6L90 Transmission Decision

P

Phishin

Joined
May 1, 2012
Messages
2,981
Location
Indiana
2018 Silverado 3500HD with 6.0L gasser and 6L90 Transmission. Truck has 155k miles. Meticulous maintenance. Runs like new.

Do you think I should consider replacing the problematic OE torque converter with a billet unit now before it fails or just carry on and see how long I can go with the stock transmission?

I plan to own this truck forever.
 
Letting a 6L80/6L90 converter go nuclear is why it gets so expensive, I can refresh a good unit for $3,000 out the door.

*Billet Front Twin Disc converter
*Sonnax Zip Kit
*New bonded pistons & seals
*All Bushings (Durabond)
*Replace pressure switch membranes
*Spacer plate & checkballs
*OE Borg Warner frictions
*Flush the coolers
*Valvoline Maxlife LV fluid
*Service the T-case
*Tune the TCM with HP-Tuners (TCC scheduling)

At the very least have a billet front converter & a Sonnax Zip Kit installed.
 
If going through the hassle of dropping the transmission to replace the converter then at that point you might as well consider the mileage and decide on finding a reputable shop perform a rebuild with all of the updates especially since you intend to keep it forever.
 
This combo is what my old work truck had in it, and personally I though it was great. My vehicles with the 6L series transmissions also get tuned and I disable commanded TCC slip, only let it apply in gears 4-6 in standard and 3-6 in tow-haul mode. I also modifiy the TCC ramp rate table to bring the converter on faster and harder to limit apply time slip. Clinebarger helped me a few years ago when I was learning what to do to save these units, so all his advice is spot on.
 
Phishin said:
2018 Silverado 3500HD with 6.0L gasser and 6L90 Transmission. Truck has 155k miles. Meticulous maintenance. Runs like new.

Do you think I should consider replacing the problematic OE torque converter with a billet unit now before it fails or just carry on and see how long I can go with the stock transmission?

I plan to own this truck forever.
Click to expand...
Just one data point. My 6L90 behind my 6.0 on my 2008 3/4 ton Suburban has 260,000 miles. It gets a pan drop every 50,000 miles. Used to tow a 9,000 lb trailer but not any more. The fluid stays a bright red.
 
Phishin said:
2018 Silverado 3500HD with 6.0L gasser and 6L90 Transmission. Truck has 155k miles. Meticulous maintenance. Runs like new.

Do you think I should consider replacing the problematic OE torque converter with a billet unit now before it fails or just carry on and see how long I can go with the stock transmission?

I plan to own this truck forever.
Click to expand...
What's the problem? Have you scanned the transmission computer for codes?
 
Furious said:
If going through the hassle of dropping the transmission to replace the converter then at that point you might as well consider the mileage and decide on finding a reputable shop perform a rebuild with all of the updates especially since you intend to keep it forever.
Click to expand...
That’s a good point. There certain upgrades that can be done to the 6L90 as recommended by Mr. Clinbarger and also in some good Videos on it.
In my case I made it to 260,000 miles with very little clutch material in the pan. The problem now is a rebuild might exceed the value of the vehicle.

There are some things a person can watch for. Drop the pan and look at how much material is on the magnet. If it’s quite fuzzy, you might go for the rebuild and hope most of the hard parts are in good shape. If it has actual metal on the magnetic better get it into the shop. I also cut open the filter with garden shears to see what's in it.

Another telltail might be a delay in the transmission going into reverse. Maybe Mr. @clinebarger can comment if that is a valid sign of an impending failure. Thoughts?
 
Last edited:
Snagglefoot said:
Just one data point. My 6L90 behind my 6.0 on my 2008 3/4 ton Suburban has 260,000 miles. It gets a pan drop every 50,000 miles. Used to tow a 9,000 lb trailer but not any more. The fluid stays a bright red.
Click to expand...

How do the magnets look and what fluid are you using?
 
martinq said:
How do the magnets look and what fluid are you using?
Click to expand...
Here is what I came across during my pan drop on my 6L90 in 2021. Click on sub title to see the pics. Enjoy.

Snagglefoot

Post in thread 'post your latest transmission lubricant change.'

Chev 6L90 in my 2008 3/4 Burb. Dropped the pan, cleaned the magnet and changed the filter. Filled wth 6 litres AC Delco Dexron 6. The pan was very clean with only a bit of debris. On this 3/4 ton I was able to pull the pan without interference of the exhaust cross over. About 215,000 miles. Original transmission and torque converter. Was doing a pan drop and flush every 50,000 miles at dealer until 150,000 miles, then pulling 3 quarts and replacing once per year last several years. First pan drop in 5 years. I did the work at U Wrench in Calgary using one of their rental hoists. One photo...
  • Like
 
Snagglefoot said:
Here is what I came across during my pan drop on my 6L90 in 2021. Click on sub title to see the pics. Enjoy.

Snagglefoot

Post in thread 'post your latest transmission lubricant change.'

Chev 6L90 in my 2008 3/4 Burb. Dropped the pan, cleaned the magnet and changed the filter. Filled wth 6 litres AC Delco Dexron 6. The pan was very clean with only a bit of debris. On this 3/4 ton I was able to pull the pan without interference of the exhaust cross over. About 215,000 miles. Original transmission and torque converter. Was doing a pan drop and flush every 50,000 miles at dealer until 150,000 miles, then pulling 3 quarts and replacing once per year last several years. First pan drop in 5 years. I did the work at U Wrench in Calgary using one of their rental hoists. One photo...
  • Like
Click to expand...

