Massive Brake Shudder - Causes?

[thewheelerZ]

Maybe a little help from the community here if anyone has any tips.  We have yet to tear down the car, and hopefully we will find something obvious when we do, but before everything is apart is there anything we should be looking for?

 

We have a massive brake shudder.  Shaking the wheel and car apart under hard braking.  Hard braking from 5th gear or high in 4th its not so bad, but as the car starts to haul down in speed it gets REALLY bad.  Brake setup is wilwood calipers using ST43 pads on the front.  2002 Nissan Maxima, Mac Struts up front.  Stock calipers and ST43 on the rear.  Shake seems to come through the wheel, not the pedal.  This should indicate is the suspension not the rotors?  We replaced the rotors and the issue didnt go away.

 

We had an issue with the right LCA on Saturday where the mounting point bolts were loosened off creating dynamic toe.  Brake shudder showed up at the same time  Just coincidence or shudder causing the bolts to loosen maybe?  Fixed the LCA by welding the pickup point to the subframe.  If the angle was off, would this create some funny suspension movements?

 

We also noticed that the caliper doesn't seem to be centered on the rotor anymore  Would a failing hub/bearing move outwards?  But there doesnt seem to be any play in the wheel bearing...?  Ball joint and other bushings also look good.

 

Could a blown shock with big stiff springs on the front create some funny oscillations ?  

 

What else should we be looking for?

[Black Magic]

Willwood fixed caliper? Wheel bearing failure\slop will reach havoc on you with this setup, as there is no float in the caliper to help handle the rotor movement\rocking relative to the caliper. 

 

Fixed calipers also can have issues if the caliper is not true to the rotor, often because the bracket is not flat or straight. Check this with a dial indicator and let us know if the rotor has measurable run out as installed on the car, and with dial calipers measure caliper body to rotor in several spot to see if the caliper centerline and rotor centerline are parallel. 

 

St43 can cause judder on pro race setups with excessive cooling, but I doubt anything in our series has that level of temp change. We tend to be on the hot side\lack of cooling. 

[thewheelerZ]

Fixed caliper yes.  Ill make sure to get some measurements on runout and to make sure the rotor and caliper are parallel.  It LOOKS like the rotor and caliper are not longer in centered on eachother and Im pretty sure they were when first installed.  Which would mean either a bent bracket or failing hub/bearing, correct?  Id be surprised if the hub moved so much, but bending the bracket doesnt seem so likely either?

[Black Magic]

16 minutes ago, thewheelerZ said:

Fixed caliper yes.  Ill make sure to get some measurements on runout and to make sure the rotor and caliper are parallel.  It LOOKS like the rotor and caliper are not longer in centered on eachother and Im pretty sure they were when first installed.  Which would mean either a bent bracket or failing hub/bearing, correct?  Id be surprised if the hub moved so much, but bending the bracket doesnt seem so likely either?

 

Depends on bracket material and temp. 

 

If the bracket is not very thick you can also get harmonics that will cause judder. Also if the pads were not square to the rotor, as they wore the chance for judder might increase. 

 

Pedal get longer (softer) during the race or about the same? Did you need to pump them up a little to get the same feel?

[thewheelerZ]

aluminum bracket, decently thick.  No idea on temps.

 

I would tend to rule out the harmonics as they have worked fine in the past.  Pads looked to be square to the rotor looking at the wear, but will check when I pull them out.

 

Final driver on sunday said they were getting a little soft (but pads were getting quite low by this point), but otherwise all weekend they felt solid.

[Bremsen]

I'd rule out hub/disc issues if you weren't getting a long pedal/knockback.

 

Brake judder is typically uneven transfer layer.  It may be that you didn't have a good transfer layer or with some pads, when you get beyond their temperature threshold, they will deposit unevenly and cause the "warped rotor" feeling.  Once its that bad, disc replacement is usually your only option.  If everything is square (IE not hub/disc/caliper issues) I would replace the discs and pads, bed them in well and try to look at your cooling setup/options.

 

Soft pedal is fluid boiling/air in the system.  You might also be experiencing some caliper flex/clamshelling at high temps.

[thewheelerZ]

18 minutes ago, Bremsen said:

I'd rule out hub/disc issues if you weren't getting a long pedal/knockback.

