Ok, so it's been a long time since I last logged in on here but I need help now. I'm building an 87 Z28 and have ran into an issue. Here's my build specs or at least the plan for it so far.
87 Z28 with t-top. Originally had tpi 305, 700r4, and posi 10 bolt with 3.42 gears and drum brakes.
The plan is a 454 with a 4l80e and manual shift controller plus a Doug Nash 2 overdrive unit. Trying to hit 500hp and trying to limit my torque to as close to 500 as possiblae. The overdrive unit is to help with fuel mileage on the hwy. Now I have a truck 12 bolt with 3.73 gears and posi. It was free.
So here's my plan. Fab up a trans cross member with provisions for dual torque arms similar to ladder bars and weld brackets on the axle tubes for them. One on each side of the differential. Transfer the rest of my suspension stuff to the new axle and I'm done.
Oh, my drive shaft lenght is 29.5" so I'm using the front drive line from a 91 3/4 ton suburban. Running long tube headers and a set of purple hornies. The car will be a daily driver along with a little bit of time at the track not to mention scaring imports at the stop lights.
So can anyone see any problems with this idea or have any ideas on how to make it work better? Trying to stay as cheap as possible by using free parts, ie: trans, od unit, drive line, rear axle.

 

Suspensions require some design and theory in their implementation.

Torque arms on the F-body maintain the pinion angle. Two would have basically no additional benefit. They don't locate the axle fore-aft from the center area of the axle. They don't locate the axle laterally without significant angle on them.

Routing a torque arm past an OD unit in the driveline tunnel of a thirdgen is going to be tight and may be impossible without significant cutting of the floor. Before carrying out that plan, research the impact of a shortened torque arm on chassis hook-up which will be a big factor in a rat thirdgen.

Whereas a large number of gears or a wide gear ratio spread has it's advantages, there's a few "big picture" ideals to look into. One is the shorter driveline. The shorter the distance from final output shaft to a solid rear axle, the more signficant the u-joint angles will become. A 29.5" driveline and it's impact on the driveline angles should be researched before proceeding.

The truck 12-bolt has a smaller pinion than the car 12-bolt (and the 8.5 10-bolt for that matter.) The truck 12 is weaker than the car 12. So I would at least tally up the costs you'll have in fitting the truck 12-bolt such as re-drilling axles or buying new ones for 5-bolt wheels. You'll also need to come up with control arm, shock and as mentioned, torque arm brackets and provisions. Your stock axle has smaller axle tubes, so it's not as easy as grinding them off the thirdgen rear and welding them to the 12-bolt. This also means the brake pattern at the axle housing flange is different. The width of the axle assembly is another thing that may play havoc with wheel fitment. Sometimes ponying up some money to buy something that damn near fits is cheaper than modifying literally every fitment aspect of a part that doesn't. And that's not even taking into account your time.

You haven't stated planned tire size. A .75 4th gear in a 4L80-E is a pretty livable highway overdrive with 3.73 rear. If the DNE2 has a .75 ratio, you're looking at a 2.10 final drive. Have you ever driven a GM car with 2.14 or 2.29 rear gear? They take forever to accellerate on the highway. Consider skipping the DNE2 and simplifying the car to a single drivetrain device with a nice lock-up stall converter.

 

Ok. I know that I will have to do some serious cutting and welding to my trans tunnel for the od unit and I'm fine with that. I also know what it's like to have 2.41 gears. The high point of the od unit is that when it's not engaged it's a 1:1 ratio. Engaged it's 0.63:1. Combined with the 0.75 of the 4l80e it gives me something like 0.42 overdrive. My rear tires are 295/50r15 or another 26" high. So in double od I should be just above 1000rpm at 60mph. The truck axle is exactly the same width from backing plate to backing plate as my stock 10 bolt. By the way, the trans plus od is similar to what was used in the 4+3 vettes and is currently stock on many medium duty trucks and motorhomes.
I hadn't thought about the issue of drive shaft angle before so I'm gonna have to figure that out before cutting the tunnel to test fit everything but couldn't that be overcome buy adjusting the orientation of the axle when welding on all the mounts? Also, would I be better off Retro fitting my car for leaf springs or maybe some sort of a four link set up?

 

Gotta disagree with both of you, and I have some practical and relevant experience with this. First, trying to do 1000 RPM at 60 MPH with a 454 seems unlikely. Even with peanut-port heads and a micro cam like a Comp HE252H10. The original Viper had 488 cubes, and was geared for 1180 RPM at 60 MPH. If you want to do that with a 454, best to do a 700R-4, then get a 2.41:1-geared 8.5" 10-bolt from a '75-'81 F-car. Secondly, at only 500 ft-lbs, one stock torque arm is adequate. No need for duals, the second would just get in the way of the exhaust, and there's no need to change the routing of that, nor fuss with trying true duals, when Mufflex offers 3.5" and 4" singles. Third, the truck 12 will survive 500 TQ on those tires, but it is not the stock 62" between the wheels. It's more like 67", which will require having custom wheels. Fitting a torque arm to it isn't a deal-breaker, but think how un-necessarily heavy those extra-thick axle tubes are. I swapped a 65" Dana 60 from a '78 D200, and my axle tubes are exactly 1/2" larger than stock. Once the welds were carefully ground away, it was easy to mark all the bracketry 1/4" from the stock axle, then cut for the D60. However, cutting any less than 1/4" seems impractical, unless you spend 3 months with a little bitty Dremel. But I need a truck axle for the weight capacity, I'm custom-building specifically for towing gooseneck and fifth-wheel-camper trailers, so the extra weight on my rear axle will exceed the stock 2900# capacity, and may exceed the 4200# capacity of your truck-12. Seems you want paddle-shift? If so, swapping the 4L80E for a built and used 4L60E is the easy solution. The real question is what you hope to accomplish by all this? A many-geared 454, overkill axle with overkill torque arms, a mega-dollar add-on overdrive, yet only 500 TQ, on 295/50R15 street radials? What's the idea? Towing a boat? Making a Camaro version of an El-Camino?

