Pad knockback

kannibul · 09-27-2009, 11:13 AM

Quote:

Originally Posted by semtex

Check out this video. I don't follow everything this guy is rambling on about, but it demonstrates how much flex is in wheel hubs when he measures the flex he can get with pressure from just one hand.

Neat vid, however, he's showing the bearings outside of the axle - if I did that with the bearings on my truck, hey'd show a lot more than 0.001" of play (more like a 1/4"). Funny thing is that it was visually a lot more than that - I'd get 0.1"

Anyhow, I can't see it being a caused by the rotors pressing the pads away from them physically by flexing, at the hub, at the bearings, etc. Sorry man. I just don't see how it would happen.

semtex · 09-27-2009, 02:47 PM

I don't think you understand how the front wheel hubs on our cars work. The entire wheel hub assembly bolts onto the front spindle, and the bearings are contained within the wheel hub assembly. There are no bearings inside of the axle! These aren't front-wheel drive cars, after all. Here is a diagram from the Service Manual:

As you can see, the bearings are contained within the wheel hub assembly. The entire assembly bolts on to the steering knuckle and stays stationary against it; the only moving part is the wheel hub itself, via the bearings contained within. Now, the brake caliper bracket mounts up to these two holes:

As you can see, the calipers also stay fixed in position. The wheel hubs have some flex. In fact, the Service Manual even has a spec for how much flex is acceptable:

Definition of Axial end play: "Most ball bearings are assembled in such a way that a slight amount of looseness exists between balls and raceways. This looseness is referred to as radial play and axial play. Specifically, radial play is the maximum distance that one bearing ring can be displaced with respect to the other, in a direction perpendicular to the bearing axis, when the bearing is in an unmounted state. Axial play, or end play, is the maximum relative displacement between the two rings of an unmounted ball bearing in the direction parallel to the bearing axis. Since radial play and axial play are both consequences of the internal geometry of the components in a ball bearing, they bear a mutual dependence." Source: nhbb :: hitech engineering :: radial play

So what happens when they flex is that the rotors (which are bolted up against the wheel hub via the lug bolts) can push up against the pads and push the pistons in slightly, resulting in more pedal travel the next time you step on the brakes. This is a basic and well known phenomenon that is common to all fixed-caliper systems. I really don't understand why you can't get your head around this. It is so elementary. Truth be told, I'm beginning to think that maybe you don't want to get your head around this, and that for whatever reason you've decided that you want to be argumentative.

StopTech has made available a technical paper explaining what causes pad knockback better than I ever could, yet you refuse to accept it because you think it's a marketing gimmick, which makes absolutely no sense because standard braking systems on passenger cars use floating calipers and don't have pad knockback. In other words, it makes no sense for StopTech to supply this write-up as a marketing tool because if anything, it would give people reason to not upgrade from a floating-caliper system to a fixed-caliper system (which all of theirs are). This paper would do more to hurt their sales than help them!

But let's see if we can approach this from a different angle. Maybe you and I are going around in circles because I don't understand exactly what it is that you're trying to argue. So, what exactly is the position you're trying to take on all this? That pad knockback is a myth and doesn't happen? Or that it happens, but it's not caused by wheel hub flex?

kannibul · 09-28-2009, 09:22 AM

Quote:

Originally Posted by semtex

I don't think you understand how the front wheel hubs on our cars work. The entire wheel hub assembly bolts onto the front spindle, and the bearings are contained within the wheel hub assembly. There are no bearings inside of the axle! These aren't front-wheel drive cars, after all. Here is a diagram from the Service Manual:

As you can see, the bearings are contained within the wheel hub assembly. The entire assembly bolts on to the steering knuckle and stays stationary against it; the only moving part is the wheel hub itself, via the bearings contained within. Now, the brake caliper bracket mounts up to these two holes:

As you can see, the calipers also stay fixed in position. The wheel hubs have some flex. In fact, the Service Manual even has a spec for how much flex is acceptable:

