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Discussion Starter · #1 ·
Hi guys im planning a gear swap in my 86 silverado 4x4.I am curently running stock 3.42 gears.What i wanted to do was go to 3.23 but need to know if i the front gears can be exactly the same or do they need to be say 3.20?The truck is a heavy halfton and uses a np208 i think.Also can i use a set of gears from a rear diff on the front or is it a different cut?thnx for your time!
 

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Before this gets tossed to the newbie section I'll try to give you some information, common gear sets for a chev are 3.08, 3.42, 3.73, 4.10, 4.56, 4.88, 5.13. I have never heard of 3.23's , so I have to assume you mean 3.73's. This is not enough of a ratio change to bother changing them, start thinking 4.10 or better. Would help if I knew why you wanted to change them, what you used the truck for, which tranny you have, and what tire size your running. Finally, Yes your front and rear gears always have to be the same ratio.
 

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common gear sets for a chev are 3.08, 3.42, 3.73, 4.10, 4.56, 4.88, 5.13. I have never heard of 3.23's
3.23s do exsist, hard to find but they do exsist, had a set in a 85 k20. oh and don't for get to add 2.73 to that list on 83 k10, had a set of those also.


i don't know y you would want to go from 3.42 to 3.23, not even enough change to bother with them. 3.42 with a 700r4 and 31" tires are a little sluggish, with 3.23 it would be even more sluggish. 3.73 or 4:10 would provide much better power and for gas milage. yes you will get better gas milage with lower gears, motors don't like to be lugged, get at the bottom of the power band (usually aroung 2000) at 60 and it will be better all around.
 

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Discussion Starter · #6 ·
thnx guys the reason i wanted to go 3.23 is milage reasons on the highway.the truck runs 10 bolt diffs front and back.the trans is a 700r4.On the highway i like to cruise at 130-140kmh,which beleave it or not :) goes through the diesel pretty good in my little 6.2 .More now since i installed the k&n airfilter.Ihave to change the rear anyway to install a posi,just wondering if i can use rear gears in the front diff :confused: and do i have to run a slightly talller gear for the front.tanx :)
 

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SInce my old '84 K20 6.2 got 21 mpg with 4.10 gears, 1:1 M465, and 235 tires, I know the engine doesn't become significanty less efficient when your buzzing it and it may get better. I'd say you have other problems or it supports big83chevy4x4's theory. 87 MPH is no way to get good mileage no matter what your gears are. SO I concur don't waste your time and money.

a fresh 4911 pump, 6.5 injectors, optimize timing, J intake, phat exhaust, timing gears will net better performance.
 

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Discussion Starter · #9 ·
So :rolleyes: can i install the same ratio gears front and back weather it be 3.23 or 4.11 or do i need a slightly taller gear for the front?and will a set of gears from the rear axle work in the front axle? :D
 

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you can put taller gears up front if you like breaking things. if not, then they must match (if you are running the same size tires on the front and rear, that is).
 

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Discussion Starter · #11 ·
Ok so i need a matched set then,the reason i asked was i recall hearing years ago that the front diffs have a tad taller gear to help pull the truck.Maybe its a ford thing i dont know.
So now when im scrouging through the junk yard can i get two sets of rear gears to make a set or does the front have to be specifically for the front?
 

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3.23 is a 10-bolt gear. They are the same gears front & back. You might be able to get them from a 2wd pickup, or an 80's cop car. (Caprice, Parisienne, Impala, etc.)

I have also seen 3.23 in a 3/4-ton front axle, matched with 3.21 in the 14bff rear. I believe it was the economy option at some point ;)

IMO that's a little on the wild side for gearing... I went to 3.21 from 4.10 on my Burb w/TH400, and went down to 29" tires because I had trouble getting to merging speed on the highway. I can't imagine OD on top of that :rasta:
 

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Discussion Starter · #13 ·
tnx u2slow youve answered both my questions :D I know what ya mean about merging onto the highway as it stands i have to leave it in drive untill i hit 100kph then i shit it to overdrive :D
 

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Actually rumpity, your right, the front diff ratio should be taller than the rear to help pull the truck, but must be with in 1% of the rears, so a 4.09 up front and a 4.11 outback would work and it come's out to .95%... but it has to be under 1.0 %. To find this, just divide the two ratios (front divided by the rear) and if it's 1.0 or less it will work.
 

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Well I stand corrected, I was just out sorting through some 14 B ff's I had picked up to sort out all the usefull spare parts I wanted and throw the rest in the scrap pile and was surprised to find one of them had 14 teeth on the pinon and 45 on the crown which works out to be about a 3.21:1 ratio. First time I have ever seen a set of these. They are completly useless to me, I only save anything from 4.56 - 5.13. If anybody wants to pay for the shipping they can have them.
 

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Discussion Starter · #16 ·
thnx tiny thats great info,i was under the same impression myself.So i guess it must be difficult to find gear ratio's like these?Probably have to aftermarket to find em.Hey smash i just dug up a 3.73 Posi 14bolt FF man are those massive units :D
 
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