Look What Mobil1 Synthetic Gear Lube Did To My Diff.
 

This is the weekend that I am changing out the POS rebuilt rear axles that I put in about a month ago. One locked up and the other was leaking grease. The quality of the replacements look much better, so I hope that they will last longer than a month. Anyway, I filled the diff with Mobil 1 synthetic gear lube after I replaced the original MB axles last month. When I drained it yesterday I was shocked to see how dirty the fluid had become. Once I got the cover off I could see why the fluid became so dirty:

http://freeweb.pdq.net/waas/mvc-039e.jpg

Mobil 1 cleaned the entire housing. I never saw the yellow coating or the two red paint marks on the inside of the housing before. I always thought it was black. There are still a few dark patches that will probably clear up down the road. I have never seen a cleaner differential in any of the MB at our house. Wow.

SW:

You can see why frequent oil/filter changes are recommended when switching to synthetic oil, and why some do not recommend doing so -- I've heard that using synthetics will "clean out" the crud that seals the pits and scratches in cylinder walls and cause oil consumption when the crud is gone.

I'm not sure I believe that, but synthetics are certainly vastly better at keeping the dirt suspended!

Good luck with the axles -- nothing worse that one that shakes!

Peter

Thanks Peter. I absolutely agree with you about the oil change frequency when switching to synthetics. Just imagine what good a synth oil can do to a 20 year old engine. I can't wait till the local auto stores start carrying Mobil Delvac 1.

My father and I just finished installing the replacement axles and it was a cake walk compared to the first time around. I am now certain that they gave me the wrong driver's side axle because the new replacement did not take more than a minute to get it in. The previous one was way too long. I'm sure it was constantly in a bind and causing the noise/vibration. I am letting the RTV sealant on the diff cover cure overnight. Tomorrow I will bolt the diff to the chassis and fill it up with Valvoline semi sythetic. If the axles turn out ok, I will drain and fill with Mobil 1 after a few months.

I'm guessing that this hasn't been done on mine in a long time.

Is the gear lube liquid, or is it more like bearing grease?

Sounds like the way to go is drain, refill w/new, drive for (???) then drain/refill.

How hard is this to do? What's the trick to refilling it after draining?

Thanks!
LT

Glad to hear the report of how well the synthetic gear oil cleaned out the differential. I had Mobil 1 in the diff for about a week when the failing boot on the passenger axle finally ripped open and caused that axle to start failing.

The old gear oil that came out was very dirty. After the Mobil 1 was in the differential was quieter.

Now I have two new axles on the way, scheduled to arrive for installation next weekend. Looking forward to getting the old gal back on the road - hopefully this is a once in 20 years repair. While waiting for axles I'm replacing the rubber sub-frame mounts.

I will be changing the diff oil each year from now on. Mobil 1 is 75W90 oil - not grease. Mercedes designed the differential for easy oil changes. One plug at the bottom drains the oil and another plug in the side is for filling. You fill until the differential oil is at the level of the fill plug and starts running out. You're going to need a 14mm hex driver (I got one for a socket wrench) to remove the plugs. Mobil 1 is available in most auto stores like Trak and Advance Auto. Easy DIY job.

Ken
'82 300D

hey guys


mobil one sounds like a great idea with some degree of risk... but the worst thing someone can do is remove the bottom drain bolt first.... just in case you cant get the top one off always remove the top one first or you may ruin a perfectly good day.

I know the the drain plugs can be very tough to break.

good luck

bob


ps do you guys think that synthetic atf is worth it
300d 243000 original tranny?

Sometimes the plugs can be stubborn. Always remove top plug first so that you don't get it drained only to find that a stuck top plug prevents refill. That can turn a routine maintainance event into a McGyver episode!

Hey Bob:

What risk are you referring to when you say "mobil one sounds like a great idea with some degree of risk"?

What's the risk?


As far as synthetic motor oil and transmission oil, I've been scared of them so far. For the motor, I like doing pure dinosaur and STP Oil Treatment with a rigorous change regimen. The change regimen is the critical part. I fear people using synthetics aren't changing oil often enough - especially on a diesel car that creates tons of soot in the oil. So, you can change synthetic oil in a diesel often - but you'll pay through the nose and not really get the benefit synthetics are supposed to bring - long mileage.

Using the dinosaur oil and STP Oil Treatment, I have run a 6-cylinder GM product (S-10 Pickup) 340,000 miles with no engine work. I attribute this to the STP - I wonder if this is a synthetic additive?

