# Blown Transmission In 2007 Avalanche



## Camper Man (Jan 12, 2006)

The transmission in my 2007 Avalanche LTZ blew last week at 26,000 miles. This happened two days after pulling my 26RS 450 miles to a campground in Gatlinburg TN. I was particularly disappointed because my Avy has the heavy-duty 4L70E transmission matched to the 6.0L engine, same as in a 2500 Silverado. I really thought this would never happen pulling a 6,000 lb trailer!

Technician notes on invoice: "No high gear. 3-4 clutches burnt. Replaced turbine shaft, pump covers, 3-4 clutches, clean and reseal complete. Flush cooler, Flow 1.0 gpm @ 73 degrees."

GM Roadside Assistance was excellent. Within an hour or so of my call on Sunday night, GM had the vehicle towed 30 miles to Volunteer Chevrolet in Sevierville, TN. Volunteer Chevrolet had the transmission tore down Monday morning and repaired under warranty by Tuesday at 3 p.m. Outstanding service!

The service writer told me they had seen quite a few of the "new body style" GMT-900 'Burb-type models with transmission problems this summer. "Not a good sign," he said.

No time is a good time for transmission trouble. However, if you are to have them, I recommend doing so with a bunch of other Outbackers -- Katrina, Prevish Gang, Wing Nut, Lilunsure, Fire 44 -- these folks, among others -- saved my hide!


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## Carey (Mar 6, 2012)

Camper Man said:


> The transmission in my 2007 Avalanche LTZ blew last week at 26,000 miles. This happened two days after pulling my 26RS 450 miles to a campground in Gatlinburg TN. I was particularly disappointed because my LTZ has the heavy-duty 4L70E transmission matched to the 6.0L engine, same as in a 2500 Silverado. I really thought this would never happen pulling a 6,000 lb trailer!
> 
> Technician notes on invoice: "No high gear. 3-4 clutches burnt. Replaced turbine shaft, pump covers, 3-4 clutches, clean and reseal complete. Flush cooler, Flow 1.0 gpm @ 73 degrees."
> 
> ...


You have the 4 speed right.. The 2009 models in all of GM truck lineup will now get the highly touted 6 speed behind the 6.0.

I wonder if the new hot rod 6.0 is a bit much for the 4L70... Next question is what motor do you have?edit I meant what hp do you have..

What a bummer... Hopefully there is either a mechanics, or electric update that can be done to help its life..

I managed a tranny shop when I was just 22 and fresh out of college.. That was back in the 700R4 and t200 days, 1986/1987... Man I hated telling people with 40k on there rigs that it needed a 1800-2000 dollar tranny.. I sure felt bad for them..

It was a highly stressful job and I only made it one year without moving on..

Sorry about the trouble, but sounds like it went as best as possible.

Carey

GM 2500 trucks got a 6speed starting in 2007 also.


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## Camper Man (Jan 12, 2006)

Colorado~DirtBikers said:


> [You have the 4 speed right.. The 2009 models in all of GM truck lineup will now get the highly touted 6 speed behind the 6.0.
> 
> I wonder if the new hot rod 6.0 is a bit much for the 4L70... Next question is what motor do you have?edit I meant what hp do you have..
> 
> ...


Yes, mine was the last year for the old-design four speed, probably millions of them out on the road. The L76 6-liter is rated at 366 hp / 380 lbs torque.


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## Carey (Mar 6, 2012)

Camper Man said:


> [You have the 4 speed right.. The 2009 models in all of GM truck lineup will now get the highly touted 6 speed behind the 6.0.
> 
> I wonder if the new hot rod 6.0 is a bit much for the 4L70... Next question is what motor do you have?edit I meant what hp do you have..
> 
> ...


Yes, mine was the last year for the old-design four speed, probably millions of them out on the road. The L76 6-liter is rated at 366 hp / 380 lbs torque.
[/quote]

Yea.. I was thinkin same... Millions... That new engine doesnt have all that much more compared to the older 6.0... Not knocking the 6.0, that engine is a heck of a horse.. I respect that motor a bunch.

Maybe that lil bit more power pushes some parts over the edge in that tranny.. If many fail a fix will be made either from hard parts or from electrics in short order.. But sadly they may be in the wait and see game on failures, so yours wouldnt have gotten updated parts yet..

I would be looking into tranny failures on those models and start building a case so if it happens again.. Maybe by then you could get the update and only pay half price or less if your case is documented and researched..

GM is looking to keep customers at this point, so Id be doing my homework to lay out to them if it fails again out of warranty.

Carey


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## garyb1st (Dec 6, 2007)

Camper Man said:


> The transmission in my 2007 Avalanche LTZ blew last week at 26,000 miles. This happened two days after pulling my 26RS 450 miles to a campground in Gatlinburg TN. I was particularly disappointed because my Avy has the heavy-duty 4L70E transmission matched to the 6.0L engine, same as in a 2500 Silverado. I really thought this would never happen pulling a 6,000 lb trailer!
> 
> Technician notes on invoice: "No high gear. 3-4 clutches burnt. Replaced turbine shaft, pump covers, 3-4 clutches, clean and reseal complete. Flush cooler, Flow 1.0 gpm @ 73 degrees."
> 
> ...


