Transmission Replacement

[ese79cutty]

No one here has pointed you in the wrong direction, really. Either a 700-R4 or 200-4R will work just fine. I'd recommend to you to come up with a total plan before you start buying parts that might not suit your end goal of cruise and occasionally run down the strip.

1st - determine the size wheel and tire you will run - you cannot choose a correct rear gear ratio if you change your mind from running a 25" tire to a 28" tire. 2nd - you mentioned a 350 install- mild 300-350HP? Need to know this for transmission.

Yes won’t be more than 350. Was thinking of getting a small block and machining it starting from scratch and just upgrading some of the major components from within. Just went soemthing I can cruise in and occasionally burn some rubber. Rn I got 14 rally wheels on but I want to change to 15 in later.

 

[fleming442]

Does a Series II 3.8 have a BOP bellhousing bolt pattern?

I don't think so, but they make adapter plates for the other way- should work.

 

[ese79cutty]

With a 200r4 a 3.42 rear gear (standard grand national setup) and a standard 235/60/15 tire size, you'd be at about 2100rpm give or take on the highway at 70mph. Upgrading the rear gears and adding transmission gears go hand in hand. you could even go to a 4.10 and make that 3.8 accelerate like a 305 lol.

If the car is factory stock, would I need to put a new rear end in the car? From my research a lot of people say the 3.42 or the 3.72 would be the way to go then they start saying something about a 10 bolt and 12 bolt rears with posi. I’m a little green when it comes to transmissions and rear ends so any suggestions or help is grateful

 

[Supercharged111]

If the car is factory stock, would I need to put a new rear end in the car? From my research a lot of people say the 3.42 or the 3.72 would be the way to go then they start saying something about a 10 bolt and 12 bolt rears with posi. I’m a little green when it comes to transmissions and rear ends so any suggestions or help is grateful

If you have a 2:41 now and add OD to that your 3.8 isn't going to be happy in OD and likely won't hold the gear. Going to a lower gear not only alleviates this, it increases acceleration so you get the best of both worlds.

 

[Gonzo1970]

If you have a 2:41 now and add OD to that your 3.8 isn't going to be happy in OD and likely won't hold the gear. Going to a lower gear not only alleviates this, it increases acceleration so you get the best of both worlds.

I have a stock peg-leg and a 200-4R with a 305, and the 305 isn't happy with all the early shifting.. 4th at 50mph, and its idling.. I run it in 3rd until I get on the highway, then put it in 4th... at 1200rpm @ 70mph...

 

[MrSony]

Too low of rpm at highway speeds the engine will basically be idling or will lug. Won't have enough grunt to safely pass and will probably be worse on mpg.
2100-2500 is the sweet spot.

10 bolt or 12 is just how many bolts that hold the ring gear to the carrier. Typically the more bolts the bigger and beefier the rear end. But not always. G bodies came with a 10 bolt rear end with a 7.5" ring gear. Grand nationals and 442s got a stronger 8.5". 7.5 are good to 450ish hp. Traction and shock loads (clutch dumps) kill 7.5s. Monte Carlo ss got a 7.625 rear with 3.73. Look for someone parting out a Monte ss and grab the 200r4 and rear.

 

[James Morris]

Given that everything in the car is factor original once I get a 200-4R would I need to do anything to the transmisson itself? Then how would I go about regearing the rear end. What parts do I need or how should I go about this. Any recommendations are welcome open minded to this. Long story short I just want something that’ll take hp, quicker acceleration, and fuel economy. Like I said I do plan on installing a sbc 350 soon but just not now

You probably won't need to regear the rearend. The 200 has a lower 1st gear which is good. Any issue would be in overdrive where you may run into frequent downshifts at lower rpms, depending on your current gear ratio. The stock 3.8 gears may be low enough that it won't be a problem.

 

[ssn696]

How to Build a TH200-4R Transmission for Drag Racing

Art Carr shows us how he builds the TH200-4R four-speed OD transmission to handle supercharged big-block power at the drag strip.

www.hotrod.com