I'm looking at a 1991 740 sedan that has a worrisome vibration in the drivers seat. Owner has taken it to a Volvo dealer service center twice to try to track it, they couldn't find the cause. The car is clean and the engine seems to run smooth and quiet, looking at it and listening under the hood. But it feels like you're in a vibrating chair. It's not really a shudder, just quite noticeable. It's stronger when shifted into drive, foot on brake. Owner says vibration goes away at road speeds. I didn't have a chance to drive it.

Owner says he replaced the motor mounts, didn't help; and a couple of controls around the engine. That didn't help. The engine's timing belt cover is missing, belt is said to be new. Hmmm. Could it be that the old belt failed, shattering the cover and messing up valves? But then, would the engine start easily and run smooth and quiet? Does the 740 have an interference type engine? I'm puzzled. Should I be concerned? Knowing something about mechanics, I assume that anything that vibrates tends to get worse, not better over time. Any insights will be much appreciated!

JimBee

 

The 740 is not an interference engine, so if the timing belt breaks, it won't damage the valves and/or pistons. Under the driver's seat, huh? The main fuel pump is under there. Just a thought.

Oh, you might be interested in www.stepbystepvolvo.com.

 

I'm working on my own bit of weird vibrations out of my 1992 740 wagon. I need to get up under it this weekend and start beating around on crap and shaking things to find out what is loose.

 

check drive shaft carefully looking for ruined carrier bearing or evidence of rust/play on universal joints

 

How about the exhaust touching part of the body somewhere? Since the vibration is only when the car is stationary with the motor running, that eliminates the driveshaft and other driveline parts. Once it gets going the geometry changes and other noises would cover up the problem anyway...

 

i had a similar vibration in my '91 740. i could feel it really bad when in gear but stopped. sometimes it would disappear at road speeds, sometimes it would be worse. it usually was worst right before it shifted (auto). turned out to be transmission mount. it's such a smooth ride now.