Zf5
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Cross-Country
Joined: Jun 2025
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Zf5
It's time to change the transmission oil in my ZF5-47. I have a gallon of synthetic Castrol Transmax universal. It says it is suitable for applications that call for Mercon/MerconvV. Can anyone verify that it will be okay to run this? I think I have run it in my ZF6 in the past without issue but I honestly can't remember for sure.
SPONSOR
Joined: Jan 2025
Posts: 500
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From: White Bear Lake
I would say it's fine if it meets the specs. I know people run all sorts of stuff in these things and they're of the age and probably mileage that a thicker more lubricating fluid would do them some good. Red Line MT90 or MTL some people use with positive outcomes. ATF is far better as a hydraulic fluid than it is as an oil. I wouldn't run straight up gear oil but something better than red water such as an actual manual trans fluid would be beneficial in my mind.
-Dan F
-Dan F
Mountain Pass
Joined: May 2006
Posts: 194
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From: Summerfield
I run 15w-40 full synthetic diesel oil in my ZF5 and ZF6 speeds. The 5 speed is behind a 472 BBF and the 6 speed is behind my 7.3 PSD. Motor oil is much better at lubricating and greatly helped quiet down both transmissions. The 6 speed has been on motor oil for 250K miles(has 420K on both it and the 7.3) now and the 5 speed was rebuilt prior to me purchasing it-Fred Jones rebuild no less, it has just been installed in my late son's '95 F150..
Laughing Gas
Joined: Oct 2014
Posts: 946
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From: Carnation, Wah
The only down side to motor oil in a transmission designed for gear oil/ atf
is that motor oil tries to keep solids in suspension so the active filter can filter
them out,
and gearbox fluids let them precipitate so that they don't stay in circulation
in unfiltered oil.
I'm sure it doesn't matter that much, but the concept is worth mentioning.
I'm overdue for a change on mine...
t
is that motor oil tries to keep solids in suspension so the active filter can filter
them out,
and gearbox fluids let them precipitate so that they don't stay in circulation
in unfiltered oil.
I'm sure it doesn't matter that much, but the concept is worth mentioning.
I'm overdue for a change on mine...
t
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Cross-Country
Joined: Jun 2025
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I run 15w-40 full synthetic diesel oil in my ZF5 and ZF6 speeds. The 5 speed is behind a 472 BBF and the 6 speed is behind my 7.3 PSD. Motor oil is much better at lubricating and greatly helped quiet down both transmissions. The 6 speed has been on motor oil for 250K miles(has 420K on both it and the 7.3) now and the 5 speed was rebuilt prior to me purchasing it-Fred Jones rebuild no less, it has just been installed in my late son's '95 F150..
Mountain Pass
Joined: May 2006
Posts: 194
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From: Summerfield
You are certainly welcome. I never liked the "gear rollover" noise my ZF6 had, even at 150K. I asked a buddy of mine who owns a 4x4 driveline shop near me about using motor oil, he said if the low temp oil viscosity is close there wouldn't be an oiling/lubricating issue at low temps, but the 15W-40 motor oil at operating temp has much more viscosity and returns a less noisy transmission and it's internals are better lubricated. It actually shifts better as well and we all know a ZF trans isn't anywhere near a buttery smooth shifting trans. Now I do live in central Florida, so low temp(under 20 degrees F) shifting and/or lubrication issues haven't been a big concern-The ZF6 has an oil pump and external cooler and I've had ZERO issues so far. If you do live in colder climates, using 5w-40 may be a great option. Good luck with whatever lubrication you choose.
Lead Driver
Joined: Sep 2002
Posts: 9,550
Likes: 2,034
From: North Texas
My S5-47 in the dually is fairly fresh with about 30k since I built it. It runs Redline D4, I fill from the top and add one extra quart. No problems, rare earth magnets on the PTO covers inside. I really would like some sort of filter for one, yet never could find one.
I run half MTL and half MT90 from RL in my Getrag 265/6. It specs ATF or a 75/90 GL4 oil, shifts excellent like that. GL5s is corrosive to the syncro rings as I recollect so no rear axle oil.
I run half MTL and half MT90 from RL in my Getrag 265/6. It specs ATF or a 75/90 GL4 oil, shifts excellent like that. GL5s is corrosive to the syncro rings as I recollect so no rear axle oil.
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