Howdy everyone,
Got a interesting issue with the th400 on my 71.
During the winter months I replaced the unknown valve body/shift kit installed in the th400 with a TCI streetfighter.
I also replaced the kickdown solenoid and vacuum modulator.
She actually runs great except for an occasional 1-2 shift up/down confusion, I believe is from very light acceleration.

The question I have is, if I take her out on the freeway everything is fantastic unless I cruise at about +70 mph and the rpm is over 3K she starts puking fluid at about the 15 minute mark into the cruise.
I drive her all around town, aggressive and wot occasionally without any fluid leaks
The leak appears around the front right area (filler tube/vac modulator/coolant lines/breather).
I confirmed its not a front pump seal or anything related to the pump.
I have confirmed proper fluid level
As we know its a PITA to check the coolant lines, and I would expect either to leak regardless of rpm and I didn't touch them during the valve body replacement. (idr tighten them anyway)
I took off the replacement vac modulator and inspected the o-ring
Doesn't look like fluid burping from the breather, tried sticking a stiff wire down the breather tube and it only goes a few inches...
Looking for some ideas?

Thanks in advance!

 

It kinda sounds like the fluid is overheating and the fluid is coming out of the vent. What is the stall speed of your converter? Are you using an additional trans cooler? I would also do a close inspection of the cooler lines and make sure one of them isn't crimped/bent to the point that it is restricting flow.

 

2500 stall, external cooler. fluid lines look great and had no issues for 2 years since I've owned it?
I see no evidence of fluid coming out of the breather... if it was blocked would pressure build or is the filler tube also serve as a breather?

 

Isn't the most heat created under stall speed or I am thinking backwards?

 

Heat is created when "work" is being done by the transmission. Constantly running over 3K rpm is a good way to generate LOT of converter heat. I'm wondering if your external cooler is big enough for the extra heat. If you have an infra-red (IR) temp gauge, check temperature at the input end and the output end of the external cooler immediately after you make a fast stop at the side of the highway after running 70mph for several minutes. If the outlet temp is significantly higher than 210F*, you may need a larger trans fluid cooler.

I should have asked if the external cooler was placed in series with the trans side-tank on your radiator, or if you have ONLY the external cooler in the loop?

 

Great questions, external in front of radiator, and I have spot checked the temp in and out at the radiator with a ir gun and if memory serves me it was like +-160 after cruising around for an hour throughout the streets and such. It really makes little sense I can cruise at 55 mph, wot and cruise to my hearts content. Get out on the freeway and let her go above 65, she pukes in 15 minutes.
It never happened until a new valve body, kick down solenoid, vacuum mod and a fluid drain...

 

Your symptoms lead me to believe that the anti-collapse spring inside the lower [suction] radiator hose is either missing or has been rusted away over the years. If that lower hose is the stock 'smooth' type (not a corrugated design which can't collapse), it NEEDS that spring to prevent the hose from collapsing when the pump rpm's are high [like at highway speeds].

When your car is fully warmed, you can open the hood and watch the lower hose as you manually work the throttle linkage. As you get the engine up to about 2500-3000 rpm, if the hose shows signs of collapsing, that is likely your problem.

 

Does the fluid look foamy when this happens ? Maybe let it puke out what it wants then DON’T refill . Test drive and see if the problem goes away . Sometimes the factory full mark is too full on hard working vehicles like a Motor Home or your stall speed and foaming from oil getting onto the Planetary Gears or leaking fluid . Trans Go has a article about it and suggest scribing a new full mark . Myself I’ve driven a 5000 stall Converter on street over 15 years and never had a transmission get warmer than 200 degrees

 

Check to see if the vent is plugged. More than likely, plugged vent would puke out the dipstick tube. If it pukes around the dipstick tube, there may be an Oring problem.

Steve O.

 

After your 15 minute drive, is the dipstick still fully seated or is it pushed up some? A blocked vent will cause this.
Where in SE Mich are you at?.....I am from Clarkston.

Jebby