I'm getting banged!

[ViperGeorge]

Now that I have your attention. I am having an issue with my 09 ACR on the track. Under heavy braking I sometimes hear a loud banging from the rear, I think more from the right side. It doesn't occur in all braking zones just some. May be related to the roughness of the surface. I may have convinced myself that it is from wheel hop but I'm not really sure that the car is even getting rear hop. We've given the car a visual inspection and can see nothing wrong. If it is wheel hop under ABS activation what should I change in my shock settings - compression? rebound? both? Anyone else have this problem? If it is not wheel hop what else would cause it?

 

[Alabaster Mamba]

Does it always oocur when you are braking hard in one direction or any direction? The reason I ask is that it could be a failed bushing if it always makes the same noise braking in the same direction. Or for that matter it could be some other suspension part that is lettng loose so to speak. Good luck and hope you find it.

 

[ViperGeorge]

Does it always oocur when you are braking hard in one direction or any direction? The reason I ask is that it could be a failed bushing if it always makes the same noise braking in the same direction. Or for that matter it could be some other suspension part that is lettng loose so to speak. Good luck and hope you find it.

It does not do it all the time. We checked under the car and noticed nothing obvious. It was regularly occuring at turn 9 at Hastings Motorsports Park but it did not occur at other turns regardless of how hard I broke. Turn 9 is a bit rougher (think washboard) than other turns. I could cause it consistently at that turn by hammering the brakes hard. All braking was made in a straight line by the way.

 

[mjorgensen Woodhouse]

Were you going to try changing the rear pad compound you are using and see if that solves the issue? I still think that the rear compound could be a bit too aggressive under hard weight transfer...

 

[ViperGeorge]

Were you going to try changing the rear pad compound you are using and see if that solves the issue? I still think that the rear compound could be a bit too aggressive under hard weight transfer...

With the Perf. Friction 03s I did not notice the issue at Road America but then again I don't get it all the time anyway. I really didn't like the way the 03s in the rear felt though, no where near as much braking force as my Raybestos pads. I will check with Porterfield to see if there is a slightly lower CoF compound. If it is wheel hop though can't I control it better by changing shock settings? What would I try? Raise rebound or compression or both?

 

[mjorgensen Woodhouse]

With the Perf. Friction 03s I did not notice the issue at Road America but then again I don't get it all the time anyway. I really didn't like the way the 03s in the rear felt though, no where near as much braking force as my Raybestos pads. I will check with Porterfield to see if there is a slightly lower CoF compound. If it is wheel hop though can't I control it better by changing shock settings? What would I try? Raise rebound or compression or both?

The banging will be when the tire bounces up more then anything, you could try increasing the compression a little and see if that helps. It may even be that you are jumping on the brakes to fast instead of smoothly in a couple places and that is really upsetting the rear of the car and not giving it a chance to get grip before the pads grab so hard?

 

[ViperGeorge]

The banging will be when the tire bounces up more then anything, you could try increasing the compression a little and see if that helps. It may even be that you are jumping on the brakes to fast instead of smoothly in a couple places and that is really upsetting the rear of the car and not giving it a chance to get grip before the pads grab so hard?

Could be that I am faster on the brakes at some places at some tracks. Kind of like that "oh $HIT, hit the brakes!" feeling. I'll try increasing compression a couple of clicks in the rear and see what that does. Keep those ideas comin though.

 

[Sonoman]

Mount a GoPro (or other smal digicam) on the car monitoring the wheel/suspension movement. I'm betting you are losing contact with grip over the washboard and then quickly regaining it, creating an oscillation. The ABS control loop may be fighting you here, might go away without ABS.

 

[ViperGeorge]

Mount a GoPro (or other smal digicam) on the car monitoring the wheel/suspension movement. I'm betting you are losing contact with grip over the washboard and then quickly regaining it, creating an oscillation. The ABS control loop may be fighting you here, might go away without ABS.

Good idea. I will attempt that the next time I go to the track.

 

[Nader]

If I remember correctly the Video of the first Nurburgring record the ACR had some banging going entering into the carousel. Pull that video and see if it is similar. If so it might be easier to diagnose.

 

[ViperGeorge]

If I remember correctly the Video of the first Nurburgring record the ACR had some banging going entering into the carousel. Pull that video and see if it is similar. If so it might be easier to diagnose.

