[Bumpstick]

Well it finaly happened... Was running at the track last night and doing very well until I was doing a burn out and heard a bang...? I then noticed I could only move about 10ft forward and backward... I thought I had broke the center pin and it was hanging out of the carrier... But when we finaly got it back to the pitts and removed the cover we found both spider gears on the center shaft had exploded and 1 large chunk had got caught on the ring gear and was stopping me from moving... It also bent one of the pins of the assembly for the locker system... The carrier is a GM factory posi unit, the type that has a block that engages the spider gears to lock them into place...


Now I`m to guess if everything else is ok...? Meaning the spider gears on the axle drive sides and the ring and pinion... Then I can just replace the spider gears and shaft and be up and running again...?


Also other idea`s on options to prevent this from happening again...? (really want to stick with the 12 bolt setup)


BTW this a 1969 Chevy PU (a little heavy @4200lbs) w/355 that runs 13.80`s

[85406]

Try this site. Go to the 12 bolt section and look under the hardened spiders and side gears.
http://www.tomsdifferentials.com/

[Robinson Robin]

I would buy an new eaton posi carrier they are much stronger than the originals and you will get all new flame hardened side and pinion gears , pin and everything else you need. Make sure you give the ring and pinion a good inspection for chips, damage ex.....

[302 Z28]

Ditto on the Eaton carrier and posi unit, very much stronger than OEM.

Vince

[BOBCRMAN@aol.com]

If you are putting any kind of h-power and torque thru it and get some good hook on the track you will break about anything in that 12 bolt but a spool. Back in the seventies I spent several thousand dollars trying to make a twelve bolt live, Moroso brute strength, Eaton type posi,etc ,just about anything I could get to keep the thing together. Then the axles started to go!. NOW its 9" Ford all the way.

[Robinson Robin]

That might be true but he said its a pick up and hes not running that much power a good posi should be easily able to live. Besides unless your sticking to the track why on earth would you want to put a spool in... my understanding is that this is a street driven vehicle. The posi is the way to go in my option

[Bumpstick]

Well finaly today a closer inspection of the cross shaft and what was left of the spider gears revealed that the spider gears were gauling onto the cross shaft...? I was running reg 80-90wt gear oil with the additive... (posi-trac additive) Also no nick`s or any other problems with the ring & pinion, also the outer drive spider gears are in great shape also as well as the locking block...? It looks like the only thing I need to repair this rearend is a new set of spider gears along with the cupped shims that they ride on...? I have another cross shaft and lock bolt (which was broke also from the cross shaft spinning on the carrier)...


Ok anyone got any spider gears for a 12 bolt GM...?

Also any idea`s as to why this happened...?

[Robinson Robin]

well if the spider gears where galling into the pin that would be adhesive wear.... to much heat and not enough lube. This generally occurred when people get stuck in the snow with an open rear and and put their food down. The spider gears aren't meant to be spinner this fast and suffer from extreme lack of lube. With a posi this should be a problem unless the clutches are worn out letting power flow to only one wheel. So would be my guess. One other thing to mention is that obtain the pin will be come loss in older carriers from where and this allows it to move a bit when ever load is applied this obtain has the effect of breaking the retaining bolt but could also contributed to the pin breaking. Unfortunately the only real fix for that one seems to be a new carrier and pin.