last chance. i need help. th400 in my hotrod was just built after tearing the bellhousing off. i have a 355 with a 6-71 15lbs boost. standard forward vb. when i pull off in low gear, i can feel no shift to second.....  third drops rpm but if on the throttle i have to let off for it to go into third. feels like a five speed slipping. havent smashed it over 4500 rpm not to break anything. no launches yet. tapped carb plate ond run it to modulator. no downshift wire. any help would be accepted before it's listed on racing junk.     thanks      big dave  

I suggest a 280-grain jacketed hollow point!

Sounds like something's screwed up in the valvebody. Have you ever had it apart?  

Valve body not assembled correctly, Governor stuck, Internal porosity (internal pressure leak), Low fluid level or intake tube drawing air by O ring. Accumulator valve(stem)broken(usually only downshift holding for band), vacuum source insufficient or modulator no good. Not sure what you meant by "tearing the bellhousing off", was it literally torn from this transmission"? Keep us posted -oldchev.  

thanks oldchev, tapped carb plate on top of blower, vac is good. dont know how to check modulator.? i am hearing that the kickdown servo could be leaking past or governor could be stuck or stripped. line pressure is good.   where is accumulator?    and the bellhousing broke 2 inches from the mounting bolts all the way around and the trans spun and broke trans mount, new rearend and mid-plate now.  

Has been a while since I did a TH400 and I misspoke about accumulator and meant front servo, which is in case after valve body removed rear of 1-2 accumulator. This would affect the front band only on downshift.  Back to story...I favor the vacuum modulator or the governor. Check the modulator using a good vacuum source (hand pump or another high vacuum line) and see if modulator pulls in and out when applying and removing vacuum source. Remove the governor, disassemble and thoroughly clean the pieces keeping all specks of dirt and lint free of reassembly. Clean governor bore in case same way and reinstall. One small speck will lock it up and won't upshift. They can be tuned with different springs and weights usually in shift kits.
Not sure if the case damage affected this but may have considered a case replacement on rebuild.  

PS: you can get a vacuum modulator replacement from Fram for about 12 bucks or consider a Large diaphragm, low vacuum unit (part Code: 44160B @ bulkpart.com) about same price.
Let us know. -oldchev  

thanks again for your responce oldchev. pulled pan, governor....no trash and moved very freely. looked very clean. pulled the little servo off the bottom of the valve body, again no trash and the o-ring was good.  pulled the tranny last night and took it back to builder. he said he thought the convertor was not all the way seated. i thought the trans would not bolr all the way up if converter was not seated. when bolted up i have to push the converter forward a quarter inch, is the guy shooting me some crap? pulled fine in reverse. i told him to go through it again, if it dosent work this time i want a full refund.  a new th400 from art carr is $1199 and i feel like i am going to spend more than that to get a tranny.     thanks, big dave  

Thanks for the info guys.  

I feel your pain big dave, There a multitude of things that can happen, wish I can catch this with one with my ideas. One of my experiences with a TH400... I had slippage when cold but performed normally when hot. Thinking my seals were toasted I completely rebuilt the trans with same results. Next I did it all over again (another master kit) this time adding a new rebuilt pump and a fresh convertor. Same results. With test gauge attached checked all fluid pressures while driving and couldn't get any application pressure forward or reverse until about 1500-1800 rpm then launched just like throwing into gear. If I drove it and stopped it was like placing in neutral until rpm's advanced as described. I then replaced the case with another using all my internals and presto, fixed! I had developed a case porosity issue (internal bleed) until it warmed up and swelled enough to seal or slow the leak. Bizarre yes.
Not a shift issue like yours but usually the convertor not engaged with the pump will not cause a NO shift issue like you described but will tear the heck out of the pump gear. Because you had to pull the convertor to the flywheel after installing, I doubt that was it but the trans can be bolted up with this condition. Make sure when installing a convertor that you rotate the convertor until you hear or feel the clunk when the tangs on convertor engage with the pump gear and internal stator splines are engaged. If it worked in reverse, I would suspect the pump was working correctly. Reverse does have higher line pressure, though.
Again you said it pulled in low but no shift to second, this means the second application pressure was absent caused by valve malfunction (not moving) or pressure failure somewhere.
I am intrigued to see how this ends. -oldchev.  

i commend your knowledge on my topic and thanks again old chev. will let you know the outcome when i get it back from ding dong. $711.00 in the hole plus $125.00 for the case. grand total $836.00 greenbacks ripped from my butt!!!!!!!!!!!!!!!  

here you go oldchev. picked it up this morning and he said "both drum pistons had bad o-rings", the low gear drum did not have the o ring (could be a pressure problem) and the high gear o-ring was broken hence the slippage going into third until off throttle. he said he actuated the pistons with air and both working properly after he replaced pistons and seals. no charge this time. also burnt were third clutches so he replaced them again n/c. i made him show me all parts replaced and they were all defective. is he correct you think? hope all is good, will install sunday and advise. thanks again,   big dave  

hello CHP readers! finally transmission works correctly! jumping with joy!  hits hard 1st, 2nd, and third. hey oldchev, do you think a th400 can hit too hard? i have m/t street slicks and if i dont roll them over one or two times when i leave the driveway, it hunts the ditch at cruise speeds when it shifts.(spins a little) will have to wait on gas to come down before i can enjoy a cruise and watch the people in town that think a 747 is fixing to land on their street! i love it! yall have a good day, and remember "IT ALWAYS FEELS GOOD TO BE BLOWN"                    thanks,Big Dave