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Old 02-19-2021, 04:02 PM   #1
rustyrodknocker
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6l90e no reverse

I may have posted about this before. But there has been a change so I thought I would repost. I bought a 08 Silverado for a 6.0 swap. It was a company truck and the guys were having a hard time getting it into reverse. They said it was clunky and it took several trys to get it to catch. The small repair shop that we were using
Took a look at it. Apparently they pulled the pan and head something fall out. Could not see any issues but the truck never went into reverse again.

I bought it thinking it was a 4l80. I had not even heard of the 6l90. Well, repair cost is ridiculous. The company got some quotes that I shrugged off as scammers thinking that a big company will just write the check.

It is crazy what the costs are $7400 to drive it out of the shop. There was places that could do it fof less but you have to take it to the dealer within 100 miles.

I found some exchange units for $3500 but you have to take it to a dealer and the one I talked to said they will only sell to a trans shop.

I have talked to several independents and most don't touch them.
It is clear these units have serious reliability issues. Especially 07 and 08 before they changed the oil routing.

But back to the point. When the guys were using it they said reverse worked fine if you could get it in reverse.

I just started it for the first time in a year and it felt like it went into gear then you get that feeling of rolling up against the park pawl.

Now that a little time has gone by is there anybody on here that has real world experience with these?

I would like to drive the truck as is for the time being. But I'm not dumping that kind of money into it just so I can run a used motor. Ill swap to a 4l80 when I put in my 66 suburban if need be.

The math just don't add up. I can still get reputable th350's for $575 exchange carry out.
I figure 5 hours out 5 in at $100 a day on the bench is $800 I've seen the parts list. Even if they replace a cracked sun shell. There parts are under $600. All in is less than 1/2 the lowest cost which still requires a trip to the dealer.
Even at a whole day out and in and another day on as computer don't get you there.
Its 2wd I can pull it in w hrs.

Any how if you have been in one or know something I would appreciate the help I'm wondering if its a single mechanical part issue. And not a wasted trans.
In a typical day they put it in and out of gear a ton but it never did any real work and spent 3 years rarely leaving a jobsite. I drove it 50 miles home forward gears are great.
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Old 02-19-2021, 06:55 PM   #2
1976gmc20
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Re: 6l90e no reverse

I just got a GM remanufactured with warranty for $3500 plus $1800 labor.

But it was totally shot; barely made it to the shop.

Not sure what the deal is with these. Some folks are reporting 200K under heavy use and other ones just break for no apparent reason.
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Old 02-20-2021, 10:44 AM   #3
rustyrodknocker
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Re: 6l90e no reverse

Quote:
Originally Posted by 1976gmc20 View Post
I just got a GM remanufactured with warranty for $3500 plus $1800 labor.

But it was totally shot; barely made it to the shop.

Not sure what the deal is with these. Some folks are reporting 200K under heavy use and other ones just break for no apparent reason.
I put close to 200k on one not knowing it was a 6 speed. It was another company truck that they bought with this one.they had quite a few of these trucks. This is the only one that I know of with a bad trans. Once I learned what it was when it did not look like the pictures of a 6l90. I then researched what it was. The 07 08 units had a lot of failures do to heat and lach of oil. They changed the oil routing to fix that.
The other common failure is weld cracking where the splined hub is welded in the clutch shell. This creates a oil pressure drop on the back side and results in slippage.

The diagnoses for that was no reverse but also no 4-5 I think.
Be for I knew any of that and the last time I drove down the high way and thru town and did not notice anything.

This is coming from a guy that put almost 200k on one but also
Thought it was a 4 gear trans.
Still don't understand why we need all these gears.

Thinking about when I pull the 6.0 I might drop in a 454 th400 that I have. It worked great in my dually with only 3 gears. Plus this truck is still a good hauler. Drives nice and has brand new tires.
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Old 02-20-2021, 12:37 PM   #4
1976gmc20
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Re: 6l90e no reverse

I actually like my six speed even though I am quite disappointed with this early failure. Only 76K miles but the first owner put on 73K of that. So who knows ...?

Pulling a load out on the highway it will drop down to just the right gear on a hill and hold speed without too much revving or hunting back and forth between gears. Going downhill it will hold back almost like a manual just by letting off the gas.

First gear is pretty low which is good for pulling a load, but normal running empty I will start off real easy until it pops into second before getting on the gas too much.

