Here's the situation: Brand new 4L70e from GM, 2400-2800 converter from GM, mated to a new LS3480 HP engine. The harness and computers are new from PSI conversion. I get a speed density tune from PCM of NC. There is no MAF, just a temp. sensor in the cold air intake. This is the 5th setup like this I've installed and never had a problem until this car. The engine runs good. I have no power to the rear wheels in any gear. This is with the trans. connector plug connected and not. On a flat level surface, the car rolls very slowly in reverse, even slower in a forward gear. Reving the engine has no effect on the speed of the car.

This is the third transmission and torque converter I've had in the car attempting to fix the problem. I've tried 3 sets of computers and 2 different wiring harnesses as well. The first two transmissions were 17 pin. I always used 15 pin trans. in the past, so switched to a 15 pin trans. now because people were telling me it was some type of incompatibility problem between the computers and the trans. I modified the original harness I bought to work with a 15 pin. I've since tried the second harness which was made for 15 pin thinking I may have incorrectly converted the original harness or something was bad with it. Still no work.

I've confirmed the flow through the cooler, checked the alignment of the linkage, and the fluid level. Fluid level starts off about an inch above the full line when cold, drops a below the full line when started, then rises to the full line when hot. Line pressures are ~85 psi in Park, ~130 in reverse, ~90 in neutral, ~115 in drive, ~105 in drive (without overdrive).

When installing all three transmissions, filled the converter with ~8 oz of fluid, mounted it on shaft, engaged in pump, confirmed with straight edge across face of bellhousing and measured distance to converter, installed trans., turned converter by hand to line up with flex plate, installed all three bolts, torqued to spec.
When I disconnected the trans. connector, I went through all the gears, still no power.
There are no strange sounds when the car is running. Sometimes when I shift back into park, there is a gear grinding noise. After a coupled of tests with one combination of trans./converter, harness, that noise did disappear, but it is back now with what's installed in the car.

I've read a few threads on various forums with the same problem as mine, but only one person circled back to disclose the problem (broken rear axle). I have a new ford 9" from Strange Engineering in the car with posi rear.

I've been in contact with the harness maker, tune provider, and local transmission shops. No one can figure it out. I have a call into GM performance parts.
So, any ideas on what the problem is?
Thanks in advance.

 

simply put...if it has no reverse or fwd at all...regardless if the harness is unplugged or not...you have something that cannot be blamed on the computer.

do you have the wrong spline axles for your 9" center section??

 

I was actually, recently called (by a technician at Chevy Perf. Parts) about a similar situation regarding an Engine and Trans purchased over the counter in NJ some time last year.
Where and when was this Power-Train Purchased?

Also Maroon Monster is absolutely correct.

 

Hmmm, I could check the axles. Wouldn't the driveshaft be turning though? With the car on jackstands and in gear. the rear wheels spin with the rpms going up with the engine speed increasing, but on the ground, virtually no movement.
The trans/converter was delivered to me from Eagle Chevy in Riverhead NY, on March 4, 2022.
How did the conversation proceed with Chevy Perf. parts?

 

yoke in far enough?

 

There is something wrong with driveshaft yoke or diff. Trans will have reverse and 3rd gear with wiring harness unplugged. The grinding noise that you hear when shifting back to park is the parking pawl tiring to stop the output shaft from turning, which tells me that something in the driveline is still spinning when the rear wheels are not.

 

I think bbond105 is right. Check out the driveshaft yoke to tailshaft fit.

 

I just reaffirmed what the others had said.

 

Doesn't this fact seem insane for it to be as simple as yoke/spline/driveshaft engagement?

 

you'd be amazed at what you can overlook when you buy something "new" and it's supposed to just "work"

You never even think to blame that part or look into it as part of the diagnostic checklist because you think it should just function because you paid a bunch of money for it.

 

But also on the other hand many new parts are blamed for being "bad" when actually its a totally missed diagnosis

 

NEW=Never Ever Worked

 

I can't wait to find out what the issue actually ends up being!

 

Thanks guys. Strange Eng. suggested checking spline counts and length of axles, so that is my next step after seeing if the driveshaft is turning. I built two cars last year with the exact same chassis and drivetrain. The first car was fine, this one not. I'm waiting for Strange to confirm if the axles ordered by the chassis manuf. were the same for both cars. Stay tuned.

 

The Phone Call that I received from GMPP/ Chevrolet Performance Parts...
was about someone who made a Purchase towards the End of 2021, in New Jersey.
(Not in New York, this Month).

So the Phone Call I received, could NOT be in relation to you.

 

The driver's side axle in the car is 5/8" shorter than it should be, so a new axle is being made and shipped to me. I don't see how 5/8" could be the difference between go and no go, but stay tuned. About 2 week lead time.

 

My wife says 5/8" can make a lot of difference.

(but seriously, hoping you get this all fixed)

 

You never mentioned if the driveshaft is rotating when you put the transmission in gear. LOL... Driveshaft must rotate to turn the axles

 

I installed the new axle, put the car in gear and she took off like a rocket. Problem fixed. Thanks for all your suggestions and help.

 

How in the world do you not notice the driveshaft spinning???! Maybe you want to check out the "posi" unit. If it is a good quality unit it should have gave the torque from the spinning driveshaft to the axle that was long enough to engage in the unit. Was this post a big joke?