kevin2392

hey guys im kinda new here but i have a 70 coupe 302 with a c4, my problem is, is that it will shift at around 4,750 rpm when its floored, i believe it should redline around 5,500 rpm right? what are some possibilities that could be causing this?

jlg2002

Engine Redline and shifting RPM are two completely different issues.

rmodel65

do you have an adjustable vacuum modulator?

kevin2392

i am not sure, where would i look for it?

Iskwezm

The vacuum modulator is on the pass side of the trans with a vacuum hose going to it. Some are adjustable and you can raise or lower the shift point by adjusting the diaphragm

kevin2392

is it as easy as it sounds or is there more to it?

toybreaker

If it is adjustable it is that easy.

rbowmar

Another solution is to put in a shift kit. Mine makes normal shifting crisper and also allows using 1 and 2 as manual shifters. I can hold it in 1st or 2nd up to redline and shift it down at any speed as well. when shifted down, the car has engine braking like a manual transmission. A great improvement over stock!

I am using the TansGo SK 4-71 for 1970-72 C4 transmissions. I paid about $30 5 years ago and had it installed along with a tranny rebuild. There's only 5 springs and a steel pin in the box so It couldn't be a big deal to install.

The experts probably know more about what's best these days.

I hope this is helpful.

Al Newman

Truth be known, your stock 302 is pretty much outa cheese at around 4,750 rpm, anyway, so, unless you have big plans (that's spelled "bucks") for the motor, you ain't gonna gain much be altering the C4 shift pattern.
Best,
Al

kevin2392

its not stock... 2 previous owners ago did all the motor work but the only things i can tell are the cam, intake, full msd, pulley sysem, headers...i recently put a holley 650 on it and alum. radiator.