Of course I would always rather have a five or six speed manual
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Old 02-21-2021, 11:57 AM   #5
57taskforce
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Re: 6l90e no reverse

Like I told 1976gmc20, Iíve had a few of them in company trucks, as a company weíve had a ton of them. They have been very reliable for us. Only 2 failures in 50+ Trucks that I know of. Iíve beat on the one in my current Ď18 2500 pretty good. 86,000 miles currently and no signs of slowing down. The 6 speed is far superior to the 4l80 or the th400, like 1976gmc20 said, your always in the right gear. Iíve always hated the huge gear drop offs on the 4l80E. Itís either you donít have enough RPM or your revving to the moon trying to pull a load. Hereís a picture I posted a while back of my current 2500HD. Itís weight, as of a couple weeks ago is 11,500, air compressor, clean and used oil pumps and tanks, torch and tanks, tools, auxiliary battery mounted in bed with power inverter etc. it all adds up. (gross rated at 9800 I believe) so figure close to an average of 2K over weight for the entirety of its life. Itís been mud bogged out in the oil fields with chains on all four wheels, and pulled trailers it probably shouldnít have. Itís got rear auxiliary air bags that in this picture were inflated past 100lbs (thatís where the air bag compressor gauge stops) pulled it just fine for ~40 miles, up a couple of decent grades with no issues.
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Old 02-21-2021, 05:24 PM   #6
1976gmc20
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Re: 6l90e no reverse

Quote:
The 6 speed is far superior to the 4l80
The 700r4/4L60 in our old Suburban had to be helped out to make it work right towing a load. It would bog down to about 25mph without shifting (D not O!) and then scream up to about 50 and shift up and then start bogging down again.

I learned to pull it down into D2 at about 45mph and then it would hold 45-50 all the way up without too much drama, which is plenty fast enough for a winding mountain pass. Of course that's just a 5.7 TBI, good engine but what - maybe half the power of a 6.0 ?

We have several big fire trucks with older model Allisons. Last summer I took the big tender out on a fire and afterwards detoured over to the nearby very small town to fill it up at the high speed well. I forgot they don't hold back when you go down hill like my six speed Silverado, but fortunately it was empty and had good brakes! Damn things make you get careless which doesn't happen with a manual. We've only got one M35 type left with a 5 speed manual, and it's kept on a volunteer's ranch down south a ways because we don't have enough room in our fire hall anymore.
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Old 02-21-2021, 11:05 PM   #7
57taskforce
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Re: 6l90e no reverse

Yea donít even get me started on the 700r4. I despise it on every level. The 4l80e is light years better than the 700r in both strength and the ratios but even then I wouldnít trade the 6 speed. Iíve actually got a 6L90 in the shop that I was going to put into my K20 behind the 6.0 it was mated too. I decided to keep the 465 for nostalgiaís sake when I do the LS swap. I donít give two craps about fuel mileage.

I donít do it much anymore but there are times when I have to drive some of our big trucks at work. Going from the newer automatics to an Eaton 10 speed takes a few miles of brain relearn to get it right again.
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Old 02-22-2021, 01:27 AM   #8
Bob B.
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Re: 6l90e no reverse

Transmission control modules on the 6L80 and 6L90 and mounted on the valve body, and have to be programed to the truck. Dealers and some of the better independants shops can do this. I suspect the wild quotes you got are from shops that know they can't handle these transmissions so they sub them out to the nearest dealer and pad the bill. Or they just don't want the job. The fleet I work for has had very good luck with the 6L90.
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Old 02-22-2021, 12:32 PM   #9
1976gmc20
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Re: 6l90e no reverse

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Originally Posted by Bob B. View Post
Transmission control modules on the 6L80 and 6L90 and mounted on the valve body, and have to be programed to the truck. Dealers and some of the better independants shops can do this. I suspect the wild quotes you got are from shops that know they can't handle these transmissions so they sub them out to the nearest dealer and pad the bill. Or they just don't want the job. The fleet I work for has had very good luck with the 6L90.
Well, for better or worse I had the Chevy dealer replace mine
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Old 02-22-2021, 09:00 PM   #10
rustyrodknocker
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Re: 6l90e no reverse

Quote:
Originally Posted by Bob B. View Post
Transmission control modules on the 6L80 and 6L90 and mounted on the valve body, and have to be programed to the truck. Dealers and some of the better independants shops can do this. I suspect the wild quotes you got are from shops that know they can't handle these transmissions so they sub them out to the nearest dealer and pad the bill. Or they just don't want the job. The fleet I work for has had very good luck with the 6L90.
The independent shops will not warranty the work unless you take it to the dealer to have the computer flashed. Several places recommended taking the old computer out and clearing the codes and put it in the new transmission. If you do a swap.
The engine knows what trans its talking to and if you swap computers it glitches without a reprogram.

I have talked to many shops about the 6l90 and most dont even want to touch it.

Its probably going to have to be a 4l80. They are a solid unit.
And 4 gears is plenty for a street truck. Now some have 10 gears in the future they may have 19. 15k to rebuild.
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Old 02-24-2021, 10:48 AM   #11
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Re: 6l90e no reverse

guy at work had a 2015 with 6l90e pump blew up at 145k
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