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Discussion Starter · #1 ·
Basic info ---Gen IV 5.3L Vortec from 2013 Silverado, 6L80 Trans. BP Automotive Harness and PCM flash

Finished the rolling chassis build and ready to check before replacing body.

Started engine, everything looked good. Good oil pressure, no leaks, steady idle. (sounds great!)

However, when I tried to basic check the transmission –

Put the rear axle on stands. Started the engine. Put the transmission in reverse. Absolutely no movement on the transmission output shaft. Slowly increased the throttle, no movement on the output shaft, and the RPM didn’t reduce when I “lifted” the throttle’. Slightly pressed the throttle a couple of more times with the same result – RPM went further up, but not down with throttle release. Never any output shaft movement. This was the same in “Drive”.

For this test, the “brake on” wire to the PCM was grounded.

I checked the connector to the transmission and it was well seated and all the pins and sockets were intact, not damaged.

The Engine, Transmission, PCM and drive by wire throttle are a “mated pair” never separated.

Any insight into what could cause this behavior??

Yes, I’m asking BP Automotive the same question, but thought the forum might have independent experience with this.
 

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does the trans have enough fluid in it???
 
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Discussion Starter · #4 ·
Thanks for your quick reply - all help is welcome
William56 - The engine and transmission were never seperated after removing from the donor.

Hotrodg726 - I checked the level a couple of weeks ago, but static (engine wasn't running at that time) Level looked good, but you may be onto something. I was all too happy that the engine was running to remember to check the trans fluid again. I'll check first thing tomorrow. Again, thanks for the wake-up. Even if it doesn't solve the problem, I shoud have slowed down and checked.
 

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Level looked good, but you may be onto something.
Engine off, the level should show over full, if the level is actually where it should be, to begin with.
 

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Totally agree on low fluid being the most likely issue. I had the exact problem you have, and the cure was easy.
Regards, Doug
 

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Discussion Starter · #7 ·
Once again, thanks for everyone's input. I'm also pretty sure it is a fluid level issue. I won't be able to verify until Monday but, looking back,I checked all the fluid levels while waiting to get the chassis into the shop for the exhasut - last step before starting. I had to postpone fully checking the transmission until the engine runs. Got excited about the engine running finally running and totally had a mental lapse (not unusual these days) about refilliing the trans before testing. Let everyone know Monday.
 

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That is one reason to make a list either on paper or a white board so you don't forget the little things. A simple mistake can ruin something expensive real quick.

One reason I say to make sure the swap is 100% complete before starting it. The "hear it run" deal before motor and trans install is DONE, will end up causing yourself WAY more headache in the end, seen it happen for years with guys getting in a hurry.
 

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Well when it came from donor did you pull it or was it a yard. Most yards drain fluids. And then put pans back on. Guess what else they do. Toss the trans filter. Make sure it’s in and make sure it is seated. Had one fall out of hole. So fluid was full but no pickup from bottom of pan no pressures no shifting.
 

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Discussion Starter · #10 ·
Thanks for the warning. Info like that can be valuable. In my case the engine and transmission were still in the donor truck and was run for me before removing. The tranmision was basicially drained by cutting the cooler lines at the radiator. After putting the engine on the new chasis, I topped off all the fluids. I put transmissin fluid in until i could see it on the dipstick, but planned to fully fill it after the engine was running so I would know the true level.
 
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