300SDL Grinding/Roaring noise at low speeds
 

At low speeds at less than 20mph, I a soft roaring and grinding. Weird part is I ONLY hear it when I let off the throttle and let the car coast forward at very low speeds

I hear it from the front right wheel, my best guess is wheel bearings are going bad.

What kind of tools would I need for a job like that, I don't mind buying special tools if need be, unless they cost a fortune.

Will this procedure be the same for the 300SDL and front bearings?

http://www.peachparts.com/shopforum/diesel-discussion/206875-replacing-rear-wheel-bearings-w123-w126.html

The front bearings supposedly aren't that bad. There are several writeups on this site to do it. You shouldn't need anything really special or at least nothing that's not easily obtained.

If you have 1 bearing roaring, consider doing both of them.

Try to buy good quality bearings. Make sure they are not coming out of China. Not worth the risk.

This may be the most important part in todays world for that job.

I just did this job on a 1991 W126 350SDL. First we ordered SKF bearings but one side was made in China and the other was made in Japan. So, we didn't use those. Next we ordered FAG brand bearings and they were a combination of made in Germany, Hungary, and Viet Nam. I guess that's about the best you can get without spending big bucks, and the FAG bearings work fine in my 1980 W116 300SD.

It might be a bigger job than you think. You'll want to remove the bearing races in the hubs (the replaceable wear surface upon which the bearings ride). I highly suggest using a large brass drift (like a foot long bar stock) so that you can hit the races from the backside and drive them out. If you use a steel tool, you'll gouge the hubs and race surface. Someone had done the job before and gouged the race surface so that when they drove in the new races, they did not set squarely and no matter how tight the bearings were, there was still slop. So I had to carefully grind off the burrs with a Dremel tool and cutoff disc on the lowest setting so the new races had a perfectly flat surface upon which to rest.

When removing the races, hit one area, then 180 degrees of it, instead of one place only because removing them is a very slow process and at first it will seem like they are not moving at all. You have to alternate so that they come out evenly and not jam.

When driving in the new races, it helps to first put the races only in the freezer for a few hours and then pull them out one at a time, wipe the frost off of them, then quickly drive them into the hub with a bearing installer tool or using the old race on top so the hammer blows don't directly hit the surface of the new race. Make sure they are seated FULLY so the bearing adjustment doesn't change too much over time.

Of course, make sure the new bearings are perfectly clean and use a high quality high-temperature bearing grease. I prefer synthetic. Don't use low-temperature drum brake grease. Yeah, you're supposed to weigh the grease used in each bearing on a postal scale, but I make sure each bearing is packed well, each race is coated, the inside of the hub is coated, and the grease cap is filled up to just below where the "bowl" starts and call it good (if you overfill the cap, the excess grease makes it nearly impossible to install them). Just make sure you don't go crazy and put an excessive amount of grease in there or else the grease can overheat from too much pressure and oxidize.

When adjusting the bearings, I highly recommend getting a dial indicator and magnetic holder. Both are cheap but you may find only SAE measurement dial indicators at your auto parts store, so you'll to convert the metric measurements to SAE (I bought a genuine Mercedes dial indicator on eBay and a cheap magnetic holder). I believe you want the new bearings to be between .01 and .02mm. On my metric dial indicator that's 1-2 lines. You put the base of the magnetic holder on the hub (not the rotor), and rest the tip of the dial indicator on the end of the spindle with a little pressure on it, then grab the hub and pull and push it hard (without rotating it as rotation affects the reading because of high/low spots) and watch the needle on the dial indicator move. If you do it by feel, they will most likely be out of spec, but maybe good enough, maybe not. It's hard to tell.

FAG Brand parts. You'll need a 5mm allen key for the rotor, 18 or 19mm for the calipers. Also, take the car off the ground and shake side to side up and down and see if you feel play. If so, it's the bearing.

To do a wheel bearing, I do mine in 25 minutes. I press them in and out using sockets and a rubber mallet. No press needed. I also use a brake rotor to keep everything center.

When you tighten the bearings tighten the locking nut tight and back it off a 1/4 of a turn and make sure the wheel spins freely

Bearing Race Removal - Take to a Shop
 

If you've never knocked bearing races from a rotor hub, the sdl hub maybe an extra challenge due to the internal hub configuration leaving little inside race edge to drive against.

If one of those races has gotten real hot (and one has if its grinding) it can be a real pita to drive it out.

Run those rotors down to Parts Store / Pep Boys / Sears / Indy and for $20 have the races punched out and new pushed in.

The rest and the job will be fun. Just follow the OP's advice.

Bottom line....better the bearing be loose than too tight. Too tight and you'll cook it fast. A little sloppy you won't wreck it and you can cinch it up.


I like the dial method but have used the "feels tight minus 1/4 turn back" method too.

THANKS for the tons of information everyone, I'll take all into consideration.

Knowing my experience level (none) this will probably take me 3 days and 3 or 4 instances of backtracking during assembly

In most cases I can see it still not being hard to do. An old trick was to get the wheel off the ground. Turn the wheel slowly with a finger on the backside of the wheels suspension. Sometimes you can even feel a bad bearing. You always have the other side to compare to.

You might be on to something. Altogether, tools will cost me, $283. The special tool going for $100...

Can you get the hub assembly out without the special tool?


Surely there's a point where giving it too a shop will save money overall because you don't buy a TON of tools.

Ummm...step back a bit. Bearing noise doesn't usually come and go as you lift. It could be something else, like the fan rubbing against the shroud due to bad motor mounts.

I broke my fan shroud and it has been removed, so that's eliminated.

Did you even check the play yet of the wheel at the wheel side to side and up and down?

You don't need a bearing tool or any special tools!

No I haven't, but i' m going to buy a jack and find out today.

Bearings are TOAST. Massive lateral play (maybe other worn supension parts too), wheels don't move freely when spun, lots of resistance, also you can hear grinding when spun.

Now I honestly don't want to drive the car at all because how bad they are.