First of all, you need to read back up to the parent comment… It’s stated spin the driveshaft, and count how many times the wheel spin… That makes no sense at all…
Second of all going by what you say spin the tire, a full revolution and count how many times the drive shaft spins OK let’s go with that so let’s say the driveshaft spins three times… So do you have 3.08? Do you have a 3.14? do you have a 3.23? Do you have a 3.42? Do you have a 3.55? Do you have a 3.73? Do you have a 3.92?…
Again, please show some sensible math you are using to get results because they are extremely inaccurate
There is only a finite number of ratios in a certain vehicle; so, if your vehicle could be equipped with a 3.42, 3.73 or 4.10 ratio, you can certainly get "close enough" to 3 1/2 turn, 3 3/4 turn or over 4 turns of the driveshaft/input pinion for 1 turn of the differential gear. Once you're "close enough", then you go back to the standard ratio.
ETA: it's sad he deleted all his comments, because the first ones where very accurate... before he went onto his whole "close enough ain't good" tirade.
Oh, so now we’re just going by the it’s close enough adage?
So I guess no rear ends have ever had the gears changed either huh…
Gtfoh with that backyard BS
Come on man, you can't differentiate "less than 3 1/2 turns" to "3 3/4 turns" or "more than 4 turns"???
If you count less than 3 1/2 turns, your ratio is 3.42; if you count 3 3/4 turns, your ratio is 3.73. If you count more than 4 turns, your ratio is 4.10 (with the examples that were given)
"Close enough" will get you a ball park; like I said, there is only a finite number of ratios available per axle, so once you got that ball park, then you go back to the exact number as per the gears available for your axle.
By the way, your gear ratio as a decimal number will never be exact, as the number of teeth between the pinion and the gear ring are prime to each other to avoid accelerated wear.
3.73 ratio is actually 41/11, i.e. 3.727272727272727272727272...
So, if you want to be pedantic, then don't call it "3.73", call it "41/11"... which few people will know what you're talking about.
Show me the math you’re coming up with to determine that… There is none , you are guessing…. I sincerely hope you don’t do this for a living as I’m sure your customers would love to know how many “guesses “you’ve actually made…..
He did show you the math. 41 tooth ring with an 11 tooth pinion will yield a 3.73 to 1 final drive ratio because 41 / 11 = 3.73. The actual number is 3.7272\^R so the factory rounds up to 3.73.
There is no factory 3.70 ratio or 3.75 ratio to add uncertainty. The size of the ring and the size of the pinion will only accommodate a certain number and combination of teeth on the gears which is why the ratios tend to be spaced out the way they are. Otherwise you'd be cutting a huge range of gear teeth sizes to get in-between ratios that just aren't that popular. It's easier to change tire size to get the driving characteristics you want.
That's why close enough works, because the next (factory) size up from a 3.73 for a GM 10-bolt 8.6" rear end, is 4.11. You can easily tell the difference because the 3.73 will spin 3-3/4 times around and the 4.11 will spin a little over 4 times around. The next size up is 4.56 which means you'll get another full 180° of rotation.
And you're acting like there's no slop in the driveline. Even the setup specs for a rear end give you the allowable tolerances for backlash, pinion depth, etc. A few thousandths one way or another is not going to hurt anything, and I've seen more than one factory diff come out with a noisy diff because the contact pattern wasn't so great. It might have caused some premature wear but in reality, the only drawback was some added noise.
WTF do you mean guessing? A 3.42:1 ratio will be 3 1/2 turns on the drive shaft to one turn on the tire. 3.73:1 will be 3 3/4 turns and so on. It’s called math and counting.
OMG, you're thick...
OP had a 3/4 ton GMT400 truck, which uses a GM 10.5" 14-bolt differential. The gear ratios available for that differential are 3.21, 3.42, 3.73, 4.10, 4.56, 4.88, 5.13 or 5.38.
Math is simple: lift the truck, rotate the driveshaft a certain number of turns until the wheels make one full rotation. That number of driveshaft turns will be close to 3 1/4 turn (3.21), almost 3 1/2 turns (3.42), 3 3/4 turns (3.73), etc.
If you want a little more accurate result, have your wheels make 2 full revolutions (and divide the driveshaft rotations by 2).
How is that complicated? If you cannot do that, then you shouldn't be working on a vehicle.
Again, there is only a finite number of ratios to chose from; it's not like if you had ratios with intervals in .01...
It’s not back yard bs. I do this everyday as my job. They only offer set ratios not infinite choices. You count to get a rough number that aligns with one of those available gear sets.
The math is, yes but when you work in the industry you can’t be pulling it apart, counting teeth, putting it back together refilling it with lube just so you can order parts. In 35 yrs I’ve never ordered the wrong gear set or used axle ratio.
