700R4 Lock Up Converter Talk and Diagnose

[89Suburban]

You should still get pretty good mpg towing in third...it still locks up.

Bro, it does not lock up, and I really could use a hand diagnosing that issue.

I have been only using 3rd and to tell you the truth, she seems to be a different animal in that gear, and I am glad I was told to run it that way. It kinda actually feels like a hidden tow/haul mode. But I really want to fix the lock up.

 

[Jims86]

Bro, it does not lock up, and I really could use a hand diagnosing that issue.

I have been only using 3rd and to tell you the truth, she seems to be a different animal in that gear, and I am glad I was told to run it that way. It kinda actually feels like a hidden tow/haul mode. But I really want to fix the lock up.

Does your speedo work(no, not the one you are wearing)?
and if lock up stopped working all of a sudden, either the break switch behind the dash, that has the big vac line going to it is mis adjusted, or, the TCC lockup solenoid is shot...which is a cake walk, compaired to the other **** you have done (and done well may I add) on that truck.
there is a test pin that you ground on your diagnostic connector under the dash that will activate the solenoid for testing. It is pin F

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[bucket]

Does your speedo work(no, not the one you are wearing)?
and if lock up stopped working all of a sudden, either the break switch behind the dash, that has the big vac line going to it is mis adjusted, or, the TCC lockup solenoid is shot...which is a cake walk, compaired to the other **** you have done (and done well may I add) on that truck.
there is a test pin that you ground on your diagnostic connector under the dash that will activate the solenoid for testing. It is pin F

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Can you run a switch to that pin F and safely use that to force lockup at highway speeds?

 

[Jims86]

Can you run a switch to that pin F and safely use that to force lockup at highway speeds?

Yes, that wire is actually spliced in with the TCC activation wire from the ECM....you can even get it to lock in 2nd, which i found out by accident last week...sumbitch locked up between 10 and 15 mph, found that wire touching the case of the ecm...the wire pulled out of the connector that I put on it.
I haven't done it, but if you do, flip the switck at 35mph, and while cruising, tap the brake to see if it unlocks....if not, I would wire a brake light switch activated relay to interrupt it when you hit the brakes.
Edit:never mind, the brake switch interrupts the hot side of the circut...should be ok running a ground switch to pin F

 

[89Suburban]

Does your speedo work(no, not the one you are wearing)?
and if lock up stopped working all of a sudden, either the break switch behind the dash, that has the big vac line going to it is mis adjusted, or, the TCC lockup solenoid is shot...which is a cake walk, compaired to the other **** you have done (and done well may I add) on that truck.
there is a test pin that you ground on your diagnostic connector under the dash that will activate the solenoid for testing. It is pin F

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Can you run a switch to that pin F and safely use that to force lockup at highway speeds?

Yes, that wire is actually spliced in with the TCC activation wire from the ECM....you can even get it to lock in 2nd, which i found out by accident last week...sumbitch locked up between 10 and 15 mph, found that wire touching the case of the ecm...the wire pulled out of the connector that I put on it.
I haven't done it, but if you do, flip the switck at 35mph, and while cruising, tap the brake to see if it unlocks....if not, I would wire a brake light switch activated relay to interrupt it when you hit the brakes.
Edit:never mind, the brake switch interrupts the hot side of the circut...should be ok running a ground switch to pin F

Hot damn, I can't wait to test this, thanks Jim!!

Yes, the speedo works. I can't vouch for the VSS behind the gauge. My gauge is cable driven. The lock up has not worked since I purchased the vehicle 3 years ago.

So if I ground that wire and it doesn't lockup it's one of 2 things then. What do I look for on the brake switch? I thought that was for the cruise?

 

[Jims86]

Hot damn, I can't wait to test this, thanks Jim!!

Yes, the speedo works. I can't vouch for the VSS behind the gauge. My gauge is cable driven. The lock up has not worked since I purchased the vehicle 3 years ago.

So if I ground that wire and it doesn't lockup it's one of 2 things then. What do I look for on the brake switch? I thought that was for the cruise?

Look for it to cut power when you press on the brake pedal.

 

[89Suburban]

Here's pics, is it the gray switch?

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[89Suburban]

Looks like there are two, a white one and a gray one?

 

[Jims86]

Looks like there are two, a white one and a gray one?

