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#1
05-04-2004, 12:26 PM
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73 GP 400/TH400
Trans had no issues at all, was parked for less than a week. Now, only shifts under hard throttle.. will not upshift unless the pedal is on the floor...then it is firm and quick. When going from park to reverse, immediate response, neutral to drive, the same. Right into gear in both cases. No notice increase in RPM from standing to whatever MPH, (slippage). Fluid checks out OK with good color and smell. Vacuum lines clear, no cracks or pinches with a good pull at the modulator. New modulator. All linkages check out ok. No noticed damage of anything. This car has receipts of a newer rebuilt trans when purchased. As stated, it was perfect with nice shifts when parked. I believe it may have had a trans/shift kit installed, by previous owner. any guesses to this one would be a help... |
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#2
05-04-2004, 12:26 PM
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73 GP 400/TH400
Trans had no issues at all, was parked for less than a week. Now, only shifts under hard throttle.. will not upshift unless the pedal is on the floor...then it is firm and quick. When going from park to reverse, immediate response, neutral to drive, the same. Right into gear in both cases. No notice increase in RPM from standing to whatever MPH, (slippage). Fluid checks out OK with good color and smell. Vacuum lines clear, no cracks or pinches with a good pull at the modulator. New modulator. All linkages check out ok. No noticed damage of anything. This car has receipts of a newer rebuilt trans when purchased. As stated, it was perfect with nice shifts when parked. I believe it may have had a trans/shift kit installed, by previous owner. any guesses to this one would be a help... |
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#3
05-04-2004, 12:55 PM
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What was your test with the modulator?
See if it holds "x" amount of vacuum for "x" amount of time? Sounds like you've done a good job making sure things are checked and in place.
__________________
69 Gto, 390 posi gears,th400 w/jim hand converter/406 pontiac/#64 HEADS/ 10:1 compression/ 190 PSI with/ TRW 160 thou domes / hooker headers 1 7/8, PRW 1.5 rockers, 405 Crower Springs, Holley 750 vac with proform upgrade, Performer RPM on points / 284 H Single Pattern Crane |
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#4
05-04-2004, 01:46 PM
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New and old modulator have same results.
By recommendation I bought a modulator $10. so what the heck. still curious.... |
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#5
05-04-2004, 01:49 PM
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sounds like a governor weight has come loose?
__________________
The thick CLOUD of tire smoke ,the SMELL of burning rubber,and the CHEER of the crowd ....PRICELESS. $90.00 fine for an awesome burn-out,worth every penny... http://www.youtube.com/watch?v=iI7beXh7xW8 |
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#6
05-04-2004, 02:26 PM
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I am just going to throw my ideas out there. I am no tranny expert by any means so take it for what it is...
Sounds to me like the governor is working fine since it shifts at WOT. The described behavior really sounds like the modulator. Somebody correct me if I am wrong here, but isnt there an actual valve behind the modulator? Since the Modulator itself checks out, maybe the valve behind it is stuck. I would pull the modulator and then pull out the modulator valve and clean it real well and put back together. Just a thought. |
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#7
05-04-2004, 02:57 PM
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Thats my understanding too about the govenor.
What is the procedure for removing the modulator valve? Just unscrew the bolt holding the piece of medal which holds the modulator in place? The turn the modulator counter clockwise to unscrew it? Then behind there is a valve that can be removed?
__________________
69 Gto, 390 posi gears,th400 w/jim hand converter/406 pontiac/#64 HEADS/ 10:1 compression/ 190 PSI with/ TRW 160 thou domes / hooker headers 1 7/8, PRW 1.5 rockers, 405 Crower Springs, Holley 750 vac with proform upgrade, Performer RPM on points / 284 H Single Pattern Crane |
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#8
05-04-2004, 03:43 PM
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I think so, been a while since tranny class. Look in a tranny manual at a bookstore or library to be sure.
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#9
05-04-2004, 03:54 PM
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Sounds like the modulator to me too. After you remove the retaining bolt I think it just pulls out and has an O ring on it. Maybe a broken vacumn line.
