6.2L 8 Speed OWNERS! GM UPDATE 15389

bass mechanic · July 2, 2015

the only thing i can contribute here is my 6.2 6 speed with 3.42 gears was at exactly 2050 rpm at 80 mph

with the new 8 speed and 3.23 rear axel at 80 mph i am now at 1800 rpm

robvas · July 2, 2015

the only thing i can contribute here is my 6.2 6 speed with 3.42 gears was at exactly 2050 rpm at 80 mph

with the new 8 speed and 3.23 rear axel at 80 mph i am now at 1800 rpm

The ratios are almost exactly the same in the last two gears

0.85 and 0.65 in the 8 speed

0.85 and 0.67 in the 6 speed

Rme2513 · July 2, 2015

Well I had the update done today and it shifts about the same but one thing I noticed if you floor it it will shift three times before it finds the right gear that sucks it use to shift once and hit around 4500 rpm and haul ass now it's sluggish and lost the service guy told me to give it a week and see have any of yall had this issue?

FeelTheThunder · July 3, 2015

You get grief for having oil change at such low KMs? As in was it still free? Mine is at 4700km right now and sitting at 60% and roughly 70 engine hours, I am debating having it changed just to get the factory oil out.

I had this update done at around the 3000km mark, mine is still shifting good, just the oddball cold 1-2 shift that seems to be the norm for 8speeds.

My dealer said they don't care when I come for oil changes. I get 4 free that's it.

I have always changed oil early on my new vehicles, I figure any mountains off the cylinder walls (among other things) are shaved down by 3000 km and are now stuck in the oil and filter.

My trans was not shifting too bad either, the cold 1-2 shift like you said and also some strange downshifts coming to a stop.

My dealer did not contact me back today regarding my trans. I left messages to both the service writer and service manager this afternoon with no response. I am super upset. I told them on Tuesday that I would need a truck by Thursday afternoon if they cannot figure anything out. The loaner Equinox cannot haul my tools.

magstar67 · July 11, 2015

My dealer said they don't care when I come for oil changes. I get 4 free that's it.

I have always changed oil early on my new vehicles, I figure any mountains off the cylinder walls (among other things) are shaved down by 3000 km and are now stuck in the oil and filter.

My trans was not shifting too bad either, the cold 1-2 shift like you said and also some strange downshifts coming to a stop.

My dealer did not contact me back today regarding my trans. I left messages to both the service writer and service manager this afternoon with no response. I am super upset. I told them on Tuesday that I would need a truck by Thursday afternoon if they cannot figure anything out. The loaner Equinox cannot haul my tools.

Do you have any updates on your transmission issues since your last post?

redwngr · July 12, 2015

Overall ratios:

8 speed 6 speed

3.23 3.42

First: 14.73 13.78

Second: 9.59 8.07

Third: 6.72 5.23

Fourth: 5.46 3.93

Fifth: 4.10 2.91

Sixth: 3.23 2.29

Seventh: 2.75 N/A

Eighth 2.10 N/A

Reverse: 12.34 10.47

magstar67 · August 11, 2015

I had this update done on my truck about 7-800 miles ago and waited to leave any feedback to see how it performed after I put some miles on it. My truck is a November build IIRC and the update did seem to help it. I don't notice the occasional odd downshifting(?) at low speeds that resulted in clunks etc that I used to. I'm happy with my 8 speed so far, no complaints.

Looking forward to tuning it, I hear Black Bear has the ability now so it is on the wish list. I think this thing will be an animal then.

Rme2513 · August 11, 2015

Overall ratios:

8 speed 6 speed

3.23 3.42

First: 14.73 13.78

Second: 9.59 8.07

Third: 6.72 5.23

Fourth: 5.46 3.93

Fifth: 4.10 2.91

Sixth: 3.23 2.29

Seventh: 2.75 N/A

Eighth 2.10 N/A

Reverse: 12.34 10.47

You add them not multiple them except for the overdrive gears

Chris · August 11, 2015

You add them not multiple them except for the overdrive gears

Ratios always get multiplied.

Rme2513 · August 11, 2015

Ratios always get multiplied.

this about the corvette but it's the same 8l90 and it says an overall ratio of 7

http://media.chevrolet.com/media/us/en/chevrolet/news.detail.html/content/Pages/news/us/en/2014/Aug/0820-8speed/0820-corvette-8-speed-lead.html

Chris · August 11, 2015

this about the corvette but it's the same 8l90 and it says an overall ratio of 7

http://media.chevrolet.com/media/us/en/chevrolet/news.detail.html/content/Pages/news/us/en/2014/Aug/0820-8speed/0820-corvette-8-speed-lead.html

A ratio when figuring out torque multiplacation andusing compound gears which this is (input to output of trans, and rear end). The two ratios are multiplied.

Rme2513 · August 11, 2015

A ratio when figuring out torque multiplacation andusing compound gears which this is (input to output of trans, and rear end). The two ratios are multiplied.

so say you are in overdrive .65 and the rear end gear 3.23 what is the actual difference in engine vs axle rpm if the engine rpm is 1500 my math says 3150

Chris · August 11, 2015

so say you are in overdrive .65 and the rear end gear 3.23 what is the actual difference in engine vs axle rpm if the engine rpm is 1500 my math says 3150

It is all multiply/divide. On a job so i cant run the math right now.

redwngr · August 11, 2015

with 0.65 transmission ratio, the output of the transmission will turn once for every .65 rotations of the engine. (OD drives the output faster than the input, while low gear (4.56 in the 8L90 case) the output turns once for every 4.56 turns of the engine.

Differential has a small pinion driving a large ring gear. Pinion is attached to drive line, ring gear to axles.

Axles (large gear) will turn once for very 3.23 turns in the input.

At 1500 engine rpm 1500/0.65 = driveline turns 2308 rpm

At 2800 driveline rpm, axles turn 2308/3.23 = 714 rpm

Overall ratio is 1500 engine / 714 axle = 2.1

As Chris posted, gear ratios are multiply/divide. (Multiply or divide depending on which way you are comparing.(From beginning to end or end to beginning of the gear train.) Makes not difference if it is an overdrive ratio or not.