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Brake fading and uneven wear


turbogrill
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Hi,

 

After just one hour of racing our left front pad was very worn, it looked like it had been in an 8 hour race. During the race I also experienced a lot of brake fade, or at least when I pushed the pedal the car didn't stop well.

Car is a NC Miata, it has ABS and the OEM electronic brake bias. Car has bilsteins shocks with stiffer springs, so no corner balance.

 

A few things:

- Front has new wilwood calipers with their most aggressive compound, rear has oem calipers with semi aggressive compound

- Tire pressure was WAY to high (started with the hot pressure instead of cold pressure...)

- I did feel a slight pull to the left while breaking

 

Could it be that the ABS engages quickly and hammered the pads, due to imbalance in brake system?

Could it be that the tire pressure was so high so I simply didn't have any traction, and this caused ABS to trigger? 

 

I didn't feel the ABS engage, this could very well be me not noticing during the race. I know that the ABS worked that morning.

 

When the brakes didn't work properly I pressed the pedal more and harder, a slight panic mode. Maybe this made things worse.

 

 

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1 hour ago, SonsOfIrony said:

How is the wheel bearing on that side?

 

Hmm...i hope in excellent condition :) How could that affect things?

 

1 hour ago, Wittenauer Racing said:

Both pads in the left front caliper, or only one of them?

 

Both, it's a 4 piston caliper. Not the traditional silding thing.

 

41 minutes ago, Team Infiniti said:

Twisted hose?

 

So not enough pressure? How would that explain the pressure?

 

31 minutes ago, IPF Racing said:

What state is the caliper in? Does it still slide? I've only had issues like that when the caliper was toast.

 

It's brand new. And it's 4 piston so no sliding pin.

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Just now, turbogrill said:

 

Hmm...i hope in excellent condition :) How could that affect things?

 

 

If the bearing has play, the caliper will try to straighten the wheel back up, and it can adversely effect pad wear.  It's usually both pads though, and it'll tend to be accompanied by a large amount of pad knockback.

 

If it's only one pad, either the pad is hanging in the caliper, or the pistons are sticky and you should be looking for a warranty from Wilwood.

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56 minutes ago, turbogrill said:

intersting! Its both pads

Both pads indicates to me that you are retaining pressure in that caliper for some reason.

 

Does it drag when you spin the wheel?

 

Try to mash the brakes and then release and see if the wheel spins the same left and right.  I'm guessing it will not.

 

Getting those pads too hot (from dragging) will make wear increase and stopping power decrease.

 

Any signs of overheating on that corner versus the other front corner?

 

Also, when the pedal is fully pushed, have you checked if the rears are working?  If the proportion is off by a lot, you are asking the fronts to do too much and will also overheat.

 

Let a little fluid out of both front calipers.  I bet the side with wear looks worse than the other side.

 

All of this could be due to a hose issue (as @Team Infiniti pointed out), or a piston sticking in the bore (not likely since it would need to be 2 pistons to do this with both pads looking bad), or a bad master that isn't letting fluid return to the reservoir on release.

 

Is there a new master?  Or did you adjust the master in any way?  The pushrod has a pretty small window of correct adjustment between letting the fluid return and having a firm pedal.

 

Any taper to the pads?  If not, that says it isn't a piston sticking in a bore, cause it would need to be all 4.  

 

I'm leaning heavily towards retaining pressure on that circuit.  

Edited by wvumtnbkr
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Check that caliper is centered and aligned properly with the rotor. Check to see if caliper adapter bracket flexes under load. Maybe paint it and do some panic stops and see if paint cracks. Magniflux if you have the capabilities.   Excessive rotor run out or pad kick back usually shows a long pedal travel under braking. Excessive front bias either by pad compound or pressure tends to overheat and wear out everything on the front end, rotors and pads prematurely. Check the run out of the rotors, centering of the caliper on the rotor and be sure the pad faces are parallel to the rotor faces. And be sure the caliper bracket is not flexing. 

Edited by TimS
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So just to clarify, the left front pads, inside and out, wore down much quicker than the right side?  The left tire was showing higher pressure?  And you were getting fade?

 

I am with Ed, check the hose or just replace it.  Or bad caliper, I know you said new but new ones can be bad too.  If you aren't getting long pedal travel at first, you are just getting fade then you wouldn't think knock back from caliper mounting or rotor run out.  I am thinking something is keeping that caliper loaded either the hose or caliper hanging.  One other thing, you mentioned ABS.  Make sure you are getting the system fully bled.  Sometimes with ABS you have to bleed quite a bit to get air out.  I have even had to pressure and vacuum bleed at the same time to get it all.

Edited by Burningham
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11 minutes ago, Burningham said:

So just to clarify, the left front pads, inside and out, wore down much quicker than the right side?  The left tire was showing higher pressure?  And you were getting fade?

 

I am with Ed, check the hose or just replace it.  Or bad caliper, I know you said new but new ones can be bad too.  If you aren't getting long pedal travel at first, you are just getting fade then you wouldn't think knock back from caliper mounting or rotor run out.  I am thinking something is keeping that caliper loaded either the hose or caliper hanging.  One other thing, you mentioned ABS.  Make sure you are getting the system fully bled.  Sometimes with ABS you have to bleed quite a bit to get air out.  I have even had to pressure and vacuum bleed at the same time to get it all.

 

Left side, but inside and outside pads are worn. Tire pressure was way to high on all tires. I got fade and think also long pedal travel. At certain times the brakes didn't work and some of my passes turned out to be douche bag dive bombs :( 

 

The second day the tire pressures where normal, problem was still there but way less. I still had to cutoff maybe 1-2s of my laptimes (I can't tell if that was all brakes or if the tires was a bit worn from the previous days high pressure).

 

Either way, lots of things that I need to check. I think I have to get back and get a good baseline and take it from there:

- Start with decent tires and pressure

- Bleed the brakes an extra time

- Make sure caliper is aligned

- Make sure hose can't be kinked/twisted

- Maybe install more aggressive pads in the rear 

 

Best case the problem is that the brakes need to be bleed, but I doubt it.

 

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Got a pic of your master cylinder?  Mine has 1 port for drivers side front, 1 for pass side front and 1 for rear.

 

This could be a master cylinder issue if the rod is misadjusted.  If it isn't letting fluid back to the reservoir through that side, it could do exactly what you are describing

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1 hour ago, Grufton said:

You might try the OE calipers (with good quality pads).  I've seen plenty of aftermarket brake setups that looked racy but actually made the system worse.

 

OE seems to work fine. But our car got crashed and we needed a new caliper. Buying a wilwood over the OE seemed like a good idea (about the same price).

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6 hours ago, turbogrill said:

Crashed on other side :)

 

Hoses are new.

 

Hose could be pinched, we have a homemade bracket for the hose...

 

Keep us posted on what you find out.

 

Not to thread hijack, but what's the local scoop on the future of COTA?  Were they already headed for insolvency before all of this stuff started?

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7 hours ago, turbogrill said:

Crashed on other side :)

 

Hoses are new.

 

Hose could be pinched, we have a homemade bracket for the hose...

 

What if the metal line is nearly pinched on that side, so the opposite side is doing a disproportionate amount of the braking?

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