Transmission Shift Points
Thread Starter
Instructor
Joined: Nov 2007
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Transmission Shift Points
So I have a 73 with a 350 CID and I believe a 350 trans, How do I adjust my transmission shift points. It likes to shift really quick and also when I get on it and the trans "kicks down" it will shift at 4k RPM.
Team Owner
Joined: Jan 2006
Posts: 37,637
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From: Crossville TN
Check vacuum modulator can on tranny; plus make sure all vacuum line connections are good. If the shift calibrations need to change in the valve body, you would have to change spring rates on the shift valves needing the change. [very unusually for driver car]
Thread Starter
Instructor
Joined: Nov 2007
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Where is the modulator? Can it be adjusted?
Also I think I have a 400 trans. the trans. was recently rebuilt and I believe the kickdown switch is bad but when I put the pedal to the floor it does. But the problem is when I'm at 60-70 mph on the freeway it will shift always at 4k and i know the motor has more in it,.
Also I think I have a 400 trans. the trans. was recently rebuilt and I believe the kickdown switch is bad but when I put the pedal to the floor it does. But the problem is when I'm at 60-70 mph on the freeway it will shift always at 4k and i know the motor has more in it,.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
The vacuum modulator is a 'can' on the right side of the THM400 and has a vacuum line going to it. If the vacuum line is connected properly to intake manifold vacuum, the modulator is probably bad. Finding an exact replacement can be a problem; replacing it with a local parts store 'generic' modulator is not that good an option. Exact replacment has some adjustment in it; generic units do not.
Safety Car
Joined: Mar 2007
Posts: 3,652
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From: Bridgewater nj
If you look on the drivers side you will see a round cover held in by a snap ring. Open that up and slide out your governer. Their are spring you can cut down or scretch to change the shift points.
Team Owner
Joined: Jan 2006
Posts: 37,637
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From: Crossville TN
Messing with the governor spring should be one of the last things that you do. I agree that it can change the overall pressure schedule of the shift circuits, but you need to make sure that the modulator is working properly first....otherwise, you'll just need to go back to the governor again later. If you do end up working on the governor spring, a lighter duty spring will cause ALL shift points [in all ranges] to come in later (higher RPM).
Safety Car
Joined: Mar 2007
Posts: 3,652
Likes: 49
From: Bridgewater nj
Messing with the governor spring should be one of the last things that you do. I agree that it can change the overall pressure schedule of the shift circuits, but you need to make sure that the modulator is working properly first....otherwise, you'll just need to go back to the governor again later. If you do end up working on the governor spring, a lighter duty spring will cause ALL shift points [in all ranges] to come in later (higher RPM).
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Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
The vacuum modulator allows early upshifts when it sees vacuum at low throttle settings; but if it is damaged, it can cause early upshifts with WOT. If it 'thinks' vacuum is present, it will cause an upshift. There are lots of "failure modes" in an automatic tranny; it's just best to get some of the external issues addressed...before going to internal stuff.
If your modulator car is of 'original' design, it will have a slotted screw at the center of the outer end of the can and a 'lockdown' nut on the screw. Loosen the nut, keep the nut from turning while you turn the screw 'in' or 'out' to adjust shift points up or down. This adjustment only allows a couple of turns in or out, so don't overdo it. This is a fine-tuning adjustment, not meant for large rpm jumps. Your tranny is shifting way too early. I suspect the modulator is defective. [If the tranny was not upshifting, I would suspect the governor.] Pull the vacuum line off of the modulator can. If there is [red] Dexron tranny fluid in it, the diaphragm in the modulator has worn out/ruptured and you need to replace it.
If your modulator car is of 'original' design, it will have a slotted screw at the center of the outer end of the can and a 'lockdown' nut on the screw. Loosen the nut, keep the nut from turning while you turn the screw 'in' or 'out' to adjust shift points up or down. This adjustment only allows a couple of turns in or out, so don't overdo it. This is a fine-tuning adjustment, not meant for large rpm jumps. Your tranny is shifting way too early. I suspect the modulator is defective. [If the tranny was not upshifting, I would suspect the governor.] Pull the vacuum line off of the modulator can. If there is [red] Dexron tranny fluid in it, the diaphragm in the modulator has worn out/ruptured and you need to replace it.
Advanced
Joined: Aug 2006
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If you have a TH400 it is most likely the kick-down switch that gives you these problems. Turn the ignition on and depress the pedal all the way down. Can you hear anything that makes a clicking sound?
No? Get under the dash and look for a switch that the gaspedal operates. See if it needs adjustment or if it's is simply dead.
The th400 should shift at 5500 rpm if the switch and solenoid is functional. It overides the vaccum modulator, but not the govenor if shifted manually.
BTW it's this one
https://www.zip-products.com/Zip/pro...722E953FF977AD
Good luck
Mr. Beam
No? Get under the dash and look for a switch that the gaspedal operates. See if it needs adjustment or if it's is simply dead.
The th400 should shift at 5500 rpm if the switch and solenoid is functional. It overides the vaccum modulator, but not the govenor if shifted manually.
BTW it's this one
https://www.zip-products.com/Zip/pro...722E953FF977AD
Good luck
Mr. Beam
Thread Starter
Instructor
Joined: Nov 2007
Posts: 103
Likes: 0
Well the transmission is a TH 400 and I did recently have it rebuilt when I did the motor.
Now today I took it to the shop because the kick down wasn't working once again and one of the mechanics got under the car and checked everything out and tightened up something, I'm not really sure what
So I'm driving home and I keep getting on the pedal to see what the hell is going on with the kickdown and it isn't happening for me.
So I'm at a stop sign and start to accelerate and figure what the heel slam the gas and the transmission down shifts finally but I get to the next stop sign and the beeotch will not shift out of first manually or automatically.
So I guess it is really back to the shop again!!!
And the worse part is it is leaking right now and I think the mechanic snapped the head off a bolt on the bell housing.
Now today I took it to the shop because the kick down wasn't working once again and one of the mechanics got under the car and checked everything out and tightened up something, I'm not really sure what
So I'm driving home and I keep getting on the pedal to see what the hell is going on with the kickdown and it isn't happening for me.
So I'm at a stop sign and start to accelerate and figure what the heel slam the gas and the transmission down shifts finally but I get to the next stop sign and the beeotch will not shift out of first manually or automatically.
So I guess it is really back to the shop again!!!
And the worse part is it is leaking right now and I think the mechanic snapped the head off a bolt on the bell housing.
