Volvo 760 vibration

[Aubergine S70]

Hi, I’m having a few problems with my 760 turbo automatic. At around 60 MPH the car makes a strange humming noise and a vibration. So far I’ve replaced: propshaft centre bearing, rear gearbox mount, new tyres, rear axle bushes.

I had this problem a couple of months ago and a member suggested slackening the mounting bolts for the propshaft and running it and then tightening the bolts. I’ve done this and has made a little difference.

It seems to be coming from the drive line somewhere. When it does it and I put the car in neutral it’s still there.

However when the car is stationary and is in park or neutral a little whiring noise can be heard from the gearbox/ bulkhead area but goes away in drive or reverse. There’s also a little whine in 1st gear when setting off or slowing down.

I’ve also replaced the rear shocks and springs as the nivomats failed and still no difference. I also drained the gearbox and cleaned the filter all with new oil and still no difference.

Any information will be appreciated

Thank you

[capt jack]

Not sure if the 760 set up at the front is quite the same, but when I had this with my 1997 S90 it turned out to be the lower wishbone bushes. The cure was two new lower wishbones.

Jack

[AllHailKingVolvo]

My 240 did this and it drove me nuts trying to isolate the issue. Turned out to be a worn propshaft UJ, had it replaced and it was quiet as a mouse.

Boring tech bit:

It tends to be diagnosable as a UJ if it happens at a specific speed rather than at a specific rev point in every gear, as the propshaft speed increases relative to road speed rather than rising and falling with the different gear ratios, and the worn UJ sets up an oscillation that at a specific speed aligns with the inherent resonant node of the propshaft itself, making it ring out. Usually if you are travelling above or below the speed that triggers it, the sound goes away.

Hope that helps!

[Laird Scooby]

Sounds like the gearbox extension housing bush to me, also have you checked the ATF level as what you're describing from the front sounds horribly like torque converter cavitation.

Do you know whether you have the ZF box (P-R-N-D-3-2-1) or the AW (P-R-N-D-2-1 and an overdrive button on the side of the shifter)?

Also you shouldn't really select N whil driving at speed, it can cause major problems with the box!

[Aubergine S70]

Hi, thank you for the information.

Ive had the car on a MOT shaker plate and all the front arm bushes are solid no play, they’re the originals but aren’t cracked or damaged. I’ve just had new genuine Volvo track rod ends fitted new tyres and tracking. The rear trailing arm bushes are good also.

When I got the centre bearing changed at a professional shop they said the UJs were all good and didn’t need balancing so they just changed the bearing.

The car is fitted with a ZF box. The noises I can hear are from the torque converter area I now can confirm and it makes sense. I’ll check the levels when hot and running and possibly buy a new filter from Rock Auto in the states.

Thank you

[Laird Scooby]

Originally Posted by Aubergine S70

Hi, thank you for the information.

Ive had the car on a MOT shaker plate and all the front arm bushes are solid no play, they’re the originals but aren’t cracked or damaged. I’ve just had new genuine Volvo track rod ends fitted new tyres and tracking. The rear trailing arm bushes are good also.

When I got the centre bearing changed at a professional shop they said the UJs were all good and didn’t need balancing so they just changed the bearing.

The car is fitted with a ZF box. The noises I can hear are from the torque converter area I now can confirm and it makes sense. I’ll check the levels when hot and running and possibly buy a new filter from Rock Auto in the states.

Thank you

Forgot to ask - what ATF are you using?

[Aubergine S70]

Hi, I use Dexron 2

[Laird Scooby]

Originally Posted by Aubergine S70

Hi, I use Dexron 2

That should be fine so i'd definitely chek the level. Be aware there are two marks on the dipstick, a cold and a hot mark. The hot is higher. Depending which dipstick you have, you may have two holes in the dipstick, one lower than the other or two lines, one either side or possibly two lines on the same side with hatching in between.
Hot and running after selecting each gear then back to P in between, pull the dipstick out, wipe it cean with a lint-free colth, reinsert all the way and immediately remove and read the level. Top up if needed.

Also worth dribbling some of the fluid off the dipstick onto plain white kitchen roll and checking the colour. Should be pinky-red.