Almost good, except you confused a locker with a spool. A locker "ratchets" for turns and the like - so you can still turn - just doing do it at fast speeds or your tires will chirp. A spool or welded differential powers both 100% of the time.

Except in the cases of cable/air lockers, like teh ox and ARB, whereas it is either fully "open" or fully "locked" (acting like a spool when locked).

Also there are some lsd/locker's out there now too - I think detroit has an electronic switch one...

 

I have a new 04 4.6 with a 3.55 Limited Slip Differential, I have always made it a point to take off as smoothly as possible until brake-in seems adequate, I feel this gives the rear-end setup enough time to wear in which can be crucial to the longevity of the third member. If you have ever ridden motorcycles and replaced the clutch it takes a while to fully brake in the plates. I think anything with a clutch would be similar as getting things to wear in properly. Just an opinion May be completely wrong.... He He GG

 

Would somebody put all this locker and friction stuff into laymans terms so that I (and hopefully there are others) can understand how it relates to the rear end feeling like it slips and then grabs on normal acceleration pavement takeoff? And what we should do about it? This is a new truck built for the street with off road capabilities I don't feel like it should be doing this stuff.

 

Okay, as simple as I can get:

Power will go the direction of the least resistance. Example? Water will run DOWN hill, before running UP hill. Makes sense.

So, if power is going to your rear differential (the "pumpkin in the center of your rear axle that houses your gears, et cetera)... there is nothing there telling it which tire to send power to. So, normally it splits the power to each wheel 50/50.

However, when one wheel is on ice or sand, it has less "resistance" than the other. Thus, the truck will be sending power 50/50, then suddenly as one tire "loses grip" it will take more and more power, until you are getting 0/100 power to the wheels, the one in sand/ice is slipping, and the one on solid concrete is sitting there doing nothing.

Quite frustrating when you realize your 2wd truck is really only 1wd! Same with 4x4, if you have no traction devices, it is very common to be in 4x4, have one rear tire start spinning (say the rear passenger side) and suddenly find yourself sitting in ruts with only your driverside front and passenger side rear tires spinning (it will normally be those two because of how torque is applied to the shorter shaft of the offset front differential).

So, people would weld together the spider gears in their vehicles. That way, it was almost like having just 1 axle shaft across the back (like some RC cars). Therefore, if one tire was on slippery stuff, it would still spin the exact amount of rotations as the one that isn't slipping, which would allow the one of solid ground to still push/pull you throuch and make it so you are not stuck. GREAT! Now your 2wd is 2wd and 4x4 is 4x4!

Problem! When you go around a turn, your outer tires are traveling a farther distance than your inner tires (simply geometry). Well, if both tires always turn exactly the same - together... then going around turns your outer tire will "chirp" and not get good traction, or your inner tire will "hop" and bounce you around... Both of which will make your tires wear poorly and last a lot shorter of a time.

So, then we have this wonderful idea of ratchet-lockers. When one wheel is slipping, it "locks" the differential (gears and all) up- so that then - both tires turn at the exact same time - like being welded! What about corners now though? Well, the locker has a "ratchetting" disconnect device, so that when you are moving slowly, such as regular turns, it won't lock up. Thus, saving your tires, and still giving you maximum traction. Bad side? A lot of people don't like taking corners slower and being more careful when they have a locker.

Applications? There are many aftermarket brands that make lockers. Some are "fulltime" - they always are ratcheting/locking and then there are selectable, which normally are electronic/cable/air pressure operated and can be switched from "fully locked" to "fully open" or even to "limited slip" so you can have a locker when you need it - and not when you don't! However, most of these switchable applications are fairly expensive, or weak (weak are generally the "come in vehicle" ones like in the Chevy Avalanche, Toyota Tacoma, et cetera... most big name switchables are good, ox/arb, et cetera).

The middle-man? Limited Slip. This system allows your tires to go different rotations - so corner is no problem... However, when a tire slips, if it reaches a certain speed/amount of power from the differential (say you are getting power at 10/90) a system of clutches in the Limited Slip (in your differential) "brakes" on the slipping wheel, and applies power to the non-slipping side, thus allowing you to get unstuck.

Then we have the spool. Basically like welding your differential, except not as weak.

So:
Welding:
Pros: No slippage. Ever.
--------Cheap.
Cons: Bad for corners/tire wear.
---------Weak, not recommended at all.
---------Not recommended on ice.

Locker:
Pros: Very minor slippage. Ever.
--------Fairly price negotiable.
--------Very strong.
Cons: Need to take corners slower or get bad tread wear.
---------Not recommended for a daily-driver
---------Not recommended for ice.

Optional Locker:
Pros: Choices!
--------Very strong aftermarket competitors.
---------Absolutely no slip, or completely open - or Absolutely no slip and limited slip.
Cons: Not very cost-efficient.
---------Some require onboard air, et cetera
---------OEM applications are notoriously weak.

Spool:
Pros: Cheap
--------Strong
--------No Slip, ever.
Cons: No slip - ever - bad for cornering and tire wear.
--------Not recommended on ice.
--------NOT recommended on a daily driver.