Definition of Axial end play: "Most ball bearings are assembled in such a way that a slight amount of looseness exists between balls and raceways. This looseness is referred to as radial play and axial play. Specifically, radial play is the maximum distance that one bearing ring can be displaced with respect to the other, in a direction perpendicular to the bearing axis, when the bearing is in an unmounted state. Axial play, or end play, is the maximum relative displacement between the two rings of an unmounted ball bearing in the direction parallel to the bearing axis. Since radial play and axial play are both consequences of the internal geometry of the components in a ball bearing, they bear a mutual dependence." Source: nhbb :: hitech engineering :: radial play

So what happens when they flex is that the rotors (which are bolted up against the wheel hub via the lug bolts) can push up against the pads and push the pistons in slightly, resulting in more pedal travel the next time you step on the brakes. This is a basic and well known phenomenon that is common to all fixed-caliper systems. I really don't understand why you can't get your head around this. It is so elementary. Truth be told, I'm beginning to think that maybe you don't want to get your head around this, and that for whatever reason you've decided that you want to be argumentative.

StopTech has made available a technical paper explaining what causes pad knockback better than I ever could, yet you refuse to accept it because you think it's a marketing gimmick, which makes absolutely no sense because standard braking systems on passenger cars use floating calipers and don't have pad knockback. In other words, it makes no sense for StopTech to supply this write-up as a marketing tool because if anything, it would give people reason to not upgrade from a floating-caliper system to a fixed-caliper system (which all of theirs are). This paper would do more to hurt their sales than help them!

But let's see if we can approach this from a different angle. Maybe you and I are going around in circles because I don't understand exactly what it is that you're trying to argue. So, what exactly is the position you're trying to take on all this? That pad knockback is a myth and doesn't happen? Or that it happens, but it's not caused by wheel hub flex?

OK, thanks for the visuals. Seems like with the hub, spindle, and bearing being one unit (and non adjustable, ie, there's no nut on the end of the spindle as in with classic spindle/rotor+hub setups?), then I can see there how that could cause some play there and relate to the issue.

My position, previously, was that it wasn't caused by wheel hub flex...I can see where I was wrong now.

Thanks!

semtex · 09-28-2009, 09:40 AM

Correct, there's no nut on the end of the spindle. The entire wheel hub assembly is held in place with four bolts. You can see the bolt holes in the diagram.

corbin09 · 10-07-2009, 12:30 PM

i have this and i only have the base package brakes!

semtex · 10-07-2009, 12:48 PM

Quote:

Originally Posted by corbin09

i have this and i only have the base package brakes!

Really? That's very odd, because the base pkg brakes use floating calipers. I've never felt knockback with floating calipers before. Has it done this from day 1?

corbin09 · 10-08-2009, 11:34 AM

No, It hasnt done it since day one.. It just started happening about 2 weeks ago. I noticed it while i wasnt driving hard, I hit the brakes to stop and when i let off i got a little clunk noise and i could feel it in the brakes. I dont get it all of the time, just every so often, i would say out of about 20 braking tries maybe 4 or 5, but it is still very annoying. I have exhaust and rims on my car.. and BANKSTON nissan of dallas happens to have the WORST CUSTOMER SERVICE in their service dept i have ever come across. The car has wheels and exhaust, and apparently this is the cause all of my problems??

semtex · 10-08-2009, 11:56 AM

Hmm...I don't know what that would be, but pad knockback isn't characterized by any clunking sounds or sensations. Sucks that Bankston's customer service is so poor. You might consider taking it to a brake place (like Midas) to have them diagnose the root cause. Yes, it sucks because it'll be money out of pocket. But if it's a choice between spending some money or risking sudden and total brake failure (i.e., the problem could suddenly get worse), then I personally would spend the money. But that's just my opinion. Not trying to tell you what to do or anything.

corbin09 · 10-08-2009, 12:36 PM

yes, it isnt a loud clunk, but there is a sound. I think im going to take it to the dealership. Tell them the problem and ask them to diagnose what it is. At that point they will tell me, it is ______________ probably caused by the wheels you put on... like usual, then i will take it to a brake place to get it fixed. Im hoping on upgrading to someones used set of akebonos soon so maybe this will just get me more motivated.

Rps13.jw · 10-09-2009, 03:15 AM

I dont have this problem in my 370z.

