I’ve got a th400 that has been sitting for a while….a long while. It worked when pulled but now it won’t go into 3rd. It has reverse and goes from 1st to 2nd just fine. I changed out the vacuum modulator, I made sure I had good vacuum to the mod. I adjusted it to maybe help it shift into 3rd. The only thing I haven’t messed with is the shift governor. So my question is….would sitting for a long time keep it from shifting into 3rd? If the torque converter was bad would that keep it from shifting into 3rd? Is there an additive to help it? Would changing the springs in the governor help? Thanks for any help.
Take the governor out and see if the spool inside is free. Just changing the springs would not help. Because it has been sitting "a long while" most likely an apply piston seal may be stuck. You could pull the pan and valve body and air test the clutch packs. The converter is fine if only 3rd is the problem. Passing gear switch OK? @jaracer to the white phone.
Passing gear meaning kick down? If so then yes it works too. Good to hear about the torque converter. I’ll drop the pan in a couple of days and take a look at that too. I just have a hard time believing it’s something detrimental if first, second and reverse works.
I'm confused. If it won't shift to 3rd, how do you know the kick down works? You could apply 12V to the connection on the transmission and see if the solenoid clicks. But even if that circuit is faulty, the governor should override it at higher speeds. I would check the governor first. You can't air test the clutch packs unless you drop the valve body, and check balls are going to fall out, so be prepared to catch them. Maybe change the fluid and drive it to see if it heals itself?
When it’s in second and I step on it it kicks down to first a goes. I just can’t get it into 3rd for some reason. The fluid is new…..well mostly new. I do need to change the pan seal. So I could drain it and add new then.
When You say long time , 5 months A Year, 5 years ? One that was working ,,, longer one sets not used , seals become hard ,pistons , check valve's stuck , then pressurized, Instantly can blow & leaking pressure internally,, There are a few books for $25 well detailed for PG -400 , A good tranny guy can bench one 1-1/2 -2 hrs if no hard parts needed .
What matters more is where it was stored...if it was outside in a humid area, it could have got moisture condensed inside. I'd probably do a little more test driving, then pull the governor and look at it to make sure it's free, then pull the pan and the valve body and make sure the shift valves don't have any crap in them, etc. If you're careful taking it apart you shouldn't have too much trouble, but it would definitely help to have a shop manual for a vehicle that the transmission was used in, to help you get it back together properly. You'll need some gaskets for both the governor cover and the valve body to case and transfer plate, if you decide to take stuff apart. I don't know where you can get these gaskets separately, might want to buy a complete gasket set before you take stuff apart.
It was stored in a shop but not climate controlled shop. I don’t mind changing the pan gasket, filter and new fluid but I’m not comfortable with going much further than that.
also make sure the shift linkage is right...if the shifter is not moving exactly into D it won't upshift to 3rd
If problem in valve body, can be done in car, drop pan , then valve body , if not trans need to be pulled seal & O rings, A good trans guy that not looking burn you , can tell whats it needs If Just seals , gaskets , It will have to pull trains disassembled , while apart add new clutches & band . if NO hard parts needed , You pull, this is 600- 800 Labor & parts
If your 1-2 shift is normal, meaning it doesn't slip going into 2, and the 1-2 shift point changes with increased throttle (early at light throttle and later with heavy throttle), the governor and modulator are probably working okay. On a 400, upshifts are made by applying clutches and not releasing any components. In D, 1st gear, you apply the forward clutch. To get 2nd gear you apply the intermediate clutch. For 3rd gear you apply the direct clutch, the forward clutch and the intermediate clutch stay applied. If for some reason the direct clutch does not apply, you stay in 2nd gear. Do you have a good reverse? The direct clutch is also applied in reverse. That will tell you if the clutch is mechanically okay. So what is causing the direct clutch to not apply in 3rd? If the trans doesn't have a reverse or it has a slipping reverse, the clutch has failed mechanically. If reverse operates okay, either the 2-3 shift valve is stuck in the valve body or the inner seal on the direct clutch piston has failed. If your fluid is clear and not burned, I would guess you have a seal problem. It takes total disassembly to replace the seal. You might be able to verify this via pressure test. You would have to have a pressure gauge connected and run the vehicle either on stands or on the road to where it should shift into 3rd. Pressure in D with high vacuum should be about 60 psi. If you pull the line off the modulator the pressure should go to about 150 psi. With the modulator vacuum line connected, try running it through the gears. Since vacuum will be somewhat lower I would expect the pressure to be in the 70-80 psi range. It will go up and down a bit with changes in vacuum. If the direct clutch inner seal has failed, I would expect to see a significant drop in pressure when the shift is made.
Good troubleshooting suggestions. Numbers 1 & 2 don't apply because he can get a 2-1 downshift and a 1-2 up shift. Number 3 is a possibility. Number 4 doesn't apply if reverse works okay. Number 5 is where I think the problem is.
When I taught automatic transmission rebuild back in the 70's, this was the required textbook. If you are good at reading and following directions (not everyone is), you can rebuild any transmission covered in this book. I've still got my copy from the late 60's.
I have been rebuilding automatic transmission's since around 1978. Any manual I can get my hands on I snag them up. I also buy the ATSG manuals when I get into a transmission I'm not familiar and buy a Transgo shift kit for said transmission to read up on their shortcomings. It helps with knowing what will need to order to my best at a repair that won't be a comeback.
Since reverse "works good", that narrows it down to either the valve stuck in the valve body, or the seal bad in the direct drum apply piston. If the unit had fluid in the pan while being stored, I, like @jaracer, would lean more towards the seal being the issue. IIRC, you can access the 2-3 shift valve from the discharge ports in the bottom of the valve body. A small flat blade screwdriver should move the valve. If it moves, probably the seal. The 400 is an easy unit to go through. A couple of homemade tools and a reference book is all you need.
As of today….. Removed and cleaned valve body New vacuum modulator New filter and fluid Still won’t shift into 3rd
^^^^ Did you access the 2-3 vale with screw driver ?, ( mentioned previously) if so , Direct Drum seal, Pump needs to be removed to access , Just asking, when you say remove clean Valve body , Was it just cleaned with brake clean? If so to clean valve body would need to be disassembled, .
Valve body completely disassembled and cleaned with solvent. Yes…took out all of the valve bodies and cleaned but they didn’t look bad. No trash, no rust assuming there would be any in there. Now I’m beginning to think it’s something deeper….ugh
I would put a bottle of K & W Trans X in it and drive it some. Getting it good and hot several times. Riding in 2nd won't hurt a thing as long as your not trying to blow it up. You have nothing to lose.
Does it leak? The reason I ask is the 400 in my Buick had been sitting for about 15 years. When I put it in the Buick it shifted fine, drove it for 4 years but it leaked bad. Finally took it out and had it rebuilt. The seals were hard and cracked. My trans guy couldn’t believe it worked ok. Yours may be the same, not worth trying to save it. May be time and money ahead to just rebuild it.
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