I took my 67 to the track and noticed the driver side slick wearing more then pass. side.

After viewing video only drvr side is spinning after water box (car is a manual, no line lock. just dumping clutch in 2nd) I jacked the car up and placed it in gear. With torque wrench on a lug nut I was able to break the spring tension and rotate the other wheel in the opposite direction at about 70lbs (I know this is not real accurate as torq wrench is not centered on axle shaft but it gives you an idea) the 70lbs is just the initial torque , once its spinning its very easy to continue rotation.

questions:

Is it worth rebuilding and old 4 series eaton posi unit?

How do you folks feel about the "tuned" units without springs (toms differential recommends them over loaded units as they will not wear the clutch plates quickly)

I did a search a while back and remember reading that these non-spring setups may not hold in the water box. Also if they go out of tune/adj. it will be like and open diff.

Any suggestions/comments.

Thanks, Ray


67 camaro
tko 600
12 bolt 4-series 30 spl.eaton 4.10
moser axles pressed on bearings

It is very common for a posi to spin only one wheel in the water. This will cause the clutches to heat up very quickly and can scortch the oil. Rebuilding the Eaton that you have would be a very good idea, as long as the other parts in it are good. If the gears need to be replaced too, or the case is worn inside then you might consider a new one. You can tune you Eaton. It isn't hard to do. If this car is drag races a lot then I would recommend changing a few things to make it lock up better. You should start with new clutches and shim them tight. Then you might want to go with the 400 or 800 pound springs, depending on how many street miles it will see. You can also leave the oil additive out to help it lock up better. Send me an email if you need more information.

If you leave the additive out will it hurt the clutches or will it just chatter in turns?

It will just chatter in turns. It is best for a street car to have the additive, but a drag car doesn't need it. You can add the additive a little at a time until the chatter goes away. You don't have to put the whole bottle in. This will help with a street/strip car.

Thanks for the info biggearhead

My car is actually setup as a lowered pro-touring type street car. Our one and only track on the island is scheduled to close permanently on 3-31-06 so everyone is now hitting the track before it closes (1 hour or more in line to make one pass!!)

Its working fine on the street. I will check the oil to make sure its okay.If we ever get another track then I will contact you for some prices on a rebuild or replacement.

Thanks again, Ray

IMO tuning a unit by shimming the clutches tight is not a wise practice, even though it works.
The axle gears have a specified CD of 0.262" +/- 0.002".
The gear tooth involute surfaces are designed to run at this CD.
If they are shimmed to a distance less the 0.260", the mating gears can be set in a "destructive interference" condition. The pinion teeth can begin to stress and undercut the axle gear teeth.
I have a picture of this condition, if someone can help me post it.
This would be like running a r&p set CD high with 0 backlash.
If a car needs more bite I have always switched to 22 plate clutch sets and the 400 or 800 pound preload sets.
Again this is just my opinion on the subject of "tuning" by shimming a unit tight. Hope it helps.
Eric