braking shimmy

[anvil]

Okay, ... I've only had the '92 nsx for a month so every unfamiliar sound or shake is worrisome, but overall it has been healthy until now. Today I drove 75 miles to a nearby city and returned tonight on the hilly backroads to listen to my nsx sing. Second was ferocious of course and third made "lift off" seem but a moment away.

But after a few turns a violent vibration shook the steering wheel whenever I tried to brake hard. After about five minutes at a more normal pace, with light application of the brakes, no hint of the shake revealed itself. The same thing happened repeatedly.

I checked the front disks when I got home, but they were only a little warm and very smooth on both the inside and outside surface.

The disks have been cross drilled. Applying the rear brakes alone gave no hint of shimmy, so I deduce that the fronts are the problem. But what is the problem??

Ideas??

anvil



[This message has been edited by anvil (edited 10 November 2001).]

[NSXGOD]

Originally posted by anvil:
Okay, ... I've only had the '92 nsx for a month so every unfamiliar sound or shake is worrisome, but overall it has been healthy until now. Today I drove 75 miles to a nearby city and returned tonight on the hilly backroads to listen to my nsx sing. Second was ferocious of course and third made "lift off" seem but a moment away.

But after a few turns a violent vibration shook the steering wheel whenever I tried to brake hard. After about five minutes at a more normal pace, with light application of the brakes, no hint of the shake revealed itself. The same thing happened repeatedly.

I checked the front disks when I got home, but they were only a little warm and very smooth on both the inside and outside surface.

The disks have been cross drilled. Applying the rear brakes alone gave no hint of shimmy, so I deduce that the fronts are the problem. But what is the problem??

Ideas??

anvil

[This message has been edited by anvil (edited 10 November 2001).]

Hi Anvil,
you have warped your front rotors; welcome to the club. You can find out more info on this in the FAQ - do a search on "warped rotors".


------------------
need more info? please private me @

[email protected]

Mark Johnson, CEO of Custodial Services @ Dali Racing, a Not For Profit Company.

[ncdogdoc]

Yep, Mark is right on about that one. The NSX does have a slight tendency to shimmy when braking at very high speeds (i.e. above 100mph and with stock rotors) but it is only light. If you note shimmy after several rounds of hard braking, then the rotors are warped, and resurfacing, or better yet replacing, will fix you right up. I had wheel shake so hard it was to drive the second day at Road America until John Vasos and his fabulous crew turned them for me Sunday morning (he had no more new rotors to sell me ), and I was able to enjoy the rest of that beautiful sunny day.

------------------
Gary Yates
1995 Red/Tan

[This message has been edited by ncdogdoc (edited 11 November 2001).]

[lemansnsx]

Originally posted by anvil:
Applying the rear brakes alone gave no hint of shimmy, so I deduce that the fronts are the problem.

Other than the parking brake, how do you apply only the rear brakes??????????????
If you're saying that you used the parking brake alone at speed you should know that this can be a real neat way to induce a spin.

------------------
Andrew Henderson
The NSX Model List Page

[This message has been edited by lemansnsx (edited 11 November 2001).]

[anvil]

Thanks for the feedback guys!

You got me Andrew, I pulled on the "parking"/"emergency" brake! Bad habit from my gymkhana days in an old Austin Healey, but a great manuever on a tight course. Are you hinting that the nsx has some unusual way of reacting to it?

Mark, I have tried to read up on old posts but couldn't find the "warped rotor" heading in the FAQ. I thought that the most likely thing myself, but so many posts seem to suggest that it could be the pads. I guess I need to "mike" the disks to see if there are different thicknesses.

Andrew, I also read some posts that said that turning the disk was undesirable or even ineffective if associated with a low quality disk to begin with. Although my disks do have the beveled cross drilled holes, I have no other knowledge of the quality or brand of disk or pad. Views I read seemed to support no holes or slotted disks, so I guess I have bad ones in that respect.

I don't know that I'm getting ready go to track events, so a full bore rebuild seems excessive. But something has to happen because I don't believe coming briskly down a curvy mountain road is outside the envelope of reasonable use of a work of art like the nsx. Aside from the brakes, it did that wonderfully well and I only saw the traction control light up once.

anvil




[This message has been edited by anvil (edited 11 November 2001).]

