It might be helpful to know more about why have an overdrive, and why is it called that? It's sort of basic to me since I started driving when all there was an automatic or a 3-speed stick. Period.

In most of the stick and auto Volvos the highest non-O/D speed is DIRECT drive, that is the drive shaft speed is the SAME as the engine speed, less any slippage from the torque convertor. That reduction ratio is called 1:1, the lower gears have the drive shaft speed much LOWER than the engine speed. Check your owner's manual for the reduction ratios of the lower gears.

The horsepower needed at cruising speeds is less than the hp developed by the enging at a high rpm. It's because of the relationship between road speed, rear axle ratio, and engine speed causes the engine speed to be actually higher than needed.

So, what to do to keep enough hp for cruising speed, but have the engine rpm's lower? That would help in fuel efficiency and engine wear.

The overdrive gears allow the drive shaft speed to be OVER the engine speed. Thus the name. On the AW70 the engine speed in o/d is about 20 percent lower.

With a tach it's easy to see by inhibiting the overdrive until the rpms hit 3000. Then allow the overdrive to engage and see the rpm's drop about 20%, down to 2400. The road speed doesn't change.

However, at the lower rpm the engine develops much less hp, so if the car requires more, like passing or going uphill or towing, the o/d can be kicked out by the push button or the kick-down cable.

Long, I know, but I've always liked to have some idea of what's going on down there. Maybe some brickster will post a horsepower and torque chart for the B230F. Having an idea of that has helped me a lot.

Regards,

Bob

:>)