TH400 questions
 

I have a couple questions about fluid pressure and routing in the th400 trans I'm hoping you guys can answer.
The outlet line to the trans cooler does that come straight from the pump? And what is the psi range there?
The inlet back into the trans from the cooler where does it head to in the trans?
And last questions the fluid going into the converter where does it come from? Is it from the trans cooler return?

I don't know, but I use to have a fluid flow schematic and if I can dig it out I will post it.

This might help..

The outlet line to the trans cooler does that come straight from the pump? And what is the psi range there?

I tested my feed line to the cooler this pass summer and I was around 60 psi hot as I can remember. From what I understand, high pressure on this line is a no no. In Cliff's book page 94 talks about reducing the size of the converter feed hole in the pump on performance builds. I think I drilled mine out to .125

Here is a good read. https://www.sonnax.com/tech_resource...-lube-circuits

I never drilled the pump for increased feed.
Cooler line should be in the 25-45PSI range, but i suppose 60 can happen.
Hot fluid exits Case cooler line from Converter. Cooled fluid enter TH400 Case and routed for lube, and dumps to pan.

Cooler line fluid in not use in valvebody controls nor clutchpacks.
However if a converter sprag grind aluminum powder then than silver powder gets everywhere.

I never drilled the pump for increased feed.

I didn't drill the pump for increased feed. It was restricted with a threaded plug then drilled out to .125 to reduce converter fill.

1 more question I'm assuming as rom rises the pressure to the cooler rises as well? Is there a max pressure going from trans to cooler that you don't want to exceed?

Naw. For example the regulated Front Pump "shifts" to 60 PSI during 3rd gear cruise.

Cooler line PSI is varied by how much Converter TQ-Multiply is goingk on.
WOT with non-slip Slicks would be the worst case cooler line PSI.
Eh, I suppose Reverse Gear with WOT and Slicks would be thee worst.

So pump output isn't based on rpm? It's controlled by a regulator? So output psi to cooler in first 1st gear should be same ar 1000rpm vs 3000rpm in 1st?

Yes, pump output (volume) is based on RPM.

Although the TH400 pump is "positive displacement" it doesn not create pressure, just flow.

Pressure is created by resistance to flow.

Pump output is far greater in the TH400 than the fluid paths available to it. So pressure on the output side of the pump is controlled by the PR valve.

The cooler supply line is one of the fluid paths available so output/flow would increase with RPM. Any pressure seen in the cooler supply or return lines would be created by resistance to flow. Since it's not a problem area with the TH400 most folks don't worry about the pressure or even check it.

I recommend reducing the feed hole size for the converter supply simply to make sure we don't use the converter like a huge apply piston and put forward pressure on the engine thrust bearing. Several schools of though (opinions) out there on that deal but we know for sure it does NOT effect converter or transmission function in any way so why not do what you can to protect your engine?

I'd also add that many transmission shift "kits" come with parts to install on the PR valve to raise line pressure which only further increases the potential for problems in that area........