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

:>)

"Is the OD always on by default?"

Not quite. OD is always enabled (that is, permitted) when the ignition is on UNLESS the orange indicator is illuminated.

OD will come ON after you've reached highway speed in 3rd, it's not floored (the kickdown cable's not pulled), and if the orange light is out.

"The manual says that everytime the car is started, the OD will automatically be engaged."

This doesn't really make sense -- you don't have OD in first gear, for example.

"...OD off and turn off engine, the OD will engage upon the next start up..."

Yes, the OD relay will reset itself and automatically enable OD when you next turn on the ignition.

"And when it is engaged, can I still drive at very slow speeds, like 5-25mph?"

Yes, but I think your tranny automatically shifts out of OD (back to 3rd) at around 40 mph, more or less. My '86 245 shifts into OD at 45 and out of OD around 40, +/-.

99.9% of the time you can forget all about OD and the pushbutton.

--
Don Foster (near Cape Cod, MA)

Unless your kickdown cable is binding or out of adjustment the overdrive in you automatic transmission will not engage until around 40-45 mph even when light on the dash is off. Having the overdrive light OFF on the dash merely indicates that when you are up to speed the overdrive will engage- it will not shift into overdrive before that time. When the light is on it means that no matter how fast you go the overdrive will not engage. The only real reason to turn the overdrive off (light on) is when towing or carrying heavy loads on inclines that might lug the engine if it was allowed to shift into overdrive. I leave my overdrive on all the time as is true with most people.

Randy