Spring Perch Welding Question

[Vozar]

Im doing my SOA in a week or two. Will an Arc welder work allright for welding the perches on.Anything i should know when welding them on.? One of my friends is doing it for me. The perches are suppost to be for 3 inch axle tubes right? Just double checking. Thanks, Matt

 

[jimbo74]

depends on what perches you use, an arc will be sufficient pending your friend knows what he is doing... also take it slow, arc yields lots of heat... mig would be better, normally yields better penetration and a cleaner weld

 

[Vozar]

Ill take a pic of the perches tommorrow and post it.

 

[410Fortune]

When we converted my 8.8 to spring over we used an ARC. As long as the person doing the welding is competent you should be allright. The key is to GO SLOW and let it cool down.

It has been 3-4 years now (cant remember) they the perches have never given me a problem.
It is EASY to punch a hole right through the axle tube with the arc, so just be careful!!!

 

[james t]

take your time. never run more than a 1" long bead at a time. swap sides. in other words, run a 1" bead on the drivers side, then go to the passenger side. wait until only warm to the touch, and repeat. do both on the outside, then next pass do both on the inside.

 

[Harry5150]

I think the ones I put on my truck were 3.25" in diameter.

I put some wet rags around the axle tube to take some of the heat from welding. Tack them on first to make sure you've got them set right. Don't forget to rotate the axle too so you keep your pinion angle correct.

 

[Vozar]

For the pinion angle should i move the axle so the driveshaft is going straight into the diff?How do u set it exactly, ive heard lots of things.

 

[Vozar]

Wait a minute! Are the perches suppost to be for 3" or 3.25" Mine dont exactly sit flush with the axle but i thought they werent suppost to because u have to have a little room for the weld.

 

[Jefe]

I think the axle tube is 3.25" or 3.5"? You can grind yours till they fit.
Welding has been discussed very well by james.
As for pinion angle, if you have a single u-joint on both ends of your driveshaft (stock), then you shouldn't need to rotate the axle at all. The angle of the pinion should be eqaul and opposite that of the T-case. And if its correct now, by adding more height both angles will change equally, and remain correct.

 

[Joey P]

Yeah the tube is 3.25.

 

[Harry5150]

I dissagree you should "try" to fix the pinion angle.

The sharper the pinion angle becomes, the more stress on the u-joint and also the more the driveshaft gets pulled out of the tranny.

[Pulls out the geometry book and blows the dust off ..]

Ok say we have a hypothetical Explorer scaled down (for simplicity) where the drive shaft is 5 feet long, and a section of the frame is 4 feet long and the height from the frame to the differential is 3 feet high.

So we have a right triangle.


Frame 4'
---------------------
- |
- | Diff height 3'
Drive Shaft 5' - |
- |


So if we use the formula c^2 = a^2 + b ^2 (Pythagorian sp?)

5*5 = (4 * 4) + (3*3)
25 = 16 + 9
25 = 25

We know that this triangle is correct.

If we do a SOA and put the leaf on top of the axle we're going to add 3.25" + the thickness of the perch + the thickness of the leaf pack.

We'll say the the axle tube is 3.25", the perch is 0.5", and the leaf pack is 1.0" for a total of 4.75".

Converting that into feet: 4.75"/12"= .3958'

New frame to diff height: .3958' + 3'= 3.3958'

So if we plug into the formula a (the fixed frame section length) 4' & the new frame to diff height 3.3958', we now solve for the new driveshaft length.

c^2 = (4*4) + (3.3958*3.3958)
c^2 = (16) + (11.531)
c^2 = 27.531
c = 5.247'

So the difference is 0.247' which converted & rounded off is 3", if my math is correct.

Therefore if you do a hypothetical SOA, you need a 3" longer driveshaft.

By rotating the diff up, you may be able to regain a precious inch of driveshaft. I'c drank too much to do the math on that right now plus that's way too much for my old ass to do.


Oh yeah, don't for get to paint them too.

Just found this on my site. Click the link, then right click the image & then click play. The red thing is a perch.

> Animation

 

[Harry5150]

Well my triangle diagram didn't turn out. You get the picture.

 

[Jefe]

Originally posted by Harry5150
The sharper the pinion angle becomes, the more stress on the u-joint and also the more the driveshaft gets pulled out of the tranny.

Very True. But to prevent driveshaft vibration, the u-joints need to be at equal but opposite angles. And the more driveshaft vibration you have the shorter your u-joint life (and possibly bearings in the t-case (or tranny) and diff)

 

[james t]

...

 

[Hotweels]

dont point the pinion straight up tp the t-case it will vibe like a ****.....
think about it a single u-joint on each end of the shaft is good for (dont quote me on this) 15* now what happens if you point the pinion at the t-case?...... the u-joint on the t-case end will be way out of phase with the other one and will vibrate horribly.
IF you install a double cardan joint you can point the pinion straight at the t-case only beacause the two u-joints at one end take up the angle of the shaft.
www.pirate4x4.com look in there tech section there is 5 full pages on how this stuff work's.
just my opinion and the way i will do mine, install the pad's on top of the axle and add 2* to compensate for the small ammount of axle wrap you will have at cruise speed's..... honestly if you cant understand this take it to a shop as mistakes in welding the pad's on can be a REAL PITA do you realy want to pull that diff twice? i sure as hell dont.