[Jmark]

I need some opinions from all you tranny experts please.
My truck is a '77 1/2 ton with a metal shell camper. Its not a tank but it is an older heavy truck.
Current engine is a mild 350 with a th350 tranny. I built both about a year ago. Both are fine. My gears are 3.41 and my tires are 31" tall. My current rpm at 65 is 2600. My driving is probably split between in town (40-45) and in town freeway at 55-60. On trips, I try to keep my speed at or below 65.

The problem is my fuel milage stinks. I"ve spent a lot of time tuning and re-jetting the carb and have managed to increase my milage about 1.5 mpg overall. I still only get 9.8 in town with the A/C on and highway is 13+ with A/C and no load in the truck. I sometimes pull a Coleman tent trailer or my boat, neither weigh that much and I don't use them much either.

I"m wondering about finding a good 700 core and building another (my second) tranny for my truck. I currently have the 9" tail shaft so I won't have to make any drive shaft mods and because i'm running a stock Qjet carb, I "should" be able to hook up the TV cable easily.
Do you think it would be worth it from a milage standpoint?
I like the lower first gear for sure, that would be great with my 3.41 gears, but i'm concerned about lugging down the engine with the 4th gear OD and the lock-up converter. I know I can lock out the converter until I hit the freeways, but I selected my cam for optimum hp and torque at cruise speed, which is right at 2600-2700 rpm, although it pulls real good down to about 2000rpm.

If I have to "get into it" more to keep it going, I'll end up in the bottom step of the metering rods and kill any milage increase from the lower rpms. Any thoughts are appreciated.

Mark

[Crosley]

Originally Posted by Jmark

I need some opinions from all you tranny experts please.
My truck is a '77 1/2 ton with a metal shell camper. Its not a tank but it is an older heavy truck.
Current engine is a mild 350 with a th350 tranny. I built both about a year ago. Both are fine. My gears are 3.41 and my tires are 31" tall. My current rpm at 65 is 2600. My driving is probably split between in town (40-45) and in town freeway at 55-60. On trips, I try to keep my speed at or below 65.

The problem is my fuel milage stinks. I"ve spent a lot of time tuning and re-jetting the carb and have managed to increase my milage about 1.5 mpg overall. I still only get 9.8 in town with the A/C on and highway is 13+ with A/C and no load in the truck. I sometimes pull a Coleman tent trailer or my boat, neither weigh that much and I don't use them much either.

I"m wondering about finding a good 700 core and building another (my second) tranny for my truck. I currently have the 9" tail shaft so I won't have to make any drive shaft mods and because i'm running a stock Qjet carb, I "should" be able to hook up the TV cable easily.
Do you think it would be worth it from a milage standpoint?
I like the lower first gear for sure, that would be great with my 3.41 gears, but i'm concerned about lugging down the engine with the 4th gear OD and the lock-up converter. I know I can lock out the converter until I hit the freeways, but I selected my cam for optimum hp and torque at cruise speed, which is right at 2600-2700 rpm, although it pulls real good down to about 2000rpm.

If I have to "get into it" more to keep it going, I'll end up in the bottom step of the metering rods and kill any milage increase from the lower rpms. Any thoughts are appreciated.

Mark

My chart shows you should be at approx 2430 rpm at 65 mph. With varibles , I can see the 2600 rpm you post

you have thought of one area most folks do not know is there...

If the engine RPM drops low enough or you have your foot on the gas pedal a bit harder in OD fuel mileage suffers. Vacuum falls off and the carb will richen up.

If it is worth the swap is a number you will need to cypher on. Cost of 700 tranny installed and the resulting fuel mileage increase if any.

you already know it is a bolt in.

Years ago I swapped my brothers t-350 out of his 1977 GMC truck with 4.10 rear gears. With the 700 tranny his mileage jumped UP 4.5 mpg on the hiway. He was happy till his wife told him to sell the truck 2 years later.

I spent a chunk of money to get better fuel mileage a month ago... Sold my F-150 Super Crew Ford and bought a 2006 VW Jetta TDI car. Current fuel mileage on the Jetta after 2k miles is 40 mpg in town.

[Jmark]

Thanks Tony. Guess I'll make some calls on a core 700. Any suggestions on a fair price for one?
Any thoughts on the parts cost to do a good rebuild? I bought all my 350 parts from Transtar last time. I really liked the guys there, super helpful and I felt the parts kit was excellent. I bought a master kit and converter and shift improver kit and don't think I had over $180 total.

I"ve read lots of the articles here on the 700 and the upgrades. Do I need to really do ALL the suggested upgrades? I"m not going to be shoving 500 horse through it, but I just need it to last.

Thought just came to mind. My wifes '86 Caprice has a 700 in it! LOL Wonder if she'd mind?

