Well I went and got a new rear end and going to replace whole thing. I'm not confrontable with pulling those spider gears out.

 

WHY??????

Just throw some Ford modifier in. It's sure worth a try. It's just clutch chatter.

 

Put in motorcraft and drove about 100 miles on it after and it's sill bad.

 

Looks like my pinion seal is leaking on my 1997 F150 8.8" LSD at 140k miles. I've got Lucas 75W140 synthetic and XL-3 modifier. I appreciate the advice from those before me on this thread. Will report back when I'm through.

 

OK, so to bring this topic back to life. I did the seal change. Getting the nut off was a big problem, mainly because of the lack of space beneath the truck for the 4 foot cheater bar I had to use. Additionally complicating things is the play that comes from the truck trying to move when working the nut. But I did get it off. I had marked it at three places - the stud, the nut, the flange. Measured with a caliper at the marks the distance between the end of the stud and the nut - 7.4mm. Sorry, I deal metric.

Seal change went OK. When tightening the nut I lined up the marks, but the caliper was showing I had to tighten it a bit more. So I did about 1/3 of a turn more. Now the caliper was showing it was about 0.4mm deeper than originally. That's 0.016 of an inch. I could not get the nut to go in the opposite direction after that, so I left it where it was.

I have the 5.4 triton with the heavier duty rear end - don't recall the numbers - it's and LSD. It took about 3 quarts of Lucas Synthethic 75W 140. I read this is what I should be putting in this diff. Also put in about one and a half of the little Ford friction modifier bottles.

Now I'm worried because the rear end seems more stiff when driving. Also I might be imagining but it seems to burn more gas. I did check the diff oil filler plug and only after about 200 miles it has accumulated some fine metal dust - this could be from the previous oil, although I did wipe down everything as best as possible on the inside, but there was at least a bit left on all the gears and the walls of the housing.

First time I changed the oil the truck had 60k miles on it. I used Valvoline synthetic at the time with just one bottle of the Ford friction modifier. I drove about 50k miles until this latest change with zero problems, and a little metal dust accumulating on the magnetic cap, with the LSD working perfectly and no binding.

Fisrt question: Is this 1/3 turn more I did a problem? I think the difference in the caliper measurements came from the nut setting slightly differently on the threads, due to rust, loctite, etc.

Second question: I added a bit more of the friction modifier because I noticed the LSD would engage the other wheel a bit more quickly than before. Before I did this I think I got a very slight binding once when reversing out of parking spot. Is 75W 140 the correct oil?

Waiting for your input. Thanks.

 

75W140 is correct. I think you did the job wrong, hence the metal shavings and the drag. You are eating the differential up. You tightened it too far. Get a shop manual and follow the correct procedure.

 

You used the correct oil and modifier.
From everything I've read or asked of people who do diffs for a living. I have to agree with glc, you're chewing up the gears.
You'll have to change the crush washer. As glc recommended, get a manual and follow the procedure it will save you an expensive repair.

 

In all my years of racing and building hot rods & engines, I have only rebuilt 1 differential. IT GRENADED! That's why I left differential building to others that were master craftsmen at building them and setting them up.

 

Hi guys, thanks for your replies!

From what I read the crush sleeve is there exactly to take care of over-tightening - is that correct?

As far as the drag goes - I did use a different gas station the same day I did the seal change. I'm hoping that's the problem. Also I'm hoping I'm imagining the drag. Yesterday I put gas from my regular station and I'll test it out today! I'll also monitor the oil plug - it didn't have any shavings i.e. pieces of metal, it had very fine metal dust mixed with thich black oil. Every time I've checked this diff plug in the last several years it always had accumulated something.

I guess the main problem is that forums and youtube are awash with people who do the seal change this way and claim to drive 10's of thousand of miles with no issues after that....

 

The crush washer, as I understand it, does not PREVENT over tightening it is what holds the pre-load on the diff (the amount of drag you see on the torque wrench). If it gets over-tightened you have to replace it because it's a one and done kind of part.

 

The differentials come from the factory with silicone, so that is why I use it.

 

40 weight motor oil is the same visc as 90 weight gear oil



Avoid Lucas like the plague...





I think I'm going to mix 90 and 140 for the rear with my light duty driving. Not going to bother with the other diffs, it's pointless as long as they are full.

 

Synthetic base stocks are just highly refined dino oil now, except maybe Redline's products being PAO and ester base which surely will reduce running temps, even to the point of recommending a grade lighter. Redline has extensive white papers on gear oils. AMSoil makes similar products, that is their corrosion test pictured above.

https://www.redlineoil.com/Products.aspx?pcid=4



The only benefit of other brand "synth" gear oils would be in cold conditions. They also might be formulated with a better additive pack, but that's unrelated to them being synth, really are just a premium product.

My experience with manual trans and mixing thin and thick MTFs for climate with an eye to horsepower tells me that I can blend the 140 down a little since I don't tow or do any HD activities. Manual Trans gets pretty stiff in cold. Pennzoil Syncromesh is the new king of MTF GL-4 fluids.

Remember, GL-5 gear oil isn't "better" than GL-4 MTF, just different in coefficient of friction additives. The synchros in a MT won't grab and spool up if the fluid is too slick.

Good ATF like Mobil 1 / Dexron 6 makes a great MTF for arctic, but Synchromesh is pretty good too.

 

There are A LOT of parts that come from the factory on these trucks that can be improved upon. For instance, the oil filter; FRAM makes the FRAM ULTRA oil filter that blows the factory filters out of the water! There are endless amounts of parts that are better than factory parts (RTV). I guarantee you most people will have more leaks using RTV on the differential cover than if they were to use a gasket!

 

Fram filters are garbage! The Motorcraft filter is a high quality filter.

I agree about using a gasket on the diff cover though. Makes the job go a lot quicker, you don't have to wait to let the RTV set before installing the cover. I do use a very thin coat of RTV in addition to the gasket, you don't have to let that set.