2015 Silverado & Sierra to get 8-speed transmission

[Jsdirt]

MUCH smaller and lighter is an understatement! Comparing a semi diff to a pickup diff is like comparing quarter mile times between a Prius and a MODIFIED Z06 Vette! There IS no comparison.

 

If there was, we'd all starve to death as our food rotted in semi trailers broken down along every highway in North America ...

[Super 8]

 

Really? Kinda wonder why I haven't burned up the 2.64 rears in my semi truck behind an 18 speed with a 550 hp 1850 lb torque engine yanking around 80,000 lb. And the truck just turned over 294,000 miles and runs great. The diff ratio is not the issue if you have the right gears and spreads between them in the transmission. I would be more at issue with the 3.08 in a pickup only because most of my driving, both pulling and not, is below 65 mph. Most of time I don't even use the 6th gear in my 2013 using 3.42 diff ratio. I haven't let it go to 6th is weeks. Just can't imagine the 8 speed with 3.08. I am wanting to put 4.11 in my diffs so that I can at least use all 6 gears comfortably for the hilly roads i frequent. Again, even at 65 with 4.11 and stock rubber, I wouldn't be turning more than 2100 RPM, which is right at the first plateau on the torque curve on my 5.3L. Get best balance of economy and power and reduced shifting cruising at 1900-2100 RPM.

What is your transmission ratio? It is either A,B or C, which each have a different formula to match to your rear end ratio's.

Example a C ratio transmission in a semi has a 12.66 ratio X 2.64 rear end ratio = 33.4, this is your starting ratio. The industry always looks for the number 45 and above for the starting ratio for pulling.

Edited August 17, 2014 by Super 8

[Cowpie]

MUCH smaller and lighter is an understatement! Comparing a semi diff to a pickup diff is like comparing quarter mile times between a Prius and a MODIFIED Z06 Vette! There IS no comparison.

 

If there was, we'd all starve to death as our food rotted in semi trailers broken down along every highway in North America ...

 

But the fact remains, whether it is a semi or a pickup, with something like a 3.08 diff ratio, the driveshaft is going to turn 3.08 times for each turn of the axle. Sure the size is different, because the vehicles are different, but the driveline dynamics are the same.

[Cowpie]

What is your transmission ratio? It is either A,B or C, which each have a different formula to match to your rear end ratio's.

Example a C ratio transmission in a semi has a 12.66 ratio X 2.64 rear end ratio = 33.4, this is your starting ratio. The industry always looks for the number 45 and above for the starting ratio for pulling.

 

I have a 14.40 bottom gear in the RTLO-18918B 18 speed in my semi with 2.64 Meritor 14X diffs with 445/50R22.5 rubber on Alcoa Durabrite 0" offset wheels. Actually, the A, B, or C designations primarily concern the top end ratios on an 18 or 13. Like whether the top is a .74, .73, etc. The "industry" is a pretty generic term and means nothing regarding trucking. The trucking industry covers too many variables. Many semi performance diesel shops are moving toward recommending setups like 18 speed and 2.64 or 2.79 diff ratios. Piittsburgh Power is one of the major promoters. The trucking "industry" OEM's are even promoting ratios down to 2.47 that are currently available, and there is rumor of even moving down to 2.25 or 2.36 in the near future. Check with Freightliner, Volvo, Detroit, Meritor, Dana Spicer, etc. The general idea is to run in direct at regular highway cruise speed for maximum effect. Even one of Eaton's senior engineers is on record that running in direct, the transmission runs cooler, and there is a 3-4% economy gain, and more actual power on the ground at the drive wheels. Bruce Malinson at Pitts Power is on record that going to overdrives, there is roughly a 5-10% parasitic loss of power to the drive wheels. The "industry" has been primarily stuck on ratios from 3.36 to 3.90 for quite a while. The last few years have brought about a significant mind shift on how to spec heavy trucks.

 

 

But either way, all that being said. It isn't like I have a laundry list of transmission models to choose from with an OEM pickup. Given the way GM is going, I will probably have to consider an alternative the next go around. Ford is still offering 4.11 in their F150. I gave the 3.42 a try in my 2013 1500 I have now. it works, but I rarely ever get it into 6th gear, and I don't even live in a town or city! Lots of two lane, hilly roads that I hardly ever see speeds over 65. The 5.3L does it's best work both from a performance and economy standpoint, on these rural roads at 1900-2100 RPM. Any lower, and it is hunting for gears on every other hill. And constant shifting is hard on a trans and not very efficient. So basically, I only have a 5 speed. I would like to use all the gears I paid for, so I am probably going to have to put in 4.11 diff gears in my 2013. At 65 mph in the top hole, I would be turning 2000 RPM on stock rubber. For the area in which I live and roads I run, that would be about as good as it gets. Problem lies in the fact that GM thinks everyone lives in town, runs freeways at 80 mph, etc. Heck, my pickup never gets on a interstate highway except, maybe, once or twice a month. it doesn't even weekly get on a 4 lane highway of any kind. Mostly two lane highways and gravel roads. Something that GM didn't take into account that still exist in America as they set their new vehicle spec options.

