ZF-6 and XT-M5-QS Full Synthetic Manual Transmission Fluid?

[Matt Saunoras]

I've known this for quite a while but I can't seem to find an answer why the 2009-2010 super duty trucks equipped with a 6.4 and a ZF-6 specify 75w-90 syn MTF while all the previous years just take plain old Merc V (Even 08 still uses V regardless of engine). 

 

Can anyone enlighten me?  Has anyone ever tried synthetic MTF in a 6.0 ZF6?  I've got one of my fleet customers inquiring about the fluid and I don't know what to tell them.  Obviously ATF is a much lighter oil and it's what is shipped in all the ZFs we ever changed.  The one 09 ZF we replaced needed the ATF drained out and MTF added.  I can't imagine what the difference could be with the actual trans.  I'd just assume the ZF isn't that picky.

[Keith Browning]

I cant answer your question specifically, but, years ago I had a customer come in with an F350 manual that was extremely hard to shift. He had just been to Jiffy Lube and had ALL of his fluids replaced. Yep. They drained the ATF and refilled the ol ZF with gear oil.  Apparently the synchros didn't like that change which makes me think that THEY need to be designed to work with a particular fluid. Perhaps the gear oil is needed to withstand the added torque/HP?  

[cbriggs]

I wonder if they did it to mitigate the horrendous gear rattle that the 08's had.

[Keith Browning]

I wonder if they did it to mitigate the horrendous gear rattle that the 08's had.

 

Have you heard the "normal" rattling that comes from a Torqshift-6 with the PTO option?  I don't think Ford cares too much about a little noise.

[Matt Saunoras]

The only thing I can think of is if for some reason the synchros use a clutch type friction material that warrants the use of ATF, I remember seeing different synchros in class some of which had a friction material on them.  I've never had one opened though and honestly I'm more than a little intimidated by the complexity of a ZF-6.  Yes I've seen them apart and no I am not anxious to ever tear one apart that has to be put back into working order. 

 

I did a quick google search to see what fluid most guys are using and it doesn't seem like there's one magic lube.  Some guys use synthetic gear oil and some guys use synthetic ATF. 

 

Next week there's one on the schedule for a customer that just installed a new ZF and they said it's leaking between the case halves.  Can't wait to fix that

[Brad Clayton]

The most difficult part about a ZF 6 speed is the amount of press pressure it takes to get the gears off the main shaft. It's a bit on the hairy side if you have a worn out press.

[Matt Saunoras]

I did a quick check of the WSM.  If I have to reseal the case on this ZF it doesn't appear to be too involved.  What a relief honestly

 

I'm hoping they just ripped the shift lever boot, now those I have successfully repaired!

[8WA Sman]

It is possible that the vehicle you are working on is a M6HD-W, which I believe is a 6S-750.< Do not quote me on this but it may be a heavier version of the earlier 6S-650 to handle the extra HP that the 6.4 puts out compared to the 6.0. Ford does list the M6HD-W separate from the 6S-650 in this document http://www.vibratesoftware.com/html_help2014/2011/Ford/Ford_Transmissions_Main.htm#6

 

The thing I find interesting is the ZF actually recommends a 75w80(ZF-Ecofluid M) manual trans fluid for the 6S 650 - 750 anyway, not to mention a lot of their manual trans. Page 5 http://www.zf.com/media/media/en/document/lubricantslists/TE-ML_02.pdf

Fluid specs http://www.zf.com/media/media/document/corporate_2/products_3/services_2/technical_information_1/misc/zfecofluidm/produktdatenbltter/Produktdatenblatt_ZF-Ecofluid_M_EN~1.pdf

 

Now I would like to add that just because this is a ZF 6S 650 it does not mean Ford did not have it built to their specs. I think the GM version of the ZF 6S 650 is some what different then Fords version. The GM trans uses Transynd manual transmission fluid, part # 12378515. One thing I would caution against is, when putting heavy weight fluid in a manual trans is to use fluid that is GL-4 or less. I was told by someone that knows a lot more about fluid the me that snycros do not like GL-5