I hual a 3 thousand pound boat and am wondering if putting a different size diff will help in any way. What size will help too?

 

First of all, is that a 2wd or 4x4.
If it's a 4 wheel drive you need to change both sets of gears to match. $$$$$$$$$$$$$
I also pull a boat, but it's a lot lighter. I use 2 of my trucks for pulling. The black one has 2:73 gears, which is good for the highway, and it pulls my boat. The orange truck has 4:10 gears in it. With the 4:10 gears I can climb up anything and I don't even notice the boat. My gas milage is terrible with the 4:10 set , but if I wanna haul something heavy, that's a good gear set.
So, it's a tough call, because all my trucks are V8's I have enough engine power to do the job.

I don't know if I've helped at all, but hopefully that's a little more information for you to think about.

I have a set of 3:73 gears for the orange truck, I was thinking about trying out, but with the amount of work involved, I'm in no rush.
I figure the 3:73 set should give me a little better fuel milage and top speed and still pull whatever load I need to, as well as climb all the hills I dare to.

 

So Chevy Lover... you OWN a gas station then.. RIGHT?.... if not.. you're buyin' one for someone everytime you hit that fuel dock..... (Just Kiddin') I couldn't resist....:P

 

Yeah, you'd have to change both the front and rear gearsets. What does your truck have stock? The RPO code list should tell you this.

 

It has stock diffs. I was looking at Summit and they have a lot of choices. I was hoping to get some info in which sizes do what?

 

Stock as in what? There are like 4 different axle ratios available... You really need to figure out what you have before attempting to change it...

Here are the RPO Codes pertaining to axle ratio for s-series vehicles:
GT4 Rear Axle: 3.73 Ratio
GT5 Rear Axle: 4.10 Ratio
GU4 Rear Axle: 3.08 Ratio
GU6 Rear Axle: 3.42 Ratio

As well as:
G80 Rear Axle: Positraction, Limited Slip

Now I think that GU6 (3.42) is the most common for blazers. Based on my RPO code listing, my Bravada has 3.73's

 

I think he has 4wd.

G/L finding 7.25" pinion ring grear set in a higher ratio. Tranny shift points will be screwed up plus you'll be winding out the motor at highway speeds. I think we can tow up to 7500lbs anyway.

I would save the gear money and put it towards more marine coolers.

 

Yeah I know he has a 4wd truck.

Doing a little bit more research, the earlier s-series trucks were available with the 3.08 ratio. Also, it seems that the 4.10 ratio was only available in 2wd trucks. So you've either got the 3.73 or the 3.42.

 

there are a TON of gear sets available for the gm 10 bolt rear.

as a general rule:
lower number (2.73... 3.08) = higher top speed, lower rpms on motor (better gas mileage), less low range power
higher number (3.73... 4:10)= lower top speed, higher rpms on motor (worse gas mileage), more low end power


gears are expensive to have installed, and its not a do it yourself job unless you know what youre doing. you have to check the wear pattern, backlash, etc etc. the local place here charges ~$500 or so to do it.

 

Thanks lunatic you made it understandable. Is that 500 dollars for both with gears? Or 500 dollars labor only for front and back? Basically I want more toque for my boat. It takes off slow. I believe I read in the owners manual that a blazer maxed out towing @ 4000 thousand pounds. Aint no way in hell my Blazer is hualing 7500 hundred pounds as a matter fact anybodys blazer can do this I like to know! With Hypertech Tuner I can change gear ratio's Low. What do you mean by Marine coolers? Oh now my blazer got the hickups but I will leave that for another thread.