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Old 09-22-2011, 03:56 PM   #1
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Default How much Wilwood flex is normal?

Has anyone ever looked to see how much their Wilwoods are flexing? Have you noticed flex or crappy pedal feel?

My pedal has felt like crap since I moved to Wilwoods up front. The pedal feel has been very vague, kind of soft at the top and seemingly bottomless. I never hit a hard bottom of the pedal. The pedal does firm up, but it never bottoms.

Wilwoods up front, stock 1.8 calipers in the rear, Wilwood proportioning valve in-line to the rears.

The system has been flushed & bled many, many times. The stock 7/8" master and booster were swapped out with another stock 7/8" master & booster, and I haven't noticed any change.

I just put in a 1" master and larger booster, but won't be driving the car for a few weeks. In the garage, the pedal feel seems about the same.

Thoughts?
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Old 09-22-2011, 04:48 PM   #2
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What are your pads and how thick are the rotors?
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Old 09-22-2011, 05:02 PM   #3
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0.81" Wilwood rotors front, stock rotors rear.

Pads are Cobalt Friction XR2 Front, XR4 Rear.
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Old 09-22-2011, 08:16 PM   #4
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I run DTC60 and a sport master and booster...the brakes feel epic with no flex. You probably have a bad bleed or bad rotors. Ever since I started reverse bleeding after lines went dry, I will never go back to a conventional "top-down" bleed on a dry line. Are you bleeding off all 4 bleeders?
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Old 09-22-2011, 10:29 PM   #5
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^^That gives me hope.

I use both top bleeders on each caliper for bleeding. Start with the outer, bleed the inner, then the outer again on each caliper. What do you use for reverse bleeding?

The rotors are good, and have like-new thickness of 0.80".

Here's a shot of the driver side caliper flexing. The caliper 'bows out', with slightly more movement on the outside portion than the inside. Pressure being applied is approx 1,000 psi (I have a brake pressure sensor on the line).

Seems like a lot of movement, considering that the caliper is not supposed to move relative to the rotor, and it's not. All the 'movement' is actually the caliper flexing.

http://www.vimeo.com/29330603

Last edited by wildo; 09-22-2011 at 10:40 PM.
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Old 09-23-2011, 12:28 AM   #6
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When you assembled the caliper to the mounting backet, did you properly measure the gap between the pistons and rotor and make sure it was even on both side and/or shim the caliper on the backet to ensure the caliper was dead-center over the rotor? If it's off even 0.5mm, the caliper will flex as it centers itself to compress the pads evenly. I'd imagein you checked this, but one never knows. I had to add one more "shim" (washer) to the caliper -> bracket area to properly center it over the rotor.
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Old 09-23-2011, 05:47 AM   #7
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Shouldn't the pistons even out any difference?
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Old 09-23-2011, 06:48 AM   #8
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Bench-bleed the master cylinder.
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Old 09-23-2011, 09:11 AM   #9
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Quote:
Originally Posted by wildo View Post
^^That gives me hope.

I use both top bleeders on each caliper for bleeding. Start with the outer, bleed the inner, then the outer again on each caliper. What do you use for reverse bleeding?
Is that a Dynalite or Dynapro? I think the cheaper Dynalite may be stiffer. I don't feel the flex. However, Stoptech is supposedly making a Dynalite replacement caliper, we'll see if it ever goes to market.

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Originally Posted by Savington View Post
Bench-bleed the master cylinder.
Or reverse bleed. I use an old Motive bleeder with a smaller hose and a zip tie. This will also evacuate air from the master so you don't have to bench bleed. Remember to "tap **** with a hammer" when you bleed.
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Old 09-23-2011, 12:27 PM   #10
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Thanks for the tips.

The master was bench-bled. A 'new' master was swapped in, and it was bench-bled too.

Finally, the new 1" 929 m/c went in, and it was also bench bled beforehand.

The calipers are centered on the rotors, but not perfectly so. I figured the same as Curly, that the pressure would even things out, no? Wouldn't the fluid take the path of least resistance?

That said, I test fit everything on a bench using a spare spindle. The calipers seemed more centered on the test spindle than they do on the car now. At the very most, I'd say they are off by 1mm total. I'll take a closer look at the bracket spacer I'm using.

So, has anyone actually looked closely at their calipers with someone stepping on the pedal? I haven't seen any flex on the stock calipers, but the Wilwoods bow out quite a bit.