[NSXGOD]

Originally posted by anvil:
Thanks for the feedback guys!



Mark, I have tried to read up on old posts but couldn't find the "warped rotor" heading in the FAQ.

look here:
http://www.nsxprime.com/FAQ/Troubles...ation_fade.htm



------------------
need more info? please private me @

[email protected]

Mark Johnson, CEO of Custodial Services @ Dali Racing, a Not For Profit Company.

[sjs]

Originally posted by anvil:
... I guess I need to "mike" the disks to see if there are different thicknesses.

Well, not really. You will use a micrometer to determine whether they have enough thickness left to allow turning, and again after to see that not too much was removed. To check for warp, you need a dial indicator with the pointer placed against the face of the rotor as you rotate the disk. Do this at several points along the radius of the rotor. On the car is not perfect due to other factors, but significant warp can easily be detected.

Anyone who want to work on their own car or even be able to diagnose problems themselves (reducing the degree to which you are at the mercy of others) would do well to add this tool to their chest. Get a decent dial indicator and a magnetic based stand. I use mine a lot for checking brakes, wheels and a variety of things where small movement needs to be detected.

[lemansnsx]

Originally posted by anvil:

You got me Andrew, I pulled on the "parking"/"emergency" brake! Bad habit from my gymkhana days in an old Austin Healey, but a great manuever on a tight course. Are you hinting that the nsx has some unusual way of reacting to it?

Ha! It was old British cars, specifically minis, that I was thinking of when I wrote that! Nothing about the NSX to worry about!

------------------
Andrew Henderson
The NSX Model List Page

[DanO]

Sometimes a “warped” rotor doesn’t exhibit any runout when cool but has noticeable runout when hot; this is due to different thermal expansion characteristics and friction changes of the metals in the rotors. Bill Z posted a super write-up on this effect on the tech list about a year ago. Maybe someone still has the post in their mailbox?

DanO

[lemansnsx]

Originally posted by DanO:
Sometimes a “warped” rotor doesn’t exhibit any runout when cool but has noticeable runout when hot; this is due to different thermal expansion characteristics and friction changes of the metals in the rotors. Bill Z posted a super write-up on this effect on the tech list about a year ago. Maybe someone still has the post in their mailbox?

DanO

Ask and ye shall receive:

Subject:
[NSX-TECH] Brake Shudder ( high speed judder) explained
Date:
Tue, 15 Feb 2000 17:15:28 -0700
From:
Bill Zachar [email protected]>
To:
[email protected]


All,

Back in December I asked the question: What is the physical process taking
place during brake shudder? There were several replies, mostly of the "I
think it's.... but I don't know for sure" variety. My curiosity was
motivated by the fact that I had experienced tremendous brake shudder when
decelerating from over 135 down to 50 at the end of the front straight at
Firebird Raceway and yet I never actually *lost* my brakes.

Through the List I was put in touch with an individual that is a mechanical
engineer employed by the #1 producer of brakes in Japan, and of OEM brake
pads in the States. He was here in Phoenix in January doing brake tests with
General Motors and I had the opportunity to have dinner with him. We spent
most of the evening discussing all the technical/engineering aspects of
brakes and he debunked a lot of the "urban legends" regarding brake shudder.
I also was able to convince him to write an explanation of the phenomenon
which he agreed to do under one condition: That I do not give out his
contact info as "I do not want to be bombarded with rebuttals or requests
for more information!" Below is his write-up. Perhaps Lud can add it to the
FAQ

Bill


High Speed Braking Judder (Shudder)

Causes: Brakes are essentially devices that convert kinetic energy into heat
energy. Since kinetic energy increases as a square of velocity, higher
speed = much higher heat. Also because of this, the heat energy involved in
a deceleration from 100 to 80 is as high as slowing from 60 to zero. The
change in kinetic energy difference between 100 and 80 miles an hour is the
same, no matter how quickly you slow down. Therefore, ignoring in-stop
cooling, the amount of heat generated is not proportional to deceleration
rate, but to initial and final braking speeds. This is why judder is a
complaint for both moderate and threshold brakers if they are going fast
enough.

