Help Me Diagnose A Suspension Vibration

[LotusGTR]

Symptoms

I was at Sandown this weekend and whilst braking from speed (say 100km/h plus, but on the back and front straight at Sandown so 200+ there I’d guess) there is a vibration evident. The faster you’re braking from, the larger the vibration. It does not manifest its self through the pedal, but through the steering column. There is no specific pedal feedback at any speed so it is not warped rotors. I’ve had this before at Philip Island with a totally standard set up (i.e. before all the mods mentioned below), but much more severely, and only braking from high speed (i.e. long straights).

Set Up

I have new (perhaps 2000 kms and 2 track days old) AP CP5555 calipers front and rear with 2 piece rotors (355mm and 343mm). Suspension set up new adjustable upper control arms, new castor rods with spherical bearings, an aftermarket swaybar, and DMS 50mm coilovers. I’m running a bit of castor and camber and about 1mm of toe in. Tyres are RE55 245/40/18 on a 9” rim.

The Question

I need a diagnosis. I’m thinking I need to look at the bits that have not been replaced or upgraded as the culprit here (I’m assuming the new bits are the right quality and have been fitted right). What’s left? Lower ball joints? What else? I’ll eventually end up giving this to a suspension specialist to fix, but I’d rather go into that conversation with some better ideas than I have now, so any assistance would be gratefully received.

I need to get rid of this vibration as it shits me and saps confidence whilst under hard brakes. Could be safety and wear issues lurking in there too.

Cheers,

Nick.

[LotusGTR]

Perhaps this helps in the discussion (that might ensue). I've circled the areas it seem possible that might be the culprit(s).

Front_Suspension.pdf

[Sydneykid]

My first guess would be wheel bearings, but don't rule out the rotors. Not necessarily warped, but I've seen lots of cars with badly fitted hat to hub because of poor surface preparation. For example if the hub is not perfectly clean when new hat/rotor is fitted then the rotor runs out of true. That pushes the outer and inner pistons in oscilation, cancelling out each other as far as fluid movement is concerned, so you don't feel a lot through the pedal.

BTW the beaking areas at Sandown are quite ripply so it may pay to test the shudder elsewhere on the circuit.

Cheers

Gary

[LotusGTR]

Thanks Gary.

Some further thoughts.

The hub issue you mention, I'd be disappointed if this was the case as the guy who fitted them does great work and is an ex racer so should have done the right thing. I will ask him. He's decent enough to be honest if he remembers there being any issues. I'd not considered the wheel bearing issue so will keep an open mind on this, especially as my brake kit supplier had mentioned in some detail (at the time of purchase) that worn wheel bearings could be a cause of pad knock off, of which I reckon I had a bit of, the first time I went out with them.

The vibration has happened with vary degrees of severity with 2 totally different brake set ups. So the hub issue is either common to both separate set ups, or it isn't the brakes, and is something to do with the wheel bearing or suspension. The first time was at PI with std brakes and no mods done to the suspension. The second time at Sandown with all the suspension mods done. The problem was far less of an issue after the suspension mods were done. At PI I had to give up driving fast, at Sandown if was a little annoying but didn't stop me.

I guess if I could eliminate each part as a potential cause that would be the most logical way to approach the problem. So, in what order and how should I approach it?

Inspect / test the lower ball joints for wear? How?

Inspect / test the wheel bearings for wear? How?

Remove rotors and inspect the rear of the hat / hub for good prep. Perhaps machine the friction surface to make 1000% sure it is not some sort of rotor distortion issue

Clearly I do not want to replace lower ball joints, wheel bearings, and machine rotors as it's a bit of a blunt and expensive way to solve a problem.

Any other thoughts as to possible causes not discussed yet?

[Sydneykid]

Thanks Gary.

Some further thoughts.

The hub issue you mention, I'd be disappointed if this was the case as the guy who fitted them does great work and is an ex racer so should have done the right thing. I will ask him. He's decent enough to be honest if he remembers there being any issues. I'd not considered the wheel bearing issue so will keep an open mind on this, especially as my brake kit supplier had mentioned in some detail (at the time of purchase) that worn wheel bearings could be a cause of pad knock off, of which I reckon I had a bit of, the first time I went out with them.

The vibration has happened with vary degrees of severity with 2 totally different brake set ups. So the hub issue is either common to both separate set ups, or it isn't the brakes, and is something to do with the wheel bearing or suspension. The first time was at PI with std brakes and no mods done to the suspension. The second time at Sandown with all the suspension mods done. The problem was far less of an issue after the suspension mods were done. At PI I had to give up driving fast, at Sandown if was a little annoying but didn't stop me.

I guess if I could eliminate each part as a potential cause that would be the most logical way to approach the problem. So, in what order and how should I approach it?

