Just an idea ive been tossing around....

[Workin' Rig]

How hard would it be to swap the C6 in my 77 F250 for the BW T18 thats in my 78 F350?

I dont know for sure if i am going to do it....if its easy enough i might. Both trucks have the 400. Im just thinking with a 4sp and some 3.54 gears the 77 would tow so much better....

Im definatly planning on swapping the rear this spring (3.07s suck for towing) I towed my camper the other day for the first time since i rebuilt the carb and i must say i was throughly impressed with just the differnce that made. But im still having to pull it into 2nd manually to keep 45-50 up hills.

Basically im just looking for more oomph all the way around.

 

[SuperCab]

It probably wouldn't be a terrible swap, but if it was me I'd just keep the c6... A healthy c6 will tow for many trouble free miles.

But not with 3.07 gears. My 74 has 3.07 gears, and my c6 died prematurely. At the recommendation of my transmission rebuilder I switched to 245/75/16 tires from the 265/75/16 I used to run. The 2" shorter tire helps a lot...

Iirc it gives me an effective ratio of 3.25??? I think??? Instead of 3.07.

The gears are your biggest issue. Even with the 4 speed t18, you'll have to start out in granny gear (no fun) or slip the clutch in second to get rolling.

 

[Workin' Rig]

Im definatly going to go to 3.54's or maybe even 3.73's this spring. I read in my owners manual that for 7000lb i have all the required stuff except for the gears. 3.54's was the minimum required. Its easy enough to find rears for 200-250 bucks for these trucks.

 

[DNFXDLI]

I'd keep the automatic myself.
Given that that engine is probably around the 160hp/250tq, I think having to downshift up a hill to maintain that speed would be expected.
Edit..If I was going to spend the time doing the swap and I knew that it was primarily for towing what you are talking about, I'd opt for the 3.73's or 4.10's.

 

[Workin' Rig]

169HP 316FTLBS

It actualy does really really well being saddled with an auto and 3.07's, but im worried if i ever take it anywhere that is hilly i might have a problem.

WHy i wanna change gears.

 

[DNFXDLI]

I stand corrected on the torque .
I still stand by the 3.73's or 4.10's....the 3.73's probably being the best compromise.

 

[m78]

Sounds like you would be a candidate for something like an under drive unit.
Hone used to be popular.

 

[Workin' Rig]

Yeah, 4.11s are definatly out of the question....i still wanna be able to be at a somewhat sane RPM at 50-55

I only tow the camper maybe once a month, and usually the truck is just used for hauling stuff or to just drive around in, so i dont wanna get to crazy with gearing.

What is an underdrive?

 

[m78]

http://www.stangerssite.com/honeodrive.html

Gearvenders is still in business.

 

[DNFXDLI]

Underdrive raises the engine's rpm's...opposite of what an overdrive does.

50mph with 4.10's and a 31'' tire : 2281

50mph with 3.73's and a 31'' tire: 2076

A couple of hundred rpm

Even at 65 you are still under 3000

3.73's : 2698

4.10's: 2966

 

[Workin' Rig]

What kinda RPMS am i turning at 50 with the 3.07's?

 

[DNFXDLI]

What kinda RPMS am i turning at 50 with the 3.07's?

With a 31'' tire?...

1700 rpm...too low IMO.

 

[Workin' Rig]

Thats lower then most of the new ones run even with an O/D....

 

[DNFXDLI]

I'd say it's in the ballpark...I can't 100% recall for sure, but I think my Shelby turns 1500 at 70 mph in 6th.
The 350 with 3.73's turns 2000 at 70 mph.
You'd be lugging that engine at that rpm with a trailer IMO.

 

[Workin' Rig]

So with 3.73's i should have the power to handle about anything with it?

 

[DNFXDLI]

I think it would improve what you have and maximize the capabilities of your truck.
If you have 31's...here is what the rpms would be at various speeds in 3rd gear:

30mph 1245
40mph 1660
50mph 2076
60mph 2491
70mph 2906

In 2nd gear:

30mph 1771
40mph 2361
50mph 2951
60mph 3542
70mph 4132

So there would still be room for a downshift if needed.

 

[Workin' Rig]

So at 55 with 3.73's i wont be turning enough RPMS to seriously hurt engine life?

 

[SuperCab]

I'd go for the 3.55s


My 87 Suburban had 4.10 gears, it was intolerable. Bad mpgs and excessive rpms on the highway... Swapped to 3.73 gears which is better, but still not where I would want it. I turn about 3300 rpm at 75mph.

 

[DNFXDLI]

That would put you just under 2300 rpm...right in the ballpark as far as I'm concerned.

 

[Workin' Rig]

I'd go for the 3.55s


My 87 Suburban had 4.10 gears, it was intolerable. Bad mpgs and excessive rpms on the highway... Swapped to 3.73 gears which is better, but still not where I would want it. I turn about 3300 rpm at 75mph.

Ive only drivin the truck at 75mph once right after i got it. Usually even on a 70mph freeway i rarely get over 65.

With the camper 60 is as fast as ill go.