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Need to know gear ratio

GruntHunter

GruntHunter

1/2 ton status
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Location
Florida (Space Coast)
:confused: I had some minor work done on my '87 Blazer today. I had my complete drive train serviced. When they had the cover off the differentials I was able to read these numbers off of the ring gear:

2GM 260151031 13 40 1 92

Can anybody tell me what gear ratio I have. The guy doing the work gave me a number that really surprised me. I need to confirm it. I didn't have time and didn't want to get in his way to count the teeth. The covers have 10 bolts in them and he said it was a Dana 44.
 
Geasr Ratio

SCRAPPY88:
Yep, that's just what he said. I was expecting maybe something around 3.50 but NOT 3.08 ! Now I know why I always felt I had a real 'dog' with no power. We talked about putting 3.73's in it with another Gov-Lok up front but he want's $1,500 to do it so I think I'm going to look around some more. He was suggesting 4.10's but with the price of gas now I'm wondering about how bad my gas milage would get with them.

REDNECKDUDE:
If I don't have Dana 44's then are they Dana 40's ? ? ?
 
GruntHunter said:
REDNECKDUDE:If I don't have Dana 44's then are they Dana 40's ? ? ?
Click to expand...

Nope, they are GM corporate 10 bolts. It was GM's replacement for the Dana 44. See if you can get a pic of the diff cover up front to be sure. A 10 bolt cover is almost perfectly round where a dana 44 has straight edges to it.

Rick
 
yep, not every axle made was made by Dana Corp...some were actually made by the vehicle manufacturers.
 
they didn't make it

a dana 40 never seen such a creature now they made a dana 50 but its easily reconized by the ball at the end of the axle tube and they were never in blazers...you cant see the axle u joints...i think hes in denial 87 blazers had 10 bolt front and back if its a dana some 1 put it in there and i dont mean gm
 
I too feel mine runs like a "dog". We have 454, TH350, NP205, Dana44 f, Corp12 r, 3.73's and 35" tires. Mileage is right at ten. Where do I go to find the optimum mix of gears, rpms, tires, trans, etc? I would like to gain the understanding and knowledge to talk and sound half-way intelligent. I would love to have a chart of the parameters. It would be helpful in planning the next major expense.

In the Oct2005 issue of Off-Road magazine, page twelve, see the letter of the month. I sent the editor an email, but it didn't go through.
 
use a search engine

but with 454 it shouldn't feel like no dog look for rpm equations or charts it will tell u what gears u need to put it back like it was stock with the bigger tires tho i'll c if i can locate 1 or at least the formula to calculate gears for tire change..maybe search for that
 
Gear Ratios

blazin blazer,

That would be good info to read. I'm running 31x12.50 R15 Pro Comp Mud Terrains and would like to change out my 3.08 gears but am not sure just what I should go to. I was thinking 3.73 but the guy who worked on my Blazer thought I should go all the way to 4.10. I don't do any rock crawling of trail riding here in Florida. I just use it on a hunting lease where it can get wet and soft in some areas at times and want to make sure I have ALL wheels pulling for me when the need comes up.

When my speedometer reads 50 mph I'm really going about 59 mph. I was always trying to figure out why. The 31's are within the factory limits. If I go to 3.73 or 4.10 will my speedometer read slower or faster than what it is now ?

Since one of my autolockers appeared to be getting a little loose and sloppy I did have him install a set of Warn supreme manual hubs. At $89 for the pair it was probably cheaper then trying to replace the single GM unit.
 
try this

http://www.4lo.com/calc/geartable.htm

it doesn't go all the way down to 3.08's but it should give u an idea of what gears to run with what tire...if you want it to be a little higher mpg or lower mpg with more grunt it shows you it also shows you about where your gears should be to be back around factory the green..it shows 4.11 to be close to factory the # in the boxes tells you what rpm your running with a certain tire size and gear ratio at 65mph its kinda self explainatory..it says for mostly around town that 3.73's are the way to go if pulling loads it says go with 4.56 with 31" tires , its a handy reference a keep it on my favorites so when i change tire i know how to change gears to keep it running about the same.. the chart i assuming a manual tranny but tells you what to expect with autos also....hope this helps
 
Gear Ratios

Blazin_Blazer

Awesome ! ! ! I really appreciate the link. Great info. Looks like 4:40 is what I deed. With my auto w/overdrive I should have a good combination for the highway also. Maybe my speedometer will get back in line :-)

Now I need to decide whether to just go with a Gov-Lok up front with new gears front and rear or change out and go to some other limited slip like a Auborn, Eaton or Tru-Trak. Are they basically all the same? I don't want something noisy.
 
