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Vibration in 1993 Volvo 940

Hi, I have a 1993 Volvo 940 that seems to have developed a curious problem...for about the last three months, it has started to vibrate at high speeds (60 MPH and over). This all the time now, no matter what the road conditions are like. My first guess was just the car's aerodynamics (it is kind of a big box), but if I press the towing mode button, which disables third gear, the engine revs in about the

4000-5000 rpm range, but the shaking stops.

My local mechanic says it is most likely caused by worn front tires, but they were replaced three weeks ago and I have noticed no difference. I don't use premium (91 octane) fuel as the owner's manual recommends, because of the prices I use regular 87 octane, but that shouldn't cause the car to shake at high speeds, right?

The owner's manual also says that low power steering fluid can cause vibrations...I haven't had a chance to check that, but at a free diagnostic clinic the dealer told me that I should never have to add power steering fluid and that it was most likely caused by a bad oxygen sensor -- I know enough about cars to know that that really doesn't sound like the cause.

Any ideas?

Reply to
Robert
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From experience of this fault I would immediately inspect the rear wheels and tyres (tires). It can be as simple as a thrown balance weight and as complex as a tyre (tire) with a bad carcass or even a buckled rim. Imbalance over around 65 mph plus is down to rear wheels/tyres (tires)being badly balanced, whereas imbalance at around 35 mph is usually the front wheels/tyres (tires).

All the best, Peter.

700/900/90 Register Keeper, Volvo Owners Club (UK).
Reply to
Peter K L Milnes

Need more information: You use the term vibration at the beginning of your post, then later characterize it as shaking.... if it were shaking does it manifest itself in your butt, or in the steering wheel? tire balance, separated belt in the tire.... bushing, tie rods.... alignment? and did the new tires have any effect on this condition? If you ran the car up in rpms momentarily while parked what happens?

Reply to
Ed

Its probably closer to shaking...you can feel it throughout the entire car, so it's not just in the steering wheel. The new tires (all four new) did not change a thing, and they were balanced and realigned as they should be. When I run the car up in rpms while in park, nothing signifigant happens. The engine revs, but the car does not move or shake from side to side as some others do, so it really has me confused. Thanks for any help you can provide.

Reply to
Robert

if you feel the shaking in the steering wheel the "rule of thumb" is to suggest you focus on the front tires/front suspension.

if you feel the shaking in your butt (through the suspension to the car frame to the car body to your car seat), then focus your attention on the back tires/back suspension.

In order of simple-to-difficult and inexpensive-to-expensive:

  1. You mention some new tires - don't rule out a bad or "out-of-round" tire that can't be balanced, including new and old tires.
  2. Make sure all tires are balanced (after completing step 1).
  3. If problem persists, have front-end-alignment.
  4. If problem persists, have steering/suspension specialist inspect and repair/replace all worn steering joint/bushings, then all all suspension joint/bushings, then all worn shock absorbers and strut cartridges.

That covers it, from soup to nuts.

Reply to
Pat Quadlander

Thank you all very much...I will do these things until the problem is fixed. Look for a reply when it is!

Reply to
Robert

You said a gear change seems to get rid of it. It could be a torque induced vibration on the drive shaft. I noticed at certain revs on my over boosted

940 Turbo that the drive shaft would vibrate even though it is generally in good condition, changing the boost to normal eliminated the problem.

So it could be that one of your drive shaft bearing or couplings is worn.

Another thing to try is putting the car in neutral or lifting off on the accelerator, changing revs etc.

Reply to
Tony Stanley

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