14b ff vs 14b sf width

[skysurfer]

I'm thinking about swapping my semi-float axle for a full-float. Found one on CL from an '86 Suburban with the 13" drums and 4.10 gears I need. Only concern I have is he lists the wms to wms as 66". I measured my semi-float axle and it's an inch wider at 67". Is that difference because his is from a 2wd and mine is 4wd? I assume it's ok to add 1/2" spacers if the front/rear track difference is noticeable. Are the spring perches all the same distance apart no matter if it's 2wd or 4wd?

Here's the pic he posted.

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[Blue Ox]

Not sure about width, but make sure you check the pinion angle between 2WD and 4WD. I'm pretty sure it's different. Again, it's been a long time since I swapped mine so memory, you know.

 

[HotRodPC]

Good question. I may have this same issue on my K10 to K20 conversion. I'm not sure what my 14b FF came out of. If 2wd is narrower?!?!? It could be the 4x4 units are wider so they have the same width as the front axle. I guess that might be a problem when it comes time to have an alignment done, but otherwise I'm not to worried about a 1 inch difference. I'd rather live with the 1 inch difference than to run spacers. Width shouldn't affect tracking at all, if so likely not even noticeable.

Seems the GMT400 trucks, the front wheels stuck out further than the rears. So how did the alignment techs compensate for that on those vehicles?

 

[HotRodPC]

Not sure about width, but make sure you check the pinion angle between 2WD and 4WD. I'm pretty sure it's different. Again, it's been a long time since I swapped mine so memory, you know.

Damn, I never thought of that either. That's easily fixed though. I have a set of lift blocks that will change the pinion angle. They look to be about a 2 1/2 inch lift block in the front side and about 2 inch in the rear, so that should lift the pinion angle.

 

[DoubleDingo]

What gears are in the semi-floater?

 

[skysurfer]

What gears are in the semi-floater?

Same, 4.10

Another thing that seems strange (from what I've read) is that after 1986 the ff drums were removable without taking out the axle shafts. This axle appears to be the older style but I'm not positive of what I'm looking at. First pic is the one for sale and the second is what I'm guessing is the newer style. Educate me if I've got it wrong.

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[bucket]

From what I remember, the big difference between 2wd and 4x4 3/4 ton housings, the 2wd housing just had longer shock mounts. And like was mentioned, probably slightly different pinion angle too.

Almost 100% positive that slip on drums didn't come until the 90's sometime.

 

[CSFJ]

I didn't think the the drums started being removable without the axle until the gmt400 or 800 trucks. The rear axle on the square bodied trucks (at least the 4x4s) was 4" narrower than the front. Iirc, the front measured somewhere around 70ish" and the rear was around 66ish". The later 400 and 800 trucks were wider. Not sure about the rear track width of the 2wd squares, I've only owned 4x4s.

 

[bucket]

I've got a C20 rear I can measure against a K30 (single wheel) rear tomorrow. It should give an answer at least as far as WMS to WMS goes.

Both 14 bolt FF of course.

 

[DoubleDingo]

Same, 4.10

Okay. I was kicking around offering to buy it if it was going to be sold. But I did a spreadsheet of various ratios with a gear splitter overdrive setup and 4.57 is the winner to run in OD with a final drive ratio of 3.34, but 3.54 is the winner to run out of OD but in 3rd OD it makes it a 4.42 final drive ratio, not a bad gear for pulling grades or hauling. Anyhow, that's why I asked.

 

[bucket]

My C20, C30 and K30 rear axles all share the same 67" WMS to WMS. And the C20 rear is under my '78 Burb, so it's hard to say why the axle in question only measures 66" across. Maybe his tape measure slipped when he was taking the picture?

Also, my C20 rear axle has shock mounts that hang roughly 3 inches below the bottom of the axle tube. I'd be interested to know how low a K20 shock mount hangs.

 

[crazy4offroad]

Van rears are typically narrower

 

[bucket]

Van rears are typically narrower

Actually the 70's and 80's vans have a wider rear axle. You can swap one in to make the front/rear track the same on our trucks. Of course the perches and stuff need moved. Also, the vans used narrower springs so IIRC, the perches are too narrow to reuse.

 

[highdesertrange]

there are 3 types of 14 bolt full float axles.

SRW
DRW
VAN

read this it explains it all,

http://www.pirate4x4.com/tech/billavista/14b_bible/index.html

highdesertranger

 

[skysurfer]

Thanks hdr, I had seen that article before but read it again to refresh my memory.

@Blue Ox. Excuse my stupidity but I'm not exactly clear on the possibility of different pinion angles between 2wd and 4wd. Are you saying the spring perches were welded on in a different fore/aft position depending on the application? If that's the case, then checking an axle that's been removed would mean checking across the flat surface of the perches and then across the nose of the pinion? Like this?

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