Watched the video but did not hear the same noise. My noise is metallic and loud enough to hear with you helmet on. I believe that what Mark J is saying is correct. It must be wheel hop that occurs when the ABS kicks in on some surfaces. He suggested increasing compression in the rear. Next time I'm at the track I'll try that.

 

[ViperGeorge]

Were you going to try changing the rear pad compound you are using and see if that solves the issue? I still think that the rear compound could be a bit too aggressive under hard weight transfer...

Mark, I actually pulled the pads front and rear last night and I am in fact running a softer compound in the rear. I'm running Raybestos ST44 in the front and ST43 in the rear. For some reason I thought they were the same.

 

[treesnake]

My car did the exact same thing this weekend on turn 9. (before I broke transmission the first day....)


IMO, one contributing factor is the MPH track surface at turn 9. I tried several different braking entry lines, different entry speeds etc...

Result was the same, hard wheel hop. At that turn only.

My "fix" was to enter turn 9 slower to where I was somewhat off the brake at that rough point, and tried to make up the time with a quicker exit speed....


Were you getting wheel hop anywhere else?

 

[ViperGeorge]

Treesnake, Thanks, now I feel better. What settings are your shocks set to? or do you run Motons? What pads are you using front to rear? Ultimately I did the same thing you did, slowed sooner for turn 9. I did not notice the banging or wheel hop anywhere else on the track. Well maybe once coming on to the front straight in 2nd, but that was nothing compared to turn 9. By the way how did you break your trans?

 

[ViperGeorge]

Treesnake, One more thing, did you also have the banging sound?

 

[bluesrt]

on the wheel hop aspect, try a few things,takes time- i would first try to speed up your rebound, may be too slow and suspension packing up, but there is allways a price to pay for this somewhere(tradeoff) so go babysteps with this and try to find a happy medium.. if that doesnt work i would try the compression setting next,soften it up a smidge.you just have to try these things and then take notes on what happens, everyones car is differant,and you have to remember everyone has a differant drive style,reaction and brake styles, so you have to personalize the car to how you drive and react to the trac. biggest thing, take notes,you will find your problem faster and improve ....

 

[ViperGeorge]

on the wheel hop aspect, try a few things,takes time- i would first try to speed up your rebound, may be too slow and suspension packing up, but there is allways a price to pay for this somewhere(tradeoff) so go babysteps with this and try to find a happy medium.. if that doesnt work i would try the compression setting next,soften it up a smidge.you just have to try these things and then take notes on what happens, everyones car is differant,and you have to remember everyone has a differant drive style,reaction and brake styles, so you have to personalize the car to how you drive and react to the trac. biggest thing, take notes,you will find your problem faster and improve ....

Thanks, as Treesnake says it may all be due to the track surface at that particular turn (and my driving style). Mark suggested stiffing compression first since he believes the banging results when the wheel rises.

 

[treesnake]

Treesnake, Thanks, now I feel better. What settings are your shocks set to? or do you run Motons? What pads are you using front to rear? Ultimately I did the same thing you did, slowed sooner for turn 9. I did not notice the banging or wheel hop anywhere else on the track. Well maybe once coming on to the front straight in 2nd, but that was nothing compared to turn 9. By the way how did you break your trans?

Yes, I am running 12-way motons. Set at "7" on both rebound and compression.
I am using 1400# rear and 900# front springs. Brembo "ACR-X" front rotors with PFC 01 pads. Rear are Stoptechs with Mintex pads.

Treesnake, One more thing, did you also have the banging sound?

Yes, I did but the sound I was hearing might have been the transmission.....

However, I was going to ride with Steve Wedel (maroon ACR) to try and figure out what a similar banging sound he was hearing was. He said it just "went away"...

I was coming down short straight into turn 12-13??? (in front of clubhouse) Anyway, the trans just completely let go. No forward or reverse gears. Clutch would engage and disengage. But that's about it...

Got the spare put in and going to Autobahn on Monday....

 

[ViperGeorge]

Treesnake,

Nice that you had a spare tranny. Can't say that is a spare I have. By the way, I think Steve had a Violet ACR. Bill Pemberton was in the Venom Red/Black ACR.