I bought a used 'working' 4l80e from CL. The fluid was red-ish and there were no parts or residue in the pan so I was feeling good. I installed a Transgo HD2 kit in it. This is my third 4l80e trans that I installed a HD2 kit into, so I'm certainly not an expert, but I have had some experience.

The trans seems to work fine. BUT if I put it in D3 and then shift it back into D4, it makes an awful grind sound. Almost like the sound if you run the starter motor on an already running engine. The only way to get it back into D4 is to turn it off.

What can cause that noise? What could I have done wrong? Or was this trans likely screwed before I touched it? What area should I look for a problem?

thanks!

 

I don't know the 4L80E well, but if this was a 4L60E I would be confident that you had installed one of the longer valve body bolts into a position that takes a shorter bolt. Generally short bolts are used near the centerline of the trans.

NOTE: I've been corrected that the 4L80E does NOT have a valve-body bolt length issue. See below.

 

I would be looking at the overrun clutch assembly first

 

The valve-body fastener/ bolt length is not an issue for the 4L80E...
unlike the 4L60E, where it is an issue.

Start by following TruckDougs recommendation... that is a fine place to start to look.

 

I like threads that have closure. Thank you for the replies. Found my problem and it was dumb. I removed the trans and pulled the pan and found a perfectly clean pan and fluid, nothing on the magnet, filter like new! So after further debugging the problem turned out to be the junkyard PRNDL switch that i was using for the reverse lights and neutral safety switch. When moving the shifter from D3 to D4 it apparently started to bleed power from the reverse light power to the starter solenoid wire! The grinding noise i heard was the starter grinding on the flexplate. Arg, so much work for dumb stuff. The trans is back in the car (less the PRNDL switch) and working great!

 

That type of problem/ noise will usually present itself to you in short time.

The starter motor will eventually over-heat, start smoking, and seize (sometimes catch fire too).
Next time you go to start the vehicle, the starter motor will not move; and you will now know what the noise was...
as you will find a cooked starter motor. LOL!


When I design and build my custom Power-Distribution Systems for my customers (and my own vehicles) the starter motor will have a "Mega-Fuse" for the Cable to the Battery , and a "Maxi-Fuse" for the wire to the actuator.
I actually use "Mega-Fuses" for anything "High Amperage"... a 250A Alternator will receive a 300A "Mega-Fuse" in my Sealed PDM.