Most common mechanism for the disturbance: A higher order (approximately
8-10 per rev.) disturbance caused by regularly spaced “hot spots” on the
brake rotor. These hot spots expand (thicken) the rotor locally, causing
brake torque pulsations. It is an unstable situation, which gets worse as
the hot spots get hotter and expand further. When the brake rotor cools,
the hot spots go away, and so does the problem.

Possible Remedies: Increase rotor thermal mass. Bigger rotors can handle
more heat before the unstable mode can begin. Rotors with thicker “plates”
(the two solid iron friction areas separated by the rotor vanes) are also
helpful. Increased cooling to the brakes also helps, because it lowers the
initial temperature at the start of braking and therefore also the maximum
temperature.

What doesn’t work: “Turning” the rotors. The most likely mechanism for the
problem is not tied to rotor run-out. If rotor runout is an issue, shudder
will also be apparent at much lower speed, and with cool brakes. Note: as a
general maintenance tip, do not have your rotors turned when brake pads are
replaced unless you have low speed, cool brake shudder, scored (deeply
scratched) rotor friction faces, or some other specific problem. The
machining equipment at speed or brake repair shops is not nearly as accurate
as that used in the original manufacture of a rotor, so you may be paying
money to create a problem where there wasn’t one before. Also,
cross-drilling of rotors is intended primarily to vent the gases released
during brake fade, therefore improving brake effectiveness in the fade
condition. This is not the same as a high-speed judder condition, and
therefore is not a path to solve this issue. Note that both turning rotors
and cross-drilling them also reduce rotor mass, which is not directionally
correct. Also note that most real race cars don’t run cross-drilled rotors.

Secondary possible cause: Breakdown of the raw materials in the brake pad at
very high temperatures, leading to an uneven and thick (relatively speaking:
it’s still measured in microns) film deposit on the rotor. This film may or
may not be visible. The solution in this case is to find a brake pad
designed for higher temperature operation. One possible avenue is a pad
homologated for sale in Europe (where high speed driving is much more
common) on your vehicle. European requirements for certification of
aftermarket brake pads are far higher than U.S. aftermarket standards. The
quality of U.S. aftermarket pads is generally very poor compared with
original equipment.

Bill posted some answers to questions a few days later:

Subject:
Re: [NSX-TECH] Brake Shudder ( high speed judder) explained
Date:
Sat, 19 Feb 2000 23:04:48 -0700
From:
Bill Zachar [email protected]>
To:
[email protected]


All,

I wanted to answer the questions that have been posed to me since I
originally posted my "Brake Shudder explained" all in one follow-up. What
follows may seem like random thoughts but are actually driven by the
questions I've gotten. I'm posting them to the list as I'm sure everyone
that was interested in the original post will be interested in the
follow-ups.


Slotted rotors serve the same purpose and drilled rotors: to expel gas under
the fade condition. Shudder is a SEPARATE problem/symptom from fade. If you
put on slotted rotors and SHUDDER went away (not fade), my engineering sense
tells me the slotted rotors probably have thicker plates, thus higher
thermal capacity, than your old rotors.

To follow up on Ken Sax's post, I've only experienced shudder when
decelerating from 135+ to 55-60 at the end of the front straight at Firebird
Raceway. If I decelerated from 120 I had almost zero shudder. I've never
experienced any shudder at normal (street) temps or brake fade with one
person in the car.


During my dinner with the brake expert I asked him about different
formulations (carbon-kevlar, carbon-fiber, blah-blah-blah) for street/track
use. He laughed and said these formulations are not magic bullets in and of
themselves and that the Geo Metro has carbon-kevlar brake pads. He went on
to say that there are too many other variables in pad formulations to make a
blanket statement such as "pads made with material X are better than pads
made with material Y". Recall that he works for "#1 producer of brakes in
Japan, and of OEM brake pads in the States" including GM. He said ads
touting carbon-fiber, carbon-kevlar, blah-blah-blah as magic bullets are
just marketing. With that thought in mind he did not have any specifics on
what specific pads/rotors would be best for street/track use.