Inspect / test the lower ball joints for wear? How?

Inspect / test the wheel bearings for wear? How?

Remove rotors and inspect the rear of the hat / hub for good prep. Perhaps machine the friction surface to make 1000% sure it is not some sort of rotor distortion issue

Clearly I do not want to replace lower ball joints, wheel bearings, and machine rotors as it's a bit of a blunt and expensive way to solve a problem.

Any other thoughts as to possible causes not discussed yet?

The grab and shake methods work for me, then a final check with a dial gauge. Jack it up, support on stands (as always), then lay on the ground and get your hands dirty, wiggle stuff, feel for lost motion and free play, listen for knocking noises, use a the old "screw driver up to the ear" microphone to get into where your head won't fit. Specifically;

Inspect / test the lower ball joints for wear?

Jack it up, grab the uppper lower halves of the wheel, one half in each hand and try to rock it, any motion (free play) will be easily felt. Plus you can usually hear the knocking.

Inspect / test the wheel bearings for wear?

Same, just grab the front and rear halves of the wheel, you will feel any free play and most times you can hear the grong grong grong of a stuffed a wheel bearing

Remove rotors and inspect the rear of the hat / hub for good prep.

Clean it with brake clean and a rag, maybe give it slight scuff with emmery paper. Once they are clean, check the hub run out with a dial guage, then bolt the rotor on and check the run out of it.

Do the same "grab and shake test" for tie rod ends. I would also suggest a rotate test for the CV joints, grab the shaft and rotate, feeling for free play and tight spots, plus listen for noises.

Don't underestimate the braking area ripples at Sandown, especially if you aren't feeling it elsewhere.

Cheers

Gary

[LotusGTR]

Thanks Gary. I would say it ain't the track as it's just not that kind of thing. You can tell by how it feels and where how it happens.

Well I've spoken to the guy who fitted the brakes who said it's possible the hub prep issue exists but highly doubts that's it. I also paid him to mechanically inspect the car before it went onto the track i.e. on the hoist, wheels off, check bolts, suspension, brakes, fluids, etc and whilst he did not specifically check for the wheel bearing or lower ball joint issues he said based on that check and his general knowledge of the car there are no obvious signs of these components needing replacing (to solve this issue)

He did agree with the wheel bearings possibly being the culprit, but with there being no real sign they are needing replacement (other than they are 20 years old.....) it comes back to the game of replace a part and see if it's that........Expensive, time consuming & frustrating. I could invest in having the rotors pulled off and do all the checks but if that turns up nothing then I'm back at sq 1 having invested in labour that could be fitting a part that could fix the problem......Damn old fast cars!

Front and rear Nissan bearings with seals are the best part of $1,000 plus fitting so it's not a cheap exercise (yes I could do the fronts only & and funnily enough they are much cheaper than the rears). Lower ball joints are nearly $500 plus fitting.

Do you know of other wheel bearing options that are not Nissan that are worth considering?

[Sydneykid]

Thanks Gary. I would say it ain't the track as it's just not that kind of thing. You can tell by how it feels and where how it happens.

Well I've spoken to the guy who fitted the brakes who said it's possible the hub prep issue exists but highly doubts that's it. I also paid him to mechanically inspect the car before it went onto the track i.e. on the hoist, wheels off, check bolts, suspension, brakes, fluids, etc and whilst he did not specifically check for the wheel bearing or lower ball joint issues he said based on that check and his general knowledge of the car there are no obvious signs of these components needing replacing (to solve this issue)

He did agree with the wheel bearings possibly being the culprit, but with there being no real sign they are needing replacement (other than they are 20 years old.....) it comes back to the game of replace a part and see if it's that........Expensive, time consuming & frustrating. I could invest in having the rotors pulled off and do all the checks but if that turns up nothing then I'm back at sq 1 having invested in labour that could be fitting a part that could fix the problem......Damn old fast cars!

Front and rear Nissan bearings with seals are the best part of $1,000 plus fitting so it's not a cheap exercise (yes I could do the fronts only & and funnily enough they are much cheaper than the rears). Lower ball joints are nearly $500 plus fitting.

Do you know of other wheel bearing options that are not Nissan that are worth considering?

Wheel bearings themselves are not normally a problem, I can't say as I have replaced a wheel bearing in an R32/33/34 ever. But they do require adjustment and regular greasing, especially when you get them super hot at a track day, even high temp wheel bearing grease breaks down eventually. A regular (road car) mechanic may not have experience with the sorts of braking temperatures you are subjecting your wheel bearings to.

I wouldn't buy Nissan branded parts eg, wheel bearings, ball joints, rack ends, tie rods etc, they are all made by subcontractors anyway. Ball joints, tie rod ends etc are all 555 brand in Nissan boxes and the 555 brand will cost half or less. Wheel bearings from memory are NKN, same story applies.

