T-case 101

[1971ford]

My '69 highboy is my first 4x4 so i don't know much about this stuff. I've googled around to learn a little about t-cases but they seem pretty complicated with a thousand little parts.
Do you change the t-case oil?? What oil does it take? SHould i change it? Not sure how many miles the truck has, it's been sitting for 4 years. How do you change it?

In a bump do you have to reverse to disengage 4wd? WIll i have any problems driving around the race course access roads with my hubs locked, but in 2wd until i get into some nasty stuff so i can just shift to 4wd and not have to get out and lock hubs?

[Wes]

your t case uses 80-90wt there are to plugs 1 to drain and 1 to fill. probably 3/8" inverted square drive. yes I would change it.
You can drive w/ the hubs locked but you will probably need to come to a stop to engage 4 hi and or 4 low. ya you'll learn the t case dance to disengage rock back and forth turn wheel back and forth, sometimes you may need to jack up one wheel depending on how hard the surface is.

[hazelnut]

your truck does not use 80-90 it uses 50 wt, ive got a 69 highboy and the 80-90 wt is to thick for a D24s. its also here on the site in the rebuild for a D24. you shouldnt have to back up to disengage because your hubs and transfercase are old school manule not like the new stuff thats automatic with the flip of a switch. driving with the hubs locked in isnt going to hurt anything, its good to lock in the hubs about once a month to keep everything moving and lubed.

[1971ford]

Sounds good, thanks

[averagef250]

your truck does not use 80-90 it uses 50 wt, ive got a 69 highboy and the 80-90 wt is to thick for a D24s. its also here on the site in the rebuild for a D24. you shouldnt have to back up to disengage because your hubs and transfercase are old school manule not like the new stuff thats automatic with the flip of a switch. driving with the hubs locked in isnt going to hurt anything, its good to lock in the hubs about once a month to keep everything moving and lubed.

No, Wes is correct these use 90 wt. If you run modern 50 wt in one you will be replacing bearings in a very short time. Thicker oils lubricate better. Some Ford literature recommended 50 wt in transmissions and transfer cases in the 60's and early 70's. By the middle 70's these recommendations were changed back to 90 wt. I have no idea why they'd change to 50wt to begin with. Fuel mileage concerns?

Ryan, your Dana 24 is pretty simple inside, there aren't much more than a dozen parts inside. When you have a chance grab the D24's front input yoke and try to wiggle it side-side and up-down. If you have any slop it needs new bearings and it will be very noisy on the freeway. Most recommend replacing a divorced 24 with a divorced (or mated) NP205 when it's time to rebuild the 24.

[cep62]

A while back some one made a post about viscosities.

It showed where 50wt motor was the same viscosity as 90wt gear oil.

[eggman918]

Dustin's advice is sound, T-case mounts are also something to look at they will be very hard on bearings if they are wore out.
Synthetic gear oil is good insurance also.
I have not unlocked my hubs in over 15 years ,I never noticed a mileage benefit so I leave them locked.
that way I dont have to get out of truck,plus I think that stuff lasts longer if it turns as there is next to no load on it in 2WD.

[averagef250]

A while back some one made a post about viscosities.

It showed where 50wt motor was the same viscosity as 90wt gear oil.

50wt is the viscosity index of 50wt motor oil. 90wt is the viscosity index of 90 wt gear oil. Please explain how these can have the same viscosity if they are rated for different viscosities?

When I bought my first Ford truck awhile ago, my 70 F-250, I read the manuals and filled the tranny and t-case with valvoline straight 50wt. 150 miles later I needed new bearings in the tranny and transfer case. I didn't make it to Seattle from Portland before I had 4th gear only in a 435 and one hell of a growl from a 24. If you feel the need to figure this stuff out the hard way feel free to support your local transmission builder or parts house and run 50wt (I own and operate a transmission shop).

[cep62]

Please explain how these can have the same viscosity if they are rated for different viscosities?

I can't explain it but someone around here had a comparison chart that showed it.
Maybe that's why we're not supposed to believe what we see on the Internet.

[fordman]

i remember the conversation. the old 50wt oil was actually a better 50 wt oil. the new 50wt oil isnt as good as it used to be they were saying. they said that the new 90wt rear end oil was a closer match that was made now days. mysefl i do not know i ma just relaying information that i read on the mythical internet.

[1971ford]

Thanks, good info. Dustin I'll try that simple test.