Vibrations

Post by **marko** » Sun Jul 13, 2003 11:08 pm

96 Parol Ute, 7" lift, 2" body lift, 5 degree caster plate and rancho steering dampener - at 60 to 70kmph it gets serious vibrations through the steering wheel. The wheels have been balanced but with no success. :puppydogeyes:

Any ideas?????

Post by **CRUSHU** » Mon Jul 14, 2003 7:02 am

is that with the boggers on? ive noticed that on a few other tucks with 37" boggers, it really rattles your teeth!

Post by **Wendle** » Mon Jul 14, 2003 7:58 am

check your panhard bushes.

then tie rod and draglink ends, and wheel bearing / trunion bearing play.

Post by **bazzle** » Mon Jul 14, 2003 11:09 am

Then try someone elses wheels to check balancing.
Many a time it still comes back to this

bazzle

Post by **Area54** » Mon Jul 14, 2003 12:06 pm

The main cause for wheel vibration in Patrols is due to using large offset rims - this throws off the correct camber settings. Don't bother wasting money on wheel balancing. Trying to correct this problem with more castor will make it worse due to the effect of 'self centering' with more castor. With offset rims the projected angle of the kingpin bearings is on the inside of the pivot point of the tyres. This puts more leverage outside of the centreline of the steering - add a rotating tyre to the equation and you will get some evil harmonics. Do this experiment - get a spinning top, spin it, then tap the top sideways a little. The top still rotates, yet on a circular axis. This is similar to what happens to the front wheels of a GQ.
Solution - run a rim with less offset on the road - offroad doesn't really matter unless you like the go fast pedal.

Post by **t-maxx** » Mon Jul 14, 2003 8:51 pm

yeah same i have a 7 inch lift and koni front xxxxl skocks in the front with a 5 link and with the mickey thompson baja claw 37's it shack like hell at 60km/h but wen i get past that its smoother but as loud as hell u can win aye!

Post by **big red** » Mon Jul 14, 2003 10:47 pm

mine does it with the 8" beadlocks/centipedes on but the 8"outbacks/bfg's dont do it .
the beadlocks stick out 40 mm more and are also much much heavier so i dont know which bit causes it .

Post by **Area54** » Tue Jul 15, 2003 8:35 am

Okay, here's a picture to help with the description. When you have excessive distance between the projected kingpin pivot point (on the ground) and the tyre contact pivot point (as in using larger offset rims), this places the outside of the wheel in a position of excessive leverage. This leverage causes the rotating wheel assembly to be more sensitive to outside influences - you would notice that small bumps in the road usually start the shimmy, correct? Once the shimmy starts, it is similar to the experiment I described above, the shimmy won't stop until the rotating assembly stops rotating. Excessive castor will make the steering correct right, then left, then right, then left and so on and on, and there's your shimmy.

Most vehicles run with a slight toe in, when the vehicle is in motion the drag causes the tyres to be parallel (helps the vehicle to track correctly). Castor is what helps the wheels to self centre after you turn a corner, and what helps to keep the wheels pointing straight ahead (similar to a NEW shopping trolley wheel, but caster is a different story) If you have excessive caster the system will want to overcorrect, therefore helping the wobbles to remain.

The remedy is to use a rim with less backspacing, to take the tyre contact pivot point closer to the projected kingpin pivot point.

These vibrations have been reported on many GQ's, with and without large suspension lifts. Wheel balancing is not the total cause of the problem.

Post by **timo_ed** » Tue Jul 15, 2003 5:26 pm

Ture, king pin effectiveness is altered when increasing wheel offset, but with 35" tyres you would normally only run 8" rims with a 20-22 neg offset. This won't make a huge difference. As Bazzle said, go to someone that can actually balance tyres of that size.

Post by **Area54** » Tue Jul 15, 2003 8:27 pm

You are missing the point of the influence that the weight of the rotating assembly has on kingpin effectiveness, in relation to the leverage placed using a larger tyre and offset rim. The more weight, the more leverage.

Somethings can be outside the limits of correction. This symptom (shimmy) is different on every vehicle - basically you might not be able to compensate enough to remove it totally.

