Details: F100 1973
Engine: 302 Gt40 heads
Transmission: C4

English is my second language so please bear with me, I am doing my best:
The previous owner converted the truck to automatic from manual and he installed a c4. I upgraded the engine with a newer engine, I got a 302 engine from a Thunderbird/Mustang from the 90's with GT40 heads and it was rebuilt; but I setup with carburetor. Being said that, after this upgrade it worked just fine, but after some use, it feels like the transmission is just small and the truck does something weird if you want to have fun; it does that weird movement like when you are learning to drive manual and you just pull the clutch too fast, does that make sense to you? this, only when you push the gas a bit hard, so no bueno.

I assume the trans is too small for that powerful engine, I have another c6 which worked fine so I am thinking in just put this c6 behind that strong 302. What is your advice? rebuild the c4 or just put a bigger, heavier transmission. What could be the reason of that behavior? which transmission you prefer? The most heaviest thing that I will put on the back of the truck will be a 24 of beers,but I want power( we all want power right? ) believe me now looks really nice, I am just in the last phase of the project.

I did not want to replace the c4 when I upgrade the engine because I have learn this in the hard way: Do not fix something that is working. what your thoughts? complains? any information will be appreciated.

Muchas gracias.

 

Your C4 has a vacuum controlled modulator that may be adjustable. You can adjust it for an earlier and softer shift. You could also have a vacuum leak somewhere that is causing the later, hard shift under acceleration.

 

C4's can be built to handle anything, but try to fix/adjust yours if possible. You might get better fun results with different gearing in the rear end. What gears do you have?

 

Sounds like the C4 just needs a competent rebuild. A C4 can handle the power of a 90's 302 engine. Might try Broader transmissions.

 

The C-6 will consume more power than the C-4, less power to the tire. If you're not going to haul anything heavy I would stick with the C-4.

Jess

 

There is a small block C-6 trans. It's basically a C-6 with a small block bolt pattern on the bell housing. I don't think came in the 4x4 trucks though. "There’s also the small-block C6 originally intended for 351W and 351C engines, which fits any six-bolt 289/302/351W/351C small-block bellhousing bolt pattern".

 

Your English is way better than Some people who only speak English!