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Old 08-14-2001, 09:33 AM
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300E 120K service. Diff oil change?

Going through the 120K service myself rather than biting the bullet and never knowing what was actually done and what wasn't

I was under the car (1989 300E) changing the fuel filter last night and noticed that access to the drain/fill plugs on the differential are easy to access (much easier than those on the gearbox of my 94 Carerra!). No where in the manual does it prescribe changing the diff juice. Any thoughts on this? If so, which fluid do you recommend and what size are those allen heads in the drain/fill bolts?

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Old 08-14-2001, 09:38 AM
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Join Date: Jul 2001
Location: Western Michigan
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You'll need a special tool to open the drain and fill plugs. I believe it is a 14 mm hex bit (I got mine from a local hardware store for around $12).

You want to open the fill plug first before you try to open the drain plug.

Mobile 1 gear oil is good.

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Old 08-14-2001, 03:13 PM
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Location: Jax, FL
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Since you don't know if it was ever done. Just do it. Follow the good advice on opening the fill plug first. I would go a step further by cleaning the vent at the top and rear of the differential. It looks like a regular bolt with a screen opening on top.
Good luck!
'86 300E
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Old 08-14-2001, 03:40 PM
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Join Date: Jul 1999
Location: CT, USA
Posts: 2,699
FWIW, I've used Red Line Synthetic Diff lube in each of my cars, since it's better able to handle heat. An ounce of prevention...
"If everything seems under control, you're simply not going fast enough" --Mario Andretti

1995 E500 street car
1986 Porsche 944 Turbo S track car
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Old 08-15-2001, 08:37 PM
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Ha! Yes, removing the fill plug FIRST is always a good idea. Hate to drain the juice and then find out the fill plug is frozen in place! Thanks for reminding me. I won't ask how you know about this.
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Old 08-17-2001, 12:18 PM
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Removing the fill plug first is only necessary if you don't have the means to invert your car to fill the diff through the drain!
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Old 08-17-2001, 05:24 PM
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Join Date: Apr 1999
Posts: 2,632
SWEPCO is a known "racers" brand, and it has proven itself on Porsches in the tranny and diff.

The Porsche 928 users use SWEPCO in tranny for better shifts (the automatic is a MB tranny), and in the diff it has saved those with even a missing top plug and only filled to half-capacity.

I personally use the SWEPCO 201 80-90WT for diff (includes limited-slip differential modifiers), and the SWEPCO 714 20WT for the automatic tranny.

I get from the RiteGear Porsche site:
$36.50/gallon for 201 diff oil
$19.95/gallon for 714 ATF

Best of luck,
:-) neil
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Old 08-17-2001, 06:09 PM
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Diff Lube is Cheap

Brother of The Benz, mikef
My 1987 300E with 179,500 miles has had the diferential gear lube changed once a year since new.
No gear noise or seal leaks.
Red Line Products are the best on the market. If I had started with that oil I would still be using it.
But I didn't so here is the way I do mine.
I use gear lube 90w and add 8 ounces of gear-moly to one gallon of gear oil(grease in some groups).
To remove the plugs using special allen wrenches, Auto-Zone has a 1/2" 3 socket set, H12,H14,H17 sizes for about $7.00 the set.
Ofcourse you would remove the plugs in the proper sequence.
After you've done it the first time you too will do it every year.
Happy Trails Beep Beep from The Spiderman in Houston!!!
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