Is the th400-700r4 worth it?

[Sawlog]

I have a 1969 c10 that I'm building a new 355 for. I have a th400 tranny in it with 3.07 rear gear.
My neighbor has a 1990 1500 2wd with a 350 tbi and jasper rebuild 700r4 in it.
The truck has 187000 miles on it and he wants to sell it to me for 400 bucks.
I ran the numbers on the tranny and it has 1990 date code on it.
So I'm thinking if I can get a overdrive tranny then I can also lower my rear gear. I do a lot of interstate driving so my 3.07s do me well with my th400 now. Would like to go to 3.73.
I don't know if I could use the drive start out of the 1990 or not, that th8ng is as big around as a coffee can!!
What do you all think?

[cleszkie]

If it were me, I'd stick with the TH400 and 3.07 gears. Sounds like this combo is currently working good for you. The 355 will give you some more low end torque if built right which should make up for some of the shortcomings of the 3.07 gears on take off. The TH400 will stand up to your 355 a lot better than the average 700R too. And it sound like the 700R already has a lot of miles on it. Figure in the cost of a rebuild for the 700R sooner rather than later when you do the math.

[tdangle]

If you had much lower gears I would say yes, but with 3.07 gears I dont think it would be worth it. That is unless you are going to go to 3.73 or lower then yes.

I have 4.10 and have an overdrive auto now. Way better on the hwy.

[jocko]

If it aint broke, don't fix it Unless you really want to do burnouts AND have reasonable RPM on the highway, it's just not worth it. You already have a great highway combo - at the expense of off the line acceleration, but unless you're towing or racing, it's just fine. And the TH400 is bulletproof compared to a 700R4 that came straight out of a 90 C1500 without any mods. So, one more vote for donna toucha nothin.

[mkmc69]

Depends on what you really want to do with the truck really. I would say, if you want to go fast and do burnouts, keep the 400. If you just want a nice cruiser for the highway, go with the 700r4. Just keep in mind, if you occasionally want to jump on the throttle, you may want to have that 700r4 rebuilt and upgraded internally.

[ubtripn]

I know it's bad but I took a crate engine and then slapped a junkyard 700R4 on it without doing anything to the tranny but painting it. I don't know my rearend gear ratio but at 2200 I am doing 65 and I can still come off the line strong. I know there are just a few years of 700R4's that are good and I made sure to get one that fell in that range and then rolled the dice. I am about 15,000 miles into now so it is doing well and the OD is nice on the freeway and MPG.

[redneckgames]

Originally Posted by Sawlog

I do a lot of interstate driving so my 3.07s do me well with my th400 now.

I think you just answered your own question right there.


To switch you are a talking a lot of money (trans rebuild, converter, rear gear, etc) when you are happy as is.

Now if you have the money and want the benefit of a lower gear, then go for it!

[BossHogg69]

I would not go through the trouble of swapping out a working TH400/3.07 combo for a used, stock 700R4 only just to turn around and swap rear gears too... I do not think the time/money involved in a trans & gear swap (all little things you'll have to change will add up) will be offset by any potential fuel savings.

I vote keep what you have.



FWIW - I run a 350/TH350/3.08 gear in my daily driver Bel Air station wagon and it's great on the highway and in town. Good balance between acceleration & economy.