95 Bonneville, 4t60e Tranny...code 740

[jasoninva]

My car was throwing a check engine light. I had the car checked out and the mechanics found a leak in the throttle body, a hole in the EGR valve tube as well as dirty fuel injectors. They resealed the throttle body, replaced the EGR valve tube and cleaned the injectors ($300). Now the car runs quite well...no check engine light anymore. So everything was fixed...except for this transmission problem. I had a code pulled...code 740 ( "tcc circuit malfunction"). The car does fine when "cold"...the tcc locks up and stays locked up. There IS a hint of vibration/shudder though even when cold. The rpms drop at lockup like they should. BUT when the car heats up, the tcc just won't engage at all WHILE MY FOOT IS ON THE GAS. Overdrive does engage. The higher rpms cased by this tcc lockup failure make it just seem like its not in "od". (I understand the tcc lockup causes the rpm drop in "OD" in this transmission.) When I manually shift into regular "d"out of "od" WITH MY FOOT OFF THE GAS, the rpms jump up and stay up, telling me that od is working. It seems that the tcc, once it gets hot, is unable to lock-up unless I take my foot off the gas. Is this what the SONNAX parts manual calls "low converter apply pressure"? All in all, the manual says that this 740 code and these symptoms point to a bad TCC REGULATOR VALVE system( isolator valve, regulator valve and regulator sleeve) . The shop quoted me $485 total, 450 labor and 38 for the replacement kit. The old transmission has a warranty. I only paid 300 for the transmission, so it looks like this will cost me about 150 if MIDWESTAUTORECYCLING honors the warranty. I just wanted to get some opinions about my conclusion. They have ordered the kit #84754-01k from SONNAX. I want to make sure I'm spending money on the right solution. Am I right about my conclusion?

[maxwedge]

Guess work here, a trans function scanner will check it the tcc solenoid is functioning, if the line pressure shows boost and whether the tcc is slipping. This needs proper diagnosis first.

[jasoninva]

Fixed it with a simple radiator flush. Can't believe this. I discovered the guy I used to have work on my car put 100% antifreeze in it about a month ago, just before I got the tranny put in. Guess what...100% antifreeze messes up the thermostats ability to read temp accurately. The thermostat wasn't opening soon enough, causing a constant heat issue. The heat prevented overdrive from engaging....some sort of tranny safety feature. Now overdrive works, but I think theres a bit more to do. I need to find out the acceptable temp range for the car. What is an acceptable range before the thermostat actuates?...mine seems to be at about 210.