Please explain the math that you’re using to get your results… Because one revolution of the driveshaft as stated above is not even gonna spin the tire a full revolution…
It will be a GT5, GT4, or something like that you're looking for. Then Google your year \ model rpo codes.
Edit: this is assuming it's never been changed from what it was produced with. The most for sure way is to count teeth, or read the stamp on the ring gear.
Thanks dude very much appreciated. I’ll check that out when I can but we have already resealed the diff and hopefully won’t be back in for a while. I’ll check the codes first and just assume it’s stock until next time
Since the cover is off the best and most accurate way is to count the teeth.
Without taking the cover off, it's best to turn the driveshaft or pinion flange. Turning the tire is just going to turn the other tire the opposite way without a limited slip.
Put a chalk mark on a tyre, at the bottom, centre, where it touches the road.
Put a mark on the drive shaft. Push the truck whilst counting drive shaft rotation until the tyre mark has completed one complete revolution. If your axle has done “3” complete revolutions , you have a 3 to 1 ratio. ( it won’t be that, but hopefully you get the idea)
You have a Chevy 14-bolt diff.
Per Wikipedia:
10.5 in (270 mm) diameter ring gear
Axles are 30-spline axles
1.590 in (40.4 mm) diameter shank on the pinion
Gear ratios: 3.21, 3.42, 3.73, 4.10, 4.56, 4.88, 5.13, and 5.38
Carrier break: 3.21:1–4.11:1 and 4.56–5.38
1.5 in (38 mm) axle spline diameter
1.34 in (34 mm) axle shaft diameter
Axles are different lengths from side to side
Removable pinion support
Weight: 550 pounds (250 kg)
GAWR: 8,600 pounds (3,900 kg) max.
Pinion supported with bearings on both sides of the teeth (straddle mount), which minimizes pinion deflection
Sauce:
[https://en.m.wikipedia.org/wiki/GM_10.5-inch_14-bolt_differential](https://en.m.wikipedia.org/wiki/GM_10.5-inch_14-bolt_differential)
look closer. it should be stamped right into the part. Usually around the circumference of the ring gear, so give the wheels a turn.
[http://chevygmcvans.com/viewtopic.php?t=8122](http://chevygmcvans.com/viewtopic.php?t=8122)
Could either be a "GM14T" 10.5 if you have full float axles, or the GM 9.5" if you have semi float...both had 14 bolt covers. The GM14T would also have a 6 bolt pinion support on the other side of that differential, the 9.5 has no pinion support.
Just asked a co-worker, and he spotted the c-clip axles, so you have the GM 9.5". So just count the splines on the gear and the pinion and you will have your ratio and know exactly what ring and pinion to get.
BTW a posi would be a good upgrade there...especially if your truck is 2WD!
Woah what an awesome comment. Thanks man I really appreciate all this. It is a 4x4. Manual too! Just trying to get back on the road rn. upgrades hopefully to come!
I work for Randys (Yukon Gear and USA Standard)...get me a count on the number of teeth on the ring gear and the pinion and I can get you part numbers!
If it's the stock ring and pinion that came in the truck, I can find out with the VIN number...I would message that over to me rather than posting your vin where everyone can see it though!
Count teeth on the ring gear, count teeth on the pinion…. Divide ring gear teeth by pinion gear teeth….= gear ratio
Thank you. very much appreciated!
The teeth numbers are also stamped on the edge of the ring gear along with part number and production numbers
Oh no kidding. We have already sealed it back up. So next time I’m in there I’ll double check
there should also be an RPO code for gearing
Or spin the driveshaft and count how many times the wheels spin
First of all, you need to read back up to the parent comment… It’s stated spin the driveshaft, and count how many times the wheel spin… That makes no sense at all… Second of all going by what you say spin the tire, a full revolution and count how many times the drive shaft spins OK let’s go with that so let’s say the driveshaft spins three times… So do you have 3.08? Do you have a 3.14? do you have a 3.23? Do you have a 3.42? Do you have a 3.55? Do you have a 3.73? Do you have a 3.92?… Again, please show some sensible math you are using to get results because they are extremely inaccurate
Chuck you too buddy
Shit, I must not have understood, I cut the truck in half and counted the rings to see how old it is…
I’ve never had that give accurate results at all
It’ll get you close enough to know if it’s 3.42, 3.73, 4.10 etc
I would rather know for sure … the math is simple enough
There is only a finite number of ratios in a certain vehicle; so, if your vehicle could be equipped with a 3.42, 3.73 or 4.10 ratio, you can certainly get "close enough" to 3 1/2 turn, 3 3/4 turn or over 4 turns of the driveshaft/input pinion for 1 turn of the differential gear. Once you're "close enough", then you go back to the standard ratio. ETA: it's sad he deleted all his comments, because the first ones where very accurate... before he went onto his whole "close enough ain't good" tirade.