Ken
'82 300D

Hey, "The Bob"
 

"The Bob", I'm wondering the same thing (Mobil 1 synthetic ATF) for my 1984 300SD's tranny. I topped off with some, but I'm trying to convince my indy to change it all the next time I visit them. I bought 9 quarts of the stuff recently because it was on sale for $4.99 a quart. Any experiences with Mobil 1 Synthetic ATF on these older trannys? Thanks, Bob

I dont know how it will go with synthetic atf. I might change it next year when i change out my fluid.... If I do I will probably go with redline as their reputation of providing smooth shifting in with thier products.

I am using delvac one in the beast and am happy with it. Most of all it should aid in the ignition of my 300d in the cold chicago winters. I do agree with the authors who state that frequent oil changes are still in order. 3 to 4 thousand seems good. Sure it is expensive but I do not want to rebuild a mercedes diesel. My basic belief is that it is far superior oil and its only money. since I do the work myself I might as well use the highest quality materials. I really like the fact that the oil has not yet lost it protective properties when i change it.... that is the whole idea....It is always protected.


I would probably buy synthetic shampoo if they sold it but I have not found it yet..


thanks for all your help


bob

Ken:

I believe that STP is indeed a synthetic lubricant.

The buzz (from the lubrication engineers at FMC, who manufacture oil additives, especially polyphenylphosphates) is that synthetic oils are simply vastly better lubricants -- squeeze-out pressures an order of magnitute higher, actually stick to metal, have much lower viscosities cold and much higher viscosity hot, don't carbonize at any temperature achieved in a normal engine (this includes the bearings in turbochargers), are natural detergents by their chemical nature, cannot sludge, will not "crack" and make varnish, are capable of holding very large amounts of acid (so you don't get acid attracting water and forming droplets of acidic water in your bearings, etc) -- and since most of these characteristics are inherent in the poly-ol or poly-ether chemical structure of the oil base, don't "wear out" -- what causes petroleum based oils to degrade in performace is the loss of the additives that give them similar lubrication properties.

Mineral oils are not capable of detergent action, hold essentially zero water, have low squeeze-out and film strength, repel metals, have high viscosity cold and very low viscosity hot, char at 300 F, coke in bearings, etc., etc.

Carbon and small (< one micron) particulates buildup is the only real problem with extended time between changes. A 5000 mile oil change (with filter) schedule and synthetic oil should make the engine run forever, provided it was in good shape to begin with.

My brother and I are going to experiment -- he rebuilt the 617 in his 75 300D last year, and now that we have an assembly related oil leak fixed, will be putting synthetic in it and will see just how long it will go!

Peter

psfred:

Thanks for the info on synthetics. I've been impressed with the STP and swear by it for engine longevity. I'll have to go back and look at the economics of moving to synthetic oil again and compare with the Shell Rotella I'm using now. I certainly have seen lots of sludge and varnish with dinosaur oil....

SW:

How did the new axles work?


Ken

Ken,

The replacement axles are great. I've already put 180 miles on them since Sunday. No leaks, no noises, and no vibrations. The entire car feels even more solid than it used to be. I can go 80+ mph and not feel the vibrations that I am accustomed to. I always thought 80 was the limit for my car but the new axles have proved otherwise. I think the car might be getting better diesel mileage also. Since I drive more that 550 miles a week, I'll know for sure after a few fill ups.

SW

when I bought my 81 Sd I took it to the local (very good) lube place and had the transmission back flushed, when they went to drain and refill the differential they found that the trailer hitch
tubing that attached to the frame member the holds the differential was much too close to get a 14 mm
hex drive on ,fotinately they knew the routine of not taking the bottom plug out first. I went home and cut a large 1 inch bolt to about 3/4 inch in length then ground a 14mm hex on it leaving the bolt head to put a flat open end 1 inch wrench on I took it to them it fit easly and they could turn the large bolt hear with a big open end wrench.The owner of the lube shop traded me the refill for the home made tool.I generaly do
most of the needed work on my own cars but have found that the small extra cost of have gearboxes drained and refilled at a place with a rack and disposil more than makes up for the extra cost...
William Rogers.....

Mobil1 synthetic
 

PSFRED

Very interesting post summarising advantages of Mobil1...it will be used to educate disbelievers in UK.Thank you.