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Question about manual transmisson

Recentley (after over 50 years driving) I managed to wreck a manuel trans. by running it dry by not knowing it takes atf. I am old school and thought it had the old 90 wt. gear oil. I have seen a small pool of atf under truck every now & again but thought it was from whoever was parked there before me & did not think much about it.When did it change from 90 wt to atf Truck is 1990 F 150 5 speed.

It takes a big man to pass his error on to others to learn from. This is definitely something to be aware of, and you have my sincere thanks. You may just have saved some others of us from making the same mistake. :slight_smile:


ATF has been used in manual transmissions since the early 80’s depending on who built the transmission. 90W gear oil hasn’t been used in lighter transmissions since the 60’s. 75W90 oils were used in the 70’s to the mid 80’s, again, depending on who built the transmission. The thinner oil helps fuel economy and still lubricates the bearings just as well. Your trans, I think, is a Toyo Kogyo/Mazda 5 speed.

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@the_same_mountainbik @Mustangman Thanks for your replies just goes to show you never get to old to learn somthing new.

How about the difff. Do they have different oil also

I know some of the older gear oils (the ones that stink) use sulfur anti-wear compounds that attack brass, bronze, and other cuprous (copper-containing) metals. (Such as synchros.)

Your transmission, I believe, is the M5OD, a Mazda hand-me-down, and had a rep for fluid leaks as it ages. Mine’s going fine…but believe me, I’m checking levels quite often as it ages!

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@meanjoe75fan Yes it defintly had leaks but I bid not realise because I was not expecting atf leaking from a manal trans. Replaced with one from a 96 F150. Only problem now have no speed or odomter due to no hole to pt speedomter cable in. So now have to use gps for speedomter. Will defintly be levil more often.

That should read checkig level more often.

When I worked in a Chrysler-Plymouth dealership in the mid `70s, some of the cars with manual transmissions called for ATF. Not all, only some models.

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Automatic transmissions have gears inside them also, so it wouldn’t surprise me that ATF works as a gear lube.
The transmissions of most Japanese motorcycles share the engine lube. The older two-stroke models by necessity had transmissions with their own dedicated lube. I remember the Kawasaki 500 three cylinder two stroke motorcycle I once owned. The owner’s manual recommended either 10W-40 or Dexron for the transmission. The clutches on these motorcycles were oil bath clutches much like those in automatic transmissions and ATF is formulated to be compatible with wet clutches.

The transmissions of Model T Fords shared the engine’s oil also, so be careful what kind of oil you use in them or you may find your clutch slipping.
Look for JASO-MA on the oil can if you buy your motorcycle oil from a car parts store.

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Yes, sort of.@meanjoe75fan is correct, the heavy gear oils are still used but they are a lot different (and smell much better) Multi-grade stuff is pretty much the norm - 75W85 or 90 and 75W140 is pretty common. Lots of manufacturers use synthetics now from the factory and require them for changes, my Mustang for example.

My 2004 GM 4WD SUV used synthetic only in the rear diff while my 2002 of the exact same model used conventional gear oil BUT recommended a change at 500 mile because it had a limited slip differential. I guess GM figured out that NO one does that service. They just put synthetic in and no longer recommend that 500 mile service.

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@Mustangman Thank you I rekon I will try to find a owners manuel for this truck as one did not come with it.

Well, such a wide range of answers are possible to your question. Some manual gearboxes today still use 75W90, the trans in your truck is a Mazda-sourced unit I believe, and many Ford manuals from the mid-80’s on specified ATF. GM Getrag manual transmissions used a specific fluid called Synchromesh, and as I recall there were a number of Asian cars and trucks that used 5W30 motor oil in the transmissions.

For what it’s worth, the shift forks and rails weren’t particularly robust in your transmission, perhaps the low fluid level wasn’t responsible for the failure. Also, the truck is 26 years old, not a bad life for a transmission.


The lubricant in a manual transmission is determined by the gear set design. Helical gears require EP lube while straight cut doesn’t. Straight cut gears with light oil improve fuel economy so that’s what the industry is moving to.

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@asemaster I thik you may be right about the fork & rails. It was defintly very low on fluid. After it was out of the truck it had to be turned on to the side to get any fluid out, also s ome metal & bearings came out also. what gets me the most was when it quit I was on a 4 lane highway running about 60 & it just quit pulling I could shift to any gear including reverse while still rolling with or without using the clutch that was 80 percent worn out. The other thing that got me was up till that point it shifted & drove good with no noise or slipping.

True, and straight cut gears are stronger too, but helical gears are quieter. Yet another sacrifice in the name of regulatory compliance.

Straight cuts can use lighter lubricants because they have greater tooth-to-tooth contact. A lubricant stands up to the compressive forces much better when there’re large surface areas in contact than when there’s small contact areas. :stuck_out_tongue_winking_eye:

Its a Ford… I’d think 75W140 gear oil is a pretty safe bet. It’s a wide temperature range gear oil.
My 2 Mustangs have required that rear gear oil and they use the same 8.8 inch axle the F150’s do.

With great respect, mustang, I think that would be a high risk assumption. The OP just destroyed a manual tranny with that assumption. My recommendation would be to check what it requires and use that.

Yep, the M5OD calls for ATF to be used, it’s a light duty transmission. Some F-150’s equipped with it have surprisingly low towing capacities, vs. the same truck with the automatic. The M5OD was first used in the F-150 in 1987 IIRC, so that’s how far back it goes.

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See the link below for a 1996 F150 truck, the oldest I could find online, page 390 in the owners manual, 80W90 rear axle lube.

80W90 seems pretty consistent across 90’s Fords and 75W140 synthetic should cover cold-to-hot conditions even better.

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