Didn't ever really come across any posts with a compilation of 14SF tech info. I copied this out of the other post I made, since the old title isn't accurate anymore. This basically is everything I've learned thus far in my 10 bolt to 14SF swap. Hope this info will help people out in the future. Originally asked about wrench size needed for rear u-bolts, answer was same as 10, 12, and 14FF. 15/16". On that same note, are the axle tubes for the 14FF and SF the same diameter? Yes Rene: "Pretty sure the SF has 3.375" tubes like the FF does. I just opened up my 1/2 ton spring plate holes a little and made them work..." In my case, which SHOULD be the norm (have heard otherwise though) the u-bolts are therefore not interchangeable between 10/12 bolt axles and the 14SF/FF. Spring plate can be made to work, but IMO might as well get those when you get the u-bolts, at least if buying used like I did. Other info I came up with so far: The diff housing cover bolts are not interchangeable with the 10 bolts. Same threads, but the length is different. (5/16 if standard) FYI, it appears at some point GM went metric on these, so be warned! Check first...8mm x 1.25 was the metric size given. Pinion shaft retaining bolt is 10MM. (5/16" for 10/12 IIRC) Bearing cap bolts are metric too, can't recall the size. Internally everything looks identical to a 10/12 bolt, except bigger. Gov-lock is same design in 10/12 and 14SF applicaitions. 14SF gov-lock was broken when I bought this axle. Something had caused the teeth to strip off of one of the governor gears and the toothed ring they ride on, rendering the locker inoperable. At least later 14SF's wheel cylinder brake line fitting comes out parallel with the axle. The 10 (and 12?) bolts come out at around a 45* angle. Expect it, don't crossthread the fittings, if you can get them out in the first place. Napa pulled a wheel cylinder for 3/4 ton "small brake" K20 Suburban that was identical to a 10 bolt. That isn't right, at least not for the later 14SF's, and I doubt any 14SF's. The diameter is smaller than the 14SF, and the fitting angle is wrong. The one they pulled for same vehicle except 1997 was exactly what I had. Interestingly, the big brake and small brake option wheel cylinders are different part numbers for 1997 at Napa, yet they are the same externally in every way, even casting number, which indicates no difference. Who knows? All the "small" brake parts for the "small brake" 14SF and 10 bolt appear to be interchangeable. Same setup inside the housing with springs, pins, etc. Here are the pics: wheel cylinder 14SF left, 10 bolt right. Notice fitting angle, diameter difference. "Width" is the same, and bolt pattern/threads on back are the same for mounting, so the wheel cylinders *will* interchange, but would probably result in weak rear brakes. 14SF orange drum, 10 bolt unpainted. 14SF orange drum, 10 bolt unpainted. "Bulge" on the 14SF drum is approximately 1/2 of how much wider the 14SF is than a rear 10/12 bolt. 10 bolt on left. 14MM studs on the 14SF, at least my year. That varies based on year/number of lugs I'm sure. Hub cutout much smaller on the later 14SF due to IFS wheels. The stock ralleys for the '73-87 trucks work, lug studs BARELY fit through wheel, but wheel is no longer hub centric of course. *Note*: The 14MM studs/lug nuts will fit with stock 6 lug wheels, HOWEVER the stock 14MM lug nuts will only pinch the wheel to the axle, they will NOT bite into the hole in the wheel as is "necessary" (IMO) for there to be a good tight fit. The holes in the wheel will need opened up or you will have to switch lug nuts front, rear, or both. I did not realize this until I tried to swap wheels to the front that had been on the rear. Once a wheel has been used with 14MM lugs/bolts, you can't use it on the stock 1/2 ton lugs. 14SF on top Axle specs from splined end to bearing surface. (measurement taken at each seperate, distinct diameter) 10B: 1.16", 1.31", 1.62" bearing surface. 14SF: 1.42", 1.655:, 1.70" bearing surface. 28 or 30 spline axles for 10 bolt, 28 spline for all 12 bolts too? 33 spline for all 14SF's. Anyone interested in more data/info I didn't provide but might be able to while this thing still isn't "buttoned up"? More info: http://coloradok5.com/forums/showthread.php?t=170383 EDIT: Disk Brake info: http://coloradok5.com/forums/showthread.php?t=176462 EDIT: Quote from u2slow "Both versions need the perches moved (same spacing 2wd and 4wd). The difference is the overall width. (talking '88+ C/K body style) RPO code "F44" gets you the 14bSF on a 88-98 K1500. Its standard issue on a 6-lug C/K2500." So on a half ton, you can ask an owner if the RPO tag has F44, that should equate to a 14SF rear axle. Not on a 3/4 ton as it is standard. EDIT: 14SF axle flange thickness is .451" The brake drum is .330" thick at the flange mating surface. EDIT: Conversion u-joints for 10B to 14SF: "Neapco 1-1153. Napa had one under p/n 447 but I think they changed the number awhile back" 10 bolt is the S44 joint, 14SF is 1350. 2WD/4WD conversion, and axle seal numbers for the numerous seals the 14SF used http://coloradok5.com/forums/showthread.php?t=311473 EDIT: Had a problem with the axle seals I installed 10 years ago lol. When I put them in they were not a press fit. I put them in with silicone. Well, the one failed, and ruined my brake shoes, which had plenty of life left. The generic part number most everyone uses is 710105. The "National" brand sold by Schucks (suck it O'Reilly's) is a press fit. The one that did not fit is marked "Timken" on the seal portion, along with the 710105. Maybe they fixed it in the past 10 years, but my calipers told me they have not. I didn't even bother trying, too long of a drive to test it out. Additionally, according to the computers, there are two axle (they call them wheel) seal diameters. One is 3.08", the other is 3.03". The 3.08" seals all appear to be flanged. The 3.03" seals are all depicted flangeless. The difference in size is appreciable when you have them back to back. It takes a good look, but you can see it. No idea where this 3.03" seal was supposedly used, the computer shoed the 710105 interchanging from 1982-1999. Perhaps the 3.03 was even later.