700R4 Lockup Torque converter control issues solved

[Turbo4whl]

You probably can't see it in the diagram I posted, the oil tap for the converter uses oil as it comes back from the cooler. This is the coolest oil in the trans and another good reason to add an extra trans cooler when towing!

 

[bucket]

You probably can't see it in the diagram I posted, the oil tap for the converter uses oil as it comes back from the cooler. This is the coolest oil in the trans and another good reason to add an extra trans cooler when towing!

And to make sure it's plumbed in after the fluid passes through the radiator cooler.

Or do what I sometimes do (which may be incorrect) and bypass the radiator cooler altogether. The side effect of this is that in very cold weather, the trans fluid may not get very warm during light use.

 

[grummy]

@grummy

The local trans shop that I used for years warned me that running a 700r4 unlocked for prolonged periods will kill it due to excessive heat buildup. They were correct and I've got over 70k of road miles with a temp gauge installed that proves it. My lifted 4x4 Suburban was undergeared for best use with overdrive. The converter spent a lot of time unlocked in 4th on the interstate due to inclines and/or headwinds. If it stayed unlocked too long, the trans started to get way too hot. The temp gauge told me when I had to back off the throttle a bit so the converter would lock again. Once locked, the trans temp would start coming down significantly.

Running it in 3rd gear (locked or unlocked) never got the trans hot.

But what is "excessive" ? 240 is generally maxed out, 225 is often mentioned as in the normal range. When I asked the local shop about my issue, they told me temps would not rise enough to actually matter, of course, they tend to like repairing transmissions for big $$$.

I do not have a gauge, but I would be willing to bet that pulling my cargo trailer into the wind in 3rd gear with no lockup for extended miles probably creates more heat than 4th with no lockup does.

I know for sure that I have to get a vacuum gauge tapped in by the tip out switch to see if low vacuum is occasionally kicking mine in and out making it feel like a misfire. It happens so quickly that I can not see it on the tach.

 

[bucket]

But what is "excessive" ? 240 is generally maxed out, 225 is often mentioned as in the normal range. When I asked the local shop about my issue, they told me temps would not rise enough to actually matter, of course, they tend to like repairing transmissions for big $$$.

I do not have a gauge, but I would be willing to bet that pulling my cargo trailer into the wind in 3rd gear with no lockup for extended miles probably creates more heat than 4th with no lockup does.

I know for sure that I have to get a vacuum gauge tapped in by the tip out switch to see if low vacuum is occasionally kicking mine in and out making it feel like a misfire. It happens so quickly that I can not see it on the tach.

Many many times it would climb to 240 before I backed out of it. If it weren't for the gauge, I would have cooked that poor trans so many times.

I can assure you, I could do whatever I wanted in 3rd and it never tried to get hot. Unlocked in 4th was the only time it ever would get hot.

 

[Jgonick]

Is there two separate vacuums I should be hooking up on the firewall or just that driver side one?

Driver side is Torque converter clutch (TCC) -
The one on the passenger side probably is TIP-in vac switch. Electronic spark control for distributor- if you are using a standard HEI distributor (or any aftermarket non-ESC distributor) it is not used.


the green wire with orange connector -is the test port for TCC.


Like mentioned- 700r4 are not all the same setup- Yours being a 1984 K5 is probably like or pretty close to the attachment.

The other attachment tells how to use the test port.

 

[grummy]

This info is good stuff as I am not exactly thrilled about the thought of having trans problems any time soon.

I've come across documentation that indicated that the "oil passage" issue only existed in early years of the 700r4, so this could be where the variables in discussion lie. If I were to guess, the change was made when the 30 spline was introduced, but we would need to have a real trans guy confirm.

My Trans is a 30 spline from a '93 G-Van. I think the 700r4 mysteries will continue forever. One local shop practically refuses to rebuild any 700r4 as evidenced by the prices they quote. They want you to put in a 4L60e instead and spend even more to get the control and harness.

 

[bucket]

This info is good stuff as I am not exactly thrilled about the thought of having trans problems any time soon.

I've come across documentation that indicated that the "oil passage" issue only existed in early years of the 700r4, so this could be where the variables in discussion lie. If I were to guess, the change was made when the 30 spline was introduced, but we would need to have a real trans guy confirm.

My Trans is a 30 spline from a '93 G-Van. I think the 700r4 mysteries will continue forever. One local shop practically refuses to rebuild any 700r4 as evidenced by the prices they quote. They want you to put in a 4L60e instead and spend even more to get the control and harness.

The trans I talked about previously was an '88 model.

I ended up pulling it and sold it to a buddy than needed a good 700r4. The overdrive was nearly useless for me, so I installed a th400 in it's place, along with larger tires.

 

[Broken85]

Is there two separate vacuums I should be hooking up on the firewall or just that driver side one? I found I have two wires blue/yellow that seem to go to the same harness that were cut on the firewall and I found this green plug just inside the firewall.

The vacuum switch on the passenger side contributes to the spark control system. The vacuum switch on the driver side is for the TCC. The green wire with the orange plug is a diagnostic circuit for a 700R4. If you give it 12v in fourth gear it should force the TCC lockup. So you can determine if you have a wiring problem or a transmission problem. There should be three wires going into a 700R4. Green, blue and yellow. Yellow goes to an egr bleed valve also part of the emissions system. The only wire that is really important at all is the blue.

There should also be a blue wire with a black stripe going into the vacuum switch if you have a K truck which will disable TCC lockup if you are in 4 wheel drive.