 

Brake judder is typically uneven transfer layer.  It may be that you didn't have a good transfer layer or with some pads, when you get beyond their temperature threshold, they will deposit unevenly and cause the "warped rotor" feeling.  Once its that bad, disc replacement is usually your only option.  If everything is square (IE not hub/disc/caliper issues) I would replace the discs and pads, bed them in well and try to look at your cooling setup/options.

 

Soft pedal is fluid boiling/air in the system.  You might also be experiencing some caliper flex/clamshelling at high temps.

 

Yeah, no excessive long pedal/knockback.  Good info.

 

Now on the bedding, we changed up the rotors on day 2 to new rotors same pads.  Still same thing.  Though, no real opportunity to bed the pads on the new rotors.

 

FWIW I will also mention too, it feels like its beyond a warped rotor kind of thing that you may feel on a street car.  This shaking is violent and literally feels like its going to shake the car apart.  Can hear wheelhop/skidding on turn in if still trail braking.

[rod rammage]

Check all of the usual suspects but also remember this:  ST43 are VERY finicky about requiring a proper bedding in procedure and laying up of a transfer layer. 
Also, when parked up in the pits at a pitstop, the drivers MUST NOT keep the pedal depressed on a hot rotor; I know, that's impossible to do at stop to pick up the egg timer etc., but these pads do not take kindly to hot pad transfer marks on the rotors from parking up hot and staying on the pedal while stationary.
 We have 12 years experience with the ST43 compound on over three dozen cars.

 

Edited May 30, 2019 by rod rammage

[thewheelerZ]

3 hours ago, rod rammage said:

Check all of the usual suspects but also remember this:  ST43 are VERY finicky about requiring a proper bedding in procedure and laying up of a transfer layer. 
Also, when parked up in the pits at a pitstop, the drivers MUST NOT keep the pedal depressed on a hot rotor; I know, that's impossible to do at stop to pick up the egg timer etc., but these pads do not take kindly to hot pad transfer marks on the rotors from parking up hot and staying on the pedal while stationary.
 We have 12 years experience with the ST43 compound on over three dozen cars.

 

 

Im wondering if may actually be improper bedding. Looking back at video the Saturday morning stint didn't seem to have much/any shake. Getting worse over the day. 

 

Would that hat be enough to cause a violent shake in the wheel though, as opposed to the pedal?

[rod rammage]

Our experience has been when the shakes start, they get so bad the driver's vision is blurred and they almost break their wrists holding the wheel, such is the violence with which the steering wheel hammers.
 Of course, make sure wheel bearings, suspension bushes, mounts, etc. are in top notch condition. Check disc runout, but I bet you will not find it out of tolerance by much at the end of a race. 

[Team Infiniti]

3 hours ago, thewheelerZ said:

enough to cause a violent shake in the wheel though, as opposed to the pedal?

 

3 hours ago, rod rammage said:

Our experience has been when the shakes start, they get so bad the driver's vision is blurred and they almost break their wrists holding the wheel, such is the violence with which the steering wheel hammers.

Yes, uneven transfer comes on after a few hours, brake shake can be bad enough to have the photographer come over to say something aint right, wear out hood pins or unscrew the valving from your strut pistons all with minimal rotor runout...

 

Thank you over temp RP2

[Wittenauer Racing]

7 hours ago, Team Infiniti said:

 

Yes, uneven transfer comes on after a few hours, brake shake can be bad enough to have the photographer come over to say something aint right, wear out hood pins or unscrew the valving from your strut pistons all with minimal rotor runout...

 

Thank you over temp RP2

 

So you're seeing that with the Carbotech RP2?

 

RP2 and fixed Wilwood calipers on cheap Mustang rotors here, nothing nearly as violent as anyone in this thread suggests, but we have been having wheel bearing failures. We've never bothered to measure brake temps, quite frankly we assumed we were on the cold side. Normally the shake starts then we start to brake a bit earlier and drive it more like a momentum car. Would make sense that the shake and wheel bearing failures are linked.... 

[Team Infiniti]

1 minute ago, Wittenauer Racing said:

So you're seeing that with the Carbotech RP2?

Frozen or cheap rotor, no matter, It seems, when rp2 is past its temperature, it behaves as described.

 

For 2 years, we, as noobs, battled extreme shudder, carbotech was of no help, against their advice we ordered the highest temp compound offered...problem disappeared.

