TH-400 upshift question
Thread Starter
Melting Slicks
Joined: Aug 1999
Posts: 3,123
Likes: 13
From: Hollywood, Florida
TH-400 upshift question
What exactly controls a FULL W.O.T. upshift? I know the regular upshifts are controlled by the vac. modulator.
I feel that the 1st to 2nd full throttle upshift seems to come in too quickly (stock torque converter),at about 3800 RPM. I'd like it to wind up a bit more before the upshift.
Thanks
I feel that the 1st to 2nd full throttle upshift seems to come in too quickly (stock torque converter),at about 3800 RPM. I'd like it to wind up a bit more before the upshift.
Thanks
Melting Slicks
Joined: Jul 1999
Posts: 3,201
Likes: 0
From: Clifton Park NY
Re: TH-400 upshift question (shoptek)
Marc,
I'm also interested in hearing the responses on this, as I seem to have the same problem: it shifts too early from 1st to 2nd, and then it draaaaaaags in 2nd forever....
-Pedro
I'm also interested in hearing the responses on this, as I seem to have the same problem: it shifts too early from 1st to 2nd, and then it draaaaaaags in 2nd forever....
-Pedro
Drifting
Joined: Oct 2000
Posts: 1,526
Likes: 1
From: Harrison Township, Mi
Re: TH-400 upshift question (Pedro'74)
The Th-400 in my GTO does the same thing. Shifts about 4200 @ WOT. Temporary solution...shift it myself manually. I'll be interested to see if anyone knows why.
Race Director
Joined: Apr 1999
Posts: 11,520
Likes: 13
From: CORVETTE 77 385 C.I. TEXAS
Re: TH-400 upshift question (shoptek)
The shift lever. In D it's controlled by the governor wts. & springs. You can get a kit to adjust it.
Maybe I should do one like Lars does for dist., on second thought if you install wrong you could shift too high & blow the engine.
Maybe I should do one like Lars does for dist., on second thought if you install wrong you could shift too high & blow the engine.
Le Mans Master
Joined: Sep 2000
Posts: 5,635
Likes: 4
From: Orlando Floriduh
Re: TH-400 upshift question (shoptek)
Years ago I went to automatic trans trade school... I have a cert on TH400's.. WOT puts the trans "on" the electric downshift solenoid This solenoid also allows higher speed kickdown. Early models have it in the carburetor, later ones are under the gas pedal under the dash. If the switch is not working or mal-adjusted or the solenoid is burnt out the trans will aways shift on the governor (a little early), and will never downshift from 3-2 at speed over approx. 50mph and will never go from 3-1 (WOT downshifts). Once this is working then you may even have to let up slightly to allow it to WOT upshift . There are may cars that suffer from a disconnected,mal-adjusted or inoperative downshift solenoid as everything else works just fine. :cheers:
[Modified by silvervetteman, 10:24 AM 1/19/2002]
[Modified by silvervetteman, 10:24 AM 1/19/2002]
Race Director
Joined: Oct 2000
Posts: 14,865
Likes: 78
From: central FL, near the beach.
Re: TH-400 upshift question (shoptek)
a solenoid above the trans pan boosts pressure to the governor; no stock vettes shift below 5000 stock. ...set mine to 5700.
Often clueless owners disconnect the circuit from the carb or gas pedal, thinking it is an emmission control device.
Apply 12v to it and you should hear a click, engine off....then hook it up right, WOT only.
Often clueless owners disconnect the circuit from the carb or gas pedal, thinking it is an emmission control device.
Apply 12v to it and you should hear a click, engine off....then hook it up right, WOT only.
Burning Brakes
Joined: Apr 2001
Posts: 752
Likes: 1
From: Springfield Oregon
Re: TH-400 upshift question (shoptek)
If I pull my car into first, floor it, and hold it there, it will still shift into second on its own at 4800rpm. At this point, if I shift it into second and keep it floored, it wraps up to 5000+ and won't shift to third until I move the lever to "3". I have seen this topic posted before and it usually just fizzles out with no solid answer. Is there any way a guy can fix this with his own tools in his own driveway without dropping the tranny? My kickdown switch works fine and my modulator is the adjustable type and works fine. If I just floor it off the line in regular drive "3" and hold it, it does the 1-2 at about 4400rpm. Really appreciate any help.
