Death Wobbles

[Not_An_Abba_Fan]

I have a question that will most likely be answered here.

My RRC has Patrol diffs and I have been experiencing the classic Patrol death wobbles. I have new wheel bearings, new swivel bearings, new panhard bushes and the steering box has very little play. It comes in at 60 km/h and I can drive through it. Every now and then it will give a brief wobble around 80 and then stop.

My question on the cause is, if I have welded the front radius arm brackets to the diff too far away from the diff, will this cause the wobble? I am limited as to how far I can put the bushes "over" the diff housing as the RHS is fairly large due to the centre being further to the right than the RRC diff.

The rough drawing is sort of what I mean. Say the black circle is where the diff housing should be but I have it where the red circle is.

Bit of history, I replaced the diff housing not long ago. It did it before too. I had the pinion parallel to the TC but I had too much caster and bugger all turning circle. When I put the new housing in, I rotated the diff so there is about 3 1/2 degrees of caster now. I had it a bit closer before because the tie rod had clearance off the radius arms, now it touches on full lock.

https://www.aulro.com/afvb/images/imported/2016/08/774.jpg

[ian4002000]

I was chatting to a Range Rover owner who had similar trouble with his classic, he eventually took it to Peddars who diagnosed soft bushes and fixed the erratic steering problem completely.
It sounds like it may be time to get Peddars to have a look and measure.....


Ian
Bittern

[Mercguy]

If you have a look on the patrol 4x4 forum it goes into great detail about the death wobbles.
Replace your radius arm bushes and the panhard rod bushes (uerthane) check the caster settings. You may need to slot the swivel housings to get it correct.

As a former GQ owner, I can assure you the bushes are 90% of the problem on a GQ.....

Extremely important to get a Wheel alignment after also.

But:
Since you've swapped a GQ front into RRC, and you've also changed diff pinion angle and caster, spring perch.... There are unknowns

Without seeing it and taking measurements, or having the details provided it would be difficult to ascertain if you have got something out of alignment or not.

Bottom line is that it's common as muck on GQ's and the urethane bushes fix it - on the GQ.... Slotting the swivels for the additional caster also req'd in some cases. e.g:
If you have a lift, then you must slot the swivels on a GQ to get the correct caster.

If you have a GQ housing in your RRC, and everything is to Rover spec (pinion angle, spring perch, swivels etc, then you'd be OK - so bushes are req'd.

If youre not offroading to the point where you need huge flex, then urethane bush in the radius arms should be OK, or use the 'holey' bush if you need the flex. These are regular routine replacements on GQ's - almost an annual affair.

Might also be worth looking at Superior's radius arms if you're having issues with clearances on the front bush / mount.

[Milton477]

I had a classic some years ago with the same wobble. Turned out to to be the swivel pre-loads. I removed some shims to tighten them up. But you have patrol diffs....

[Not_An_Abba_Fan]

Radius arm bushes are polyurethane, although they are about 2 years old and I punish the car so I dare say they need doing. Panhard bushes are polyurethane. My caster angle is 3.5 degrees, Patrol spec. As I mentioned, I did have the pinion angle parallel with the transfer case originally, but that gave me too much caster and no turning circle so I reset it to Patrol spec thinking that may help my issue. The swivel hubs have the correct preload. The only things I haven't replaced in a while are shocks and steering damper, they are 4 years old. The wobbles started about 12 months after I did the conversion. I found a broken bracket on the diff so it was effectively only held in by 3 bolts on the radius arms.



This is my flex.

https://www.aulro.com/afvb/images/imported/2016/08/751.jpg

https://www.aulro.com/afvb/images/imported/2016/08/752.jpg

[Mercguy]

Is your steering damper a return to centre type or plain damper?

[Not_An_Abba_Fan]

Sorry for the late reply. It's a standard one. Don't like RTC's used to run them on mine vehicles and the springs continually broke.

I have ordered a new radius arm bush kit, new shocks and damper. We'll see how they go.

[Mercguy]

Some p-troll owners had issues with RTC dampers and death wobbles. If anything the failing RTC damper exacerbated the wobble - right at about 80km which is not pleasant.

I've heard of RRC and defender owners complain of similar damper-related issues (non-rtc types as well- bilstein comes to mind) - however usually accompanied by bigger lifts (3-4") and larger tyres.

In some cases a new damper made the problem worse - occasionally the damper is not fitted correctly (especially on the hardened aftermarket track rods with the adjustable brackets).

Plenty of fun to be had changing out those radius arm bushes. Hopefully the new bits resolve your issue ;)

[Not_An_Abba_Fan]

My mounts are custom anyway as I had to weld the RRC damper mounts to the Patrol track rod. From memory, I think I have the other end mounted to the panhard, the RRC factory mount is the diff. I might have to fabricate something....

I have polyurethane radius bushes already, easy peasy to change

I might ask this in this thread as well. The angles on my rear A frame and trailing arms are the wrong way I believe. I am experiencing too much "squat" in the rear, especially when climbing. After researching a front 3 link conversion, I have concluded that my A frame mount needs to be higher on the diff so that the A frame is closer to horizontal than the trailing arms. Currently, my instant centre is way above and in front of the car, if I move the A frame diff mount higher, I can bring it back and down about where it should be. This would explain why I lose front traction pointing uphill. Every time I get the front wheels up on a ledge, all the car wants to do is tuck the rear. All this suspension wizardry is starting to make sense lol. So does this sound right?

[Mercguy]

Have you got the MR 2" raised adjustable A-arm balljoint installed? or are you still running a standard height one?

[Not_An_Abba_Fan]

Still using the standard one.

I have worked out that my ball joint mount is too high. What I said above was incorrect. My instant center is actually inline with the chassis mount of the radius arm. I have worked out an AS of about 120%, too high. As I climb an obstacle, the front gets up quite easily, but because of the way the rear is set up, under power, it pushes the rear axle down instead of allowing the suspension to compress and the rear tyres to crawl up over the obstacle.

My solution is to drop the chassis mount of the radius arm 2", raise the radius arm diff mount 2" and I can drop the ball joint mount on the diff about an inch by trimming off the excess thread on the ball joint. That should give me closer to 90% AS. I'd be happy with that.

[Not_An_Abba_Fan]

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.

[Snagger]

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.

[Not_An_Abba_Fan]

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.

[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.

[Not_An_Abba_Fan]

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.

[Not_An_Abba_Fan]

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.

[Mercguy]

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.

[Not_An_Abba_Fan]

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.

[Snagger]

Glad it's mostly sorted.

Any buckling of the wheel would cause a lot of vibration, even if mass balanced, so that should be another improvement if you found a bent one.

Tyres do change their balance as they wear, especially if you rip big lumps out of the tread off road, so occasional rebalancing will be needed. But at least that is cheap and simple. I have never tried balancing beads inside the tyres, but some swear by them and they, of course, are going to keep the tyre balanced even as it wears, and should also account for different RPM better than fixed weights. I don't think I could put up with the noise of them rattling around inside the tyres, though.