194K mile Transmission Failure REPAIRED

Jedibusiness · June 14, 2019

I sell, fabricate, deliver, install and train workers how to use my packaging lines. In 2015 selected 2500HD WT 6.0 as the platform to use as my office (Truck Camper) and and tow vehicle. It provided great HD service and economical (per mile basis). On a trip to OR noted a resonance with my thumb on the steering wheel, when engine load changed going over an overpass. At first I thought it was roadway groves, but the rhythmic vibration stopped when manually dropping into a lower gear, increasing to 3000 RPM's.

Not willing to chance break down north of Mount Shasta, returned home, switch vehicles and headed north. Upon return the rebuild search began.

Deep dived into transmission repair cave and almost selected a remanufacture unit from Certified Transmission but learned shops are under no obligation to use their products and there's limit participation on the left coast. Most shops refuse to install a third party transmission citing warranty issues. Finally settled on a local shop in West Sacramento that rebuilds your transmission to the level you want.

As a bonafide cave dude wanting to understand the how transmissions work, why they fail and how to repair, called (late Friday) Pro-Built Transmission and spoke to Don the owner. I outlined in detail what the problem was, and through a series of questions from Don about the trucks' service history and how I use it, he was confident what the problem was. Arrived two hours late from my Monday 8 am appointment, Don pulled me through (no signage stating for insurance purposes you can see what we're doing to your ride gate) his shop showing various components, their failure points and although the 6L90 is a simple transmission pointed out common failure points. He showed various 6L90's requiring rebuild, some under 60K miles, and could not believe mine made it to 194K. I relayed after the first transmission filter change, started pulling 5.5 quarts out and replacing every other oil change, in other words, a poor man transmission flush. My reasoning was pay 25 dollars instead of $250 for a complete flush. Don smiled and said that explains it, noting above all else, fluid change saves transmissions. Satisfied Don wasn't a hack, dropped off the key and within an hour, after a test drive and noting data stored in in codes sent me this.

I knew it was bad and knowing a bottle of shudder stop wasn't gonna fix this, authorized repair. With high mileage, I asked about universal joint replacement, Don relayed he had a shop that could replace joint, balance the driveshaft and check the center bearing. Also since transmission was removed, and although showing no signs of leakage, had him replace the rear oil seal as well.

Don pulled the transmission and confirmed what he suspected, torque converter friction plate failure. The metal on metal grind produced fine grains that worked its way pass the bell hosing bearing and through the pump.

Damage continued through the valve body and solenoid pack (TCM).

Solenoids contaminated

Note the metal grit in the screen on the right.

What was unexpected was the metal grinds didn't make to the clutch packs. After 194K miles, 90% were still serviceable with some showing wear on the outer ring.

What's interesting with GM is, instead of applying full pressure to the clutch plates, they control the amount of pressure applied. The black rubber ring on the piston drum engages the plate outer section. This accounted for the most wear on the clutch plate. Don showed how the replacement piston drum engages the full surface of the plate; provides a sharper shift and lowering the wear.

THE FIX.

Drive shaft showed the center bearing was bad and was along with universal joints replaced.

Don sent the pump face (forgive if I don't name the parts correctly) to be machined smooth (8-9 thousandths).

He switched solenoid rods from alloy to steel, and spoke about the OME cost. Chevy spends perhaps 50 cents on alloy rod where as three steel one cost him $80.00. He installed a new pump and higher valve pressure components.

Here's a picture of some parts replaced in my 6L90.

Don sent out the torque converter to another shop. They split it open and here's the condition.

Don then explained his vendor replaces the back half (part the friction ring presses against) with a thicker (1/4 inch instead of the 1/8 inch) material machined from a billet. This handles heat better and prevents the converter material from warping. They also flash braze vane tabs to prevent movement (picture of open converter is not mine)

If you get a good shop and can wait four days, one can retain the original unit and get upgraded parts. Note the remanufacturing industry is designed for a quick turnaround for transmission shops. They cite a higher level of expertise, however the reality is they created a process based on volume allowing a price point favorable to the transmission shops. Nothing wrong with that and note I wanted to retain my original transmission.

Programming

Invoice. Yes its high, but keep in mind two other shops were involved, addition work was completed and Don took time to educate me on the transmissions, AND its a tax write off.

In the final analysis and under heavy duty conditions, if you have a 6L90 strapped to a 6.0 and do fluid changes, your transmission will survive to 150K miles. If I had a better understanding of transmissions when observing the gray paste material surrounding the pan magnet at the last transmission filter change, I could minimize cost with just a torque converter change.

As for this repair, (most expensive during ownership) it cost me .0229 per mile. This and the top end rebuild posted earlier,

gives a total cost of $5944.85, (.03 cents per mile) returning my truck to service, hopefully getting another 150k miles. Test drove my truck and report shifts are crisper with the only change being when going over overpasses, and sensing the torque change, rpm will drop 25-50 rpms and return on completing the elevation change.

Next week I'll go up the Grapevine with a 4k pound truck camper and report how she does.

Edited June 15, 2019 by Jedibusiness

GTBensley · June 14, 2019

Awesome write up, thank you for the information.

Wiggums · June 14, 2019

Nevermind, misread the bill.. thought it was $12 an hour for labor.. now I know it's 12 hours at $125. Still reasonable.

Edited June 14, 2019 by Wiggums

DeePa · June 14, 2019

One more reason to tune a truck. Get rid of torque management (clutch slippage)

CamGTP · June 14, 2019

3 hours ago, DeePa said:

One more reason to tune a truck. Get rid of torque management (clutch slippage)

The 6L80e and 6L90e actually use TM to operate though, removing it is the opposite of what you want to do. A custom tune can request less TCC slip and quicken/firm up shift times but the issues aren't exactly torque management related.

Overall the stock calibration in a heavy duty truck operates rather well, it's made to last a long while with the correct service.