Technical Attempt at narrowing my 9", where'd I go wrong?

Hey guys, I don't post much but I lurk often.

I'm in the middle of building my first hotrod, a 30 model a coupe. I'm trying my hand at narrowing my 9" housing to fit the car. My dad has a Mittler brothers narrowing kit I'm using to keep everything in line. My plan was to cut off the old tubes on the housing and get new ones, narrow it to the correct width and weld new bearing ends on.

I took the original housing and made a jig for the housing in order to weld the new tubes in the fixture to keep everything inline. . Fast forward to today, I have new tubes welded on my housing and am using the mitler bro kit to weld my ends on. I got everything together and my ends aren't square on the tubes, they're off about 1/16"-1/8". So somehow when I welded my tubes on my housing, they became unsquare.

My question is, should I have tacked my bearings in on the tubes, then installed the tubes in the housing, then install the mitler bro kit to keep everything aligned, then weld the tubes on the housing?

The guys that have done it, how do you guys do it?

Here's a pic of my housing fixture I made for reference.



Thanks fellas

 

I don't even have a jig to go under axle housings. I put two jack stands on the welding table. The solid bar, the pucks that go where the differential carrier bearings would be, and the pucks that go where the axle/wheel bearings ALL need to be in-place BEFORE even your first tack weld, on a tube beveled down to 1/8", on both sides.

 

1/16 to 1/8 is not a problem, the housing can eaisly be strightned. Looks like in the picture that your spring mounts are just tacked on. We weld all the brackets , spring mounts, shock mount, panyard bar mount, rear brace etc.completly before putting the ends on. as stated above , bevel the ends of the tubes and the housing ends.
We center the pinion on all the housings we do, they come offset from the factory.
Will be happy to answer any Questions you have

 

So the new tubes aren't in the housing correctly?
You have 3 options,
1st is to re do the tubes i.e. Correct the problem, not chase the symptoms
2nd is to put the bearing ends where they belong and let the tubes land where they land.
3 rd would be to straighten the housing out and walk the tubes over to meet the bearing ends wherever they are when in correct position.

 

Thanks for the replies guys.

I want the bearing housings to be pretty much lined up so I guess I'll have to cut the welds and redo the tubes.

I was hoping my fixture would eliminate the need to assemble everything loose and weld all the joints at one time. I was worried about warpage from welding.

The fixture clamps the housing down in 6 different spots. That's how I welded the tubes in and they cooled completely before I removed the housing. Not sure how it moved.

 

Kinda the way You need to think is...It's a lot easier to"float" a 1/4 of an inch over four different points... Say your off a 1/16 on everyone, WHEN you have the mitler set-up in. . That would work out fine, definitely tack everything before burning down....

 

I think I see where you went wrong, how it moved.
the fixture must not be (sure doesn't look it any way) strong enough to hold back the forces of welding.

 

You do not need to cut it apart. I have read on here that you can straighten that out by heating or welding a spot on the axle tubes at the right spot to fix it. It involve understanding how to shrink metal. I would probably just use a press and push it.

 

The tubes can be off, no big deal those of us that narrow see considerably worse. It is the ends that have to be true to the carrier bearings, not the tubes. The only time you have to worry about the axle tube being perfect straight is when you have the rear in a chassis jig and you have a fixture bolted to the pinion support to align it to the engine crank saddles. If the tube is off you'll go nuts trying to get it aligned proper.
I have tried the heat thing on round tubes and it doesn't really work well. The problem is that the tube is round, you heat one area and the rest of the tube resists movement (the very reason that round tubing is used for racecar & airframe chassis) and about all you accomplish is to add lots of tension with little or no movement.
Let it go,use your alignment bar to weld the new ends true to the carrier bearings.

 

My fixture has a 2 inch bar and wide bearing mandles , With bar and mandles in place I heat completely around housing and let cool . After cooling it will than be happy....

 

I'll have to take a picture when I get home from work of the offset between the tube and bearing housings, it's probably more the 1/8, probably closer to 3/8.

It's actually only one side, the other is close enough not to worry about.

I may try the press idea to see if I can square it up that way. Otherwise the only way I see if cutting the weld and redoing it.

Oh and as far as my jig setup, it's 1/8" wall square stock because that's all I had. I was questioning the wall thickness before I built it. Not sure if that played a role.

I'll update you guys in a couple of days. Thanks a bunch for all of the help.

 

I think if you tried to cold press that much and you were successful you'll more than likely fatigue the tubing or break loose some of your previoue welds.
I would cut loose about 75% of the weld on the side of the tube that needs to be moved.
I also would have the ends tacked on and double check it with the alignment bar before continuing. 31Vicki has it right, that tubing is pretty marginal in both overall size and wall thickness to be effective for this kind of fixture.
This type of fixturing isn't often used, I think the problem was the tacking and overall order of how you went about using the alignment bar (process) that caused this.
Sounds like you got lucky at least on one side.

