When I had the rear end gears changed out in my 03 Mustang GT, everyone was saying that the 80W90 was too thin, and that the you really wanted 75W140 to quiet things down. That’s what I used, and never had any problems.
75W140 is the required fluid for both my 07 and 13 Mustang GT’s. Hard to think of 80W90 as being thin…
The synthetic 75W140 ( I don’t think that’s available in conventional oil) seems much thinner than the old 80W90 oil at room temp.
I think the idea was that it was thinner when it was cold, but thicker when warm.
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Update I checked with ford dealer they said to use 75W140 for my truck.
@Mustangman Thank you that link was very helpful
To further complicate the issue, I think I recall a conversation here that some front wheel drive vehicles – where the differential is part of the transmission ass’y – use a different fluid for the transmission part than for the differential part. Am I remembering this correctly? Or is it just that there are two separate fill and drain ports to deal with on these vehicles, but the same fluid is used for both?
I looked at Mustangman’s link . . .
He’s talking about what kind of gear oil the rear diff needs
But OP was mentioning the fluid for the manual transmission
In any case, it seems his specific manual transmission most likely needs Mercon, just as he had mentioned
I just looked at another source . . . and it went as far back as far a 1992 F-150 . . . and it said the R2 5speed manual transmission gets 3.8qts of Mercon atf . . . the S5-42 5speed manual transmission gets 3.4qts of Mercon atf
It also lists the 4speed T-18 manual transmission, and that gets 3.5qts of 80W . . . that may be the older transmission design which OP was thinking of?
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The thread kind of migrated to diff fluid from the original trans fluid discussion with a question from the OP.
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Which modern, non-racing, automobile transmissions use straight-cut gears for their forward speeds?
Large commercial trucks
All that specify oil that isn’t “EP.”
The vast majority of motorcycle transmissions use straight cut gears, mostly because some of the gears double as dog clutches and you don’t want the shift forks to have to fight axial thrust when the gear is under load.
Nearly all, (I can’t think of any exceptions) motorcycle transmissions are un-synchronized (crash boxes), like the old F1 and Indy car transmissions.
Do recent F150 transmissions specify “EP”?
I don’t believe that any of the current 5 speeds in F150s use EP but I’m not sure. All the 3 speeds used EP as did the 4 speed overdrive but they are likely no longer used. Heavy duty models may use old gear boxes requiring the heavy oil. For years I was clueless what was in a transmission until I pulled the fill plug and stuck my finger in. I can assure you that adding a significant amout of 90W to a transmission with straight cut gears will result in difficult shifting in normal weather and nearly impossible shifting when the temperature drops below freezing.
The API ratings of gear oils do not correspond with the SAE ratings of motor oils. 80W gear oil is actually quite similar in viscosity to 10-40 motor oil.
At least with the gps you get a dead-on speed reading! ;D
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As I recall EP-90 is similar ro SAE 40 engine oil. In an effort to discourage shops from using motor oil in gear boxes requiring extreme pressure additives gear oils were given a drastically higher implied rating. Hypoid rear axles wouldn’t last long without the EP additives.
I remember starting cars in the 50’s and 60s. In winter (temps sometimes around -40F) it was really difficult to move the shifter to neutral until the engine transferred some heat to the tranny. Once it warmed up, everything was fine. It also highlights the old saw about starting slowly until the car warmed up. Today’s cars’ lubricants protect the drivetrain, but in old rear-drive cars, the heavy gear oil wouldn’t adequately lube the differential gears (and probably the bearings around the banjo housing). Drivers who “warmed up” their cars by letting them run in the driveway until the frost was melted off their windows, then driving away like it was mid-summer, probably caused a lot of damage to the diff gears (whining gears at least).
@stargazer72 Yes the gps doe’s get a dead on speed reading. I used it before this problem due to oversized tires. the speedometer was 7 to 10 miles faster than it should have showed. The only problem I have now is that I have to estimate elapsed milege.
You are backwards, @Renegade… Bigger tires would show a lower speed than actual and smaller tires would show higher speeds.
And GPS speed only works when it can “see” multiple satellites. That fails in cities with high buildings and cloudy days.