# Trans. Rear, Tire size Help



## mtman (Feb 2, 2014)

OK, Here's what I got. Rebuild my TH400, 10 bolt rear with a posi 3.23 or 3.42 gears, with tire size 245 60r15. 
Or, pick up a 700r4 rebuilt, 10 bolt rear posi 3.73 gears, with 245 60r15 tires.
Now the second option is more money, but I'm looking for long term. Any help with these choices, or maybe something different. 
This is going behind a 400cu.in. .30 over, KB dish -17cc pistons, 62 Heads 75cc , roller tip rockers, mild cam, stock intake, Qjet carb, I don't know what else you need? The car is more of a cruiser, out here in the middle nowhere Mt. every thing is a good drive away. Thanks Mike


----------



## geeteeohguy (Feb 2, 2008)

If you are in the middle of it, and have the cash, and it's long term, and you are going to stay in Montana, Choice Number Two is the best. 3.73 is a great gear for performance, and with an OD trans, will be excellent on the open road. I swapped out the 3.36 rear in my '67 for a 2.56 posi because it was free, and am running a TH400 and 225/70/14 tires. Lost a lot off the line, but it'll still smoke the tires. Flip side, it is a highway star, and gets 20+ mpg at 75-80 mph on the open road. The ultimate solution is an OD trans, though: you can have your cake and eat it, too.


----------



## PontiacJim (Dec 29, 2012)

X2 on the OD & 3.73's if long term ownership -spend the money now and save later as you drive it.

I too had a '67 GTO 400CI 4-speed that I installed some 3.08 gears into (yes, changed the speedo gear in the trans). Fine tuned the Q-jet and played with the distributor and back in the day when the speed limit was 55MPH, I got 24 MPG when I took the car on my honeymoon trip from Connecticut to the Pocono's in PA -I think it was a 5-6 hour drive. Did it going down and back, so I knew it wasn't a fluke.

You can actually get good gas mileage if you set the car up to take advantage of the torque and not go crazy with a cam. My 1976 Pontiac Lemans with 350CI, Q-jet, & TH-350 cruising @ 70MPH on flat highway would regularly get 20-21 MPG's with I believe 2.76 gears. Not so good around town in stop and go -it was horrible on gas.


----------

