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hard shift from TH400

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Old Dec 13, 2011 | 03:54 PM
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Default hard shift from TH400

about half the time i shift from park or neutral to either first or reverse i get a nice smooth shift. the other half of the time it bangs into gear. i cant seem to be able to tell if it does it more cold or warm. is something failing or clogged ? or is my tranny fluid just real cold.....and what sort of damage will these hard shifts do ? sorry i am a TH400 noob.
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Old Dec 13, 2011 | 04:11 PM
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My TH400 will shift hard into Reverse if the idle is a bit high. I usually won't shift until I have brought the idle down by reving it after it has warmed up. That will usually limit the harsh shifts when going into reverse. Not sure if that helps, but wanted to share my experience.
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Old Dec 13, 2011 | 04:13 PM
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Originally Posted by Spacecoast
My TH400 will shift hard into Reverse if the idle is a bit high. I usually won't shift until I have brought the idle down by reving it after it has warmed up. That will usually limit the harsh shifts when going into reverse. Not sure if that helps, but wanted to share my experience.
how high is high idle ? i guess mine does it more when its at cold idle @ around 1000rpms. normal then ?
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Old Dec 13, 2011 | 05:14 PM
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Originally Posted by boltnut
how high is high idle ? i guess mine does it more when its at cold idle @ around 1000rpms. normal then ?
That's pretty normal at 1,000 RPM's. If you are between 650 and 800 RPM's you should not have any problems.
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Old Dec 13, 2011 | 05:45 PM
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with no other information to judge by, just turn the idle down....1000 is way too much for a stock car
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Old Dec 13, 2011 | 10:18 PM
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Only 1000 at cold idle. 700 warm. It usually shifts hard when cold at 1000. It still does it sometimes when warm at 700. It just seems sporadic. If it always did it when cold and never when hot I would get it. If an occasional hard shift when I need to drive before the engine is warm is ok then I won't worry. I was just getting worried something was starting to fail and giving me warning signs.......
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Old Dec 14, 2011 | 08:55 AM
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I would say about 1,000 rpm is when it will shift hard. Once I tap the gas to drop the idle, it goes to between 650-700 and then shifts fine.
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Old Dec 14, 2011 | 05:20 PM
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If the trans has been modified with some types of shift plates which increase the size of the orifice leading to the forward or reverse clutch, the aggressiveness can increase.
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Old Dec 14, 2011 | 07:11 PM
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Originally Posted by larrywalk
If the trans has been modified with some types of shift plates which increase the size of the orifice leading to the forward or reverse clutch, the aggressiveness can increase.
PO said it had a mild shift kit. the thing is it seems like its not consistent. sometimes i get a hard shift when my idle is lower....sometimes i get a smooth shift when the rpms are higher. maybe im just paranoid.
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Old Dec 14, 2011 | 07:54 PM
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Differential snubber bushing?
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Old Dec 14, 2011 | 08:10 PM
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Originally Posted by paul 74
Differential snubber bushing?
yes.
One reason it might do that is the time before you might have shifted into reverse and set the rear that way and then going into first completely reverses everything.
but the snubber bushing is shot if it hasnt ever been changed.
if your going to keep the car forever get the poly bushing.
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Old Dec 16, 2011 | 06:53 PM
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Default Th400

Hey Boltnut,
Mine shifts hard almost all the time and has been doing it for the last 27 years. Hasn't quit working yet. never been out of the car. I have my fast idle on cold mornings (below about 35 degrees) set at about 800 rpms. I try to let the engine warm enough to be able to kick it down off of fast idle before I put it in gear. during the summer months when the nights are warm, when I start the car for the first time that day, my fast idle will usually catch but just barely then usually comes off fast idle as soon as I touch the gas. Or it will drop off fast idle fairly soon after start up. Winter time fast idle is about 800rpms, winter normal idle is about 650, with about 550 in gear. Summer fast idle is about 700 with 650 to 600 normal idle and about 550 to 500 in gear. The shift into drive or reverse from nuetral or park is pretty hard except when the engine is at or near its lowest idle point. But even then it is harder than you would feel in a '90s or later car. Like I said, 27 years its been acting that way.
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Old Dec 16, 2011 | 07:35 PM
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Originally Posted by Tim H
yes.
One reason it might do that is the time before you might have shifted into reverse and set the rear that way and then going into first completely reverses everything.
but the snubber bushing is shot if it hasnt ever been changed.
if your going to keep the car forever get the poly bushing.
80k car .....you might be on to something there...
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Old Dec 16, 2011 | 07:36 PM
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Originally Posted by oldchev
Hey Boltnut,
Mine shifts hard almost all the time and has been doing it for the last 27 years. Hasn't quit working yet. never been out of the car. I have my fast idle on cold mornings (below about 35 degrees) set at about 800 rpms. I try to let the engine warm enough to be able to kick it down off of fast idle before I put it in gear. during the summer months when the nights are warm, when I start the car for the first time that day, my fast idle will usually catch but just barely then usually comes off fast idle as soon as I touch the gas. Or it will drop off fast idle fairly soon after start up. Winter time fast idle is about 800rpms, winter normal idle is about 650, with about 550 in gear. Summer fast idle is about 700 with 650 to 600 normal idle and about 550 to 500 in gear. The shift into drive or reverse from nuetral or park is pretty hard except when the engine is at or near its lowest idle point. But even then it is harder than you would feel in a '90s or later car. Like I said, 27 years its been acting that way.

Good to hear ! Like to know the occaisional hard shift isn't really tearing stuff up !
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