I'm swapping out my 8.2 for a chevy 12 bolt. I have the housing and stock axles. I plan on getting a new eaton posi unit (unless i can find a deal) and more than likely 3.08's (the 12bolt currently has 3.31's maybe reusable) I'm guessing I'm on the edge of needing moser/superior axles. Was planning on keeping the c-clips since it's a street car. now what about the yoke? upgrade to steel or is the old iron one ok? will be changing to 1/2" studs. so questioned upgrades. girdled cover? c-clips or elimination kit? new axles? yoke? nate
Stock a 70 Stg1 455 made near 500 ft lbs of torque, so did Pontiacs '71-72 455 HO's. The 455HO Pontiacs came stock with McKinion built 12 bolts that had better axles than the typical Chevelle 12 bolt & the McKinnion built 12 bolts also came with 3R u-joint flange. While capable of handling 500 ft lbs of torque, in a stock application, add another 80 lbs of torque, a well set-up suspension, & a pair of 10" slicks, & even the McKinion 12 bolt will fail. The problem will be with the stock Eaton spider gear/side gears & even the HD stock axles can break. In the garage, my 455HO GT-37 sits with a NOS lh 1/4 installed due to such a broken HD 12 bolt axle, a ported head 455HO combo, & a set of slicks. 500 hp/ 500 lbs of torque really doesn't tell us much. With 500-550 hp & 580-600 lbs of torque, I'd normally assemble a 12bolt with parts to create a safety margin different than say with an A-body automatic car with 400-425 hp/500-525 ft lb of torque engine. With long term goals to approach the 500-550 hp & in the high 500's torque level, it makes good sense to skip the $225 aftermarket c-clip axles & go with bolt-in tapered bearing axles. This will require having hsg ends cut off, & new tapered bearing ends installedon the hsg in a line-up bar. One ends up with a TON better situation than pos c-clim elims! Pricewise, going to un $175-300 more than aftermarket c-clip axles & c-clim elim kit, but tapered bearing axles are much more forgiving than c-clip elims. Staying at the near 400 hp-500 ft/lb level with automatic & 3.07's, just buy a pair of Moser c-clip axles & be done with it. 12 bolt pinion flanges... I've used up several original 3R 12 bolt flanges on rears that were in BOP A-bodys that consistently ran low 1.40 60 foots & were sprayed into the high 9's. While the stock flanges heldup, they are at their limit. Problem is the 3R 12 bolt flanges are rare, not of the best metallurgy, & can be easily damaged (chipped out corners) when compressing crush sleeves... needless to say, there are better alternatives avail aftermarket, just as there are solid pinion spacers & shims to do away with crushsleeves. Recently, for 12 bolts in such really quick rides, I've been going with spicer 1350 sized aftermarket pinion flanges. Ck Tom's or Randy's for whatever version you need. On 12 bolt posi carriers, again, if 400-425 hp/500-525 ft lb of torque engine is what you're content with, a new std duty Eaton 12 bolt posi carrier should suffice, esp with tight automatic, 3.07's, in a heavy (4000lb) A-body. On the other hand, planning towards 500+ hp & near 600 ftlbs of torque with lower gears, more stall speed, & sticky tires or slicks, I'd consider something along the lines of a Tom's tuned Eaton unit with solid clutchs, specially heat treated side gears & spiders, & more spring pressure. Basically, that is what I usually build out of empty "140" 3 series Eaton posi cases. The performance rear cover, while of advantage in really quicker cars with hard biting launch, really provides little stability advantage in a build with a 400hp-500 ft/lb engine. In quite a few higher torque builds, I'll fit a steel lh cap, & run a stock rear cover, on others that customer request will run a T/A rear cover. On several F-bodys with high flow crossmounted mufflers, I haven't even had room for an aftermarket cover. Hope this helps, have other questions, feel free & post, or drop me an e-mail. Got Posi? :3gears: Roger
