How to Butt Weld solid rod?

[73k5blazer]

Ok, I need to join two pieces of steel solid rod end to end. They are different diameters.
What's the proper welding method for that? chamfer the edges slightly and weld away?
What it is, is my free hydro booster I scored, but it had the wrong rod to connect to the brake pedal, with the wrong eye size and everything. So I cut that off, so I have a piece of rod sticking out of my hydro boost unit, 3/8" diameter, then I took my OEM rod from my vacuum booster, which is 5/8" diameter, and cut it down so total length will match original. It of course has the proper eye on the other other, and is the right diameter to seal through the firewall and such.
I need to weld them together. My idea was just to chamfer the edge of the smaller diamter piece and weld 'em. But I'd thought I'd check first.

 

[kennyw]

If your gonna weld them you would need to chamfer them... But I think that is a scary way to hook up your brakes. Why not find a core hydroboost with the correct rod end and swap it out on your good one? They are replaceable I believe.

 

[73k5blazer]

YOu have to tear apart the hydroboost to get the rod out. ANyway, It's a newer unit from a CK 92-00 style. They have smaller diamter eyes and rods, no unit from that era comes with the correct size rod or eye. (Eyes and bigger, rod is way smaller, go figure). The hole going into the unit is just big enough for the 3/8" rod to pass through, an dno rod from the '73-87 era is going to fit it. I suppose I could machine and tap my original '73-87 rod, but that still would require tearing apart the brand new boost unit to get that rod out and the new one in.

I was thinking the same thing at first about hodgepodging it like this, but there isn't any heavy pressure on the rod in use, just compression from the pedal, so I'm not too worried about that.

 

[k5freak44]

weld a bead around them end to end after tacking and makeing sure they are in the right spot.

After giving it a good weld ll the way around what my teacher always told us to do is cut Vs into the side of the weldand fill that in with a bead. Do it all the way around and it should be one stout piece.

 

[fatbob]

How about using a die to cut some threads on the 3/8 rod, then drill and tap the larger rod? It would be adjustable and would be a whole lot cleaner.

 

[73k5blazer]

Ohhh..thats not bad, I didn't think of that.

Well, I just measured, and that's not going to fly becasue our trucks require such a long rod, there's just enough of it to make the length. Would't be enough lengthto screw it on, I'd only have a couple threads on there. The newer CK trucks have really short rods, the boost units on those don't have the 6" spacer bracket like our trucks do, they are mounted to an indentation directly to the firewall. Our trucks have a huge bracket, that bolts to a reinforcment. The reinforments is bolted to the fire wall with 6 botls, and 4 of those are also the pedal bolts. Can't get rid of the bracket/reinfocment set up without major fab work.

 

[Supreme70]

if you want the best weld for the rod you should grind a chamfer on each one and then put one root pass in and then a filler with a cover, are you planning on using a mig or a stick welder. if you use a stick u should only have about a 1/8 land on the front and keep the parts about 3.32 away from each other then put in the root pass, if you use a mig then put only a 1/16 land on the end and keep both pieces about 1/16 apart and put in a good root pass and them just cover it. to keep the piece's straight use a piece of angle iron and put the rod ends in it then tack it together. should be more then strong enough if done right good luck.

 

[garlicbreath]

You said you could machine and tap? What about throwing a piece of cold rolled steel in a lathe and turning the different diameters into each end, and use it as a sleve to weld on? Otherwise, what they said above works.

 

[73k5blazer]

That would work. I don't have a lathe, but a friend of mine does, I go there about every month, so I'd have a to wait a few weeks to use it if I wanted to.
I think that may be overkill, but there's no such thing as overkill when it comes to brakes, right? Well, I already welded the pieces together anyway. I chamfered the smaller dia. one, welded it up, cut into it a little, and welded it again all the way around covering completly the original weld. Before I did it to the real pieces,, I tested the technique on the little eye I cut from the end of the hydroboost, and some other 5/8" rod I had around. I welded those first, then proceeded to try to bend and break and beat the crap out it. I bent the hell out of the eye piece, and the 5/8" rod was bent too, the weld was holding strong. So I was then confident in doing the real pieces. I just had to do a little at a time, so as not to heat and ruin the seal the rod slides in on the hydroboost unit.
It worked great. Thanks for all the help and suggestions, I think it's a safe setup, may not be the prettiest and cleanest, but I don't think it's coming apart. It's covered by a round plastic shroud anyway, I'll never see it again, hopefully!