GruntHunter said:
Blazin_Blazer

Awesome ! ! ! I really appreciate the link. Great info. Looks like 4:40 is what I deed. With my auto w/overdrive I should have a good combination for the highway also. Maybe my speedometer will get back in line :-)

Now I need to decide whether to just go with a Gov-Lok up front with new gears front and rear or change out and go to some other limited slip like a Auborn, Eaton or Tru-Trak. Are they basically all the same? I don't want something noisy.
Click to expand...

If I read your post right, and you want to stay with the 31"tires, go with 4.10's since they are more common and cheaper to get. If you go much higher, you will be revving pretty high at freeway speeds. Your 700r4 will be a big help with the OD. You might even see a slight improvement in mileage since the engine will be in the optimum/efficient rpm range.

AFA as what type of carrier to get, if you Easton posi units, but they are kind of pricey. You might want to try finding some used axles with the right gear ratios. It may prove to be cheaper than spending $1000 for all new parts and then paying to have them installed.
If you need or want any help with all this, pm me. I'd be happy to help you out, even if it means sending you somewhere else to make sure you get what you need at the best possible price. :wink1:
 
i was just poionting out some math formulas

i wasn't condoning any vendor over another i was just showing him the chart and math.....looks like you be in good hands now
 
Shane74,

You're correct. I read my reply and just noticed I had made a typo. I did mean 4:10 gears.

Yeah, the guy who did the work for me suggested Auborn limited slips front and rear with 4:10 gears but he wants to charge me $2,235.54. $500 of that is for labor with $425 for gears, $920 for posi's, $235 for bearings and $29 for misc plus 6% tax. He did offer up a used Gov-Lok for up front but still wanted $1,551.84 out the door. That just seems way to high to me. I see adds from $wheel Parts for kits that are supposed to have everything for around $1,100 and then I'd have to add installation costs. I was expecting to be in the $1,400 to $1,600 range for all new stuff!
 
What do you plan to do with this truck? Are you going to lift it later? If you are, gear NOW for the bigger tires. For example, if you plan to do 35" tires later, gear it 4.56 now. Now, if you are mud running only, limited slips might work, but if you are keeping it 31's, you'll save money by just dropping in a quik-lok in the back.
 
89GMCSuburban,

I have no intentions of lifting it. It's a hunting vehicle and I just need to get through the 'soft' spots in the roads and pastures. I have a hitch carrier on the back to load my deer and pigs on and it's real nice to be able to lower the rear window and be able to reach in to get something without needing something to stand on.

It currently has the GM Gov-Lok in the rear with an open front. I would like to have gone with 33's but the 31's on 8" rims was the best I could do. I probably should have gone with a 2" lift so maybe I could have fit my 31's on 10" rims. I like the widest footprint I can get going through the soft stuff.
 
You might want to think about getting the matching speedo gear for the tranny, so your speedo is not too far off. My 1 ton had a tranny replaced, and now the speedo is 30 mph off at highway speeds. Obviously, the speedo gear in the trans is for a highway gear, not the 4.10 that I have.
 
Just another opinion...for perspective. I've got an 87 with 3.73s (w/gov-lok) and 31s and I really like the combination. At 65 mph the engine's turning just under 2000 rpm, which is a bit below the peak torque (2600 rpm), but if I need the torque I just kick it down to 3rd and it puts me right at 2600. Using 3.73s gives you a real overdrive gear and you'd still have about a 30:1 crawl ratio for your hunting forays. 4.10s gives you a 32.75:1 crawl ratio and puts your overdrive gear at about 2600 rpm at 65 mph, which would lower your gas mileage. Unfortunately, 3.73s were the lowest gears GM offered for the Blazer in the 10-bolt. If you want to save some dough and you're patient, I'll bet you could find front and rear 10-bolts with 3.73s and a gov-lok (rear) for a lot less than all new hardware. Good luck, Dude.
 
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