SOA rear drive shaft breaking

[Rosey]

Hi Guys,

I really need some help with this. I've broken 2 brand new rear drive shafts in the last week. Its costing me a killing. I'm running the broken back setup and it drives smooth and quiet on the highway upto 120kmph. Both times I have broken the rear drive is when doing hill climbs, nothing to serious though. I've been looking at the springs and can't see any obvious signs of axle wrap, are there any tell tail signs?

I'm starting to think the shaft breaks when there is load on the truck and the suspension is compressed. Its broken both times when the truck has started to bounce. It keeps breaking at the diff end where the slip yoke is, thats the right way around isn't it? Its also the expensive end to replace, $240 and $220 so far. I'm really temped to bugger off this broken back setup and weld the perches parellal to the factory perches although there will probably be vibration... I don't know what to do!! arrrhhhh

I worked out the diff angle using a angle level taking the measure from the back of the transfer shaft then using a picture I found on the internet I calculated the new angle (180 - calculated angle, i think it was) then added 2 degrees to account for axle wrap under acceleration. It looks right on the truck although the diff does point right up.



I'll probably post something in the toyota section to see what those SOA guys do in thier shorties, I must have something wrong. You can kinda see the angle of the diff in this pic.

thanks for any help you can offer

cheers
Rosey

[Wendle]

it's wrapping the springs and binding the uni's for sure. especially with so few leaves in the pack. use the energy you were going to put into re-welding the perches to build a torque rod instead.

[Rosey]

as i'm running broken back setup, wouldn't it have to wrap to the point where the diff was pointing down and out of the uni's range? which means a massive deflection, which i would have thought would have bent the springs?

[Wendle]

wrong way, it wraps the axle backwards as the tyres are trying to turn forwards. so it probably only takes 5 or 10 degrees or so..

[Rosey]

oh sh*t, your right, it would be turning the axle backwards. That explaines it then. everyone else agree? so the diff angle looks ok, not to much?

thanks heaps Wendle, i wish i had asked earlier.

cheers

[V8Patrol]

Ahhhhhhhhhhhhhh he joys of sorting out an SOA

[bigpat]

Just further to this thread guys...
I know that when Cheezy does 4" lifts in GQ shorties, he extends the bottom control arms (rear) to keep the diff pinion angle same as standard. I think this is so the uni angle at the g/box and angle at the diff are equal, to cancel the vibrations. ( Angle in has to equal the angle out)

Although GQ's are 4 links, would the same theory work with leaves to turn the diff nose down to near standard pinion angle? I can't see why not.

Wendle is right though Rosey, you probably should run a wrap bar with those light spring packs...

Cheers,

Pat

[Screwy]

You are definatly binding the unis up as wendle says.

but im qeustioning the fact that u said the slip yoke is at the diff end.
thats not right, the FAT long part of the shaft should be at the diff end and the slip at the top near the handbrake drum..............

Mate are u sure?

cheers

[Wendle]

shouldn't matter which way the shaft is. it is better to run the slip joint at the pinion end if you are driving rocks, as it is a solid piece of steel, and much more resilient to spinning on rocks than the tube end of the shaft.
just run a single link (cut up a GQ lower link or something) from about 150mm above your spring packs on the axle, forward to a crossmember that is in a convenient spot. get it as flat as possible and try to get it about twice as long as the front half of the springs as a minimum....