How do I check the condition of my posi traction?

[chrisjkruse]

With both wheels off the ground and the transmission in park, how difficult should it be to overcome the posi clutch? I can grab one wheel and turn it without too much effort.
Is there a rule of thumb for this?..Its the stock unit, but the posi was replaced by the buick dealership about 50k miles ago.

[Keller]

Why was it replaced, and with what? GM/Eaton unit, or something else?

With tranny in neutral, jack it up in the middle of the rear end, and turn one wheel. If the wheel on the other side spins the opposite direction its an open (non-posi) diff.

With tranny in neutral, just jack up one side and try to turn the wheel. If you can't turn it, its a posi, if the wheel turns the drive shaft its open diff.

[chrisjkruse]

Well, a long time ago my wife hydroplaned, hit a curb and bent the original axle and housing. The first body shop replaced the rear with a non-posi rear..so we complained to Allstate and they had the Buick dealership install the posi unit and make sure everything was back to original condition
It is definantly a posi, I've seen the inside.
I had checked it in PARK with both wheels off the ground and one wheel went backwards easily when I was bolting the tires back on.
I will check it in neutral with one wheel on the ground like you said.
Thanks

[Keller]

The OEM Eaton posi has 400# springs. It would be pretty hard to turn one wheel against the other given the tension. If you use the methods described above, you'll be able to see it work (or not) very quickly.

[vettestr]

The method used for determining clutch and system performance to a testable standard is = (must resist or not not turn @ or below 250 LBS torque) A little old school but a test used years ago when I worked on the Dealership Heavy Line. Use a torque wrench to measure the minimum allowable resistance of the posi assembly. required to turn one axle while the other is held in place. If it fails to turn at 250 LBS then is passes the the clutch test.

I still have the tool but it would be easy to make a home version. Weld a 1/2 drive deep socket to the center of a 8" length of thick wall square tube. Jack only one wheel off the ground and chalk the other wheel so it won't turn. Place bar/socket tool on the axle face with the tools end hitting a wheel stud. Now try to rotate the axle using the tool and torque wrench in the forward direction. If the breakaway torque wrench clicks at a setting of 250 LBS before the axle turns the assembly is working to the allowable standards.

[chrisjkruse]

Thank you Jeff,
I get confused trying to understand how our positraction works. I assumed that when I had it up on jacks and in Park that there would be
considerable resistance just getting both tires to go in opposite directions.
I did what Scott has said and I was unable to move the raised tire, so i am ok with what I have..
But, to have an actual torque specification is very much appreciated. I thank you. .
Could you ( or anyone) answer this question for me:
Do the clutches get tighter when on the road and goosing it? Or is it just a set spring pressure?
This is something that Iv'e been trying to understand..but just can't seem to "get it"

[kenmosher]

Kind of ... basically the clutches engage when one wheel is spinning faster than the other.

Dug this up...

http://auto.howstuffworks.com/differential4.htm

[vettestr]

Originally Posted by chrisjkruse

Thank you Jeff,
I get confused trying to understand how our posi-traction works. I assumed that when I had it up on jacks and in Park that there would be
considerable resistance just getting both tires to go in opposite directions.
I did what Scott has said and I was unable to move the raised tire, so i am OK with what I have..
But, to have an actual torque specification is very much appreciated. I thank you. .
Could you ( or anyone) answer this question for me:
Do the clutches get tighter when on the road and goosing it? Or is it just a set spring pressure?
This is something that Iv'e been trying to understand..but just can't seem to "get it"

Chris, Ken linked a photo showing views of a differential. That gear on the top is what makes it all work. Remember your old physics instructor talking about actions having an opposite but equal reaction? Gears inside the housing are being turned or driven by the side gears (splined gear with axle going through it) and these turn the spider gears (technically the pinion gear). As the side gear turns the spider/pinion gear rotates around it. If wheels are turning at same speed these gears simply turn together without need for 1 gear to get away from the other. The side gear can rotate but not move in the housing but the pinion gear slides on a shaft (pinion shaft) but is kept in place by the spring plate and clutches.

If a wheel (axle-side gear) starts to turn faster than the other (wheel spin) then this is where the spider gears are not happy !! They try to get away from the gear forcing it to not simply rotate at same speed. The spider gear tries to move on its support (pinion shaft) and this applies pressure on the clutches and floater plates (5@) to keep it going the same speed. The clutches apply force (opposite and equal) to force making it turn at different speed or orbit until they are the same. The harder the gear tries to get away from gear driving it the harder the clutches lock up. The point you can measure the clutches ability to lock up or turn is or should be GREATER THAN 250 LBS. or the spec mentioned earlier. Note: this is without the mechanical ratios and multipliers of the gears being applied inside.

I have taken a few artistic liberties here but hope it works for you in the end.
This is all for the GM Eaton type but there are other methods GM has used over the years, this one works well IMHO. Jeff C PS sorry so long winded

[chrisjkruse]

Thanks for the info Jeff.

I mispoke when I said that I checked it based on Scotts instructions. Actually the entire rear was up on jacks, so early in the morning before I had my coffee i put in neutral, dropped one wheel to the ground, and couldn't move one wheel against the other..so I assummed everything was ok..then left for work.
Then I realized that I had forgotten to release the E brake! I installed new brakes and I engaged the E brake the night before,

So anyway.. this is what I have...all tests on jacks indicate an open diff. or posi with no preload.It is defininately a LSD though.

I parked one wheel on dry pavement and the other wheel on very wet grass. FOOT OFF the BRAKE. I goosed the gas and the car launched with a squeal.
I did this twice..once with the driver side in the grass, and once with the passenger side in the grass. The results were the same,
the patch of rubber on the street was 5 feet long and the patch of (merely scuffed) grass was about 6 inches longer at the end of the burn.
QESTION:
Do I have a different type of lsd? It has an " S " shaped spring and clutches. It was installed in 1992 by the Buick Dealership.
Or is it just wearing out. (no preload) Anyone please respond. Thanks Chris


PS. I wouldn't even have a question if i hadn't spun one wheel and the other went backward. It seems to work just fine for driving and traction..

[Keller]

Originally Posted by chrisjkruse

the patch of rubber on the street was 5 feet long and the patch of (merely scuffed) grass was about 6 inches longer at the end of the burn.

Not to add to the lingering pain of an ongoing thread that simply won't end...but what you said here means that both wheels were spinning in your "creative" launch, right? If it wasn't a posi, only the wheel with less traction (i.e. on the grass) would have spun, no?

Would it hurt to do the suggested test properly? I do believe it is working correctly. And the "S" spring clip indicates it is a posi.