 

Based on what I thought the DNE2 OD was,
it would be .75 * .75 (0.5625) * 3.73 = 2.098125

If you've verified this one as .63, that's
.63 * .75 (0.4725) * 3.73 = 1.762425 which is a complete waste of time. The only way that will be useful will be with a complete ***** cam and EFI for the sake of low rpm drivability at the loss of power upstairs.

A 4+3 was either .68 or .60 overdrive and you're grasping at straws in comparing a manual 4 speed + automatic overdrive unit to an automatic 4 speed overdrive with manual overdrive unit attached that significantly overshoots the ratios of known valid combinations.

Adjusting the orientation of the axle is done with the adjustment of the pinion angle (such as adjustable torque arm for a third-gen)

Leafs have enough downsides on top of the placement of a rear hanger location in the thirdgen chassis. It would be in no way, shape or form an improvement over the torque arm setup.

The torque arm, trailing arms and panhard bar are a valid suspension and are going to save you time, money and design time. The only question is how you'll fit the torque arm and how long you'll make it. Which you sound prepared to tackle.

 

Ok, so I looked up the specs on the od unit and it a .80 od so when combined with the trans and axle it gives me something like 2.20 final drive. Perfect for the freeway.
As for the parts I'm using, the trans came from a 91 suburban we hauled to the scrap yard. The od came out of my friends 74 Chevy 3/4ton two wheel drive, Andrew the rear axle came out of his 73 step side chevy. The reason I'm trying to limit my torque is due to me not having and idea how to get it to hook up. Even with a 300hp small block in my last one it kept the tires lit throught third and chirped them into fourth. Those were 275/60r15 and a manual trans. I figure with a big block I can run a single plane intake, large primary long tubes, glass packs and still make more than enough torque off the line. I'll probably never run slicks. And I do prefer the simplicity and sound of long tubes and glass packs. I have measured the rear axles and they are both the same width. Hell, even the 14 bolt in the mud truck is only an inch wider. All measurements were backing plate to backing plate. Anyway, I know this isn't the best axle to use but it's free. Once it breaks maybe I'll have the cash for a nice after market 12 bolt or maybe I'll try a corporate 14 bolt and leave it an 8 lug just to make people wonder. But for now I'm just trying to make what I have laying around the shop work. I suspose I could just drop a 350 with a t-5 back in and call it good but where's the fun in that.

 

the pig on a 14 olt would drag the ground under a 3rd gen

 

Lol. Ok, hadn't thought about that. Would probably need taller tires and a lot of suspension work. Bad idea. But I bet I couldn't break it.

 

Won't work. The only axle width measurement that matters is WMS to WMS, meaning Wheel Mounting Surfaces, meaning between wheels.

 

Nope. Got that axle under a trailer, on 205/55R16s, plenty of ground clearance.

 

You don't need it. If you want to adapt a strong axle on no budget, use a Ford 8.8" from a Lincoln Town Car. However, the 14-bolt having the bolt-in pinion support would make a good attachment for a torque arm. And this may well get tested if my D60 proves too tight with new stock Dodge 16x6" dually wheels mounting 215/60R16 tires.

 

considering a 14 bolt comes close to the ground on even a truck id say theres no way your fitting one under a camaro

 

I've thought about the Ford 8.8, especially the independent version out of a Thunderbird or lsc but I just can't bring myself to put a Ford part in my car. That's why I started looking at the 14 bolt on the truck.

 

why not just use vette irs, which has been done various times. youre going to come into clearance issues with a 14 bolt. why not build a good ford 9 or 8.8 or stock axle, and eliminate all the mod work.

 

Right now I'm just trying to work with what I have on hand. Every bit of money I get is going into the engine. Later Im sure I will need to buy a better axle. Hell, I'll probably go ahead a four link it at some point. I'd. Live a vettes IRS but at $2500 it's not in the budget. And I just refuse to use anything that is not a GM part. Maybe one day I can afford all the nice after market stuff that everyone talks about but for now I'm pretty much stuck with what ever parts I can beg barrow or steal. I don't expect this axle to last forever. Or the transmission. Hell, even the engine I expect to throw a rid or flatten a cam at some point. It's rare that any of my cars might make it a year before needing major repairs.

 

By the way, my so called smartphone can't spell for ****. It keeps thinking that it's smarter than me.

 

The 14-bolt isn't a ground clearance problem, you'd still have at least 5", but the weight is 550 # with the stock drum brakes! Convert to discs, it's still around 500! Your stock 7.5" axle is under 200#, complete. Do the ford 8.8". Nobody cares who made it, it's just a silly fear you need to face. Using the right tool for the job does NOT include checking to see if it's a Craftsman, a Snap-On, a Cornwell, or whatever. Or in this case, Gm vs Ford. The war isn't GM vs Ford, it's America vs the world. The 8.8 is readily available for nearly free, plenty strong, easily upgrade-able, relatively light, and has the best aftermarket support. The Mustang guys are using it to run low 9s.