For a wheel balance to be effective, the weights need to be as close to the outer periphery as possible. The larger the tyre you have, the more sidewall you have, the larger distance the weight is from the most effective place it should be to have the most effect. The rim won't flex, but the tyre will - The rim is a constant, the tyre is a variable. Maybe you should look at what the trucks use - liquid balancing fluid (BELTEC I think it's called, but there a few brands)

Post by **Robbo** » Tue Jul 15, 2003 11:20 pm

Hi all how they hangin. Well am I glad I loged on cos I was just about to post a question that I think area 54 has answerd for someone else. I have a GU wagon with 5" coil lift, panard rods, shorter top rear links, lite truck koni's, (rancho's too soft abit like drafty)caster bushes etc etc. Two nights ago 120ks western fwy on the cruise BFG allterains 33" But I run ROH alloy wheels with 80 series offset cos it fills the guards looks better & hit a very small dip with right wheel & HOLLY S__T lookout yeh now I was awake. It wriggled me into the drain shook the phone from the holder the mike from its clip & tiped over the rest of my mackas coke.(not happy jan) Had done it once before on my nackerd set of jungle t 2s but never on the allterains. So why after 12 months of running this set up has it started this crap. Am going over to On Track 4x4 tomorrow to check a few things out, so will let you no what we find.(water in both diffs do you think drafty)

Post by **Robbo** » Thu Jul 17, 2003 12:51 am

Hi am back & it turns out I need 7deg caster plates also throw the caster bushes to the shithouse. Yeh good any takers to tell the missus for me? :roll:

Post by **Area54** » Thu Jul 17, 2003 7:24 am

In For Sale I have some castor plates... but it might not fix your problem. They are 7 degree plates, need no drilling to fit. The shimmy will remain - possibly get worse due to the extra castor giving you more 'return to centre' effect. These plates a great at returning correct castor settings, but if you run a larger tyre and large offset rim on road, the effect on shimmy won't change. Probably shoot myself in the foot (no sale) but I'd rather be honest and give you good advice.

Post by **timo_ed** » Thu Jul 17, 2003 10:47 am

Robbo, 7 deg is excessive for a 5" lift. The general rule of thumb is 1deg or castor for every inch of lift, however this is only a guideline. Excessive castor will increase the occurance of castor slap, and exacerbate any shimmy problems.

If your bushes are flogged as you say, then get them fixed first. Then just go and get your front wheels re-balanced. My bet is that some or all of your wheel weights have come off whilst driving.

Rgds,
Tim

Post by **Robbo** » Thu Jul 17, 2003 11:21 am

Thanks for all your imput guys, the 7 deg caster adjustment came from the Bearepair dealer that had it on machine for nearly an hour (no charge) yesterday & said all aspects of wheel alignment were spot on including panard rod adjustment, but with the 2 deg bushes presently fitted it was neg 2 deg. So as I understand it with OE bushes refitted it will need 7 deg according to them. Does this all make sence. Maybe I should go back to Nissan offset & kiss the flares goodbye!

Post by **Drafty** » Thu Jul 17, 2003 11:24 am

Go back to standard suspension and 31's and give me you panhard rods. :finger:

Post by **Robbo** » Thu Jul 17, 2003 11:43 am

Yeh thats a goog idea next you will be telling me to buy a 100 series with IFS. OK out on the road when the flag drops the bullshit stops. Yours sincerly faster GU than yours. You dream about my uni chip drafty!

Post by **bazzle** » Thu Jul 17, 2003 2:19 pm

I run a 4 to 6 inch lift with offset rims and 35 Mud terrains.
My caster with OME 3 degree bushes is at 1 degree pos.
0 toe
.8 camber
Ive found that on mine and others that 90% of the time it comes back to a correct balance.
Other causes are
1. Too much caster (plates)
2. Loose wheel bearings
3. Worn panhard bushes
4. Worn tierods
5. Damaged valves in shocks (no small movement damping) (truck shocks?)
6. Damaged tyres

Post by **ozy1** » Thu Jul 17, 2003 10:10 pm

all i can say, is i have had this problem, no matter how many time i had wheels ballanced, and evrything checked, it continued to happen, i adjusted evrything, to correct specs and all, now i have drop boxes and all is well, i dont like em casue they sit low, but i havnt been caught up on em yet, but i have hit them heaps. Shiit happens hey

Post by **bazzle** » Thu Jul 17, 2003 10:27 pm

I agree.
Take whatever works for you.