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#10
05-04-2004, 06:15 PM
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Some times the governor will indeed stick and cause this problem. Run it around town by shifting the car manually and that just might clear up your problem.
__________________
Dave "Big Injun" Anderson dave@4mypontiac.com www.4mypontiac.com For GTO Celebration items click the tile coaster. 
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#11
05-05-2004, 07:29 AM
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Thanks for the info...
The governor is located behind the modulator like said in above responses ? Just a ? before I go climb under again. thaks again |
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#12
05-05-2004, 09:37 AM
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Have since removed new modulator, pulled governor rod, checked, not stuck moves freely. Reinstalled new modulator, when flush, feels "spring loaded". Retested, same results, shifts good at @ 3800-4000RPM.
Any ideas??? |
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#13
05-05-2004, 09:40 AM
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I believe the govenor is located near the rear of the transmission with a plate and multiple bolts.
That's what I've heard but I'm sorta at the same place as you. Behind the modulator is a o-ring and some valve that can be inspected from what I gather.
__________________
69 Gto, 390 posi gears,th400 w/jim hand converter/406 pontiac/#64 HEADS/ 10:1 compression/ 190 PSI with/ TRW 160 thou domes / hooker headers 1 7/8, PRW 1.5 rockers, 405 Crower Springs, Holley 750 vac with proform upgrade, Performer RPM on points / 284 H Single Pattern Crane |
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#14
05-05-2004, 03:13 PM
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The Modulator valve is behind the Vacuum modulator. The Governor is on the other side of the trans under a cover (either bolted or held with retainer clip. Not sure which on a th400.)
Another thing you should check first is if your kickdown switch is stuck. This happens on my buick all the time. That would cause this exact behavior. |
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#15
05-06-2004, 10:36 AM
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This car was purchased in Feb. Prior owner converted to a Holley 4bbl.
In regards to the "kick down switch" My understanding is this switch is located drivers side intake manifold with wire and connection to transmission ? My switch has no mechanical connection to carb or linkage. It has multiple connectors (elect.)with one attached to a vacuum switch with two vacuum tube connections...of which nothing is attached. No hose of any sort is close by. Should this be connected? If not would it just NOT downshift in drive instead of the higher RPM upshifts? Nothing appears out of place (since bought) underhood, and was working fine when parked. next is the governor... I hope this thread helps others as well, it seems a simple problem. Thanks |
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#16
05-07-2004, 09:01 AM
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bump....
anyone ? |
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#17
05-07-2004, 02:16 PM
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I do not think that is your kickdown switch. Most TH400 kickdown switches are mounted to the accelerator pedal bracket and is actuated by the accelerator pedal. Look down by your accelerator pedal and push it down and see if you can see what I am talking about.
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#18
05-07-2004, 04:36 PM
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I had the same problemwith my trtans just recently. Drove me crazy, I checked everything that was mentioned here. It was my kick down switch, was stuck on and would not shift until aroung 4000 rpms, but would not shift under light throttle,it felt like it was slipping.There should be 2 wires that are connected to the trans, on the drivers side. The switch screws into the trans. the other end of the 2 wires goes to the switch. You can hook it up to you accelerator linkage or your pedal. Check your swicth, if it is stuck on it will not allow the trans to shift until high rpms. good luck. Derek
__________________
http://firstgenfirebird.org/show/closeup.mv?CarID=326 |
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#19
05-14-2004, 07:56 AM
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OK, checked kickdown switch and found it to operate smoothly and to be in proper position.
Would unhooking the switch, make this problem worse, or the opposite, meaning the trans would Not downshift? I have not tried this, unhooked. If not...next...governor is next ? |
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#20
05-14-2004, 08:25 AM
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Try disconnecting the switch and see what happens. I would disconnect it at the transmission 1st. If trouble goes away reconnect it and disconnect it from the switch, just to prove the wiring out. If it's still good the switch is bad. Trouble back, wiring is shorted. I had a problem with high shifting and it was because the vacumn port I was using was too small. Showed good on the gauge but car wasn't shifting right. Changed to a larger manifold port and works well now. Side note Now is the time to get your govenor shifting at your rev limit. alan
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