Hi,
My 1991 740T wgn M46 has an annoying vibration/drumming sound. Not noticed under heavy acceleration from a stop.
It is most noticeable in 3rd gear at around 3000 rpm (smooths out around 3500) & 4th at around 2000 (smooths out at 2600).
You hear it coasting in neutral w/ the clutch in, you hear it as soon as you start moving & when you slow to a stop.
Everything is tight underneath. New U-jts & the center bearing has about 5k miles. No oil leaks at trans or rear diff.
Trans. mount has similiar play to my 88-740 M47 which has no vibration issues.
Runout measured halfway btwn center brg & flex cplg is the same on both cars (0.010").
The only difference I see is my Turbo has twice as much drivetrain backlash as my 88. I can roll the driveshaft about 3/4" before the gears stop you.
Anyone know what the spec. for backlash is? FCP sells output bushing for auto trans. but nothing for M46. Anyone opinions?

Cheers ibs740

Manual trans in the car w/ the vibration problem/noise (M46)

Now I have my 88-740 winter beater running despite the dirty lying miserable Volvo shop (mickey moused every fix)that sold it to me. My fault too trusting. He did sell me my 740 turbo which has been great for 5 years now.

The 740 (M46) is going up on stands this wkend & I'll run the car & see what's shaken.

I'll let people know.

ibs740

The M46 has no bushing on the output,just two ball bearings.If they failed I think you would have an oil leak, possibly a failed OD and vibration.

I would check the front motor mts.

Make certain the U-joints are in the same plane.

Any missing balance weights?

Flex disc OK? Also there is a 3 legged locating plate that needs to bolt between the disc and trans. output flange. If this plate is attached opposite the driveshaft it will vibrate.

Haynes has diagram but this is easy to mis-interpret.

Shimming the center bearing up or down is covered in the faq's I believe.

Good luck!

Hi there,

just crawled out from under my 740, similar moaning noise which became worse.

So I put the rear of car (wagon) on jackstands , using a pole on the accelerator I ran the rear wheels up to speed until it started making that noise and observed, (from the side of the car), the output flange at the rear of the tranny was vibrating.

In short order it galled the output flange bearing area against the tranny bushing, luckily it didn't damage the rear tranny housing.
Mechanic quoted me $375 plus parts.

I picked up an output flange for $40 from the junkman, a rear housing gasket, bushing and seal for $12 new. This a known wear point, if you wait too long it can ruin the rear housing too, another $150.
A pic of the offending parts,
and one of the housing.

http://savoycatering.com/Albums/bread/Image15.htm#top

http://savoycatering.com/Albums/bread/Image14.htm

Either way, if theres noise there could soon be damage unless you track it down.
See if theres any play, side to side,up/down at the front of the driveshaft.

Is this a manual tranny only problem, or both manual/auto?