89 7.3L ZF5 tranny fluid Question? Synthetic Mercon or is Synthetic Mercon LV ok?

What about the Tcase? Is normal non Synthetic dex/merc fine in it?

 

You don't need any fancy fluid in a manual trans. Just go to Walmart and get the stuff labeled "Automatic Transmission Fluid". This is for older Mercon applications and will be perfectly fine in your ZF5, xfer case or PS pump.

 

so you're saying non synthetic is fine? or you just saying i don't need royal purple or something along those lines? im really curious the difference between mercon and mercon LV (low viscosity). everything i read says the LV is for newer vehicles, which mine is not. so wondering if its not what i wanna use.

 

Synthetic or non-synthetic should be fine. Synthetic might give you a very slight fuel economy boost, and might make your trans run cooler (though that's not really an issue on manuals). I wouldn't use LV, though, just regular Mercon.

 

Yes, non-synthetic is fine, even preferred, IMO.

 

I would use synthetic, it takes heat better without breaking down. Dont use LV though, the synchronizers might not like it.

 

I went with the royal purple synchromax stuff because I didn't want to ever replace the oil. I know synthetic works pretty darn nicely for a *long* long time, and I expect the oil to outlast this transmission at this point. I also added a quart or so of Lucas oil stabilizer at the suggestion of an auto parts guy.

So far, it seems to be doing well, so I'm happy. I'm pretty sure the extra viscosity of the stabilizer has helped a little with the horribly warn synchros on this transmission, and I know the transmission gets hot after an hour of highway driving... so the extra safety margin of the synthetic is nice.

I will point out, however, that these transmissions are simple and not easily destroyed. So long as you put in something as roughly thick as ATF, you'll probably not hurt anything greatly. Just don't add gear oil.

 

Mine will be getting 50 wt synthetic ATF when I install it... no two ways about it:

Oil change for ZF-5 Transmission

ZF 5 smf rollover noise

 

awesome!! thanks for the info. i totally get that noise too

 

is there an easy way to clean the magnet inside the case?

 

You might be able to get to it through the PTO covers, but I don't know for sure. There was some discussion about flushing the internals a while back, and iirc the consensus was that it was a bad idea. Flush the bottom of the case with solvent if you can, but keep the stuff off the gears and synchros. Let it evaporate completely before refilling.

 

I went with Redline MTL(manual transmission lube). But RoyalPurple Sychromax or Penzoil Synchromesh should both work great too- they are similar to the ATF but also have a friction modifier that helps keep your synchros doing what they are meant to do, without heating up and burning out.

I filled up with that stuff 2+ years ago and my synchros don't chatter one bit more(hot) than they did when I got the thing. So I call that a win, as my 3rd gear synchro is fairly worn.

Best part-- the cold performance is only a little worse than the hot performance. It just doesn't have that same nasty thick feel as before when I had the gear oil in it. I must say I never tried ATF, but if you do make it synthetic. But if you wanna pay for synthetic ATF, get MTL!

Hope that helps,
Joshua

 

I can't seem to find the thread, but there was a guy on OBN said he put Royal Purple in his ZF and it shifted like crap. He couldn't stand it. He drained it and went with Amsoil synthetic 50 wt ATF and loved how it shifted, especially in cold weather it was much better. I know everyone has their brand biases, but I'm definitely convinced on the point of a heavier wt synthetic vs thinner dyno oil, or even thinner synthetic.

 

ended up going with this
gonna run of bottle of seafoam transtune before i drop the fluid. thing i may get a magnetic drain plug too, but thinking there is no point cause ill never pull it after i dump lucas in it. do you think it would be good for my tcase too? replace the standard mercon in it with lucas?

 

The magnet sits flat in the bottom rear of the case. Its a flat round magnet that slides into a slot where the two case halves meet. I think its about the size of a quarter.
The gears are likely in the way for you to get at it from the PTO ports, but possibly with a flexible wand type thing.