golfboy

I put new races and bearings in my 420SEL Friday night. Sunday I drove to work and back, when I got home I smelled a nasty "hot" smell and saw that the grease cap had blown off, taking the Mercedes center cap with it.

I don't know when it happened, but my best guess is that I drove about 10 miles with that cap off in snowy/salty/wet conditions.

First, anyone know why this would have happened? I filled the inside of the cap to the line with grease like the manual said, and it was fully seated.
And secondly, should I replace the bearings again, or just get another cap and repack the bearings?

.

Hattaresguy

Ok I am far from a wheel bearing expert. But did you tighten and pack them properly? I have never seen a bearing cap blow off, they must have been really overheated!

golfboy

I haven't seen that before either. I did pack the bearings and then put extra grease in and around the spindal and inside the rotor hub. Then the manual calls for almost an inch of grease in the cap before you put it on.

I had forgotten to put in the radio static suppressor, and pulled the cap, put in the suppressor and reinstalled the cap.
I'm wondering if the cap is a one-time install.
I'm not sure that it "blew off" as I described it, just that it's gone, along with the wheel center cap. It could have been off balance and wiggled off... I don't know.

I guess I'll pull the wheel this evening and see if the spindal/bearings are burnt. That'll tell me if it got hot... before or after.

schwarzwagen

depends on if you deform the dust cap.

did you tighten the bearings to spec also?

golfboy

Possible that I slightly deformed the cap. I used a rubber mallet to TAP it on... didn't pound it and couldn't see anything deformed.

As for tightening to bearing, I snugged the nut down until I couldn't turn the rotor (by hand) then backed it off 1/3 turn.

golfboy

Well, the bearings are definately shot. I can't even get the rotor off the car!
Pulled the wheel and the caliper then tried to pull the rotor/bearings... they won't budge.
The rotor still spins just fine, but the outer bearing won't come out.

I even remounted the wheel, and tried to use the extra leverage to wiggle the bearing out... won't work.
Is there a puller tool for wheel bearings?

Why can't ANYTHING be easy?

schwarzwagen

something out of the ordinary is going on here because the outer bearing should be removable quite easily. ie, with your fingers. sometimes the inner sealing ring doesn't want to free from the spindle, but even then you can get it free by just pulling on the rotor with some force.

golfboy

Agreed. I ended up buying new rotors (needed to be replaced anyway) and another bearing kit. Took a sledgehammer to the old rotor (not too hard) until the bearing broke free.
Spindle looks fine, but I still don't know what happened so I'm a little nervous about reinstalling the new stuff.

I need an alignment anyway, so I'm going to put it together, take it into my mechanic and have the alignment done and have him check the bearing setup.

mleskovar

Never done wheel bearings on a W126 but the adjustment technique you used is new to me. Is that the accepted method? Some wheel bearings need a slight preload but most are tighten until play is removed only.

schwarzwagen

there is a precise free play measurement spec from MB, but i doubt many of us DIY guys have micrometers. best rule of thumb is to back off 90 or 120 degrees.

golfboy

It was new to me too, but it's what was shown in my manual. I was hoping someone else would have a manual that would tell me if I did this correctly.
Unfortunately, there haven't been any responses about it.

Hattaresguy

I did my front wheel bearings just like you did, tighten them up and back off about 1/3 of a trun. 20k miles later and they are still fine.

Actualy according to the FSM you are supposed to weigh the grease. MB gets a little nuts sometimes but I guess on the Autobahn at 150+ you have to.

golfboy

Thanks man, that makes me feel better about it. I've been driving it around town for the last week, but I haven't had the nerve to go too far away from home until I knew I had it right.