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Discussion Starter #1
I just changed the rear Differential fluid in my F250 w/95k. The truck has a 3.73 LS rear end based on the door sticker (axle 3L). I used a fluid evacuator to draw the fluid out of the fill port.

The fluid I removed had some gray material (graphite?) suspended in it. Was this normal for a limited slip differential? Perhaps material from the friction discs or clutch pack in the Differential. The fluid didn’t appear to be abnormal in any other way (no water, good viscosity, etc).

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OJ
 

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Its not graphite. Ground up clutch material is the most likely culprit.


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Yup. I would pull the cover and try to get the rest out.
From what I understand, if you fill with a synthetic fluid, you don't need as much/any friction modifier/lsd additive.
You start with just the gear oil, then add the additive to quieten the chatter. But from the sounds of it, your clutches may be toasted anyways. http://www.fourwheeler.com/how-to/transmission-drivetrain/1512-diy-rebuild-ford-visteon-sterling-10-5-inch-traction-lok/
You could jack one tire off the ground with truck in neutral and see if you can spin the tire. (You shouldn't be able to)

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Discussion Starter #4
The gray material was only in a small portion of the gear lube I removed (< 0.2 qt). I may pull the cover the next time I do a significant service, but I will prob get an aftermarket Differential cover with a drain port to reinstall.

The OEM cover has cooling fins already, but a drain would of been nice.

I’ll try the LS dif check the next time I have the rear end or wheel off the ground.

Thanks
OJ
 

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You will most likely “hear” your LS chatter when turning until you add the fluid.

I used a synthetic gear oil and had to add 1/2 the recommended amount (one 4-oz bottle of Ford "friction modifier" XL-3) and then the rear diff quieted down.
 

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If the rear end fluid that you used is synthetic and is rated GL4 then you shouldn't need to add any additional additive.

On the bits you found I agree that they are pieces of the clutches and I can foresee a rear end rebuild in your future.
 
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One form of rust is black, so that's probably at least half of the powder you saw in the oil. It appears in axles with open diffs at the same concentration (for the same age/miles), so it's not necessarily clutch material, and it doesn't indicate impending failure. Just remember to clean the magnet.
 

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I just did this job a month ago and now thinking about the magnet.

I think it was just the FILL plug that was magnetized?

Does that sound right?

EDIT:

Worth a lookover:

http://www.guzzle7pt3.com/rdiff.php

.
 

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Discussion Starter #9
One form of rust is black, so that's probably at least half of the powder you saw in the oil. It appears in axles with open diffs at the same concentration (for the same age/miles), so it's not necessarily clutch material, and it doesn't indicate impending failure. Just remember to clean the magnet.
The drain plug was magnetized, and there was a little of the same gray material on the end, so that makes sense now. There were no metal shavings or anything alarming.

Is there another magnet in the diff or cover? I would probably have to remove the diff cover to access.

Thanks
OJ
 

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There is not another magnet on the cover - unless you add one. I bought a couple of Neodymium magnets from https://www.kjmagnetics.com/products.asp?cat=1

I got some in the 35 pound range - axially magnetized. I have one on my oil filter and one on my differential cover. They've both been there for the past 100,000 miles. Obviously, I pull the oil filter magnet and move it to the new oil filter each oil change.
 

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I always use synthetic fluid in the diff. I tried without it once and could feel/hear the LS clattering. 4 oz of modifier did the job. I had close to 300,000 on my last 99 and LS still worked fine. I always pull rear cover and take a look, reseal with RTV and let set for a day before refill.
DENNY
 

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...a drain would of been nice.
The drain plug was magnetized...
Was there a drain plug, or not? The FILL plug should have an embedded magnet:


(phone app link)


I put a factory IRS cover on my 8.8" axle, which gave me a cast Aluminum (puncture-resistant) cover, fins, another fill, a drain, & another vent:


(phone app link)


I haven't found a use for the bolt ears yet, but they don't interfere with anything, so I haven't cut them off, either. The closest thing for your Sterling axle would be aftermarket.
 

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Steve83,

Guzzle's link above discusses only a 3/8" Magnetized Fill Plug.

Welcome to guzzle's Rear Differential Maintenance Web Page

I have been working on several pieces of equipment the past month and can't keep them all straight.

Thanks for the correction.

I also agree with DENNY's experience that one 4-oz bottle of Friction Modifier is typically required even when using Synthetic Gear Oil.
 

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Discussion Starter #14
...a drain would of been nice.
The drain plug was magnetized...
Was there a drain plug, or not? The FILL plug should have an embedded magnet:


(phone app link)


I put a factory IRS cover on my 8.8" axle, which gave me a cast Aluminum (puncture-resistant) cover, fins, another fill, a drain, & another vent:


(phone app link)


I haven't found a use for the bolt ears yet, but they don't interfere with anything, so I haven't cut them off, either. The closest thing for your Sterling axle would be aftermarket.
Sorry, I should of said the “Fill plug” was magnetized. There was no drain plug on the OEM diff cover as originally stated. Sorry about that.

OJ
 
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Figure I'll mention it, since it was brought up....
Clutch material won't stick to the magnet...

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I've wasted my adult life away overhauling everything from Eaton 2 speeds to many tandem axle semi differentials and never drained the oil where the last few drips didn't look like fine metallic paint particles---it's normal with mileage and age. Same with a manual transmission. And if a magnetic drain plug is used, it will always have some metallic "fuzz" stuck to it. Since Ford in their infinite wisdom didn't spec a drain plug in the axle housing, after pulling the back cover to completely drain gear oil it's a good idea to drill and tap a 3/8 or 1/2 pipe plug hole in the bottom of the housing and use a magnetic drain plug for in the future.
 
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