TH400 Automatic Transmision Problems

Discussion in 'Troubleshooting & Diagnosis' started by Suicyko, Apr 4, 2006.

  1. Suicyko

    Suicyko New Member

    May 9, 2004
    Villa Hills, KY USA
    I’m having problems with a JEGS TH-400. Any help other than get a manual transmission would be great.

    I’ve written e-mial to JEGS, and TCI. It’s been 5 months with no replies. I have even resent the e-mail to their other e-mail addresses with no reply.

    First time I took car to local track, the transmission hated 2nd Gear going almost straight to 3rd.

    I figured this to be a problem stock gear shifter, and vacuum kick down.

    If I was in water pit, the car would go through all three gears. When trying to not burn out and accelerating, it goes clear through 1st, then hits 2nd. The 2nd gear lasts for like 1-2 second then shifts directly to 3rd.

    Even if I pull the shifter back to second it would downshift and stay in 2nd for like 1-3 second, and shift again to 3rd. I if left my finger of the lock button and pulled stock shifter into 1st/2nd it would stay in second. But I had to keep beating the stock shifter to get it to shift to 2nd

    So I buy a new kick down, a B&M shifter, and thought what the heck I had car up decided to stick in a TCI Trans Scat shift Kit.

    :( As my luck, now the transmission only has 1st gear now…

    I had a hell of time getting the parts out of Valve Body and think this is my problem. The instructions from TCI suck. Plus I have no idea how much to grind, and probably screwed this part up, but it already kind of looked like this part already. I guess JEGS used a weak shift kit that resembles this shift kit.

    I’ve checked and rechecked the adjustable cable on B&M shifter, and it seems to be ok, because Park, Reverse, Neutral all are fine. Just Drive-1st all get 1st. I can hear the transmission click, when shifting 3rd, 2nd, 1st, and back so I doubt this is the problem.

    With out knowing there was a problem, I took car back to track the next weekend.

    Funny thing is the car runs faster at track with only 1 gear than it did with 1½ gears.

    The other funny thing is, it ran faster with only 1 gear than most stock Japanese non turbo cars. :eek: It ran the ¼ at 16.5 sec at 64.4mph. The 1st time at track the car was running 17-18 seconds at 75-85 mph, because the car wanted to be in 3rd gear.

    Since the parts in the valve body were such a bear to get out, and I think I screwed these parts out, and grinding on it. So I ordered a TCI Trans Scat Valve Body Shift Kit from Summit Racing.

    I’m guessing I might have to go get reamed at transmission shop.

    Some old guys with old nova, the other with Chevelle, said I probably blew up 2nd gear.

    I never felt a snap/surge/metallic sounds. I’ve broken bands and gears on other GM cars, and every time I heard all kinds of sounds every time they were loud and nasty sounding.

    This transmission has never made any of those sounds. It acts like there is a stuck valve, such and the 1-2 valve that I had problem with in valve body. Or something else is stuck. Like there isn’t enough line pressure or something to pop it to next gear.
    Last edited: Apr 7, 2006
  2. SecGenLvr

    SecGenLvr Member

    Feb 8, 2006
    Tucson, AZ
    Well not a huge tranny man, but if you blew a gear, your fluid prolly smells like shiot so check that first, after that check your transmission modual, that is the main vacuum reason for shifting... and check your vacuum pressure to the module because if it is weak because of a leak or crimping of the metal line you wont get many shifts out of it...
  3. GoldenOne7710

    GoldenOne7710 Veteran Member Lifetime Gold Member

    Jun 23, 2004
    Athens, GA
    I'm no expert either, but I thought TH400's were electric kickdown via a switch mounted at the accelerator pedal. The modulator valve COULD have needed a simple adjustment or was not getting sufficient vacuum. I wouldn't expect Jegs to help you from this point. When you "worked" on it yourself, you voided the warranty. I still think they should've replied with at least some ideas about what could be wrong with it. Jegs customer service is usually decent.
  4. Cardinal