 

None of our issues were caliper/bracket/fluid/bearing/ runout, nor was it from holding brake when hot... it was all related to pad transfer, it destroyed the rotors unevenly.... your results may vary.

 

4 pot fixed calipers, 3300lb car with automatic trans (no engine braking= lots of extra heat) Yes we have brake ducts, 2x 3.5 in ducts per rotor.

 

[thewheelerZ]

3 minutes ago, Team Infiniti said:

Frozen or cheap rotor, no matter, It seems, when rp2 is past its temperature, it behaves as described.

 

For 2 years, we, as noobs, battled extreme shudder, carbotech was of no help, against their advice we ordered the highest temp compound offered...problem disappeared.

 

None of our issues were caliper/bracket/fluid/bearing/ runout, nor was it from holding brake when hot... it was all related to pad transfer, it destroyed the rotors unevenly.... your results may vary.

 

4 pot fixed calipers, 3300lb car with automatic trans (no engine braking= lots of extra heat) Yes we have brake ducts, 2x 3.5 in ducts per rotor.

 

 

We may be in the same situation! Big heavy car, fixed calipers.  Which carbotech pad compound do you use now?

 

[TimS]

Wheel bearings, rotors warped or not set on hub properly, tie rods, steering rack/box, caliper mount flex, overheating, over cooling,  alignment, and tire pick up all can contribute to violent brake shake. Does pedal pulsate or just the front end trying to shake apart?  Best to check for obviously worn parts first, setup alignment, try new or different tires. I have had slightly worn wheel bearings and tie rods cause this before. I also didn’t have rotor set on the hub flat and had a similar problem. Pulsating pedal is likely rotor or bearings 

[TimS]

Picking the proper brake pads is important for sure. You can try the heat paint or an infrared temp gun to check temps during testing or pit stops. This will help determine best pad choice. I always tended to run highest temp rated pads with cooling ducts and tape them closed if ambient temperature was low 

[thewheelerZ]

4 minutes ago, TimS said:

Wheel bearings, rotors warped or not set on hub properly, tie rods, steering rack/box, caliper mount flex, overheating, over cooling,  alignment, and tire pick up all can contribute to violent brake shake. Does pedal pulsate or just the front end trying to shake apart? 

 

Sooooo pretty much everything!! hahaha.  Its definitely more front end shaking apart than pedal pulsation.

 

The post race euphoria is starting to wear off, so I really just need to start tearing it apart and see what comes of it.

[TimS]

Most of the items to check can be done quickly. Check all the control arm bushings and mounts too. 

[thewheelerZ]

3 minutes ago, TimS said:

Most of the items to check can be done quickly. Check all the control arm bushings and mounts too. 

Yeah for sure.  I was just kidding.  Definitely will tear it all apart and check each of those.  Hopefully something obvious pops up and we dont have to start throwing parts/money/testing at this to try and solve it

 

All great info so far, thanks guys!  This forum can be such a huge help!

[Snake]

It happened once with us in the old 300zx.  Turned out it was the pads.     

[Team Infiniti]

44 minutes ago, thewheelerZ said:

 

We may be in the same situation! Big heavy car, fixed calipers.  Which carbotech pad compound do you use now?

 

What works for us may not for you

 

XP24

[TimS]

We used Wilwood Polymatrix B pads(we were also using Wilwood calipers and rotors). 

[Bremsen]

@thewheelerZ Do you have ducting?  If so, can you describe or snap a photo?

 

I really liked what @Black Magic said in his video about what to do with brake cooling, but I was disappointed he didn't mention some things not to do.  High temperatures typically don't crack discs, large temperature differentials are what crack discs.  The one thing I see most often that you never want to run a hose to the inside disc face.  Cooling the inside face will cause that side of the disc to run significantly colder than the other which will lead to a coned and possibly cracked disc.  Also, when cobbling [err engineering] a brake setup like many of us do for this series, try to make sure the pads cover the entire friction face of the disc.  When a pad doesn't cover the entire face, you automatically create a cold area which can lead to cracking. You want to the iron temperatures to be as even as possible.  Also, never go out and start hammering on the brakes when they're cold.  Its important to bring the disc up to temperature gradually and evenly to avoid shocking it (which can crack/explode the disc).  Lastly, try to avoid large temperature deltas when using brake cooling.  Some tracks might need all the cooling, while others might cool the disc and pads too much between brake events.  This can also affect various pad compounds and cause uneven transfer.  A place like VIR-full or Road Atlanta doesn't need nearly as much cooling as Sebring, WGI, Laguna, etc.  When there are long periods between brake events, retaining some heat in the brakes is beneficial.

