I just rebuilt the stock Th200c and installed a HD shift kit thinking it would help a bit, which it did. Now I'm looking for more, so is it worth it to try and get a Posi for it? Once I have enough money I want to put in the T56 with a posi, but until then im not sure if i should just wait it out or go ahead and get one, help?

Your rear axle has the 26 spline axle shafts, just like mine did. What I did was bought a used zexel torsen posi from an LSx powered 4th gen, and then got some 28 spline axle shafts for a 3rd gen. You'll be good if you do that.

I think paying money for a 26 spline posi unit is a waste of money since your axle shafts are also a known weak link.

You didn't say what your budget was so I just listed my favorite low budget way to do it.

If you put a posi on that 200c and beat on the car it will probably break. Wait til you get the T56 or an upgraded auto. I've seen two people do this on stock type 305 motors and both of them broke the 200c, it's just not a very strong trans....

Yeah I found out the 200c was not very strong once I put in the new 350, hence rebuilding it. It's been holding strong since the rebuild and has made me proud on many occasions. My biggest problem with it is I commute 50 some miles to and from work and it is terrible for mileage, that's why I want the t56

You know, maybe there is another way to do it economically.

I have twice in the past replaced a TH200c with a 2004R successfully with very happy results. They can easily be built to withstand 11 second Grand Nationals if the need arises, and you don't need much beyond a stock GN build.

Anyway, the 2004R is a direct replacement for a TH200, even using the exact same driveshaft. The problem for you is that the transmission mount is moved to the rear and there is no torque arm mount provision. This is easily solved for you, since both problems can be remedied with a conversion crossmember from SPOHN. They make one for the 2004R for our cars with torque arm mount.

You can even reuse your 200c torque converter in a used 2004R. I did that in my last Cutlass.

So really it depends on how much you can get a second hand 2004R for. I've seen the GN ones on craigslist for 400 bucks around here before. Not all the time, but if you keep it in mind, it will turn up.

Just a thought.

The OP wording looks like the posi is a transmission thing rather than an axle thing. I was using 26-spline shafts when my '88 IROC-Z ran that 10.21 second blast, but I was running a welded differential, and was careful that I never had one rear tire on a higher-traction surface than the other rear tire, because that's what breaks 26-spline shafts: shock-loading with all the part and all the weight on the one shaft that has high traction. As long as you're running street radials, no wider than 245s, I'd say the posi is worth doing, if you can find a used one for around $50.

I would love that! I want speed on takeoff but i want some fuel economy. I was under the impression that it would cost a whole lot of money to swap to an overdrive, not as much as to a manual, but enough where i figured id just spend the little extra to go manual. im sure this has been asked before in these forums, but how does the 2004r do with a 3.73 or 4.10?

Doing a 200-4R can be a $200 proposal, if you score a good one at Pick-N-Pull. I've done this, but I say the 700R-4 is worth having to also buy a matching driveshaft, because of the stronger parts, and because of the provision for the torque arm. Driving a 700R-4 with a 3.73:1 axle gives a combined first of 11.40172727:1. It's a lot, but not TOO much for a SBC that breathes well enough to pull 5500. Doing a 4.10:1 with a 200-4R gives a combined first gear of 11.23621564:1, which is close enough, on the safe side. Now, let's consider OD: With the 700R-4 and a 3.73:1 axle, the effective result is 2.594181818:1. With the 200-4R and 4.10:1 combo, it's 2.7630433:1, which I'd say is worse for most street cams, but better if you want to run way too much cam.

Alright, now would you be able to dumb this down a bit? Sorry, if it wasnt already obvious, but I know very little about transmissions.