Replacing the driveshaft oil seal in Differential

This is a 1990 Ford F150, 4WD 5 liter engine Manual Trans.
I was just doing a little work on the parking brake on this truck when I noticed that there is a rather large puddle of rear end lube on my
garage floor, coming out of the oil seal behind the flange where the driveshaft connects. (The REAR differential).
I just replaced one of the universal joints on that rear drive shaft, a few months ago. So, getting off the driveshaft is no problem. However, I have never replaced a grease seal on a differential, although I've replaced several of them on the rear of automatic transmissions, as well as many in brake rotors.
I am asking about this because I am not sure if this is something I can do at home, or should I let a mechanic do it? (I try to do as much of my own work as I can, but there are limits, and one of them is working on the ground under a vehicle).
I looked at a photo of a Ford differential on a website, and see how it all goes together. Basically from what I see, I remove the U-bolts on the drive shaft univ. joint, and get the shaft out of the way. Then I remove that large nut in the middle of the flange. Then, I (somehow) take the flange off, and change the seal. It looks easy enough, but how hard is it to remove that large nut? I'm using hand tools, although I do have an impact air wrench, but my compressor has a hard time keeping up. I guess what I am asking is Can this be removed by hand, and assuming I block the wheels, (leaving the truck on the floor), can I remove it without the differential turning? Are the threads on the nut a standard thread, or a reverse thread (CCW)?
Assuming I am able to get the nut off, how do I get the flange out. Does it just pull out, possibly with a little tapping and leverage from the rear or it? Do I need to mark the spline teeth so it goes back the same, or is there a key or larger tooth or groove?
Finally, will anything fall out (such as bearing), or will the spline drop, push inward, or any other unexpected things?
I'll assume the oil seal is just the common type like on the automatic transmission rear shaft, and I pry out the old one, and I carefully tap in the new one, using a block of wood against it. (yeah I know they make special tools for that).
That about covers it. I'd greatly appreciate any advice about this. I dont want to get into the job and find myself unable to do it. I noticed on that website, they call it a "pinion seal", not a grease or oil seal.
One other thing. On that website they show an 8.8 and a 10.25 differential. What are they measuring? I know they'll ask me that when I go to get the part. Will I need a model number too, or is the size enough? If I need a model number, where is the number or tag on Ford differentials?
Sorry for all the questions, I just like to know what I'm doing before I get out the wrenches.
By the way, do all Ford differentials take the standard 90 weight lube, or do they need something else?
Thanks for all help.
F.D.
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A decent service manual takes a lot of the guess work out of most jobs. Before diving inside the differential, I would highly recommend getting one. It will pay for it's self over & over (assuming you keep the truck for a long time).
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On Thu, 07 Feb 2008 04:37:59 -0600, snipped-for-privacy@invalid.com wrote:

Has anyone read this?
F.D.
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Shawn did and gave a very helpful reply, most of the answers to your questions would be answered by following his advise...
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wrote:

Thats weird, it never showed up on my server. I never saw any reply at all.
I thought aioe.org sometimes missed posts. Now I know it obviously does. Or maybe there's some other reason ????
Could you or anyone be kind enough to quote it again. I'll look on google archives, but who knows if it's there. Usenet gets weird at times.
Thanks
F.D.
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A decent service manual takes a lot of the guess work out of most jobs. Before diving inside the differential, I would highly recommend getting one. It will pay for it's self over & over (assuming you keep the truck for a long time).
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wrote:

