8 3/4 Axle Clunking When Turning

[toocheaptosmoke]

Have been helping work on a friend's '73 charger and we ran into an issue at the end of last season.  After finally getting the engine and trans back together was out doing some test drives to break things in, all was going well.   That is until we were coming back from wing night and needed to test the burnout capabilities of the fresh 440.   Did a couple small burnouts, one wheel peels, which was nothing surprising since we assumed it had open gears, you could roll one tire in the air and the other would spin backwards. 

So anyways, doing a peg leg burnout from a stop when after 50 feet the axle locks up and we're now spinning both.    Well, that was odd?   Make a turn onto another road and CLUNK CLUNK CLUNK...   Crap, must have blown out the spider gears.     When jacked up, now both wheels turn the same direction when spun.   Tried moving the car around the driveway and its popping and banging, almost as if the drive gears are binding up.   



Fast forward to today, pulled the third member out, and to our surprise it looks to have a sure grip?  And even stranger everything looks good inside, no obvious damage or chunks of metal.  I'm not familiar with these sure grips, has anyone had this happen before, or know what commonly fails?  I've been trying to research the issue but having trouble finding similar symptoms.  Appreciate any help!

[Charger_Dart]

Not sure if this will help or not -

I bought a 70 Road Runner last fall that had seen very little mileage for many years. This spring when I took it out, it would clunk, clunk when you made a turn to the left or right. Going straight it was quite. I talked it over with an older retired mechanic and he thought the sure grip clutches were the issue from it sitting for a long period of time. He suggested I drive to a parking lot and make 10 tight circles to the left followed by 10 tight circles to the right. Then drive it 5 miles down the road and return and do the same circles again. Much to my amazement it completely fixed the issue and have not heard a single clunk since.  Its only been a couple of months but it seemed to have fixed the issue and I didn't have to pull it apart. Mine is a Dana 60 but I would think the sure grip unit would be similar.

[Nacho-RT74]

Being a 73 and assuming is original to the car this is a cone kind, so no clutches

[John_Kunkel]

Look closely at the housing where the spider gear cross shaft is, not uncommon to find the housing wallowed out allowing the shaft to move.

[toocheaptosmoke]

Will take a closer look at the pins, then go from there.  Will let you know what we find, thanks! 

[toocheaptosmoke]

Was able to take things apart, found that the cross shaft roll pin sheared.   The pin was still solid in the housing, it wasn't wallowed out like the one pictured.   

Was trying to source a replacement cross shaft, but most places don't list anything for the 8.75" axle.  Does anyone know where I could find a part number or something to get a replacement?

[taxspeaker]

I have used member Birdflu (Gary) here and highly recommend him

[John_Kunkel]

Part number for the shaft is 1633928 and the pin is 455313. Judging from the galling in the shaft bore, the spider gears are probably distressed too...IOW, the whole differential is probably junk.

[Birdflu]

You need a new Sure-grip. The reason your pinion shaft roll pin broke is because your Sure-grip 'cone clutches' are worn and were, more than likely, bottomed out in the case halves. The worn cone clutches caused your internal gears to spin too fast (essentially someone did some ferocious one wheel peels) which caused your 2 smaller pinion gears to 'weld' themselves to the cross shaft in turn, (pun not intended!) created enough grip on the shaft to shear the roll pin and cause the shaft to spin in the differential case. PM if you'd like  

[toocheaptosmoke]

You nailed it Birdflu!    Didn't even realize the pinion gears were seized solid on there.   

The current gears were 3.91's with the bad sure-grip, was able to find a spare 3rd member with 3.23 gears and another sure grip that appears to be in better shape.   Just have to decide now whether to toss the 3.23's in and roll, or swap all parts around to keep the 3.91's.    Car isn't a drag racer, just a weekend cruiser.

Thanks guys. 

[c00nhunterjoe]

3.91s are a great middle of the road gear in my opinion. Chevy guys wish they had them going from 3.73s to 4.10s.