Hi all,

I just had a rebuilt (on the cheap) TH700 installed in my 85 Z28. It shifts P->1->2->3 very smoothly in D, and the reverse is also true.

However, in OD it only shifts into 4th and locks up the converter when I constantly apply some throttle. The moment I let off, it drops back into third. Fluid level is correct, and I have auto-adjusted the TV cable. What should I check next? The old tranny shifted into 4th just fine with the same cable set up. Torque converter is also the same old.

 

Next, you need to borrow or purchase a Automatic Transmission Line-Pressure Gauge.
It need to read to at least 300 Psi... and you are going to need a very long hose for the gauge.

The best thing to do, is to install the Hose into the Line-Pressure Port on the Driver's side of the Transmission Case.
The port is just rearward of the Bell-Housing. There is a 1/8" NPT Plug installed into the Port.
Shown in the image below:



You are going to need a very long hose, so the hose can go from the Port in the Case...
all the way up to the Windshield.
Tape the Gauge to the outside of the Windshield, so that you can read the Gauge while driving.

You need to watch the Line-Pressure Gauge to see of the Pressure drops while the problem is occurring.
If the Line-Pressure does drop down low...
Post a reply here with the Line-Pressure reading while driving with no problem.
... and also the Line-Pressure reading while driving when the problem is occurring.

 

Thanks, sounds logical that this would be a line pressure problem, since all gears and lockup do work, the problem is when they engage. Will return with results.

 

Update: Today after some brisk acceleration getting onto the highway overdrive and lock just started working, no problem staying in gear anymore. I drove around town today, parked her for a couple hours in between, and everything works like it should. So apparently the rebuilt trans just needed some driving to get back into business. Hopefully it will last me for a long time now