My '03 Track had some hub flex/pad knock back since it was new, but after 3 years of auto-xing on R-comps it had gotten pretty bad, even on street tires. I replaced both front hubs last week and it did help the problem, but it didn't completey fix it. One interesting note is the new hub flanges are thicker than the originals. .235 vs .200

 

Update:
After having my pedal literally go the floor after the corkscrew at laguna, I decided to change my hubs.

It did nothing for me..

The only issue I have with left foot braking before they brake zones is that they computer seems to cut the throttle when you hit the brake and gas at the same time.

I'm considering knockback springs next, but am hesitant because of the drag they produce. The Z still is my daily driver.

 

If hub flex is causing the pedal to go to the floor, there are MUCH bigger problems at play.

Pedal to the floor is plain and simple air in the brake fluid... or not enough fluid caused by brake pads worn down and not topping off the fluid over the course of the weekend.

Puts some brake ducts on the car (aimed at the hub), make sure you're running a high-temp fluid like AP Racing 550, Motul 600, ATE, etc... and stop riding the brakes in the braking zones!

 

Hello,

This is an interesting thread... I guess I just can't run away from flexing hubs. Since 2001, I've been working with this problem. The WRX had it in a huge way. The STI had it less with the big bearing package that the R180 diff change necessitated. And now the 350Z...

Joel

 

Thanks for the advice. I can assure you that I properly maintain my brake system and have effective ducting in place. The corkscrew is a very brutal sequence on a car. It is a left/right turn with a 9 story drop that puts a lot of stress on hubs. I'm not the only one to experience this at Laguna.

Based off of feedback from another 350Z racer, I will be putting knockback springs in my stoptechs. I'll post back next year after the season opener.

 

Might want to also try full floating rotors if the StopTechs are not that already.

 

Hello,
That's the intent of crushing your spring washers and then turning them around and rebuilding the hat-rotor assembly. That flattens the washers out, gives you complete float, and makes rattling noise, which is why StopTech doesn't advertise that procedure (you know how it goes - people want "race" stuff and then they complain about the noise).

I think DaveH said he'd done that already (or UniTech had helped him with that, or something?)?

Joel

 

I posed a question regarding the use of the word "floating rotor" in the link below. I was merely questioning why the stoptech rotors are only radially floating, whereas an acquaintance of mine has brembos brakes, drives much faster than me in his E46 M3 on 275 hoosiers, and is not getting any knockback. He uses Brembo brand FULL floating rotors. Nobody addressed my questions. I was expecting Zeckhausen to say something about it, but he didn't chime in.

Post #53
https://my350z.com/forum/showthread....otor+AP+racing

I'm willing to live with some rotor chatter if it gets rid of the knockback, or most of it.

I also had brake pedals go to the floor after going through the corkscrew, and I was on street tires and just learning the course.

Can anyone chime in and tell me how to rebuild these rotors for lateral float? Or, is it that easy...just crush the washers...

 

daveh.....I know what you're saying about left foot braking cutting the throttle. From what I've found there seems to be a threshold pressure. If you stay below it, very light pressure, a couple small pumps, my car doesn't seem to react.

Stack....I can vouch for daveh. There is a traffic round-about on my way to work(way too much fun) and if I'm not paying attention and don't pump my brakes afterwards my pedal goes a long way before anything happens. Add some track fade and it could be down right scary.

 

I haven't done any research, but are there any temp springs that ca be installed for a track weekend and then pulled afterwards? Many people swap out the track pads anyways.

 

I'd check with Jason H & Rob Hines both members who run their 350Z's in T2. They will have some good insight into this problem.

 

Having done the rotor rebuild to get more float, I wouldn't recommend it. They rotor become very loud and mine eventually broke at the attachment points because of the excess moving/rattling about. It only marginally helped with knockback.
My springs will arrive this week and I might install them before a potential test and tune day in December. Stay tuned..

 

I've got a pretty good source for NHBB bearings, both standard application and custom. If someone wants to send me a front hub/bearing that they've pulled and replaced I can try to source an upgraded bearing to see if that reduces the problem.

FYI... I have not felt any knockback on my stock 2006 base 350Z.

 

I had a pretty good amount of hub flex at track with my large rotors.
There are two solutions to fix the problem -

1. Install 4# springs behind the pistons inside the calipers. (I really don't like this solution, as springs are linear devices so you get more resitance when the pad is new and less when they wear. You also are causing heat in your calipers all the time!)

2. Install a larger master cylinder or a dual master cylinder. This way when the pads push back a little, you don't have to push the pedal as much to push them back the pads back to the rotor. This is a better solution than above, but your brakes will have a different engagement point depending on how much flex you had before the braking zone.

I had the idea to try the 300ZXTT hubs as they are stronger, they just won't fit. Does anyone know if another Nissan cars hub would fit, from a vehicle that is much heavier - like the Xtera?

 

Someone is selling 350Z hubs on Ebay Motors for $99.99 from crashed cars. If you source one - let me know.

And you don't feel knock back unless you go with a large diameter rotor.

 

Now, I am just going out on a limb here and try to explain what I just read and see if I got this right. Your brakes fade (or don't contact right away) because your hub wobbles to the point that the rotor pushes pistons in the caliper back. That sounds downright dangerous and something that nissan better get ontop of because thats a lawsuit waiting to happen. Now, this whole pad knockback business does someone care to explain? Are you talking about the pad catching the rotor and getting slammed into the caliper because it fits loosely? If so that sounds like some downright ****ty designed rotors.

 

Hello,

Fishey, it's simple that the hubs flex when you have good traction and you drive hard. That flex translates to the rotor moving side to side in the caliper, while you're cornering and not on the brakes. That side to side motion pushes the pads away from the rotor. They end up moving less than a millimeter from the rotor surface. You go to hit your brakes and instead of the brake fluid moving the pistons just a hair, they have to move that fraction of a millimeter, which means your foot sinks almost all the way down to the floor as you take up that little amount of space.

This is a very common problem in many cars. Subarus have it, especially in the non-STIs (ie, Impreza, WRX, Legacy, etc.). Many cars have a noticeable amount of hub flex and the effect gets worse when you use larger diameter rotors (imagine the top of the hub moving 0.2 mm during this bearing movement, so that 4 inches away, that movement is something like 0.8mm, and 5 inches away, it's 0.9mm). So the bigger the rotor, the more magnified the problem is.

Add to that the propensity for buying stickier tires for track day folks and racers and you exacerbate the problem.

For most cars that exhibit hub flex, you will never encounter the problem with stock tires driving under normal, safe street conditions, which is what the OEM is selling the car for. The hubs are strong enough, usually, for the OEM's intended use, and thus, they don't "need" beefing up.

The unfortunate side-effect of the "excellent for the intended use" design is that when you use the car like the very small percent of us who go to the track, you run into unforeseen and difficult to resolve problems...

Joel

 

I'm thinking the phenomenon has gotten worse (or at least more noticeable) with the much more common use now of 17, 18" wheels... especially when combined with R-comps or ultra-sticky street tires.

Certainly too it must have a little something to do with driving style... those that tend to 'push' through a low speed turn (fast in, power out) I would think would exaserbate the problem since the forces on the 'turned' front wheels (g-loads) would be greater than someone that gets all their speed scrubbing done in a straight line and then gets on the throttle early to power THRU the turn (not just out of it).

 

Well it's not all driving style, because I get quite a lot of knockback when I complete a drift style course where the rear end is sideways the whole time. Obviously even with now understeer, the front end takes a lot of load, when we transition side to side.

I've just gotten used to this, and got in the habbit of pumping the brakes everytime I need them. I'm starting to think it's very normal, I see all of the race car drivers doing this when I watch the in car footage.

 

I have never had do this in any of my cars or any other car I drive at the track. Hell, I had not even heard about it untill yesterday when I read this forum. We have issues with our cars and hubs but its nothing like what you guys experiance over here on the 350Z board.