost?
(My car once lost clutch operation while driving as the slave cylinder had momentarily stuck and the washer had dropped out and been lost. A passing AA man knocked up a replacement by hammering a depression in an ordinary washer)

If you don't have a longer rod you can easily make a temporary one to try out of a length of threaded rod or a bolt, with a nut and suitably contrived dished washer.

Check that the operating fork is not cracked or bending. They are known to be weak - somewhere here I remember someone welding on a strengthening piece.

[BarryS]

Thanks for the comments thus far. Agree that a longer and/or adjustable push rod should work but the Volvo parts manual does not appear to show any dished washer associated with the hydraulic clutch release bearing fork and slave cylinder push rod interface. There is one on the cable operated system though.

Here is an update and my initial plan of action.

I have confirmed that the Plastic Ball Pivot Seat does fit my Release Fork and with addition of a washer, overall length equals length of the long ball pivot – see below. (note that long and short ball pivots are both normally fitted with one washer)

Therefore, my intention is to fit the short Ball Pivot with two washers which, in conjunction with the Plastic Ball Pivot Seat, should set fore/aft position of the Release Arm exactly as it was when fitted into the gearbox that I replaced. Fingers crossed, this will solve the clutch slave cylinder piston/push rod over travel issue and I will update again with the result.

In the mean time, I am wondering what grease should be used with the Plastic Ball Seat as I understand that some grease can adversely affect some plastics. Any recommendations from experience please?

[nu11eaf]

I have read about this problem several times after people had swapped gearboxes in the landrover forum I also frequent, Depending on gearbox or year there are different slave cylinders (same slave cylinder but longer push rods) the correct push rod usually sorted the problem of fluid being pushed passed the seal due to the shorter original pushrod.