TH400 problem need pros help.
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From: port st lucie florida
TH400 problem need pros help. I just got my car running with a th400. Its used but I know it worked fine before I put it in my car. It sat for about a year before I put it in. The tran shifted fine for the first drive. Then I fired the car back up after a couple hours and it had no 2nd gear. You drive it 1,fine, shift 2nd it stays in first, shift 3rd goes into 3rd. It has 1st twice. Ive checked the shifter and it is adjusted fine. It just wont shift into second and it just has 2 first gears. I think its something small like a seal or stuck valve but I would like a pros opinion. Thanks
you may have a sticking shift valve or it may have broken the pressure plate on the intermediate I have seen this on a few of the th400s. possibly it coud have blown the seal out also.
Is this a manual vb or an auto? Sounds like a bad intermediate sprag or clutch. I have seen if the intermediate lugs break out on a TH400 it can lock the rear tires up. This is caused by the intermediate pressure plate locking up the direct drum. 
The TCI transbrake valvebody does this too. 2nd oil brings the low band off in 2nd (and if you blow the lugs you lose 2nd oil pressure obviously)
With the shifter in 2nd or 3rd? I really have not installed many of these TCI brakes so I'm really not familiar with them. IMO the ones I have done I really did not care for. Vince
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Shifter in 2nd or 3rd.
The low band is fed DRIVE oil on the TCI brake and copies.
The only thing that de-applies the band is 2nd oil, which stays on in 3rd gear on most TH400's.
So anything that causes a loss of 2nd oil (blown case lugs, blown int lip seals, cracked int. piston) results in immediate low band apply.
That can be pretty ugly at 100+ mph.
There is a reason I designed my 4L80E brake to only apply in manual low...
The low band is fed DRIVE oil on the TCI brake and copies.
The only thing that de-applies the band is 2nd oil, which stays on in 3rd gear on most TH400's.
So anything that causes a loss of 2nd oil (blown case lugs, blown int lip seals, cracked int. piston) results in immediate low band apply.
That can be pretty ugly at 100+ mph.
There is a reason I designed my 4L80E brake to only apply in manual low...
Thread Starter
TECH Resident
iTrader: (94)
Joined: May 2003
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From: port st lucie florida
It drives fine in first and third. It just has two first gears. You clickbit into second and nothing happens as in it's like it's still in first. Rpm stays the same and then I shift into third and it's fine. I don't believe it's a tci break but I didn't have it built so I can't say for sure. Looks like I'm going to have to pull it out and bring it somewhere to get it looked at .
Know any specs of the trans?
I'd bet it has a roller type direct drum and if thats not the problem it needs to be changed out for a 4L80E sprag type drum or it'll fail down the road.
You're not going to hear a lip seal blow out or apply piston break.
If you think it's a stuck valve go out and put the shifter in 2nd and power brake it just like you would in the water box at the track, that'll loosen it up.
I'd bet it has a roller type direct drum and if thats not the problem it needs to be changed out for a 4L80E sprag type drum or it'll fail down the road.
You're not going to hear a lip seal blow out or apply piston break.
If you think it's a stuck valve go out and put the shifter in 2nd and power brake it just like you would in the water box at the track, that'll loosen it up.
Considering a RMVB TH400 doesn't have any shift valves to stick, I don’t think that's the issue anyway.
Well it was the intermediate sprag.
Weird setup. It has an aluminum drum, 4L80E circlip, but only a 16 element sprag.
This was the only damage in the trans, my guess is the previous owner might have put it in neutral at high speed after every pass and it over ran the drum which threw all the oil off the sprag.
Any opinions?
Weird setup. It has an aluminum drum, 4L80E circlip, but only a 16 element sprag.
This was the only damage in the trans, my guess is the previous owner might have put it in neutral at high speed after every pass and it over ran the drum which threw all the oil off the sprag.
Any opinions?
Last edited by Jays_SSZ28; Jan 30, 2018 at 08:01 PM.