That bites. Glad GM responded satisfactorily. Did they install a new or rebuilt unit?

The Tranny in my 2005 F250 went in May. Only had 29,000 miles on it and never pulled a trailer. It was still under warranty and they replaced it with a rebuilt unit. They claimed it is better than the original. We'll see. The warranty on the rebuilt is 12,000 or one year. I was told that if I paid for the rebuilt, the warranty would be 36,000 or three years. Don't understand that and plan on having serious discussions with Ford if it goes again.

Gary


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## battalionchief3 (Jun 27, 2006)

I noticed my trans temp when towing at 200. Then I looked at the minature cooler GM put under the hood.







My next step was to get a hugh cooler and a deep pan. After the cooler and the new pan I am up to 19.5 qts of ATF and I cant get the temp above 175. It is a B&M cooler with a 750cfm fan on it with a Mag Hy-tech pan. I would bet you have the same cheesey cooler. I would look to upgrade all that stuff, heat kills trnasmissions.


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## camping479 (Aug 27, 2003)

battalionchief3 said:


> I noticed my trans temp when towing at 200. Then I looked at the minature cooler GM put under the hood.
> 
> 
> 
> ...


Good point! We also changed out the small cooler on our old yukon and it helped a lot to keep the trans temps down, too much heat is not good.

Mike


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## samvalaw (Feb 17, 2005)

So what can a "non mechanic type" do to protect against tranny failure? My Suburban 2500 tows the 21rs just fine, but I see it hovering around 200 on long tows?


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## having_fun (Jun 19, 2006)

I hover at 190, it can go to 200 on a hill in 98 degree weather. 175, man that would be great!

Were the any symptoms? Hard shifting, etc before it blew?


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## OutbackPM (Sep 14, 2005)

samvalaw said:


> So what can a "non mechanic type" do to protect against tranny failure? My Suburban 2500 tows the 21rs just fine, but I see it hovering around 200 on long tows?


 The best you can do for your transmission is to change the fluid regularly and or change to synthetic fluid that has a higher break down temperature. The fluid is expensive but may save you a failure if you have only a short spike in temps from a steep grade. The subject of this thread does not sound like a poor lube issue so may not have helped but in general the fluid is key for protection.

The other thing you can do if your transmission has it is to use the tow haul mode. This locks the torque converter earlier and longer to prevent the 'slippage' of the converter generating more heat. My Allison trans locks at 23 mph in tow haul and 45 mph in normal mode. My temp only creeps up when I am in traffic with allot of stop start to generate the heat. Once moving on the highway with the converter locked it alway drops to about 180 F from about 200F in traffic on mine.


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## compass49 (Feb 4, 2008)

This is interesting.....I wonder if the tranny went due to the HP on the 6.0 as CDB eluded to.

I have the 5.3 and usally tow in the "tow/haul mode". Next time into a dealer I inquire if the tranmission has been failing on the 5.3 litres too.


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## Rubrhammer (Nov 27, 2006)

My tranny temps are consistantly lower in OD than in 3rd also. This is on a 4L60E.
Bob


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## Camper Man (Jan 12, 2006)

Addressing a few of the questions / comments posted above:

BattalionChief3: Based on everything I've heard, it would be a good investment to replace this dinky OEM cooler. I will check with my local Chevy dealer first, just to make sure I don't get any arguments from them if further problems arise over the course of my 5 year / 100,000 mile powertrain warranty.

Garyb1st: They rebuilt my current transmission. Apparently the innards weren't affected enough to warrant a rebuilt or new transmission. If I have further problems, however, I will insist on a new unit.

Having fun: My tranny also runs around 185-200 when towing in hot weather. On long grades, I've seen it as high as 208 but it quickly drops back on the downgrades.

There were no symptoms prior to the failure. We had towed normally on Thursday and Friday, and toured around Gatlinburg on Saturday and Sunday. That afternoon, as we were headed back to the campground, the transmission suddenly felt like it was taking off in 2nd gear. Then it would clunk down into first, shift normally to second, and not go any higher. You could tell it was trying to shift to third - but slipping constantly. I limped the couple of miles back to the campground and called Raodside Assistance.


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## Camper Man (Jan 12, 2006)

Rubrhammer said:


> My tranny temps are consistantly lower in OD than in 3rd also. This is on a 4L60E.
> Bob


Bob, can you clarify this. While in tow-haul mode, do you reguarly tow in third gear, rather than in "D"?


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## Rubrhammer (Nov 27, 2006)

Bob, I never ever tow in 3rd. Tow haul gives me an incrased shift point so it cuts out excessive shifting. I don't even use tow haul all the time. On the flats I don't need it and in urban areas the shift points are needlessly high. Your 6.0 and I thought it was a 4l80e should have less hunting than my setup due to the OD not being as steep as the 4l60. Not to mention you have gobs more tq than I do.
Bob


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