Is it necessary to replace wheel bearings?
 

To all, I'm about to embark on a total brake job for the 1991 560SEL, i.e. new rotors, new pads, new brake lines and flush replace the old brake fluid with new fluid and possibly rebuilding all the calipers with rebuild kits. The cars mileage is 175,000. I don't know if the wheel bearings have ever been replaced. I do have new bearing seals and was thinking of repacking the old bearings and putting the car back on the road. I've done some cursory research on the issue and it appears that the acquisition of several specialty tools are required in order to replace the bearings.

So......can I or should I repack the old bearings or should I take this opportunity to replace them? Or, I could take the car to a shop and have them replace the wheel bearings perhaps at less expense than acquiring the various tools required to replace the bearings?

Personally, I would simply wait until you are in there. Remove the old bearings and clean them up, and then examine them, and the races (they will still be in the hub) and if they are not pitted, scored or discolored, then simply repack them and reinstall, properly adjusting them. Wheel bearings are pretty robust, and if properly maintained (period cleaning, regreasing and adjustment) they can last hundreds of thousands of miles.

If on the other hand they show signs of excessive wear, then buy the bearings and take them and the hubs to a machine shop, they can easily R&R the outer races for you for a modest sum.

If you're otherwise disinclined to try that, then just take all of your parts to the shop and have them do all of it. The labor to R&R the wheels seals mostly includes the labor to R&R the brake parts, since all of that has to come off to get to the wheel bearings.

All of the above applies only to the FRONT wheel bearings. The rear wheel bearings are not separately serviceable and are simply replaced when they start making noise.

Good luck.

you wont need any special tools to service the bearings, an old can of cerelac or coffee some gasoline or acetone to wash them and some grease to pack them.

Your autozone/orielly/aap have a bearing press assortment for rent (basically free) which makes the job a breeze, you only need to buy a brass punch to remove the races

In your car the wheel bearings are packed anytime the brake disc requires change as the disc is inboard.

How would the wheel bearings become scored or bad? From lack of grease? If so, then you probably don't need to worry about that. I recently opened up a w201 in a junkyard that looks like it had been sitting for a year + in there with 290k and I pulled the wheel/bearing/hub out and that thing was super packed with the green OE grease....a ton of it! I took it apart because I thought about doing mine, but after seeing how the one in the yard looked, I figured I was ok on that front. No dust or any dirt in there either and this is the desert with huge sand storms.

Make sure you have a DTI / clock gauge before you start the wheel bearing job - read through the procedure in the FSM

For the fronts, no special tools required, just care when removing/installing the races that you don't score any surfaces.
You can borrow bearing race drivers from Autozone if you want.
Bearings are robust, but also cheap. I replace mine inthe 100-120k range. Good prices at NAPA for some MB models - the house brand is made by SKF.

Typically, bearings fail because the seal fails. The seal is a wear item. If the bearing looks good, repack it with new seals. Most of the other bearing failures are due to poor practices when servicing a bearing, such as letting dirt in, improper preload, and damaging the seal or not seating it square. It doesn't take much to shorten the life of a bearing. One must be nothing less than perfect when servicing a bearing.