How tight should a differential be?

[blykins]

I have an Auburn Pro for my 9"....I was just wondering how tight it was...one of my buddies came over, and we took some breaker bars and stuck it in between the lugs (no wheels or tires on the car yet)....he held his side, and I couldn't budge it. I know posi-trac diffs should be tight....but this tight?

[gsharapa]

If your going to race the car you want them set up tight. On the street and some racing I'd recommend a bit looser. You should beable to turn it.......Put the wheels and tires on and try it as it should turn with more leverage. If not I'd have checked!

[David Kirkham]

blykins,

I am not sure about your differential as we use the Power-Lock differential, but...

The differentials are supposed to be tight, but two guys can move the tires opposite of each other without grunting too much. I am not sure what that translates to in foot pounds of torque, but I have done it several times without bustin' a vein. Just grab the wheel and crank. You shouldn't have to strain.

I am not sure if this helps...

David

[blykins]

Unfortunately I don't have any wheels and tires yet....this kinda scares me now...We each had a 1/2" breaker bar between the lugs...They turn freely together...I built the rearend...and the axles were sent to me with the axle housing from Shell Valley...it's their standard setup. I would hope that they didn't mess anything up.

[blykins]

There's not anything funky you have to do to an Auburn diff before installing it is there? It seems like the only other way the axles woudn't turn independently would be if the axle shafts were rubbing against each other.

All parts are new...

[cobrashoch]

blykins - I have a 9in. Auburn Detroit locker. When it was new with a new ring and Pinion it was fairly tight but after about 10 hours of use it loosened up. Try this. Jack up the rear end of your car with the wheels on, break the driveshaft to the yoke, and see if you can turn the wheels by hand at the yoke.(about 5 lbs torque) On my car you can, with the rear end hot.
Of course there is more to this simple test than meets the eye.
Like brake drag, wheel bearing resistance and so on. Generally the easier it is to turn the rear the more power you car will transfer to the wheels, aka racing 101.
With the driveshaft off and one wheel on the ground I can turn the other wheel at the lug with about 10 lbs of torque on a torque wrench, to simulate going around corners.
Other stuff, don't run any trick gear lube in a Auburn, just straight 90 wt. dino goo. And change it after about 20 or 30 hours of use on a new break-in. I tried red line synthetic on my first change and started to get ring gear wear. So I switched back to Kindall dino lube and I noticed it was also quieter, esp. going around corners. click,click,click,click.
I'm using pro gears BTW. And I can't tear the da#n thing up either.
cobrashock

[blykins]

That may be the reason you got a little wear....Pro gears are much much softer than the regular gear sets...It's mainly for drag racing. The shock of a hard launch could potentially break a regular gear set...so they came up with this Pro series...it's got a lower yield strength, so instead of breaking, it just bends and yields plastically when lots of torque goes to it.

[Morris]

Blykins

When we set up the Diffs for racing..... we used between 125#- 150# of torque .....

With one wheel on the ground and a torque wrench on the other wheel....

Or we'd do it on the work bench.... same numbers...

It is real important on corner entry..... turn in........

To tight will cause the car to understeer... or push....

Just some thoughts.....

[cobrashoch]

blykins - Actually I strarted with a old Zoom set of street 410 gears then switched to the Richmond pros later. Pro gears are angle cut different than street gears also, and are actually stronger than stock gears, and noisier. And they wear out faster also, esp. on the street. For that reason I've allways had my pro street rear ends set up a little "loose" down through the years,,,,,,,,,,,,,,,,, Spools are another story. I think you will like your locker if it is set up right , but it could be a little stiff at first though. Depends on who and how it was set up. The only thing that I didn't like about my rear end was it really grabs hard on hard turns, when you pour the coal to it. Took me a while to get used to that. Straight line - it's the berrys.
cobrashock

[cobrashoch]

Morris - I'm not sure what you are talking about when you talk about your setups. It's not you, it's me that's confused I'd bet. I know of no way to set a preload into a Detroit Locker. They are all or nothing rear ends and can't be "set" like a "True Trak" or some of the other newer lockers that are out there. Confused in Indy.
Cobrashock

[Morris]

Ron

Your right .... we were using a Salibury diff and we made our own rear end housings out of magnessium....

The salsbury was a limited slip differential.... and you could establish break away torque's for corner entry.

I guess I didn't read his post.... just went into auto brain engagement.....

That's what happens when you get into middle age..... and that goes into the 70's....