Sick 6L80 Transmission - P0700 & B2AAA, P0741 & B2AAA - Resolved $$$

Hi. I need advice.

Situation: 2016 two wheel drive Tahoe with a 6L80E and the Max Trailering package.

I bought the Tahoe three years ago with 80,000 miles and have put 40 thousand miles on it. It now has 123,000 miles. I had the pan dropped and the fluid and filter changed at 90,000 miles. I have pulled a 3,300 pound Casita Travel Trailer about 10,000 miles with it. The trailer weight is based on weighing ready to depart on a trip. No idea what the previous corporate owner did with the Tahoe. I do not have the trailer on my current trip.

Earlier on my current trip, I filled the tank with fuel. Immediately thereafter I experienced a hard shift from 1st to 2nd followed by jerking. I immediately pulled over to check the transmission fluid level and it was correct and the fluid looked reddish, not brown. By feathering the throttle I was able to get it to drive to a motel. I thought bad fuel. But, I noticed that when I put it in Reverse, it didn't do anything and then engaged with a clunk.

Running at 60 miles per hour in fifth and 2000 RPM on the level, the torque converter seems OK. But when I go up a hill, the RPM increases. So I figure a slipping torque converter lockup clutch. So, I back off on the accelerator when going up hills to prevent the RPM from increasing.

I took it to a NAPA shop and they said there were no codes, but observed the hard shifting and shuddering. They used their controller to command the lockup to not occur, and the shifts were smooth with the usual smooth overall operation, albeit without the lockup, fluid coupling only.

They said that flushing the fluid "might" improve things if I wanted to spend the money on it. They said the fluid they removed from it had fine pieces of metal, "sparkles" under light, in it.

Initially it was a little bit better, but it deteriorated. The 4th to 5th shift occurs at the usual RPM when the transmission temperature is below 170F but is delayed when the temp is above 180F. The temp is between 180 and 195 when warmed up. I've never seen a temp above 200F. Usually it is 185 or less.

I am limping home using fifth gear for cruising and modulating the accelerator pedal to prevent or minimize torque converter clutch slippage. All gears are now hard engaging except for first thing in the morning when the fluid is warming up. When above 180F, I have to rev it up to 3,000 RPM and 70 MPH, and then back off the accelerator pedal abruptly to get it to upshift from fourth into fifth.

Initially I had about 2,500 miles to get home. For the first seven or eight hundred miles, there were no Check Engine Lights. Since then I have had four or five CEL's in the last couple of days. I have a Scan Gauge II and check the codes and then clear them. The throwing of the codes normally is associated with one of the delayed upshifts from fourth to fifth. Most of the code combinations have been a P0700 with a B2AAA. Once there was a P0741 with a B2AAA.

I understand the premise that a re-manufactured transmission may or should have upgraded parts in the torque converter and elsewhere to prevent known problems. I will also change the fluid as specified in the "Maintenance Schedule - Additional Required Services - Severe" schedule. I have no information on whether the fluid was ever changed before I bought the Tahoe with 80,000 miles on it.

Do I conclude that the transmission is toast and get a GM or Jasper re-manufactured transmission to have something that will last for another hundred thousand or more miles without interrupting a trip on me? Do I get it "repaired" with a shorter warranty?

The Owner's Manual says to drain the fluid and replace the filter, which requires dropping the pan. Flushing the fluid does not allow changing the filter. Is it better to
1. drain and refill including changing the filter or is
2. a "100% change of the fluid" by flushing better?
I can drain the fluid at home a lot more cheaply than at an oil change shop and may just do it every other year depending on whether that is the recommended way to change it. I'm not set up for a "100% flushing".

Regardless, I will ensure that a TSB 70 Centigrade Thermal Bypass Valve goes in. I wish I had known about it when I did the fluid and filter change 30,000 miles ago.

Thank you all in advance for sharing your knowledge. Rob

@NickTransmissions Nick, our resident transmission expert, will be along later as he is west of your hometown.

In a general sense, you did good. Most of these fail at around 100K, the years of high temperatures taking their toll on the converter and the clutch material gives way and wrecks the valve body and can cause other issues such as you are experiencing. Whether this transmission is repaired or replaced, put in a lower temperature thermostat for it so it'll live longer. Make sure whoever does the work, flushes and flow tests the transmission coolers and lines to make sure they are still in spec. Change the fluid on the severe service schedule, less if towing.

