4L80 transmission shifts hard when at operating temperatures

Hi guys!

Suburban 2500LT owner from Norway here. Bought myself a 2000 Suburban 2500LT December of last year. Main issue, among many, is that when the transmission is at normal operating temperatures, like driving for +/- 20km, or 12 miles in freedom units, without any load like a trailer or in the car, is that it shifts REALLY hard from 3rd to 4th. It might do this between other gears as well, but 3rd to 4th is the first and most noticeable. I have not done anything to the transmission other than add some stopleak-stuff/gasket renewer because of a, well, leak, which has stopped. The transmission did this before I added the stopleak so I don't think this is the reason for the hard shifts. Anyone here experienced this before? Is the transmission shot, or could this be an easy fix?

I'll try to add some pics of the 'burb below, don't kill me if they don't show up on my first post :-D



With wintertires/rims, summertires are 285/55R20's (might add pics later)



Changed every bulb in front to LED, never tried the headlights in traffic yet, since this part of Norway has basically almost sunlight all the time this part of the year. (So I don't know if they blind oncoming traffic or not ;-D )
The DRL's/park lights are switched out with switchback-leds, so both operate as DRL's and turnsignals.
(Believe me, the 4 extra lights in front makes everything look like daylight when it's dark outside)



Edit: The car has +/- 176000 miles on it, and to my knowledge this is the original transmission.

Have you scanned it for code? Hard shifting is often because the ECU commands high line pressure (due to an electrical issue or some valve body issue). A common issue on these transmissions if the electrical harness that lives under the pan. You can remove the big case connector, and with the aid of a pin-out diagram, check resistance for the circuits and see if everything is within specs.

Nice rig and welcome to the forum from Texas!

Hi, and thanks for the swift reply!

No, I have not scanned it yet since I don't have a scantool, yet... I was planning on checking the connector, saw a few youtubes where oil leaked into this one and caused all sorts of issues. Let's say I don't care about the hard shifts and they are caused by some ECU-command because of a false/wrong signal, how damaging is this for the trans?

Regards!

VH2K said:

Hi, and thanks for the swift reply!

No, I have not scanned it yet since I don't have a scantool, yet... I was planning on checking the connector, saw a few youtubes where oil leaked into this one and caused all sorts of issues. Let's say I don't care about the hard shifts and they are caused by some ECU-command because of a false/wrong signal, how damaging is this for the trans?

Regards!

Click to expand...

How much do you drive the truck? Like how many kilometers per month?

The way these transmissions work is: the pump pressurizes the fluid and the EPC regulates the pressure DOWN, to specified levels. It's a fail-safe design so such that, if there's a fault, it commands line (maximum) pressure, instead of the other way around where a failure will leave you with NO pressure.

It's not ideal to run it like this because it causes unnecessary shock to the internal components. In extreme cases, it can blow out case lugs, seals, drums, etc. and cause damage to hard parts. Will that be your situation? "probably" not, but there is that risk...

Yes, do the easy tests first. Those harnesses are currently around $75 here, and not that difficult to replace after dropping the pan.

stutaeng said:

How much do you drive the truck? Like how many kilometers per month?

The way these transmissions work is: the pump pressurizes the fluid and the EPC regulates the pressure DOWN, to specified levels. It's a fail-safe design so such that, if there's a fault, it commands line (maximum) pressure, instead of the other way around where a failure will leave you with NO pressure.

It's not ideal to run it like this because it causes unnecessary shock to the internal components. In extreme cases, it can blow out case lugs, seals, drums, etc. and cause damage to hard parts. Will that be your situation? "probably" not, but there is that risk...

Yes, do the easy tests first. Those harnesses are currently around $75 here, and not that difficult to replace after dropping the pan.

Click to expand...

Usually I only drive it like 9km, or 5.5 miles, to and from work, and this never happens. It's only when the trans reaches operating temps. According to the needle in the dash this never exceedes mid-point (even when towing heavy-ish loads), i forget what that is, but like 90-ish degrees C, or 194 degrees F(reedom)?

If I get a hold of a scanner, what codes would I be looking for? Is this car advanced enough so that it would remember what codes it was throwing yesterday, say?

Do you know or have a list of codes that would be useful? (Me coming from VW and an OBD11 scanner which really functions great for DIY'ers)


Again, thanks for the quick reply!

Welcome to the forum, from Oregon.

Make sure that the scanner you get will do transmission codes as well as engine codes.

ORVietVet said:

Welcome to the forum, from Oregon.

Make sure that the scanner you get will do transmission codes as well as engine codes.

Click to expand...

Scanner suggestions?

VH2K said:

Scanner suggestions?

Click to expand...

Check out the possibilities from Autel, Foxwell and Top Don. If you want to just pull codes, would be pretty inexpensive.

Then you can branch out to Live data and Bi-Directional choices. ABS brake bleeding is another "want".