What's the weak link?

axles

Both. I've seen NA guys with minor bolt ons complain of 1 wheel peel's after not a whole ton of miles (~60k) .. so apparently the trac-loks don't last long.. or maybe we're looking at it the wrong way.. perhaps doing burnouts at least once a month is good preventative maintenance, and they're going bad from lack of use.

axles will break if ran on sticky tires. but the trac-lok weakens fast on all cars. mustangs are not a exception.

I have read the axle are the week point. Some people say the trac-lock but that is just the clutches from what I have read not the unit itself breaking.

you can rebuild with etxtra cluthces and stiffer s-spring from what I have read. they are cheap and easy to rebuild as well. I pulled my 28 spline apart and put it back together in like 10-15min after I pulled it out this weekend just to see how hard/easy it was.

I just got 3.73 gears, 31spline trac-lok ($194 summit), moser axels ($250 summit, FRPP were only $225 but they were on back order), t/a rear cover/girdle ($150), install kit ($120).

cost me about $860 total. I welded the tubes this weekend and the housing is off being powedercoated as we speak. I would not have done this but it is for free since the local guy owes me a favor. I am doing the install to save money. bought a predator used on ebay for $250 so it is costing me about $1100 top to bottom to do this the whole rear end and acomidate for the gear change. I had 60k on the rear and just replaced the bearing for pice of mind. if were just doing axels, diff and girdle you could do it for about $600 everthing brand new. proably for about $500 rebuilding a used 31 spline track lock.

there is also m-4204-318C whick is a 31 spline trac-lok that has carbon fiber clutches like the eaton. the problem is the rebuild kit is not for sale right now. that diff was $300 through summit but I think randy stinchcomb over at MD can do them a bit cheaper but I don't know what shipping would be as it is not light.