just rebuilt my first auto transmission. i like the feel of shifting at my own pace and feel i can judge the shifts better. ive heard its not rough on the trans but ive heard others say the opposite. is it safe? whats the proper way to manually shift the auto? ease off gas, shift and at what speeds should i downshift back down to first or second once in high gear.? also is there a break in period for a trans, or should i just take it easy on it for the first 100 or so miles? thanks
Sporty, the auto should be shifted without moving the throttle from its current position - letting off the gas lowers the pressures in the transmission and will cause wear. In spite of the way you feel - the C4 can tell best when it is time to shift. (sorry about that) Unless you installed a shift kit the C4 won't let you down-shift unless it is safe. The C4 will not let you down-shift to 1st until you are below 25 mph or so and from 3rd to 2nd won't happen unless you are below 50mph. These are about the same speeds that the down-shift linkage will shift it at wide open throttle. If you want more control over the shift points I suggest installing a TransGo reprogramming kit. Part# 40-2 for 70 - up and #47-2 for 67-69 C4s. This will give you full manual control of 1st and 2nd gears and still auto shift when it is in Drive. NOTE: with the kit you can downshift into 1st or 2nd at any speed - and shifting to 1st at 70 mph can over-rev your engine causing damage to the engine. With the TransGo kit you have to be aware of when it is ok to down-shift and what gear to use. 40 mph is about as high as I care to hit 1st gear but it all depends on your engine and rear gears - if you have a tach it will be easy to decide how far you can go. Manually shifting the C4 - if it is done correctly will not hurt the transmission. Don't let off the gas when shifting - up or down - until it is in gear.
alright thanks, i wont ease off gas next time haha, the 40-2 is what was used during the rebuild as ive heard it recommended by you before . i dont have my passing gear linkage hooked up right now and going up hills right now is whats causing me to shift at my own pace rather than creep up them.
Get that linkage connected! It increases the line pressure in addition to adding to governor pressure and by-passing the modulator pressure. When you are in 1st, 2nd, and reverse (manually selecting the gears) the pressures go up so you don't hurt the C4 but in drive the pressures can drop to 60 psi - not enough to prevent slipping of the clutches. That is something you probably wouldn't notice until they burned up. Even moderate acceleration (manifold vacuum above 10" HG) will slip those clutches and shorten the life.
That is exactly what it does - but it has to modify internal pressures to do that. When you examine the oil flow in the valve body you find that a lot of different parts are affected as soon as that valve starts to move. When it moves full travel then it completely shuts off some flow and maximizes others. It is like a hydraulic computer but instead of binary (on and off) it is an analog computer - operating on levels of pressure to make multiple things happen to decide what gear, how much pressure to give to the parts that make that gear happen and how long to hold it there. Changes happen thousands of times a second and the valve body responds to all of them. Properly operating C4s are a thing of beauty and as simple as they are because the complexities in the background make it seem so simple. Manual valve bodies do away with a lot of the complexities because they operate at full pressure all the time - then you have to decide when it is supposed to be in which gear and how long it should be held there.