[CHEVY4LYF]

I think you'll be very happy with the 700R4 if mileage is your goal. The drive ratio in 4th gear (overdrive) is .7 to 1 versus 1 to 1 with a TH350. In other words, for every .7 revs of the engine, you get one full rev of the output shaft on the tranny...nice!

An additional note. Although some people don't like the 700 for performance, they can be built for some serious applications. There are a number of different accessories and parts you can buy to optimize your tranny for your particular application. For instance, they have a wiring kit for the lock up to reduce slippage. They also have what looks like a little cylinder that goes inside the tranny and allows you to stay in 4th gear with the hammer dropped (if you want to). Otherwise, the stock ones will drop back to 3rd gear for acceleration...I think the 'vette ones might not do this.

Anyway, just "google" some of these parts and I'm sure you'll find something that will help.

John

[Crosley]

Originally Posted by Jmark

Thanks Tony. Guess I'll make some calls on a core 700. Any suggestions on a fair price for one?
Any thoughts on the parts cost to do a good rebuild? I bought all my 350 parts from Transtar last time. I really liked the guys there, super helpful and I felt the parts kit was excellent. I bought a master kit and converter and shift improver kit and don't think I had over $180 total.

I"ve read lots of the articles here on the 700 and the upgrades. Do I need to really do ALL the suggested upgrades? I"m not going to be shoving 500 horse through it, but I just need it to last.

Thought just came to mind. My wifes '86 Caprice has a 700 in it! LOL Wonder if she'd mind?

Transtar near McDowell road?

cores are running 100.00 - 125.00 for 1988 -up tranny core.

Common sense rebuild is needed.

Bushings, check drive shell, Raybestos Z Pak 3-4 kit, TransGo JR 700 kit.

The 3-4 clutch pack in the 700 has been a problem since the trans was introduced. I would use the Z-Pak from Raybestos... IMHO

IF the 700 tranny has a .422 main boost valve , block the line bias valve in the v-body. Main press will be 210 psi max. A nice setup for the street.

I like the Sonnax billet OD servo. I put one in my 2006 Silverado with 380 miles on the truck

[Jmark]

Tony,
Yes, Transtar is near 35th ave and Mcdowell.

I'll copy down your suggestions and see what I can find.

Where is a good place for the cores? Junk yards? I'll check the paper too. Do I need to stay with the 700 or can I use the later model 4L60/or E tranny?

I called my buddy in Black Canyon city with all the goodies, but nothing that new. He's into the old stuff.

[Crosley]

Originally Posted by Jmark

Tony,
Yes, Transtar is near 35th ave and Mcdowell.

I'll copy down your suggestions and see what I can find.

Where is a good place for the cores? Junk yards? I'll check the paper too. Do I need to stay with the 700 or can I use the later model 4L60/or E tranny?

I called my buddy in Black Canyon city with all the goodies, but nothing that new. He's into the old stuff.

1988 to 1992 are better units to start with. 4L60E needs a computer / controller to operate.

We deal with brokers. A yard may want more cash for a 700 core. i've not bought from a yard in 2 years myself. In fact I have bought no cores for 2+ years

[Drewnashty]

I'm sorry this is an older thread, but what do you mean by you purchase the cores from brokers? I am a local to PHX and looking to drop a 700R4 in my '76 Blazer, was thinking about taking the one out of my S10 but I don't want to run into problems with having two non working vehicles at the same time. Where and how might I get my hands on the cores you speak of to rebuild.

[Jmark]

Hi Drew, I called a few local trans shops and found one at Dennys transmissions on North Cave Creek road for $150, then he took my old TH350 in trade and knocked off $75. We were both happy. Make some calls and see what some shops want for the full conversion. I wanted to build my own so its not too bad cost wise, but parts and upgrades are more on the 700. I think I have about $450 in parts now, plus the cost of the core. I can do the install myself at my sons shop so thats a plus too.

[Crosley]

the company I work for buys 100 to 250 cores at a time

Originally Posted by Drewnashty

I'm sorry this is an older thread, but what do you mean by you purchase the cores from brokers? I am a local to PHX and looking to drop a 700R4 in my '76 Blazer, was thinking about taking the one out of my S10 but I don't want to run into problems with having two non working vehicles at the same time. Where and how might I get my hands on the cores you speak of to rebuild.

[Drewnashty]

Thanks for the info.

[fast68]

it should get a little better mileage than that, you can buy a new Q jet carb for 150 at o reilly auto parts i got one for my '77 4x4 with the original 400 sb in it and it really good on gas alot better than your c-10 is getting by FAR

its all in the carb

run a Q jet

they are fuel efficient, more than other carbs are

or get a car or later truck,

also your axle would be 3.42 not 3.41

there was also 3.40 in these trucks these years it was RPO code HE4

check RPO sticker in glovebox

you may be confused with the 2.41 ratio of the late '70s GM 7.5" 10 bolt axle cars




good luck