TH-400 shift problems...... where's reverse??????? - Off-Road Forums & Discussion Groups
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post #1 of (permalink) Old 05-03-2005, 03:46 PM Thread Starter
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TH-400 shift problems...... where\'s reverse???????

Buick 455
TH-400 (2wd..linkage was installed by me, so it is suspect, the shifter free floats with no stops. all "bumps" and "clicks" are directly from the tranny) kick down is vacuum actuated, and hooked up to the carb.
Divorced 205
Drive shafts are installed and transfer case is in rear wheel drive. The rear axle is elevated so the tires free wheel.

P
R
N
D
2
1

Park works, locks up the intermediate shaft with a solid click.
Reverse makes the tires spin FORWARD for about 2 feet and then the tranny "locks up" like it's in park again.
Neutral makes the tires spin forward, gas it with the brake pushed in and it is clear that it is not in neutral. It has torque to move the tires in the forward position.
Drive seems like drive (again moving tires forward)
2nd seems like second (again moving tires forward)
1st seems like first (again moving tires forward)


What gives??????
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post #2 of (permalink) Old 05-03-2005, 07:55 PM Thread Starter
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Re: TH-400 shift problems...... where\'s reverse???????

I talked to the P.O. of the engine tranny combo, he is a friend of mine, and he has convinced me that it was in good running order when he pulled it.
Most of the fluid had leaked out and I topped it off. When I check it, the fluid has lots of little bubbles in it.
I unhooked the linkage and manualy shifted it at the tranny with no changes in performance.

Are there some adjustments that can be made somewhere?

[img]/ubbthreads/images/graemlins/confused.gif[/img]
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post #3 of (permalink) Old 05-03-2005, 09:10 PM
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Re: TH-400 shift problems...... where\'s reverse???

If you have bubbles in the fluid it means it's getting lots of air and not enough fluid through the pump. Keep checking the fluid (try to get it warmed up, shift through all the gears, check fluid while running). You only get a reading from what is in the pan area, won't tell you if it's missing a bunch in the converter.

Best I can give you...
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post #4 of (permalink) Old 05-03-2005, 09:29 PM
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Re: TH-400 shift problems...... where\'s reverse???

Ditto! Do you have the OEM dipstick/tube? (or something close?)

Seems like mine was low after initial install and would lurch around in both direction (clearly in PARK!) when low....

The vacuum basically controls upshifts, etc. and has no correlation the the AWOL reverse.
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post #5 of (permalink) Old 05-03-2005, 09:36 PM Thread Starter
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Re: TH-400 shift problems...... where\'s reverse???

[ QUOTE ]
Ditto! Do you have the OEM dipstick/tube? (or something close?)


[/ QUOTE ]

yup, what's the best way to bleed the system?
It's also freshly plumbed into a cooler.
The fluid never went down after filling it. Guess I can't seem to burp the air out.
It seems to have full power in the forward drive gears though.
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post #6 of (permalink) Old 05-03-2005, 10:10 PM
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Re: TH-400 shift problems...... where\'s reverse???

Also, the TH400 uses an electric switch for the kickdown mounted above the throttle pedal.
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post #7 of (permalink) Old 05-04-2005, 05:48 AM Thread Starter
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Re: TH-400 shift problems...... where\'s reverse???

[ QUOTE ]
Also, the TH400 uses an electric switch for the kickdown mounted above the throttle pedal.

[/ QUOTE ]

[img]/ubbthreads/images/graemlins/confused.gif[/img] Could you elaborate on that a little bit?

This is out of a 1971 Buick, I haven't seen anything on the tranny resembling this.

Also, Will, does it sound to you like the tranny is shot, or just in need of fluid.

Thanks
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post #8 of (permalink) Old 05-04-2005, 08:55 AM
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Re: TH-400 shift problems...... where\'s reverse???

The switch is mounted on the inside of the firewall above your foot when it is on the throttle pedal. There is a single wire that runs to the driver's side of the transmission a little behind the gear selector. This switch has nothing to do with not having reverse. It is for the kickdown only. As for why you don't have reverse, I don't know what is wrong.
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post #9 of (permalink) Old 05-06-2005, 03:18 PM Thread Starter
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Re: TH-400 shift problems...... where\'s reverse???

Bump

I am being reasured that this tranny should be in good running order, and that I most likely have a simple problem that is keeping me from successfully moving in reverse. [img]/ubbthreads/images/graemlins/confused.gif[/img]

Anyone?????

Anyone?????

Does the outgoing tranny cooler line need to plumbed to the lower port on the cooler?

I am convinced that there is still some air in the tranny, lines, or cooler somewhere. How should I go about getting it out?

What else could I have overlooked?

The engine was already bolted to the 400 when I got it. (it was also mounted in the vehicle)

Please help, I am desperate to not have to pull this thing out.

[img]/ubbthreads/images/graemlins/crybaby.gif[/img] [img]/ubbthreads/images/graemlins/crybaby.gif[/img] [img]/ubbthreads/images/graemlins/crybaby.gif[/img] [img]/ubbthreads/images/graemlins/crybaby.gif[/img] [img]/ubbthreads/images/graemlins/crybaby.gif[/img] [img]/ubbthreads/images/graemlins/crybaby.gif[/img]
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post #10 of (permalink) Old 05-06-2005, 03:27 PM
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Re: TH-400 shift problems...... where\'s reverse???

Do you have the required amount of ATF in the transmission?

As you were pouring in the ATF did you work the gears?
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