I would be willing to bet it's set-up too tight then.....people make this mistake often,thinking it'll make it work better when the exact opposite is what really happens....that and the synthetic oil,IMHO anyway....

I think the reason mine chatters when cold/turning is becasue my car will "sit" sometimes for a month or more without moving and the clutch pac will "try out" causing the clutches to not dis-engage right off....once driven a few miles and warmed up, it works correctly with no chattering...
This may not be accurate,and if it's not,someone please correct me, but years and years ago,an old Ford mechanic told me the Ford factory trac loc rear was designed with the clutch pac to have some "slip" in it, and when one wheel spins 1.5 rotations, the clutch pac should engage and apply power to both wheels......

A lot of drag racers would rebuild their clutch pac and stretch the springs or add shims to tighten it up to act as a locker for drag racing. this may be o-k for a dedicated drag racer, but that's all it's good for, not good for street driving...
Setting up a unit too tight will only make the clutches wear out faster than normal.......

Mine as 115,000 miles all total on the original unit with only oil changes every 10 years or so. I took the 3rd member out of my daddy's F-150 when it had 85,000 miles on it and only changed the ring/pinion gear and put it in my car and it's still works perfectly to this day...
David

I was Ford H.D. mechanic in the 70's. We used to always set them up a bit loose so that they didn't grab in corners. When the spiders "see" torque differential they lock the off side through the clutch pack. The worst problem I ever saw with a worn out trac-loc is that they would waddle when backing up. It made it interesting sometimes backing a trailer.

It certainly sounds too tight for a light car. I kind of doubt that burning or wearing it in will work but it's worth a shot. I still recommend pulling it down and maybe put the old steels back in. It could be built right for specs but not for application.

I have taken the unit out and will be pulling it apart next week, in checking the set up would you recommend setting it up on the loose side of the specs?

The first thing I'd do is a tear down inspection piece by piece. It's not impossible that the parts going in were out of spec/defective. If everything checks OK, then start thinking about loosening it up some. You won't fix the problem until you find it first. Don't just go throwing parts at it blindly.

I would try more friction modifier,Amsoil for example is ready to use without adding the modifier.Been building and setting up my rearends for years and always used Synthetics,never had a problem.

the synthetic thing seems to take on a personality of its own.

redmt, is the set-up what determines the lock up or does the differential s action lock it up. and if so how does it work in the trac-lok

My understanding is that the action of the spiders exerts force on the clutch pack to lock it up. The tighter the pack then the less slip it has in the unloaded or light load condition. When one wheel is spinning, it puts rotational force on the off side. That rotation causes the spiders to "climb" on the idlers forcing side play against the clutch pack.

This may be the best explanation of how it actually works
http://en.wikipedia.org/wiki/Limited_slip_differential

This link should show you how to measure the clutch shims.

This elusive expensive tool (shim template) is 0.455" difference in where it sits on the clutch hub and where the feeler gauge is used. So with some care, straight edge, and depth gauge, you can do the math without this $175 unobtanium tool.

http://www.miraclemustang.com/photog.../V2D749056.pdf

olddog, thanks that is the first time I have seen that tool. I have used stub axle shafts and a torc wrench to set them up.

Interesting.I have set up a lot of 9" centers and always used stub axles and a torque wrench.Always shoot for near 200 lb ft or a little less to slip the packs.Rears are quiet and work great.Use the same method on GM posi as well.For years used the additive,now only synthetics (Amsoil)

Any idea what the slip torque is using this tool?

I set this one up at 150# and was surprised when it chattered.

When first started doing posi centers did a 68 Vette and forgot the additive.Drove 60 miles or so before the rear started complaining.Got it home called a pro he said put the additive in and it may take a while.It did and was fine after that.Now always soak the parts in the correct fluid before assembly.Let us know what you find.

Sorry been away for a while.

I'm just reading up on this subject, as I am doing my first rear end. I have searched the web. There is some absolute silly stuff out there, but the link I posted seemed to be credible.

From memory, I believe I read that the factory set up was about 70 ft-lb of torque while slipping. It takes more to break it lose, but that number wasn't listed. So I guess you would need a pointer arm type torque wrench. My guess is 100 ft-lb or more to break it lose.

I have read to soak the clutches in oil with the slip modifier already added. Others say to soak them in pure additive. Maybe somewhere in the middle like a 50/50 mix of additive and oil, would be a good compromise of the two opinions?

One write up I read said that the springs only provide a small clamping force for when you are turning corners, when the clutches need to slip. The spider gears are supposed to push much harder on the clutch pack, when torque is applied. They claim that torque is what locks the clutches up. Therefore increasing the spring pressure only causes the clutches to wear out quicker, drive-ability issues, and does little to improve performance.

The height of the clutch pack, affects where the axle gear is relative to the spider gears. In other words, the depth of the teeth engagement, which would impact the backlash. Some people talk about using the backlash of the spider gear to judge if the clutches have the right shims.

It stands to reason, that if the gears were too tight (not enough backlash), the thrust from the spiders could lock up the clutches with very little torque applied. So the torque to slip the clutches via the spring pressure, may not be the only or most important parameter.

Keep your foot on the gas and the tires spinning hard, Chatter will be the last thing on your mind:D

Terry, hey there.

Did you put ALL of the clutches in? :LOL:

:D :D

Way back when I was gathering info the standard slip torque was always 180 lbs or so using stub axle and beam torque wrench,which served me very well on all my posi setups.Soak my clutches in Amsoil only.Rears are always quiet, very positive,work exactly the way they should.Going around corners leaving intersections with a little throttle play,the inside tire will always let me know it's on the money.Love that statement usually getting attention,always doing it respectfully you understand.Standing start hard accelleration,setup/scaled suspension always leaves two exact tattoos.Damn I'm going for a ride,will always love driving these pure Muscle Machines!