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Old 07-20-2017, 05:19 PM   #1
Mossbeard
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66 TH400 transmission question

Is this normal?

I have a TH400 behind a 327 in my '66 C20. When I shift from park to drive (or reverse) the whole vehicle lurches and there's a thump like I've been rear-ended.

If not normal, where should I start investigating?
I was under the truck recently (fuel leak) and the drive shaft had no slop in it.

Also, the last time I drove the truck I stayed below 45mph but I remember feeling like it wasn't shifting. I don't have a tach but the engine seemed to be revved high. At what speed (roughly) should I expect to feel a gear change?

Thanks
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Old 07-20-2017, 08:45 PM   #2
yelmer
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Re: 66 TH400 transmission question

check the fluid level truck must be running
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Old 07-21-2017, 01:21 PM   #3
Dead Parrot
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Re: 66 TH400 transmission question

Possible a u-joint failed since you were last under the truck. Chock the tires on level ground, trans in neutral and check for slop again.

Check the springs and associated bushings, perches and such for correct and tight.

Is it possible the indicator is off and you were really in L2?
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Old 07-21-2017, 06:43 PM   #4
YoungPup1977
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Re: 66 TH400 transmission question

the PR spring scenario again...be careful....may break the pump gears in the transmission.....
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Old 07-22-2017, 04:13 AM   #5
goofy063
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Re: 66 TH400 transmission question

check the vacuum hose going to the modulator valve a vacuum leak will cause high idle and delayed shift
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Old 07-31-2017, 01:36 PM   #6
mattfranklin
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Re: 66 TH400 transmission question

Is your idle speed too high?
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Old 08-02-2017, 11:51 AM   #7
rideblue00
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Re: 66 TH400 transmission question

any updates?
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