Checking Differential Fluid

[J. Huber]

Can anyone refresh my memory on how I do this on the 230SL? I cannot for the life of me remember how I did it last time. Recall dipping my finger but that is about it. Thanks.

[awolff280sl]

On my 280sl, I check the fluid level with the diff warm. I crawl under, both wheels on the ground. The fluid should be just at the lip of the fill bolt hole as verified by a shiny fingertip.

[SteveK]

Just one more thing; I found that filling it from the left wheel well with a tube works great. 

[J. Huber]

Thanks. Will I know the filler bolt when I see it?

[graphic66]

It is on the back of the differential. It is a big allen type wrench. A special wrench of course, not in your normal tool box. You can make one out of a large bolt, get the bolt with a head that fits into the plug, weld a nut on the bolt and use a socket to fit the nut. Or just buy the allen socket at your tool dealer. I forgot the size. You can press a thin piece of paper on the plug to get an impression to take to the store with you to match the size. The drain is the same size wrench, located on the bottom. Just make sure your axles are level when checking. To fill I use a long clear piece of tubing that fits onto a funnel and into the fill hole. I suspend the funnel alongside the car with the hose going under the car and pour the oil in while watching for it to overflow out the filler then let the oil drain out until just level with the filler and replace the plug. I would recomend draining the axle completely and filling it with Mobil One Synthetic gear oil.

[awolff280sl]

I use a hand pump that screws onto the oil cannister to pump it in.

[Benz Dr.]

I use a suction gun. Kind of looks like grease gun with a tube coming out of the end. Since we do this job on the hoist the wheels tend to drop down a bit at each side. In this case, I remove the check plug and stick my little finger into the hole. If the tip of my finger hits oil, it's OK.
We also remove and clean the breather vent on the top of the axel. They will get plugged over time and pressure will build up inside of the axel as it heats up. This pressure will have a tendancy to push oil out of seals around the axel tubes and the pinion.

NOTE:
Always remove the filler plug first. If you remove the drain plug and find that you can't get the filler off, how will you put more oil back into the axel?  Better to find out you can't fill it first before you drain. In most cases it's better to leave it alone unless you know for sure that it's dry or empty and wait until you can fix it. I find that the amount you need to fill the axel up after a seaons driving is really not that much if it's not leaking.

[ja17]

Hello,

One other thing, remember that the fluid level is meant to be checked with the axel tubes in the level (loaded) position, as when the car is on the ground. Of coarse if you are starting with a drained diff, you will only need to know the exact qty to inject.

Yes as awolf has stated the little pumps that screw on the plastic gear oil containers work well. I have also used the suction gun. You can even just use the pointed end of the container and squeeze it in, but you can never get it all out of the container using this method so have extra fluid on hand. The funnel and tube method allows the rear axel to be on the ground with the tubes level.

Some years back I got a grease pump tank for a Catapillar (bulldozer) at a garage sale.  It was used to grease heavy equipment. It is small  enough to carry (about the size of a military fuel can).  It has about a three or four gallan tank, a hand pump on top, and a rubber hose.  After cleaning the grease out of it, I installed a six foot hose with and a metal hook shaped pipe on the end so it could be inserted and hung in the fill opening. Works great with gear oil. Fast and easy, no mess or special rigging. I just let the car rest on the ground level, and inject enough gear oil until it emerges from the fill opening.

[Bernd]

Joe, if the 230SL is the same as the 280, then I am just about positive it will take 2.9qt of gear oil to fill it IF your axles have been drained.

[graphic66]

The 230SL and 280Sl have different axles and probably the 230SL holds a little less as it is smaller. Just a guess from memory.