 

I'm not always a proponent of sealing plates with single 3" hoses attached.  It definitely depends on the efficiency of the disc, but for most I think simply running some air from the front of the car in behind the wheel and directing at the brakes/hubs in a general way is overall the best way to keep the brakes cool.  You see this setup on a lot of modern sports cars with deflectors attached to the control arms (C7s, 911s, etc).  Doing this provides the disc with fresh/cool air to pull from, without limiting volume, as well as cooling the caliper, but its not so direct it causes large temperature differential or delta issues.  It also might allow a much larger duct to be run from the front of the car since you don't have to be concerned with running the hose out to the brake disc.  My duct setup is going to be just a large house gutter downspout with a curve at the end.

 

Some really good advice here.  I agree that ball joints and other steering, suspension and wheel/tire issues are often mistaken for brake judder.  This is my life.  Last one turned out to be driveshaft balance. You will almost always be able to see uneven transfer because the disc will look very splotchy. 

 

 

[Black Magic]

33 minutes ago, Bremsen said:

@thewheelerZ Do you have ducting?  If so, can you describe or snap a photo?

 

I really liked what @Black Magic said in his video about what to do with brake cooling, but I was disappointed he didn't mention some things not to do.  High temperatures typically don't crack discs, large temperature differentials are what crack discs.  The one thing I see most often that you never want to run a hose to the inside disc face.  Cooling the inside face will cause that side of the disc to run significantly colder than the other which will lead to a coned and possibly cracked disc.  Also, when cobbling [err engineering] a brake setup like many of us do for this series, try to make sure the pads cover the entire friction face of the disc.  When a pad doesn't cover the entire face, you automatically create a cold area which can lead to cracking. You want to the iron temperatures to be as even as possible.  Also, never go out and start hammering on the brakes when they're cold.  Its important to bring the disc up to temperature gradually and evenly to avoid shocking it (which can crack/explode the disc).  Lastly, try to avoid large temperature deltas when using brake cooling.  Some tracks might need all the cooling, while others might cool the disc and pads too much between brake events.  This can also affect various pad compounds and cause uneven transfer.  A place like VIR-full or Road Atlanta doesn't need nearly as much cooling as Sebring, WGI, Laguna, etc.  When there are long periods between brake events, retaining some heat in the brakes is beneficial.

 

I'm not always a proponent of sealing plates with single 3" hoses attached.  It definitely depends on the efficiency of the disc, but for most I think simply running some air from the front of the car in behind the wheel and directing at the brakes/hubs in a general way is overall the best way to keep the brakes cool.  You see this setup on a lot of modern sports cars with deflectors attached to the control arms (C7s, 911s, etc).  Doing this provides the disc with fresh/cool air to pull from, without limiting volume, as well as cooling the caliper, but its not so direct it causes large temperature differential or delta issues.  It also might allow a much larger duct to be run from the front of the car since you don't have to be concerned with running the hose out to the brake disc.  My duct setup is going to be just a large house gutter downspout with a curve at the end.

 

Some really good advice here.  I agree that ball joints and other steering, suspension and wheel/tire issues are often mistaken for brake judder.  This is my life.  Last one turned out to be driveshaft balance. You will almost always be able to see uneven transfer because the disc will look very splotchy. 

 

 

 

Most of the home brew setups I have seen would lack the airflow required to make any significant temp differential  

 

A few of you guys have really great setups that can, but at that level of design most of you have already created something with reasonable airflow distribution. 

 

Given the rest of our suspension (crappy street car stuff) I could see making "floaters" for your fixed willwood calipers and being better off for it. Bronze\oilite bushing in the willwood bolt locations and run a longer bolt as a pin\slide. I would only allow small float, like 1/8"-3/16", but that might be enough on many setups to fix the issues we have from hub\bearing\knuckle flex and mount misalignment. Too much float and it may be possible to get enough uneven pad wear to push one side of the pistons out. 

[thewheelerZ]

@Bremsen Yeah, simple ducting with 3" hose from the fog light housing  and attached to the LCA.  Points in general direction of the rotor but certainly isnt flush up against it.