Cheers

Bazzle

Post by **John H** » Wed Jul 23, 2003 9:11 am

I am very interested in what Area54 had to say about king pin angles and vibrations on a GQ - it made a lot of sense to me.
I wanted to run a question by Area54 (or anyone else with an opinion) about my Patrol.
My GQ has a 7-inch lift with 35-inch Goodyear MTR’s mounted on Sunrasia 8-inch rims. I have slowly been working my way through all of the handling quirks that the lift created.
It currently goes well with adjustable panhard bars, castor correction plates and two steering dampers. The most important thing was making sure that all of the bushings and steering ball joints were 100% with no slop whatsoever. My truck has none of the uncontrolled steering wobble or vibration described in the original post by Marko however it still has the ever-present ‘bump steer’. When I hit a pothole you get a kickback through the steering wheel.
I had always assumed that this was due to the relatively steep angle of the panhard rod and the steering arm (pitman arm to swivel hub). I was looking at modifying these angles to get both arms to sit flat – ei: lowering the pitman arm and panhard to chassis mount or something similar.
Reading the post made me think twice about this. Could the king pin angles cause or a least be a contributing factor in the bump steer on Patrol’s? I didn’t think my offset was that extreme (8-inch Sunrasia’s and 35’s) what do you recon?
I also had the thought that as you go to a taller profile tyre the relationship between the king pin angle and the ‘tyre contact pivot point’ improves. The higher the swivel hub is off the ground the further out the line drawn through the king pin is where the tyre contacts the road. Does this make any sense at all? Any ideas would be greatly appreciated, Thanks

Post by **Area54** » Thu Jul 24, 2003 9:17 am

Hey John, I got your pm, thought I'd answer here.

You're right about the larger tyre's contact pivot point being closer to the projected kingpin point, but the extra weight and leverage of the larger (than standard) rotating assembly is what contributes to the problems. This might be something that Nissan owners have to live with.

You have answered your own question relating to bump steer - the panhard rod and steering drag link (and pitman arm) angles are causing the bump steer. As you hit the pothole, dip, bump etc the link that controls the diff (panhard rod, cast leading arms to a lesser extent) in the direction of travel (upwards) deflects the diff sideways as the angled panhard rod travels in the arc set by the mounting point on the chassis. The wheels stay in the straight ahead position due to certain factors - castor & toe in - as the diff travels upward. The draglink (rod between the pitman arm (short arm attached to the steering box) and the knuckle housing on the passenger side of the diff) is not a perfect match in length and angle to the panhard rod, this variation in dimension during the range of travel of the panhard rod is what causes the bump steer (the steering wheel to rotate slightly in your hands when you hit a bump). The diff moves to one side as it travels upwards, pushing the draglink to one side, pushes/pulls the pitman arm, rotates the shaft in the steering box, rotates the steering rod connected to the steering wheel. (sorry to simplify it, but I hope it helps some people who don't wrench on their own junk to understand). Twin dampers don't really help because the steering box ratio is 17:1 - the draglink doesn't travel that far laterally (side to side) for the dampers to work during a bumpsteer situation - you'll probably find that the damper rubber/poly bushes are compressing before the damper starts to compress/extend. Although some poeple say that twin dampers can save excessive wear and tear on the steering box - the jury is out.

The kingpin angle would not be a contributing factor to bumpsteer in this case, as they remain a constant in the diffhousing as an assembly.

With the amount of lift you are running you would not be able to totally remove the bumpsteer from the system by lowering the chassis panhard mount, and using a drop pitman arm. You will minimise it, but you have to weigh up the cost/benefit/rootaround factor in this. Everything is a compromise, it might be something you have to live with.

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