    Cardinal Veteran Member Lifetime Gold Member

    Jun 22, 2003
    Endicott, NY
    Hard to believe that Jegs wouldn't talk to you. I've had nothing but good results from them, Summit, PAW, Speed-O-Motive, Northern Auto Parts, etc. Summit even let me send back a Lakewood SBC bell housing, Zoom 11" clutch, pressure plate, and throwout bearing after I'd had them in the box for over a year. They credited my accout for what I paid for them but I called first to explain what I had and all I wanted was to get credit for what I paid for it (and use it to buy more parts). I'm about to test Jegs by sending back the Headman S10 V8 shorty hedders (too small primary tubes for our racing engine) but I'm sure that they'll credit my account for them.
  5. night rider

    night rider Veteran Member

    Aug 6, 2002
    Bremen, Ga
    Souds to me like your very mixed up..

    The th-400 does not have a kickdown cable. Driver's side of trans case is a male spade plug. That is the elec. hoop up for a micro switch that you mount to your throttle pedel or to the carb. The run a wire from trans to switch, then from switch to 12 volts keyed.

    Shift points are set by the weights/springs in the gov. and the set screw in the modulator valve.

    A full intake vac (vac line from intake to the transmission's modulator valve) must be hooked up to the modulator valve or it won't up shift right.

    You can adjust shift points some by un hooking that vac line and looking in the nipple of the valve. Theres a screw in there you can turn.

    The shift kits from TCI is one of the better ones not cheap junk by any means. It's the closest you can get to the best (trans go)
  6. TenSeven

    TenSeven Veteran Member

    Jan 30, 2006
    Huntington Beach, CA
    I really hope I'm not over-simplifying, but I often ran into the same problem with 4th-Gen F-bodies with a 4L60E (4 speed auto) trans.

    The problem commonly turned out to be that the trans oil level was too low, especially after a trans / converter swap.

    After putting in the new trans and running / breaking it in for a bit, did you recheck the fluid level?
  7. Suicyko

    Suicyko New Member

    May 9, 2004
    Villa Hills, KY USA
    First of Thanks to ALL for all the help.

    I don't know jack about an automatic's except what very little I was able to see on the crappy TCI instuctions, so any help is great.

    I thought the vacuum on side was the modulator and kick down... Because the th-350 had steel cable from carb ran down to it. And my old 78 Buick LeSabre Cop Car th350 had vacuum.

    So does this vacuum - kick down, hold it in gear, allow it to shift up, or all the above?

    Also the wire on the driver side of tranny I thought this was park/neutral saftey switch.... But like I said know nothing about the working of it, other than change a filter, and check the fluid.

    Oh, do I know this smell well. I've tore up 1 of 3 blown tranmissions on my brother's 1998 Grand Prix GTP. My first was a 85 Buick with an IRON Duke 4 banger, I never could kill the engine, all I did was kill the tranny.

    My Camaro's fuild still looks new, and it smells the same as it came out of the bottle. After the beating I put on car the fuild should have been boiling at the race track.

    I'm going to pull pan and see if there is any metal.

    If there is no metal, then I'm going to install the new Valve Body that is already has the modified valve in it to see if that works. According Summit Tech, he thought it was the valvebody after he heard my story. He thought it was stuck causing poor flow. which was 1st causing goofy shift, and now no shifts.

    If there is metal, I'm either going to junk it and go manual, or possible get it fixed if it doesn't cost alot. I'm just sick of messing with it. All I thought I would have to is get a custom drive shaft, and move the crossmember.

    My car orginally had th350 with the throttle wire kick down. ( I think thats what the cable was used for, it ran from Carb to passenger side of TH350) I junked that tranny when I put new engine in car and bought a new TH-400.

    If my car was stock it would of had electric petal kick down setup. I have nothing around my gas petal except for the brake petal and it has button it for the brake lights....

