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#1
05-31-2004, 04:41 PM
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I have a turbo 400 in my Buick GSX. The car shifts at 2800 RPM under full throttle while in drive. Normally I would take out the governor and grind away at the weights and/or change the springs in the governor and this will make the tranny shift later. However I tried this, and it didn't work. Tranny still shifts the same.
The modulator as I understand only works under a vacuum condition and there should be No vacuum under full throttle, so in that case the tranny should get regulated by the governor. But that obviously isn't the case here. The only thing I can think of, is the modulator valve is stuck in position and will not let the tranny upshift any higher. Does this sound like a likely cause?? Or do I not know what the he** I'm talking about? Help tranny experts, make my tranny shift at 5500rpm
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http://www.stockappearingdrags.com http://www.stockappearingdrags.com Come on get off that lawn chair and drive that car like it was meant to be driven. 69' 400 RAIV Judge Conv... 12.86@107 Factory Stock 69' 400 RAIV Trans AM .....12.48@110 Factory Stock 69' 400 RAIV Judge HT..... 13.07@104 Factory Stock 73' 455 SD Trans AM........13's?? not run yet 66' 455 GTO Convert.........12.20@112 non original 63' 421 SD Catalina...........restored fast as h*ll |
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#2
05-31-2004, 04:41 PM
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I have a turbo 400 in my Buick GSX. The car shifts at 2800 RPM under full throttle while in drive. Normally I would take out the governor and grind away at the weights and/or change the springs in the governor and this will make the tranny shift later. However I tried this, and it didn't work. Tranny still shifts the same.
The modulator as I understand only works under a vacuum condition and there should be No vacuum under full throttle, so in that case the tranny should get regulated by the governor. But that obviously isn't the case here. The only thing I can think of, is the modulator valve is stuck in position and will not let the tranny upshift any higher. Does this sound like a likely cause?? Or do I not know what the he** I'm talking about? Help tranny experts, make my tranny shift at 5500rpm
__________________
http://www.stockappearingdrags.com http://www.stockappearingdrags.com Come on get off that lawn chair and drive that car like it was meant to be driven. 69' 400 RAIV Judge Conv... 12.86@107 Factory Stock 69' 400 RAIV Trans AM .....12.48@110 Factory Stock 69' 400 RAIV Judge HT..... 13.07@104 Factory Stock 73' 455 SD Trans AM........13's?? not run yet 66' 455 GTO Convert.........12.20@112 non original 63' 421 SD Catalina...........restored fast as h*ll |
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#3
05-31-2004, 05:48 PM
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Modulator valves don't cost very much. Put new one on and see if that's the problem. If not you eliminated that as a possibility. There also a spring behind the plunger that works the modulator(if I'm not mistaken). Make sure it has the spring behind it for easier shifts. I had a 400 turbo years ago that didn't have the spring and the local tranny shop gave me one. I don't know whether some come without them or people take them out but one never knows until you look...
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#4
05-31-2004, 08:18 PM
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The spring behind the modulator is an item that some valve body kits have. I've never seen a virgin TH400 or 350 for that matter, have one in 20 yrs of trans rebuilding. I do agree that it may be a sticking modulator valve. It should move in and out freely. Also make sure you have good vacuum on the line to the modulator also.
Jeff
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North Dakotas fastest REAL GTO 10.10 @ 131 MPH in the 1/4 Hoping to get it back together some year. www.jandjrepairandrestoration |
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#5
06-01-2004, 09:28 AM
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Have you tried this with the detent hooked up?
The detent valve will bypass the modulator valve until line rise overcomes the solenoid. = later shifts and /or a test for hydraulic problems. You may try a fast acting modulator also. A dual red stripe will react to a low vacuum condition (WOT) better than any other. If there are any restrictions in the vacuum line remove them. The restriction acts somewhat like a check valve at the modulator, slowing it's action at WOT. You can plug the vacuum line and note any change also. I would be more inclined to think the governor bore is worn allowing forward oil (line) to enter the governor circuit, forcing the valve outboard toward the modulator. The valve usually "sticks" inboard not outboard. But anything is possible.
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A Government big enough to give you everything you want is strong enough to take everything you have. - Jefferson  "If ever a time should come, when vain and aspiring men shall possess the highest seats in Government, our country will stand in need of its experienced patriots to prevent its ruin." - Samuel Adams Right and wrong doesn't need facts all the time. -Lighthouseman ("lawyer") Starnes Performance Automatics www.Starnesperformance.com |
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