Hi,
I am investigating converting my 1976 F-250 Crewcab 4X4 with a divorced transfer case from the 4 speed manual to a C-6. Do you know of any technical articles that will outline the work involved. I searched the tech articles and forums in this web site and could not come up with what I needed. I did print the article on removing and installing a C6 in a 4x4 van.

Your help is greatly appreciated.

 

Why? The C-6 transmission, althiough bullet proof robs about 58 hp. from the engine to run the pump. Will hurt your milage too.

 

I am converting to the auto because I mainly drive the vehicle around town (unfortunately) and would like to eliminate all the shifting (I'm lazy I guess). The 4 speed is needing a rebuild and I thought now would be the time to make the change.

 

my best guess would be to use a c6 from a 2wd truck, the np435 is suppose to be the same as whats on a 2wd truck, so i would think it would be the same as a c6. im not sure, just my best guess

 

You'll need a C6 out of a car or 2wd. I'd look for a ribbed C6 case, there a lot stronger.

 

I'm not sure it would be an issue for you, but I am doing the same swap on my 79 F250 4x4 with a C6 and a married 205 transfer case. Transmission bolted up fine, even retained the same rear mount on the transfer case. When I went to hook up my front driveshaft the double u-joint is up against the edge of the transmission and pan...still haven't figured that out but I'm working on it!

 

Lastchance,

I assume you have a married transfer case to have a clearance issue with the transmission. Is this true? The things that have me worried are if the flexplate is the same and I was told by a transmission shop to make sure the pilot key on the crank of the 390 is at least 1.848" (I won't know this until I pull the old tranny). Seems like it should be a pretty straight forward conversion, please let me know if you encounter any curve *****.

Thanks.

 

Yes, I have the married transmission and transfer case. That's been the only hard part of my swap so far. I pulled out a dying 302 and dropped in a 300-6 cylinder at the same time so I'm still working on changing a lot of stuff over!!!

 

Lastchance,

I know there are others in this forum that would disagree with me, but I think the 302 to 300 conversion is a good choice for a daily driver. You may not get as much HP but should feel better torque out of the 300.

Good luck!

 

Gary, where did you ever come up with 58HP to run the pump? That has got to be WAY off. While I have not calculated the power draw for the pump 5.8HP might seem to be a better figure. I don't have a C6 pump to measure at the moment. I could pull apart an E4OD pump I have for a check tho.

 

I have seen these very high figures printed in several differant sites
just swapped out a 303 to C6 in my 76 e-150 w/ 300
99% intown driving
pulls better, smoother and quicker
imagine that with 50 less horsepower

 

If that 58 HP figure is true, I feel really bad for the guys that have a 351M in their trucks.

That would mean ,only about 90 HP gets to the rear axle

 

That is a tiny pump, it is only used to circulate fluid thru the TC and pressurize the controls. I KNOW what a 50+ HP pump looks like from years in the hydraulic business. And these pumps only operate at 100-150 PSI. The pump in a C6 is a crescent internal gear pump. I think I may have some formulas somewhere on Internal gear volume/revolution that I can use to figure the HP required to turn it. It is a very loose fitting pump with no pressure compensation or anything. probably less than 75% volumetric efficiency even at these low pressures. There is a company called VOITH that produces very good crescent internal gear pumps if anyone is interested in how they work.

 

I changed over to a C-6 in my '77 crewcab 4x4. It also has the divorced transfer case. My tranny came from a van. You will need to get the correct tailshaft housing that has the bolt hole for the transfer case shift mount. I used the same transmission crossmember, but had to relocate the crossmember. I used a 75 3/4 ton 4x4 to get the bolt hole locations off of the frame for the crossmember's new location. Some of the trucks have frames with multiple holes for the crossmember to mount to. I guess it was for various engine and transmission combinations. I had to shorten my driveline about 6 inches too.

There are other changes too, like removing the clutch pedal, wiring for the back up lights, the correct tranny oil dipstick tube that matches your engine, cooling lines to the radiator, vacuum line and kickdown rod. All in all, it wasn't too difficult.

Good luck

 

Have you ever been IN a truck with a C6 and the 351M ???

I don't think the HP is lost in the pump, per se, but the rest of the crapola of an auto - mostly in the torque converter. Don't buy into a torque converter actually being a gear reduction (and torque multiplier by definition) - it's just a way to let the motor spin faster than the tranny input shaft. Lots of lost energy going into swirling all the tranny fluid around in the big bag of fluid called a "torque converter"...