I know what you mean about good driving.. I have had LS diffs in 4 trucks.
Never have I had one that worked well enough to warrant having in there.
If you go low on the modifier it may chatter and wear quicker. I instead use lockers. My first one was a lockright in a toyota, both ends..I had the LS in my super duty that was a joke. It worked great on pave but I didn't need it there. For those who have never tried the detroit soft locker its better than a limited slip in everyway that I can see. It makes no noise doesn't chatter and always gives you power to both wheels when you need it. All that crap about ice driving sliding etc is the same for LS. Anyone who knows how to drive wants to slide the back end out..LOL aint that true..

 

So true. I think that came from the manufacturers of the different LS's to sell them. They don't lock up as positive as a true locker so they won't catch an inexperienced driver out and cause a slide as quickly, but it can still happen. I think Ford purposely put too much friction modifier in from the factory for this very reason.

Hey, have been able to go snowmobiling? Didn't you get a new sled last year?

 

We have 5 inches. Really bad year for plowing. No new sled I still have a 79 AC and an 89 yamaha..good enough for an old man of 50 with a 5 year old and a 7 and a 10 and a 22..in the navy.


Dick

 

Unless you plan to off-road that dually often, a full-time locker is a bad idea. They wear tires like crazy and the understeer on an already poor turning truck isn't all that much fun. Full lockers were never meant to be put on street rigs. And if you have a need for a full locker on a street rig, go with an ARB or some other selectable locker. I'm not positive, but I think Eaton makes an electric one for the Dana 80 as well.

Otherwise just do what Darren (Ronin007) suggested and play with the friction modifier a little until you get the type of lock-up you're looking for in the stock LS. They really aren't that bad of a unit. The factory just tends to keep them a bit on the loose side. You can imagine how many people would be flooding into dealer service department's complaining of a "broken" rear-end because it made a "funny noise" going around a corner if the LS locked-up easier.

 

OK help me out here, I have a 04 PSD and want a locker cuz this thing has so much torque that it spins the wheels no matter what. If I play with the friction stuff...how do I do that?? Please advise...... never messed with a rearend, just broke a few posi units in my younger years! Back then you just went to the bone yard and grabbed a new one and slapped it in a away you go.

 

My 2005 LS didn't work at all when I got it. Dealer said that's the way it's suposed to work. So I changed the fluid last summer and left out the friction modifier and it works pretty good now. Still waiting to try it in the snow. We got some snow the last two days but not enough on the roads here. Might have to go off-road.

 

Drain your diff. Fill it with gear lub without the friction modifier. Try it. If it seems too tight or chattering add 1/4 of the amount of modifier stated for your LS. Keep trying adding a little more until you get the effect you want. I usually end up betewwen 1/4 and 1/2 or the reccomended amount.

 

Ford puts 8 oz of friction modifier in from the factory. That is also what is recommended in their service manuals and what the dealership will put in when they service your truck. But as Ken mentioned the best thing to do is drain it and add only what you need. Most start with none and add in 2 oz increments until it works and does not clatter. That really seems to vary from truck to truck. Some work good with none while others will need the full 8 oz. Still there are others that don't work good no matter what you do so then the search is on for what LS or locker you like for the way you use your truck.

 

If you have a dual rear wheel setup and wonder about possible down-sides to locking differentials, let me tell you what happened to the previous owner of my '68 F-350. It is a flat-bed, set up for a fifth-wheel. The rear axle is a Dana 70 and was set up with a Detroit Locker. He had a fully loaded trailer with plenty of weight on the fifth wheel 12" ahead of the axle. The tires were Michelin LT radials with plenty of foot-print. On dry asphalt pavement he had to pull up a steep, sharply turning driveway. No problem as he had a 391 with a New Process 540 5-speed and 4.56 rear gears. He heard a "snap!" as one of his 31-spline axles broke.

On a turn on dry pavement, many pickups and cars will squeel a tire when turning if the driver gives the locker enough torque to initiate lockup. This is merely an annoyance. With a loaded dual rear wheel setup, it can be more costly.

