Lubricants in ZF5, BW1356, & Rearends

This been posted & talked about lots in the past but I can't find mostly what I'm looking for currently. 2-3 mo ago some you guys, @The_Josh_Bear , & others talked about some good fluids.

I been running regular Merceron/Dextron ATF in my ZF5 for yrs as well as my BW 1356 I put in about 4 yr ago when I put that D60 under front of my '90 CCLB Dually. About at same time I drained & cleaned the D60 as well as my rear 10.25 Sterling & IIRC refilled both with 80/90 or so.
D60 & rear doing ok. ZF doing & shifting ok, great.
The BW1356 has slow gasket leak/seep I been keeping an eye on & slightly overfill when I check oil level. (usually drive truck rt side up on small block to refill) Other day I checked it & was still full & some ran out. Something's going on. The ATF fluid had really fine shinny metallic flakes in it. I rarely use the 4x4 except in winter etc. And things been sounding ok.

Anyway my question.....I've about decided that maybe it's time for me to quit being cheap & tight, go ahead and get some better fluids for front & rear ends, ZF, as well as my BW1356.
As I said I remember @The_Josh_Bear & others talked about & named some good/better fluids to use.

I would be checking the shift fork pads in the tcase, shifter function, and slip-yoke /spline condition. Regular ATF should be fine. If its overfilling, there may be a chance the trans is leaking into the tcase.

Diesel ZFs should get synthetic ATF per factory spec.

I have run basic 80-90W gear oil in diffs my whole driving life (nearly 30 years). Cheaper by the bucket. Get a bucket pump to make filling easy. Murphy's law dictates that you will have to crack the diff open again shortly after you fill it with $$$ oil.

For the ZF I love the Redline MTL. There are other brands that have similar(also very good) MTL's so pick your favorite brand there.

I do synthetic ATF for the T-case. Valvoline was on sale last time.

I agree on 80-90 in the diffs in my case I run Shaeffer moly lube(fully synthetic) and then don't have to touch it for a long time. Some guys run heavier in the rear diff cause they tow heavy, I never tow more than 5k and I figure synthetic+moly will be just fine for the years to come.

Ok thanks.
BTW Josh what do MTL stand for?
And now I remember you mentioning Redline before. Where you usually get Redline?
Or what other brands maybe seem pretty good?
I’ve just always got basic good fluids, usually WMart stuff. However as things age and wear and technology broadens there are in fact better stuff out there than 30-35 yr ago.

MTL means manual transmission lube.

I like using syn atf in the trans and t case. Have always used synthetic gear oils in the diffs, but have read lately a couple gear manufactures claim that unless temps are in the extremes (hot or cold) that non syn is better???????????

I run 80-90 in the diffs. If you are in ND, Superior/Duluth, AK or AB/MB Canada I would go to 75w in the diffs
In the T-case I run Synthetic ATF - usually Amsoil
In the ZF I run 30W synthetic trans oil from Amsoil. Based on friends with tow trucks that had ZF trans'. Most of their problems went away when they started running 30W oil rather than the ATF. Your fuel mileage will go down about 5% though.

If you want to go with synthetic engine oil (what I run in my Getrag G360 5spds) I wait until Castrol Edge comes on sale locally for $30-40 (5L jug). It comes in various viscosities.... 0W20 to 5W50.

Shouldn't be any problem running that in a tcase either. ATF is a fluid of convenience there.

Old thread, but @The_Josh_Bear , you talked bout Redline MTL. Which one is it? The

Red Line 50205 MTL 75W80 GL-4 Gear Oil​

like I found on Amazon for $76.99/Gal or some other kind of Redline MTL? Is the 75W80 too thick for our ZF5 & BW1356 Transfercase?

It looks like this in quarts. The price is about right for what I paid for it. I don't think that the thicker oil matters as much when it's fully synthetic.

ttman4 said:

Is the 75W80 too thick for our ZF5 & BW1356 Transfercase?

Click to expand...

I would not recommend that....I would run a much lighter weight full synthetic...the ZF has fiber syncros...much like the material in an auto trans...and the T-case probably has a pump in it for lube and trying to pull heavy gear oil and then push it forward is going to load the pump gears excessively...

Heavy gear oil is meant for splash lube...not for going through a pump of any kind for our purposes...unless you happen to be in extremely hot weather on a regular basis...it just does not want to flow when cold...

Keep in mind that gear oil viscosities are not on the same "scale" as engine oil!
See, for instance: https://bobistheoilguy.com/viscosity-charts/

Unless it is in NV4500s, which seem kinda picky and calls for… syntorq? Think it has a viscosity rating of 60. There is another fluid out there now that syntorq is getting harder to find, I can’t remember it’s name.

80-90 is what I use for diffs, some older transmissions call for 80-90 but seem smoother with a 50 weight, like for big trucks.

I like 30W CAT transmission fluid, I’ll probably run it in my ZF5 and BW1345 transfer case. The transfer case had gear oil in it, and the ZF5 calls for ATF but I prefer a thicker fluid.

We talked about this recently in this other thread, and some good information was shared:

ttman4 said:

Ok thanks.
BTW Josh what do MTL stand for?
And now I remember you mentioning Redline before. Where you usually get Redline?
Or what other brands maybe seem pretty good?
I’ve just always got basic good fluids, usually WMart stuff. However as things age and wear and technology broadens there are in fact better stuff out there than 30-35 yr ago.

Click to expand...

Walmart has a good price on Dexron 6. That is the upgraded latest fluid that is recommended for the zf. It's synthetic or semi-synthetic, I can't remember which. You can put that in your transfer case also. Backward compatible with all previous dexron varieties.