440 CVT Auto gearbox

[mollusk]

Evenin' all,

Situation normal - confusion reigns over the CVT.

Very difficult to find any information on the 400 series CVT - I don't know of any aftermarket publications that cover the subject and the Volvo factory 'green books' have long been unavailable. What info the main stealers have is computer based.
I will try to clear a little of the fog !!

Firstly the CVT in the 400 series is nothing like a 'conventional' automatic gearbox and nothing like the twin 'rubber' belt drive system of the 300 cars. (the only similarity with the 'Daf/Volvo 300' CVT is both types use a belt/s driving one or more pairs of variable diameter pulleys).
The 400 series has never been fitted with the rubber belt, twin pulley system.

The only 400 series cars to have the option of a CVT were those with the single point injection B18U engine (1.8lt).

As simply as I can describe it, the system works, by giving a seamless, infinite number of gear ratios (between set limits) by varying the diameter of a driving pully linked to a secondary pully by a belt of steel blocks (several hundred) carried on a laminated steel band (when together it all looks like a cross between a car 'fan belt' and a expanding watch strap!!). The whole package is enclosed in a transmission case which is oil filled.
The 400 CVT does not have a clutch (as the 300 system has), nor a torque converter (as has a conventional automatic). Instead the transmission is linked to the engine by a torsional vibration damper fitted to a modified engine flywheel.
Drive take up (and 'in gear creep') is through a multi plate, hydraulic, forward
clutch unit inside the gearbox casing. This clutch is operated by, and bathed in the gearbox oil - it is engaged by pump generated oil pressure controlled by a cable linking the throttle quadrant with the gearbox. (like a so called 'kick down' cable in a conventional auto box). To effect reverse, a separate reverse clutch engages an epicyclic gear train (reversing the direction of the variable driven pulley).
'Up shifting' is achieved by 'squeezing' the halves of the driven pulley together causing the drive belt to 'ride up' (effectively changing a small wheel turning a big wheel (low gear) into a big wheel turning a small wheel (high gear). The secondary pulley 'simply follows' opposite to the driving pulley. The secondary pulley passes the drive to a differential (conventional) and through driveshafts to the wheels.

343GL - your description of the problem initially sounds like a forward clutch failure - but reverse would be ok (different clutch) however if you have a pressure pump problem this would affect both clutches. Its is just possible you have a problem with the torsional damper that links the engine to the gearbox but I doubt it.
One possibility is a problem with the cable linking the throttle to the CVT - this controls oil pressure, which would affect clutch engagement. Note though - low oil pressure would also reduce the boxs' ability to change up (you would seem to be stuck in low gear).
The snatching you describe definitely point to clutch drive take up problems (most likely oil pressure related) rather than a pully and belt problem (pulleys won't move until you open the throttle).
If I had to make a suggestion (diagnosis VERY difficult at long range) I would go for a failing pressure pump - probably spreading contamination around the box. (if you look at the oil on gearbox dipstick can you see little silver particles in the oil). But do check the 'kickdown' cable first.

I hope the above makes some sort of sense,

Good luck - Mac. (mollusk)