The one with the big vacuum line, i think its the one closer to the passenger side...Schematics say there is a puple wire, and then a pink and black wire, which should be the hot wire. Key on, BTW...LoL

 

[GOBR]

Lockup should only work in "D". The brake switch would cut lockup and/or cruise control when activated.

The higher the rpm when cruisin the easier to tell if its lockin or not.

Hey jims86, when you ground the pin to test the solenoid can you keep it grounded and tap the brakes to see if the brake switch works? Like if you ground it and it locks, can you keep it locked and then tap brakes to see if it disengages, or does grounding the pin overide everything?

 

[Jims86]

Lockup should only work in "D". The brake switch would cut lockup and/or cruise control when activated.

The higher the rpm when cruisin the easier to tell if its lockin or not.

Hey jims86, when you ground the pin to test the solenoid can you keep it grounded and tap the brakes to see if the brake switch works? Like if you ground it and it locks, can you keep it locked and then tap brakes to see if it disengages, or does grounding the pin overide everything?

Yes. The wire in pin F of the diagnostic connector is spliced in with the lockup actuator wire(switched ground) from the ECM. The brake switch interrupt is on the hot side of the Converter lock solenoid...so even if you leave it grounded, it will unlock when you hit the brakes. But if you dont pull it before you let off the brake, it will lock up in second gear.
Trans will lock in d(3rd gear) and OD.

 

[bucket]

If you run a switch and leave it locked up, will it automatically unlock when you slow down enough for it to kick into first gear? Basically, it could actually be driven (slowly) with it locked up all the time?

I'm just a bit confused by the whole situation, after having dealt with several THM125's that the lockup solenoid gets stuck and the engine dies when you come to a stop.

 

[Jims86]

If you run a switch and leave it locked up, will it automatically unlock when you slow down enough for it to kick into first gear? Basically, it could actually be driven (slowly) with it locked up all the time?

I'm just a bit confused by the whole situation, after having dealt with several THM125's that the lockup solenoid gets stuck and the engine dies when you come to a stop.

As long as your foot is on the brake, cutting off positive power to the TCC solenoid.
Mine didnt lock up in first when my wire was grounding out, There is a pressure switch in the valve body I think that prevents it(HR?)

 

[89Suburban]

Yo Jim, over here, lol...

So if I understand this right, I should be able to use a test light and show current on that pin then shouldn't I? That should be hot all the time unless the brake switch is engaged? And the computer ground signal is the final step in that loop? So if I am sitting in park, engine running, foot off brake, I should show that pin hot? I am going to try and look at this tomorrow, and adjust that timing if it isn't terribly hot out or storming.

Also, I have been driving this thing around in 3rd gear all week, it is like a different truck. Firm shifts, brakes better, overall better driveability it seems for around town and towing the boat. Holds speed better at 55-60 going over the bridge with the cruise on. Seems like when it is in O/D, it coasts in third gear, but if I am in third, it feels more connected, I don't know how to explain it.

It's not the lockup, I know what that feels like from driving other GM vehicles with it, you know when that is on, it feels like direct drive.

Just seems like when in third gear it's not as "slushy". I don't know if that makes any sense to you or if anybody can explain why.

 

[Jims86]

Yo Jim, over here, lol...

So if I understand this right, I should be able to use a test light and show current on that pin then shouldn't I? That should be hot all the time unless the brake switch is engaged? And the computer ground signal is the final step in that loop? So if I am sitting in park, engine running, foot off brake, I should show that pin hot? I am going to try and look at this tomorrow, and adjust that timing if it isn't terribly hot out or storming.

Also, I have been driving this thing around in 3rd gear all week, it is like a different truck. Firm shifts, brakes better, overall better driveability it seems for around town and towing the boat. Holds speed better at 55-60 going over the bridge with the cruise on. Seems like when it is in O/D, it coasts in third gear, but if I am in third, it feels more connected, I don't know how to explain it.

It's not the lockup, I know what that feels like from driving other GM vehicles with it, you know when that is on, it feels like direct drive.

Just seems like when in third gear it's not as "slushy". I don't know if that makes any sense to you or if anybody can explain why.

Yes, with the key on, foot off pedal, you should see power there. press the brake, and you should see no power.
the better around town performance in third is no surprise, these engines are really happy in the mid range RPMs, you have more torque there, compaired to just lugging around in OD.
I dont like the harsh downshifts on mine when im in OD lockout, so I stay in OD most of the time, unless Im cruising these country back roads between 45 and 50.
I do pop it up into OD before I come to a stop.