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Discussion Starter · #1 ·
Hey guys. I have a dilemma. I own a 2001 for f250 7.3 4x4 6 speed 201,000 on the clock. 1 year ago the bearings went out in my rear diff which is a sterling and requires 75-140 synthetic. Well the reputable shop I took I to said that the 75-140 is to slippery for the clutches to engage properly so he put in 85-90 conventional with 3 bottles of friction modifier in it. Now a year later I have to have a new clutch pack put in due to it now putting a whole lot of fines into the oil with a small piece of steel and a sliver also found on the magnet. Now I am a firm believer in putting the proper oil in but I took his word for it. What do you guys think about this? Also is this failure due to the wrong gear lube in the diff or just mileage? Also I have only tow with this truck 3 times. Thank you, Jeremy.
 

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The clutches on these differentials never survived this long anyway. If you want a locking diff, you're going to have to get a Detroit TruTrac or similar. I'd be more worried the chunks on the magnet came from bearings that weren't properly pre-loaded or a mis-adjusted gear set.

I think you should pull the cover and inspect. Then replace the fluid with the correct fluid. I have two Neodymium magnets on my cover to help keep metal out of the circulating oil. Put them low on the cover to keep them away from the VSS sensor.
 

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Discussion Starter · #3 ·
rear diff lube

Thank you RT for the information about the issues that maybe causing this problem. I am going to be at the shop and I will be watching as he pulls the diff cover off so I can look at the ring and pinion and the bearings. To see if anything bigger has settled in the bottom. About the neodymium magnets what is the pull force on the one's that you use? I have found a couple with 20 to 23 lbs of pull force. What is the best gear lube for our diff's in the 75-140 synthetics catagory? I read alot of different opinions on this subject. Thank you, Jeremy
 

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Thank you RT for the information about the issues that maybe causing this problem. I am going to be at the shop and I will be watching as he pulls the diff cover off so I can look at the ring and pinion and the bearings. To see if anything bigger has settled in the bottom. About the neodymium magnets what is the pull force on the one's that you use? I have found a couple with 20 to 23 lbs of pull force. What is the best gear lube for our diff's in the 75-140 synthetics catagory? I read alot of different opinions on this subject. Thank you, Jeremy
I wouldn't use that shop again. Not only did they knowingly use the wrong fluid, they used faulty logic. Ford calls for 75/140 syn, and two bottles of friction modifier. If the mechanical was worried about it being "too slippery", why add three bottles of friction modifier?

From my reading around here, I ended up just adding one bottle of modifier, and would add more if the diff chattered (like when making a turn into a dry parking lot). I never needed to add more.

I used the ford fluid, but I was having a hard time finding the correct weight and synthetic fluid without the modifier already in it. If you search around here, there are lots of posts about what people have run successfully.
 

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The magnets I have are a little stronger, but those will work fine. This is where I buy mine - K&J Magnetics: DX08B-N52

You've got to be careful with those little buggers. They will break your fingers if you don't watch it.

I use Valvoline - you can get it at Autozone and other places. I do the same thing Little Giant did - start with one bottle and listen. I've never heard chatter with one bottle and I highly suspect that's because all of our clutches are gone by now.
 

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Discussion Starter · #6 · (Edited)
Little_Giant I have been thinking the same thing about not going back to him. It would end up the same way. As for the lube that is bad on me I should have told him to put the right gear lube in but I trusted him because he has been doing this kind of work for so long. I called a shop for a quote on a full rebuild which I hope I do not need they quote me $900 - $1500.
 

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Discussion Starter · #7 ·
RT thank you for the magnet information and about being careful with these magnets I did not even think about what they are capable of due to the strength that they have. I did call a shop about 60 miles from me and I asked what it would cost to do a full rebuild which I hope I do not need they quoted me $900-$1500 I was like wow but I know they really have to know what they are doing to prevent problems like this.
 

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The limited slip rear ends in these trucks are a joke even when they are brand new you can and will still get stuck on wet grass.

Instead of rebuilding it for that price I would look into a Detroit Locker, then you know that you have something that is going to spin both rear tires if you need to.
 

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I guess my truck is an aberration. I recently tested the limited slip feature of my F250 and it appears to be functioning correctly. One tire in the grass and one on pavement while attempting to pull a vehicle stuck in a swamp and both tire receiving power.
 

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2 bottles and 75-140 like the book says. People without will get chatter with a load in bed pushing down while making a sharp turn and or then turning up a steep drive or road.

I would video that inspection and get him talking his non sense while videoing on your phone. I would have taken a picture of the trash. I would then speak with the owner to inform him, his mechanic did not follow the manufacturers service guidelines. You want a new axle.
 
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