i have a carb setup with a 406 sbc, th350 tranny and stock rear end. I came across a 4th gen rear end (3.42 gears, disc brakes and posi) that i thought was a good deal, but in the past i came across some threads that didnt recommend using gears above 2.77 or something like that because of gas mileage. Even tho i already screwed myself with gas mileage when i swapped in the 406, i still wouldnt want it to get any worse, but wouldnt mind having that 4th gen rear. And do 4th gen rears use a torque arm too? if so, can i use the stock one i have in my car already? Any input is helpful guys. BTW, my car is an 82 trans am. THANKS

The torque arm pad was carried over, so the swap is painless, except that now your rear tires might stick out past the fenders. That, and getting the brake situation dialed in just right.

thank you for the input Atilla. Although i do understand most of the swap process(the only thing i really need to get is the proportioning valve). Main thing im asking is if the gas mileage really sucks that bad with higher 3.42 4th gen gears combined with my th350.
thanks for the response Atilla.

What wheels do you have? And what is the backspacing on them?

The stock 16" (of the later years) will SIT out further, but not STICK out. They still sit under the fenders. It depends on what wheels you have/the backspacing on them.

they're stock 14 inch turbos.. upgrading to 15 in

The 15" fit will depend on what width & bs you go with. With a 4th gen rear end, you'll need more bs, with a wide wheel. I assume you'll want wide, with a 406 in front of them.

does the torque arm mount up directly on the 4th gen rear as it was in my car?

Yes. But you will need to switch the torque arm bushing on the tranny mount end, or use your original torque arm. The direction of the way it faced changed around 86 on 3rd gens. The axle mount ends are identical.

If you have drum brakes, you might consider swapping the proportioning valve under the master cylinder, over to a 4-wheel disk one.

cool. all i really need answered now is whether it is a good idea to do this or not considering the 3.42 gears compared to my stock gears.(mpg with th350)

Like you said in the beginning. A 406 isn't exactly an engine for a guy that wants high mpg. TH350, no overdrive, 406 + taller gears? Your MPG will drop, no doubt there.

700R4 (for Overdrive) or a T56 (double overdrive) will get your MPG back for you.

should i just put my original th200 in there instead for the overdrive? i wont be doing much drag racing. The only reason i have this set up is cuz my old 305 was crapping out and my neighbor was selling a 406 as a combo with the beefed up th350. (i think he was having his midlife crisis) Tranny was a pain to bolt on especially the 3000 stall converter. But maybe i'll be willing to swap the th200 back over and sell the 350.

I don't know anything about the 200s, except that there was one was behind the TTA V6 in 89. Which is more of of higher RPM engine. It was stout then (V6 dyno'd at 300 hp, dunno about torque), but one designed in 82?

Drag launches are the biggest killers of trannies. With a 3000 stall, it sounds like he planned on a strong street car & launch, not full on drag race launches.

Maybe a guy with 200 knowledge will chime in here.

Good Luck!

so 3000 stall converter is more for street use? im not too knowledgeable in converters.
i read threads that th200 were decent enough. The one i had didnt really give me problems, just the engine kept running rich and leaking fluids from every crease imaginable.
im gonna suck it up for the mpg cuz i already paid my neighbor for it and im already balls deep in the swap. All i need is the 350 crossmember/torque arm bracket so i can bolt up the tq arm.
so no turning back.

a 3000 stall isnt too bad for street use. hell i used to daily a 350/th350 with a 3k stall, that thing would launch. just do it and have fun getting to know the local gas station attendents.