Th400 wont shift - Hot Rod Forum : Hotrodders Bulletin Board
Hotrodders.com -- Hot Rod Forum



Register FAQ Search Today's Posts Unanswered Posts Auto Escrow Insurance Auto Loans
Hot Rod Forum : Hotrodders Bulletin Board > Tech Help> Transmission - Rearend
User Name
Password
lost password?   |   register now

Reply
 
LinkBack Thread Tools
  #1 (permalink)  
Old 11-22-2007, 05:36 PM
Registered User
 
Join Date: Nov 2007
Location: alberta
Posts: 2
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Th400 wont shift

i have recently put in a th400 in my supercharged 92 gmc in place of the stock 700r and i have hooked up the forced downshift wire, and the vacume modulator to the intake manifold. i put a check valve in line to the modulator so when i made boost it wouldnt effect the trans. it wouldnt shift out of first unless i placed the shifter into neutral then back into drive several times. i thought there wasnt enough vacume to shift it so i ran a vacume "t" to both the carburator ports and the intake, but still it wont shift it has plenty of vaccume to the transmition. what could this be??

    Advertisement
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #2 (permalink)  
Old 11-22-2007, 05:59 PM
Crosley's Avatar
Hotrodders.com Moderator
 
Last wiki edit: T-350 rebuild tech
Last journal entry: Bar under the dash
Last photo:
Join Date: Nov 2002
Location: ... USA
Posts: 8,057
Wiki Edits: 1659

Thanks: 314
Thanked 94 Times in 91 Posts
Quote:
Originally Posted by travismacdonald
i have recently put in a th400 in my supercharged 92 gmc in place of the stock 700r and i have hooked up the forced downshift wire, and the vacume modulator to the intake manifold. i put a check valve in line to the modulator so when i made boost it wouldnt effect the trans. it wouldnt shift out of first unless i placed the shifter into neutral then back into drive several times. i thought there wasnt enough vacume to shift it so i ran a vacume "t" to both the carburator ports and the intake, but still it wont shift it has plenty of vaccume to the transmition. what could this be??

Install a vacuum gauge at the line near the modulator to see the reading. 12 inches of vacuum at minimum should be there. 15 inches at idle would be better.

Was this t-400 known 'good' before the install? Fresh rebuild. Dyno tested after the build?

Does the wire you hooked to the trans case connector have 12 volts full time... it should not.



__________________
Some people are like Slinkies... Not really good for anything, but they still bring a smile to your face when you push them down a flight of stairs.
Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 11-24-2007, 12:47 PM
Registered User
 
Join Date: Nov 2007
Location: Mass
Posts: 5
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
The circuit from your carb thru however you are controlling the juice ( micro switch) or other off of your throttle linkage, should be from a switched power supply. Mine is wired thru the ignition switch.

It should only be flowing current to the tranny solenoid connector at close to wide open throttle.

Quick check, if the solenoid in the tranny is working is to enregize and listen for a click from the tranny.

Do you have a one or two wire connector at the tranny?
Reply With Quote Quick reply to this message
  #4 (permalink)  
Old 11-24-2007, 10:32 PM
Registered User
 
Join Date: Nov 2007
Location: alberta
Posts: 2
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
i figured out the problem and it was much simpler than i expected.... it was just a bad modulator so i switched it with a new one and now it works great.

thanks alot for all your inputs. they were a lot of help.
Reply With Quote Quick reply to this message

Recent Transmission - Rearend posts with photos

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the Hot Rod Forum : Hotrodders Bulletin Board forums, you must first register.
Please enter your desired user name (usually not your first and last name), your email address and other required details in the form below.
User Name:
If you do not want to register, fill this field only and the name will be used as user name for your post.
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.




Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

Posting Rules
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
? about a shift kit in a TH350 or TH400 Streetmaster Transmission - Rearend 1 04-26-2006 08:35 PM
TH400 rebuilt delayed shift into "d" oklowride Transmission - Rearend 7 12-14-2004 09:39 PM
th400 early shift/ soft shift 69er Transmission - Rearend 3 11-15-2004 07:16 AM
th400 2-3 shift?? camaroman7d Transmission - Rearend 6 04-22-2004 01:06 AM
th400 slow 2-3 shift amxerhull Transmission - Rearend 4 11-13-2003 03:19 PM


All times are GMT -6. The time now is 08:27 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0 PL2
Copyright Hotrodders.com 1999 - 2012. All Rights Reserved.