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#1
07-13-2022, 10:59 AM
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Th400 won't shift into high gear
Trans fluid looks good. What should I be looking for? This is in a 68 Catalina.
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1963 Catalina 2 door hardtop 1968 Catalina 2 door sedan |
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#2
07-13-2022, 11:30 AM
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Vacuum modulator issue
Loose hose ??? |
| The Following User Says Thank You to Scott Thelander For This Useful Post: | ||
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#3
07-13-2022, 11:33 AM
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I will check the hose. Do modulators go bad or is typically something else?
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1963 Catalina 2 door hardtop 1968 Catalina 2 door sedan |
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#4
07-13-2022, 11:45 AM
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Yes, the just go bad and with my experiences with that failure it's was always after the trans sat a good while and then got put back into use.
If the motor or car was apart besure its hooked up to full Manifold vacuum!
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I do stuff for reasons. |
| The Following User Says Thank You to 25stevem For This Useful Post: | ||
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#5
07-13-2022, 11:55 AM
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the modulator shifts the trans at part throttle high vacum conditions the governor shifts it at WOT no vacum
no shift at all can be more serious issues easiest place to start is vacum lines |
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#6
07-13-2022, 12:58 PM
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The car did sit for some time but I have put 7-8k miles since. Will check vacuum line tonight.
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1963 Catalina 2 door hardtop 1968 Catalina 2 door sedan |
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#7
07-13-2022, 07:34 PM
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Has a hard line off the modulator to the back of the 2 brl with this short piece of hose that was leaking.
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1963 Catalina 2 door hardtop 1968 Catalina 2 door sedan |
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#8
07-13-2022, 07:42 PM
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Does it reach 3rd now?
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#9
07-13-2022, 07:53 PM
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No, has a max mph of 30-35.
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1963 Catalina 2 door hardtop 1968 Catalina 2 door sedan |
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#10
07-13-2022, 08:17 PM
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Quote:
I'd expect you could go faster than that in first gear, never mind second. Has the gear for the governor sheared? Governor weights stuck? |
| The Following User Says Thank You to Schurkey For This Useful Post: | ||
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#11
07-13-2022, 08:55 PM
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Definitely highway gears, guessing 2.56. 225/75/r15s
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1963 Catalina 2 door hardtop 1968 Catalina 2 door sedan |
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#12
07-13-2022, 09:10 PM
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It's possible that the kickdown solenoid has failed or is leaking.
Or the kickdown switch above the gas pedal has failed.
Try unplugging the switch and taking it for a drive. Any difference? If not, plug it back in and put the car on ramps or stands. Lay under there with the engine OFF but the key ON and have someone manipulate the switch to imitate full throttle and no throttle. You should hear the solenoid click when it actuates. Changing it requires transmission pan removal. https://www.youtube.com/watch?v=fUYNTeTzIvo |
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#13
07-13-2022, 09:12 PM
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How is the hose down with at modulator if you pop it off the modulator and you get any transmission fluid showing your modulator is bad they are cheap go to Napa and get a good one it will come with a new short prebent hose and you’ll be off and headed to get that milkshake
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#14
07-13-2022, 09:44 PM
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When the vacuum modulator looses signal the trans will still upshift but the shifts will be late and firm. It may take vehicle speeds well over 50mph so see a 2-3 upshift, but it will still happen. The 1-2 happens much sooner with most TH400's but it will eventually complete the 2-3 upshift w/o modulator vacuum.
The kick-down solenoid will create a very similar scenario. Never being able to reach high gear and it does not got to "neutral" or stays in second indicates something stuck or sticking in the VB (assuming the modulator, governor and down shift solenoid are working as they should.......
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If you can read this, thank a teacher. If you can read this in English, thank a Veteran! https://cliffshighperformance.com/ 73 Ventura, SOLD 455, 3740lbs, 11.30's at 120mph, 1977 Pontiac Q-jet, HO intake, HEI, 10" converter, 3.42 gears, DOT's, 7.20's at 96mph and still WAY under the roll bar rule. Best ET to date 7.18 at 97MPH (1/8th mile), |
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#15
07-13-2022, 10:07 PM
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Quote:
Are you sure the trans shifts 1--2? That thing should go 70 in second. No shifting out of first, seems likely to be a failed governor or unusual valve body problems. |
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#16
07-13-2022, 10:17 PM
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Probably not getting into second. Will fix the vacuum leak at the carb tomorrow and go from there.
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1963 Catalina 2 door hardtop 1968 Catalina 2 door sedan |
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#17
07-13-2022, 11:29 PM
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No upshifts at all are usually governor related. Not all that uncommon to see the governor gear sheared. NOTHING happens past low gear when it's not turning......
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If you can read this, thank a teacher. If you can read this in English, thank a Veteran! https://cliffshighperformance.com/ 73 Ventura, SOLD 455, 3740lbs, 11.30's at 120mph, 1977 Pontiac Q-jet, HO intake, HEI, 10" converter, 3.42 gears, DOT's, 7.20's at 96mph and still WAY under the roll bar rule. Best ET to date 7.18 at 97MPH (1/8th mile), |
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#18
07-14-2022, 10:37 AM
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Quote:
i had a th400 in a 78 t/a back in the late 80s/early 90s that was put in by my friend that was the cars prev owner, neither of us knew about the kickdown switch (wasnt even there on a 78) or solenoid & it was left completely unhooked... trans shifted perfectly fine in all gears for the almost 10 years i owned & daily drove/abused the car. its nice to have it there for kickdown but not seeing how it would matter for upshifts... at least it didnt on my car. |
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#19
07-14-2022, 11:50 AM
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The above experience is what I have found with TB400s also!
__________________
I do stuff for reasons. |
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#20
07-14-2022, 12:08 PM
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If the KD switch contacts are closed for whatever reason, the solenoid will be energized all the time.
Unplug the switch or solenoid to verify.
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Ed 1968 GTO (Thanks Mom) 2006 Silverado 2007 Cadillac SRX 2015 Chevy Express  
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