Hey Everyone! I'm currently building a 1978 F100 Super cab 2x4 with a 351W bored 30 over. with a c6 trans that's currently pouring out fluid as we speak, so i'm taking a NP435 4 Speed and replacing it. my first question is will this be the best trans for a truck that wont be towing a lot. i intend to use the truck as a cruiser, with the occasional pass at the local drag strip. im rather mechanically inclined, but im not sure about drivetrain specifications. the truck also currently has a 2.75 gear, and is slower than shizz on takeoff and highway speeds aren't existent. im wanting this truck to be a good running and rather quick on takeoff, without breaking the bank. any recommendations would be great. one other issue this truck has is its got a tick from the top end of the motor, after overhauling the block and putting new heads, rockers, pushrods, guide plates and lifters. it does increase with rpms, and appears to act like a skip. motor has less than 500 miles since rebuild so im not sure if i just need to get the trans swapped and just drive it, or if i should tear it all back down and start again. Needless to say im up to my head in crap im not 100% sure what to do about. thanks for reading and any information that can help me out. Thanks!!

 

The NP 435 is a good truck trans, unless starting a heavy load, first is never used, and it doesn't shift near like a performance trans, if it's slow off the line with the 2.75 and C6 tranny, trying to drag race it, you'll need a push truck. Changing the rear gears to 3.73 or 4.10's will let you cruise, and make a better off the line charge, can't help with the tapping noise in the engine.

 

Thanks for the info. ive got a 3.25 gear rear end im swapping out of it this week along with the four speed. i just wanted to hear some other ideas cause im afraid im gonna build it and not like it as much as im hoping. so with the 4 speed and a 3.25 Gear, im expecting it to be a little better than the 2.75 with a C6

 

Lets do this in 2 parts:
Ok the NP435 is a truck transmission has a granny first gear so you start in 2nd gear, Truck transmission read can not be speed shifted = slow shifting, so forget it at the drag strip.
If you were going to pull heavy loads this is the trans to have.

Then you have to install pedals, linkage that goes with it, bell housing, flywheel balanced for your motor, clutch kit. May need to do something with the drive shaft as it may not fit the NP435.

On that 2.75 rear gear, yes it is a dog from a start but on the high way it keeps the RPM down. If you were to go with say a 3.50 or 3.73 if they make them for your rear axle the RPM will go up for the same speed you are going. There are sites that you can figure when your RPM will be with different gear ratios.
That 2.75 ratio with a manual trans you would need to slip the clutch more unless starting in granny gear but that is a PITA pulling it out and into 2nd gear from every stop. The 3.50 / 3/73 would be easier on the clutch but again the RPM goes up.

By this time the C6 is looking pretty good. I would pull it and give it to a shop for a rebuild. Most of the $$ if the R&R of the trans from the truck.
Have a shift kit installed and you should be good.

If you want to lower the RPM even more with either the C6or NP435 look into Gear Vender over drive.
If you go with a lower gear (higher number) you can do the math with the over drive and have a good off the line truck and cruise with some what good MPG.


I would pop the valve cover off and give a look over.
In the 80 - 86 area a member just installed a reman motor, did the cam break in I dont know if he ever took it for a test drive and had a knock from inside the motor. It turns out a cam lobe & lifter went bad and was the cause for the noise, replacement motr is installed but has not started it yet.

With the cover off he set each cly. to TDC and when at TDC he tried to turn each push rod and found 1 that was loose.
Digging more is when he found the bad lifter & cam. So I would start at the top covers and valve train and go from there.
Dave ----

BTW I have a 81 F100 flare side with a 300 six, NP435 and Advance Adapter over drive, 2.75 rear gear running 235 / 75 / 15 tires and yes it is a little hard from a stop but the 300 has a lot of TQ off idle so its not to bad.
75 MPH in OD is 2000 RPM in 4th it is 2700 RPM speed limit is 70 here.

 

Do the gear change to 3.25 but keep the C6 with a shift kit.
The converter helps make it better off the line as it multiplys the TQ a clutch dose not have that.
Dave ----