Manual Transmission Fluid

[ashley]

I am soon to change my manual trans oil, the tech manual just says use ATF, there are several different choices these days, does anyone have a recommendation?

[jameshoward]

I used a synthetic DIII Castrol oil and I wish I hadn't, if only because I attribute that to my now pretty ocean going disaster of a transmission oil leak. I asked on the forum a few months ago if anyone knew of a more traditional, perhaps less aggressive and 'thin' ATF than that I'd used, but as I recall no one answered. So, not much help, but it'll be interesting to see if you get more of a response. Sticking to the adage of every cloud having a silver lining, the one plus to the bright red oil I use is that you can see where you've been, or parked, which means that you don't have any worries about it being engine oil.

JH

[Benz Dr.]

That's odd James. I won't use anything but synthetic in my 5 speed. They all seep a little bit but I never had the Exxon Valdees run agound under my car so I'm thinking it's a good idea.

  You must of already had some very worn seals and once filled to the correct level it found an easy way to leak out. I've never been conviced that synthetic will leak out any faster than any other oil. ATF has some unusual properties that make it an aggressive detergent, locks up moving parts at the required times, yet lubricates all the time.   

[ashley]

So it seems that we have one vote no for synthetic and one vote yes, any other opinions, anecdotes etc.. My shifter is getting a bit stubborn into all gears, and chances are the oil has never been changed with 110 k miles on it. If I choose non-synthetic is the standard dexronIII/mercon the stuff to use? Also whats the common choice for the rear differential oil ? Thanks for the input....

[Benz Dr.]

I also use a garden variety ATF you can get anywhere. All ATF type are supposed to be compatible today.

I generally use a 80 W 90 gear lube but sometines use other weights as well. I almost always use a synthetic which is often Quaker State but has been other brands.

[peller]

I just recently acquired my '68 and have noticed a fairly substantial pee spot under the vehicle. It's definitely ATF. I was surprised to learn that you use ATF rather than std gear oil for the manual tranny. Regarding the type, I would think traditional ATF rather than synthetic would be a better choice if you got a little oozing as most of these cars seem to develop.

In my case I figure I need to start monitoring the level of the fluid more closely since this leak has developed. My question is how do I check the level? I suspect there is a port on the side of the housing that you remove and add fluid there. The level should be just up to the port correct? Any trouble if I over fill it slightly to lengthen the time between checks?

Thanks for the advice. Part of the deal with my wife to get this car was that I would need to DIY as much as possible so pardon the dumb/obvious questions.

[ja17]

Hey Ashley, is your speedometer needle bouncing around a bit these days?  Tough shifting, along with a bouncing speedometer needle is usually a result of a loose slotted nut at the transmission output shaft.

In addition to ATF, I also have a Mercedes Service Bulletin which states that straight 20W engine oil can also be used in their standard transmissions. I have always used Dextron ATF or equivalent, but have no issues with using synthetic also.

[Benz Dr.]

So........ anyone know why we use ATF and not gear lube? There is a reason.

[JimVillers]

Dan ... I believe that MB specified ATF was the best high contact pressure gear lube with a lower viscosity than gear lubs of the day.  The lower viscosity allows the syncros to spin the gears more easily than normal gear lub for easier shifting.

If you have a fluid leak, fix it.  If you use 90W gear lub, shifting will be hard and you will wear your syncros.   

[Benz Dr.]

That's pretty close Jim.
 
  From what I've read about this, gear lube has a lot of zinc in it as an anti wear additive. Whatever they use in gear lube, it hardens the surface of  gears and it can make them chip. I think it's not as effective as ATF for needle bearings which are found in MB transmissions.

[ashley]

Well, ja17 as a matter of fact my speedo is bouncing a bit, thanks for asking, and I will certainly check the slutted nut on my output shaft.

[Benz Dr.]

Well, ja17 as a matter of fact my speedo is bouncing a bit, thanks for asking, and I will certainly check the slutted nut on my output shaft.

I haven't one of those in a while. Probably a good thing too.........

[ja17]

 

[Benz Dr.]

Uh...... yeah, looks like Joe got it.

  I meant to say, '' I haven't seen one of those in a while. '' 

   Anyone can make an interesting typo once in a while.........

[stickandrudderman]

I alway use dexron II/III in the manual ytansmission but I do remember from my early days that MB used to offer a choice of this or something we in the workshop used to call "200" whereas the ATF fluid was known as "220". 200 was a slightly thicker oil and was a pale yellow colour. I haven't seen it for 25 years though...
Dan, I don't know if you work on any of the more modern transmissions (7G) but in those you MUST use a different oil called "AVT".

[Benz Dr.]

No I don't work on anything that new or at least those cars are all auto.