How do I know if I screwed up my wheel bearings?
 

Recently, I had just completed rebuilding about 75% of the front end on my '84 SD. The only remaining projects ore shocks and guide rod mounts. I replaced the old wheel bearings with new, packed them with mobil 1 grease. The hubs were tightened not with a dial indicator, but the old "tighten the nut and back it of a bit" technique. The car was driving great and felt much tighter. The guide rods still make a clunk but that's about it. LEt me get to the point: I was driving out about 30 miles and sort of noticed a rhythmic thumping. The thumping graduated to somewhat of a grinding/ scraping/ pulsting sound. It is especially mor noticeable when driving at parking lot speeds. It could be the brakes but I doubt it. I've never had wheel bearings die on me before so I'm not sure of the telltale signs. The tires aren't great and the old centra wheels have two 5mm spacers on them that used to be glued to the wheel but now I just fit them in place.
If it is the bearings, can the situation be rectified, or do I have to start back at square one?

Any and all help is greatly appreciated!

My opinion is you have to take them apart to make any judgments... the parts you refer to are not supposed to make any noise.... and most people consider the brakes an important item on an automobile....
Be sure to buy the crush rings if your car uses them before you take it apart...... and use the dial indicator... or proper alternative and tighten BY THE BOOK... or you will always feel uneasy about them....

Lift the front end off the ground, remove wheels, push pads back in calipers, and rotate the rotor. It must turn smoothly with minimal noise without the brake pads rubbing.

Any grinding, growling, or crunching indicates that the bearings are too tight.

The best way to set clearance is a dial indicator, and I strongly recommend one. Clearance is small, and cannot be felt when set correctly.

Lacking a dial indicator, the best way to set bearings (and I've done this for at least 25 years now) is to run the adjusting nut in until you feel resistance to turning the rotor. Not necessarily locked, but distinct resistance. Back the nut off until you can move the thrust washer easily, but will some light drag, with a screwdriver. Lock nut.

On the MB, you will need at least 1/3 turn, usually more to get the proper clearance.

If you then pull out and push back on the rotor, you mush not feel it move -- that is, no thump. If it does, they are too loose.

Chances are either you have bad brake pads or you got the bearings too tight, and they fried.

Peter

one more question
 

Thanks for the info. One other detail that I had left out was that I'd feel the hub after driving to see if it got abnormaly hot. The hubs (especially the dust cap) got warm at most. Would this correlate to tight bearings?

Assuming you are putting in a new crushable spacer.. which MB calls for new each buttoning up of the wheel...the reason you really need the dial indicator is that it will show you if you have crushed the spacer too much (easy does the nut tightening..I crushed it too far even being careful the first time)... just as bad as not tight enough....so borrow one once so you know it is right....

Crush spacer
 

Leathermang, what is this crushable spacer you mention? My 300SD doesn't have one. Performance products doesn't list one for the 126 chassis.:confused:
Jeff

Hopefully you don't have one... I don't have factory books for your car.... but my answer was also designed for anyone addressing wheel bearings... because most cars in the world do not have a set up like this...MB uses this method to create a NO clearance situation.... you put a new one in and crush it a SPECIFIED AMOUNT...thus your position on the axle and the clearance are set automatically...( if you don't screw it down too much ).....
Does it list it for the 1981 300 tdt for instance ? If not maybe it is only a dealer item....
But this is aside from the fact you need to take your system apart to evualate the source of the noise you hear....

my 83 has crush bearings on the rear only. I when I had a CV go bad it ruined one rear bearing so I had the shop replace both sides. Took some special tools besides the dial guage that I don't have and the cost was reasonable. I watched and they had to do one side three times because the mechanic got it to tight twice. My fronts I just did like any other wheel bearing when I repacked them last year. Just got them tight and backed off about a 1/3 till it felt right. 25k miles and no problems so I either got it right by feel or got lucky.

How does one replace wheel bearings in 300td
 

I have an 85 300TD and started to hear loud squealy noises from the rear. My husband thinks it's the bearings (on jacks the wheel can be spun only 1/4 inch and you hear this metal to metal squeal) so I stopped driving the car and we are considering doing the job as we have no good mechanics around here. We've only had the car a year and have done simple jobs on it like adjusting the valves, diagnosing the vaccum probs, and replacing the glow plugs but we aren't sure we are up to a job such as this. Any insight as to what tools we'd need, time estimates for novices doing the job and sites that may reference details on the process as well as anything else you think may help, such as what else we should replace while were into this, would be greatly appreciated. Also if we should check into other possible problems that could be causing this squeal.
Thanks much.
AKchick

AKCHICK,

From your description of only moving 1/4", I am tending to think that the parking brake is not releasing. Some PB Blaster penetrant, especially on the cables, might be what it takes.

If so, you are in luck because the rear wheel bearings take a couple of special tools.

There is a slight chance that you did not drive the new bearing races to the bottom. If so when you drove the car one was forced back to the bottom. Possible loose hub assembley now. Jack up and try to see if play now present. Happens once in awhile. A brand new bearing like anything else can go bad but not usually.