Yep, the magnet was definitely doing its job and the pan / fluid looked extremely clean. Good job!

If that was mine I'd be tempted to add magnets (for the fun of it) and reuse the fluid after a pan drop. Did you ever notice any changes after a fluid change?
 
martinq said:
Yep, the magnet was definitely doing its job and the pan / fluid looked extremely clean. Good job!

If that was mine I'd be tempted to add magnets (for the fun of it) and reuse the fluid after a pan drop. Did you ever notice any changes after a fluid change?
Click to expand...
To tell the truth I never noticed any change. The old fluid was a slightly darker red but the way it operated did not change.
 
Is there anyone else out there who wants to report on their 6L90’s longevity. Mine has lasted 260,000 miles with a lot of light duty rural driving, some towing in the past but not anymore. Coincidently I have just noticed it sometimes takes a full two seconds for reverse to engage. That is with the transmission cool. Is this something that might be a warning to do a pan drop to check for wear? Opinions?
 
Last edited:
Snagglefoot said:
That’s a good point. There certain upgrades that can be done to the 6L90 as recommended by Mr. Clinbarger and also in some good Videos on it.
In my case I made it to 260,000 miles with very little clutch material in the pan. The problem now is a rebuild might exceed the value of the vehicle.

There are some things a person can watch for. Drop the pan and look at how much material is on the magnet. If it’s quite fuzzy, you might go for the rebuild and hope most of the hard parts are in good shape. If it has actual metal on the magnetic better get it into the shop. I also cut open the filter with garden shears to see what's in it.

Another telltail might be a delay in the transmission going into reverse. Maybe Mr. @clinebarger can comment if that is a valid sign of an impending failure. Thoughts?
Click to expand...

'14 & up 6L80/6L90's have a higher converter clutch failure rate & the Pressure Regulator Valve wears faster.

'07-'09 had Stator Support sealing ring issues (1-2-3-4/3-5-R Drum)

Several different tuning calibrations were used over the years.....'07/'08 6L90 were some of the best at not overworking the converter clutch.

The friction weld on the 1-2-3-4/3-5-R Drum can fail on any 6L80/6L90 unit, Seems more common on 6L90's with the drum being physically larger & heavier.....I'm sure pressure spikes from a worn PR Valve doesn't help.

Early '07-'09 unit's tend to fail early or run forever even with less than ideal Stator Support sealing rings.
Mid years '10-'13 are likely the best.
Late unit's '14-'20 are hands down the worst.
 
clinebarger said:
Letting a 6L80/6L90 converter go nuclear is why it gets so expensive, I can refresh a good unit for $3,000 out the door.

*Billet Front Twin Disc converter
*Sonnax Zip Kit
*New bonded pistons & seals
*All Bushings (Durabond)
*Replace pressure switch membranes
*Spacer plate & checkballs
*OE Borg Warner frictions
*Flush the coolers
*Valvoline Maxlife LV fluid
*Service the T-case
*Tune the TCM with HP-Tuners (TCC scheduling)

At the very least have a billet front converter & a Sonnax Zip Kit installed.
Click to expand...
how long does it take?
 
Marcozi said:
What's the problem? Have you scanned the transmission computer for codes?
Click to expand...
No codes, no problems. I'm trying to avoid any catastrophic issues. I do extensive PM on this truck. I'm thinking I'm going to just run it out and see how long she'll run.

And when she blows, I'll buy another upgraded unit at that time.
 
clinebarger said:
Letting a 6L80/6L90 converter go nuclear is why it gets so expensive, I can refresh a good unit for $3,000 out the door.

*Billet Front Twin Disc converter
*Sonnax Zip Kit
*New bonded pistons & seals
*All Bushings (Durabond)
*Replace pressure switch membranes
*Spacer plate & checkballs
*OE Borg Warner frictions
*Flush the coolers
*Valvoline Maxlife LV fluid
*Service the T-case
*Tune the TCM with HP-Tuners (TCC scheduling)

At the very least have a billet front converter & a Sonnax Zip Kit installed.
Click to expand...
If I was planning to keep my truck “forever” and the above is what I would do. $3k is dirt cheap in the grand scheme of things.
 
Snagglefoot said:
Is there anyone else out there who wants to report on their 6L90’s longevity. Mine has lasted 260,000 miles with a lot of light duty rural driving, some towing in the past but not anymore. Coincidently I have just noticed it sometimes takes a full two seconds for reverse to engage. That is with the transmission cool. Is this something that might be a warning to do a pan drop to check for wear? Opinions?
Click to expand...
Are there any TSBs for this vehicle related to the transmission?
 
You must log in or register to reply here.

Similar threads

U
6L90 codes
Replies
6
Views
802
UNC200
Z
My 4L60E Transmission Service
Replies
3
Views
400
clinebarger
buster
How GM Transmissions are designed To Fail with NextGen Drivetrain
2
Replies
33
Views
1K
buster
R
High mileage 6L80, perhaps I saved it?
Replies
7
Views
1K
redhat
Z
4L60E Servo questions
Replies
8
Views
1K
zhaarnak02
Back
Top Bottom