RobH said:

Hi. I need advice.

Situation: 2016 two wheel drive Tahoe with a 6L80E and the Max Trailering package.

…

Thank you all in advance for sharing your knowledge. Rob

Click to expand...

Rob,

Trans is likely half past dead…4-5-6
clutch is heavily stressed/prob burnt at this point (that clutch takes the brunt of of the damage inflicted by overheating thus why it only actually upshifts when you let off).

Harsh shifts arise from the TEHCM increasing line pressure to adapt to (compensate for) slipping components (clutches) in the case. Harsh engagement into reverse in combination with delayed engagements into 3rd also indicate stressed 3-5-R clutch pack (drum is probably leaking at the base welds - probably the first or second most common failure in those things (1-2-3-4 piston, converter, 3-5-r are the unholy trinity of failure points in the 6l80e).

Those converters are pieces of shit that come with a converter clutch disc that’s only .020 thick. All my rebuilds get a .070” thick converter clutch and billet cover when towing/hauling is apart of the equation.

That said, the root cause of your overall problem (and specifically, p0741) likely lies in TCC regulator valve wear in the lower valve body or TTC control valve in the pump. If either (valve and or bore) sufficiently wears, the valve wont fully stroke when commaned to do so by the TCC pressure control solenoid thus insufficient apply oil pressure is delivered to the converter clutch when in “lock up” causing fall out of lock up and begin slipping. Slippage builds heat which begins to damage more components which leads to failure.

In your case, Id go GM reman as you arent towing anything overly heavy that would require things like billet 4-5-6 hub/shaft or kolene steels everywhere.

I think the warranty on those is 3 years/100k and should come with brand new pump assy, valve body assy and TEHCM with the fast adapt performed at the factory so you just stab it and go once you have a converter. I would recommend you have a converter specialist build you a converter with a billet cover and installs at least a .050” thick converter clutch.

Ill edit this if i think of anything else…

Thank you very much for your info, Nick. If I am hearing you correctly, you are recommending a GM re-manufactured transmission. Apparently the transmission does not come with a torque converter. Thank you for the info on the lockup clutch lining thickness.

Does the Jasper transmission come with a decent torque converter or is the torque converter separate with the Jasper transmission also? Jasper information sheet describing some upgrades attached. I can ask them Monday if their transmission includes the converter.

I have deliberately taken it easy with the engine and transmission for the last forty thousand miles since I bought the Tahoe, deliberately letting off on the gas when the transmission is about to upshift. I generally control/allow the upshifts with the rocker switch on the shift lever. I have been trying to drive the engine and transmission for longevity.

If I have to source the torque converter separately from the transmission, who would be a recommended source?

Apparently the GM and Jasper transmissions have the same three year/100,000 mile warranties with nationwide service. It might be easier to get the labor if I get a GM transmission. I might run into delayed parts availability. Or a statement that "we con't get to it for two weeks". The answer is to get a transmission which will not need warranty support.

AAMCO will give me a three year/50,000 mile warranty.

Are the 6l80 and 6L90 the same size and equivalent otherwise? If so, I might go with the 6L90 even though it might be overkill for my use just to increase the odds of avoiding getting a trip messed up like my current trip. I really dislike automatic transmissions although I have had some good ones. I've had good service with my seven cars/SUV's with manual transmissions. Plus my family has had five other vehicles with manuals in my lifetime. Oh well.

I've traveled a little over 2,800 miles since it started acting up. 360 more miles gets me home. At least I am in Texas now and my son-in-law can come get me if it dies.

I suspect that an auxiliary transmission cooler is also cheap insurance. My 1995 ex-highway patrol Caprice had one from the factory in addition to the heat exchanger in the radiator tank.

Thanks again, Rob

RobH said:

Thank you very much for your info, Nick.

Click to expand...

You’re welcome, Rob.

Buy a 6l80; the ‘90 is longer and would require mods to get it to fit. Circle D is a good converter builder.

I don’t know enough about Jasper transmissions so can’t speak to their quality vs GM’s but I would want to know how their warranty works if it has to be used. Quick glance at the attachment tells me they don’t provide a brand new TEHCM or IMS, just a good used/rebuilt ones they test; the spacer plate update refers to 06-08 units and the sealing rings on the stator are a decent upgrade but doesn’t address the main two problems with that drum (see #1&2 below).

