View Full Version : OT could use your input on yet another tranny problem

09-03-2007, 11:03 PM
Hey guys -

I've got a 700R4 ('89) that has about 52,000 miles on it. It hasn't been shifting worth a darn because, at first, the TV valve was stuck. Then it didn't shift because the valve was leaking. (It was egg shaped and emerying it down to slide nice and easy resulted in a leaky valve and subsequently low line pressure)

I recently installed a TCI constant pressure valve body and the included .50" boost valve/sleeve. Along with the TCI valvebody, they also included a new improved servo and a new wiring harness that eliminated one of the switches that normally bolts to the valve body. Instead the switch that is installed on the valvebody had two terminals and one of those wires fed to the negative TCC switch and one postive lead went to the TCC switch.

Well today i drove it in 86* weather down the highway at about 70 mph (the speed limit here) and it was shifting great and crusing along. Well about an hour and a half into the trip fourth gear dropped out and it started smoking like crazy. I pulled over and, after letting it idle a bit, shut everything off. I could still hear the tranny fluid boiling in the pan. It sprayed a good bit out of the breather from what i can tell so i refilled the transmission and put it in "D" instead of OD and continued on my way at a much lower speed. It made it the rest of the way home with no issues but whats the deal with the overheating? Something wrong with the TCC? I followed the directions...

Also it has the stock depth pan. Does the CP valvebody tend to generate more heat? I would have thought it would decrease the heat by creating more positive shift and less slippage but i dont know. If thats the case maybe i need a deep depth pan and a cooler.

this is on an '89 3/4 ton chevy p/u - it was mostly empty, just me and a duffle bag and some tools.

and on a machining related note, :D
Anybody made there own oil coolers? I seem to recall someone making a cooler for compressed air but anybody have and expierence with transmission coolers?

<edit> thanks guys - before anyone gets ticked off at the OT, i did post this on a car tech forum but they generally take along time to respond and are not nearly as helpful as you all are.

09-03-2007, 11:59 PM
To start I'd have the transmission pressures checked for internal leakage.
Sounds like a pressure drop causing slippage.
Good Luck

09-04-2007, 12:18 AM
Oil does not boil, it just gets hot and then starts to smoke. If you can hear a boiling noise you either have water in the system, (not likely), or you have a lot of entrained air in the oil. Pump sounds like it is picking up air on the suction side of the system or valve body. Is the cooler in the rad functioning properly, no leaks water to oil, oil to water, plugged? Can you verify transmission temperature with an infrared thermometer or temperature indicating crayons. The smoke may have been from oil blowing out of the fill tube onto the exhaust.
Good luck, let us know how you make out.

09-04-2007, 01:38 AM
I dunno what the noise was but it sounded like boiling - even a few seconds after the engine was shut off. There's no water in the oil - or at least not enough to change the color at all.

I can try to check the temp some how - maybe i can find some crayons in the shop here.

And yes the smoke was from the spray of oil, the catalytic converter is right next to the tranny by the vent tube.

Thanks for the replies!

OH! And now it doesnt shift right - it holds first until about 4000 rpm. It had been working great ... now not so much. Its dark now but when its light again i will check the TV cable to make sure it hasnt broken or binding

09-04-2007, 02:56 AM
Hi again,
First gear is usually spring applied and oil released so if you are losing pressure inside you will still have first but may not be able have it release at the right time.

09-04-2007, 12:13 PM
Hmm you know i've read through three transmission books and poked around on the internet and no where did i find what you just said. Those are the kind of things that are good to know about a transmission but are never printed anywhere. I suppose a good manual would have it but the haynes ones suck.

jim davies
09-05-2007, 01:07 PM
I can't recall an auto trans that is spring applied/hydraulicaly released. The 4 speed torqueflytes use a system like that for the overdrive/direct clutch in the O/D section and then there is the old original single coupling hydro from 1939-56 but other than that...

FWIW, there is a recall on GM pickups with this trans which puts a piece of hose on the end of the vent tube and routes it to the other side of the trans to keep oil off the cat. Many of these pickups burnt up because of the original placement, especially when towing.

Your torque convertor clutch is locking up properly? If you drive in O/D at low engine RPM/high load with the TC clutch unlocked you will have exactly the type of problem you describe.
Bottom line for anything that uses a lockup T/C nowadays is it has to be working, or you'll have a bad day.

09-05-2007, 07:14 PM
Hi Jim,
You are correct, I was thinking Hydromatic. I went to school back in 1953 for Hydromatic transmissions at the armys Armored Center at Fort Knox Kentucky. They used them in the M24 tank at the time.
I am almost 75 years old and things have changed. I was thinking that the principles were the same.