741 Cone Type - looking for tear-down/build up info

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Joe Mc

Joe Mc

No Car Like A MoPar!
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Before anyone mentions they'd chuck a 741/2 and go 489, I'm operating on a budget and am looking for specific info from folks in the know about these cone stye SGs.

I got a book DVD set on HP Differentials which is a decent reference, however, on the cone type diffs it states: "Borg-Warner originally manufactured the cone type from 1969 to 1974. The cone type cannot be rebuilt; your best option is to purchase an aftermarket unit if yours is not working correctly."

So the point I'm at now is I just picked up the complete drum to drum from a 72, springs included. Before I move forward with anything other than the tear-down I've done so far - removed springs, axles & Chunk - I want to tear-down the SG posi and inspect. Since there isn't anything of help in the manual/DVD for the cone type I know there are folks that have machined the cones and shimmed the gears with good success out there.

I'm asking if someone can provide some specific info as to what to look for during SG tear-down as far as: where and what the heck are the cones - I can't find any pictures anywhere that specifically point to the "cones" so I know what the heck I'm looking at, is there a torque that it diff should slip at when one axle side is secured and you're torquing the other axle so you can judge whether the cones need to be machined, and measurements of the cones prior to machining?

Other than that missing info I should be good with everything else.

Thanks
 
Google Aurburn limited slip. They are essentially the same. Yes, they can be rebuilt....sort of. I've done several. The cones wear the case to the point that they bottom out in the case ends. when this happens, they lose the ability to lock up. I have successfully dissassembled several units and repaired them. Here is how I did it. Dissassemble the carrier, some bolt together in two pieces Some are one piece. Remove the preload springs, spider and pinion gears. Remove the side gears and finally the cones. On the outside face of the cones (the small side) you will need to remove enough material so that the "screw" portion of the cone will again engage the inside of the case. How much is strictly up to you and how badly you think the assembly is worn. I have removed as much as .100". It is very important that you add this same amount removed in shims on the large side of the cone, in between the cone and the side gears. Failure to do this will not get the preload you need and could also result in the side gears disengaging from the pinion gears. This is not covered or suggested in any repair manual. It is just a trick that I learned through the years and it will work well if done properly. It will work even better if you install new preload springs. I don't recommend this repair for anything but mild street cars. It was simply out of being broke and destitute that I concocted it in the first place.

Here is a diagram.

diff-exploded.jpg


The diagram makes the cones and side gears look like they are one piece. They are not. the shims you need to add go behind the side gears in between the side gears and cones.
 
StrokerScamp - BINGO! Now everything I've been reading makes sense - Thanks.

Oh how true the saying "A picture paints a thousand words" indeed is.
 
Well just remember.....it's not a textbook repair, but if it's done the way I outline, it will restore the limited slip function and will probably last a good while if not abused. Oh, and I always use a brake lathe to remove the material from the end of the cone. works real good. Good luck.
 
Is there a break away torque number to see if its still good before I start removing material?
 
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