TH400 seized? And has drive in all positions?

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Nikkormat
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Re: TH400 seized? And has drive in all positions?

Post by Nikkormat »

OK so IF I understand correctly, I can simply remove "the nail" and slide the comb over enough to remove the valve. Is that right?
Gabe, "reformed" Jeep hoarder.
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Tatsadasayago
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Re: TH400 seized? And has drive in all positions?

Post by Tatsadasayago »

It's been years since I tore into a TH400 but I think you can get the manual valve out without removing the valve body.
If not, it's not a big deal but you have to take care to avoid the check balls falling out. The best way is to drop it straight down into your floor pan without turning it on it's side.
When you have it out you can check all the valves for proper and smooth movement.
1977 Cherokee Chief - The Blair Jeep Project III
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Curly
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Re: TH400 seized? And has drive in all positions?

Post by Curly »

I think you are correct that the valve body doesn't have to come out to remove the manual valve. Before you do anything, have some one work the shifter through all its ranges several times. I think you are going to find the shift shaft that moves the Manual Valve to be loose.

Curly
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BenTaylor
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Re: TH400 seized? And has drive in all positions?

Post by BenTaylor »

Any update on this? I think I’m having the same issue. I don’t have reverse or neutral. Forward works fine but shifts really hard and hangs in the gears way to long.

Topic author
Nikkormat
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Re: TH400 seized? And has drive in all positions?

Post by Nikkormat »

No, I never opened the trans I found a rebuilt one very cheap. I hope you find your issue!
Gabe, "reformed" Jeep hoarder.
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HeavyMetalThunder_81
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Re: TH400 seized? And has drive in all positions?

Post by HeavyMetalThunder_81 »

BenTaylor wrote:Any update on this? I think I’m having the same issue. I don’t have reverse or neutral. Forward works fine but shifts really hard and hangs in the gears way to long.
Sounds like the vacuum hose for the modulator fell off or is rotten and has a leak.
-Jonny B.
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1979 Cherokee Chief - Parts
1979 Cherokee Chief - Parts
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BenTaylor
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Re: TH400 seized? And has drive in all positions?

Post by BenTaylor »

HeavyMetalThunder_81 wrote:Sounds like the vacuum hose for the modulator fell off or is rotten and has a leak.
That definitely explains the shifting but would it also explain the no reverse? With the truck off I cant get it to go backwards in reverse or neutral. from everything im reading i'm SOL and need a rebuild.
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BenTaylor
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TH400 seized? And has drive in all positions?

Post by BenTaylor »

So I pulled the tranny and I think I found the problem. The vacuum hose from the modulator to the steel line was completely rotten. And also when I pulled the tranny apart the spring in the rear servo is broken and the piston was crooked and jammed.

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BenTaylor
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Re: TH400 seized? And has drive in all positions?

Post by BenTaylor »

Just an update on my situation, I rebuilt the tranny and installed it back in the jeep and all is good so far. it seems to shift hard into reverse but my trans mounts are pretty worn so I I'm pretty sure that the problem. When I pulled the clutch packs apart I found 3rd gear packs were completely @#%&ed and I'm pretty sure that was causing forward gear to always be engaged. That may have been the cause for the reverse servo spring to break. the hard shifting was definitely caused by no vacuum to the modulator, the rubber hose was completely rotten.

It was a fairly simple rebuild, I watched this video a lot while doing it [youtube]https://youtu.be/_TMFibSiwVw[/youtube] it was a huge help. I did install a lip seal backwards which then stuck the piston and ruined the seal, I ordered a new lip seal and everything else went fairly smoothly.

Cheers!
Ben
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