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I read my glovebox tag....

PhoenixZorn

PhoenixZorn

1/2 ton status
Joined
Mar 17, 2005
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Location
West Allis, WI
I noticed that my truck came stock with 31x10.5x15s... I was under the impression that Blazers came stock with 29s?? After looking over the mileage chart at 4lo.com, I'm just wondering if it's possible that my truck not only came with 31s, but with 4.11 gears as well?? It's a dog on accelleration, and in 3rd (465 with Low) gear, it doesn't get up and go really well, but it can accellerate from 65-85 in a few seconds. I had the rearend rebuilt... but I don't think the shop ever looked at the ratio.... so I can't even ask them what it is... I'll know for sure when I change my diff case oil this summer, but I need "educated guesses" right now.
 
should say on that tag what the gear ratio is. If not, jack up the truck, spin the tire and count how many times the pinion goes around, if it goes around just over 4, you have 4.10s. Now, Im not positive, but if its an open diff, you may have to divide the number by 2, but Im sure someone else will chime in.
 
Jack up one wheel, put truck in neutral, spin wheel exactly two times, count driveline revolutions.
 
31's and 4.10's would be quite snappy. I'd say 3.08's or 3.42's are way more likely. My Jimmy which was also a SM465/NP208 truck stock had 2.73's and 31's from the factory.

Rene
 
Rene, I do believe my truck was a Jimmy when it was brought into the world... but due to lack of any identifying badges except for the Sierra tag on the dash, I have no proof of either Blazer or Jimmy. There is a Bowtie grille on it, and all other badging, including the GVW sticker and original Engine compartment sticker have been removed. It was originally an automatic, so I don't know what the gearing is. I didn't see the gear ratio on the dash tag, but I'll run out there now to check it.


**EDIT**

Just checked the tag, it's a Jimmy for sure but I'm still going to continue badging it as a Blazer because Jimmy is just a P*ssy name... it had 3.08 gearing and it did have the 465 stock... I'm kinda pissed about that since the guy I bought it from put in an automatic, non-tilt wheel, and it came with tilt wheel from the factory. It also is still painted it's original Apple Red color, but the topper was white, and that's now red too. Not that I mind, I love the red, but I keep finding things here and there that the guy lied about when he was selling it. I don't know if it had any gear changing done, but it is a slug... I do love the highway mileage though, since my entire drive to work of 19 miles is 55mph highway and I can take it at 65 and 2400 rpm. NICE... I got 12.69 mpg on the last tank, up from 10.5 on the first... before acetone... I just put in 2 oz for my 20 gallon fillup, don't want to ruin a good thing yet.

Anyway... when I put 35s on the truck, I'm going to change to 4.11s or 4.56s... what's a good price to pay for both axles? Also, should I get a higher ratio for the fronts, or keep them the same front and rear?
 
31" and 2.73 were most common

3.42 one of the least common,

in the K-5's and K-10's

i have some spid labels that list 31 x 10.50 from factory, white wagons, etc.

gm made em that way
 
Either your tach is off, or Im misreading a gear ratio chart. With a true 31" tall tire, at 65mph, turning 2400rpm, you have 3.42's.
 
Well... I'm not sure either way... but for the first tank of gas after my engine replacement, I was running at 2600rpm at 65, and as I got down to the end of the tank (and neared 500 miles travelled) the rpms actually went down. I think that's why I am getting better mileage now than on the first tank. Now I'm running at 2400 rpm at exactly 65mph, and around 26-2700 at 75... not a bad deal...
 
Well... even though the tag says 3.08, I'm gonna go with the 3.42 since my rpms and tire size suggest it. Until I find out otherwise anyway... what should I expect to pay for 4.11 or 4.56 gears?
 
Gear swaps cost about $300 for labor, $200 for ring and pinion, and $100 for new differential bearings and seals, per axle. So about $1200 total, if you pay someone to do it (it can be very difficult to do right if you have never done it). If you think your RPM's change at the same speed with a manual, don't trust your speedometer or tach (or both!). Also, a claimed 31" tire is not 31" and even less as the tire wears. I'm pretty sure you have 3.08's.
 
If you are only looking to go 4.10, the cheapest answer is to buy 3/4 ton axles. 4.10s are common and if your not in a hurry you can usually get them for $200.00 a set. How attatched are you to your current wheels?
 
thor, why the question about my wheels? because of the 6 lug thing?

I have Baja Widetracks, and I measured them... they are just shy of 31 inches under load at 30psi. Why shouldn't I trust my tach and speedo?? It was working just fine before I swapped my engine, and everything else is the same... The RPMs dropped to 2400 from 2600 after 500 miles of breaking in the engine at 65 mph, and I've checked that against my wife's car also travelling 65mph with cruise control.
 
38377k5 said:
Gear swaps cost about $300 for labor, $200 for ring and pinion, and $100 for new differential bearings and seals, per axle. So about $1200 total, if you pay someone to do it (it can be very difficult to do right if you have never done it). If you think your RPM's change at the same speed with a manual, don't trust your speedometer or tach (or both!). Also, a claimed 31" tire is not 31" and even less as the tire wears. I'm pretty sure you have 3.08's.
Click to expand...


If I have shorter tires, my rps would be higher... yet you just said the opposite. At 2400rpm, and 31s, I would have 3.42 gears or non-stock tranny gearing.
 
My bad about the tire thing, you are right (I didn't really think about that one). If nothing changed (i.e. your rear end ratio or tires), the RPM's cannot be different at the same speed because you have a manual transmission. Hence, either the speedo or the tach is not being consistent.
 
So there's no chance that a brand new un-broken-in engine would have to have higher RPMs to spin the tranny at the same speed as a broken in engine?

<---- Self proclaimed engine newb...
 
Nope, if you have a manual the RPM of the drivetrain (including the engine) has to spin an exact RPM to make the vehicle go a certain speed. If the revs go higher, the vehicle goes faster and vice versa.
 
Well... then maybe I was imagining things, and my RPMs never went down... i do know my mileage is improving though...
 
PhoenixZorn said:
If I have shorter tires, my rps would be higher... yet you just said the opposite. At 2400rpm, and 31s, I would have 3.42 gears or non-stock tranny gearing.
Click to expand...

With 35's or 36's and an SM 465 4.10's are a good choice. A 10 bolt front you can live with but I'd seriously think about putting a red cent into a rear 10 bolt. Most everyone here will recomend going 3/4 ton, just because it makes the most sense. For less than a third the cost of re-gearing your 10 bolts you can get a 10/14FF combo with 4.10's already in them. The only 'extra' cost is a set of 8 lug rims.

With 4.10's and 35's you'll be turning a hair over 2500 rpm at 65, so your mileage shouldn't really change much if any.

Rene
 
Cool... I'll look into it when I have money again... I'm still paying off the engine work that was just done, and I need to pay for my break-in oil changes to make my warranty valid...
 
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