I'm hoping when I remove the inspection cover on my '92 Mark VII that I'll find a worn out Trac Lok looking all sorts of despondent and in desperate need of a rebuild. (Not likely, but I'm hoping.)
So, naturally, I started researching rebuild procedures. An interesting tidbit came up during my research; apparently some people like to leave out the "s" spring when they rebuild their diffs. When they do this the rear tires can move at different speeds until the axle spider gears ride outward on the teeth of the diff case spider gears and engage the clutches in the diff packs, locking both axles together.
Other people reuse the O.E. "s" spring and achieve O.E. lock up.
Still others use an F150 "s" spring due to it's higher rate that effectively keeps the clutches engaged 100% of the time, acting like a spool until they burn up. Great for drag racers.
Some people play around a bit with stacking strategies to increase the contact area, thereby increasing breakaway torque.
My thinking was that leaving out the "s" spring and letting the rear diff act like an open diff during the initiation of a turn would suit my application perfectly and, I assume, prolong the life of the clutches since the rear wheels will be allowed to turn at different speeds for a bit without resorting to clutch slippage.
Does this sound right?
It makes sense to me but, I've believed as many as 6 impossible things before breakfast. 
Edit: Whoops...the title should have read A traction lok theory. The way it's worded now makes it sound like THE traction lok theory, but it's only A, not THE. 
When we rebuilt mine i used the stock S spring but my clutch packs are built with an extra clutch. I can track down the measurements but my packs are thick enough that its locked with one tire on pavement and the other in dirt.
Did have to upgrade to the 75/140 frpp recomends for heavy duty use. The rear end wasnt happy with 80/90 plus additive anymore. My cars just a cruiser that occasionally does some hooning. Not sure if this tight would be ideal for anything near handling.
I think my packs are .200 thicker then stock rebuild.
Make sure you put a steel by the gear. This increases the contact area on the last clutch. You'll see what I mean when you take it apart. Leaving the spring out might help on turn in, but will let the inside wheel be more sensitive to lift-related spin.
I road raced a Mustang and I did the "special" repack of the diff using one extra clutch disc per side and one less spacer. I just reused the stock spring or the OEM replacement one that came with the kit. What I've found on my own and also talking with other Mustang racers using the stock Traction-Lok is that using the S spring or not will effect how you drive the car.
In my case with the S spring I felt that the car cornered better if I slowed down for a turn and then applied power at turn in locking up the clutches. For someone who tries to carry speed into a turn and then applies power midturn the more open diff of the S springless diff worked better.
IME clutch wear directly relates to axle endplay. The axle endplay is determined by the axle hitting the crosspin going in, and by the C-clip hitting the side gear going out. The spring pushes the side gears against the clutches. The more the clutch wears, the more the side gears spread out in the diff, so axle float opens up.
So you should be able to check the clutch packs by just measuring axle end play. Worst I ever had was massive, felt like an 1/8"+ per side.
Also FYI: The clutch pack kits from Summit don't fit without heavy grinding on the ears.
Why don't they fit? Can you elaborate? I have an 8.8 to rebuild!
In reply to Trackmouse:
The ears on the clutches were about 2x as long as they should have been, so they wouldn't fit in the case.
The frpp kit worked great for me. Its even fords improved clutches.
If you let your clutches get too worn out, you'll break your spider gears. Ask me how I know. :/
Yes, shimming the clutch pack so that you can barley get the cross pin in; is the way to go. I even went so far as to sand off a bit of metal off the end of the axle so that I didn't have to use the next thinner shim and loose some preload. Zero axle play is what you should shoot for.
In reply to jimbbski:
And this is why I really don't like this style of diff/rearend. If you have disk brakes, that endplay translates to piston knockback even if your caliper slides are nice and free.
While I could use this as a ranting point in favor of my Crusade For Rear Drums, that must take a backseat in favor of Rearends That Don't Suck.
Get a nine inch. You can break an axle, and still keep the wheel (sorta). :)
snailmont5oh wrote:
Get a nine inch. You can break an axle, and still keep the wheel (sorta). :)
If one is a serious road racer you can fit/weld 9 inch style axle ends to your 8.8 and gain that advantage.
If your using floating rear calipers you shouldn't have a pad knock back issue, I didn't until I upgraded to Wilwood fixed calipers in the rear. But a tight clutch pack and Wilwood check valves on the brake lines fixed 90% of that problem.
snailmont5oh wrote:
Get a nine inch. You can break an axle, and still keep the wheel (sorta). :)
I started breaking Mazda axles, so I'm putting a 9" in my car. You can, in fact, drive on one wheel, as long as it's not the left side breaking in a spiral fracture that drives some chunks outward and reaming/swedging the inside of the case larger, moving the diff over in the housing and turning bearing preload to "monstrous" and gear lash from .004" to -.0!!" causing much heat and scary whining sounds.
So I'm putting a 9" in my car. After scope creep happened, as per normal Knurled practice, I realized I could have saved money by getting a truck/Ranger 8.8", a Motorsport diff, and 9"-ended axles made to the length and spec I want. Since I ended up having custom axles made (plug for Dutchman!) and I am going to have to narrow and re-end the 9" housing I have.
Wow, thanks for the new (to me) info!
This is exactly what I was hoping for; experiences from people who have been down this road.
