2009 Re-gearing Question

jrdifranc · September 17, 2009

I was wondering if anybody had any opinions on re-gearing a 2009 Silverado that has the 6-speed transmission (w/ manual shift function) to accommodate 35" tires? I currently have 3.42 gears. Not sure what the relationship is between the transmission and rear end. Also, if yes, what is recomended and does any re-gearing need to be done up front? I'm getting ready to put a 6" lift on.

Thanks, Ron

brims · September 17, 2009

The 6L80E with 3.42 rear end is equivalent to the 4L60E with a 4.50 rear end. A lot of guys seem to go to the 4.10 rear ends on the 4 speed, some go with the 4.55.

If you regear the rear you have to regear the front otherwise you'll have issues in 4 wheel drive.

Matt_ · September 17, 2009

4.10 is a good gear for the 6spd with 35s.

i went into detailed discussion on this in anothher forum... ill try to copy and paste later tonight

in short, the 4.10s will give you the equivalant of 5.13s (actually deeper) off the line and the choice of 4.88 or 4.10 as a highway cruising gear (due to dual OD gears in the 6spd) when compared to the 4spd

jrdifranc · September 18, 2009

Thank you both. Sounds like I shouldn't have to worry about it, realizing I will lose some current performance, but I really don't plan on racing around town with 35's on. I just purchased a diablo sport and plan on having a custom tune done by a local performance shop so I'm sure that will help offset any negative performance affects the larger diameter tires may have. I would be interested in the previous posts on this topic if not too much trouble. Thanks again, Ron

Matt_ · September 18, 2009

Hey Ron, you're definitely going to want to regear with 35s. You'll otherwise be rendering 6th gear useless...and the truck may even have trouble staying in 5th depending on the type of highways you drive.

If you're not towing and are way more concerned with gas mileage... 3.73s would work well. But from my experience (ran a whole bunch of tires and gear combos and now have the 6L80E) and my understanding of final drive ratios; 4.10s are possibly the most ideal combo for a 6L80E truck with 35s. IF you were planning on towing a lot and lived in mountainous terrain, 4.30s would be something to consider.

Here's two of my posts:

Very true. And that's the beauty of the 6 spd trans... both 5th and 6th are considered OD gears. 5th is .85 and 6th is .67 (4th in the 4spd is .70).

So... if you're on nice flat terrain and without a huge headwind, the 4.10s & 35s will cruise right along at a few RPM's less than 4.10s would in the 4pd. But, if you're in a section with a lot of hills or maybe there's a big head wind thats taking a lot of your power you can put your truck in 5th gear and have a slight mechanical advantage over a 4spd truck running 4.56s in terms of final drive ratio.

The one downfall of a 6spd trans is due to the large span of ratios, it's extremely hard to please both ends of the spectrum at the same time. GM, ingeniously BTW, understood this and designed the 6spd with 2 overdrive gears AND gave the user the ability to choose which gear to cruise at with on-the-fly control using the gear selector.

If it was any other way where we didnt have the choice and/or control over 5th & 6th gears... and the OP was doing a ton of highway, then I would agree that 4.56s should be given more consideration (or a 4.30 ratio)... but, since we do have the control; 4.10s really are optimal. You'll have MORE off-the-line power than a 4spd with 5.13s and still have the "option" to cruise on the highway with either lower RPMS than a 4spd with 4.10s or slightly higher RPMs than a 4spd with 4.56s.

FYI:

1st gear in 4L60E = 3.06

1st gear in 6L80E = 4.02

4.56s in the 6spd would be equivalent to 6.00 (mathematically) in the 4spd

^^ IMO this would make 1st gear near useless

4.10s in the 6spd would be equivalent to 5.38 (mathematically) in the 4spd

^^ A little more gear than a 4spd truck with 5.13s off the line... not bad IMO

Just had a quick idea... here's the gears and comparisons:
4L60E

1st 3.06

2nd 1.75

3rd 1.00

4th 0.70

4L60E Final drive ratios with 4.56 gears(use for more comparing on your own with the final drive ratios posted below with 4.10s in the 6spd)

1st 13.95

2nd 7.98

3rd 4.56

4th 3.19

6L80E

First:4.02

Second:2.36

Third:1.53

Fourth:1.15

Fifth (OD):0.85

Sixth (OD):0.67

6L80E w/4.10 gears and equivalent 4L60E gearing (gearing is mathematical and may not exist)

First Gear = 16.48 Final Drive Ratio. Same as 5.38s in 1st gear with 4spd.

Second Gear = 9.67 Final Drive Ratio. Same as 5.53s in 2nd gear with 4spd,

Third Gear = 6.27 Final Drive Ratio. This is an odd one... its like having 3.58s in 2nd gear OR like having 6.27s in 3rd gear. Not really a fair comparison since 1st/2nd/3rd in the 6spd are all about accelerating and 3rd in the 4spd is about "maintaining"....

Fourth Gear = 4.71 Final Drive Ratio. Same as 4.71's in 3rd gear in the 4spd. Using 3rd for the comparison since these would be your max-capacity towing gears. So if you would run 4.88s w/35s in the 4spd and think that's good for towing, then 4.10s in the 6spd are good for towing (see the similarity?)

Fifth Gear = 3.48 Final Drive Ratio. Same as having 4.97s in 4th gear (OD) in the 4spd. Here's where the 4.10s will perform well on the highway with 35s if there are hills & such.

Sixth Gear = 2.74 Final Drive Ratio. Same as having 3.92 in 4th gear (OD) in the 4spd. Ideally, this should yield some good gas mileage on a flat highway.

Basically, check out 1st and 2nd gear with the 4.10s. Its like running 5.13s off the line.... that truck is going to move! And then 4th/5th/6th gears with the 4.10s let you choose... 4th for towing is ideal with those 4.10s, just like 4.88s in 3rd gear is ideal with the 4spd. And then 5th & 6th let you adjust your OD gear based on conditions.

jrdifranc · September 18, 2009

Excellent. Thanks for the clearity and your time. I will look more into the cost and details of having this done with my local 4x4 shop. Cheers

J-man67 · September 18, 2009

Excellent. Thanks for the clearity and your time. I will look more into the cost and details of having this done with my local 4x4 shop. Cheers

I read that the pinion bearings in the 09s are not yet available in master install kits so you might consider buying one from a dealer if the shop that puts the gears in is not confident they can re-use the old bearings!