Thanks for the reply Mike. Those things check out OK. The trans was rebuilt and when I took it out for the first time it wouldn't up shift and it puked some fluid out of the dipstick tube. I switched the new modulator with a used one I had here from another trans, blew through the vacuum tube and checked for vacuum leaks. I suppose the used modulator could be bad too but neither one had fluid in it. Is there anything inside that would cause this?
Mike, If you built the trans, the first question I would ask, would be "did you air pressure check the clutches during assembly, and ensure that the intermediate sprag clutch outer race rotated clockwise, as the direct drum sat on the bench, with the sprag clutch assembly up ? If your answers are yes... or someone else built it, I would do two things before starting the below proceedures : 1. Insure that the modulator valve moves freely. Do this by removing the modulator, and with a small magnet, attempt to pull the valve out. It should slide out freely. 2. drop the pan, insure that the detent solenoid has the correct type of gasket in good conditon for the type of solenoid (oval can solenoids use the thin metal gasket, square can detent solenoids use no gasket, as it is intregal in the solenoid (rubber seal that you don't change). And double check the valve body and detent solenoid bolts, to make sure they are tight. If all that checks out, then drop the valve body, physically manipulate the 1-2 shift valve to make sure it is not stuck, and insure all the gaskets and check balls are in place. If your fixing this trans, then the book from Ron Sessions titled "How to work with and modify the TH-400 trans" is an invaluable resource guide, even more so than the factory service manuals of the era. If all that checks out, then go onto the below testing and evaluations. You need to get yourself a transmission pressure gauge, and screw it into the line pressure tap on the driver side of the case. The trans pressure gauge should be available at most professional auto parts stores. It goes from 0-300 psi, and has a hose long enough to easily reach the inside of the car, when installed in the trans. Be careful to route and secure the hose away from the LH exhaust head pipe. You have the situation which leaves the most probabilities for conditions which can cause this situation (a fresh rebuild). Any of the below causes can cause a no-upshift condition, with the unit saying in low range. 1. Stuck modulator valve 2. stuck 1-2 shift valve 3. Stuck governor valve 4. cross leaks in the valve body/separator plate/case 5. numerous other hydraulic system issues including, other leaks(most commonly in the detent system), missing seals, missing check balls ect.. Now, the first thing that needs to be discovered is if the trans will force upshift (assuming you did not perform the low range at any speed mods) Even held in low manually, the stock trans will upshift to intermediate range (second gear) at aprox 50 mph or so. The question in your mind, as a troubleshooter at this point in time is "did it try to shift and couldn't, or is it even not trying". You should take the car out, wind it up to the engines redline in low, and see if it will shift to second, with the selector lever in "D". Have the pressure gauge installed, and viewable as your driving. If the trans attempts to shift but "neutralizes", then the most probable cause of failure is related to the mechanical or hydraulic systems which control the intermediate clutch. A hydraulic leakage situation will be seen by a quick drop in the needle, and then it staying at a lower pressure than was seen during low range operation. At moderate throttle, with one horseshoe clip in the regulator, pressure should be right around 60-75psi, and in normal operation will drop for just an instant as the 1-2 shift valve moves, and directs fluid to the intermediate clutch, and as that clutch fills and applies, and then it should return to nearly the previous pressure read. This, in a well set up trans, will be just a quick "bob" of the needle. If the pressure drops and stays low, then you have a hydraulic leak to trace and resolve. If the pressure gauge "bobs" as would be normal, but the trans neutralizes, and the trans is equipped with a intermediate sprag clutch (stock on all 64-70 transmissions) then the most likely cause is that you have the intermediate sprag installed on the direct drum upside down. I am just scratching the surface here, with what just comes to the top of my head sitting in my home office, without looking at any manuals or hydraulic schematics, but these are the first steps to diagnosing the issue at hand. Once you secure the gauge, it will be helpful to install it on a working TH-400, and familiarizing yourself with the normal hydraulic readings that you will see on the gauge, at various throttle openings, and during shifting. I am not sure if you built this, or someone else did, but the most common issues after rebuild, are the aforementioned issue with the intermediate sprag, as well as lip seal and sealing ring issues. Good luck. JW
Mike, Like JW said, if the detent solenoid is activated all the time, or has the wrong gasket, the trans won't upshift except at WOT. Check for a constant 12 volts at the detent (vertical) tang on the drivers side of the trans. If you find that, check the gas pedal switch for a shorted condition. pull the connection off the side of the trans. If it upshifts, you've found the problem.
Thanks guys. I had someone else rebuild it and I just spoke to him and it looks like I'm pulling it out this afternoon. I put the used modulator on and took it down the street and it shifted but the shifts were very soft and the trans is slipping. It doesn't seem to do it all the time but it is definately slipping often. I also put a new 2800 stall converter in and I've never driven a car with a stall converter so I don't know what its supposed to feel like but I still think there's something wrong with the trans as its still puking fluid out of the dipstick. The guy who rebuilt it said if I pull it he'll come pick it up and go through it again. I was wondering if the converter can be checked while its out? Can a trans shop do this?
Good points here, but I beleive if the internmediate sprag is installed upside down, the trans will shift to 2nd gear but will lock when it tries to go to 3rd gear. Only seen this once so i don't recall 100%. Jim Burek
OK, so I finally got it mostly worked out. It was just a number of small things. First It appears as if the modulator WAS bad. It just took three modulators before I got a good one. Then, the vent tube on top of the trans was plugged up which was causing the fluid to blow out of the filler tube. It was also causing me to get incorrect readings when checking the fluid level. I was tipped off to something being wrong when very little fluid came out when I changed the modulator. So now it shifts but way too early so I need to adjust the modulator and it doesn't slip except on the 1-2 shift but hey, that's why I had it rebuilt right? The guy who rebuilt it also said it already had a shift kit in it which it most certainly does not. Very aggrivating. So now I just have to get a filler tube that doesn't leak and actually fits the car so I can accurately check the fluid level, adjust the modulator, put a shift kit in and figure out the 1-2 slipping issue. Oh, and then there's still the fact that the new motor won't run with less than 30* initial advance. Are we having fun yet?
