What rearend do I have?

[davbell22602]

What's the rearend gear ratio on my 1988 C1500 2WD? 10 bolt semi float.

 

[89Suburban]

That sure is a catchy title for a thread!!

Go here, compliments of HPRC.

http://www.gmsquarebody.com/forum/showthread.php?t=720

 

[davbell22602]

My fault on the question. What gear ratio do I have?

 

[89Suburban]

I think there were 2 different ones it could be. Go here and check out your specs.

http://www.gmheritagecenter.com/gm-heritage-archive/vehicle-information-kits.html

Hotrod posted this link in this thread. And Retro started the thread with a link to another place you can also look. Good sites

http://www.gmsquarebody.com/forum/showthread.php?t=496

 

[Swims350]

the only true way to check the gear ratio is to pull the cover the gears could have been changed, pull the cover count the teeth on both ring and pinion or art least look on the ring gear for the teeth count markings, like gm 41-10. or something along those lines.

 

[davbell22602]

Ok, This site lists 6 different gear ratio's. Mine is a scottsdale.

http://www.car-part.com/

 

[89Suburban]

Or chalk a tire and count driveshaft turns.

 

[Old77]

the only true way to check the gear ratio is to pull the cover the gears could have been changed, pull the cover count the teeth on both ring and pinion or art least look on the ring gear for the teeth count markings, like gm 41-10. or something along those lines.

^^this

 

[davbell22602]

Ok, I have 2.73 ratio rearend which is RPO code GU2. I found the rpo code label in the glove box.

 

[89Suburban]

Ok, I have 2.73 ratio rearend which is RPO code GU2. I found the rpo code ladel in the glove box.

 

[HotRodPC]

So its correct if your gears haven't been changed. 2.73 is the wussiest gear you can get. 3.08 is pretty much wussy too.

I usually do the count thing. Lift one wheel. Turn the tire exactly 1 full revolution and count how many times your yoke spins per 1 tire revoloution. IF you got a locker, its 1:1 ratio, so for example if the yoke turned just a hair over 4 times, then you have 4.10. If it turned 4.5 times, then you have 4.56 gears. If it turns 2.75 or 2 3/4 turns, then you have 2.73 gears. So you see, those are pretty easy. BUT, if its an open differential peg legger, you muliply by 2, becase the spiders are turning in an opposite direction at the same time. So here are some examples.
1.5 or 1 1/2 turns x 2 = 3 is 3.08
2 turns x 2 = 4 is 4.10
2.25 or 2 1/4 turns x 2 = 4.5 is 4.56
1 3/4 or 1.75 turns x 2 = 3.5 is 3.42 or 3.54

Its very easy and very basic math. Notice I rounded these off. So for purpose of being even more acurate, a 3.42 ratio is going to be just under 1 3/4 turns and a 3.54 ratio will be just over 1 3/4 turns. Its helps to know what gear ratios are available in your model of rear end to determine the ratio. I happen to know in the Chevy 1/2 ton trucks for example they run a 3.42 ratio and a 3.54 is not available. 3.54 is availabe in Dana 60 and Dana 70 though. 1/2 ton Fords in the older body styles didn't run a 3.42, they ran a 3.55 so as long as you know what gear ratios are available for your model and can do basic math, you can alwasy determine your gear ratio without removing the cover, although, that is the most accurate way to do it. I've never been wrong on determining a gear ratio by counting yoke turns off a wheel spin.

 

[davbell22602]

Junkyards in my state are selling that 2.73 anywhere from $200-$450.

 

[HotRodPC]

Ok, I have 2.73 ratio rearend which is RPO code GU2. I found the rpo code label in the glove box.

Did you by any chance see an RPO Code of G80 in the glove box label??? If you do, that means you have the G80 Locking Differential. Nothing to get to excited about really. Its an Eaton Gov-Lok system and it has its advantages, but it has more disadvantages. The toothed gov ring likes to strip teeth, and that unit only works under 25mph, so if you are drag racing and need to heat your tires, its not gonna work cuz you'd be spinning tires at 35-50mph during a burnout to heat up. It works great for pulling a boat up a wet boat ramp though. Probably just as good as a locker would unlike a limited slip unit.

 

[davbell22602]

Did you by any chance see an RPO Code of G80 in the glove box label??? If you do, that means you have the G80 Locking Differential. Nothing to get to excited about really. Its an Eaton Gov-Lok system and it has its advantages, but it has more disadvantages. The toothed gov ring likes to strip teeth, and that unit only works under 25mph, so if you are drag racing and need to heat your tires, its not gonna work cuz you'd be spinning tires at 35-50mph during a burnout to heat up. It works great for pulling a boat up a wet boat ramp though. Probably just as good as a locker would unlike a limited slip unit.

These are the only "G" RPO codes in the glovebox. GMC, GQ1,GU2

 

[HotRodPC]

Junkyards in my state are selling that 2.73 anywhere from $200-$450.

If you are wanting to know for puposes of selling it, check your glove box for G80 RPO Code. Since those lists are in order, it should be right there just past the GU2 RPO code. If you got G80, advertise it as with G80 Locking Differential for $225 on CL and I bet it'll sell to the first person needing that rear end, and it might even sell to someone not needing a rear end and wanting ot upgrade to a locking diff. Just don't tell them that some dude on my truck forum, HotRodPC said they are junk and he'd rather have an open diff and add a Powertraxx Lock Right.