Never mind the having to quote the messsage from Shawn, I found it on googlegroups.
However, a manual is not going to answer whether or not it's possible to remove the nut while working on the garage floor. I did get a parts exploded view on autozone.com, along with the basic instructions. But that still dont tell whether I can do this job with hand tools and no hoist. Manuals give "how to" instructions, but only experience can tell whether the job is possible under specific conditions.
F.D.
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On the floor with hand tools? Yes... depending on your desire and/or dedication to the task... I wont.
The first requirement is to measure the rotating torque of the pinion... it is important that the bearings be returned to near the same preload as they had before the disassembly.... The pinion nut is TIGHT.... You'll need a decently long lever and some way to hold the pinion from turning.... Air tools can help, but they need to be used carefully and wisely to keep from "gaining" preload.
Service manuals need to be read carefully... The pinion seal isn't a "zip-zap" deal.... but I will admit that many have made it a "zip-zap" deal and have had luck on their side (these are the guys that will call this repair a "no brainer". I'm top heavy on apprentices at this time... and this repair is far from a "no brainer".... a mis-step can be very, very spendy. DAMHIKT.
These same service manuals can either explain the repair in great detail.... or be written by someone that assumes the reader has some previous knowledge and experience. If you find a service manual that has an inch/pound torque wrench in the required tools list and mentions "rotating torque" in the procedure.... this is the one you need. IF (and this is a very big IF) you have "the feel", you can probably do fairly well without the inch/pounds torque wrench... After nearly 40 years, I still reach for it regularly....
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Another approach is if the job seems too difficult, you can always drop the rear axle assembly & take it to a driveshaft shop & have the "pros" change the seal. It may cost you some for the labor & seal(s) but you will save a considerable amount by removing & installing the axle unit yourself.
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You really want him to do a lot of extra work for nothing. On a hoist it is maby, oh 5 min. to remove the drive shaft, and that is all he will save. This is a job I probly would sudjest he take to a shop. It is not that expensive a repair and won`t risk a expensive mistake. Or if you have a mech friend with experince to be there to guide you through it that would be ok also. KB
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On Sat, 09 Feb 2008 07:37:17 GMT, "Jim Warman"

would "hold the pinion"? Doesn't keeping the wheels on the ground mean the pinion is not going to turn? That's where I question how this would be done on a hoist, at least without ripping the whole differential apart to lock that gear (somehow) from the inside. Otherwise I pretty much got the picture of what to do.
Actually, I think I am going to leave this one for the shop to do. That's why I asked. I like to DIY most of what I can, but I dont see how I can get a long enough lever on that nut when the truck is on the ground, not to mention that preload stuff. I have a torque wrench though. Rarely use it....
As for manuals, I find most of them are pretty useless, unless they are the ones directly from the factory. The factory ones are excellent, but very costly. Those Chiltons books and others like them are fairly cheap, but not worth much of anything except for a beginner who is trying to do a tuneup. Years ago, everytime I got a newer car, or different brand, I'd buy one of them. They're really so generic that they are almost all the same. Almost every one, regardless of make, model, and year have the same thing in about 80% of the book. About the only thing specific to the make, model and year are the specifications, and a once and awhile they may have a few photos of the vacuum hoses and wiring for that particular vehicle, and even then, it covers several models so it's never 100% accurate.
That autozone.com site is probably more useful than most of the generic books I have boughten. The last time I bought a Chiltons manual was before the internet existed. These days there is more online than in those books. The tuneup specs are always online, and that seems to be the main reason I bought those books in the past, if I was too busy to spend time at the library.
Thanks
F.D.
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My Son & I did this same proceedure on an old 1989 Ford stick, straight 6, 3/4 ton. We did it on the gravel driveway a few Summers ago. It really wasn't a bad job -easy for me to say b/c it was my son laying on the ground. I don't reacll getting the old seal out as a problem (I think we just hooked it out) but hammering the new one in was a bit tricky. Being a bit of a wood worker I made a small hardwood shape with a cenrtral hole so he could hammer the seal on over the pinion spline & drive it into the housing using a small hand sledge on the wooden form. We may have used a torque wrench when we loosened the pinion nut off &/or got a spec for the retightening torque. You must not overtighten this b/c on many rear ends there is a compression sleeve assembly that must not be collapsed . So use no more than the torque that it took to loosen it off (or a repair manual specs). We used lock tite to make sure the pinion nut didn't loosen off. We had the rear end open & the diff gears out b/c we redid an axle bearing but I don't think that is necessary to do the pinion seal. Just be sure the assembly rotates easily by hand w/o too much drag before reinstalling the drive shaft. (Jack it up with wheels off & no brake drag). If the pinion nut is too tight the rolling friction will be considerable & won't feel smooth. Hope this helps, BCinBC

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yes
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snipped-for-privacy@invalid.com wrote:

I had mine in an 03 Excursion replaced a few weeks ago. was around $140~ including lubricates and the additive. Was well worth the expense to have it done at a shop...
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