I could be wrong, or I could be misinterpreting what I'm seeing, but it seems that the pedal gets pushed down at a smooth, linear rate. The pressure also builds at a smooth, linear rate, and the micrometer also sweeps in a smooth, linear rate. That indicates to me that the hydraulic system is working correctly. No big air bubbles or issues. The pedal force directly corresponds to the flexing of the caliper:

http://www.vimeo.com/29410003

I spoke with Wilwood and they said that some flex is acceptable. According to the rep I spoke with, the DynaPro is stiffer than the DynaLite, and the Radial DynaPro (or any radial mount caliper) is significantly stiffer and less prone to flexing than lug-mount calipers.
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Old 09-24-2011, 01:36 AM   #11
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Have you checked the snugness of the caliper housing bolts? I'm sure if they were loose you'd have a lot of leakage though. Cool video really. .020" is nothing though.

It's the third law, for every action there is an equal and opposite reaction. The fluid is pushing the piston which is pushing on the pad. The pad then pushes back on the piston, through the fluid, and against the caliper body.

What brand brackets do you have?
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Old 09-24-2011, 01:57 PM   #12
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FTR- My Wilwood 11" kit (all Wilwood componants) has some flex. I saw this when I was bleeding the calipers and someone else was pumping the pedal. I did have to add 1 shim (provided with the kit) to reduce the movement (thinking like Curly, that a little off would be self corrected). So far, I have not noticed an adverse effects of the flex since putting the brakes on.
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Old 09-24-2011, 02:13 PM   #13
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Quote:
Originally Posted by curly View Post
Have you checked the snugness of the caliper housing bolts? I'm sure if they were loose you'd have a lot of leakage though. Cool video really. .020" is nothing though.

It's the third law, for every action there is an equal and opposite reaction. The fluid is pushing the piston which is pushing on the pad. The pad then pushes back on the piston, through the fluid, and against the caliper body.

What brand brackets do you have?
The brackets are made by Wilwood - the ones designed for their MINI kit.

In the video, it looks like the dial indicator's stand moves a bit as does the rotor. The test rig could have been setup better. I'd say that the actual maximum flex is 50-100% more than the dial captured. It may not sound like much, but considering that the same amount of flex happens at both calipers, and that the flex more than doubles at on-track temperatures, it adds up. Adding it all up, total flex is likely 2-6mm under race conditions.

All of the bolts were tight, except that there were only 2 lugnuts holding the rotor in place. I loosened the bracket/spindle bolts and caliper/bracket bolts yesterday, then with someone standing on the pedal, I torqued down the bolts. That appears to have squared things up a little, but it was at the end of a long day and I was getting tired.

The spacers I am using for the bracket/spindle mount were machined down 0.035", which should center caliper on the rotor better. Next step is to put it all back together then start on the passenger side.

The Wilwoods are definitely flexing, but perhaps there is something else going on too.
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Old 09-26-2011, 02:59 PM   #14
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Some observations;

Flex is common on all calipers and based upon line pressure, piston area and caliper construction.

The DPr is not a hardcore racing caliper. It's an enthusiast level part capable of light to moderate track use when fit with proper pad. You're using it because you wanted a compact fit on a smaller rotors and it's in good company there. A larger body caliper such as the FSL or W4A will prove much stiffer for the same input pressure simply due to its size.

DESCRIPTION



The larger the piston, or smaller the master, the higher the line pressure. A 7/8 bore generates pretty high pressure and if you are recording line pressure of 1000psi and expect to see that on the track, it's not happening unless you have a really bad choice of pad in it. Or you're already in a skid headed to the tire wall...Most line pressure use on track will be in the 400-600 range with occasional spikes upwards of 800. If you boost the pad Cf you need even less pressure.

Shimming, centering, bolt torque can hall have some impact but what you're seeing is spread. You're clamping the rotor and the caliper is pushing outward. This additional spreading can be caused from over stressing (like all this 1000psi video work) and from softening of the caliper body from over heating. The older and hotter the caliper has been run the softer it can become.

However on the plus side the flex does not have a huge impact on the braking. What's lost is a bit longer pedal. A bit of time loss and in short some wasted energy being absorbed by the caliper rather than put to use on the rotor.

What can you do to prevent it? Run a proper pad for the intended use, fit a larger rotor, fit a larger piston caliper requiring lower psi or install a larger bore mc generating less pressure. *less psi then boosted by more leg would be the same net result.
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Old 09-26-2011, 08:18 PM   #15
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I have Wilwood Dynalite's and also have a **** pedal feel. I've never been able to get all the air out of them. I'm going to give reverse bleeding them a shot. That's when I pump fluid into the calipers, right?
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Old 09-26-2011, 08:44 PM   #16
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Neglected to also mention that piston area has a lot to do with that. The DL calipers should be no more than 1.375 bores.

As for the bleeding, don't listen to anyone suggesting that all four bleeders be bled. The lower bleeders are only there for the caliper to be universal mount- ie. R and L where they switch location. In fact if you want to really do it right; remove the brass fitting and install blanks. (DL is 1/8npt and DP is M10-1.0) Flush seal allen plugs work great in the DL, DP parts are harder to find and must be tapered seat.

