Originally Posted by imkzru
I also have a 2010 Silverado LT Crewcab 5.3l engine with the tow group and was wondering when you go over mountains and the truck downshifts, what RPM are you taching? I just went from Virgina to West TN and going over black mountain on the down hill side the grade is 5% for about 6 or so miles and I found that every time I tapped my brakes the truck downshifted and I was taching between 4.5 and 5k RPM. To be honest I do not like this as it does slow you down, but when the speed limit is 65-70 and you have idiots that want to ride their brakes and truckers that want to ride a little close, this rapid decrease in speed I can see causing and issue. But beside that the RPM's has me concerned. Most V8 engines that I'm familiar with red line at 4k or 5k. My truck does not have any yellow or red line marked on the tachometer, but that high of RPM on a V8 can not be good. Do you know what the red line of this truck is?
What axle ratio & tranny does your truck have? Two examples:
6 speed trans'
4.10:1 axle when in 5th (0.85:1) = 3.48:1 final drive ratio
4.10:1 axle when in 4th (1.15:1) = 4.71:1 final drive ratio
3.73:1 axle when in 5th (0.85:1) = 3.17:1 final drive ratio
3.73:1 axle when in 4th (1.15:1) = 4.28:1 final drive ratio
W/ the ratios being what they are in the 6 speed, it's quite a drop going into 4th. That's probably what is causing what you're encountering and rightfully so. A greater than expected deceleration. My truck was ordered w/ the 4.10s (I'm a firm proponent of More's Law
). I was doing the math around the time it was being built (too late to change order) & realized what the final drive ratios were going to be. For whatever reason (whether a mistake or content change), my truck was built w/ the 3.73s. It turns out I'll probably be happier w/ the 3.73s.
Originally Posted by slpybeartx
Thanks for those codes, revrnd! I am very intrigued by the "6L80". I would like to trade in my 2008 Z71 for a 2010 Z71 to pick up the new tranny and increased towing power.
Anyone have any comparison between the two?
Everything you wanted to know about the recent GM automatic trannies:
4L60E Trans (LD Trucks):
4L80E Trans (HD trucks):
6L80 trans (RPO MYC) LD trucks & SUVs:
6L90 trans (RPO MYD) HD trucks:
Allison Model 1000 trans (RPO MW7)
HD trucks w/ Duramax diesel:
Note: 6th gear & manual gear selection capability was added for the 2006MY.