Thread: Death Wobbles

I was having a thought last night. I am contemplating splitting the A arm to two separate control arms so that I can get my top mount lower and improve my AS figure. I was thinking of fabricating a mount down a bit on each side of the pumpkin using Heim joints to get the top mounts lower. The problem with the Patrol diff is that it's just so big and my top arm angle is wrong. It's either this or do what I suggested in my previous post.

When you get into modifications, the causes of problems can be much more varied.

Firstly, I'm not quite following what you have done. Have you just replaced the diffs, or the whole axle? If it's the diff, then that could upset the alignment of the half shafts inside the axle unless you were able to get them exactly centred along the axle case centreline. Likewise, the prop shaft can be affected by having a different length pinion, changing the deflection angles of the UJs which will cause vibration at harmonic frequencies. You can confirm or eliminate the prop shaft by driving with it removed (lock the centre diff if you have an LT95 or LT230) and drive gently as you'll be putting all the torque through one prop and axle, but get it up to the usual wobble speed - if it persists, then its not the prop or front diff inclination, if it's gone, then it is that. LR used altered phasing of the UJs at each end of the prop, not in line like the rear, to get rid oft he vibration - there is an equation that dtermines how far out of rotational alignment the yolks must be for differing UJ deflection angles at each end, and only on applications where both UJs are at an equal deflection should the yolks line up.

If you changed the axles outright, then you shouldn't have any problems with half shafts, but the pinion axis and prop shaft geometry is likely to be off.

3.5 degree castor is so similar to the original 3 degrees LR use as to be insignificant, and the mounting position of the axle tube relative to the radius arm, as per your drawing, won't make a difference as long as both sides are the same.

I'll be suspension bushes, swivel bearing preload, prop shaft geometry or wheel balancing.

If it's the vehicle path wobbling, rather than a vibration through the suspension or steering, then I'd suspect a tracking alignment problem. The original axle should have had a 0-2.4mm toe out at the wheel rim, but tht is based on several factors including castor, camber angle and scrub angle. If you have changed the axles, as I think I understand you have, then though you kept a similar castor, the scrub angle/radius could be very different and this would change the tracking requirement. But you'd be amazed at how sensitive steering stability is to tracking adjustment.

A bit of history. When I did the conversion, I replaced the whole housing, it didn't vibrate at all. One time, coming back from a run, it vibrated really badly at about 40-50km/h. I put it down to mud in the wheels. After cleaning them, the vibration was there at about 50-60km/h and also when I braked.

It has new swivel bearings set at Patrol preload, new wheel bearings, new pads and rotors as well as new panhard bushes. I have also just fitted new shocks and a steering damper and radius rod bushes on the diff. I haven't balanced the wheels yet and the only bushes I haven't replaced yet are the radius rod bushes to the chassis.

Drove it Sunday and it still vibrates. Well, wobbles is a better term. I can put my head out of the window and see the front wheel wobbling as I drive.

If you're using the wheels and tyres in the photo of post 5 unbalanced, then that'd have been the first place to look. They are heavy lumps of rubber and off road tyres are notorious for being well out of balance even when new, as are wheels, especially inexpensive, oversize aftermarket wheels. It's also not impossible you got some mud inside them when running at reduced pressures.

I haven't driven it yet, but I balanced my front wheels last night. Each wheel was over 300g out so I guess that wouldn't have helped. I have to fit a transfer case mount tonight as I broke it on the weekend so I'll take it for a drive afterwards and see if it has fixed it.

Had it out yesterday, the wobble is just about non existent now, I can still feel it around 60-70km/h but very very minor. I can live with it.

I also discovered something else though, because I drive it with the front hubs unlocked, I have to have the transfer case locked so I have drive to the rear. It makes a lot of noise and has a fair bit of drive train vibration. Coming home from our outing yesterday, I thought I'd try a driving it with the front hubs locked and the transfer case open, was a lot smoother, no noise and felt a lot better. The only thing I have to remember is to back off the throttle when I want to turn as I have an auto locker in the front. On the tracks it isn't an issue, but I kept forgetting on the road and a couple of times I had to go straight through an intersection rather than turn the corner haha.

Originally Posted by Snagger

If you're using the wheels and tyres in the photo of post 5 unbalanced, then that'd have been the first place to look. They are heavy lumps of rubber and off road tyres are notorious for being well out of balance even when new, as are wheels, especially inexpensive, oversize aftermarket wheels. It's also not impossible you got some mud inside them when running at reduced pressures.

Funny how the obvious is completely overlooked both by the original post and subsequent responses... why? Because we assume the obvious troubleshooting has already been done, and has been proven time over, to assume, is to make an ASS out of U and ME ...
Nice work snagger.

To be fair, I knew I had to balance the front wheels, but other components were worn and needed to be replaced anyway and seeing that the parts I replaced contribute to the dreaded death wobble, I was eliminating all possibilities. I may have done things in the wrong order, but everything that can potentially cause the wobble has now been rectified. Even though the vibration is still there, I can only put that down to the fact that I also have a bent rim. These are next on my list of to do's.