(Not) Good Vibrations
 

My '89 560SEL has developed an alarming front end vibration. It's somewhat intermittant, generally starts around 50mph and seems to be the right side front wheel.

The vibration stops when I drag the brake a bit, but there doesn't seem to be any wheel bearing play or pad kick back.

When I lift the car to check, everything seems normal and I can't find any play in the ball joints, tie rods, wheel bearings, etc.

I replaced the outer tie rod end (no play, but it seemed a bit more free than the others). I replaced the front shocks at the insistance of my local tire shop.

Any other ideas? Or should I just replace things one by one until I find the problem?

based on your description your problem is the brake reaction rod bushings.if you look under car you will see thick angled rod at approx 45 deg to direction of travel that starts at bottom of spring and terminates at body with two large round bushings supporting the lower side.these are sometimes called the castor joints because adjustment alters the castor.to check have car driven at 3mph while you stand by front wheel and have them stomp on brake .you will see the wheel move in the wheel well.

Correction
 

The units you refer to are on the W126 called Guide rod and bearing bracket, and the issue described does not match either units normal failure mode.

Suspension Guide Rod Replacement
on the 1985 300SD
http://www.peachparts.com/Wikka/W126GuideRod

http://www.detali.ru/cat/oem_mb2.asp?TP=1&F=126039%5F568&M=117%2E968&GA=722%2E323350&L=765%2E706&CT=F&cat=568&SID=33&SGR=030& SGN=02




Have a great day.

Answer:
 

#1. Have the right front tire balanced and inspected for shifted belt, bent rim.
#2. If the issue is still there, I would inspect the idler arm and ball joints; if they are good, replace the RF wheel bearings, (cheap insurance).
#3. Should the issue still be there, take it to your local MB dealer for inspection and diagnosis, it may be a major safety issue.