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Old 10-08-2014, 03:35 PM   #1
sgt1022
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Tramission problem

I have a 71 c10 with 350 and a Th400. The rearend has a 3.08 gear. My trans shifts from 1-2 rather quickly. Itll be in 2 by the time I round a corner. It shifts firm, not neck snapping, but firm. I do not have a trans kickdown attached yet, the truck didn't have one when I bought it. I want to figure out the problem before install TCI shift kit. I haven't replaced vacuum modulator yet, but have new filter and clean fluid. Any recommendations on kickdown cable would be appreciated also.
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Old 10-08-2014, 03:37 PM   #2
cdowns
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Re: Tramission problem

sounds like normal
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Old 10-08-2014, 03:39 PM   #3
sgt1022
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Re: Tramission problem

hmm. Ok this the first vehicle ive owned that has a th400 so I dont know what's normal for it.
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Old 10-08-2014, 04:06 PM   #4
JointTech
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Re: Tramission problem

it shifts out of first really quick unless you stomp on it. something like 10 or 15 mph.
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Old 10-08-2014, 04:07 PM   #5
john
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Re: Tramission problem

TH400's also have electric kick down switch.
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Old 10-08-2014, 04:26 PM   #6
sgt1022
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Re: Tramission problem

That's about right. 1-2 at about 15. 2-3 at about 35-40. I thought I had a problem with it shifting so soon.
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Old 10-09-2014, 12:39 AM   #7
Wildcard
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Re: Tramission problem

Hello I am a trans tech by trade, and new to the forum.

you can get a red stripe adjustable vacume modulator and it will alow a bit of adjustment by turning the little flathead screw in the nipple the vacume line goes on it will raise or lower the shift points buy don`t screw more than 1 1/4 turn in either direction, clockwise will raise shift point and counterclock wise will lower buy put on first and drive. make sure your vacume line is coming off the intake manifold and Not a port on the carb makes a difference in proper vacume to the modulator.

Kickdown cable on a 350 does not effect upshift its only for forced downshift same with the electronics on a th400 does not effect upshifts. vacume and governor pressure control this.

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Old 10-09-2014, 12:43 AM   #8
Wildcard
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Re: Tramission problem

Oh and don`t recommend a TCI and never a B&M shift kit they are junk, have a Transco put in it make trans last not just create firm hard shifts been putting Transco in for 20+ yrs

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Old 10-09-2014, 02:58 AM   #9
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Re: Tramission problem

Quote:
Originally Posted by sgt1022 View Post
I have a 71 c10 with 350 and a Th400. The rearend has a 3.08 gear. My trans shifts from 1-2 rather quickly. Itll be in 2 by the time I round a corner. It shifts firm, not neck snapping, but firm. I do not have a trans kickdown attached yet, the truck didn't have one when I bought it. I want to figure out the problem before install TCI shift kit. I haven't replaced vacuum modulator yet, but have new filter and clean fluid. Any recommendations on kickdown cable would be appreciated also.
You need a governor re-calibration kit.
http://www.summitracing.com/parts/bmm-20248

Adjustable modulator, if you don't already have one. Remove the vacuum line and see if there is a small allen screw inside the pipe.

http://www.summitracing.com/parts/sum-g110/overview/

Detent switch. You should have the bracket under the dash above the gas pedal. Just install the switch and wire it up. You will need to go to the Chevy dealer to get the switch.

http://67-72chevytrucks.com/vboard/s...d.php?t=156985
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