ChrisSlicks · 10-09-2009, 07:46 AM

Quote:

Originally Posted by corbin09

yes, it isnt a loud clunk, but there is a sound. I think im going to take it to the dealership. Tell them the problem and ask them to diagnose what it is. At that point they will tell me, it is ______________ probably caused by the wheels you put on... like usual, then i will take it to a brake place to get it fixed. Im hoping on upgrading to someones used set of akebonos soon so maybe this will just get me more motivated.

On floating caliper setups like on the base model this can sometimes happen if the grease on the brake pads dries up. The pads hang-up for just a bit and then skip as they jump back out into position. A little lube on the backing plates and on the side edge usually does the job.

semtex · 10-09-2009, 07:47 AM

Quote:

Originally Posted by ChrisSlicks

On floating caliper setups like on the base model this can sometimes happen if the grease on the brake pads dries up. The pads hang-up for just a bit and then skip as they jump back out into position. A little lube on the backing plates and on the side edge usually does the job.

Great tip = +rep!

Modshack · 10-09-2009, 11:13 AM

Quote:

Originally Posted by ChrisSlicks

On floating caliper setups like on the base model this can sometimes happen if the grease on the brake pads dries up. The pads hang-up for just a bit and then skip as they jump back out into position. A little lube on the backing plates and on the side edge usually does the job.

And don't forget the slide pins!

ChrisSlicks · 10-19-2009, 09:11 PM

Quote:

Originally Posted by semtex

Great tip = +rep!

Thanks! But you have the sport model don't you? The issue is a little different with the fixed caliper setup, but I have to say the 370 has much less pad knockback than the 350 did.

semtex · 10-20-2009, 08:01 AM

Quote:

Originally Posted by ChrisSlicks

Thanks! But you have the sport model don't you? The issue is a little different with the fixed caliper setup, but I have to say the 370 has much less pad knockback than the 350 did.

Yeah, I know your tip doesn't apply to my car. But I was repping you for helping out corbin09.

09-27-2009, 02:47 PM	#17 (permalink)
semtex A True Z Fanatic Join Date: Jan 2009 Location: Behind enemy lines Age: 54 Posts: 5,995 Drives: People to drink Rep Power: 32	I don't think you understand how the front wheel hubs on our cars work. The entire wheel hub assembly bolts onto the front spindle, and the bearings are contained within the wheel hub assembly. There are no bearings inside of the axle! These aren't front-wheel drive cars, after all. Here is a diagram from the Service Manual: As you can see, the bearings are contained within the wheel hub assembly. The entire assembly bolts on to the steering knuckle and stays stationary against it; the only moving part is the wheel hub itself, via the bearings contained within. Now, the brake caliper bracket mounts up to these two holes: As you can see, the calipers also stay fixed in position. The wheel hubs have some flex. In fact, the Service Manual even has a spec for how much flex is acceptable: Definition of Axial end play: "Most ball bearings are assembled in such a way that a slight amount of looseness exists between balls and raceways. This looseness is referred to as radial play and axial play. Specifically, radial play is the maximum distance that one bearing ring can be displaced with respect to the other, in a direction perpendicular to the bearing axis, when the bearing is in an unmounted state. Axial play, or end play, is the maximum relative displacement between the two rings of an unmounted ball bearing in the direction parallel to the bearing axis. Since radial play and axial play are both consequences of the internal geometry of the components in a ball bearing, they bear a mutual dependence." Source: nhbb :: hitech engineering :: radial play So what happens when they flex is that the rotors (which are bolted up against the wheel hub via the lug bolts) can push up against the pads and push the pistons in slightly, resulting in more pedal travel the next time you step on the brakes. This is a basic and well known phenomenon that is common to all fixed-caliper systems. I really don't understand why you can't get your head around this. It is so elementary. Truth be told, I'm beginning to think that maybe you don't want to get your head around this, and that for whatever reason you've decided that you want to be argumentative. StopTech has made available a technical paper explaining what causes pad knockback better than I ever could, yet you refuse to accept it because you think it's a marketing gimmick, which makes absolutely no sense because standard braking systems on passenger cars use floating calipers and don't have pad knockback. In other words, it makes no sense for StopTech to supply this write-up as a marketing tool because if anything, it would give people reason to not upgrade from a floating-caliper system to a fixed-caliper system (which all of theirs are). This paper would do more to hurt their sales than help them! But let's see if we can approach this from a different angle. Maybe you and I are going around in circles because I don't understand exactly what it is that you're trying to argue. So, what exactly is the position you're trying to take on all this? That pad knockback is a myth and doesn't happen? Or that it happens, but it's not caused by wheel hub flex? __________________ "There are no small accidents on this circuit." -- Ayrton Senna 316.8whp & 248 ft/lbs (Dyno Dynamics) \| 319whp & 256 ft/lbs (DynoJet) (04/23/10) Stillen G3 CAI, CBE, Pulley / F.I. LTH / GTSpec Ladder Brace / Setrab Oil Cooler / UpRev-tuned by Forged Perf. Last edited by semtex; 09-27-2009 at 04:26 PM.

