Volvo 340 and 66 Variomatic CVT Clutch Repair
By George Dickinson
Clutch wear and adjustment for the Volvo 66 and 340 CVT
(Diagram references are made to the Haynes 715 Workshop Manual)
There are only two items on a CVT needing periodic adjustment, namely the rear pulley gaps to maintain correct belt tension and position, and the clutch clearance.
The clutch is the less well known and thus more neglected of the two. The clutch is basically conventional in that there is a clutch plate gripped between a steel pressure plate and the rear face of the engine flywheel. However, there is a subtle difference. In a conventional car, the clutch is normally "closed" and the operation of the foot pedal "opens" it. In a CVT car, the clutch is normally "open" when the engine is at rest or turning slowly. As the engine speed increases, rolling centrifugal weights move outwards and press the pressure plate towards the flywheel to "close" the clutch. The weights are contained in. a domed clutch cover fixed to the flywheel, which encloses the pressure plate and clutch plate. Haynes 715, Fig 5.4, on p. 178 in the 1989 edition, shows the various parts, the flywheel being on the left. When the CVT clutch is open, there are clearances between the parts: (a) between flywheel and clutch plate and (b) between clutch plate and pressure plate. These clearances are necessary to prevent 'drag' before the weights move out to close the clutch. In practice, the sum of clearances is measured together, between the flywheel and the clutch plate, the (a) gap, because the clutch plate slides along the shaft to touch the pressure plate, closing the (b) gap during clearance checking. See Haynes Fig 5.4, the measured clearance being A.
Referring to the accompanying diagram, the difference in total thickness between a new plate and a fully worn plate is only about 2 mm, from 7.3 mm new to 5.3 mm worn. Clutch plates normally have riveted linings. If too much wear occurs before the plate is replaced, the rivets will damage the flywheel and/or the pressure plate. Mild scoring can be accepted (in practice, though not officially), but exposed rivets will soon cause irreparable damage to the steel surfaces of flywheel and pressure plate, requiring machining of the flywheel face and replacement of the pressure plate. 'The books' recommend a total clearance of 0. 1 to 0.3 mm, or 4 - 12 thou inches. In reality this is much too tight, and the clutch will drag. A dragging clutch turns the propeller shaft and makes it impossible to engage forward or reverse gear silently (or at all). A practical gap is 0.4 to 1.0 mm or 16 - 40 thou. inches. In other words a new clutch should be set to about 0.4 mm, 16 thou inches, and reset back before it has worn to 1.0 mm or 40 thou. The method of setting is described later.
First of all it is necessary to examine the existing clutch plate. For this, an opening or port is provided under the clutch housing, underneath the car. A small mirror enables the edge of the clutch plate to be seen. The engine will probably need to be turned to a suitable position to see through one of the gaps between the flywheel and the curved edge of the domed clutch cover (see later for turning the engine). The clutch plate itself can be turned by revolving the propshaft. Each half of the lining should be not less than 2 mm thick (see diagram), each half should be about the same, and the wear should be reasonably even right round the clutch plate. If the thickness of the plate is satisfactory, the clearance between flywheel and plate is next checked, using conventional feeler gauges. If the gap is greater than 1.0 mm, 40 thou inches, it needs adjusting without delay. If it is less, it can be left for the time being, though the nearer the clearance is to the practical minimum 0.4 mm or 16 thou inches, the better. It will be found that, as the clutch plate wears and the clearance increases, the engine speed needed for the clutch to engage will rise. This is because the weights need to move further to exert more pressure against the throw-off springs to cause the clutch to close.