    I guess I should have kept the old th350 in it, and then replaced when the new engine killed it.

    My friend said when he tested vacuum, the engine was pulling more than enough vacuum

    He only knows engines, and manual trans, and like me doesn't know much about Auto transmissions. He's the one that said junk it and put in Muncie 4 speed. Which I'm about ready to do that.

    I never knew it could be adjusted, but it should have when run the engine 6,000-6,200rpm... OR at least one would think so...

    Well the problem was: Jeg's never replied to me After I stuck the tranmission in and all I had was 1st and 3rd. So they never replied after two attempts, and even a 3rd.

    Since JEG's wouldn't reply I stuck the TCI Trans Scat in it. Then the transmission wouldn't shift at all. So I contacted TCI for help.

    First TCI didn't reply, after another e-mail they said that the JEG's tranmissions already came with a shift kit and to stick that back in... Well if the transmission did have sucked. The new shift kit may only have 1st gear, but the old setup was weak compaired to 1st gear power the car has now. I don't know which is worse. 1 to 3 shifts, or only one gear.

    Since I had a retarded reponse from TCI, I tried e-mail both JEG's And TCI again stating the WHOLE history pretty much like I did on first post, and again it went back to no replies from them again so I gave up on them, and car has been sitting since November.

    I called Summit and they actually tryied to helped. They didn't even sell me the junk transmisison or the 1st shift kit.

    Summit Tech kind of agreed with me, saying there might have been something wrong with the valve body since I had a hell of time pushing the valve out, because his Chevelle has the shift kit, and he said it pushed out and went back in with no problems.

    I'm guessing it was & is bound up. When I finally got it out, took it out I didn't notice anything wrong like burrs or scratches, just that valve was tight, I did some grinding to valve and had a heck of time putting back in too. I just cut a peice of maple and tapped it back in with a rubber mallet.

    Last edited: Apr 7, 2006
  8. jforb

    jforb Veteran Member

    Feb 10, 2006
    sunny southeast AZ
    Some basics about the TH400.

    The vacuum modulator and governor work together to control shift points and shift firmness. If there is no vacuum supplied to the modulator, the trans will shift late and hard. As long as the vacuum modulator is connected to a vacuum port in the intake, it should work ok. The adjustment screw is a fine-tuning thing, it won't prevent it from shifting.

    The kickdown on a TH350 uses a pull cable. The kickdown on a TH400 uses an electric switch. You don't need to connect the kickdown wire on the 400, but it will shift early and soft on D full throttle shifts if you don't.

    Fluid level in automatic transmissions is critical. Too low is bad, too high is bad. Check it with a known matching dipstick and tube, with the trans warmed up from driving several miles, and with the engine running, trans in park. I make it a habit to apply the brake and run the shifter thru the gears first. Pull the dipstick, wipe it off, put it back in and pull it again, and read the level carefully, looking at both sides of the dipstick. (engine running!) If it's above the ADD mark, you should not need to add any fluid. Note: the aftermarket Lokar type dipstick setup is a real PITA to check and fill correctly.

    also it sounds like the valve body is screwed up, the valves have to move (although the sleeves don't), so if it's a shift valve that's stuck, that could explain why it's not shifting.
  9. Suicyko

    Suicyko New Member

    May 9, 2004
    Villa Hills, KY USA
    :crazy: I think it's fixed. :p

    Prodigy16 just put the new valve body in for me, and fired it up while on jack stands. I'm at work, so I'm guessing it's fixed. We still don't have the electric kick down hooked up yet. But I'm going to road test it possibly this weekend and next weekend it hits the track for a real break in.

    The little round castle looking thing in the valvebody was in bind. I guess this may have been in bind due to go the stuck valve in the valvebody?

    Have no real idea what parts do but I'm pretty sure they need to be moving since Prodigy said the new valve body had the Castle looking valve flush with top of valve body.

    Thanks again for help and suggestions.

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