Questions about Transmissions - c4 / c6

[ZeroBurn7]

Well.... I have my '69 F100 SWB and I recently had to have the transmission rebuilt. When this was completed the gentleman at the service place told me that I have an FMX trans. He says this is like a two speed with Overdrive.(???) Anyway... that needs to go. My question is what are the difference between the C4 and the C6?? I have a decent motor that I think can put down some good power but it seems like with my FMX it is in vain. Which application would be better for me??

Any suggestions are appreciated.

Thanks

[Leadfoot]

well the C4 is smaller weaker & lighter. But it takes less power to run from my exp. C4s do not like say 325 hp plus.

the C6 is a good trans its very strong and you don't need to do as much performance upgrades. Normally just a shift kit. but its heavy.

Now with that said at the race tracks a very common swap is the turbo 350/400 (Chevy trans) with a after market bell housing all though costly. (machining involved). it dose make a nice trans.

[pat67shorty]

What engine does it have, and what do you want to do with the truck?

[ZeroBurn7]

Well... I have a 351W that I wanted to have rebuilt and toughend up. Right now not that much power but I would like to see over 300 horse. Preparing for the future is all.

[stockr]

you can probably get away with a rebuilt HD c4...but for a 351 i would say c6...

[Jake11]

A C4 won't last too long in a 351 P/U. Find a C6 if you can, or keep
Cruis-O-Matic till you do. Good luck, KP

[crazy larry]

you can build or have built a c4 that'd take it.

if was me, and it was track only, i'd go c4 simply due to less parasitic powerloss and it's lighter weight. if it was for ddd, i'd go c6.

[xxxtina63]

Since you say 300hp, I'm guessing you plan on stepping on it now and again and probably using it for light truck stuff. Yes, a C6 does use more power, but in the long run it will out last a C4 any day. You have to ask yourself, is it worth 20-40 more HP to go with a C4, or would I rather have it last longer (or forever) with slightly less hp?

[ZeroBurn7]

Yeah, This would be like a weekend driver.. I never really plan to take it to the track ... but .. i'd like it to hold it's own. So let me get this right .. on a c6 there is alot of parasitic power loss (don't know if spelled correctly) ?? Oh and yeah... i'd like to do some "truck stuff" with it once and a while.

thx

[pat67shorty]

If you want to use it like a truck go with a C6. The most common sorce for a small block pattern 2wd C6 is a 73-80ish Econoline.

[Jake11]

A C4 is fine for a light car. The clutches in a C4 are as big around as a
small coffee can. The ones in a C6 are as big around as a big coffee can.
Same thing with the planet gears. Go ahead and put a C4 in it. Keep a
couple spares handy. Get good at changing out trannies. Have fun.

[BigBlue'72]

I have a fully rebuilt, competition built c6 with the SB bellhousing pattern sitting around. Those are beefy units and great for towing etc. If its a play truck not doing heavy hauling a C4 is fine as long as its built right.