chris99gmc

I have a re-built 4L80e that I did myself about 2 years ago. The transmission has about 15k on it and hasn't skipped a beat since day one. As far as the details on the build went, I installed a brand new valve body, the stiffer shift 'feel' spring(have a stall), Hi energy BW frictions and Bandd, new roller clutches, seals, bushings, etc.... I did the Transgo shift kit, without the pressure relief portion of the kit. I also did the dual feed mod for the center support, machined aluminum TH400 pistons, Sonnax Line to Lube valve, billet reverse servo.. This is all based on memory so I could have missed something.

The trans has always had higher than normal pressure. It isn't terrible, but I know it should be less. I have anywhere from 75 to 85psi in gear and at idle. Close to 200 at WOT in gear. When I hear the noise, it sounds like a definite pump whine and It only happens in 1st gear. doesn't matter where the gear selector is... If I shift to manual 2nd, the noise goes away. I hear the noise more prominently when the Truck is warmed up and sitting in traffic. Trans temperature is within normal range.

Any ideas what it could be or any areas I should check out? I plan to pull the pan and turn down the EPC just a touch here pretty soon. I just want to make sure I get everything looked over while I'm at it.

vorteciroc

From what you have stated thus far...

It seems that; you are hearing a whining sound that is most prominent when the vehicle is warmed up, and stopped in gear at an idle... as well as accelerating from being at a stop while the automatic transmission is in first gear... once the transmission shifts to second gear, the noise stops.

When a whining noise can be heard from an automatic transmission; the following would usually be one of the more common causes...

-Automatic transmission torque converter damaged, or contains a worn thrust bearing/ torrington bearing. (usually this is heard under heavy engine load)
-Automatic transmission pump assembly worn/ damaged/ creating cavitation due to low fluid level/ or creating incorrect pressure. (usually this is heard with increased engine/ vehicle speed)
-Automatic transmission filter-pick up/ vent damaged/ obstructed/ or sucking air. (other than damage or fluid level is very low, this is usually heard only under hard acceleration or wheel standing)
-Automatic transmission planetary gear set severely worn out/ thrust bearing worn out (usually heard near peak acceleration and more so on hard deceleration)

The way that the transmission line pressure is evaluated from GM for the 4L80E is based on the corresponding amperage of the electronic pressure control solenoid (also referred to as a variable force motor)
Here are two examples at far opposite ends of the spectrum:
- 0.0200 Ampere = 157.00 Psi - 177.00 Psi
- 0.9800 Ampere = 35.00 Psi - 55.00 Psi

Unless you possess access to powertrain scan tool, the above information will not be of any value to you... I'm sorry.

According to GM, ATRA, and ATSG The minimum transmission line pressure in Park, Neutral and forward drive ranges should be over 35.00 Psi when completely stock (This is too low for me personally)
According to GM, ATRA, and ATSG The minimum transmission line pressure in Reverse should be over 67.00 Psi when completely stock (This is too low for me personally)

I am assuming that, when you measured the transmission line pressure... The gear selector was in Overdrive and the readings were between 75.00 Psi and 85.00 Psi at an idle? If so, that is fine.
200.00 Psi is a healthy maximum line pressure.
For this transmission in particular (as well as the GM THM400/ 3L80) be careful of excessive line pressure in the reverse gear range. Many builders; including myself, delete the reverse boost circuit in this transmission (and the THM400/ 3L80) when increasing the line pressure.

I have some questions for you...

What year and model are your vehicle? what engine is installed?
What year is your 4L80e automatic transmission; if not original to the vehicle?
What is the make and model of the toque converter?
What is the advertised stall speed of the torque converter?
What RPM do you feel the torque converter engage the transmission compared to the advertised stall speed? Lower/ Higher... what RPM?
What automatic transmission fluid is being used? I am assuming the ATF was new 2 years ago/ 15,000 miles ago after completing the rebuild?
What is the condition and current level of the ATF?

What is the ATF pressure in all the ranges at idle? You gave me the Overdrive range i believe?
If you can mount a gauge temporarily; what is the ATF pressure in comparison while driving/ accelerating? I would like to see if the pressure does something strange when driving and the noise occurs.

Does the noise occur while the vehicle is warmed up and stopped at an idle with the gear selector in the first gear position? ...instead of in the overdrive position.
Does the noise occur while accelerating from being at a stop with the gear selector in the first gear position? ...instead of in the overdrive position.
Does the noise ever occur during a second gear to first gear downshift when accelerating abruptly from a 15 to 10 MPH roll?

Are there any other driving scenarios that have caused the noise to occur?

chris99gmc

Thanks for the detailed response.

To answer your questions, The vehicle is a 2000 GMC Sierra(in sig). The motor is a Lq9 iron block with a 408 kit. .050 bore. Stage 3 heads, headers, Mild cam. The Transmission has a circle D 3200 single disk stall. I installed a brand new OEM GM valve body when i built the trans. I used Hi energy BW frictions, new steels, replaced all the seals, and bushings, did the dual feed mod, Transgo kit without the pressure relief valve spring modification to the seperator plate, I have a TruCool 40,000 cooler in series with the stock trans cooler. Running braided -6an cooler lines. I have installed an inline Micron filter on the line going to the cooler. I had considered the cooler line being a possible restriction, so I bypassed the coolers temporarily but saw no change..

When the noise comes on, its only in first gear. I have manually shifted to 1st gear Low and the noise was still there. It immediately stopped when I shifted to manual 2nd. The noise in first gear is most prominent when the truck is warmed up and happens in 1st gear regardless of where the shift selector is in manual Low, Drive or Overdrive. The noise is only heard when in motion at low speeds, but not at idle.

I have a temp pressure gauge hooked up to the service port of the trans. I have noticed anything that appears to be unusual with the pressures(but i'm not a professional builder, so I could be missing something)

madmann26

When I did my 80e swap in my truck, I had a local builder build it his way with only one requested modification, internal dual-feed mod.

It has had the 1st gear whine since day 1. I attribute it to the straight-cut gear set vs the helical gear set which is supposed to reduce/remove the whine. Like yours, mine has never missed a beat. I have no abnormal trans temps or pressures either.

Others will disagree.

vorteciroc

Do you ever here the noise in reverse?

Anyway, If I was in your shoes...

I would be removing the unit to examine the two rear planets and measure rear section end-play.

This is the sort of thing, that i believe most people just let go until a more significant problem occurs...

It is up to you of course.

madmann26

Mine does not whine in reverse.

I’ve had it the truck for 14 months now, roughly 15k of not so easy driving.

I’ve read enough to know that plenty of folks just let it go and I believe there was even a TSB about it at one point.

Some folks also report it happens in 2nd and 3rd.

I think the reason it doesn’t concern me is my builder gave me a 2yr, 24k warranty, in writing.