He did ask if I had any info on what aftermarket brakes/pads were available
for the NSX. I emailed him the links to CT, Dali and RMs sites be about a
week before our dinner. At dinner he said he looked at the sites and told me
to get the biggest possible brakes for the NSX. He recommended getting 13"
brakes for all 4 wheels over 12.4 fronts-only. I had 13" Brembos installed
all around last week.

In summary: Everyone here realizes the big enemy is heat but the ultimate
solution may not be as clear. The take-home message in all this is you need
bigger thermal capacitors, the rotors, to really solve *all* the problems.
Pads, OEM size after-market rotors, fluid, etcetera are only good up to a
point. Case in point: NSXer Frank Heydrich and I did our last run session at
Firebird a couple of weeks ago playing follow the leader. I led for a few
laps with him right behind me, the he led for a few laps with me right
behind him. My car is supercharged and his is NA so it was easy for me to
stay with him when I was behind. We get near the end of the front straight
and I'm going 130 and I start to brake way early to make sure Frank has time
to brake since I know he usually carries 120 MPH at the end of this
straight. I see his brake lights come on, the nose of his car dips down and
then the nose of his car COMES BACK UP! He made it into the corner safely.
In the paddock afterwards I asked him if he lost his brakes when I saw his
nose come back up. He said,"With you pushing me I was carrying 130 MPH and I
cooked my brakes". He was running RM slotted rotors, RM pads and had Motul
600 in the reservoir. I had my OEM rotors, OEM pads and Motul 600. At 130
MPH his RM slotted rotors, RM pads and fluid didn't save him from the same
problems I was having.

Bill

------------------
Andrew Henderson
The NSX Model List Page

[This message has been edited by lemansnsx (edited 12 November 2001).]

[ncdogdoc]

Wow, a long, but VERY informative post. Thanks Andrew for the lookup and posting of this description. I guess I am going to be running some ductwork under my car to my front brakes before I head out to VIR in December! (Along with new rotors) Alas, I do not have the 4 g's for a new big brake setup as of yet.

------------------
Gary Yates
1995 Red/Tan

[justin hall]

wow, excellent post.

[DanO]

If you're looking to get the max out of your OEM brakes at the track, then you may want to read http://www.danoland.com/nsxgarage/br...rack/track.htm for some more thoughts on the subject.

DanO

[anvil]

My cup runneth over!!!

I guess it all boils (no pun intended) down to this, cool the rotors and/or get bigger, unslotted and undrilled rotors. A good grade of pad should do okay. (Is Brembo the only big rotor option?)

And so normal, no shudder braking under ordinary use is the principle indicator that this phenomena is occurring and a check of the runout with a dial indicator as suggested won't help with this question?

anvil



[This message has been edited by anvil (edited 12 November 2001).]

[F=MA]

Hi all,
I am new to the forum and the NSX.
In July I traded my 911track car (and a pile of cash) for a 92 NSX. Three weeks ago I instructed with the PCA at a driving clinic. The instructors had 20 minutes of track time to play around. This was my first track drive in the NSX. 18 minutes into the session the pedal felt very mushy, before I made it to pit in, I had a complete brake failure. Fortunately I made into the paddock without any problems. I had to drive around the track support roads for 30 minutes to cool the brakes off. What is the deal with Honda? I am completely baffled by the philosophy of not matching the cars acceleration capabilities with deceleration end of the equation. Can someone explain this? Since that day, I have switched to Motul, removed the brake shields and I'm ready to install air ducts. But from what this thread indicates, those measures will not solve the problem. I am concerned about the situation next season at a track like Watkins Glen. I would hate to have a brake problem at the inner loop. I know this is heresy (and inviting flame), but I sort a wish I would of bought a Porsche.

[DanO]

Originally posted by F=MA:
Hi all,
I am new to the forum and the NSX.
In July I traded my 911track car (and a pile of cash) for a 92 NSX.

Cool!

But from what this thread indicates, those measures will not solve the problem.

Unfortunately, I think you’re starting to hit the nail on the head. In general, if you want to drive the car on the track at the instructor level, then a brake upgrade (at the very least--pads and rotors) is in your future. The OEM pads and rotors are just not up to the task. It’s unfortunate that Honda designed the brakes this way, but they work very well for the street .