Limited slip:
Pros: Maintain good cornering while still having a traction device.
---------Hardly any less tire-life.
Cons: Not as much traction as lockers/spools
---------Generally aftermarket they cost more than a stronger locker.



Also be aware that there are front and rear applications for these, and front applications take much more research than rear, as it will do all sorts of things to how you need to drive (yes, even in 2wd) - because of how torque may now force your driveshaft to spin et cetera and so on.

 

Thanks for the explanation. My truck does have a 3:55 limited slip and I understand the principal behind it. This jerk problem is getting worse, to the point when my wife can feel it both as a passenger and driver. The truck will begin to move forward and then bump/jerk/thud whatever like something just locked in or caught. This is on straight ahead pavement takeoffs usually slower than other traffic. I can keep it from happening by crawling forward very gingerly but then I'm holding up traffic. Is this lash? Clutches? Do I need to change the fluid / friction modifier? Please tell me I don't have to live with it, I'm going crazy hearing questions from people like "what is that jerk in your new truck." I intend to take it in to the dealer but want to be speak intelligently about it as well as know what to ask/expect be done about it.

 

This was happening with mine as well... 3.73 LS. It wasn't too severe and only noticable when the truck was "cold". I took it to the dealer and they soaked the differential clutches in friction modifier overnight, reinstalled and road tested. The problem hasn't returned as of yet... it's only been about 3-4 days, though.

 

Have I got slippage due to not enough friction modifier? Does it make the clutches lock? Is this "bump" the clutches locking in?

 

I realize this isn't any help to those who're having continuing probs with this, but my 4x4 standard diff Screw, which was doing this early on, has all but stopped it at 6k miles. I believe it is still there, but is so reduced in "amplitude" that I'm simply not aware of it during normal street driving. I believe this was a break-in issue. Hopefully, yours will also reduce in time.

 

and more frequent..... I have a call into the dealer. Other than That it's a great truck!!!!!

 

I also have noticed this issue. I now have 2k on the truck and have had the same issue like most of you since day one. I though at first I had a real sensitive bum. It happens here and there mostly when moderate acceleration is applied it is a quick slip..lock type of feeling from a stop. Thought it felt like a ujoint at first but I think it is the LS rearend. I have owned numerous Ford LS in the past and have never had this issue. As soon as anyone has a fix please post here. It sounds like soaking the clutches overnight in Friction Modifier might be the fix.

Jimmy

2004 FX4 3.73 LS

 

They said bring it in, they have had two already. One they fixed by adding friction modifier, one they swapped rear ends. I'm going the modifier route first.... Will update.

 

I posted this same message in a different forum. I believe it will answer quite a few questions...

I had a "shudder" resonating through my entire 2004 FX-4 truck every morning whenever I accelerated from a dead stop while turning at the same time. After the truck warmed up, the "shudder" would almost completely disappear.
While checking out many of the threads on the Forums, I found quite a few '04 owners had the same problem. Needless to say, I was amazed! Many of those same threads kept refering to the "clutches" in the limited slip rearend.
I took my truck to the dealer and told him to keep it for a few days and every morning to take it out and test it under the same conditions as I previously described.
I told him about this forum and how I was convinced that it was most likely the clutches in the rearend. He chuckled and said he hadn't heard anything from Ford about the problem. I told him to fix it anyway!!!
He gave me a "loaner car" and several days later, he called to tell me the truck was ready.
He said: "Ray, I have to confess... I thought you were kidding me about those clutches being bad in the rearend. But each morning my mechanic and I would test drive it and sure as **** you were right... It did shudder when cold. So I got on the phone with a Rep from Ford and I explained about the Forum you referred to. Ford told us to go ahead and replace the clutches. And then we tested it again and found the "shudder" completely disappeared".
My receipt shows that the dealership did indeed remove the clutches. But listen to this... It also says on the receipt that they replaced with "UPDATED" clutches!!!
I have test drove the truck myself several times now, and am convinced it's properly corrected. It now drives "smooth as silk".
I would advise anyone with the "shuddering" problem to have their dealership perform this "fix" attempt first.

My Dealership is: ED MULLINAX on RT 58, in Amherst, Ohio.
My Service Manager's name is: Jay Thoman

If your dealer has questions, tell him to contact Jay.

As ever, Ray
(LuciferRay)

 

Sorry for the delay in posting the outcome from the dealer.( I have been on 7 day, 12 hours a day since I had my truck at the dealer)

They installed a new driveshaft. The truck seems to be better, but it still shudders on takeoff. We had three inches of snow last month. The truck hooked up well without using four wheel drive. For now I will live with it. The truck seems to be getting faster and smoother.

I feel like Im driving a hooptie when the wife leaves me our 2000 expy.

 

I have had a "jerk / slip / bump" sometimes on takeoff that I have yet to make it to the dealer for. After reading these posts I am wondering if this is related to the driveshaft yoke sticking as mentioned in an earlier post in this thread. Is it possible that it is not moving freely in and out on the spline?

Also, when the truck is cold - and I takeoff out of the driveway or any other right angle turn I get a shutter / flutter effect. Is this a ratchetting of the rear end clutches. It does not seem to do this after driving a while. To me these are two different problems. Someone please help who knows!