1970 c10, new trans opinions

[Wallee]

Like the thread title says, what do you guys think is the best transmission to buy new for a guy who is looking to get the best fuel economy out of his ride? th350? 700r4? or?

[jocko]

Regarding the two options you posted, 700R4 will always get better mileage than TH350, simply because of the o/d gear. Lots of threads on here about the "best" o/d trans for our trucks also - usually comes down to a discussion about 700R4 vs 2004R. 2004R allows stock driveshaft length. Anyway - to your question, generally speaking, any overdrive trans will get better mileage than a 1:1 final drive trans (TH350/TH400, etc) simply because the engine will be at lower rpm at higher speeds. Personally, I like the 2004R, but we'd need to know about more about your truck first... eng/rear gears, etc.

[Wallee]

I was looking online and the 700r4 is a lot more expensive right?

[Fitz]

Originally Posted by Wallee

Like the thread title says, what do you guys think is the best transmission to buy new for a guy who is looking to get the best fuel economy out of his ride? th350? 700r4? or?

Depends on what engine you are running, but a 700R4 is a good choice if you aren't doing full throttle burnouts with a big block. With a big block, the 200 4R would be my choice. Ratios are shown in the table below:

Trans 1st 2nd 3rd 4th Reverse
Powerglide 1.82 1.00 1.82 R
Turbo 350 2.52 1.52 1.00 1.94 R
Turbo 400 2.48 1.48 1.00 2.08 R
700R4 3.06 1.63 1.00 .70 2.29 R
200 4R 2.74 1.57 1.00 .67 2.29 R


Not a lot of difference between the 700R4 and the 2004R except in 1st and 4th. I personally prefer the 2004R.

[67swb72klb]

here is another thread on them

http://67-72chevytrucks.com/vboard/s...d.php?t=652154

[Wallee]

Where is the cheapest place to get my hands on a new r4? Also what has to be done to fit it?

[slikside]

Not sure they're the cheapest (probably not), but I know guys on here have bought

www.bowtieoverdrives.com

and were very satisfied with them.

[Wallee]

Talked to a guy that owns my local trans shop and he said he could rebuild mine for 300-500$ depending what parts were bad and needed replaced. Think that would be an ok route to go?

[Mike C]

No. Rebuilding your existing trans won't give you a lick better mileage unless it's stuck in first gear or the converter is slipping like crazy.

If you have 3.73 gears you could change to 3.07 and that would be the cheapest way to get the RPM down on the highway.

Even easier to bolt on the tallest tires you could find in the back, that just looks goofy.

Bowtie Overdrives a great place to start. I would buy a TH200 4R if it was mine. And I'm planning on doing just that for my '69 short bed.

Honestly, you didn't put a lot of effort into trying to figure this question out. Search is your friend whether on this board or just on Google. You can get more information about OD trans in 30 minutes than you know what to do with.

[Wallee]

I haven't checked the fuel milage on my current set up anyways. It has been under the knife the entire time I have owned it. So I have researched it abundantly but was looking for more opinions. I guess what I should have or could have asked rather might be what kinda fuel milage out of a th350 is possible? My mind changes like the wind and I am in the brainstorming mode of a build so...

[Longhorn 70]

I like the 700R4 I switched to in my C20. My driveshaft needed work as well as mounts.

I helped a buddy do a 200-4R in a 65 C10. It went in easy, used the same mounts and has been dependable. Get a quality build, get it built strong and get a warranty.

[Mike C]

2.73 rear gear, lowered truck for better aero, fuel injection, smaller motor. All are ways to get better mileage from a TH350. The answer to better fuel economy is overdrive if you want performance of the truck to stay the same or get better. Then you can try and tune your way to better mpg.

My 70 GMC with 402 got 14 mpg with 3.54 gears and TH400 when speed limits were 65 on the highway and not 75.

I think you should put it together, tune it best you can, then figure out where you are.

[Wallee]

Originally Posted by Mike C

2.73 rear gear, lowered truck for better aero, fuel injection, smaller motor. All are ways to get better mileage from a TH350. The answer to better fuel economy is overdrive if you want performance of the truck to stay the same or get better. Then you can try and tune your way to better mpg.

My 70 GMC with 402 got 14 mpg with 3.54 gears and TH400 when speed limits were 65 on the highway and not 75.

I think you should put it together, tune it best you can, then figure out where you are.

Exactly what my father in law said! He advised me to get it running well first with what I have, then pull the trans and have it rebuilt or replaced. But after he told me that I think I might do just that. He swares he believes my old engine still has plenty life left in it do he is wanting me to grab a new carb, points, and wires and see what I have. Trans is coming out very soon though, it's not shifting out of 2nd so it's got to be done.