What's the diff.....??

[Rocketman72]

I have a rear differential I bought some time ago and I'm not sure what it is. out of so I really don't know what reference to use when ordering parts.

I'm pretty sure it's a 14 bolt Corp. SF gov. bomb with 6 lug axles, that fine and the ring gear says 11 40 so I'm pretty sure it's a 3.73. It is approx. 67" wide and the axle tubes are 3 1/4 wide, drums measure 11 1/4" I.D. and 13 1/2" O.D with approx. 3" lining or brake surface.

Numbers on cast iron are GM 1 and CFO 9690. Rt. axle tube is stamped RAL C2231.

Anybody have a hint at what I might have? What year/model it came from that I can refer to when ordering parts? Can I get a disk brake set up for this axle? Where?

Thanks.

[b454rat]

14 bolt semi float 6 lug came in 88-up heavy halfs. I believe they are too narrow for a square, but not 100%

[Rocketman72]

Originally Posted by b454rat

14 bolt semi float 6 lug came in 88-up heavy halfs. I believe they are too narrow for a square, but not 100%

I'm planning on using it in a 72 K5 Blazer. Would that still be too narrow?

By the way, I'm not too saavy on the lingo yet, what do you mean by "heavy halfs" and what's a square? (besides me)

[Redcap]

Originally Posted by Rocketman72

I'm planning on using it in a 72 K5 Blazer. Would that still be too narrow?

By the way, I'm not too saavy on the lingo yet, what do you mean by "heavy halfs" and what's a square? (besides me)

"Squares/squarebodies" are the nickname for 73-87 Chevy/GMC trucks.

[andrewmp6]

What he means a heavy half its kinda between a 1/2 ton and 3/4 ton truck.How wide is the axle in the blazer tho?

[Zoomad75]

A 6 lug 14bolt semi-floater is common to the 454ss trucks. I think the guys that have those trucks are pretty rabid about them only being in a 454SS. Play your cards right and you could probably unload it to one of those guys for a nice chunk of change and allow you to build up a 12bolt that should have come in your 72.

[Ziegelsteinfaust]

No 5 lugs came in the 454SS.

6 lugs are quite common in the light duty 3/4 tons.

[USSkoval]

There's a 2wd width axle and a 4x4 width axle, the 4x4 version is great for the older trucks because it makes the rear track width closer to the front.

[Rocketman72]

Originally Posted by andrewmp6

What he means a heavy half its kinda between a 1/2 ton and 3/4 ton truck.How wide is the axle in the blazer tho?

I think it's about 64."

The semi floater 6 lug is approx. 67". It seems that it would be approx. the same as the front.

[Rocketman72]

Another item that may reveal the year of this diff is that it seems that a 1/2" wrench seems to fit the rear cover bolts better than a 13mm. Also, it's difficult to determine if the backing plate bolts are 3/4" or 19mm. They both seem to have the same free play.

Another thing I noticed was that the lugs are very large, probably at least 1/2" diameter. does anyone have any guesses from this additional information?

[BigRed76]

The 14 bolt semi-floater differentials were used in the 88-98 Light Duty 3/4 ton trucks. I don't know very much about the differentials, just the trucks they were put in. The 454SS trucks had the 14 bolt SF also, just with 5 lug axles.

The wheel studs are 14mm diameter, can't remember the thread pitch though.

[SoCalK20]

The GM 14 bolt Semi Floater with 6 bolt lug pattern, is a good piece. Not quite as stout as the Full Floater, it is a very good upgrade from the weaker 10 bolt gov locker which is the one known to grenade with even running 33's. Popular swap for Chevy/GMC obs trucks that came with 10 bolt rears and want to stay with 6 lug wheels.

[Rocketman72]

Originally Posted by BigRed76

The 14 bolt semi-floater differentials were used in the 88-98 Light Duty 3/4 ton trucks. I don't know very much about the differentials, just the trucks they were put in. The 454SS trucks had the 14 bolt SF also, just with 5 lug axles.

The wheel studs are 14mm diameter, can't remember the thread pitch though.

88-98..... That will at least give me something to order parts by. I have been reading that these came also in some 73-87 trucks also. Is that bad information?

IIRC the change to metric in the GM vehicles happened around 1979. It seems I might have SAE bolts holding the backing plate to the flange yet metric bolts to the rear cover. Could mine be 1980 or earlier?

[Bigdav160]

I'm pretty sure the bolts were still fractional when I quit the business in the late 1990's

[BigRed76]

Well the 14 bolt semi floater was not used until the 88-98 generation trucks, so there's no way it any older than 88. As far as the metric vs. standard thing, I think the trucks themselves started using metric fasteners in 88, but the engines and drive trains still used standard fasteners all through the 90's. And you can't always judge whether a bolt is standard or metric just based on the size of the head of the bolt. As far as ordering parts, order them for a 88-98 light duty 2500.

