I am going to make an attempt to put together a complete diagnostics for the C4 in the following posts so that folks can go through step by step to find out what went wrong with that transmission that has been working fine - up 'til now. The C4 is a three speed automatic transmission. In 1964 it was introduced as a new cruise-o-matic with Park, Reverse, Neutral, Drive, Drive2, and 1 selections on the shifter. (Green Dot C4) In 1967 it was re-introduced as a "select shift" with a position for each gear: P,R, N, D, 2, 1 with the only real change in the valve body and porting in the case. This version stayed in service until 1970 when Ford introduced the first factory manual shift C4 and a newer version of the "select shift". The changes were in the valve body and in passages cast into the case. Aside from the diameter of the input shaft, the inside diameter of the pump stator support and the forward clutch pack splines, all internal parts swap from one to the other. The case porting on the 1964-66 is different than all the other cases and to update you need a new case. The case porting on the 1967-69 cases is different from the later models and the valve bodies will not interchange. There are three types of valve bodies in the 70 and later C4s. In 1970 only, the manual shift C4 has now automatic shifting. It uses a 26x26 spline input so the forward clutch drum splines are not usable in any other transmission. The 1970 - up automatic C4s used a 24x26 spline input shaft and some are hardened while others are not. There are two valve bodies for these transmissions. One has the line pressure limit valve and spring held in place with a roll pin though a boss on the valve body and the other has the limit valve and spring held in place with a part of the filter. These are the most plentiful C4s and are the ones used most often to upgrade for performance use. There are two cases. On that the bellhousing bolts to the pump (case fill) and one that the bellhousing bolts to a built in flange on the case (pan fill). The pan fill case is slightly stronger because of the build up inthe area of the flange. Either case can take up to 1000 HP but the internal parts must be modified to handle the power. In order to correctly identify the C4 that you have you must have the small rectangular tag bolted to the servo housing or the date code on the left side of the transmission and the stamped in number that can be found under it. Morning Sickness: If your C4 is suffering from "morning Sickness" - that is if it hesitates to go into forward gears on the first start-up of the day but otherwise it runs fine; you have a poorly sealing forward clutch. This is usually caused by the seals on the forward clutch piston getting hard from too much heat and years of it. The only repair is to rebuild the tranny. Yes, I know there are myths about putting everything from diesel oil to brake fluid - and any number of stuff off the shelf - into the C4 but think about it. If this stuff will soften the hard brittle seal in a clutch pack what is it going to do to the converter seal that is already soft? It is the first seal that will be affected by whatever you put in your transmission and it has to hold oil in your transmission to keep it alive. If you are running a cooler that has any length of rubber hose to it the softening agents (usually alcohol) will also ruin those hoses too - and they are under about 70 psi at times. You are a lot better off when this problem first arrises to let the transmission take it's time to engage (don't rev up the engine) and once it engages drive it gently. I have seen cars last for two years with this problem. This will give you time to get a replacement or schedule the time for the rebuild. No Reverse: If you have no reverse but still have all the other gears working fine (including high gear) then you are the lucky one! This is a relatively easy problem to correct and it can be done with the transmission in the car. Your rear servo seal is probably cracked. the seal is moulded to the steel piston and comes as an assembly - piston and seal. You will need a piston, cover seal (a square cut o-ring), about two quarts of type "F" fluid and some loc-tite 518 sealer. Once you have your parts, you can jack up the car far enough to be comfortable underneath it. Use solid stands or block it up with wood (two by two crib style). Loosen the band locknut (on the oposite side of the tranny) and tighten the adjusting screw to 10 foot pounds. Place a drain pan under the rear servo and remove the four bolts that hold it in place. BE CAREFUL there is a spring behind the piston and the cover will pop out - with a resulting splash of oil. If the piston doesn't pop out all by itself you can use the spring to get it out by pushing the piston back in and then letting it "POP" again. You will be ready for the oil this time. Clean the cover, coat the o-ring cover seal in loc-tite 518, coat the piston seal with vaseline and re-install making sure that the spring is in place. Hold the cover in place while you start two bolts on oposite sides of the cover. Then you can let go of the cover and start the other two bolts. Tighten the bolts in a "cross" pattern evenly and when they are snug torque them to 18 foot pounds. Now back the adjusting screw off 3 turns exactly and hold the screw while you tighten the lock nut to 40 foot pounds. Start the engine and let it idle in park while you check and top off the transmission level. Go for a test drive and enjoy your new found reverse gear operation. My C4 shifts too soon: This is actually a lack of a problem! The C4 should idealy shift from 1-2 before you cross an intersection from a stop and into third very quickly after that. My wife's C4 shift 1-2-3 before the back of the car crosses the stop line on the other side of a two lane road - it shifts so early you can hardly tell it has shifted. (NOTE: the C4 in it is a 500 hp unit that I built with a stage 1 valve body for street only use) It shifts under light throttle just as it did when it was new (with less overlap and a bit faster engagement). When she pushes the throttle to half way down and pulls away fast it does shift later and with much more authority. If you simply MUST have a C4 that shifts later than stock you can do this two ways. Shift it manually - then you are in complete control of when it shifts and you can't hurt your transmission doing this. The other way is to get a new modulator (green stripe is the best but it might require some mods for those who have a two diaphagm modulator - more on that later.... You will need a new green stripe modulator, a quart of type "F" fluid and a modulator rod (make it from a 8d nail) that is 1.6 inches long. You can do this by jacking the car at the rear end of the car. (block the front wheels so it won't roll) Use stable jackstands or good blocks. Remove the extension housing bolt that holds the spring that keeps the modulator in place. Put a pan under the modulator and remove the hose that connects to it. (if there is any oil in the hose then your modulator was leaking and needed to be replaced anyway) Pull the modulator out - the pin will probably come with it so watch for it. Place some vaseline on the o-ring that seals the modulator (they usually come on the modulator), place your new pin into the modulator and slide the modulator back into the transmission. If you push it all the way into the case it will spring back about 1/4" - that is normal. If it springs back more than that then you have missed the hole in the back of the valve spool with the pin - take the modulator back out and try again holding the pin in the middle of the bore for the modulator. Once it is in place re-install the spring retainer and extension housing bolt that holds it in place. Plug the hose back in and let the car down. Start the engine and let it idle in park while you top off the transmission oil. Take the car out and see if it shifts more to your liking. If you still want more there is one more thing that you can do: Where you plug the hose on the back of the modulator there is a small screw. You can turn that screw in one turn at a time until you reach a shift point that is ok or no more than 3 turns. (you turn it in to make the shifts later - righty tighty) Mark the modulator with the number of turns that you have turned it - the next guy may want to do the same thing you did and if the modulator isn't marked the modulator will be ruined and the car will either shift eratically or leak fluid into the hose (and the manifold) sucking the C4 dry and making lots of white smoke on decelleration. the mark I make is with a paint pen or permanent marker and it is a simple +1 or however many turns you have turned it. ("+2.5" "+3" "-1") If you reach 3 turns and still aren't happy with the shift timing then you need to shift manually - there is nothing that you can do to make it shift later automatically without hurting the transmission.