Diff gear swap done

bgbdwlf2500 · March 29, 2018

So after all the posts I've read and replied to, here's my very very very initial experience and I will tell you why I say that a little later. I've had the truck a little over 2 years now, got on this forum and without really looking happened to find that my 2010 Sierra crew 2wd Z60 has 3.08 gears. Initial thought was there's no way a truck would have 3.08 gears but they did. So after this 2 years these are my observations with the 3.08 and it should be noted that I bought the truck used, it should have had whatever tires come with the 20" rims but it had 18" 275/70/18 which is a 33" tire. I can't comment on any difference in feel from factory tires to the 33" tires with that gearing because they were on it from day 1. Acceleration from a stop has felt sluggish from day 1, I don't run my truck hard but you can tell that it doesn't have the go that it should have for a truck. On a 45mph road, if someone slows down in front of you, you can't make the truck go again even to keep up with most cars and trucks out there without forcing a downshift because it's in 6th gear at 45mph. Highway - you'd think highway would be great with 3.08s and at certain speeds it absolutely is those speeds however are between 60 and 75 but only on flat ground. Anybody in front of you that slows you down will demand a 1,2 or 3 gear downshift to even remotely feel like the truck is trying to accelerate. On a hill just give up until it hits the top. Anything faster than 75 the wind resistance becomes too great for the size of brick going down the road and there's not enough power to overcome it which again creates a downshift. Some speed vs rpms I've noticed:

45 mph 900 rpm

60mph 1200rpm

100 mph 2000rpm just before it runs out of juice and downshifts to 5th. Was done on wide open road with speed limiter and rpm limiter disabled. Even at 100 in 5th was around 2500 rpm but still not accelerating just maintaining.

That being said, my very very very short experience with the 4.10s is that the first 4 gears go through quick. At 50 mph looking at about 1400 rpm which is still very very smooth. Flat highway at 65, truck is able to slow down and ease into the pedal while accelerating without a downshift. And that concludes my testing so far as the mechanic that installed them found a broken engine mount. I knew there was something wrong but thought it was the drive train slop I've read about. That being said it may not always be in driveshaft, check your motor mounts. I haven't seen many or any posts on motor mounts but it is apparently very common by looking on youtube. I am having it replaced tomorrow and will do some more testing and add more info. So far I will say that the 4.10s may be more than needed on 33s or smaller. 3.73 may have been a better choice but the trans is learning the new gears. I am using superchips to compensate for the tires and now the new gears. Sorry for the long post but wanted to throw out as much info as I could from my experience not theories

Grumpy Bear · March 29, 2018

May I ask what motor you have? Thanks and nice write up.

bgbdwlf2500 · March 29, 2018

15 minutes ago, Grumpy Bear said:

May I ask what motor you have? Thanks and nice write up.

5.3 iron block aluminum heads. I bought the truck with 103k it has 130500 now

Edited March 29, 2018 by bgbdwlf2500

muddkatt · March 29, 2018

So I take it that you are both impressed with the 4.10's and would make the same choice again?

swathdiver · March 30, 2018

Another reason your truck feels sluggish is because of torque management in the stock tune. This can be lessened or removed resulting in greater drive ability and making use of all of the engine's horsepower with a custom tune from companies like BlackBear.

My truck is doing 82 mph while turning 2,000 rpms with 3.42 gears. At 45 mph it's turning just over 1,100 rpms in 6th.

Now you should be turning about 1,300 rpms to do 45 mph, right?

bgbdwlf2500 · March 30, 2018

13 hours ago, muddkatt said:

So I take it that you are both impressed with the 4.10's and would make the same choice again?

After I get the engine mount done today I will push it a little harder and see how it feels. I used a gear calculator before I made my decision and I mainly went with 4.10s because it's not a factory option. I think with ratio in first in the trans that the 3.73 would probably be better all around unless you're on bigger tires.

2 hours ago, swathdiver said:

Another reason your truck feels sluggish is because of torque management in the stock tune. This can be lessened or removed resulting in greater drive ability and making use of all of the engine's horsepower with a custom tune from companies like BlackBear.

My truck is doing 82 mph while turning 2,000 rpms with 3.42 gears. At 45 mph it's turning just over 1,100 rpms in 6th.

Now you should be turning about 1,300 rpms to do 45 mph, right?

I know the torque management doesn't help but a 3.08 gear adds to that. I can disable tq management with my superchips but I have chosen not too for nowsince I'm still paying on the truck. Yes, around 1300 at 45 and was pushing 2000 at 70

bgbdwlf2500 · March 30, 2018

Here's the motor mount

bgbdwlf2500 · April 1, 2018

So after having the motor mount changed, big difference in feel of the truck just from that by the way, I'm liking the gears so far. The truck accelerates smoother and I think the shifts are better also. First gear is really short, there's no doubt about that 2 to 3 and 3 to 4 do happen quicker also. It gets into 5th and 6th around the same time but is able to maintain them way better than before. I haven't gotten it out on the highway for any time yet but I start a new job tomorrow so depending on traffic I may get a chance to see how it runs. I may post one more time after this week and then I will probably get a good long run on it for mpg numbers and driveability. I will respond to any questions I see though

bgbdwlf2500 · April 15, 2018

So my new job is 64 miles round trip, 2 weeks down at this point. I checked friday morning, trip was at 340 miles fuel remaining was 100 so I'm not seeing a loss in mpg, which really isn't a surprise to me since the engine was lugging with the 3.08 gears. My commute in the morning usually goes smoothly without much stopping, but there definitely is some slowing down and not running highway speeds, usually ends up being about a 45 min ride. Afternoon is quite a bit of stop and go and usually takes an hour or a little longer. Performance wise I couldn't be happier although at 45 mph in 6th gear it still doesnt want to pull through the gear, it's just too high of a transmission ratio. Anything above 50 or 55 it will pull through the gear and will actually accelerate even going up the 2 steep bridges I have to cross on the way to work where before it was downshifting just to maintain speed. I am contemplating raising the shift points as 1st 2nd and 3rd are really short and in stop and go traffic that sucks. Also contemplating disabling some of the tq management to see how it feels without it.

One thing to note, the more you spend on the gears the quieter they will be. I bought the gears and master rebuild kit on Amazon for 185. If you don't spend 400 + on just the gears you will have some noise. The mechanic set mine up to where the noise is when the truck is coasting when you're just at the point where you're barely on the gas. If you're in the throttle its quiet, if you're totally off the throttle its quiet. The noise is a slight humming noise, its not very loud especially with the windows down and the radio on. The mechanic told me a little heavier oil may help so I'll let the gears break in for about 5000 miles and change the fluid.

So final thoughts, I'm happy I did it. If I bought a truck with anything less than a 3.42 I would do the swap again but now that I know gm puts gears like that in the trucks I'll make sure to check this time. Before the swap I wouldn't even think about trying to jump out in traffic and accelerate because the truck was such a slug that I didnt want to chance it but now i have a lot more confidence that it'll go when i need it to. The truck has the hd cooling so I added roughly 2000lbs to the towing capacity.

bgbdwlf2500 · April 21, 2018

bgbdwlf2500 · April 21, 2018

So here's 2 shots, trip meter and remaining fuel meter. I am actually seeing the average mpg go up slowly but it hasn't been reset in 10000 miles or so. Keep in mind this is some true stop and go traffic in the afternoon, took me 1.5 hours to go 32 miles yesterday.