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International Coal Roller
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383 Posts
Discussion Starter #1
So I have a 2002 with a ZF6, soon after I bought it I changed all the fluids over to synthetic, put mobil1 ATF in my tranny and as soon as I changed it I started to have issues. The PO couldnt tell what fluid was in it, all he could tell me was "whatever Les Schaub puts in" so he was no help there. Whenever I try to down shift from 5th to 4th it want to grind just a little unless I slam it in, seems like the synchros arent working right, but only in that particular shift. Since this issue immediately started after the fluid change, and not before it leads me to think that the fluid is to blame, and it is a PIA especially when towing. I was reading up on some posts on here and saw one about using Amsoil MTF or MTG instead of ATF. I was wondering if it would be a good idea to change the fluid over to Amsoil, and if so which one, or can I mix MTF and MTG, when to change, etc. Its annoying, and Im scared Im gonna tear up the tranny or the synchros if it keeps on as I dont have the money to fix a tranny right now as Im about to PCS across the country. Sorry for the long post and thanx in advance.
 

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Coal Blower
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569 Posts
Leave the ATF in it. I've used all kinds of mixes but ATF keeps the trans the coolest. Gear oil does shift nice, but it heats up too much. The synchros have a clutch like material on them and it needs to keep cool.

How old is the slave and master?
 

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International Coal Roller
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383 Posts
Discussion Starter #3
They are 10 years and 157k miles old to my knowledge, and I put approx 2k miles on the truck before changing tranny fluid, problem started immediately after changing. On a side note figured wth and called the Ford service dept. near me and talked to a couple of techs who claim to have a lot of experience with the ZF6. According to them the ZF6 was designed to run on Mercon III, and since they apparently dont make it anymore Ford recommends Mercon V synthetic ATF or an equivalent which is thinner and as such might be causing my problem. They recommended keeping the ATF I have and adding a Justice Brothers additive, or going to a slightly heavier lube. According to them as long as the oil in the tranny isnt too much heavier than the mercon III and has a good additive package the pump and cooler should have no problem keeping the tranny in a safe temp zone, and claim Amsoil stuff usally works great. So I guess now the question is ATF with Justice Brothers additive(never heard of these guys) or Amsoil MTF?
 

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International Coal Roller
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383 Posts
Discussion Starter #4
Well after some thought I decided since had new fluid in the trans I would try something I did with my old ZF5. I drained out 3/4 of a quart of ATF and put in the same amount of 75w140 gear oil. Worked like a charm, doesnt shift as smooth as having just gear oil in it, but it doesnt grind any more on any shift, and with over 5qts of ATF still in it and with the built in cooler I feel confident it will be diluted enough to keep everything cool.
 
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