2005 HD rear axle question

[SLT556]

Do the 2005 2500HD's have a locker or posi? I thought they were lockers.

[DmaxMaverick]

Eaton Gov-Loc, which is a locker.

[EWC]

I don't consider the Gov-Loc to be a locker but more of a speed excited posi . You can rotate the wheels in different directions , until the governor kicks out , and then the posi is locked . I did this once on a brand new K1500 that I bought . Had it up on the lift and just started playing with the rear tires . You could turn one tire and the other would not turn , but get them up to a certain speed and the other tire would kick in . A locker ( to me ) is like the Detroit Locker where it operates just the opposite way i.e. when you turn a corner the outer wheel will rotate at a faster speed than the inner wheel and the locker will unlock . The locker is always locked until it is unlocked . The Gov-Loc is unlocked until a certain speed ( assuming dry pavement and equal traction to both wheels ) and then the governor locks the posi . The Gov-Loc has frictions , be they cones or clutch plates , while the Detroit Locker is all mechanical and very strong . I had a Detroit Locker in a 68 Camaro with a 468 big block , Doug Nash 5 speed and drove this on the street . It eventually went 10.25 @ 136 MPH with the Detroit Locker . The Gov-Loc wouldn't have come close .

[SLT556]

So, it's basically a posi that can engage and disengage? Any manuals you know of where I could read up on this?

[More Power]

You can read more about the Eaton Gov-Lok here (http://www.truckworld.com/How-To-Tech/Lockers-Differentials/4x4Lockers-Diffs.html). (click the blue text)

And, you can see photos of one HERE (http://www.thedieselpage.com/reviews/randys.htm). smile.gif

While I was at Randy's R&P this past September, I snapped a couple photos of an AAM1150 rear diff out of a 2500HD that was in for service.

http://www.thedieselpage.com/images/2500hdrear01.jpg
http://www.thedieselpage.com/images/2500hdrear02.jpg
http://www.thedieselpage.com/images/2500hdrear03.jpg

MP

[ 12-12-2004, 12:14 PM: Message edited by: More Power ]

[EWC]

The only manual that I have that talks about the Gov-Loc is an older Mitchel manual covering the 1988 models . I have a 95 G van manual that doesn't get into the specifics of the Gov-Loc . An overview of how it works or the testing of the Gov-Loc : for A/T 600-800 RPM in drive , brakes on and apply one parking brake cable to lock wheel . Slowly release brakes , parking brake applied wheel should stay locked and the free wheel should start to rotate . As the speed begins to increase , the locked wheel should start to rotate or stall the engine . It may be nessary to increase the speed to 10 MPH before locking occurs but not more than 20 MPH . They do get into a 2 piece and 1 piece Gov-Loc case that looks like 14 bolt cases and smaller . The point to remember is that it may appear that you don't have a functioning posi if you just spin a tire . There has to be that speed differential and then the governor locks the posi . You will know when it locks ( scared the !@#$ outa me ) ! Have you tried any of the Eaton websites or off road magizines ?

[David Utz]

Posi is a limited slip type where clutches distribute some torque to both rear wheels. A locker has a gear to gear connection that, when engaged, lock both sides of the axle together. They can provide 100 % torque to either wheel. The G80 is a locker. It is normally unlocked until one wheel spins 100 RPM faster than the other. This allows you to turn corners. The Detroit type is normally locked until the difference in wheel torque forces it to uncouple. While this type of locker works great for drag racing and industrial uses, it is not a good choice for normal day-to-day driving. They can stay engaged if you are accelerating and keep you from turning until you back off. A third type is the manual locker. It is unlocked until you hit the switch, then stays locked until turn it off. The G80 is a compromise that allows normal turning but can lock when needed without driver intervention.

[EWC]

That's a good shot , from Randy's R&P , that shows the governor weight , crescent shape to the right , that rotates out to lock the posi . There are other posi's ( Gleason and others ) that are totally mechanical and work with spur gears . The theory with this type is that one type of gear can turn another gear one way but not in the reverse direction . They use these in Indy type cars but I have read there is another name for these and they are produced for the street .

[EWC]

Dave , I consider the Gov-Loc to be a posi for a few reasons . One is that most posi's have a clutch pack of some kind to drive the rear wheels . There is a preload or exceeding torque value that will cause the clutch packs to fail or not split the torque evenly to both wheels . Most have a set of springs to preload the clutch pack . The Gov-Loc uses a governor to apply the preload at a certain speed . Consider when the vehicle is traveling at a speed greater than 20 MPH , the rear will be locked . What happens when you encounter at turn at a speed above the lock up point ? The posi component of the rear is locked but the differential component still works i.e. the vehicle can turn a corner without the wheels hopping or chattering . This is accomplished by the slipping of the clutch packs . If the clutch packs have failed , for one reason or another , the governor can still try to lock the posi but the clutch packs will not distribute the torque . As you said a posi has clutches that distribute the torque and the Gov-Loc has clutches . The torque still has to go thru the clutch packs to drive the rear wheels in a locked condition and that is not a gear to gear connection . It is still a speed differential sensitive posi , 100 RPM as you stated , whereas a locker is mechanical and usually locked most of the time . The Detroit Locker has to unlock in turns , outer wheel overruns inner to unlock , and this is by design a totally mechanical differential . I did read about the " problems " with driving them on the street and going into turns under power and getting out of shape but I didn't encounter any problems like that or steering problems in turns . To be honest , I had more problems with a Ford 9" posi , that I had shimmed way to tight , as far as turning corners .

