Rear Axle Wheel Bearing Grease Fittings for 280SL?

[WillS]

I'm repacking the wheel bearings and renewing the axle & hub seals in my 280SL rear axle. Something I found that was interesting and disturbing is that both wheel bearings (and the wheel bearings on another axle) didn't have grease in them but were running fine. Do they stay lubed from the very little bit of axle oil that gets past the axle shaft seal?

To deal with that situation, there appears to be a nice little spot to install a grease fitting in the axle tube to allow greasing of the wheel bearing. There is an annular 45 degree surface between the axle shaft seal and the wheel bearing outer race seat that I could install a 45 degree grease fitting and vent at the seven o'clock and one o'clock positions, respectively (see attached photo). This should allow fairly easy access to the grease fittings with a grease gun.

Has anyone done something like this? Is it a bad idea for some reason? On the good side, it would allow easy greasing of the rear wheel bearings, which we all know are a pain in the behind to do. Would appreciate input on this idea, it'd be great to be able to grease my rear wheel bearings easily, but don't want to create other problems.

[Benz Dr.]

I've done that before and in pretty much the way you described it.
I think there would be a desire to grease the bearings far more often than what's required and that's why MB didn't go this route. Once every five years might be enough but not at every greasing interval.

If there is no grease left in your bearings it was washed away by the gear lube. These bearings would probably run OK in either lubricant but you can't always depend on there being enough gear lube getting by the seals to work properly.
IN fact, it's not supposed to get by the seals at all and it can cause all sorts of braking problems on drum brake axles once it does. Not to mention the mess it makes when it starts leaking past the outer seal.

[WillS]

I guess if the axle seal is leaking enough to wash out the grease, it's also enough to lube the bearing. Then if the hub seal fails it will show on the outside of the hub indicating the need for repair. Do you still install grease fittings if an axle reseal/wheel bearing pack job comes up? Sounds like you might be saying it isn't of all that much extra value to do.

[Benz Dr.]

I haven't been lately. I did my own car like that several years ago but I'm not driving the 190SL right now. I think MB says the wheel bearings should be done about every 50,000 miles so it's not like it would be coming apart very often.
If I'm doing a rear brake job ( on drum brake axles ) I sometimes pull the axle out to have a look since it isn't that much extra work after the shoes are off.

[WillS]

Thanks, appreciate the benefit of your experience. I'll just pack the wheel bearings well and call it good.

Wil

[stickandrudderman]

The wheel bearings are by design lubricated by the axle oil. The set up gives very reliable service save for the seal failure as described by Benz Dr. However this seal failure is rarely sudden and so imminent contamination of the brake shoes by the leaked oil should always be spotted early if regular inspections are employed.

[waqas]

The wheel bearings are by design lubricated by the axle oil.

The inner axle seal is supposed to keep the bearing isolated from the oil. The bearing is supposed to be lubricated by just the grease. If there's a leak in the inner seal, the grease is washed away by the oil, leading to eventual bearing failure.

Am I wrong in this understanding?

[ja17]

Hello Waqas,

I think you got it right. If the bearings were designed to run in gear oil, MB would have not had the inner seal. 

[Larry & Norma]

Did mine earlier this year, replaced bearing and both seals. I packed the bearing with bearing grease.
Pretty sure there is something in the technical manual about it.

[jacovdw]

...If the bearings were designed to run in gear oil, MB would have not had the inner seal. 

There is definitely an inner oil seal to separate the grease packed bearing from the oil in the differential.
The amount of grease needed per side is about 35 grammes.

I have not found any clear indication as to when to clean and repack the bearings with grease, but in the Service Manual mention is made to discard bearings that has done 100 000 km's even though they appear to be in good order as the remainder of their serviceable life is unpredictable.