Additionally, I would want to know (from both GM and Jasper) if the following is done/included:

1) Installation of billet aluminum 1-2-3-4 piston (oe piston frequently cracks)
- I install the Sonnax version in all 6l80s I rebuild

2) Welds reinforced on 3-5-R drum (standard practice on all to prevent leaks at the 3-5-R apply piston)

3) Updated Boost, Pressure Regulator valves (pump) as well TCC regulator valve installed (lower valve body); Id also ask about the compensator feed reg valve (lower valve body) as the OE valve also likes to wear, causing clunky shifting on up and down shifts

- Sonnax valves feature re-designed balance spools to minimize wear and promote better sealing in the bore)

Yes, get yourself an Aux trans cooler. Helps to keep temps under control in hotter months and/or when towing etc.

Agree about auto transmissions in general. My Tahoe is the only vehicle that has an auto (4L60E). My Bimmer and TA WS6 both have manuals and wouldn’t have it any other way.

Are you able to do the install yourself? If so I would suggest you go direct to GM and buy a new one with torque converter. You're only looking at a few bucks more. I have had way too many issues with remaned transmissions and it boiled down to those companies and churning out product as cheaply as the can do so and you never know what you might get.

If you doing the labor is not possible. Take it to Aamco but make sure you research that particuliar shop first. They are franchised so not all equal.

The 6l90e is a different length and also has a different output shaft versus the 6l80e. A competant transmission shop can make the 80 as strong as the 90, you just have to tell them what you want it to do.

Lastly, while the transmission is out, its a good time to have the rear main seal replaced too. It's right there.

Best of luck!

THarber said:

Take it to Aamco but make sure you research that particuliar shop first. They are franchised so not all equal.

Click to expand...

+1; I have rebuilt several Aamco 4L60s and they leave a lot to be desired in most cases. Though you will occasionally run across an Aamco that has one or two transmission rebuilders employed, lol.

I'm 78. I can do oil changes and fluid changes myself but not a transmission change.

Nick, I understand your questions for the rebuilder, but am not sure if I will be able to get them answered. Assuming I get home, I'll make a list of them and see if I can talk with the AAMCO technician. When I asked the salesman some questions, he said he would have to ask his technician. AAMCO services anything, so I wonder how deep their expertise is on the 6L80. Of course, there are a lot of 6L80's around, so they may do a lot of them.

As you said initially, going with the GM reman may be the best route. On Monday, I'll talk with the local GMC parts department and see what the order time is on a new/reman 6L80. It may be that a new 6L80 is not available.

Do you ship 6L80's, Nick? You can PM me if you like.

I'm attaching a copy of the GM TSB concerning the 70 Centigrade (about 160 Fahrenheit) Thermal Bypass Valve for those readers not familiar with it. MYC = 6L80 and MYD = 6L90. There may be later versions of the Service Bulletin. I understand the part number for our 6L80's is 86774933. There may be a later part number.

Thanks again, Rob

Might check out Precision Transmission

RobH said:

Do you ship 6L80's, Nick? You can PM me if you like.

I'm attaching a copy of the GM TSB concerning the 70 Centigrade (about 160 Fahrenheit) Thermal Bypass Valve for those readers not familiar with it. MYC = 6L80 and MYD = 6L90. There may be later versions of the Service Bulletin. I understand the part number for our 6L80's is 86774933. There may be a later part number.

Thanks again, Rob

Click to expand...

You’re welcome, Rob. Unfortunately i dont ship anything as its just too much of a hassle. I do build for folks in the region (in addition to vegas, i have customers in Utah, AZ, Cali and briefly investigated shipping them nationwide but decided against as if there were to be a problem w/the trans requiring it to come back to me, id have to coordinate and pay for the return shipping as well and its not worth it for me.

I agree with @Fless, call Richard at Precision Transmission. He’s in Amarillo and would build you a better 6L80 than either GM or Jasper. Perhaps he can ship regionally or it may be worth it to pay for the freight if it’s not too expensive (just saw you’re in San Antonio). Richard would do all the same things i would to a 6l80e to ensure it’s reliable and gtg.