I've got a consistent vibration in my '90 300SE that happens at exactly 37 MPH and lasts until about 50-55 MPH, diminishing as I get there. It's very noticable and feels more like a 'vibrating bed' than a wheel vibration.

Any ideas?

Thanks

__________________
Marc Galassini

'93 300CE 38K Sold
'89 560SL 19K Sold
'91 300SE 191K Totalled 11/6/08
'90 300SE 90K

Could this be a harmonic which would indicate merely that you need to get one of your wheels better in balance?

Doesn't sound like a wheel/tire imbalance, those typically start at higher speeds and get worse the faster you go.

This does sound like out-of-round tires. This typically feels like an odd shimmying at surface street speeds, as if the pavement were slightly wrinkly, but fades away at highway speeds.

If the tires are substantially worn it's probably best just to replace them. Otherwise have them tested on a Hunter roadforce balancer to evaluate the runout in addition to the balance. This will tell you whether one or all are out of round and by how much.

- JimY

Here's a partial list of things to inspect....

1) Tire/Wheel balance or tire deformation
2) Warped rotor and/or sticky caliper
3) Motor mounts, transmission mount, differential mount
4) Ball joints
5) Steering damper
6) Idler arm bushings
7) Wheel bearing adjustment or excessive wear
8) Front shocks

All but the wheel bearings are likely to need replacement at that age anyway. If you haven't yet done your motor/trans/diff mounts yet, do them anyway as this will make a huge improvement in vibration, idle smoothness, etc.

-tp

I didn't realize you were talking about a '90 300SE, I was going by your handle. Guess I should read more closely.

The 300SE is VERY prone to having vibration issues when the motor mounts are shot. Also, the exhaust likes to sit on the idler arm when this happens.

After I changed out the mounts on my 300SE, it felt like I had a new motor.

If your motor mounts are shot, do them along with the trans and diff mount and your issue will likely go away.

-tp

That describes a worn driveshaft center support to a "tee". The worn support allows the driveshaft to turn in a orbit until it eventually gets enough speed where centrifugal force pulls it back to center, usually occurring and diminishing around the speeds you have listed.
Try having someone in the back seat to see if they can feel the vibration in the driveshaft tunnel area or have somebody else drive while you check.

__________________

90 300TE 4-M
Turbo 103, T3/T04E 50 trim
T04B cover .60 AR
Stage 3 turbine .63 AR
A2W I/C, 40 LB/HR
MS2E, 60-2 Direct Coil Control
3" Exh, AEM W/B O2
Underdrive Alt. and P/S Pulleys,
Vented Rear Discs, .034 Booster.
3.07 diffs 1st Gear Start

90 300CE 104.980
Milled & ported head, 10.3:1 compression
197° intake cam w/20° advancer
Tuned CIS ECU
4° ignition advance
PCS TCM2000, built 722.6
600W networked suction fan
Sportline sway bars
V8 rear subframe, Quaife ATB 3.06 diff