Lockup TC Problem - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**tdangle** · 12-14-2018, 11:17 PM

I have a overdrive 4 speed automatic with a lockup tc in my truck. I have it wired up with a 4th gear only pressure switch (grounds when in 4th) going to the solenoid and from the other lead on the solenoid going to 12V thru a brake light switch. The way I get lockup in 4th but it disconnects when I hit the brakes. The problem I'm having is the tc seems to be sticking in the lockup mode when stopping and almost kills the engine just before coming to a complete stop. I monitored the 12V and it is being disconnected when I apply the brakes. If I keep it in 3rd lockup never happens and the problem goes away. I disconnected power so it never locks up and no problem. TC solenoid sticking?? Did I overlook anything?

kaycee · 12-17-2018, 09:11 AM

Yeah I would venture to guess it is sticking,I was going through the same thing .I had to pull my trans for a front seal leak and while it was out pulled my sillynoid out and bench tested ,it would work off and on not being consistant. May check your ground first

rpmerf · 12-17-2018, 09:52 AM

2 ideas for troubleshooting.

Wire the output of the relay to a light in the cab to be 100% sure when the lockup is getting power.

Wire the relay up to a switch so it is easy to engage / disengage. With the switch you should be able to engage / disengage and see if you feel it / notice the RPMs change.

**tdangle** · 12-17-2018, 02:02 PM

I have done all the checks that I can think of. Replaced it yesterday, then had to leave so hopefully I can road test it tonight and see if problem is fixed.

**tdangle** · 12-24-2018, 12:32 PM

Followup - I changed out the lockup solenoid and problem is fixed. Now I'm going to look into a vacuum switch to unlock when pulling up a hill.

kaycee · 12-24-2018, 12:59 PM

Cool glad it worked for ya , I got a TCI setup in my 69 and blocked the vacum part off and ran it to a switch on the dash . I only lock it up above 60 mph kinda of a pita but I know when its locked or not. I have the same setup in my 63 but ran it through the brake switch and lockup in 3 or 4 I never know if its locked up or not. Its your preference on how to do it just a little info for ya

12-14-2018, 11:17 PM	#1
tdangle Senior Member Join Date: Mar 2005 Location: Jurupa Valley, Ca Posts: 1,209	Lockup TC Problem I have a overdrive 4 speed automatic with a lockup tc in my truck. I have it wired up with a 4th gear only pressure switch (grounds when in 4th) going to the solenoid and from the other lead on the solenoid going to 12V thru a brake light switch. The way I get lockup in 4th but it disconnects when I hit the brakes. The problem I'm having is the tc seems to be sticking in the lockup mode when stopping and almost kills the engine just before coming to a complete stop. I monitored the 12V and it is being disconnected when I apply the brakes. If I keep it in 3rd lockup never happens and the problem goes away. I disconnected power so it never locks up and no problem. TC solenoid sticking?? Did I overlook anything? __________________ Terry 1970 Custom Camper/C20 , GM Crate 350/7004R, Dana 60, factory AC

12-17-2018, 09:11 AM	#2
kaycee Registered User Join Date: Jan 2000 Location: Wyoming USA Posts: 2,445	Re: Lockup TC Problem Yeah I would venture to guess it is sticking,I was going through the same thing .I had to pull my trans for a front seal leak and while it was out pulled my sillynoid out and bench tested ,it would work off and on not being consistant. May check your ground first __________________ 2001 Silverado K-1500 2005 FXDWG stage3 69 CHEVY Short/Step 327/4L60 373 posi 63 IMPALA 327

12-17-2018, 09:52 AM	#3
rpmerf Registered User Join Date: Feb 2011 Location: Parkville, MD Posts: 1,024	Re: Lockup TC Problem 2 ideas for troubleshooting. Wire the output of the relay to a light in the cab to be 100% sure when the lockup is getting power. Wire the relay up to a switch so it is easy to engage / disengage. With the switch you should be able to engage / disengage and see if you feel it / notice the RPMs change. __________________ 1970 C20 Custom Camper - 350, TH350 1997 GMC Suburban 1994 Acura Integra GSR 1987 Dodge Daytona Shelby Z

12-17-2018, 02:02 PM	#4
tdangle Senior Member Join Date: Mar 2005 Location: Jurupa Valley, Ca Posts: 1,209	Re: Lockup TC Problem I have done all the checks that I can think of. Replaced it yesterday, then had to leave so hopefully I can road test it tonight and see if problem is fixed. __________________ Terry 1970 Custom Camper/C20 , GM Crate 350/7004R, Dana 60, factory AC

12-24-2018, 12:32 PM	#5
tdangle Senior Member Join Date: Mar 2005 Location: Jurupa Valley, Ca Posts: 1,209	Re: Lockup TC Problem Followup - I changed out the lockup solenoid and problem is fixed. Now I'm going to look into a vacuum switch to unlock when pulling up a hill. __________________ Terry 1970 Custom Camper/C20 , GM Crate 350/7004R, Dana 60, factory AC

12-24-2018, 12:59 PM	#6
kaycee Registered User Join Date: Jan 2000 Location: Wyoming USA Posts: 2,445	Re: Lockup TC Problem Cool glad it worked for ya , I got a TCI setup in my 69 and blocked the vacum part off and ran it to a switch on the dash . I only lock it up above 60 mph kinda of a pita but I know when its locked or not. I have the same setup in my 63 but ran it through the brake switch and lockup in 3 or 4 I never know if its locked up or not. Its your preference on how to do it just a little info for ya __________________ 2001 Silverado K-1500 2005 FXDWG stage3 69 CHEVY Short/Step 327/4L60 373 posi 63 IMPALA 327



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