Please explain how Clutch packs work?
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Elder User
Joined: Apr 2003
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From: Perkasie, Pa.
Please explain how Clutch packs work?
The rear differential on my 2004 Expy has gone bad twice now. Can someone be so kind and explain to me how the Clutch packs on the differential work and why they keep going bad? Thanks. It's very frustrating. 
Post Fiend
Joined: Jun 2003
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Imagine a stack of CD's (out of their cases). Now add a friction material to their faces and some heavy spring to squish them together. It would be hard to rotate the top disk in a clockwise direction while the bottom disk remained stationary. This force represents the torque applied to both rear wheels before the clucth assembly 'breaks loose' (allowing one tire to rotate faster/slower than the other, which is required to go around corners.)
A special lubricant additive (called a friction modifier) allows the faces to slide across one another without snapping or chattering.
When I built posi's in my olds days, we would soak the clutches in this 'friction modifier' for a day before assembly. If we did not, they would chatter. Also, if the spring tension is too high you'll get chatter or a complete lockup.
Most likely your failures are due to improper assembly (too high spring tension or insufficient distribution of friction modifier within the friction material).
A special lubricant additive (called a friction modifier) allows the faces to slide across one another without snapping or chattering.
When I built posi's in my olds days, we would soak the clutches in this 'friction modifier' for a day before assembly. If we did not, they would chatter. Also, if the spring tension is too high you'll get chatter or a complete lockup.
Most likely your failures are due to improper assembly (too high spring tension or insufficient distribution of friction modifier within the friction material).
Senior User
Joined: Feb 2005
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Try this link. I think the CD explanation was great.
http://auto.howstuffworks.com/differential1.htm
http://auto.howstuffworks.com/differential1.htm
Senior User
Joined: May 2004
Posts: 236
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From: Ottawa, Ontario, Canada
I have learned a lot from this forum about dealing with the "chatter" (that is putting it mildly) from my 2000 EB differential. I changed out the rear diff fluid - twice - with Ford fluids, adding fresh friction modifier each time. The first time lasted for over a year with virtually no rumble. It did come back and that is why I changed the fluid the second time in less than 15,000 miles. It did not go away the second time, but GOT WORSE! I was going to have the thing rebuilt, but read somewhere that unequal tire circumfence front to rear, even just a bit, can cause the clutch packs to chatter. I needed new tires anyway, so I bought four and guess what? Rear diff problem is GONE! I drove it on a 10,000 mile trip three months ago with no noise since. Moral of the story is buy new tires and rotate them properly. Maybe this will help in your situation.
Freshman User
Joined: Apr 2004
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I just had mine done by a guy that builds racing transmissions and he said the original ones in my truck were a bad design. They clutch disks had a large tab on them that would not allow them to spin all the way around, causing uneven wear. The new ones he put in were perfectly round, allowing them to spin 360 degrees, and he said they should wear better.
This was a 2000 4wd 5.4, original clutch packs when after 45k.
This was a 2000 4wd 5.4, original clutch packs when after 45k.
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