Outer Limits 4x4 Board

i have a lwb with a turboed 1.3 spua 6.5 rockcrawlers gears new 33's lockrite 2inch old man emu springs, the springs still have all springs in them, full pack.
at the weekend i was going up a rutted hill with some rocks in 3rd gear low range. and my car bounced a bit then teared the rear yoke on the diff apart and destroyed the uni. i inspected the uni and it looks like it was worn. i had checked before trip and there was no movement. however the cross on the uni is dis-coloured and looks a bit melted.
i was wondering if i needed an anti wrap bar because of the extra power and traction. or if it is just a old uni that let go
my rear shockers also shows signs of leaking and have become a little bouncy.
i have searched for anti wrap bars. but most older posts don't have pictures and i found alot of discussion about bars being single or bouble joint and the diff. thanks again for any help.

Put a new uni in it and get someone to have a look for axlewrap.

do some hard launches in 2high with someone watching the diff.

My guess is it's got some axlewrap, but if you've got full springs in the car it shouldn't be excessive.

I'd vote it's a combination of wrap, power, the locker, the big tyres and the driving style.

Hitting stuff with patchy traction in 3rd low is likely to be giving the driveline a hard time.

If you put a traction bar on it the next thing might well go - likely an axle or R&P.

I try and get off the throttle if it starts bouncing. I've seen (and had) too much stuff break once the bounce starts.

Steve.

yeah i thought my driving style plus power and traction was probably the cause. i will get someone to check ale once i track done another yoke. thanks steve.

i must see pics of this.......so i can evaluate my answers

but steves right, more bounce, more break

Oh, just adding -

Play isn't always a good way of assessing uni condition. If one cap is going out they can get tight which is what will lead to heating and rapid failure. One way of checking this is to drop the shaft and roll the uni around feeling for tightness.

You can feel for tightness when you pull away though. If the car feels shuddery at all when you come off the clutch it's a sign you've got a uni going out, or you have excessive axlewrap causing the uni to go close to bind.

PS I was driving a spoa car home to the shed for a rebuild some years ago and it threw a driveshaft uni. It was a combination of axlewrap, angle and abuse (mud) from the previous owner, along with high load - button clutch, 1.6, heavy tyres, no diff gears. It was shuddering like mad pulling away from the lights and on transient throttle. about 50km into the drive it leg go completely.

It blew the uni apart so hard the cross was melted and I couldn't even pick up the driveshaft from where it was lying, smoking, on the road.

Steve.

on my zook spua, 34s, 4.57 diff gears, 4.9 tranny, 1.3L, 2inch light duty OME full pack rears i was getting some pretty full on axle wrap...although I haven't seen a spoa axle wrap so have no comparison on how bad it really is....With my 20v 4age and 323 springs in the rear I may have to beef up the pack a bit...

Gwagensteve wrote:Oh, just adding -

PS I was driving a spoa car home to the shed for a rebuild some years ago and it threw a driveshaft uni. It was a combination of axlewrap, angle and abuse (mud) from the previous owner, along with high load - button clutch, 1.6, heavy tyres, no diff gears. It was shuddering like mad pulling away from the lights and on transient throttle. about 50km into the drive it leg go completely.

It blew the uni apart so hard the cross was melted and I couldn't even pick up the driveshaft from where it was lying, smoking, on the road.

Steve.

I knew there was a reason I sold that car ...

i broke another rear uni at the weekend.

i was wondering if the 1 litre tailshafts have smaller unis than 1.3's. axle wrap isn't real bad.

my pinion angle is pointing upwards a fair bit, (when car is on level ground pinion points upward about 40degrees) when i fitted the wt diffs, i mounted them the same angle as they already were

Sounds steep , need a pic please , Cheers Paul.

40˚ Baby jesus wept!

Stock is nose up less than 5˚

Basically, 1.0 and 1.3 unis are the same size but they are not really interchangable (they sorta are but not as a long term fix, they're slightly different sizes), and the 1.0 unis have internal clips and 1.3 unis have external clips.

That means you can sort of use 1.0 unis in a 1.3 but you can't use 1.3 unis in a 1.0.

But really, you need to keep like for like.

Bear in mind, your transfer case is basically at 0˚ effectively, you have two unis at 20˚ out of phase to each other, with one at maybe 5˚ and the other at 35˚. That's going to kill them.

You need the two angles to cancel each other out, so if the pinion is up 5˚, the transfer is down 5˚, so the angles across both unis are bascially 0˚

That has to be the case because unis change speed as they cycle. if the angles are mismatched then the two unis are fighting each other.

At 40˚ add some axlewrap and you're going to be going way critical - as the pinion climbs, angle will be decreasing at the transfer end and increasing at the uni at the diff. Beyond about 40˚, your unis will last seconds if loaded hard at that angle. suzuki unis can apparently operate at up to about 46˚ but they wont take high load at that angle, or take it for long.

THe manufacturer sets unis to run at 3-5˚ maximum at ride height.

Steve.