[DmaxMaverick]

EWC

I dissagree. The current Eaton Gov-Loc will only lock with a wheel speed differential of 100 RPM's. That means that one wheel has to spin 100 RPM's faster than the other. It will not begin to lock at speeds above 20-25 MPH, but will remain locked, if already locked, above those speeds until the differential torque is equalized. If you start a tight turn and traction at one wheel is lost, the Gov-Loc will lock, and stay locked, until you get straightened out and traction is equalized.

The current Eaton Gov-Loc is designed with a carbon clutch disc that preempts engagement, which makes the unit more civil, less harsh. The clutch is more comparible to a synchro in a tranny than a clutch pack in a limited slip. The carbon friction surface only aids in initial torque distribution, then the diff is locked mechanically if the wheel speed difference continues above 100 RPM's. In effect, it is both a limited slip and a locker. It will allow limited slip up to a 100 RPM differential, then lock by way of hard parts. This allows the rear end to prevent a locking condition if a slight torque shift overcomes the traction condition and the wheel speed differential falls below 100 RPM's. 100 RPM's may seem like a lot, so try to visualize it. That's less than 1 1/2 revolutions per second. In most cases, the lock will occur in less than one wheel revolution.

[EWC]

Ok , maybe I don't understand totally how the Gov-Loc works . The article that MP put in his post states that it is a hybrid posi/locker and will not work above 20 MPH for cornering reasons . How is the locker " locked " and how does it corner when locked ? The torque is still transfered through the clutch pack , right ? That is still a posi , with clutch packs , and a different way to apply the torque through them . Do the weights and governor apply pressure to the clutch pack causing the side gear to compress against the differential housing ? That is a posi . Maybe there is a very thin line between locker/posi , when talking about the Gov-Loc , but to me a posi has some type of clutch pack , that can slip even if locked , where a locker is mechanical and has no clutch pack .

[SLT556]

OK, I got it now. I was getting confused by people calling it a posi and saying it engages and disengages. I thought I was dealing with some kind of rear end development that I some how missed all togther. I have plenty of posi experience with the Eaton unit in the 12 bolt in the back of my 71 SS Chevelle. Based on the description of the Gov-Loc, I would definately say it's a locker since it does mechanically lock together. Thank you for the replies and explanations.

[DmaxMaverick]

EWC

I guess I'll try it again.

I think that a lot of the confusion here is the terminology. Really, there is no such thing as a "posi". That term came about years ago, and maybe meant something then, but not now. "Posi" is short for "POSItive traction" only means there is some sort of device in the rear end that manages torque differentials.

The locking device in the current (I say current because Eaton's Gov-Loc design now is different than years ago) Gov-Loc does not rely on the carbon clutch to transfer torque, it only aids in the engagement. The Eaton locking device is similar to the Detroit, but operates oposite to the Detroit. The process is progressive, not on/off until the locker is fully engaged. Under some conditions, it can be quite a violent engagement.

As I said before, it the locker is locked, it will stay locked due to torsional forces until it is relaxed by equal (or near equal) wheel traction, even above 20 MPH. It is just like trying to shift a manual tranny under load. Try it yourself by doing a burnout with one wheel on pavement and the other on a loose surface (ice, gravel, mud), and make an imediate sharp turn before backing off the power. I think you'll come to the understanding that it ain't no "clutch" causing all that commotion back there. If your's feels sloppy, like a limited slip, it's broke.

[EWC]

Dmax , I agree with you that there is some confusion in the terminology . However you have stated that the carbon clutch is there to aid in engaugement . That is the entire point ! The locker in always locked and not RPM dependent to be engauged . Perhaps the terminology of " locking the rear " or " the rear is locked up " is incorrect . There is no " locking " of any kind with the Gov-Loc . What happens is an application of torque due to an unequal balance of RPM's . Furthermore the rear cannot remain locked above 20 MPH as this would make it very hard to turn corners at a high rate of speed , being that the rear wheels will continue to drive the vehicle in a straight line resisting any side movement such as turns ( almost like a spool ) . That is where the clutches come into play , there is an amount of torque that will cause them to slip . Try that turn you suggested on dry pavement , at slow speeds , and see what happens .

