Any help would be appreciated with this ongoing problem I'm having with my '89 420SEL:

Intermittantly, while the car is in motion (seems to only occur at speeds above 35MPH, though most frequently at highway speeds), something under REAR LEFT of the car whines quite audibly. It sounds exactly like a loose belt under the hood, but the sound definitely emanates from the rear of the vehicle. (My 7-year old has taken to calling it "the mouse under Daddy's car...)

The whining lasts anywhere from 1 second (a "chirp') to 15 seconds every time it occurs. That is, unless I let off the gas, in which case the sound dies down quickly. I also noted during the summer that turning the air conditioning on and off would sometimes start or stop the "mouse".

Final observation: the cold weather here in New York has definitely reduced the frequency of the squeals, but they still do occur.

All fluids are clean and filled; and the car is generally well maintained.

I suspect the tranny (or possibly the differential) given the location from where the sound emanates, but I really know very little about the innards of these systems. Shifts are a little rough, but no more so than before this problem started.

Has anyone experienced similar symptoms? I would love to know what I am dealing with here...

__________________
Eric

1991 560SEL-Euro (214,000 miles)
1989 420SEL (Retired from daily use at 325,000 miles; Use as donor vehicle)

Fuel pump or fuel filter?

The fuel pump and filter are rear RIGHT (aren't they), and the sound definitely comes from LEFT of center.

(Although it would be great if you're right... A filter or pump are a lot cheaper to replace/rebuild than a transmission!!!)

Problem really worsens (in terms of frequency) on longer drives. Anyone else have experience with a similar situation.

Is this going to be an expensive fix (i.e. a new transmission)? Or will I be able to tackle it myself?

I'd really appreciate some additional guidance here...

Thanks!

Hi there,
I'm not familiar with the 420, but does it have a center bearing on the driveshaft? It sounds like a dry center bearing to me... if it has one, get one of those long skinny needle grease tips and go under the bearing seal to grease it and see if the noise goes away. If it does, replace the center bearing! I had a Datsun pickup once that exhibited the same exact symptom, and I replaced the transmission before wising up and lubing the center bearing! At least I replaced a 4 spd with a 5 speed.

Good luck,
Richard Wooldridge
1982 300D/4.3LV6
1994 Ford Taurus (wife's car)
1988 Astrovan
1977 Jag XJ6L
Etc...

Thanks for the suggestion, Richard!

I'll climb under the "Queen Mary" over the weekend with my grease gun, check the bearings, and lubricate them as I go along.

Will let you know how it goes...

__________________
Eric

1991 560SEL-Euro (214,000 miles)
1989 420SEL (Retired from daily use at 325,000 miles; Use as donor vehicle)

Never posted the resolution to this problem... After checking everything I could think of (and everything you all recommended) under the car with absolutely no success, the path to the ultimate solution dawned on me.

Actually, a totally different problem with the transfer case in my wife's Jeep tipped me off... In short, just because a sound seems to be coming from one location doesn't mean it actually originates there: resonance really was playing with my ears here.

In the original post, I noted that the whine sounded just like a loose belt. Well... you guessed it: it was an under-tensioned V-belt on the air conditioning compressor. To me (and everyone else inside the car) it sounded like it was emanating from below. It wasn't until I asked my wife to drive and I stuck my head up and out through the sunroof that it became apparent that the squeal was from under the hood.

Upon rereading my original post, it seems so obvious; but then hindsight is 20:20!

Thanks for the support. Glad to report that this mouse has been trapped!:p

PS: What a pain in the butt loosening the fastening bolt on the tensioning pulley is! REALLY tight quarters in there, and the bolt abslutely refused to budge. With no other recourse, I eventually bit the bullet and bought the specially designed 10mm hex socket tool (117 589 05 07 00) to generate enough leverage to do the job...

__________________
Eric

1991 560SEL-Euro (214,000 miles)
1989 420SEL (Retired from daily use at 325,000 miles; Use as donor vehicle)