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I'm going to put some new fluid in the trans (M50D), t-case, and diff. Do I use mercon for all 3? Any fluids better than others in your guys' experience with Broncos?
 

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The differentials use differential fluid 80W90 and a friction modifier, I wouldn't use Mercon in the differentials.

Search for differential lubricant (Search on this site is your friend)

And welcome to FSB
 

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The differentials use differential fluid 80W90 and a friction modifier, I wouldn't use Mercon in the differentials.
Search for differential lubricant (Search on this site is your friend)
And welcome to FSB
Use Mercon in the M5OD and Transfer Case. That is what is spec'd.

Use 80W90 gear oil and need friction modifier in the diffs if a limited slip from the factory.
 

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Clearly calls for Mercon.

The OP said "I'm going to put some new fluid in the trans (M50D), t-case, and diff. Do I use mercon for all 3?"

I said that the "diff" uses a different lube, what are you saying, to use Mercon in the axles?
 

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For diffs you need to use gear lube not trany fluid. If you've got posi trac be sure to add the friction modifier.
 

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The OP said "I'm going to put some new fluid in the trans (M50D), t-case, and diff. Do I use mercon for all 3?"

I said that the "diff" uses a different lube, what are you saying, to use Mercon in the axles?
That's how I read his response. Maybe he missed the diff part.

bottom line: Gear oil goes in both diffs.

Tcase takes Mercon

don't know about the manual trans.
 

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I put mercon in the t-5 in my mustang.
 

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I put mercon in the t-5 in my mustang.
Nice to know, but the OP doesn't have a Mustang nor a t-5, he has a Bronco and an M5OD (The M5OD uses Mercon)
 

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The OP said "I'm going to put some new fluid in the trans (M50D), t-case, and diff. Do I use mercon for all 3?"

I said that the "diff" uses a different lube, what are you saying, to use Mercon in the axles?
The way you worded it sounded like you were telling him not to use Mercon at all.

I missed the "all 3" part.

I didn't dispute the 80W-90, though upon reading my response today mine was a bit confusing also.

Transfercase and M5OD use Mercon.
 

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@slw210 - I edited my first post for clarity. Bottom line, I hope the OP doesn't use Mercon in the axles, or we'll be looking at a thread like "I put Mercon in my axles and they blew up"
 

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I used Mobil 1 gear oil in the rear diff. It is supposed to have the friction mod. in it already. Apparently there is not enough. I ended up with some strange sounds coming from the back end. I ended up adding a few ounces of modifier and the sound stopped.
 

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I used Mobil 1 gear oil in the rear diff. It is supposed to have the friction mod. in it already. Apparently there is not enough. I ended up with some strange sounds coming from the back end. I ended up adding a few ounces of modifier and the sound stopped.
I have seen that on every automotive forum about all of the synthetics, the ones that do not use the additive have problems.
 

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Discussion Starter #18
Just put Merc in my trans and t-case. Feels MUCH better! Thanks for all of the help
 

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For diffs you need to use gear lube not trany fluid. If you've got posi trac be sure to add the friction modifier.
Where do you get friction modifier? And how do you know if you have to use it? As in how can I tell what rear I have? Slip or no slip? It is my first Bronco
 

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Tony there should be a tag on the diff under one of the cover bolts. Usually if the tag has a "L" in the numbers this deignates the limited slip. If some goober has removed it then you are going to have to pull the cover and look to see if the carrier has clutch packs. If it does then the friction modifier has to be added to the gear oil. I would go to Ford to get it . The parts stores quit handling the good stuff. They have this crap in a toothpaste tube that doesnt smell anything like the real deal. If you have an inland Truck parts in your locale they may have it as well or possibly a driveline shop.
 
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