Hey everybody, i'm trying get an answer for my buddy with a 78 K5. (i'm a Jeep man myself) He's wondering if he can weld the tubes to the diff to prevent them from twisting. I have heard of people doing this on a ford 8.8 because the diff housing is cast steel and not cast iron. (so i've been told) Is this the case with the chevy rearends too?

btw, jeeps rule:flipoff2:

Originally posted by MossMan
btw, jeeps rule:flipoff2:

Yeah, Barbie thinks so!:flipoff2: I've never welded the tubes, but I guess he could do it if he wanted.

Dana rear axle center sections are nodular iron. I assume, but do not know, that the Chevy center sections are also.

There are ways to weld and anneal nodular iron to steel. The problem you get into is with fatigue. The weld toe will crack over time and the housing will leak or break.

The reason the tubes are pressed into the housing and retained with rosette welds is to eliminate the weld carrying the bending load. The torsional load is carried by the combination of weld and interference between the housing and tube.

The best advice I can give you is not to weld the tubes. If you have a problem with the tubes spinning in the housing, just replace the housing or step up to a 14 bolt. You could also machine out the rosette welds and reweld them.

I would tell hem just to go 8 lug and get the 14 bolt FF. He can get it out of any 3/4 ton pick up from 73 to 87.

As far as welding the tubes, I know a lot of drag racers were doing it. I had a 12 bolt car axle that had the tubes welded but I never used it. It's supposed to be hard to weld the 2 different types of steel together. Has he spun any tubes in the housing yet?

btw, jeeps rule

Too bad you couldn't even tow another one home from the trail. They can rule from the top of my trailer any time.

Originally posted by chvyhs
I would tell hem just to go 8 lug and get the 14 bolt FF. He can get it out of any 3/4 ton pick up from 73 to 87.



I'm pretty sure that the 3/4 tons are SF, not FF. You'd need a 1 ton for a FF.

There are a lot more FF 3/4 tons than SF 3/4 tons.

Originally posted by Dieselmh
I'm pretty sure that the 3/4 tons are SF, not FF. You'd need a 1 ton for a FF.
Older 3/4 tons (back to early 70s) were all C14FF. Late 80's+ (I think that's about right) had some of each.

How is this different than welding bracketry to the housing?

J. J.

Welding bracketry to the axle tube is typically fine since they are drawn material. Welding to the center casting is a little trickier.

If you weld the tube to the center section or on the bottom of the housing the weld is in tension and the stress is perpendicular to the weld toe. That combination can lead to more rapid fatigue cracks.

If you preheat the housing and tubes, weld using stainless or high nickle rod, and post heat you can avoid most of the problems associated with ductile to steel welds.

It's just more difficult than welding on spring perches to a tube.

I've read where people on this board have welded with 7018 or 6011 or just run a wire welder to attach brackets to the center section with success. However fatigue is a progressive failure. It takes time for the crack to develop to a sufficient length for full failure.

With a tube/center section weld it may leak before the crack is long enough for the whole section to fail. Then again it may not. It depends on how much load is applied and at what strain rate.

The real question is why are the tubes spinning in the first place? The rosette welds are more than strong enough to hold most mildly built powertrains.

I'm pretty sure that the 3/4 tons are SF, not FF. You'd need a 1 ton for a FF.

The Suburbans and Vans had the SF's. Pick ups had the FF. The 3/4 ton FF's are a direct bolt in. The only problem is the way the e-brake is engaged and getting a hybrid ujoint. A FF out of a 1 ton is different because the spring perches are a different with than the 3/4 and 1/2 tons. I have a 1990 Suburban with a stock SF, I'm installing my FF from a 1978 3/4 ton pick up.

Originally posted by lt1yj
Welding bracketry to the axle tube is typically fine since they are drawn material. Welding to the center casting is a little trickier.

If you weld the tube to the center section or on the bottom of the housing the weld is in tension and the stress is perpendicular to the weld toe. That combination can lead to more rapid fatigue cracks.

If you preheat the housing and tubes, weld using stainless or high nickle rod, and post heat you can avoid most of the problems associated with ductile to steel welds.

It's just more difficult than welding on spring perches to a tube.

