Overdrive not working

[Andreas Wickman]

Really a great forum this. So many helpful guys out there-. Attached is a wire diagram that shows how the OD in my trans is powered. I'm wondering if someone can explain what happens inside the trans with the components shown in the diagram. A Normally closed switch and a relay by-passed one way with a diod?? Anyone understand the function?

 

[Matt69olds]

Looks to me like the throttle switch allows the converter clutch to engage with more than 10% throttle, and disengage at WOT. There is a pressure switch in 4th gear, however I don’t understand exactly how it’s suppose to function. It says it showed open momentarily on a 4-3 downshift, I’m guessing that’s a misprint I bet it’s supposed to be a normally open switch that closes when the trans shifts to 4th gear.

You can monitor the TCC on the orange test connector, wherever that is.

 

[Bruce Wingate]

Looks to me like the throttle switch allows the converter clutch to engage with more than 10% throttle, and disengage at WOT. There is a pressure switch in 4th gear, however I don’t understand exactly how it’s suppose to function. It says it showed open momentarily on a 4-3 downshift, I’m guessing that’s a misprint I bet it’s supposed to be a normally open switch that closes when the trans shifts to 4th gear.

You can monitor the TCC on the orange test connector, wherever that is.

If found this on another forum:

The TH700R4 / 4L60 doesn't have a TCM. The test wire should have + voltage when the ignition is on and the TCC brake pedal switch and TCC vacuum switch are passing volts to the Torque Converter Clutch engagement wire on the transmission.
There's no Serial data stream like CLCC, EDC, TPI, and TBI sent out through the ALDL data port under the dash.
From this thread: http://forum.73-87chevytrucks.com/smforum/index.php?topic=34708.0

Does this mean that if I hook a test light up to the test port and a ground that it will light when the torque converter is locked up?

 

[Itali83]

If found this on another forum:

The TH700R4 / 4L60 doesn't have a TCM. The test wire should have + voltage when the ignition is on and the TCC brake pedal switch and TCC vacuum switch are passing volts to the Torque Converter Clutch engagement wire on the transmission.
There's no Serial data stream like CLCC, EDC, TPI, and TBI sent out through the ALDL data port under the dash.
From this thread: http://forum.73-87chevytrucks.com/smforum/index.php?topic=34708.0

Does this mean that if I hook a test light up to the test port and a ground that it will light when the torque converter is locked up?

No, it just means power is going into the transmission. It then has to go through the pressure switch on the valve body and then solenoid. It’s just a test port to see if the fuse, brake switch and in your case throttle switch are working.

Ben

 

[Vbb199]

My words guys. The 6.2 does not use ANY VACUUM OF ANY SORTS for the 700r4 transmission or it’s converter. The vacuum converter switch was only for the gas jobs. The 6.2’s have an electric throttle position switch on the injection pump that will lock and unlock the converter depending on throttle position.

Not saying I know everything but I’m tellin’ you. Forget about vacuum with this truck and it’s converter.

Ben

This is some good info. I know about 700's, and I know about gas motors, but I had no idea how the diesel and 700r4 play together for lockup control

 

[wlwarnke]

Looks to me like the throttle switch allows the converter clutch to engage with more than 10% throttle, and disengage at WOT. There is a pressure switch in 4th gear, however I don’t understand exactly how it’s suppose to function. It says it showed open momentarily on a 4-3 downshift, I’m guessing that’s a misprint I bet it’s supposed to be a normally open switch that closes when the trans shifts to 4th gear.

You can monitor the TCC on the orange test connector, wherever that is.

I believe the momentary 4-3 unlocks the converter during the downshift, the. It can lock again once in 3rd.

 

[Andreas Wickman]

OD o lock up? First, please tell one that dont eaal y can sort this out. Look att the attached diagram. OD or lock-up?
Then; vacuum is for sure not included. The attached wire diagram is how my trans is wired. I have installed a control lamp that lights up once the green wire down to the trans is hot. And it does, so I know its not any fault outside the transmission. It can be that there is a fault in the connector on the trans. I have to lower the oil pan to check that. If not its definitely inside the trans.

 

[Andreas Wickman]

Now I learned some basics. My problem is the lock up/TCC. (Because overdrive=4th gear not any 5th gear). So my remaining question is:
What prevents the solenoid to be engaged on every gear? As I read the attached wire diagram (previous post) it looks to me the solenoid has power supply all the time, no matter which gear the trans is running on. The only interruption is when throttle is below 10% and when down shifting from 4 to 3. Anyone that can explain?

 

[wlwarnke]

It appears the 2wd diesel locked up every gear.

The throttle switch unlocks below 10% throttle (think stop light, take off, coasting)
Then briefly unlocks during the 4-3 downshift.

Mine used to have this but when i converted to gas, i rewired so that it would basically be locked anytime it was in 4th gear.

Also, not shown on the diagram, so maybe a later model thing, I seem to remember a temperature switch in the harness that would prevent lockup until the trans warmed up.

 

[wlwarnke]

If you are getting power on the orange test wire (just hanging under the dash) then externally, the trans is being sent a lockup signal.

With the truck off, ohm this wire to a good ground. Should see about 23.5 ohms according to the manual. If so, the 4-3 switch and solenoid are "electrically good".

If that's good, then again, with truck off, jumper 12v to this orange test terminal, and listen for the solenoid to click.

If that's good, then either the TCC is done or it's not getting pressure to engage it. A leak somewhere internal (solenoid has an o-ring, end of input shaft has an o-ring) or the spool valve itself is stuck.

From the factory, the TCC solenoid also has a small filter inside it. Most people delete this during a rebuild.

 

[Andreas Wickman]

Yes I talked to a friend driving a 1989 Silverado with diesel, and he say it locks up on every gear. I have tried to hear a click from the solenoid, but cant hear anything. I have ordered a new solenoid, filter and gasket. As soon it shows up I drain the trans and take a closer look. Thanks for good advice.

 

[Andreas Wickman]

So now I have drained the tranny and done a complete check of the electric components: Connector into the tranny: CHECK, Pressure switch 4-3 down shift CHECK, Soleniod with valve CHECK, And it does "click" when throttle is more than 10%.
So the sad conclusion is one of the options meant above:
1. Either the TCC is done or
2. It's not getting pressure to engage it or
3. A leak somewhere internal (solenoid has an o-ring, end of input shaft has an o-ring) or
4. The spool valve itself is stuck. Where is the spool valve located?

I have bought a new converter, shall arrive next week. Now my question: Is it possible to in one way or another check the pressure? Guess it will be an outlet on the tranny somewhere? And if pressure, internal leakage? By the way. The oil looked super fresh, clear red and no dirt at all in the pan. And the transmission shifts up and down very smooth and at the right rpm.

Happy for all good tips.

Greetings from summer Sweden

 

[Matt69olds]

The TCC valve is directly above the solenoid.

Have you air tested the solenoid? If you apply air to the end of the solenoid, air should vent. Apply power the the solenoid, the vent should close.

 

[Andreas Wickman]

Yes I did that test and it worked as you say.

 

[Andreas Wickman]

The valve above the solenoid, can one move it with a a pin when the solenoid is removed, to check the valve isn't stuck?