Again , the article that MP referenced in his posting above stated that the Gov-Loc does not work above 20 MPH due to the weights having springs to inhibit their movement . If you think about it , why would you need a posi at 70 MPH ? I'm not trying to be an a$$ but the definitions and the workings of the Gov-Loc have not made any sense . The power flow through the rear is

1. From the pinion to the ring gear

2. The ring gear to the differential case

3. If this is an open rear the power is then transmitted through the pin that holds the differential gears to the case ( some cases have 4 differential gears , the 14 bolt looks to have 3 )

4. The differential gears in turn transmit the power to the side gears ( some people call them spider gears ) and out the axles

If the open rear has equal traction to both tires , the power will be divided evenly . If there is a loss of traction , to either wheel , the torque will go to the wheel with the least traction . Where a " posi " comes into play is the resistance of the side gears from just spinning in the differential case . Remember the power comes down through the pin that attaches the differential gears to the case . This is easy to see with the rear axle cover off . No posi and in park , one wheel will turn in one direction and the opposite wheel in a reverse direction to the first . The ring and pinion will not be moving but the differential and side gears will be rotating . This is where a " posi " of some kind is helpful . The side gears are kept from rotating and are forced to rotate with the case . If both the side gears rotate with the same RPM's as the case , there is no slippage and the torque is divided evenly between the 2 wheels . When the side gears do not rotate evenly , the differential gears and opposite side gear will rotate around the gear that has the same RPM as the case i.e. the wheel with the most traction . The Gov-Loc has an operating window that looks for a difference of 100 RPM's before it will engauge . The Detroit Locker has no such window , it is fully engauged unless the RPM's of the axles are enough to cause the outer wheel to overrun the inner wheel . If the inner workings of the Gov-Loc were removed and set beside an Eaton " posi " and a Detroit Locker , which one would they most resemble ?

Again I refer to the article that MP lists in his posting , the Gov-Loc is listed with the " posi " section and not the lockers .

[DmaxMaverick]

EWC

Read my reply(ies). The Gov-Loc IS a locker. It locks. Period. It will not unlock until the conditions that caused it to lock have gone away (or something fails). Period. Even above 20 MPH. It will not LOCK (engage) above 20 MPH, but will stay locked above 20 MPH until the torque is equalized between the wheels, like driving straight. The example I gave with the manual tranny applies. Meshed gears under load will stay that way unless there is enough force to overcome the friction or the load goes away.

Using your understandings, a Detroit locker is not a locker at all. It is an UNlocker. What does it do? It unlocks. It does not lock, it is already in that condition. The gov-Loc, E-Locker, ARB, Ox, etc, are lockers. At rest, they are open. Something has to happen to make them LOCK. The Detroit at rest is locked. Something has to happen to make it UNLOCK. Once again, terminology.

In a locked condition, the Gov-Loc is every bit as positive as a Detroit, lock-wise. It will lock solid. No slip. The detroit will only stay locked under conditions of lost traction on one wheel, or while turning, if there is sufficient resistance within the locker. While turning (Detroit), it will unlock to allow the outside wheel to turn faster, unless there is sufficient resistance, like under power. The resistance is the input of torque (engine) vs. the traction at the wheel. The only way a Gov-Loc will be locked at 70 MPH is if you got it locked below 20 MPH, and it stayed under power, with differntial torque between the wheels, or you are in a turn. The conditions that may cause this to occur are probably conditions that you would like it to stay locked. An example of this, perhaps, could be an attempt to get out of a bog. Wheel speed is key in mud, and wheel speeds well above 20 MPH with a ground speed of maybe 1 MPH is not uncommon. Been there, done that. JK's response to this condition is the pair of burnout marks left on the pavement. In his case (and many others), 20 MPH wheel speed is achieved well before there is any ground speed. A sustained locked condition would be desirable in this situation.

There may be times when the Gov-Loc does not unlock when you would like it to. That is the nature of the beast, and is a fair trade-off, IMO.

[Viking]

Do the carbon clutchs wear out? If so does the differential still function as a normal "locker" but with a harsher engagement? I am led to beleive that the darkening of the fluid is due to carbon clutch wear. At what point would the clutchs be considered worn out?

[More Power]

I took a bunch more photos while at Randy's showing a variety of cut-a-way lockers/limited slip diffs. If you guys are interested, I could run some of those here.

MP

[EWC]

MP , I'd like to see some pics of the rears ..PLEASE !

Dmax , the article that MP references does a pretty good jod of describing the different differentials and then www.traction.eaton.com (http://www.traction.eaton.com) talks about " The Locker " .

[More Power]

Here are a few of the differential display photos I shot while at Randy's Ring & Pinion (http://www.thedieselpage.com/reviews/randys.htm).

http://www.thedieselpage.com/reviews/randysdiff01.jpg
http://www.thedieselpage.com/reviews/randysdiff02.jpg
http://www.thedieselpage.com/reviews/randysdiff03.jpg
http://www.thedieselpage.com/reviews/randysdiff04.jpg

This last one is of an Eaton Positraction.

MP

[ 12-14-2004, 04:21 PM: Message edited by: More Power ]