I've read where people on this board have welded with 7018 or 6011 or just run a wire welder to attach brackets to the center section with success. However fatigue is a progressive failure. It takes time for the crack to develop to a sufficient length for full failure.

With a tube/center section weld it may leak before the crack is long enough for the whole section to fail. Then again it may not. It depends on how much load is applied and at what strain rate.

The real question is why are the tubes spinning in the first place? The rosette welds are more than strong enough to hold most mildly built powertrains.

What the difference between using rod and using wire? I was planning on using my MIG welder to weld bracketry to my housing. Why don't I have to worry about getting high-nickle content wire?

J. J.

If you're welding to the cast center section, you will want to use stainless or high nickle content rod and make sure you weld in position otherwise the weld will just run out. I haven't found high nickle content wire but stainless is pretty common. I use 308 stainless for mine but 309 is a good choice also. You will need to change your gas mixture also. I preheat and post heat using a rosebud.

The big difference between stick and solid wire is the quench rate. Solid wire quenches faster than stick because the flux retains the heat more and the weld puddle cools slower which yields a softer, less brittle weld. You can achieve the same effect using flux core wire in your mig welder.

Pre heat and post heat will slow the quench rate and again make a less brittle weld.

Originally posted by chvyhs


The Suburbans and Vans had the SF's. Pick ups had the FF. The 3/4 ton FF's are a direct bolt in. The only problem is the way the e-brake is engaged and getting a hybrid ujoint. A FF out of a 1 ton is different because the spring perches are a different with than the 3/4 and 1/2 tons. I have a 1990 Suburban with a stock SF, I'm installing my FF from a 1978 3/4 ton pick up.


I have a freind with a 3/4ton pickup with the SF in it. It's the original axle. :)

I have welded the tubes on every axel I have ever worked on. Never any problems!

Originally posted by chvyhs


The Suburbans and Vans had the SF's. Pick ups had the FF. The 3/4 ton FF's are a direct bolt in. The only problem is the way the e-brake is engaged and getting a hybrid ujoint. A FF out of a 1 ton is different because the spring perches are a different with than the 3/4 and 1/2 tons. I have a 1990 Suburban with a stock SF, I'm installing my FF from a 1978 3/4 ton pick up.

Some 3/4 ton P/u's had S/F also!

I've seen 3/4 pickups with both SF and FF 14 bolts, some of the SF 14 bolts that I've seen have 6 lugs. I've heard a few guys say that 6 lug SF 14 bolts never existed but I know where there are 3 for sale, they would be a great swap for a 6-lug 1/2 ton truck

3/4 ton trucks from '73 to '80 used the FF 14, '81 to '87, many were SF, some were FF, before '73 it was the FF Dana 60 for a while, before that is was the EATON HO72, after '88 is when everthing hit the fan and you could buy a 3/4 ton truck that was missing two lug nuts off each wheel, and you had to get a 1 ton or HD 3/4 just to get a FF, and even some 1tons were SF. I swapped a FF into my '91 K3500 cuz it had the SF, I used a '73 suburban FF and had to move the pads out cuz the IFS truck have a wider frame and the rear springs are angled.

Oh yeah, don't weld the tubes to the housing, it's bad.

I was just wondering how you anneal two peices of metal together? since the last time I knew....the annealing procces is a hardening proccess not a welding or jointing procces....just thought I'd clear that up before someone got cunfused

To clarify my earlier post.

You would weld first THEN anneal the part to reduce the residual stress left from the welding process and reduce the hardness in the weld toe. The annealling process has nothing to do with joining two pieces of metal together.

Originally posted by MossMan
Hey everybody, i'm trying get an answer for my buddy with a 78 K5. (i'm a Jeep man myself) He's wondering if he can weld the tubes to the diff to prevent them from twisting. I have heard of people doing this on a ford 8.8 because the diff housing is cast steel and not cast iron. (so i've been told) Is this the case with the chevy rearends too?

btw, jeeps rule:flipoff2:

I welded my 12 bolt on my '71 after I spun a axle tube & almost spit out my 4" block. My diff. cover was almost facing straight down to the ground, thank god I had a fix yoke not a slip one. Anyways, the weld eventually crack all the way around. I used a miller 250 mig welder. You are better off going the juckyard & get a new axle. later, Dave..............