Automatic Transmission Question
Thread Starter
Intermediate
Joined: Nov 2008
Posts: 29
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From: Lawrence Kansas
Automatic Transmission Question
I've got a 71 with the stock original auto trans in it and it does not kick down to 1st when I put my foot on it any time after it has already shifted into second. I can be puttering along at 10 to 15 mph in second and stand on it and the trans won't kick down to first. I have a fellow 71 owner who says that his doens't have this problem. I know that there is a kickdown solenoid in the trans, but I'm not sure if this is the only cause or if it might be a combination of things. It kicks down fine from 3rd to 2nd. I have hooked up a manual switch to check the solenoid and I can hear a faint clicking, but that's it. Anyone have any ideas and if I do have to replace the solenoid how much of a pain is it to do? Thanks for any help you guys can give.
Team Owner
Joined: Jan 2006
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From: Crossville TN
Very curious. You say that it does kick down from 3rd to 2nd, but that it doesn't from 2nd to 1st... Hmmmm. That would indicate that the kickdown system....[consisting of a switch on the accelerator pedal linkage under the dash and a solenoid switch attached to the bottom of the tranny valve body inside the tranny oil pan]....is working properly--but not in low range. Somehow the pressure signal from the solenoid valve is not causing the shift valve to shuttle. Either the solenoid valve is partially plugged up or not sending an adequate pressure signal to the valve, or the shift valve is [somehow] restricted from its normal movement.
If you are in second range and pull the shift lever down into "low", what does it do? If it will downshift under this condition, the problem is NOT your valve body or clutches. I think that changing out the solenoid valve would still be the way to go to resolve your problem. If the tranny won't downshift manually, there has to be a problem with the hydraulic circuit in the transmission and changing the solenoid/switch would be a waste of time and money.
Order the replacment solenoid [note: in the 1960's, GM was paying less than $3 for this thing...I bet it's a bunch now], drop the pan and dump the oil, remove the bolt holding the filter then the filter. The solenoid is bolted to the valve body with two short bolts near the rear of the channel plate. Disconnect the lead wire connector and remove the bolts. Replace the switch making sure to use the correct bolt torque (5-7 ft-lb, I think). Now is a good time to change filter, gasket and tranny oil.
If you are in second range and pull the shift lever down into "low", what does it do? If it will downshift under this condition, the problem is NOT your valve body or clutches. I think that changing out the solenoid valve would still be the way to go to resolve your problem. If the tranny won't downshift manually, there has to be a problem with the hydraulic circuit in the transmission and changing the solenoid/switch would be a waste of time and money.
Order the replacment solenoid [note: in the 1960's, GM was paying less than $3 for this thing...I bet it's a bunch now], drop the pan and dump the oil, remove the bolt holding the filter then the filter. The solenoid is bolted to the valve body with two short bolts near the rear of the channel plate. Disconnect the lead wire connector and remove the bolts. Replace the switch making sure to use the correct bolt torque (5-7 ft-lb, I think). Now is a good time to change filter, gasket and tranny oil.
Thread Starter
Intermediate
Joined: Nov 2008
Posts: 29
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From: Lawrence Kansas
Yeah, it will downshift if I pull it into low myself, just not under hard throttle alone. I didn't know if maybe in high it ignored the solenoid and only worried about the modulator or something. It does downshift to first on it's own when at low speeds, but I have to practically come to a full stop to do so. I can roll up to a red light at 5 to 10 mph that turns green and when I get back on the throttle it is sometimes still in 2nd. Honestly I need to rebuild the whole trans anyway since the seals are leaking, but I just haven't really had the time yet. The rear crossmember does drop out without too much effort right? I know it's a two piece setup, but I didn't know how hard it was to pull the top piece. To add to the fun somewhere along the line before I bought it someone fully welded the exhaust, including the pipes to the collectors, so I'm not sure if I'll be able to slide the crossmember back far enough to clear the tail of the trans or not.
Team Owner
Joined: Aug 1999
Posts: 30,995
Likes: 99
From: Ontario
Yeah, it will downshift if I pull it into low myself, just not under hard throttle alone. I didn't know if maybe in high it ignored the solenoid and only worried about the modulator or something. It does downshift to first on it's own when at low speeds, but I have to practically come to a full stop to do so. I can roll up to a red light at 5 to 10 mph that turns green and when I get back on the throttle it is sometimes still in 2nd. Honestly I need to rebuild the whole trans anyway since the seals are leaking, but I just haven't really had the time yet. The rear crossmember does drop out without too much effort right? I know it's a two piece setup, but I didn't know how hard it was to pull the top piece. To add to the fun somewhere along the line before I bought it someone fully welded the exhaust, including the pipes to the collectors, so I'm not sure if I'll be able to slide the crossmember back far enough to clear the tail of the trans or not.
Thread Starter
Intermediate
Joined: Nov 2008
Posts: 29
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From: Lawrence Kansas
I might know what you are getting at, but let me make sure. Are you thinking that the switch isn't triggering or that I'm not getting enough vacuum from throttle? I have actually hooked up a manual push button switch and driven down the road and pressed it and still got nothing.
Team Owner
Joined: Aug 1999
Posts: 30,995
Likes: 99
From: Ontario
I might know what you are getting at, but let me make sure. Are you thinking that the switch isn't triggering or that I'm not getting enough vacuum from throttle? I have actually hooked up a manual push button switch and driven down the road and pressed it and still got nothing.
Last edited by Paul L; Nov 16, 2008 at 05:17 PM.
Thread Starter
Intermediate
Joined: Nov 2008
Posts: 29
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From: Lawrence Kansas
Okay. I did somewhat of the same test in a different way, but I'll see. I actually took a button and wired it in place of the switch on the throttle and held it in my hand while driving and pressed it and got nothing. With the car sitting in the garage I put my head under the car and pressed the switch and could hear a faint clicking, but it didn't seem to affect anything while driving.
Team Owner
Joined: Aug 1999
Posts: 30,995
Likes: 99
From: Ontario
Okay. I did somewhat of the same test in a different way, but I'll see. I actually took a button and wired it in place of the switch on the throttle and held it in my hand while driving and pressed it and got nothing. With the car sitting in the garage I put my head under the car and pressed the switch and could hear a faint clicking, but it didn't seem to affect anything while driving.
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Team Owner
Joined: Jan 2006
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From: Crossville TN
I'll say it again.... if the trans will downshift into low manually and will downshift with the kickdown system from 3rd to 2nd but not from 2nd to 1st, your problem is a weak or partially blocked solenoid switch. Change it out. [It is producing enough of a pressure signal to trigger the 3rd to 2nd shift, but not enough for the 2nd to 1st shift. The problem is NOT in the transmission hardware or hydraulic circuit.]