what do you think

[wibilly]

i wanna up the mpg's in my 69 so maybe i can hit some board meets this summer. i have astock 350 [ 1980] 4 speed and 3.73s would i do better with a 700r4 with the 3.73s or with the 4 speed and 3.07s i hate to part with my 4 speed, thats what makes it a truck imo. i'm in the 13 - 15 mpg range now with this truck

[samwise68]

i'm no expert, but i think in the end, a stock tranny and 3.07 is about the same as a 700r4 and 3.73.

personally, i'd keep the 4-speed (gotta love granny gear), and put some 3.07's in the back.

should make it a pretty easy cruiser, with 60-65 mph around 2400...pending tire size and all that..ish?

-Sam.

[Longhorn Man]

15 MPG on the road is pretter good in all reality.
Between the two choises you are looking at, I'd go locate a rear end with 3.07's in it. That would be WAY cheaper and a lot more durable than the 700.

[67_C-30]

Originally Posted by Longhorn Man

15 MPG on the road is pretter good in all reality.
Between the two choises you are looking at, I'd go locate a rear end with 3.07's in it. That would be WAY cheaper and a lot more durable than the 700.

X2

I have got as good 18mpg on the highway with my TH350 and 3.07's in my '69C10 with a similiar engine (freshened up, smog-headed 350 with a Q-jet).

[chris71]

actually

.7(700r4's 4th gear) X 3.73 (rear gear) = 2.611 final ratio

1(350's and 4 speed final gear) X 3.07 (rear gear) = 3.07 final ratio

so you would be better off with the 700 and the 3.73 because 2.611 is less than 3.07 (my apologies samwise68)

now here is one thing to remember, whatever you spend for the rear or tranny swap. it will take you time to regain that money back in gas savings. i will try to make it simple say you gain 2mpg from a swap (rear or tranny) 15 to 17

15mpg / $3 a gallon = .200 (cost per mile)
17mpg / $3 a gallon = .176 (cost per mile)
.2-.176=.024 (difference from old to new)

so say you pick up a used 3.07 rear and with fluid etc costs you $200. it will take you 8,500 miles to break even with the added 2mpg gas savings 200/.024.

lets say it takes you $1,000 to get a rebuilt 700r4 (they arent cheap) with fluid, cables, etc included. it will take you 41,666 miles to break even on gas expense 1000/.024=41,666 with a 2mpg increase or 30,303 miles to break even on 3mpg increase.

these are just some rough figures i was playing around with but you get my point. alot of guys want a 700r4 for gas savings but the amount of miles /time it takes just to break even on the added expense of a 700r4 instead of keeping a th350 or whatever is big. just my thoughts.

[AuggieStyle]

very good point chris.....

[Longhorn Man]

the 700 swap doesn't stop with just a $1000 tranny though.
Tranny cooler
tranny lines
cross member
speedo cable
tranny mount
flex plate
driveshaft
TV cable
Kit to properly adjust TV cable so it'll last more than 20,000 miles
shifter or column with shifter
converter controller
case of ATF


Did I leave anything out?
We're up to what... 50,000 mile pay off assuming a 3 MPG increase?

[bryanw1968]

Yah, beer!

[ChevLoRay]

Y'all just killed my wanting to replace my TH400/3.07's with a 700R4. Looks like getting a more-efficient powerplant will be my best attack. My tranny is in excellent shape, with a little "tweaking" that was done by an old hot rodder (who has a transmission shop) to make it shift a little better.

If there is a "cool" factor in having an OD gearbox, you guys just took the cool out of it.

Thanks. Saved me some $$$

[wibilly]

i have every thing to do either at no cost, but this truck is used as a truck. idealy i would like to use a manual od tranny. i have a np833as well anybody know the final drive ratio of them? i want a nv4500 i think. what is FDR of them? i may have one of them too i gotta look

[Boog]

Originally Posted by wibilly

i wanna up the mpg's in my 69 so maybe i can hit some board meets this summer. i have astock 350 [ 1980] 4 speed and 3.73s would i do better with a 700r4 with the 3.73s or with the 4 speed and 3.07s i hate to part with my 4 speed, thats what makes it a truck imo. i'm in the 13 - 15 mpg range now with this truck

13 to 15 mpg is in the normal range for a carb'd 350 in these old trucks. Of course there are some exceptions but most will tell you that's about right. If you want to work this truck as it's intended you probably want to keep those gears and trans. Dropping down to the 3.07 gears will lower the rpm by a couple hundred but may not increase the mpg by all that much. Some do but not all. Too many variables. Besides, I am not all that impressed with the 700 series trans. I hear you can build one up to handle all kinds of HP but if GM built them like the old 400's you wouldn't have to.

[wibilly]

yeai have herd no good about them either.if it can't work in od then why have it? i go up hill as well as down

[68C15]

follow Andy's lead, swap in a 3.07 gear. you will NEVER get a 700R4 to work like a true truck 4 speed.

just bring that NP833 to Ne. in may.