ANY time you open the lowers and attempt to bleed fluid you're all but certain to get air in. Air goes up to the top, not the bottom. If you're lazy (like me) you can open one upper at a time and let it just drain out into a bucket. Close and repeat after 15min with the other, just keep topping up the reservoir. Gravity is a wonderful thing!
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Old 09-26-2011, 08:51 PM   #17
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Air goes out the top, but in the four-bleeder Wilwoods I've disassembled, there is a crossover at only one end of the caliper. If it's mounted on the car so that crossover is at the bottom, you can flush the whole caliper by bleeding only the uppers. If the crossover is at the top, you can get all the air out by bleeding only the uppers, but you must open the lower bleeders if you want to flush all the old fluid out of them.

On a 280 rotor with 1.8 rears, I'd go with 1.25-in. pistons. Don't know why Wilwood's own kit gets that wrong.

I couldn't watch the video earlier. That is actually a much better caliper than a Dynalite. I've looked at it before and thought it's not horrible.

Last edited by SolarYellow510; 09-26-2011 at 10:52 PM.
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Old 09-26-2011, 09:00 PM   #18
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While you are correct about the cross over being on the top or bottom depending upon mounting the bleeding remains the same.

You're right that to drain it; opening up the bottom (or removing the caliper) is needed.

It makes a flush a bit awkward in that as you gravity bleed the situation would be a cross blend of old and new fluid taking time to run clear. Whereas on the bottom you could force it through quicker with pressure.


FWIW, BDL, DPr, DPLM, NMDP, FBDL, PL, DLS and now FSL are all internal single cross feed calipers. (Wow..lot of letters there huh?!)

Last edited by Todd TCE; 09-26-2011 at 09:05 PM. Reason: turned the wording over! lol
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Old 09-27-2011, 01:26 AM   #19
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Quote:
Originally Posted by Todd TCE View Post
Some observations;

....
The larger the piston, or smaller the master, the higher the line pressure. A 7/8 bore generates pretty high pressure and if you are recording line pressure of 1000psi and expect to see that on the track, it's not happening unless you have a really bad choice of pad in it. Or you're already in a skid headed to the tire wall...Most line pressure use on track will be in the 400-600 range with occasional spikes upwards of 800. If you boost the pad Cf you need even less pressure.
Todd,

Thanks for your response.

Are you sure about those numbers? The Miata's stock brake proportioning valve doesn't start doing anything until close to 600 psi, so wouldn't a track-driven Miata spend most of its time above that?. I installed the brake pressure sensors before installing the Wilwoods. With a completely stock 1.8 Miata brake setup a large portion of braking time was spent at 800-1,000 psi. I have run Carbotech XP12/XP10 pads and have been running Cobalt Friction pads XR2/XR5 for some time now.

My contact at Cobalt Friction told me that they typically see 1,200 psi though some of the aggressive pro drivers peak at 1,600 psi before they back off. I told him what I was running, and he indicated that my numbers were right what they'd expect. For what it's worth, my proportioning valve is set to about 75-80%, so if front is at 1,000 psi, rear is at 750-800psi. Max braking on my car is -1.4g's, I don't have ABS, and I don't flat-spot tires.

Quote:
Shimming, centering, bolt torque can hall have some impact but what you're seeing is spread. You're clamping the rotor and the caliper is pushing outward. This additional spreading can be caused from over stressing (like all this 1000psi video work) and from softening of the caliper body from over heating. The older and hotter the caliper has been run the softer it can become.
I can't imagine that I'm running mine hotter than some others, and these calipers aren't very old - they've been on the car for 10-12 events.

Quote:
However on the plus side the flex does not have a huge impact on the braking. What's lost is a bit longer pedal. A bit of time loss and in short some wasted energy being absorbed by the caliper rather than put to use on the rotor.

What can you do to prevent it? Run a proper pad for the intended use, fit a larger rotor, fit a larger piston caliper requiring lower psi or install a larger bore mc generating less pressure. *less psi then boosted by more leg would be the same net result.
The piston sizes are 1.38", for a total piston area of 3.0 sq-in, versus the stock Miata's 3.17 sq-in. Pads are proper. Rotors are larger and so is the m/c! I haven't tracked the car with the bigger m/c though.

Any other trouble-shooting type suggestions?

My plan in the off-season is to ditch the power booster as I don't think my car is making much vacuum. This will likely mean going to a longer pedal ratio and dual master cylinders.

Cheers,

Will
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Old 09-27-2011, 01:56 AM   #20
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Chase your proportioning rearward until it gets interesting, then back off slightly. With that piston area and the larger front rotor, I suspect you'll be close to no prop valve activity.
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