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[Svo] Rearend Question {5}



I had lunch with John Ames today and we discussed Mustang Traction Lock rear
ends at length. If you know anything about autocross, you've heard of John
Ames. He currently holds 19 National championships in Solo and Pro Solo, most
while driving F-Stock and E-Street Prepared Mustangs. More recently in a '93
Probe GT, 3 years in a '93 RX-7 TT, and '96 and '97 in an SLP sponsored, LT-4
engined Camaro SS. 'Nuff said.

The Traction Lock diff has friction plates that alternate between plain steel
and plates with friction material on both sides. There may be shims on one or
both sides of the clutch pack that set the preload. During the first thousand
miles or so is when the majority of the clutch pack wear takes place, leaving
the pack with little or no preload, and ergo, little or no limited slip action.
Call it the break-in period. The fix at this point is to reshim the clutch
pack, which John says will keep it working properly for 5000 to 10K miles,
until it needs reshimmed again. The mistake some folks make here is replacing
the clutch pack each time, forcing them thru the 1000 mile break-in period each
time.

The key to TL diff longevity is to avoid abuse. Knocking off a few tire burning
donuts is a quick way to permanently lose a third of the clutch pack preload.
You'll also want to add 4 ounces of friction modifier (M-19546-A) to the lube
fill.

Breakaway torque can easily be checked by jacking up one rear wheel and
measuring the torque necessary to turn the wheel with a torque wrench. The Ford
spec is a ridiculously low 25 ft-lbs, which is about what it takes to overcome
the fluid drag of the gear lube. Smart, aren't we?  There's a tool available
that bolts to the lugs and catches the torque wrench drive at the axle
centerline, but you can just use a lug nut if you're consistent about placing
the wrench at the same angle wrt/the axle each time.

John recommends setting preload at 50 to 75 foot-pounds. Below that and the
limited slip action isn't sufficient to keep the inside rear from smoking while
cornering. He once had it up over 100 ft-lbs and the rear axle hopped during
cornering, it also pushed pretty badly.

Gary Morrell
gmorrell@ford.com