09-28-2009, 09:40 AM	#19 (permalink)
semtex A True Z Fanatic Join Date: Jan 2009 Location: Behind enemy lines Age: 54 Posts: 5,995 Drives: People to drink Rep Power: 32	Correct, there's no nut on the end of the spindle. The entire wheel hub assembly is held in place with four bolts. You can see the bolt holes in the diagram. __________________ "There are no small accidents on this circuit." -- Ayrton Senna 316.8whp & 248 ft/lbs (Dyno Dynamics) \| 319whp & 256 ft/lbs (DynoJet) (04/23/10) Stillen G3 CAI, CBE, Pulley / F.I. LTH / GTSpec Ladder Brace / Setrab Oil Cooler / UpRev-tuned by Forged Perf.

10-08-2009, 11:56 AM	#23 (permalink)
semtex A True Z Fanatic Join Date: Jan 2009 Location: Behind enemy lines Age: 54 Posts: 5,995 Drives: People to drink Rep Power: 32	Hmm...I don't know what that would be, but pad knockback isn't characterized by any clunking sounds or sensations. Sucks that Bankston's customer service is so poor. You might consider taking it to a brake place (like Midas) to have them diagnose the root cause. Yes, it sucks because it'll be money out of pocket. But if it's a choice between spending some money or risking sudden and total brake failure (i.e., the problem could suddenly get worse), then I personally would spend the money. But that's just my opinion. Not trying to tell you what to do or anything. __________________ "There are no small accidents on this circuit." -- Ayrton Senna 316.8whp & 248 ft/lbs (Dyno Dynamics) \| 319whp & 256 ft/lbs (DynoJet) (04/23/10) Stillen G3 CAI, CBE, Pulley / F.I. LTH / GTSpec Ladder Brace / Setrab Oil Cooler / UpRev-tuned by Forged Perf.

10-07-2009, 12:30 PM	#20 (permalink)
corbin09 Track Member Join Date: Jun 2009 Location: Dallas tx Posts: 665 Drives: 370z Rep Power: 280	i have this and i only have the base package brakes!

10-08-2009, 11:34 AM	#22 (permalink)
corbin09 Track Member Join Date: Jun 2009 Location: Dallas tx Posts: 665 Drives: 370z Rep Power: 280	No, It hasnt done it since day one.. It just started happening about 2 weeks ago. I noticed it while i wasnt driving hard, I hit the brakes to stop and when i let off i got a little clunk noise and i could feel it in the brakes. I dont get it all of the time, just every so often, i would say out of about 20 braking tries maybe 4 or 5, but it is still very annoying. I have exhaust and rims on my car.. and BANKSTON nissan of dallas happens to have the WORST CUSTOMER SERVICE in their service dept i have ever come across. The car has wheels and exhaust, and apparently this is the cause all of my problems??

10-08-2009, 12:36 PM	#24 (permalink)
corbin09 Track Member Join Date: Jun 2009 Location: Dallas tx Posts: 665 Drives: 370z Rep Power: 280	yes, it isnt a loud clunk, but there is a sound. I think im going to take it to the dealership. Tell them the problem and ask them to diagnose what it is. At that point they will tell me, it is ______________ probably caused by the wheels you put on... like usual, then i will take it to a brake place to get it fixed. Im hoping on upgrading to someones used set of akebonos soon so maybe this will just get me more motivated.

10-09-2009, 03:15 AM	#25 (permalink)
Rps13.jw Base Member Join Date: Jul 2009 Location: California Posts: 38 Drives: 370z Rep Power: 16	I dont have this problem in my 370z.