rear axle ratio RPO

[70shorty]

Yo dudes, what's up,,,
I have a question about the numbers on the drive axle,,, what do they mean...WRD ? 343 2 the rest of it was to hard see,,,
Just replaced my old rear end with this one,
my old one was WRD C 258 1,,
I'm tring to find out the ratio on the new one,,,
old one is a rpo code GU-6 3.42's HELP,,,

[70shorty]

Ok here's one,,, Why the hell do I have to spin both tires to get the pinion to turn,,,? use to be all I needed to do was spin the right rear to check ratio,,,
Checking the ratio the old skool way,,,

[drperry]

If it's the 4 banger, you don't want 3.08. 3.23 would be the tallest I'd put in it...

If it's a single cab short box, you could maybe work with the 3.08... But 3.23 or 3.42 is what you'd want.

[70shorty]

Hey thanks for the come back,,,
Yeah it's the 98 4.3 ext. cab short box,,, I had the 3.42's in it had to swap it out for another rear end my old one cracked when the u joint on the rear of the shaft let loose at 80+ on the hiway,,, what a ride that was,,,felt like a paint shaker,,,,
So now I'm thinking I have 3.73' not sure yet,,, I need to pull the cover and check.
I like the new exceleration, so I'm thinking I have the 3.73's..
But I need also to reprogram the computer,, cruising the hiway at 3 grand, speedo's at 97mph and there's nothing left in the throttle,, sucks man,,up against the gov..

[drperry]

My bad, forgot to quote the post I was replying to and didn't check for a new page, lol.

Yeah, you probably have the 3.73s now...

[70shorty]

That's what I thought,,, now to find someone who can reprogram my ECU,,, Or swap out the gears,, hate to loose the 3.73's but what ever works the best.
I did think of buying the scanner for myself but, not sure I want to spend a couple of hundered for a one shot deal...

[Gator4x4]

my 96 4x4 4.3L has the 3.42 axle now i put 33x12.50 x15 on it with steel wheels and now my power is suffering a lil and it has to shit down on the highway to pull most hills now, should i change the gear ratio in the front and rearend, or just the rear and if so, what ratio should i go with i was thing 3.73 or 4.10 someone help me!

[Gator4x4]

my 96 4x4 4.3L has the 3.42 axle now i put 33x12.50 x15 on it with steel wheels and now my power is suffering a lil and it has to shit down on the highway to pull most hills now, should i change the front and rear axle or just the front and which gearing should i go with i was thinking 3.73 or 4.10, someone let me know!

[Hoover]

got a 96 S-10 4.3 auto with a 3.42 rear end and RPO G80

I have a silverado with the G80 locking diff and I know what it feels like when it is locked and my S-10 does not even come close. I've gotten stuck in wet grass and dug a hole with just 1 wheel. I'm the second owner, the first was an older gentleman that didn't change anything on the truck. Don't know if its just a mistake with adding the RPO code of if its just the locker itself worn out.

Any kind of help would be most appreciated.

[lowereds10extcab]

alright i am very confused. i have a 93 2.8L v6 with a 5spd. and i know i have 3.08 diff gears. but it rpms super high and has absolutly no power, (i have to downshift to at least 3rd gear and a million rpm to get up any incline) would it hurt or help to go to like a 3.73 gear. SOMEONE PLEASE HELP ME.

[personnaobscura21]

ok lemme cap what a locker open diff and a posi really are(and limited slip for those of u who think thers a difference between lim-slip and posi-trac)
lets start with the standard

"open differential" which is simply a standard rearend with a standard spider gear which by flaw of design directs all the power to the one wheel without traction.

A "differential locker" is a non street legal diff when locked that employs a lil device that locks the spider gear so that power is spread evenly across the axles at all times. downfall, one whell loses traction both lose traction.

finally my favorite the street legal "limited-slip differential" alsoo posi-trac(positrac is merely a brand name for limited-slip differential for those of you who think thers a difference) anyway the limited-slip diff allows for SOME variation in speed between the two sides of the axle, up to a preset limit so that if one spins too much faster the other will be forced to pick up slack in the traction and also this way if one wheel loses traction the other is allowed to stay hooked up and deliver power to the pavement.

with a lil practice this third "posi trac" can be manipulated thru feathering of the throttle/clutch to keep both wheels hooked up at all times seemlessly

[personnaobscura21]

Quote: Originally Posted by Gator4x4

my 96 4x4 4.3L has the 3.42 axle now i put 33x12.50 x15 on it with steel wheels and now my power is suffering a lil and it has to shit down on the highway to pull most hills now, should i change the front and rear axle or just the front and which gearing should i go with i was thinking 3.73 or 4.10, someone let me know!

thers really no need to blow the extra bill on axles the loss of power is because of the wheel size when u up the tire diameter any significant amount its the same as using a higher gear ratio

solution: install lower geared diffs fer example ur runnin 3.42 try 3.75s or 4.00s

matter of fact ill keep u posted on this cuz i kno in one of my off road mags somewher thers an equation u can use to calculate exactly what gears will bring u back to stock performance

[personnaobscura21]

Quote: Originally Posted by Gator4x4

my 96 4x4 4.3L has the 3.42 axle now i put 33x12.50 x15 on it with steel wheels and now my power is suffering a lil and it has to shit down on the highway to pull most hills now, should i change the front and rear axle or just the front and which gearing should i go with i was thinking 3.73 or 4.10, someone let me know!

sweetness check it out i found the equation i was talkin about i just need ur old tire size to calculate for u
so heretis

New tire diameter
old tire diameter x current axle ratio(:1)= new axle ratio(:1)

for those math illiterates say u had 18 inch tires stock u change em to 22 inch tires and ur stock gear ratio is 3.75 soo u take ur new tire 22 divided by old tire 18 times stock gear 3.75 gives u 4.58333
22/18x3.75=4.58333 round it up or down to the closest available gear set on the market and whala feels like u never did nethin cept now u got some sweet meats

[personnaobscura21]

this will also fix ur speedo calibration

[cruzerman350]

so i just checked and my 84 doesnt have a code in te glovebox and the codes dont match anyhting on the vin so how else can i find the gear ratio?