For OEM fitting pads and rotors, a lot of people go for the stuff at www.daliracing.com and www.rmnsx.com Last year I finally broke down and put on a big brake package, now my NSX stops like a Porsche .

DanO

[justin hall]

F=MA, I think ultimately you will be pleased with the NSX. I dont think your comment will invite flames since most people know you are coming from what are widely known as the best brakes out there to the NSX mediocre (at best) brakes.

The long and the short of it is you will need to do a brake upgrade. Many people have upgraded fluid, pads and experienced success, you might as well.

I went a different route, brembo fronts w/pagid pads, slotted+drilled rear rotors @oem size w/oem pads, ate super blue fluid, and ss lines. I found this setup to provide a very nice balance front to rear, and I have not experienced any further issues on the track. Thanks MJ at www.daliracing.com for pointing me in this direction.

[Andrie Hartanto]

F=MA, what do u mean when u said complete brake failure? Did the pedals went to the floor or extreme pad fade?

[F=MA]

Andrie,
The brake pedal went to the floor. No amount of pumping would restore functionality. I used the hand brake to stop the car in the paddock.

[sjs]

Originally posted by anvil:
My cup runneth over!!!
... And so normal, no shudder braking under ordinary use is the principle indicator that this phenomena is occurring and a check of the runout with a dial indicator as suggested won't help with this question?

anvil

Checking runout is still worth doing. From my experience, they will still be sufficiently warped cold to detect, and you can always heat them up before you pull it in the garage. They take a long time to get really cool.

I had exactly these symptoms on OEM parts. I found them out of spec, had them turned, and did two track events and 7 months daily driving without another problem.

[sjs]

Great write-up! As noted in my post above, don't assume that you need to throw things away. If the rotors can be turned and remain within spec, it's worth trying but get a good shop and check them again when they're done. I've done the same with many cars besides the NSX.

One minor point about braking from 100-80 being the same as 60-0. As with so many calculations, it's important to account for as many factors as possible. In real life, stopping from high speeds is helped somewhat by aerodynamic drag, rolling resistance, engine braking, etc. (Lift off at 130 and see how fast it slows to 110 without even touching the brakes!) Granted, if you're talking about max braking, this is probably not great, but it is still a factor, and if you are braking more gradually (as also discussed in the post) it is a big factor.


[This message has been edited by sjs (edited 13 November 2001).]

[anvil]

Thanks sjs,

If you have had the same experience that I have described and did find measurable runout, then my unwillingness to "fix what ain't broke" compells me to at least check the runout. Turning, if it works, is certainly cheaper than Brembo's without a doubt, though Bill's remarks sure discourage this as an approach in general. However, IF there is measurable runout, I would think turning the most reasonable first thing to try.

I am not regretting MY choice, by the way. If I waver I just have to take a run to ... to anywhere, and the smile is back! Of course I didn't come here from a Porsche, ... just a lowly GSR.

anvil

[nsxtasy]

The brake pedal went to the floor. No amount of pumping would restore functionality.

This is entirely different from the shudder symptoms (although both are caused by excessive heat). This failure is NOT normal for the NSX, even under heavy track use. This could be caused by fluid boiling (due to old fluid or low-temp fluid).

Regarding shudder, beware of having the rotors turned. This will make them more susceptible to the shudder returning quickly in the near future.

[anvil]

I'm confused, nsxtasy.

What else could you do if the rotors have measurable runout other than turn them or replace them?

anvil

[sjs]

Originally posted by nsxtasy:

Regarding shudder, beware of having the rotors turned. This will make them more susceptible to the shudder returning quickly in the near future.

While there is certainly some truth to this, I still think it is largely BS put out by people wanting you to buy new ones. If I had replaced rather than refaced through the years I never would have saved enough green to buy an NSX. Seriously though, I’ve had a lot of rotors turned over the years and rarely been disappointed.

Sure, it marginally decreases mass and therefore heat absorbing capacity, but look at it this way, it also cools faster and reduces unsprung weight. (all true, but hardly significant.)

If you want to replace rotors every time they need to be turned, please send me the old ones and I'll pay shipping.