a343f not pumping fluid to cooler

[dogfishlake]

I went to do a transmission fluid exchange on my 97 with the a343f transmission and got zero fluid flow. A small amount dripped out when I unhooked the hose but that's it. I drained the oil in the pan after that, got my near 4 quarts and it looks pretty lousy and smells burned too. It has been shifting fine. I had an issue 2 years ago in CO from sitting idling for a long time in drive after climbing a long steep climb. When I went to take off nothing happened. I shifted to park, then through the gears and it moved but was slipping. It seemed hot, but after getting moving it was fine. I did several drain and fills in a row and all good. I have little doubt that I will need to service the transmission but I can't believe it shifts so well with no flow to the cooler. Is there a warm up bypass valve that is stuck closed pissibly? Not great info in the regular fsm and not finding any threads.

I was supposed to leave for Colorado today, but obviously this throws a wrench in the works.

Just trying to decide if I should keep looking for answers or start unbolting for a transmission swap real quick like.

Thanks!

 

[inkpot]

Which hose did you remove, and was the engine running?

 

[John McVicker]

Bummer @dogfishlake, no help at all but hope you get figured out in time to still make SAS2.

 

[dogfishlake]

Which hose did you remove, and was the engine running?

I took off the hose on the top of the cooler in front of the rad. After nothing there, i removed both hoses at the bottom of the radiator. Still no go.

There is a plug and some sort of sender/switch right where one of the lines comes off of the transmission. Not sure if that is a temp sender? Or peehaps a solenoid to bypase the cooler until the trans is at operating temperature? Wishful thinking.

 

[dogfishlake]

Bummer @dogfishlake, no help at all but hope you get figured out in time to still make SAS2.

Well it's definitely a kick in the rear but I'm still on vacation, have a couple of day window, and a spare transmission. It is in kind of unknown shape but I might be finding out real quick!

I figure I can R and I a transmission in a long day.

 

[John McVicker]

Agree, doable...be a whole bunch more doable with an xtra pair of hands tho. No matter what, it's a long day...wish you success.

 

[george_tlc]

Presumably a PO didn't bypass the cooler?

cheers,
george.

 

[dogfishlake]

Presumably a PO didn't bypass the cooler?

cheers,
george.

It looks to be original and properly routed. It's midnight hete and I'm spent so I will pick it up again in the morning. I have to believe that the pump is still working because the truck shifts fine. I always thought that transmission made a ton of heat, and now I know why! Shame on me for never doing more than drain/fill with oil changes.

Tomorrow I'll pull the lines at the trans and look for a blockage.

 

[flintknapper]

Had a similar problem recently with my 99 LX (same transmission) high temps but no shifting issues.

I would recommend you do what I did. Disconnect both lines from the radiator cooler (located at bottom of the radiator, one on each side). Blow air (low pressure) through the fittings on the radiator and check for blockage/obstructions. IF fluid comes out freely...along with the air...then you should be good there.

Next blow each disconnected line back toward the transmission (low pressure, shouldn't take much, just enough to tell if you are moving air through the lines). IF you detect no obstruction there...then move on to the A/T cooler itself. Disconnect the two rubber hoses (they will be tight). Blow air through the Cooler and check for obstructions (most likely it will O.K.) but this will confirm the cooler itself is not blocked.

Last...blow both lines that you had disconnected from the cooler, this is where I found my problem.

One line was clear...the other was moving no air. I increased the air pressure on that line and it finally cleared with a 'whoooosh' sound... and I heard something fall into the metal catch pan I had below the line.

It was a damn 'shipping plug' of some type. Just the right size to barely fit into the rubber line. How it got there...I don't know...but it did. It looked like a plug that might been where the dipstick tube inserts.

I'm not suggesting you will find the same thing, but you need to carefully check the entire fluid circuit to be certain fluid CAN move through it. Because other than blockage...your transmission pump is the only other thing that can cause the issue. And your transmission wouldn't shift well (if at all) with low line pressure.

A343F Trans & ScanGauge II what are your temp readings?

 

[dogfishlake]

Had a similar problem recently with my 99 LX (same transmission) high temps but no shifting issues.

I would recommend you do what I did. Disconnect both lines from the radiator cooler (located at bottom of the radiator, one on each side). Blow air (low pressure) through the fittings on the radiator and check for blockage/obstructions. IF fluid comes out freely...along with the air...then you should be good there.

Next blow each disconnected line back toward the transmission (low pressure, shouldn't take much, just enough to tell if you are moving air through the lines). IF you detect no obstruction there...then move on to the A/T cooler itself. Disconnect the two rubber hoses (they will be tight). Blow air through the Cooler and check for obstructions (most likely it will O.K.) but this will confirm the cooler itself is not blocked.

Last...blow both lines that you had disconnected from the cooler, this is where I found my problem.

One line was clear...the other was moving no air. I increased the air pressure on that line and it finally cleared with a 'whoooosh' sound... and I heard something fall into the metal catch pan I had below the line.

It was a damn 'shipping plug' of some type. Just the right size to barely fit into the rubber line. How it got there...I don't know...but it did. It looked like a plug that might been where the dipstick tube inserts.

I'm not suggesting you will find the same thing, but you need to carefully check the entire fluid circuit to be certain fluid CAN move through it. Because other than blockage...your transmission pump is the only other thing that can cause the issue. And your transmission wouldn't shift well (if at all) with low line pressure.

View attachment 1758179

That's crazy. Cool you found it. My radiator is new and I had both lines unhooked up by the front of the engine. There is certainly the chance of a blocked front to back line though so I will check that in the a.m.

Thank you!

 

[Tools R Us]

I'm not a transmission expert, but this is the way I recall it being explained: The cooler flow is basically bypass, the pressurized fluid does work in the transmission, if there is any left, it goes to the coolers. This is one of the reasons that turning up system pressure is good, more cooler flow makes better cooling.

There are two ways to increase the pressure, adjusting the "kick down" cable, it controls the progressive regulator and turning up the main pressure regulator. The first thing I would try is; pull the kick down cable and see if there is more flow. Don't know if that is the problem, but is a simple test.

Improving Transmission Shifting

 

[dogfishlake]

I'm not a transmission expert, but this is the way I recall it being explained: The cooler flow is basically bypass, the pressurized fluid does work in the transmission, if there is any left, it goes to the coolers. This is one of the reasons that turning up system pressure is good, more cooler flow makes better cooling.

There are two ways to increase the pressure, adjusting the "kick down" cable, it controls the progressive regulator and turning up the main pressure regulator. The first thing I would try is; pull the kick down cable and see if there is more flow. Don't know if that is the problem, but is a simple test.

Improving Transmission Shifting

I read that thread back when you made it, very cool. I forgot to mention that I had done the transgo kit (on high perf setting) a couple of years ago. It shifts very hard now. If I did it again I'd drop to the middle setting.

I pulled every line apart and put a hose on each section and can blow air through them easily, including the coolers. I dropped the pan and the screen looks clean and all looks good in there. Before dropping the pan I fired up the truck and pulled the cable wide open while idling, still nothing. Revved it up pretty high, still nothing.

I am getting closer to just swapping in my spare trans. PITA but gotta-go-to-Colorado!

If I do that I am going to do the same to my spare trans that you show on your thread.

 

[Zjohnsonua]

Whatever happened with this trans, Pat? Did you sort it out?

 

[RivMan]

Whatever happened with this trans, Pat? Did you sort it out?

I own this truck now.

After looking back at Dogfishlake's old posts, he did end up swapping the trans and running to Colorado with the new one. I hadn't heard if he found an issue with the original or not.

-Rob