Arizona Z type front brakes

[gira]

I have this big brake set up on one of my race cars. This is the first time I have tried this before on a race car. Here is my problem. Something up there is flexing enough to cause the pedal to be very long in between using the brakes. As Long as I am going straight, the issue doesn't come up, great pedal. If I swerve as to warm up the tires, pedal to the floor. Everything up there is tight.

Anyone run into this before? Someone told me they have heard of this and spindle is flexing. Wow!

Greg Ira

[John Coffey]

Pad knockback. There's enough flex in the hub and/or caliper mounting that the pads are pushed back into the caliper bores with any kind of lateral load. Common problem on 350Zs. Stoptech and others sell some light springs that go behind the caliper piston that keep the pads in slight contact with the rotors.

Or, you get in the habit of doing a "confidence pump" before you get to any braking zone. If you look at footwork videos of most pro racing series (Australian Super Cars is the best for footwork videos) you'll see lots of pros doing this before any big braking zone.

[rjracin240]

I have this big brake set up on one of my race cars. This is the first time I have tried this before on a race car. Here is my problem. Something up there is flexing enough to cause the pedal to be very long in between using the brakes. As Long as I am going straight, the issue doesn't come up, great pedal. If I swerve as to warm up the tires, pedal to the floor. Everything up there is tight.

Anyone run into this before? Someone told me they have heard of this and spindle is flexing. Wow!

Greg Ira

Grow a pair Greg, then you wont need brakes!!!!

Good seeing you and Guy the other weekend

Russ

[jmortensen]

I followed panchovisa's example and put a gusset between the strut and the flat spot behind the spindle, you could do something similar to what I've done.

I'd be looking other places first to solve the problem with the pedal though. Pad knockback on a Z is not something you hear about very often, even with the fast autox guys who would presumably be totally screwed at the end of a slalom if this were a common issue. The caliper mount is integral to the spindle in the front and back, so it's not as though flex between the spindle and strut affects the relationship between the caliper and rotor.

There could be some flex in the caliper mount, seen that on Hybrid Z in this thread: http://forums.hybridz.org/index.php?/topic/70436-wilwood-caliper-damage-pics/ That thread wasn't complaining about knockback though, the problem was found incidentally.

Stupid question: are your wheel bearings tight?

Here are some other interesting threads on knockback:

http://forums.hybridz.org/index.php?/topic/89473-at-cmp-with-the-13-inch-floating-rotor-set-up/

http://forums.corner-carvers.com/showthread.php?t=29864

http://forums.corner-carvers.com/showthread.php?t=42896

Edited May 10, 2010 by jmortensen

[260DET]

Could be axle flex, machine spacers to fit between the inner and outer bearings. That has to be done accurately of course because then bearing adjustment will no longer be available by adjusting the nut. Which has to be done up tight to lock the spacer against both bearings.

[gira]

Great information guys. Yes, the bearings were tight. That's the first thing I checked. I mean the flex is huge, just in a warm up lap going straight and going back and forth caused the flex issue. Gees, if I rode up a curb that would be even worse. We'll work on it for next time and let you guys know what works.

Thanks

Greg

[gira]

Come to think of it, of all the Z cars I have driven on the track, this is the first time I've run into pad knock back. Is that weird?

No issue on the ITS 240Z that I know of.

No issue on the EP 240Z, with ZX brakes.

Do you guys have pad knock back on your IT cars??

Greg

[Marty Rogan]

I just bought a track car a couple of months ago with these brakes on it. I have only had 3 test laps with the car so far though. I think I have experienced that issue as well. My next event is June 7th, so I will get a better idea of its performance then.

I would really like to hear how you solve this issue.

Marty

[preith]

FWIW I have the same brakes and no knock back that I can tell, if present it's negligible. I do have it gusseted similar to Jon's. I did not have the issue with my non-gusseted 280 struts either (now using 240's). With that said I have to wonder if this matters as the gusset is there for strut flexing and the entire forging, including caliper mounts, would therefore move together.

I am on ITS spec DOT's, perhaps slicks exacerbate the issue?

My biggest problem with these brakes was rotor run out due to the combined hat/rotor tolerances. I have a local shop skim cut them whenever new ones are installed.

[John Coffey]

Generally the cause of knockback is hub flexing. Check the hub, bearings, races, and spindles. Check the spindles for cracks. Swap out the hubs after crack checking the replacements. Aftermarket brakes that move the caliper farther out from the hub via adapter brackets exacerbate knockback.

[rjracin240]

Taking a guess here but is the rotor centered on the caliper not sure if it would make much difference or not

[DatsunDoc]

Never had that problem on my CP 240Z with stock calipers.

Mike