Rear Axles, What Changed in 1977 ?

[440sixpack]

So it turns out the difference is the 10 bolt front axle. since the spacer isn't specific to front or rear they just say not for anything older than a '77 since the 10 bolt started showing up in late '77.

Another problem that can occur is the older models had a larger flange on the axle shaft . I've run into this before and you have to do minor grinding to get some wheels to clear. same would apply to the spacer. since it's lug centric it isn't a big deal.

 

[Bextreme04]

If you don't like spacers, you can use an axle out of van. I know the 14B FF were the same width as front axles but don't know on the 1/2t models.

I had to trailer my K5 one or two times and the only way it fit was backed on trailer so in that rare instance, it came in handy. For reference, my K5 had D60 and 14b ff and 12.5 wide tires.

My truck is a 1980 with factory 14BFF and front Corp 10 Bolt. The front is wider than the rear, so this is not true.

 

[Bennyt]

My truck is a 1980 with factory 14BFF and front Corp 10 Bolt. The front is wider than the rear, so this is not true.

You have a van? My post was in regards to the 14B FF out of the vans. It was a popular swap for many years to get them out of vans as they were wider 70", same as front axle in 4wd trucks. Stock truck 14B FF are 67.5.

 

[Bextreme04]

You have a van? My post was in regards to the 14B FF out of the vans. It was a popular swap for many years to get them out of vans as they were wider 70", same as front axle in 4wd trucks. Stock truck 14B FF are 67.5.

Ah, I was confused by your comment. Here are the widths for 14BFF axles of various flavors.

All truck 14FFs are 67.5" from 73-00' with the exception of the C&C axle which is 63.5".

The van axle is 70".

The full width dually 14FF is 72".

Of course none of that matters here, since he has a 1/2 ton truck and would need to do a full 3/4-1 ton swap for it to make any sense... which seems like a whole lot more work then just putting spacers on his current setup

 

[80BrownK10]

I have a 12 bolt rear and a Dana 44 front. the spacers are for the rear to correct the narrow axle thing so it shouldn't matter then. I think the rear went to a 10 bolt as well but not until the 80's I' thought.

80 was the last year for a 12bolt in a half ton. I have an 80 and mine is a 12 bolt...but I also know with the 81 they went to a standard 10 bolt rear.

 

[80BrownK10]

I should of also posted that my front is a 10 bolt.

 

[Octane]

So it turns out the difference is the 10 bolt front axle. since the spacer isn't specific to front or rear they just say not for anything older than a '77 since the 10 bolt started showing up in late '77.

Another problem that can occur is the older models had a larger flange on the axle shaft . I've run into this before and you have to do minor grinding to get some wheels to clear. same would apply to the spacer. since it's lug centric it isn't a big deal.

My 77 was built march of 77,with the corp 10 bolt front diff.12 bolt rears didnt change in 77.Dana 44 was a 10 bolt.

 

[Battlac40]

80 was the last year for a 12bolt in a half ton. I have an 80 and mine is a 12 bolt...but I also know with the 81 they went to a standard 10 bolt rear.

Nope, my stock 81 1/2 ton has a 12bolt rear w/ posi and a 10bolt front.

 

[rpcraft]

1978 I think they started attempting to switch to 10 bolts but because they still had a surplus of 12 bolts I think you could still find them up until 1980 or 1981'ish from what seems to be seen and I am not sure if GM would really code a 12 bolt or 10 bolt in the build package or not. I'm not a looking up the RPO codes kind of guy unless I am looking for a LSD.

 

[cstew47]

I was ready to order some 1 1/2' spacers for the rear axle of my '77 K10 and noticed the product says '77 up. I think my rear axle is original but the glove box sheet says I have posi and I don't so I'm not positive. what is different in 1977 so I can be sure before I order ?

Hopefully you will do it correctly and get the bolt on spacers with their own wheel lugs. The cheap spacers that are just shims are dangerous.

 

[cstew47]

I was ready to order some 1 1/2' spacers for the rear axle of my '77 K10 and noticed the product says '77 up. I think my rear axle is original but the glove box sheet says I have posi and I don't so I'm not positive. what is different in 1977 so I can be sure before I order ?

This is my 78 with 1 1/2"spacers on 35 x 12.5 x 15 tires. I have a 4" lift and nothing rubs. The front is a Dana 44 and the rear is a 12 bolt.

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[Octane]

1978 I think they started attempting to switch to 10 bolts but because they still had a surplus of 12 bolts I think you could still find them up until 1980 or 1981'ish from what seems to be seen and I am not sure if GM would really code a 12 bolt or 10 bolt in the build package or not. I'm not a looking up the RPO codes kind of guy unless I am looking for a LSD.

They started switching from dana to 10 bolt corp. during the making of the 77 model year,hit or miss what you actually got.Mine was built march 77 and has the corp 10 bolt.From what I'm told that no dana on 78 or later.But the way everybody modifies these trucks anything is possible

 

[cstew47]

They started switching from dana to 10 bolt corp. during the making of the 77 model year,hit or miss what you actually got.Mine was built march 77 and has the corp 10 bolt.From what I'm told that no dana on 78 or later.But the way everybody modifies these trucks anything is possible

My 78 has a Dana 44 front axle and 12 bolt rear. A previous owner may have changed it, I don't know. It looks like the NP 203 was swapped out for a 205 and wheel hubs added, so, it's possible.

 

[dvdswan]

Yep, I had a D44 and 12 bolt on my 78. I think the switch was actually in 78 mid year, then it was hit and miss.

As far as rubbing, one should be careful how you put your words. Saying you have a lift and it doesn't rub may be fine if you drive on the street or graded dirt roads. I had a 4" spring lift with 33x12.5x15s on 8" rallys and when flexed the front tires would rub the fenders.

 

[Octane]

GM possibly took additional year models to phase out the dana.People always thought my truck had the dana.But the bolt cover etc proved otherwise.As far as I'm concerned one is as good as another.