Which axles to buy?

[Vetteman61]

I have an '87 K5 Blazer. I put a GM 12 bolt in it years ago, but I'm not sure what year the 12 bolt is (5 lug). I have a new components to install, but I also need new axles and I'm not sure which ones to order. I know it has 30 splines and one axle is 30" long No measurement on the other one. Are all the axles for the 12 bolts basically the same as long as I get the spline count correct?

I just want to make sure I order the correct part. Thanks.

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[Vetteman61]

This rear end originally came out of a Chevrolet Truck, but I do not know the year.

Are there any identifying markings on the housing anywhere that would let me know exactly what type of axles, or what type of truck this came out of? Anything to point me in the right direction?

 

[Frankenchevy]

I feel like @bucket would know this. In the mean time, there are a few places with identifying markings on the axle housing. Passenger tube and front driver’s side webbing iirc.

 

[bucket]

Far as I know, all the truck 12 bolt axles had the same spline count. Depending on the size of your brakes, you may just need axles and drums for a K10 or K5 to make the rear match the front. Assuming that is the goal?

 

[dvdswan]

My thoughts are...

What is you gear ratio right now?
Does the axle match the front? Only ask because you have a 2WD in it, have you used 4WD since installing the axle?
How much money are you going to drop on the 2WD axle parts?

Depending on how much, why not upgrade to a 14 bolt semi-float from a GMT 800. They are plentiful and already have 6 lugs.

 

[Vetteman61]

I'm not sure I understand. I've had this 12 bolt rear end in my K5 since 2006. I already have new ring and pinion, carrier, install kit... I have everything, except when we got inside of it, the axles need to be replaced. I just need new axles for the rear housing. When I go to look them up, I see they have a lot of different options in length. Some 30 inches, some 31 inches, some 30.*** inches. Since I don't know what year truck my rear end came out of, I'm asking to so I can know how to make sure I order the right part.

for example (this is not real, i'm just making it up as an example).

1) all Truck GM 12 bolts used the same 30 spline axles, so it doesn't matter what year you look up when ordering
2) all trucks from 1974-1979 used one size, and 1980-1987 used a different size
3) there were many different options sizes depending on what ratio you had, or if you had a step side or fleet side, so you need to decode the number on the driver side tube and it will tell you which size axle you need.

 

[Vetteman61]

OK, I think I may have figured out the confusion, and it's cause is on account of I'm an idiot. This is a 6 lug, not a 5 lug.

I haven't driven the truck in many years and it's in my friends shop while we get it back in shape. I had thought it was a 5 lug. I went over tonight to get some measurements and got the numbers off the housing.

Housing numbers:
3896839
GM76

 

[bucket]

OK, I think I may have figured out the confusion, and it's cause is on account of I'm an idiot. This is a 6 lug, not a 5 lug.

I haven't driven the truck in many years and it's in my friends shop while we get it back in shape. I had thought it was a 5 lug. I went over tonight to get some measurements and got the numbers off the housing.

Housing numbers:
3896839
GM76

On the forward face of the passenger side axle tube, there should be some numbers that give more specific build info. They can be hard to read and if there is surface rust, a wire brush will be needed to uncover it.

 

[Vetteman61]

OK, thanks for the info

 

[Vetteman61]

These are the other numbers. Appears to be a G9 6. I flipped the photo upside down to make it easier to read.

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