Clutch adjustment is achieved by shims, shaped rather like boomerangs, Haynes Fig 5. 1, top of picture. They can be seen, edge on, from below the car. They are made in a range of thicknesses (see table) and are fitted in matching sets of three. A new clutch usually needs somewhere between 2.7 and 3.0 mm total shim thickness. A wearing clutch needs progressively less shims. The amount of shim to be taken out equals the clearance found less the clearance required. In other words, it is theoretically possible to calculate the shim change needed, though it doesn't usually work out exactly in practice. The table shows the thickness steps available, being every 0.1 mm except five between 1.0 mm and the approx. maximum of 3.0 mm. Before starting a clutch adjustment, it is worth buying at least a set of three 0.5 mm and three 1.2 (assuming that 1.5 + 1.5 are already fitted) or, preferably, a complete range (three of each) except perhaps 1.5. It is also worth checking the thickness of each shim with vernier calipers or a micrometer and writing it on with a marker pen. To change shims requires the engine to be turned, using a 19mm A/F socket on the pulley bolt at the front. The job is much less tedious if one person does the clutch work and another person turns the engine. WARNING: If the job has to be done with the car on ramps by somebody lying on his back with his body projecting forward under the engine, the spanner MUST NOT be left on the engine pulley bolt while not actually being used to turn the engine UNLESS there is a pan to catch the spanner if it falls off the bolt. The engine is easier to turn with the spark plugs removed. On Volvo 340 cars with full electronic ignition, an easy method of locking the engine against turning while the six Allen screws are released (see below) is to insert a suitable bolt or rod into one of the holes in the circumference of the flywheel, which can be seen at the very top of the housing behind the engine. Attach a piece of string to the bolt and tie it up to prevent it accidentally falling.
Each shim is clamped between the domed clutch cover and the flywheel by two Allen screws, shown in Haynes Figs 5.4 and 5.5. The Allen screws are (should be) very tight in the flywheel. A perfect, i.e. preferably new, 6 mm Allen key is required, in order to avoid burring a screw head (in which event you are in real bother, i.e. engine out; there is no scope for a Mole wrench!). To loosen a screw, first ensure that the hexagonal hole is completely clear of any debris. Insert the Allen key FULLY, tapping it in if necessary. Use a small diameter box spanner or a piece of tube to increase the leverage on the key. Then, pressing the Allen key firmly into the screw head with one hand to ENSURE it won't twist and damage the head, turn the Allen key anticlockwise with the other hand. The screw should release with a sharp "crack". Thereafter it will wind out fairly easily.
To minimise the tedium of engine turning, proceed as follow:
First full turn of engine: release all six Allen screws in sequence and wind them out a couple of turns (NOT right out). KEEP YOUR FINGERS OUT OF THE CLUTCH WHILE THE ENGINE IS BEING TURNED. During the second full turn of the engine: change one shim (or shims) at a time, one end at a time. The engine will need to be turned slightly back and forth at each shim position. (Remember, the total thickness of shim MUST be the same in all three positions). Third full turn: tighten all six Allen screws in sequence. Then check the clutch plate, clearance and ensure that the prop shaft is still quite free to turn without any clutch drag. If the clutch does drag, then increase the shimming to the next available step (see table), following the three-rotation sequences before After the clutch adjustment is completed, check the servo adjustment (see Haynes).
When the clutch plate has worn down to about 5.3 mm total thickness, it will need to be replaced. For a Volvo 340 this can be done from below the car with the engine in situ and the prop-shaft removed (see Haynes), but should only be considered if a pit or high hoist is available. For the DlYer with only ramps to raise the car, it is recommended to remove the engine to dismantle the clutch. For a Volvo 66, the engine must be removed, because the propshaft cannot be drawn off the clutch tailshaft (unless the whole transmission is first supported, unbolted and, drawn back!). For DIY engine removal, a suitable frame and hoist are needed, preferably a wire rope hoist rather than a (nylon) cord/rope hoist. DO PLEASE USE PROPER EQUIPMENT FOR ENGINE REMOVAL. Bodging and improvising are dangerous. The cost of an accident may far outweigh the cost saved by not having bought safe equipment. In any case, the equipment will cost less than garage labour charges. When doing this sort of a job, a pair of steel toe-capped safety boots and some tough industrial gloves are also a good investment. KEEP YOUR FEET OUT FROM BENEATH SUSPENDED PARTS (LIKE AN ENGINE). One benefit of having the engine out of the car and the clutch housing removed is that setting the shims is very easy to do and no engine turning is required. Clutch clearance checking and re-shimming when necessary are part of the prescribed routine maintenance. It is evident that they have all too often been ignored by garages. The clutch in a CVT car used for reasonable journeys (i.e. not just start/stop work; can easily last over 150,000 miles if appropriately cared for.
It has to be admitted that it really is a chore for an owner to check and re-shim using ramps for access, but with a pit or high hoist it is not at all difficult (i.e. for a garage) to do