Differential
Postmaster
Joined: Apr 2002
Posts: 3,613
Likes: 6
From: Coal country
If the nuts are in the front, then you have a Ford 9" in an F-100.
If they are in the rear, you have a Dana most likey.
For a Ford 9", no, you don't have to have a new gasket unless you remove it, or it is leaking.
Even then, just use RTV instead of a gasket and you will be fine.
I would replace the gear oil with plain old 80-90W - it is probably original, and 40 year old gear oil isn't the best I would think!
If they are in the rear, you have a Dana most likey.
For a Ford 9", no, you don't have to have a new gasket unless you remove it, or it is leaking.
Even then, just use RTV instead of a gasket and you will be fine.
I would replace the gear oil with plain old 80-90W - it is probably original, and 40 year old gear oil isn't the best I would think!
Hotshot
Joined: Oct 2002
Posts: 18,488
Likes: 22
From: The Big, Oregon
If it has a limited slip, use either synthetic oil or a limted slip additive. The tag on the housing will say what it is, for a 3.73 ratio: 3L73 for limited slip or locker, 3 73 for open. If the tag is gone, with the tranny in neutral and the parking brake off, jack up one side and give the tire a spin. If it spins and the driveshaft turns, it's open. If it won't spin at all, it's probably a limited slip. If you can rock it back and forth and make it unlock, it's a detroit locker.
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Cross-Country
Joined: Feb 2006
Posts: 84
Likes: 0
thank you very much! big 7/8" or one inch nut keeping the oil in. bought the 80-90W for replacement next week. there's old oil all over the bottom of the differential and axle. what can I do to stop that? also, must I siphon old oil out?
Laughing Gas
Joined: Aug 2004
Posts: 964
Likes: 1
From: Roseburg, OR
Assuming that your differential is leaking between the 3rd member and the housing, you need to unbolt the driveshaft from the differential, remove the 3rd member from the axle housing, install a new gasket on the axle housing, and reinstall the the 3rd member. Removing the 3rd member will ensure you get all of the old gear oil out, too.
Hotshot
Joined: Oct 2002
Posts: 18,488
Likes: 22
From: The Big, Oregon
To get the center chuck out, you also have to jack up the truck and remove both axles. pull the tires and drums, the four bolts you see holding the backing plate on the tube also hold the axle retainer. Just pull those four bolts, and give the axle a yank.
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Laughing Gas
Joined: Aug 2004
Posts: 964
Likes: 1
From: Roseburg, OR
Yeah, I skipped that whole axle removing step somehow... 
The third member is the front portion of the differential that has the "guts" of the differential attached to it. Technically, the 3rd member IS the differential. Look at the front of your axle housing and you'll see... what is it, 12 nuts? Something like that. They are holding the 3rd member to the axle housing.
The third member is the front portion of the differential that has the "guts" of the differential attached to it. Technically, the 3rd member IS the differential. Look at the front of your axle housing and you'll see... what is it, 12 nuts? Something like that. They are holding the 3rd member to the axle housing.
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Cross-Country
Joined: Feb 2006
Posts: 84
Likes: 0
ok! i have ten bolts on the front side of the differential. with that, i guess i have the ford-9", 10-bolt. i plan to order 2 new u-joints and a gasket. is there any compelling reason to order the case assembly and internal parts kit with the pinion gears?
Postmaster
Joined: Apr 2002
Posts: 3,613
Likes: 6
From: Coal country
No, don't order the parts and DON'T disassemble the punkin (chunk, 3rd member) unless you know what you are doing. There is a specific process for adjusting the pinion depth and play, and it sounds most likely that it is beyond your capability at this time.
Unless the gears are terribly worn or beat up, or there is a lot of slop in the rear end, leave the punkin alone.
If you have a question, take it to a machine shop for evaluation.
Be careful under the truck, that thing is HEAVY!
Finally, check the rear bearings on the axles. Since you have them out, they may very well warrant replacing. You will also need two axle seals, one for each side.
You might want to research this a bit more in the rear axle forum here at FTE.
I know this sounds complicated, but it really is simple, as you will see once you tear into it. I have a friend who uses a 4.11 ratio in the rear for city driving, but changes the rear punkin to a 3.00 for taking his truck on the freeway on vacation to get better mileage. And back again when he gets home.
Good luck!
Unless the gears are terribly worn or beat up, or there is a lot of slop in the rear end, leave the punkin alone.
If you have a question, take it to a machine shop for evaluation.
Be careful under the truck, that thing is HEAVY!
Finally, check the rear bearings on the axles. Since you have them out, they may very well warrant replacing. You will also need two axle seals, one for each side.
You might want to research this a bit more in the rear axle forum here at FTE.
I know this sounds complicated, but it really is simple, as you will see once you tear into it. I have a friend who uses a 4.11 ratio in the rear for city driving, but changes the rear punkin to a 3.00 for taking his truck on the freeway on vacation to get better mileage. And back again when he gets home.
Good luck!
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Cross-Country
Joined: Feb 2006
Posts: 84
Likes: 0
good advice banjopicker! i have no experience doing this kind of stuff-just read about it and figured i'd give it a shot. i've got a healthy leak between the front of the differential and the drive shaft; is this a bad rear seal? how do i stop said leak? is the drive shaft the "chunk" and the front of the differential the "third member?"
Laughing Gas
Joined: Aug 2004
Posts: 964
Likes: 1
From: Roseburg, OR
The seal you're talking about is the pinion seal. (FYI, the third member and "chunk" are the same thing, just different terminology.) As far as I know, when you replace the pinion seal, you have to reset the preload on the pinion bearings (one of those "let an expert do it" jobs). For reference, here is an exploded diagram of the 9":
http://www.texracing.com/ford_9_exploded_view.htm
Number 3 in that chart is the pinion seal, number 5 and the small bearing in front of number 6... those are the main pinion bearings.
http://www.texracing.com/ford_9_exploded_view.htm
Number 3 in that chart is the pinion seal, number 5 and the small bearing in front of number 6... those are the main pinion bearings.