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Unread 05-02-2013, 05:58 AM   #1
2Xtreme
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TH400 shifting problem

Last night I took the CJ out for a ride and noticed some weird shifting issues. Note, I was driving in town with moderate traffic (up to 30-35 mph), so I have no idea how this would have continued at higher speeds:

In D, the vehicle will take off and accelerate as would seem normal. To a point. But it wont upshift. The RPM's just keep climbing until I back off. Then I can press and let off the accelerator with no affect on speed. The RPM's fluctuate, but vehicle doesn't move any faster.

If I drive it in 2, it seems to act normal.

Starting to feel very defeated with this thing.
Every time I fix one thing, something else crops up.....

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Unread 05-02-2013, 07:08 AM   #2
VooDoo2
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Easy fix = Shift solenoids. Around $15-20 plus a filter kit and gasket

If its not the solenoids its the clutch bands which means a rebuild BUT id put money on dirty fliud, stuffed shift solinoids and a service required.
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Unread 05-02-2013, 07:14 AM   #3
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Thank Gawd!

I was planning to attempt a rebuild in the near future, but not just yet....
Hopefully this will do the trick.
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Unread 05-02-2013, 08:48 AM   #4
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Haven't had a chance to do any research yet.

Is this something that can be done with the trans in the Jeep??
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Unread 05-02-2013, 11:02 AM   #5
Jon In Tucson
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Quote:
Originally Posted by 2Xtreme View Post
Haven't had a chance to do any research yet.

Is this something that can be done with the trans in the Jeep??
Most of those services can be performed in frame. I respectfully disagree with VD2 as to solenoids on a th400. I think those are servos that engage the bands via the valve body hydraulic pressure and the vacuum controlled modulator. Never the less, it is a relative inexpensive fix. A comprehensive fluid and filter change will cure a lot of gremlins of those transmissions. Don't forget to make sure the transmission pan is good and flat before putting back on with the new gasket. God bless.
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Unread 05-02-2013, 11:21 AM   #6
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....I think those are servos that engage the bands via the valve body hydraulic pressure and the vacuum controlled modulator.....
Oh boy... the confusion starts to set in.
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Unread 05-02-2013, 11:47 AM   #7
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Oh boy... the confusion starts to set in.
Start with a fluid and filter change and go from there. K.I.S.S.
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Unread 05-02-2013, 12:59 PM   #8
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... K.I.S.S.
LOL!

Well, if I am going to be in there already, why not do the solenoids or whatevers instead of dropping the pan and drainging it twice?
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Unread 05-02-2013, 01:28 PM   #9
Jon In Tucson
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Originally Posted by Dngrs1 View Post
Start with a fluid and filter change and go from there. K.I.S.S.
X2

If you haven't done a filter and fluid change, definitely do that first. If you find any large (that is, bigger than your thumbnail) pieces of metal or band material, then it's time to rethink the direction you're going... Chances are the tranny is coming is coming out then anyway. God bless.
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Unread 05-02-2013, 04:39 PM   #10
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My Mistake (it was late here)

ON the newer gearboxes they are electronically shifted via solenoids and they get blocked and stuff up. i did my 4L60e repair with them.

The old er TH400/700r is mechanically shifted so use the cable and vac controlled servo's. Doing a service on the box can free up the gunk that can collect and get the servo's moving. As it still shifts from 2-3 should mean only the 1-2 shift is the issue. The TH400 is a very simple box. Ebay has a heap of shift kits and service kits available. Drop the pan and all can be done on the car.
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Unread 05-02-2013, 06:15 PM   #11
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The most probable things are also the cheapest.

1. Vacuum line to the modulator cracked, broken, or fell off.

2. Vacuum modulator itself went bad.

3. Valve behind the modulator sticking.

4. Parts missing/broke from the elbow of the modulator.

5. Sticky governor.
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Unread 05-03-2013, 02:00 AM   #12
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I would second checking the vacuum line and modulator parts. I'll add that mine started shifting funky one time, and a fluid and filter change took care of the problem, hasn't come back in years.
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Unread 05-03-2013, 06:18 AM   #13
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Thanks for all of the info!

Will look into it this weekend.
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