C4 diagnostics and data

Discussion in 'Transmissions' started by PaulS, Aug 20, 2008.

  1. PaulS

    PaulS Member extrordiare

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    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 This version stayed in service until 1970 when Ford introduced the first factory manual shift C4 and a newer version of the "select shift".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.
     
    Last edited: Sep 2, 2008
  2. PaulS

    PaulS Member extrordiare

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    No second gear:
    Test this by trying to start out in manual second by placing the selector in the "2" position. If the car moves forward in first then you have no second - you will note that in DRIVE the transmission starts out fine and then doesn't shift until your at a high enough speed to shift into "3". This happens sometimes to those who "hotrod" an older C4 or appears just after having passed a car. There are many causes but the usual cause is a broken band or a "dropped" link. If it has been a long time since the bands were adjusted - get it done or do it yourself! the only reason for a dropped link is that there is too much clearance in the band adjustment. The other cause is a broken band. a broken band is a good reason to rebuild your C4 - unless you just rebuilt it. There is a repair that can be made to a street cruiser (low HP - NO drag racing) car. The repair is done with transmission in the car but it does require the removal of the valve body (a good time to install a TransGo 40-2 kit in the valve body).
    You will need a "Snap Band", 3 - 6 quarts of type "F" fluid, a new pan gasket and some loc-tite 518. ( a couple of 3" pieces of threaded rod and two nuts are very helpful). Jack the car up high enough that you can get under it comfortably and block it with stable stands or cribbing. Place your drain pan under the transmission pan and remove the bolts from the rear forward until you get to the last two bolts. Just loosen these bolts and pry the rear of the pan down until it breaks the seal on the gasket. As you further loosen the front bolts the rear of the pan will drop more until the transmission has drained most of its fluid into the pan (or close to the pan). You can then hold the pan while you remove the bolts completely and set the pan aside. Now remove the bolts that hold the valve body in place and drop it down placing it carefully into the pan you just removed. Check the pan for a broken piece of the band (usually it has the heavy metal end on it). If you do not see it in the pan look up in the transmission toward the front pan rail. Try pulling on the adjuster links - if they fall and part of the band comes off with it then you know for sure that you have a broken band. Pull the other side down - it will slide around the drum and come out faily easily. Keep the links - you will need them later. If the band is broken skip the next section.
    .....If the band doesn't seem to be broken but you have the symptoms then it is time to air test the transmission with 40 - 60 psi to find out if it is working or not. If the servo is not operating then you will need to remove the front servo piston and cover to find the problem. It might be a broken piston retainer (a small snap ring), a broken piston or a cracked cover. Look all the parts over before you decide it is just a bad seal ring......
    Installing the Snap Band:
    When you bought the "Snap Band" it came in a box with instructions... FOLLOW THEM. (if you need help e-mail me: paulstephens at q.com) once in adjust the band to 10 foot pounds and back it of 1 1/2 turns.
    Once you have it adjusted then in opposite corners of the valve body mounting bolts install your two pieces of threaded rod a few turns in. put the valve body up on the rods and start the nuts on the threaded rods. (this will help hold the valve body while you check to make sure that the manual valve and downshift linkage are both engaged as the valve body goes up into place. When you get the valve body about 1/4" away from the mounting surface see if the downshift lever is engaging the valve - it should move in one direction and spring back. Try sliding the manual valve back and forth - it is slides then line it up with the peg that sticks out from the shift linkage and move the valve body up to 1/8" away from the mounting surface. Recheck both linkages to make sure that the valves and levers are connected. the downshift lever should move in one direction and spring back on its own and the manual valve should not slide in either direction more than 1/32".
    When the linkage is right you can start the bolts around the valve body and snug them up to the valve body. Pull out the two threaded rods and nuts and install th other bolts. (NOTE: the long bolt goes into the end of the filter) tighten the bolts down in a back and forth pattern from the middle of the valve body to the outsides just finger tight. Torque the bolts in the same pattern to 20 inch pounds. Coat the pan gasket with the thinest possible film of loc-tite 518 and place on the pan. Put the pan in place and start all the bolts. Draw the bolts up evenly until they are finger tight. Tighten the bolts until the gasket just starts to bulge (very slight - DO NOT CRUSH THE GASKET). Put three to four quarts of type "F" fluid in the transmission. Start the engine and let it idle in PARK until you fill the transmission to half-way between the ADD and FULL marks on the dipstick. Turn the engine off and let the car down. start the car back up and run it through the gears (not going anywhere yet) and place it in PARK idling. Check the fluid level and bring it back up to 1/2 way between the ADD and FULL mark. Take the car for a test drive making sure to use the manual "2" position to make sure you have second gear.

    No Reverse or High gear, Compression braking works in manual low:
    All these symptoms point to a Dir/Rev clutch not applying. It is most likely a bad direct clutch piston seal.
    You can find out for sure if you jack the car up high enough to get under it comfortably remove the pan (drain oil into drain pan) and remove the valve body. Check the action of the clutches and bands with 40 - 60 psi. if the direct clutches just hiss you can be sure that the piston is not sealing. You will have to remove the transmission is going to have to come out to be repaired.
     
    Last edited: Sep 2, 2008
  3. PaulS

    PaulS Member extrordiare

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    To be continued... as time allows.........
     
    Last edited: Sep 2, 2008
  4. CornedBeef4.6L

    CornedBeef4.6L Voted off the Island

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    great info!!
     
  5. facelessnumber

    facelessnumber Drew Pittman

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    Hey Paul, thank you for taking the time to share this excellent guide. Regarding the two valve bodies you mention above, is one any better than the other, or have characteristics that differ in any other way besides that roll pin?
     
  6. PaulS

    PaulS Member extrordiare

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    Facelessnumber,
    the valve bodies are different - the one with the valve held in place with the roll pin is considered the "Pinto" valve body and the internal passages are different enough that not many people bother to modify it. The 40-2 TransGo kit does address the difference and works with either. My modifications that are listed in the tech area do not address this valve body. I commonly use the valve body with the valve and spring retained by the filter. I do have notes somewhere on the other valve body but I would have to look them up and go through it all to use the "Pinto" valve body.
     
  7. facelessnumber

    facelessnumber Drew Pittman

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    Interesting. I have both types. Currently I'm running the "Pinto" style valve body, which I did apply that Trans-Go kit to. No complaints so far. It came from a '77 Comet transmission (it also had the large bellhousing, which I think may have been a '77 thing.) Are there any advantages or limitations between one or the other? Any functional differences between them?
     
  8. PaulS

    PaulS Member extrordiare

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    Not really, there are just fewer of the "Pinto" style valves around. The 40-2 kit handles both well. You should have no issues at all.
     
  9. cenc1984

    cenc1984 killa 72

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    ok so what if the car will not go forward, but go backward just like it should (up untill yesterday it was running fine) today it was grinding gears and shifting hard/ bucking, sliping and now nothing. wont move in 1st 2nd or drive....help me on this Is there a second clutch for reverse? did I burn out my clutch?
    ps. my fluid smells fine and my P valve isnt leaking any fluid when I pulled the vaccume line off. thats what I know any help is, well........ helpfull

    thanks a million
    ALex O
     
  10. newtoford

    newtoford Member

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    ive been dealing with morning sickness on my daily comet amost a year now. i used to only do it when it was really cold out side but now its alot more noticable

    anything i can do to prolong its life besides going easy on it?
     

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