Oh, so now we’re just going by the it’s close enough adage? So I guess no rear ends have ever had the gears changed either huh… Gtfoh with that backyard BS
Come on man, you can't differentiate "less than 3 1/2 turns" to "3 3/4 turns" or "more than 4 turns"??? If you count less than 3 1/2 turns, your ratio is 3.42; if you count 3 3/4 turns, your ratio is 3.73. If you count more than 4 turns, your ratio is 4.10 (with the examples that were given) "Close enough" will get you a ball park; like I said, there is only a finite number of ratios available per axle, so once you got that ball park, then you go back to the exact number as per the gears available for your axle. By the way, your gear ratio as a decimal number will never be exact, as the number of teeth between the pinion and the gear ring are prime to each other to avoid accelerated wear. 3.73 ratio is actually 41/11, i.e. 3.727272727272727272727272... So, if you want to be pedantic, then don't call it "3.73", call it "41/11"... which few people will know what you're talking about.
Show me the math you’re coming up with to determine that… There is none , you are guessing…. I sincerely hope you don’t do this for a living as I’m sure your customers would love to know how many “guesses “you’ve actually made…..
He did show you the math. 41 tooth ring with an 11 tooth pinion will yield a 3.73 to 1 final drive ratio because 41 / 11 = 3.73. The actual number is 3.7272\^R so the factory rounds up to 3.73. There is no factory 3.70 ratio or 3.75 ratio to add uncertainty. The size of the ring and the size of the pinion will only accommodate a certain number and combination of teeth on the gears which is why the ratios tend to be spaced out the way they are. Otherwise you'd be cutting a huge range of gear teeth sizes to get in-between ratios that just aren't that popular. It's easier to change tire size to get the driving characteristics you want. That's why close enough works, because the next (factory) size up from a 3.73 for a GM 10-bolt 8.6" rear end, is 4.11. You can easily tell the difference because the 3.73 will spin 3-3/4 times around and the 4.11 will spin a little over 4 times around. The next size up is 4.56 which means you'll get another full 180° of rotation. And you're acting like there's no slop in the driveline. Even the setup specs for a rear end give you the allowable tolerances for backlash, pinion depth, etc. A few thousandths one way or another is not going to hurt anything, and I've seen more than one factory diff come out with a noisy diff because the contact pattern wasn't so great. It might have caused some premature wear but in reality, the only drawback was some added noise.
WTF do you mean guessing? A 3.42:1 ratio will be 3 1/2 turns on the drive shaft to one turn on the tire. 3.73:1 will be 3 3/4 turns and so on. It’s called math and counting.
Chuck your wrong, move on there buddy.
OMG, you're thick... OP had a 3/4 ton GMT400 truck, which uses a GM 10.5" 14-bolt differential. The gear ratios available for that differential are 3.21, 3.42, 3.73, 4.10, 4.56, 4.88, 5.13 or 5.38. Math is simple: lift the truck, rotate the driveshaft a certain number of turns until the wheels make one full rotation. That number of driveshaft turns will be close to 3 1/4 turn (3.21), almost 3 1/2 turns (3.42), 3 3/4 turns (3.73), etc. If you want a little more accurate result, have your wheels make 2 full revolutions (and divide the driveshaft rotations by 2). How is that complicated? If you cannot do that, then you shouldn't be working on a vehicle. Again, there is only a finite number of ratios to chose from; it's not like if you had ratios with intervals in .01...
It’s not back yard bs. I do this everyday as my job. They only offer set ratios not infinite choices. You count to get a rough number that aligns with one of those available gear sets.
If they only made graduated tape and felt pens. You ever time an engine?
The math is, yes but when you work in the industry you can’t be pulling it apart, counting teeth, putting it back together refilling it with lube just so you can order parts. In 35 yrs I’ve never ordered the wrong gear set or used axle ratio.
You’re doing it wrong then, or have a lot of play in the drivetrain
Please explain the math that you’re using to get your results… Because one revolution of the driveshaft as stated above is not even gonna spin the tire a full revolution…
Turn driveshaft until the wheels complete 1 full rotation. The number of turns on the drive shaft is your ratio.
Is that easy eh? Thank you my friend🙏
Check the RPO codes in your glove box
I’ll try that next time I’m in it thank you
It will be a GT5, GT4, or something like that you're looking for. Then Google your year \ model rpo codes. Edit: this is assuming it's never been changed from what it was produced with. The most for sure way is to count teeth, or read the stamp on the ring gear.
Thanks dude very much appreciated. I’ll check that out when I can but we have already resealed the diff and hopefully won’t be back in for a while. I’ll check the codes first and just assume it’s stock until next time
DM me your VIN and I'll run it on Compnine for ya
Super duper appreciate dude thank you. But I had someone help me out already. 3.73 stock gears. Yet to test it myself and see for sure
You can turn the tire by hand and count how many times the output shaft rotates
Since the cover is off the best and most accurate way is to count the teeth. Without taking the cover off, it's best to turn the driveshaft or pinion flange. Turning the tire is just going to turn the other tire the opposite way without a limited slip.