Cheers

Gary

[MrStabby]

One other thing to check (might as well since its so easy) is the hat to rotor bolt torque. I had some weird brake vibrations that were linked to this. Torqued up and locktited and its all good now.

[LotusGTR]

I've just got off the phone to the guy who supplied the brake kit and he suggested the following. Worn wheel bearings under lateral load will move (though still not making any noise or outward signs of wear). The disk then moves too. This disc movement then causes part of the disc to be in contact with the pads. The disc then picks up pad material in certain spots and causes the steering wheel judder. He said it's more likely to be picked up in the steering wheel than the pedal.

The fix in his opinion is to very lightly machine the discs, whilst they're off check the hub prep, replace wheel bearings (said go Nissan not ANOther brand) and re-grease with something better than what they come with.

[Roy]

Your hubs were in great condition when we swapped to the RDA rotors, i would be surprised if it was run out resulting from corrossion

[LotusGTR]

Your hubs were in great condition when we swapped to the RDA rotors, i would be surprised if it was run out resulting from corrossion

Hello. Agreed. I'm doing the wheel bearing and light machining thing to see if that sorts it. I'll get every moving part up front wiggled and jiggled and anything with any slop we'll get sorted too. Soon I will have the $6m car.

[Bass Junky]

Watching this.

[Roy]

What pads are you running with the APs?

[bnr#@]

The wheel bearings (front atleast) are NTN (or NSK, dont remember which exactly but deffenitley one of the 2), they have a part number on them which any bearing supplier can get for you. Just did mine a little while back and had no problems getting them from a normal bearing supplier, dont quote me but Im prety certain the fronts were arround $100 each

Edited July 9, 2009 by bnr#@

[LotusGTR]

What pads are you running with the APs?

SBS ‘Dual Carbon’ or ‘Carbon Ceramic’. I can't quite remember. They're Danish (Scandinavian anyway) made and the brand is most typically used for competition motorcycles. Wierd but the brake guy reckons they're the way to go for me. Link below.

http://www.sbs.dk/index.dsp?area=84

[Marlin]

Mate, sounds for all the world to me to be a flat spotted tyre.

[LotusGTR]

Mate, sounds for all the world to me to be a flat spotted tyre.

Nah, happens across different rims and tyres, and I've not flat spotted anything.

[Sydneykid]

Your hubs were in great condition when we swapped to the RDA rotors, i would be surprised if it was run out resulting from corrossion

I agree hub corrosion is pretty unikely, but that doesn't mean it's not a hub alignment issue. An example of the shyte that happens. I did a brake upgrade on a GTR a while back and it was fantastic for the first race meeting, but the next race meeting it had brake shudder. I got a desparation phone call for help so I suggested cleaning the hub to hat contact area, that was dismissed as the hubs were clean two weeks ago and the hats were new. So I jump in the car and go out to Oran Park and look at it myself. What do I find? When the guys were changing the tyres and checking the brake pads the front rotors had flopped over and a lump of brake pad dust had fallen down between the hat and the hub. When the wheel was put back on the lump of brake pad dust caused the hat not to seat properly on the hub. The result was rotor run out and brake shudder.

Rule #1, don't assume that just because it was OK yesterday, that it's OK today.

Cheers

Gary

[LotusGTR]

I agree hub corrosion is pretty unikely, but that doesn't mean it's not a hub alignment issue. An example of the shyte that happens. I did a brake upgrade on a GTR a while back and it was fantastic for the first race meeting, but the next race meeting it had brake shudder. I got a desparation phone call for help so I suggested cleaning the hub to hat contact area, that was dismissed as the hubs were clean two weeks ago and the hats were new. So I jump in the car and go out to Oran Park and look at it myself. What do I find? When the guys were changing the tyres and checking the brake pads the front rotors had flopped over and a lump of brake pad dust had fallen down between the hat and the hub. When the wheel was put back on the lump of brake pad dust caused the hat not to seat properly on the hub. The result was rotor run out and brake shudder.

Rule #1, don't assume that just because it was OK yesterday, that it's OK today.

Cheers

Gary

Good example Gary. The rotors are coming off anyway, so the hubs will be checked as a matter of course. I'll be sure to post the result.

[LotusGTR]

Well I've got new wheel bearings, a new passenger side lower outer ball joint, a new / secondhand front drivers side CV shaft (mine was worse for wear), lightly skimmed rotors, and lots of money out of my bank account. Upper ball joints have some play but there wasn't the time to sort these this time around so I'll have the cross my fingers that the work done has sorted this out.......

Nothing worse than spending money on this that aren't exciting.......