Did any of your other cars have fixed calipers, or are they the sliding type? 95% of factory cars come with sliding calipers. If all your previous track cars had sliding calipers, you won't experience knockback despite flexing hubs.

 

Hello,
That's a very good point... it's pretty much only cars that come with Brembos from the factory or have aftermarket BBKs that have immobile calipers. Good for braking (well, wear), bad for flexible hubs.

Joel

 

My 944S2 has fixed Porsche calipers
My 911C2 has fixed Porsche calipers
My 924S (daily driver with no track time) has whatever weird calipers that it uses.
My Volvo S60R has Fixed brembo calipers (Never seen R compounds or Track) but nothing noticed on the street.

However, the design of the hubs of my 944S2 (the fastest car) is very very diffrent then that used on a 350Z..

 

944 Hub Front...

http://www.9ss1.dk/porsche944/dele/pic034.gif

944 Hub Rear...

http://www.9ss1.dk/porsche944/dele/pic042.gif

 

Two things I notice when looking at the diagram you posted are that the bearings in your car are much further apart than the Z's and your car doesn't use a preassembled hub with bearing preload set from the factory. Both of these things, space between the bearings and preload, can have a huge effect on how much the hub flexes.

Another thing to consider is caliper position. The closer to the top or bottom of the rotor the more any flex will be noticed.

Finally....master cylinder size. A manufacturer can/will use a smaller mc bore to get large caliper forces without large pedal force. The side effect is more pedal travel to get the same force. I don't know what Nissan did, but this is a common compromise.

 

Stoptech's are rebuilt and knockback springs are in! I've only had a chance to do some maneuvers in an empty parking lot, but my first impression is that my knockback is totally resolved !
I'm nost sure how much the drag on the rotor will affect heat at the track or rotor wear on the street, but the thought of having confidence in my brakes is wonderful.

 

Glad to hear it, Dave...

 

Maybe its just me... and maybe its just because I've never experienced knockback before... but I would think having to do a quick brake tap before a braking zone would be preferable to dragging brake pads

When your pads drag, you add excessive heat to the braking system which will cause worse problems than the knockback ever caused:

1. Excessive fluid temps - possible boiling - pedal to the floor (problem not solved)
2. Excessive pad temps - possible glazing or gas expulsion causing a dead pedal (problem not solved)
3. Added stress on the engine and drivetrain
4. Added wear on the brake pads, reducing their longevity

I recently figured out that my front right brake caliper on my BMW was dragging (not enough to stop the wheel from spinning by hand, but enough to stop the rotor spinning by hand.) This caused my Pagid Blue pads to wear down in a 1/4 of the time they should have, and it reduced my fuel mileage by about 6mpg.

I'm not saying don't give it a shot... I'm just saying be prepared for other problems besides pad and rotor wear

 

daveh has been doing the left foot tap for some time now. I finally got it down to a habit, but sometimes, I tap too much and feel significant, but momentary, loss in acceleration. It might be attributed by some throttle cutoff by the CPU, but I haven't confirmed it. I recall daveh saying something about throttle cut, but for me it feels like momentary application of brakes. We all know how sensitive the pads get when properly heated, so the slightest pressure is all it takes to feel sudden loss in acceleration especially at high speeds and in the taller gears.

dave, I hope those springs work out for you. I only have a few spots where the left foot tap is hard to sneak in between turns with very short straight in between.

 

just bumping and checking in - 03 track with stoptech 14" and big tires here checking in. i take my car out in the middle of the night and go maniac on the ramps and the pad pushback is unacceptable - has been for a couple years now.

is it possible that the aluminum knuckle itself is flexing? if someone had a spare knuckle laying around that they felt like sending out, we could machine a steel brace on the CNC that would connect the caliper mounts to the hub mounts using longer bolts to attach.

i guess the problem is most likely in the hub itself. i replaced mine with brand new ones and had absolutely 0% improvement first day back on the road. that was a while ago, i cant remember what the hubs looked like compared to the countless hubs i have seen. is it possible that we can try increasing the tension before installing? was there a big nut on the inside of the hub?

 

A quick tap does not always totally fix the knockback and the problems you list are not even noticable. Remember I only added a 4lb spring. It takes hundreds of pounds of force to stop a car. 4lbs is nothing.
I can spin the tire (and rotor) freely when the car is in the air and I don't feel drag at any time. I can still push the car around the garage and the car still roles at a stoplight when in neutral.

To your point, knockback springs are not for everyone. I would only recommend it if someone is entering a timed competition and every 10th counts. I'm very happy I put the knockback springs in and only wish I did it a year ago.

I'll report back in July if I have any heat related issues.

 

Interesting idea to brace the caliper.

You do realize that the knock back issue comes from the wheel/hub assembly deforming under load, pulling the rotor with them while the caliper itself is fixed?

Meaning, a caliper “more fixed” will not help and can only hurt the pad knock back issue…

I have to rebuild my calipers this winter. Where can I get the knock back springs Dave?

 

You misinterpreted what I said. I did not say that securing the caliper more rigidily would solve a problem of hub flex. I DID ask if its possible that its not the hub that is flexing, and if its possibly the steering knuckle that is flexing instead - if this WERE the case, my suggestion of a brace has warrent. Thus, why I asked.

 

Here is what I don't understand about adding springs, springs are linear devices - the more you compress them the more force it takes. Therefore when you have new pads you will add more force then when they are almost warn. So are the 4# springs for new pads, warn pads or something inbetween?

 

We're talkin of a 4lb spring (I'm assuming it's 4lb/in) so the pads it self is probably getting pushed on the rotor with a force of 4 lb or less.

I figure 1/2in compression in both cylinders? Let's say 10lb of clamping force total just to round things up.

The brake system is capable of generating fluid pressure above 1,400psi... 10lb is nothing compared to that.

 

Just finished a track weekend with the knockback springs and saw no heat issues and suffered no knockbadck. My pedal was always in the same place and braking was predicatble once again. An added benefit in the rain is that the slight pressure on the rotors keeps the brakes dry and ready to work. No pumping needed to evacuate water. The only thing that I don't care for is that pad changes require a little more muscle because the pistons close when you remove the pad. If you work fast enough, the new pad goes in fine. If you're too slow, your working to pry the pistons back to insert the new pads.
The knockback springs are definately a worth wile mod for track hounds.

 

Thanks for the feedback Daveh. I'll have to order a set of those springs.

With regard to MoodDude's question. Do I have to replace the 4lb spring with for example a 6 lb spring when the pad gets worn down because theoretically there's less pressure on the pad.

 

That's a good question. My pads are at 50% right now and the springs seem to be ok. Stoptech did suggess the stiffer springs but I wanted to start with the softest spring possible. I'll report back this summer when my pads are worn down more.

More info on springs here:
http://www.apracing.com/car/caliper/springs.htm

 

anyone ever cross reference part numbers on the hubs and spindles on the later Zs to see if they have changed them? maybe now that the 07s are out?

 

Has anybody found a Brembo application spring set? Would the AP springs work with the OEM calipers?

I'll be rebuilding my front brakes soon, I might as well put these in at the same time.

I know Brembo offers an antiknock back pressure seal but I'd rather get a set of springs instead.