[drperry]

Put a mark on the tire and the ground, or fender, then put a mark on the drive shaft and axle housing... Count how many times the driveshaft goes around when you turn the tire in one rotation.

[ChopperCharles]

Quote: Originally Posted by DoubleDown

that is correct. they need to use the low gear ratio to multiply the little amount of torque the 4cyl puts out. damn near every s10 with the 4cyl and auto tranny has 4.10 rear ratio.

My 95 S10 regular cab 2.2L came with a 3.73. I HATE it, especially with 30" tires. SLOW. The 98 extended cab I used to own (that was bounced off a tree) had much, much more power due to those 4.10 gears.

Charles.

[DaRkCyDe]

hmm.. my truck is a 96 and i have no sticker.. its a 4.3 vortec extended cab.. what all does it have? lol

[RADSonoma04]

I Have been doing a lot of research on lifting my 2004 GMC Sonoma. I also know that I will be needing a gear swap. Whenever larger-than-stock tires are installed on a truck, it will have a direct effect on the truck's performance. Why? It has to do with the effective gear ratio. Your truck comes from the factory with the optimum axle gear ratio to work with the truck's engine, transmission, and stock tire combination as well as provide a good balance between acceleration and fuel economy. When taller tires are installed on a truck but the axle ratios stay the same; the effective gear ratio is reduced. This means the engine is forced to operate below its power band, and performance and fuel economy suffer as a result. In order to restore the effective gear ratio (and the truck's performance), you'll need to have the axle gears swapped to lower (numerically higher) ratios.

The chart is divided into three categories. The rpm highlighted in black are optimum for the tire size and ratio combination. These will most closely give you the best overall drivability. If you're looking for a ratio that will give better fuel economy for highway driving at the expense of some acceleration and overall performance, choose a ratio in the yellow shaded area. If you're looking for a ratio that will improve acceleration and towing power at the expense of some fuel economy, choose a ratio in the blue shaded area.

[philntx]

Where did you come up with this chart?

No modern OEM transmission has a final drive ratio of 1:1, which is what this chart is based upon.........

You should delete it and replace it with one that reflects overdrive transmissions. (or at least qualify your data better)

Your chart shows a 31" tire with 3.73 gears running at 2,628 rpms. However, you don't show the speed. My stock ZR2 would be running around 90 to 95 at those RPM's

[RADSonoma04]

Quote: Originally Posted by philntx

Where did you come up with this chart?

No modern OEM transmission has a final drive ratio of 1:1, which is what this chart is based upon.........

You should delete it and replace it with one that reflects overdrive transmissions. (or at least qualify your data better)

Your chart shows a 31" tire with 3.73 gears running at 2,628 rpms. However, you don't show the speed. My stock ZR2 would be running around 90 to 95 at those RPM's

You are abosolutely correct. I forgot to add:
This chart is based on engine rpm at 65 mph with the transmission in a 1:1 gear ratio (Third with a three-speed manual, Fourth with a four-speed manual, or Third with an Automatic). Remember, the actual rpm indicated in the chart will be slightly higher (between 100 and 300 rpm) on vehicles equipped with an automatic transmission. This is due to the slip present in an auto transmission's torque converter.

I hope this helps

[RADSonoma04]

I don't know if this will be helpful or not. I Have asked around and I have a buddy who is a genius or a good Bull$hitter. It makes sense to me.

About Mile per Hour and Revolutions per Minute
First find the vehicle speed, MPH and the consequent engine RPM operating range:

Formula for MPH
MPH = TIRE RADIUS ÷ 168 x ENGINE RPM ÷ GEAR RATIO

Example: What MPH at 6500 RPM with a 4.9 rear axle and 14 inch radius
tire in 4th (1:1) gear?

MPH = 14 ÷ 168 x 6500 ÷ 4.90 ÷ 1 = 111 MPH

Example: in 3rd gear (1.34)?

MPH = 14 ÷ 168 x 6500 ÷ 4.90 ÷ 1.34 = 83 MPH

Note: Tire Radius is distance, in inches, from center of wheel to the top of the tire.

Note: Gear Ratio is Rear Axle ratio divided by Transmission Gear ratio.


Formula for RPM
RPM = 168 x GEAR RATIO x MPH ÷ TIRE RADIUS

Example: Using the first example, what will be the RPM after shift from 3rd to 4th gear at 83 MPH?

RPM = 168 x 4.90 x 83 ÷ 14 = 4880 RPM




Formula for Gear Ratio
GEAR RATIO = TIRE RADIUS x RPM ÷ 168 ÷ MPH

Example: Using the first example, what Gear Ratio is required for 120 MPH at 6500 RPM?

GR = 14 x 6500 ÷ 168 ÷ 120 = 4.51


Formula for Tire Radius
TIRE RADIUS = 168 x MPH x GEAR RATIO ÷ RPM

Example: Using the first example, what tire radius for 110 MPH but at 6000 RPM with a 4.11 gear?

168 x 110 x 4.11 ÷ 6000 = 12.7 inches

Note: Approximately a 25" diameter tire. Remember that the tire radius will be less during hard acceleration than when the vehicle is standing still. Also, radius will be greater at high speed due to tire expansion from centrifugal force.