Tranmission crossroads.

[redandwhitechevy]

Alright heres the deal my truck has a th/350 in it now with 2.73s. Its a total dog off the line, it does alright on the highway. But I wat to get away from the th/350 so I bought a 700R4 that I wanted to swap in, but now Im thinking a 4 speed would be more of what I want. I do drive on the highway just about everyday. I have a borg warner T-10 in my 70 z28 and I love it, so I'm thinking that maybe what I want. What do you guys think would be an easier conversion?

[Pyrotechnic]

You gotta decide what you want.

The 2.73's you have now are basically like having overdrive. A 700R4 won't help you. Infact, to even use 4th gear you would have to being going 90-100+ MPH. A 4 speed manual wont help you either, you will have to slip the clutch a lot off the line.

Now if you swap rear end gears, to 3.42's or 3.73 your options open up. The 700R4 will work great. If will be quick off the line and good on the highway. You could also use a 5 or 6 speed overdrive manual transmission with these gears and it would be great.

If you want both acceleration AND highway mileage, the 4 speed manual will not work for you.

The cheapest and easiest route would be a 700R4 with new rear end gears.

[krue]

The Th-350 with 3.07 gears ain't a bad combination. BTW Welcome to the board from South Mississippi!

[Ivan D.]

Originally Posted by krue

The Th-350 with 3.07 gears ain't a bad combination. BTW Welcome to the board from South Mississippi!

Agreed, that's what I have - off the line I do fairly decent considering I got 33s on my rear axle, and on the freeway if I keep engine speed at around 2k my fuel economy goes up to near 20mpg, and that's consistent over many trips too. Granted that's only 55mph or so, but tis and old truck after all, tis supposed to be slow

[rfmaster]

I have 33" tires with 4:11 gears with 700R4 in my 75. Off line take off is great (for 3/4 ton). On the highway I turn 2050 RPM while at 65 MPH (no lock up) Should drop another 200 RPM with TC engaged.

//RF

[gchemist]

Welcome to the site.
You need to consider what tire size too.

I run a 700R4 with 3.08 gears. The tire size is 26.5 inches. Great takeoff and great highway speeds. If was using a tire taller than 28" inches then the combo would not work.

[redandwhitechevy]

Well I want to ditch my gears either way I runn a 29 inch tall tire so that dosen't help. What I am concerend with if I put the 700r4 in there is the lockup wiring and the kickdown, I wasn't do it for gas mileage I get terrible gas mileage anyway. I just wanted faster takeoffs and a funner truck.

[piecesparts]

Originally Posted by gchemist

Welcome to the site.
You need to consider what tire size too.

I run a 700R4 with 3.08 gears. The tire size is 26.5 inches. Great takeoff and great highway speeds. If was using a tire taller than 28" inches then the combo would not work.

I converted my Son's truck to a 700R4 tranny and he had 3.08 gears. The
RPMs at 70 MPH was around 1900 to 1950 and that was not bad (SO WE THOUGHT). The mileage SUCKED big time (11.5 MPG) because the motor and the cam was not aligned to the basic IDLE condition as you go down the road. We upgraded by changing the rear end over to a posi 3.73 gears and the mileage INCREASED back to what it was--around 14 MPG and the acceleration is phenomenal. The cruise control works and does not wear out the throttle by trying to catch up on the hills all the time, like it was with the 3.08 gears. We run P295/50/R15 tires that are around 26.8" diameter and that works well with the gears and the tranny.

[jermasaurus]

A 7004r with the 2.73 gears is an ok combo. I had a th350 with 2.73 rear and swapped to the 700. It helped off the line with a noticeable difference.

It does great on the highway I'm probably around 2500 rpm at 65-70 mph in 4th.
No problem with overdrive and that rear end.
BTW I have 275/60/15 tires. I never did get the tcc wired up. this trans is ok to leave the tcc non working as far as I know. Some newer ones aren't

I do want to change the rear in the future to get off the line better and for pulling the boat out the water.

Go for the 700. Makes a nice difference off the line and is good on the highway.

[MylilBowTie]

The 84 I have has a 355, th400, 3.08 gears. Its a not a slug off the line but not much better. The 86 has a 305, th350, 3.42 gears its way better off the line. I know the th400 eats a little more power than the other transmission. I really think its the better gears in the 86 that help it. It seems to make up for the lack of 350. Then again the 305 has 240k miles on it.

[77GMCTruck]

I have been wondering about this myself. If changing the transmission to a 700R4 and the gears in the rear axle would improve the gas mileage of the truck any. I honestly don't know what tranny is on the truck. Haven't had it long enough to really get under it and look. I know it's the stock one from 1977 that came on it. I'm trying to figure out what will make it run easier on the highway and maybe improve gas mileage a bit.

[PhilaTruck]

Hey, welcome to the board!

What kind of cam/stall situation do you have? Where does your cam want to make power? I can assume they're both stock, but it can make a big difference.

I know for mine, I'm switching out to a 3.73, but I have over 70 degrees overlap in my cam. Need to make power in higher RPMs. With my 700r4, I'll still cruise at a decent RPM, like piecesparts said about his son's truck.

-Todd