C4 diagnostics and data

chromed302 · Jan 6, 2014

c4 problems.

Hey Paul, hopefully you can help me i have a 77 c4 case filled green stripe modulator and what its doing is... i can put it in park, neutral, reverse and drive and it does just fine but when i put it in drive its stuck in low gear(1st) and doesn't shift and it wont shift manually from 1st to 2nd to drive just stays in that low gear(1st) i been told to check governor and vacuum modulator and the psi on it i put a new modulator in it and i have it running to a vacuum tree on my intake and the valves in the governor move freely what else can i check out? Thanks!

danford1 · Jan 6, 2014

I don't think anyone reads this forum anymore.
I asked the question above yours 2 months ago and never got an answer.
Yes, my trans still isn't fixed. I need to know what to check to fix it...
Perhaps try to find another trans forum and ask your questions there.
I hope you are able to find an answer.
Danford1

Craig Selvey · Jan 6, 2014

Paul is no longer is active on this forum as well

chromed302 · Jan 6, 2014

well is there any trans forums that are good that could help me resolve my c4 issue that any of you may know of? Thanks

Rasit · Jan 6, 2014

Here's one...

http://www.network54.com/Forum/260730/

GreyGhost74 · May 19, 2014

Got a c4 that 1st and second always engage, but 3rd and reverse wont until the transmission warms up. And it leaks a lot of fluid. First i thought it was the pan gasket. Replaced that. Now it looks like its leaking from above the pan drivers side rear corner of the transmission pan is where most of the fluid is...

CarlFredrickson · Aug 19, 2014

I have a question I rebuilt my C4 in my 65 mustang and shifts perfect when cold slips when warm new bands new seals and new clutches and first thought was trans was overheating so installed external cooler still starts slipping after driving about half hour

Mavit · Jul 17, 2015

CarlFredrickson said: ↑

I have a question I rebuilt my C4 in my 65 mustang and shifts perfect when cold slips when warm new bands new seals and new clutches and first thought was trans was overheating so installed external cooler still starts slipping after driving about half hour
Click to expand...

if you guys are having transmission problems and need someone to help with trouble shooting
the place I found that has the best C4 section is Ford Muscle Forum !
There you will find a bunch of guys that can answer your Questions and they frequently check the C4 section of the forum!

CarlFredrickson · Jul 17, 2015

CarlFredrickson said: ↑

I have a question I rebuilt my C4 in my 65 mustang and shifts perfect when cold slips when warm new bands new seals and new clutches and first thought was trans was overheating so installed external cooler still starts slipping after driving about half hour
Click to expand...

Sorry didn't update this found problem planetery gears were going out was the problem

Dcarriker17 · Aug 20, 2016

Ok so My c4 will only go into reverse fine when it starts uk but when it's warm I have to almost redline it to get it to shift to reverse. Every other gear works.

Mavit · Aug 20, 2016

Reverse is Activated in the C4 By a Servo piston located on the drivers side of the tranny this piston is Steal with a rubber seal around the outer edge this rubber will crack and leek when it gets old! The Servo piston can be seen from the out side of the tranny by pulling the 4 bolts in the cover. To replace it you would need to remove the pan and Valve body, under the Valve body you will see a linkage on the end of the servo piston that hooks to the hard reverse Band!
This is some thing that a back yard mechanic can repair him self! Remember if you pull the Servo piston from the out side the link will fall into the pan and the valve body will have to be removed to reconnect the Link between the band and the servo piston!

Kenny8080 · Nov 13, 2018

PaulS said: ↑

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.
Click to expand...

PaulS said: ↑

The last two posts are on the same topic so I will touch on that here and then add it to the list at the top of this forum.

The condition where the engine seems to run up between shifts is called a "flare" and when the engine seems to hang and feels mushy betwen gears is called overlap. Flare usually happens when an "R" servo is installed to replace a different servo with a larger disengagement side. The servo disengages before the direct clutch has time to lock up so you get a flare. There are two cures and a hack for this condition:
Fix 1. put back in a servo with a larger disengagement side. "C" or "H" are recommended
Fix 2. restrict the flow to the disengagement side of the servo (difficult to do without restricting the apply side but it can be done.
Hack: Tighten the front band adjustment up to 1 turn in 1/4 turn increments. This may ease the flare but it will cause rapid wear of the band and extra heat in the C4. It is the "fix" that a lot of weekend racers use.

Servos and the reason there are differences:
(I hope this formatting comes out well)

-------Apply--Apply--Release--Release
Servo--force--area----force----area----Use
--C----1529--7.6sq"---2250----11.3sq"-** up to 700 hp (700 ft lbs)
--H----1376--6.9sq"---2250----11.3sq"-** up to 600 hp (600 ft lbs)
--A----1254--6.9sq"---2250----11.3sq"-** up to 500 hp (500 ft lbs)
--R----1249--6.2sq"---1675---- 8.4sq"-----up to 450 hp (800 with mod)
--B----1154--5.8sq"---2250----11.3sq"-** up to 390 hp
the rest are maginal for anything but stock engines and some can be used with the mod to use on higher HP (torque) applications. The "K" and "W" servos are the ones to use for up to 1000 hp appications after the mod has been performed. They are NOT recommended for street applications and the force applied can break bands and cases with high pressures. The force numbers are in pounds with an operating pressure of 200 psi. Some of my transmissions use pressures over that point and some use slightly less. The valve body (separator plate) has restrictions that match the timing of the release of the band with the application of the direct clutches. improper mods to those restrictions will always cause Flare or Overlap. Installing a different servo can accentuate the problem and make it intollerable. For street and street/strip applications you almost never have to change servos or the porting to the point where flare is caused. Overlap is supposed to be eliminated to a very large degree in any performance transmission.
This will be discussed in my initial trouble-shooting guide above as I have the time to devote to it.
Click to expand...

Kenny8080 · Nov 13, 2018

trouble with 66 C-4 after rebuild has strong reverse but starts in second no upshift and no 1st gear

74bronco · Apr 21, 2019

Does anyone know if PaulS has passed away?? he was a awesome guy with great knowledge of the c4 tranny.

captainmack · Apr 22, 2019

i do not know but he was a wealth of knowledge that he freely gave. years ago he said he was going to leave this forum due to health issues. Thats all i know.

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C4 diagnostics and data

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