There is a tremendous mechanical advantage in differential action. The torque of the engine is multiplied by grannie gear and again by the axle gears AND then once more by the differential action (or lack there-of) -- that is why it is easy to squeel a tire. In this example, the axle is the weakest link.

If it hasn't been sold, I still have the locker stored at a friend's place in CA if anyone wants to buy it. The F-350 has had an open differential since the incident and as my friend says "It is a hard truck to get stuck."

Archie

 

A Detroit Locker is locked all of the time, when the vehicle is traveling in a straight line. It "unlocks" in turns, allowing the outside tire to freewheel. The downside of this is that the inside wheel will be providing ALL of the driving force. I'm guessing that the guy's inside axle broke, for that reason.

And the squeal is the inside tire spinning briefly, until it reaches the same speed as the outside wheel, at which time the Detroit will lock back up, and provide torque to both wheels. So in essence, that squeal is the sound of your axle not breaking.


In a conventional open differential, the torque is divided equally between both wheels at all times (note that I said torque, not power). This is true whether going straight or turning, and it is also true when one wheel gets on ice and starts spinning; the torque to both wheels drops to near zero. That's why you can't get anywhere with an open diff and one wheel on ice, the torque to the wheel on firm ground is also near zero.

When going in a straight line, the Detroit drives both wheels at the same speed, but the torques on the two axle shafts can be drastically different. The wheel on ice doesn't create much torque at all, while the wheel on pavement gets full drive torque. In fact, it really can get up to twice the torque that it would get if there were an open diff, because in an open diff, the drive torque is always divided between the axles equally. That's why Detroits are inherently harder on axle shafts, and why they are better for off-road applications, when a little slip at both wheels can be expected.

 

This statement confuses me. "Posi" is slang for positraction, which was (is?) Chevrolet's name for the limited slip differential. It has grown to be a generic name for limited slip (like kleenex for facial tissue). It isn't any better or worse than the Ford limited slip differential.

 

My take on the way a detroit works is this.. both axles will lock together in a corner depending on the amount of torque applied to the diff. If the torque is very little such as a down hill corner both axles are allowed to spin at different rates. Even going straight when you get off the gas both axles are allowed to be independent.. Thats why I like detroits compaired to ARB's cause when an ARB is locked its a spool. Going downhill can be more dangerous esp in slippery conditions..So the design is when power is applied to the Detroit it locks together. One of the worst ways to drive with a detroit is to power around corners. Going uphill with a load and turning with dually's will break axles on dry pavement. If he was to speed up to the corner and float through it the axle would have not broken no matter how much the truck weighed.
This is impossible sometimes thus the main drawback with the detroit. But I wouldn't have anything else.

Dick

 

It's all explained here, with cool animation:

http://auto.howstuffworks.com/differential.htm

Open, limited slip and locked are all explained; it even goes into Torsen differentials.

 

Yes, it's a cool page, but they don't talk about the Detroit at all. It does not require electrical, pneumatic, or hydraulic application, like the ones they discuss.

Nice that they mention Torsens, though. That's the route I would take, if I were going to upgrade. I believe the Truetrac is a Torsen, and I believe they have a clutchless version. I think that is the best of both worlds, for all-around use.

 

I thought I would include a link to the patent for the Detroit Locker. Of course it has the typically vaguely-worded description of how it works, but if you get around to looking at the diagrams, you'll see that this mechanism is elegant in its simplicity (I wish I would have invented it!)

Anyhow, the outside wheel unlocks and freewheels, while the inside continues to drive.

Here's the link. If it doesn't work, search on patent number 4,498,355 at www.uspto.gov:

http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnet ahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=4498355. PN.&OS=PN/4498355&RS=PN/4498355

I think Detroits are cool, but anyone who uses one for any kind of heavy-duty application should understand how they work, because they seem to be capable of putting a lot of stress on individual axle shafts, as Acheda pointed out in his very interesting case history.

-Jeff