Edited August 18, 2014 by Cowpie

[Super 8]

14.40 X 2.64 = 38, this wouldn't work for me but sure it does in an on pavement only environment.

The Columbia I just purchased has a 12.66 first gear X 3.58 = 45

[Cowpie]

Mine goes off pavement frequently, and I have no problems. I live down gravel roads and I usually take a load home a couple of times a week. I have a, somewhat, of a U shaped driveway that goes around the grain bin and barn. I get around there all year round with 46K or more in the box. It can be pretty soft ground certain time of the year. Enough that I also have full lockers in both drive axles and have to engage them sometimes. There were a lot of folks that tried to tell me that this setup wouldn't work. I asked them if they had ever tried it, and no one ever had. Well, I have for 294,000 miles and I have no regrets. To be fair, most of my running is on the highways, for sure. But that also includes a LOT of two lane, very hilly stuff with heavy loads. Numbers do look fine on a spread sheet, but they do not always reflect the broad picture. It is an unorthodox setup, but one I was willing to try and it has done just fine. I probably wouldn't have set it up this way if all I was ever doing was running in and out of rock quarries all day long. That is why we can spec trucks for what we do. Too bad we don't have the flexibility to do our pickups the same way.

 

You have 3.58, which is the same speed in a .73 top as mine is in direct. And that was my motivation. To run primarily in direct drive, which is 16th. It is more efficient and more power is not lost thru the parasitic overdrives. One could wonder why I didn't opt for a direct 10 instead of an 18. Well, because the direct 10 is not setup to handle the hp and torque mine is putting out. And I have 16 gears from the bottom up.

Edited August 19, 2014 by Cowpie

[redvett]

The 8L90 is a HD trans and wont be available in a #1500 truck. This transmission is not a joint venture with ford. A LD 8 speed is in the works.

[LongrangeLauber]

The 8L90 is a HD trans and wont be available in a #1500 truck. This transmission is not a joint venture with ford. A LD 8 speed is in the works.

Wrong. The 8l90e is going in all trucks and suvs with the 6.2 for model year 15. I'm sure by model year 16 other engines will get it as well. The HD trucks will probably stick with the current 6l90e for a while

 

Sent while in 'Murica...

[redvett]

The 6.2L is a restricted engine due the fuel economy and will not be the mainstream engine in any LD chassis. The 8L90 will not be used with the current V6 and small V8 engines. The MFR's are downsizing engine displacement for fuel economy. Expect smaller displacement engines and turbos in the future.

[Zane]

Hi everyone,

The email sent out today had the wrong link. Oops!

 

Click here to read my 8-speed impressions--> http://www.gm-trucks.com/forums/topic/163882-i-drove-the-new-8-speed-yesterday/

[Daryl Z71]

And they can expect me not to buy it. We've got a turbo charged Cruze that's my Wife's that's enough of a headache already.

[Zane]

The 6.2L is a restricted engine due the fuel economy and will not be the mainstream engine in any LD chassis. The 8L90 will not be used with the current V6 and small V8 engines. The MFR's are downsizing engine displacement for fuel economy. Expect smaller displacement engines and turbos in the future.

I very much expect the 8-speed to make it into the 4.3L and 5.3L 1500 Silverado and Sierra.

[kovs]

How about them getting their heads out of their @ss and realize people that buy the 6.2 for the tow want 3.73 or 4.10 Even with the new 8 speed it would be awesome!!

21-22mpg with my 10' 6.2 3.73 and it's stays in 6 th

Down where they test them and it's flat for 200miles where speed is 75-80 mph maybe 8 spd with 3.08 s is good. Not up here in canada.

My 25cents

How about the Eco tech 6.2 in a 2500 too instead of the tired old 6L

Not everyone wants the costs associated with a diesel .... Guess there are other brands to buy

[Guest Johno]

People have no idea what they are talking about when they say you need a 3.73 or 4.10 with the 8 speed. Rear axle means next to nothing. The overall drive ratio in each gear is all that matters.

[Jsdirt]

Are you serious??? Maybe if you commute to work exclusively in a pickup ...