Troy
Troy
Thread Starter
Melting Slicks
Joined: Aug 1999
Posts: 3,123
Likes: 13
From: Hollywood, Florida
Re: TH-400 upshift question (silvervetteman)
Thanks for all of the input.
Silvervetteman, how is the solinoid adjusted? What is the correct procedure, or is it "very" internal to the tranny?
I have the kickdown switch under the gas pedal. I followed the adjust procedure for it, and also had a Vette shop check it for me last year. He said it was working, but come to think of it, I don't get a downshift above 50-60 MPH, and I don't think I get a 3-1 downshift really at all.
drives61, thank you too for the help. How did you adjust yours for the higher upshift point?
I do see a plug on the tranny, but unfortunately I also noticed some cut wires from Bubba. I do believe these wires were for the TCS though.
[Modified by shoptek, 1:28 PM 1/19/2002]
Silvervetteman, how is the solinoid adjusted? What is the correct procedure, or is it "very" internal to the tranny?
I have the kickdown switch under the gas pedal. I followed the adjust procedure for it, and also had a Vette shop check it for me last year. He said it was working, but come to think of it, I don't get a downshift above 50-60 MPH, and I don't think I get a 3-1 downshift really at all.
drives61, thank you too for the help. How did you adjust yours for the higher upshift point?
I do see a plug on the tranny, but unfortunately I also noticed some cut wires from Bubba. I do believe these wires were for the TCS though.
[Modified by shoptek, 1:28 PM 1/19/2002]
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Le Mans Master
Joined: Sep 2000
Posts: 5,635
Likes: 4
From: Orlando Floriduh
Re: TH-400 upshift question (shoptek)
If you are absolutly sure that the solenoid is working, which it may or may not be, (The switch not be working from the gas pedal) then you can re-calibrate the governor with a spring kit. To check the solenoid you need to varify that with the gas pedal and carb in WOT, the solenoid should be engaged. An easy way to do this is to drive off normally and let it shift into 3rd, slowly slow to about 25-28 mph withe trans still in 3rd. Now punch it and it should downshift into 1st. If it only goes into 2nd, the solenoid is not engaged. TH 400's will go back to second via the throttle pressure/vacuum modulator but not to 1st. As a matter of fact they will not even go from 2nd back into 1st without the kickdown working. I really shounds to me like the kickdown solenoid is not working. I had a 71 that would redline the engine before it would shift up. Before I fixed the kickdown it would shift at about 4400 both shifts WOT in (D).
[Modified by silvervetteman, 12:46 PM 1/19/2002]
[Modified by silvervetteman, 1:18 PM 1/19/2002]
[Modified by silvervetteman, 12:46 PM 1/19/2002]
[Modified by silvervetteman, 1:18 PM 1/19/2002]
Le Mans Master
Joined: Sep 2000
Posts: 5,635
Likes: 4
From: Orlando Floriduh
Re: TH-400 upshift question (shoptek)
The solenoid is easily accessable by removing the pan, You will see it bolted to the valve body. BUT... First see if it is getting 12 volts when the throttle is to the floor. The switch On the carb or under the dash needs to "make" at WOT. It is a pull out /self adjust type used by GM. The pedal may not be going WOT.... Also a common thing on older C-3's. If it does get 12V then you should hear a CLICK from the trans. If not then the solenoid is bad and you need to replace it.
[Modified by silvervetteman, 12:47 PM 1/19/2002]
[Modified by silvervetteman, 12:47 PM 1/19/2002]
Race Director
Joined: Oct 2000
Posts: 14,865
Likes: 78
From: central FL, near the beach.
Re: TH-400 upshift question (silvervetteman)
excellent advice from silvervetteman.
Most with a broken kickdown circuit would be all :D if they just got it working properly.
But I added a small green light, hooked to the kickdown switch, on top of the dash. I use it to up/downshift with the gas pedal, sort of like a paddle shifter. If i am taking a sweeper at high speed and accelerating, the last thing i want is a downshift; i look for the light to stay off to avoid a jolt that will send my 72 sideways.
but now the local cop says i corner too fast! :rolleyes:
Most with a broken kickdown circuit would be all :D if they just got it working properly.
But I added a small green light, hooked to the kickdown switch, on top of the dash. I use it to up/downshift with the gas pedal, sort of like a paddle shifter. If i am taking a sweeper at high speed and accelerating, the last thing i want is a downshift; i look for the light to stay off to avoid a jolt that will send my 72 sideways.
but now the local cop says i corner too fast! :rolleyes:
