This hub flex is driving me nuts. My brake pedal goes half way to the floor after cornering. Will replacing my hubs fix this or will I just be wasting my money? I called my local dealership and they said they've never heard of anyone having this problem and that it wasn't a warranty item because I upgraded to stoptechs (not that that is what is causing the problem).

I posted in the race related forum because I though it would apply more this audience.

 

I have yet to experience that problem. I know the GA Cup teams said they had problems with hub bearings wearing out quickly. And I've heard a few people complain about hub flex. I'm sure Nissan is not going to really take that complaint too seriously though. How many people come in complaining of hub flex?? Check with BJ and see what they did maybe?

 

On the streets too?!?!?! Considering that you spend every weekend at the track, I'd think you would get it out of your system and drive like a grandma on the streets. Apparently not... :-)

Unfortunately, once we swap out the stoptech's, and reinstall the OEM's the hub flex is masked...so even the warranty route is moot.

Have you tried adjusting your hub; tightening it a bit? I have to do that with my other car because it loosened enough to where it was actually rattling! Other than that, it sounds like your hub is wearing out, especially since you're flexing it at lower lateral g's now. Great...now we have to stock hubs in our garages, along with the piles of tires, brake pads, tools, oil, and brake fluid....

Did you ever master the left-foot tapping technique? I certainly couldn't, so I'm back to right-foot tapping.

 

This is an inherent design deficiency. The only solution at this point is to do what we did on the race car: Add springs behind the pistons. This almost completely eliminates the problem, but will put a bit of brake drag on the rotor. You can get different spring pressures. We use 4 psi, I think...

The Z32's were cursed by this as well. It has to do with caliper location, bearing size, etc.

 

Springs may be a last resort. Unitech reversed the mouting bolts on my rotor hats to give the rotor more float and I think that may have marginally helped.
I don't drive hard on the street at all, that's why the hub flex was a concern to me. (20k on my original stock tires and going strong speaks to that)
It almost got me into trouble last week when I took an exit ramp at speed and didn't need brakes until half an hour later when I had long since forgotten that I needed to pump the brakes. I am worried that someone else will be driving my car and not know how to handle this situation. On the track I left foot brake after long corners without even thinking about it.

Nick at what point should I change out the hub/bearings? It amazed me that hubs can flex so much without my wheels flying off the car. They feel tight by the old wheel shaking test.

 

Our hubs/bearings will get changed at the end of the season (December). I've not had a wear problem yet, though this is part of regular preventative maintenance schedule for us. We are on full slicks, and put a lot of force onto those poor items.

 

even on falken azenis, it is terrible for me as well. i think, as racin mentioned, it is to a large degree a matter of caliper location; that is, because the calipers are placed relatively close to 12 o'clock, any hub flex is magnified in pad knockback. if the calipers were closer to 9 or 3 o'clock, the deflection wouldn't be so noticeable. i don't get it on the street, so that would worry me some, although at this point i drive like grandma on the street - damn fairfax county VA revenue generators are brutal, so i'm not sure how hard you drive. on the track, absolutely, every turn, particularly long sweepers, must be followed up with a dab at the brake pedal to get the pads back where they belong.

where do the springs fit? between the pad and some form of backing plate?

ahm

 

The springs fit inside the caliper, seating on the piston and the back wall of the piston bore. They push the piston gently outward.

 

While I have pad knockback on the track, I have never experienced it on the street. If it did occur on the street, then I would be seriously inclined to replace the hubs and bearings immediately.

 

I have discussed pad knockback with some rennlisters since one of the members have recently experienced this problem on his porsche 996 with stoptech BBK. He has stated that he's had the kit for over 20 track days, and had his first pad knockback experience. Other DE/racers chimed in stating that they replaced their bearings, and the problem went away.

For us, the knockback seems to happen whether the bearings are healthy or not. I had my BBK installed at around 10,000 miles, and with only two track days within those miles. That knockback was there from day one.

So far, CRayZ and Zillinois are the only two that I've heard of who do not get the knock back problem. You guys have exceptionally strong hubs and bearings!

Dave, do you still have the problem outside the track, or have you replaced your bearings? I'm considering just replacing the bearings on this thing and hope that it improves. I don't know how you tap your brakes with the left foot...I have small feet, and it still gets all caught up trying to go from the dead pedal to the brake pedal.

 

I don't think my bearings are very strong, because I had my passenger rear hub bearing go out. It had to be replaced at about 20,000 miles. I can tell you that I radically altered the way I drive and brake this year. That may have something to do with it.

 

Geoff,

You "radically" altered the way you drive and brake this year, and you believe that has caused bearing wear? Do tell...was is because you went to r-comps, then drove the living hell out of car designed for sporting cruises along the coast?

BTW, how does one know when a bearing is about to go? By the time I find out, I'm afraid it might be too late, and my hub and bearings will just explode in an awesome display of sparks and shrapnel. So I'm wondering how many track days I can get out of these... 20k miles on the odo is not much, but if you've got a real problem (or addiction), you could easily fit in three dozen track days within those miles.

Don

 

I did make the move to R-compounds this year. I think that coupled with a lot higher g-force driving may have had something to do with it. I got a terrific instructor out at Watkins Glen this year who basically showed me the fast line. He was a national PCA club racing sign off guy (forgot the official name for that), instructor and a great guy. I don't break very hard anymore and I don't turn in very hard, but my cornering loads went up and my lap times went down. My first time at the Glen I ran a 2:20 with a stock motor and when I got back to my home track which I have run probably 20+ times I lopped 3 seconds off on a 1.8 mile track. On one corner alone I increased my mid-corner speed by 9mph!!

You can check the hub bearings by jacking your car up and trying to wiggle the tire. If you grab either side of the tire and wiggle the wheel side to side, does it move? It should not move more than say an 1/8 of an inch. Ideally it should not move at all.

I went to change my pads one day and I jacked up the car before I loosened the lugs. (Doh!) When I went to remove the wheel it didn't come off of course, but it did swing like a barn door. I bet I could wiggle the tire about an 1-1/4" in either direction. It was horrible. This was the passenger rear wheel.

Mine also had the symptom of squirming upon hard acceleration. Hard to describe the sensation other than the rear end is not fishtailing but it kind of feels like it is. I had 16k on the car. I really couldn't believe they went out.

 

One other way to check the bearing is by jacking the car and spinning the wheel by hand while holding the coil spring. If you feel vibration/grinding, it's time for a new bearing.


How big are your discs guys? You probably get lots of displacement with a 14" BBK !

 

Yeah, I got the 14" ones, which magnifies the problem a bit. CRayZ beats his car too, but says he doesn't get knockback. He's running r's and is faster around Thill than me.

Thanks, Kolia, I'll try the vibration test. The shake test I performed a months ago had indicated everything was A-okay.

 

I run on R's and didn't get any knockback until very recently. I attribute it to bearing wear (52K on it now) and will probably repack and re-torque the front hubs before next season. I mentioned the lack of hub flex in my '04 to a Z racer (Racin on this board) and he said that Nissan beefed up the hub casting for '04. I'm sure it's not a cheap part, but if you have an '03 and replaced your bearings already it may be the next step....

 

Can one of you guys explain this phenomenon in a little more detail? This is the first I've heard of this (of course, I don't drive a 350z either.) I had a Z32 NA Auto but never had this issue on that car either

Thanks!

 

Heavy lateral loads deflect the rotor enough to push the pistons back into the caliper a bit. When you go for your next braking event the free play of the pedal is increased noticably. Here's a great explainantion;

http://www.stoptech.com/tech_info/wp_knockback.shtml

Ever see the footwork shots they somtimes show on ALMS coverage? Sasha Maasen in a GT1 Porsche? A left foot stab of the pedal 1-2 seconds before every heavy braking section. Same with NASCAR at road courses.

An STI guy was complaining of knockback to me at a track day last summer, many heavy cars with a lot of grip may be susceptible.

 

Exellent! Thanks, I have now been schooled

 

I don't get this all the time, but it does happen to me. I have a totally stock car (with stock track model Brembos) and run on street tires. It seems to happen most when I go through sharp, slow stuff. (ex. Oak Tree at VIR). Of course those sharp, slow turns always lead to long, fast straightaways and you REALLY want brakes at the end of them.

I switched tires this past season and the new tires don't have as much grip. That sucks of course, but I haven't noticed the hub flex/pad knockback once since the switch. I anticipate it to become more of a problem when I head for the land of R-compounds next season.

It is strange how erratic of a problem this is...with some having it and some not. There is obviously a list of factors (tires, suspension set-up, driving style, track, etc.) that increase/decrease the problem. However, the easiest thing to do right now is to treat the symptoms rather than the disease.

LEFT FOOT BRAKE TAPPERS FO' LIFE, YO!

Sean