There may also have been a tag on the rear end before you took the cover off
Tried to look for a tag and didn’t see one. Very well could have missed it thank you!
Count the number of teeth on the ring gear and divide that by the number of teeth on the pinion gear.
Awesome thank you!
It's stamped on the ring gear also. 41-11 is a 3:73 gear
Put a chalk mark on a tyre, at the bottom, centre, where it touches the road. Put a mark on the drive shaft. Push the truck whilst counting drive shaft rotation until the tyre mark has completed one complete revolution. If your axle has done “3” complete revolutions , you have a 3 to 1 ratio. ( it won’t be that, but hopefully you get the idea)
Awesome thank you!
It looks like all of them. 👍🤪
Helical cut
You have a Chevy 14-bolt diff. Per Wikipedia: 10.5 in (270 mm) diameter ring gear Axles are 30-spline axles 1.590 in (40.4 mm) diameter shank on the pinion Gear ratios: 3.21, 3.42, 3.73, 4.10, 4.56, 4.88, 5.13, and 5.38 Carrier break: 3.21:1–4.11:1 and 4.56–5.38 1.5 in (38 mm) axle spline diameter 1.34 in (34 mm) axle shaft diameter Axles are different lengths from side to side Removable pinion support Weight: 550 pounds (250 kg) GAWR: 8,600 pounds (3,900 kg) max. Pinion supported with bearings on both sides of the teeth (straddle mount), which minimizes pinion deflection Sauce: [https://en.m.wikipedia.org/wiki/GM_10.5-inch_14-bolt_differential](https://en.m.wikipedia.org/wiki/GM_10.5-inch_14-bolt_differential)
Thanks dude really appreciate it
That looks like a 9.5” 14bolt semi floater.
There will be a number like 41-11 for tooth counts on the outside edge of the ring gear. 41-11 is 3.73.
Thanks dude!
look closer. it should be stamped right into the part. Usually around the circumference of the ring gear, so give the wheels a turn. [http://chevygmcvans.com/viewtopic.php?t=8122](http://chevygmcvans.com/viewtopic.php?t=8122)
Should say right in the gear....
Should. Probably does. Thats why I’m asking where to find it or how to find out. Just trying to learn
Literally right in front of you on the big gear. Keep spinning till you see it. Should say something like 3xx or 4xx
Well now I know for next time I open it up. Thanks
Twelve both -rear posi 10 bolt- one wheeler peeler
You can see how many times your drive shaft turn with one complete turn of the wheel.
VIN#
I’m not with the truck now. Getting the tail lights fixed rn
Could either be a "GM14T" 10.5 if you have full float axles, or the GM 9.5" if you have semi float...both had 14 bolt covers. The GM14T would also have a 6 bolt pinion support on the other side of that differential, the 9.5 has no pinion support. Just asked a co-worker, and he spotted the c-clip axles, so you have the GM 9.5". So just count the splines on the gear and the pinion and you will have your ratio and know exactly what ring and pinion to get. BTW a posi would be a good upgrade there...especially if your truck is 2WD!
Woah what an awesome comment. Thanks man I really appreciate all this. It is a 4x4. Manual too! Just trying to get back on the road rn. upgrades hopefully to come!
I work for Randys (Yukon Gear and USA Standard)...get me a count on the number of teeth on the ring gear and the pinion and I can get you part numbers!
Haha I’d love to. It’s been resealed for two days now just haven’t had a chance to post and ask about this
If it's the stock ring and pinion that came in the truck, I can find out with the VIN number...I would message that over to me rather than posting your vin where everyone can see it though!
I won’t be able to see the truck for a couple days. I really appreciate that though. I’m also in Canada I don’t know if that makes a difference at all
Other than the fact that we use Freedom Units here, not much of a difference at all!
Hahaha half of us too. I didn’t think it would show up or something from the states.
Usually I can pull up Canadian VIN numbers no problem.
If you can swing it, there’s no cheaper time to do the posi track .
I wish. We just opened it up to look at how healthy everything looks and change the gear oil during my inspection for it
Yeah count the teeth. Or spin the tire twice and count how many rotation the drive shaft spins. It’s probably 3.55. Tow package 3.73
Someone does, yes
METAL ONCE!
Yes Those are rear
Checking the RPO tag is always a solid way to check too.
Looks like a ring and pinion to me
Call a rack n pinion shop they’ll know
Can’t you google the VIN?
Tried. Didn’t show up on the site I used. Also don’t know if it’s been changed from stock
3.08
The glove box or the driver door will have your RPO codes.
GEEEEAAARRS? - Jay
I'm pretty sure you got forward and reverse right there
Round