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12-30-2023, 10:09 AM | #1 |
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Re: Shifting at high RPM
If it was mine, and the trans was getting full vacuum, and a new vacuum modulator makes no difference, I would buy a Transgo shift reprogramming kit. When replacing the springs in the valve body valves I'll bet I would find a stuck valve even though I have never seen it happen before. Maybe it has a stuck or broken spring. I still think it will be something simple when you find it. just my .02
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12-30-2023, 01:17 PM | #2 | |
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Re: Shifting at high RPM
Quote:
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12-30-2023, 01:32 PM | #3 |
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Re: Shifting at high RPM
Agreed.
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12-30-2023, 01:45 PM | #4 |
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Re: Shifting at high RPM
Always the simple and obvious things get you
But what is? I’m still waiting to know the reason of oil spillage?
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1972 GMC Sierra C2500, V8-350 1986 GMC Sierra C2500, V8-454 1986 GMC Sierra C2500, V8-LS1 1986 GMC Sierra K2500, V8-350 1987 GMC Sierra R3500, V8-454 1997 GMC Sierra K2500, V8-454 |
12-30-2023, 02:21 PM | #5 |
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Re: Shifting at high RPM
Oil level in the transmission while running is approximately at the oil pan gasket level. Vacuum Modulator is above the pan. If the truck sits for any amount of time the torque convertor will drain out some raising the level in the pan until you start the truck again. So to answer your question...it depends.
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12-30-2023, 02:45 PM | #6 | |
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Re: Shifting at high RPM
Quote:
But still the issue isn’t resolved
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12-30-2023, 12:44 PM | #7 |
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Re: Shifting at high RPM
Don't think it was ever mentioned but does it do fine in reverse? And switch properly from reverse to drive and back? Its just not going from 1st to 2nd to 3rd?
In case you missed it, there is a sticky tread on the TH400 under the Engine and Drivetrain section. Might be helpful if you have to dig deeper. |
12-30-2023, 01:20 PM | #8 | |
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Re: Shifting at high RPM
Quote:
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12-30-2023, 03:15 PM | #9 |
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Re: Shifting at high RPM
Possibly it’s the detent switch that’s the culprit.
Says that in my motors manual. Here’s a thread I found that might help. http://67-72chevytrucks.com/vboard/s....php?p=7037666 |
12-31-2023, 09:52 AM | #10 | |
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Re: Shifting at high RPM
Quote:
I asked one garage that says he is expert in transportations he said “ you need to replace your trans cuz your clutches are gone!!!!, but I’ve a used one to sell?” How stupid he thinks! If clutches are gone, trans will not shift, or it will slip. So I’m searching for a solution. Thanks for the info
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1972 GMC Sierra C2500, V8-350 1986 GMC Sierra C2500, V8-454 1986 GMC Sierra C2500, V8-LS1 1986 GMC Sierra K2500, V8-350 1987 GMC Sierra R3500, V8-454 1997 GMC Sierra K2500, V8-454 |
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12-31-2023, 10:06 AM | #11 |
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Re: Shifting at high RPM
Did you try to just unplug the connector on the detent switch and then test it?
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12-31-2023, 11:00 AM | #12 | |
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Re: Shifting at high RPM
Quote:
If it’s the kickdown switch by the gas paddle, that has a single wire connected to left side (driver side), yes I disconnect it, drove the truck, nothing it’ll not shift. I appreciate your help
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12-31-2023, 11:17 AM | #13 |
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Re: Shifting at high RPM
Bypass everything and unplug it on the transmission.
The switch is on the drivers side at the back. Pic in here. https://www.gm***************/thread...kickdown.1107/ |
12-31-2023, 11:28 AM | #14 | |
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Re: Shifting at high RPM
Quote:
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12-31-2023, 11:33 AM | #15 |
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Re: Shifting at high RPM
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12-31-2023, 11:51 AM | #16 | |
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Re: Shifting at high RPM
Quote:
The only connector is coming from the 4x4 firewall to the top left side, I think it’s for 4x4 engagement and light, See pictures
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12-31-2023, 12:05 PM | #17 | |
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Re: Shifting at high RPM
Quote:
Hopefully I can load it
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12-31-2023, 12:06 PM | #18 |
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Re: Shifting at high RPM
Pictures are attached,
The website will not allow me to upload more than 2, or it keeps say your message is toooooo short
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12-31-2023, 12:15 PM | #19 |
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Re: Shifting at high RPM
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12-31-2023, 12:19 PM | #20 |
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Re: Shifting at high RPM
I did disconnected it, as I mentioned before, nothing.
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01-04-2024, 12:24 PM | #21 |
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Re: Shifting at high RPM
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01-04-2024, 12:38 PM | #22 |
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Re: Shifting at high RPM
Yes I did and nothing still will not shift from 1st gear
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01-04-2024, 10:24 AM | #23 |
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Re: Shifting at high RPM
Any ideas?
I’m not getting any luck with this trans. I managed to get me a vacuum gauge but I’m not sure what to do or to look for? Any suggestions
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01-08-2024, 05:26 AM | #24 |
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Re: Shifting at high RPM
Greetings to you all for helping out in my truck gear issue.
Update I test drive the truck last night, and it shifts in all gears, I don’t know what happened, but it’s working fine, Again, thank you all for your suggestions and recommendations, I wish I knew what was wrong with the tranny.
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01-08-2024, 12:23 PM | #25 |
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Re: Shifting at high RPM
Probably a piece of that silicone
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