 

What he said and weld ALL your brackets on before welding on bearing ends

 

I don't know what a mitler bros kit is. But I do know that you should tack everything up before you ever weld a thing. Where you are now is that you have to break it down and start over, or you get everything lined up and use heat to square it, or you live with the housing ends being cocked as long as your bearings and axles run true.

 

So I should completely weld ALL my brackets completely before I weld the bearings ends?

I've heard people often recommend this and I understand why. What would I have done if I just bought a housing built to my width and weld my brackets on? What are your thoughts?

 

it would be like most hot rod rearends, and be warped a little bit.

 

I try to get everything tacked up and weld the entire thing at once, skipping around a lot. Everyone has their own approach to it. You have to decide what is acceptable to you and not do it the way I do because I say to do it that way. The way I do it works well for me, but I may not be doing it the accepted way.

 

Unless you're a lot better welder than I am, every time you cut the tubes and reweld them (close to the pumpkin) the ends of the tubes are gonna move around. If it were me, I'd finish welding the brackets, then straighten the tubes to the best of my ability, then weld the housing ends on. I know there are folks that weld everyday that can draw the tubes straight while they're welding them on, but it's not me.

BTW, I'm dealing with the same thing right now myself. I'm trying to build a fixture to bolt the rearend into and use a couple of bottle jacks to straighten the housing before the ends go on. I've got a torch with a rosebud too. I'll let ya'll know how it turns out, if I can ever get the time and motivation to get back on it.

 

The way you should go changes based on from where you start.
One of those Chevy chase movies has a great scene. Laugh you're ass off if you get it. guy in the car asked they guy on the porch for directions. The porch guy says " well if I were trying going to there I sure wouldn't start from here". Then later tells the lost guy to "turn left 3 miles before the dead end."

If you have it just in all pieces then weld it all and let all the bowing bending twisting be done and over with. Straighten it once or just let the bearing ends bed where the lay.

If you get the housing ordered in, they welded and already bowed and straightened it & you paid for that. Now you weld your brackets and you straighten it back again. Generally if you weld full circle on the tube it won't end with a bent tube. If you weld less than 1/4 circles it doesn't bent very much. When you weld more than 1/4 but less than full you get the tube walking around.

 

weld a bracket the same size, on the other side of the tube

 

I've never narrowed a rear end but as a pipefitter, I straighted lots of pipe used in industrial shower sleeves in which the pipe has to be straight after welding. First of all, the rear ends I have seen narrowed were done at the ends and not the middle. The guy I use has a large solid piece of round steel that slides in the housing and the housing ends are put in place and the whole unit is clamped at the ends. The housing ends are tack welded at opposite sides and fully welded going from one tack to the next and than rotating it to get to the opposite side. Usually takes a large rubber mallet to drive out the shaft but you know if the shaft comes out, it's square. You can heat shrink a piece of pipe that is bent fairly easily but thats not the same as trying to correct for a piece thats welding crooked.
The first thing I would do is set the housing in jack stands and then measure from the face of the housing to see if the housing ends are the same distance from a parallel line to the front of the housing to see if one end is further forward than the other. I would then measure to see if the ends are parallel to each other. You can't fix the problem until you know these measurements.

 

Does your Mittler deal have bushings to go in an empty center section so that your alignment bar passes through 4 bushings, two in the center and one on each end of the tubes? No one has mentioned one. How did you plan on getting the new tubes to line up anyway?

 

If it is a complete setup, yes, four bushing per setup.

I own and use one.

I know of no way to do it precisely without all four in-position during welding and cool-down.

 

Yes my mitler kit has the inner "pucks" for the inner axle bearings and outer pucks for the outer bearings.

Here's a pic of the end I'm having trouble with

 

I'm finding out that's where I went wrong. I should have left the 4 joints loose with the mitler jig in place.

 

That is a five minute fix with a good wire welder. You need to lay a bead halfway around the tube on the side that needs to come up as close to the housing while still on the tube. Cool the weld with the wet rag, it will "pull" in the Direction you want to go. You may have to do it more than once and in slightly different locations to fine-tune the pull but when done it will be right in line with the flange. When the housing is cool you can sand off the weld beads and weld that flange. Tack first, finish weld. Oh, make sure all your brackets are finish welded first.

 

Actually, the center two pucks/mandrels/rings that go where the carrier bearings would been should have had the bearing caps torqued to factory spec over them.

 

I've fixed worse. Use the above described method of welding on the tube. The closer that you do it to the center section, the bigger the change will be. If you are close, but still off, move away from the center section.

 

Use a rose bug for heat instead of wire bead, no shit to grind off. Quenching with water will almost stop the shrinkage. I would get the spot cherry-dull orange hot about the size of a quarter and let it cool on its own. It will shrink more that way. Like mentioned earlier, do this close to the center section. If the tube is out of tolerance at say, 6'o clock, put the heat at 12'o clock.

 

A couple of tips from the Mark Williams tech:
"Make sure you use a gasket when you bolt the carrier in to locate the line up bar."
and
"You know our housing ends are 4130 don't you? TIG it."