Rear belts keep getting chewed up

Hi, i am new to the forum and have joined to try to help my husband fix his mum's car. Wonder if anyone can help? She has a 340 GL, 'F', 1988, automatic, during the last year my husband has changed the rear drive belts twice, as they had gotten slack, and then slipped which led to them getting 'chewed up' on one side. My mother in law brought this to my husbands attention as the car seemed to rev up excessilively, with less speed.
He now needs another belt as it has happened again. Each time the belts have been replaced the car has been fine. On inspection of the belts prior to replacement the driver side belt is a lot more slack and thin due to it slipping. Does anyone have any thoughts as to why this should keep happening? Could the mechanism inside the centrifugal drums that pinch the belt when accelerating be at fault? Any thoughts would be really appreciated as my mother in law is lost without her car. Thanks in anticipation.

[Peter Milnes]

It sounds as if an imbalance has occurred between the two sides of the front pulleys. They have seperate piping to the vacuum connections. It would be a good idea to thoroughly check all the vacuum piping for leaks/splitsholes etc. It could also be due to the seals inside the pulleys being damaged so that the pulley no longer works as it should. German, Swedish and French have the belts at £72 per pair. Alternatively I have a complete gearbox unit (with belts) from a 66 which is the same gearbox as the 343. I live in South Wales, 7 miles from the M4 J34 and a similar distance from Pontypridd.

All the best, Peter

I agree with Peter but would add that it`s very easy to check the vacumm pipework without even getting under the car.

You simply need to disconnect the pipes that lead from the vacumm control valve to the transmission one at a time and blow down each one. You should be able to blow some air in before it gets hard and stops. When you stop blowing it should blow back at you.

If you can keep on blowing, you have a leak - either in the pipe work or the gearbox - or as is more often the case, in my experience, a pipe has become detached.

If you cannot blow any air in at all, the the mechanism that moves the pulleys under vacumm may be jammed.

If this is the case, I don`t know how much of a job it would be to repair - if indeed you could find somebody to take the job on. Might be best to get her a new one - you could pick up a nice 340 now for the price of a few pairs of belts.

Will Plummer