[BigRed76]

Originally Posted by Rocketman72

88-98..... That will at least give me something to order parts by. I have been reading that these came also in some 73-87 trucks also. Is that bad information?

IIRC the change to metric in the GM vehicles happened around 1979. It seems I might have SAE bolts holding the backing plate to the flange yet metric bolts to the rear cover. Could mine be 1980 or earlier?

The 14 bolt full-floater was used in 73-87 trucks, but the 14 bolt semi-floater was 88-98.

[b454rat]

14 semi float didnt' come in till 81 in 3/4 ton 8 lug only trucks, 2wd and 4wd. Prior to that was either 10/12 bolt or 14 full float.

88-up saw the use of the 6 lug 14sf in both 2wd and 4wd. 2wd are narrower than 4wd, so not a good candidate for a swap.

[83GMCK2500]

BigRed76 incorrect, see b454rat's post.

To add further information, in the GMT-400 (88-02, technically) platform the 6-lug 9.5" 14 bolt semi float was in 1500s that had the RPO F44. In early -400s GM built those ridiculous 6-lug 2500s which also had the 6-lug 9.5" axle. I call them ridiculous because GM should have just called it what it was, a heavy half... There is an 8-lug 9.5" also used in the -400s on lower gvwr (I think <= 8,600#) 2500 trucks. Can't forget to mention the rare 5-lug 9.5" 14 bolt SF either, 454SS trucks.

[ryanroo]

here is a weird one, i knew an old guy that bought an early GMT400('88) k3500 with a 9.5 14 bolt. 8 lug semi float. WTF. he bought it brand new and never did a thing to it. that one totally baffled me. why even call it a one ton?

[BigRed76]

Originally Posted by 83GMCK2500

BigRed76 incorrect, see b454rat's post.

To add further information, in the GMT-400 (88-02, technically) platform the 6-lug 9.5" 14 bolt semi float was in 1500s that had the RPO F44. In early -400s GM built those ridiculous 6-lug 2500s which also had the 6-lug 9.5" axle. I call them ridiculous because GM should have just called it what it was, a heavy half... There is an 8-lug 9.5" also used in the -400s on lower gvwr (I think <= 8,600#) 2500 trucks. Can't forget to mention the rare 5-lug 9.5" 14 bolt SF either, 454SS trucks.

Guess I should've specified I was talking about the 6-lug 14 bolt SF, since I don't know anything about the 8-lug 14 bolt SF's. I do agree that GM should've called them heavy halfs rather than 2500's, since I have a '95 2500 with the 6-lug 14 bolt SF, and it truly is a half ton with bigger rear axle, bigger rear brakes, and an extra leaf on each rear spring. I was also under the impression that the GMT-400 platform ended in 2000, even though it is generalized as 88-98.

[83GMCK2500]

Originally Posted by BigRed76

Guess I should've specified I was talking about the 6-lug 14 bolt SF, since I don't know anything about the 8-lug 14 bolt SF's. I do agree that GM should've called them heavy halfs rather than 2500's, since I have a '95 2500 with the 6-lug 14 bolt SF, and it truly is a half ton with bigger rear axle, bigger rear brakes, and an extra leaf on each rear spring. I was also under the impression that the GMT-400 platform ended in 2000, even though it is generalized as 88-98.

The 3500HD chassis cabs were produced through 2002. 01-02 model years you could get an 8.1L in them too.

I saw a couple wild ones the other day, 98 or so 454 truck with 8 lug semi-float, did not know you could get a 454 in a truck with that low of GVWR as to not have a 14FF.

ryanroo, I saw one of those TOO! It was in my friend's wrecking yard, extended cab long bed TBI 454 K3500 with 14SF.

[Rocketman72]

I really appreciate you folks giving me the benefit of your knowledge and experience. I will consider it an 88-98 rear end and order my brake parts accordingly. I will likely change over to disc brake rear at a later date..... Money is an issue right now.

I'll be mounting this under my '72 K5 Blazer build that I have going on at this time. I had this vehicle on the road once upon a time but after installing a 454CI in it I blew out the 12 bolt rear. I'm hoping this rear will be a little stronger. I do not intend to take it off road anymore so it should work fine.

[Orange Crate]

Info here too:


http://www.pirate4x4.com/tech/billav...ble/index.html

[Rocketman72]

Originally Posted by Orange Crate

Info here too:


http://www.pirate4x4.com/tech/billav...ble/index.html

Thanks for that but that article pretty much covers the 14 bolt FF. Mine is a semi floater.

[b454rat]

I have an 88 K3500, but it does have the full float rear, Dana 70 not the 14ff. I've seen a bunch of 3500s with the 8 lug semi, but were all 2wd. I do believe that any truck that came stock with a 454 would have a full floater, not the semi. I've seen 2wd pampered street trucks with the semi grenade...

I think the 6 lug semi's all had the same breaks, so pick a year and try it. Or pull the cover and see what the rear gear says...