Baffling Problem - Engine Revs Truck Does't Move

[swathdiver]

When it revs and doesn't go anywhere in gear, that's usually the torque converter or the pump.  My vote is the pump since it runs for a little bit and then dies.  A good scan should be able to see this, a Tech-2 or equivalent.

[Marleay]

I thought maybe the torque converter originally but the guy at the transmission shop said that torque converters either work or they don't - I wouldn't be able to drive for 2-3 minutes and then it start free-wheeling. He suggested checking for flow at one of the cooler lines.

 

One thing to add is that if I start the truck and leave it to warm up for a couple of minutes and then get in to go it will be already in the free revving mode and won't move. Seems more like a time based problem than a driven mileage one.

[Supreme Pizza]

I had a 78 Camaro once. I know..... Fascinating right.??? Anyway, the trans was shot, so I throw'd another one in there. After that the used transmission that I installed worked great, until it warmed up for a few minutes. Then reverse would slip worse and worse until it didn't work at all. Once it cooled off - reverse worked fine. Something about bad seals allowing hot trans fluid to slip through better than cold fluid bla bla bla. . All in all, it sounds like your truck has a problem, then another problem, and then another problem. Then it started running really bad, and then it started running worse. Then it ground to a halt, and just would not go anymore. Then you get a phone call about "something is wrong with my truck, it doesn't go anymore when I push on the "go peddle".... 

[Marleay]

Yeah fascinating.

[swathdiver]

On 12/20/2021 at 2:13 AM, Marleay said:

I thought maybe the torque converter originally but the guy at the transmission shop said that torque converters either work or they don't - I wouldn't be able to drive for 2-3 minutes and then it start free-wheeling. He suggested checking for flow at one of the cooler lines.

 

One thing to add is that if I start the truck and leave it to warm up for a couple of minutes and then get in to go it will be already in the free revving mode and won't move. Seems more like a time based problem than a driven mileage one.

That's why I'm leaning towards the pump.  

[Marleay]

To wrap this post up for future reference: the apparent problem after changing out the oil sensor without any change to the original issue was a clogged transmission filter. 
 

Although the fluid level was ok, colour seemed good and did not smell burnt - when we dropped the pan to drain the transmission fluid we found a clogged filter. 
 

When the filter was replaced and new ATF was put in the truck is now running normal. 
 

The MAF sensor solved one problem. The oil pressure sensor solved another but it was a lack of regular transmission maintenance that caused the now not-so-baffling issue. 
 

Thanks for the help. 

[Supreme Pizza]

Can you please upload a picture of a plugged transmission filter? Can you also show a picture of the inside of the filter, by disassembling the filter? I would like to have it for reference, in case I see a similar problem in the future.

[Marleay]

Sorry no pictures of the filter.

 However the main clue was how heavy the old filter was - as if it was full of sand, for reference sakes.

The bottom of the pan had sludge from the plates.