Rear end scraping noise

madmaxx · #1 (**permalink**) 11-16-2008, 07:55 PM

Hello,

I have a fairly new SPF and notice if I go over a "dip" in the road I get a scaping noise from the rear. My ride height is 27" and there is no evidence of any tire rub on the fender. I have checked all bolts and they are tight. It is not a squeak but what sounds like the tire rubbing the inner fender. Any ideas would be greatly appreciated. It started a couple weeks ago. It is not the trunk prop rod either.

Thanks

PurpleVenom · #2 (**permalink**) 11-16-2008, 08:09 PM

Trust me, it is the tire rubbing the inside of the fender, you just haven't hit a big enough dip/bump to leave "scars" yet on the tire. Your ride height, it's 27"?!?

madmaxx · #3 (**permalink**) 11-16-2008, 09:08 PM

Sure sound like it is, what should the ride height be?

STL Mark · #4 (**permalink**) 11-17-2008, 12:38 AM

Yep - 27" is right - but it is probably scraping. Could raise it a bit with out doing much harm (1/2"). What tires are you running? What air pressure? Also - very important - check your axle bolts!

madmaxx · #5 (**permalink**) 11-17-2008, 04:04 AM

I am running the bfg 275 60r 15 with 20 psig. I guess I can crank it up to 28" as a test and see what happens. It appears the passenger spring is not quite as strong as the driver spring since i had to crank it up higher to get the same ride height as the driver or is the passenger side of the car heavier.

By axle bolts are you referring to all the bolts or is their one in particular.

I laid on the garage floor with a flashlight and to my surprise on the passenger side wheel well there appears to be a "clean" spot on the inner fender lip, but I have no idea how the tire sidewall could contact it. The suspension would have to really compress alot. There is no way the tread is contacting anything.

Ron61 · #6 (**permalink**) 11-17-2008, 04:42 AM

Just a suggestion and yo have most likely already did this, but have you checked the clearance from the side of the tire to the inside fender lip? I have seen a couple of cars where the clearance wasn't the same on both sides.

Ron

madmaxx · #7 (**permalink**) 11-17-2008, 08:12 AM

Ron 61,

I have no doubt the fender lips are not identicle, from the inside I could see slightly different radius. I am going to make it look like a jeep and really crank up on the ride height. If noise persist than I will know it is not the tire rubbing, if the noise goes away then solution is to lower until it rubs. Originally the ride height was 26.5" so I put anothe 1/2 inch.

In houston everything is built on clay mush, so when I say wavy roads I mean some pretty big dips, I would imagine in most cities and roads this would be a non issue.

MaSnaka · #8 (**permalink**) 11-17-2008, 01:55 PM

Just a couple suggestings, that clean spot under your fender...spray it with some flat black spray paint. See if it gets rubbed off again. Also when the suspension moves the tire clearances are going to change as a result of body roll. 275/60/15 doesn't sound too oversized. Something I noticed with those same tires was that with 28 lbs pressure you will be slipping and sliding. Much better to keep the pressure low like you have it.
I hope this helps. Good luck.

John

Blas · #9 (**permalink**) 11-17-2008, 02:16 PM

Take a look where the rear axles pass the frame on both sides. Any evidence of the boots hitting the frame sections there? You mentioned that your spring perch heights a quite different from left to right in back? How different are the exposed thread lengths on the shocks? Does the rear of the car seem to squat more on one side under hard exceleration? Good idea to spray over the rub spot that's there now and see if it reappears...Wheels and hubs are on tight I assume....27" is the suggested standard height for the car...
Calipers secure? Look inside the rime for any evidence of a caliper scraping on the inside of the rim.

madmaxx · #10 (**permalink**) 11-17-2008, 02:22 PM

Great suggestions, I am afraid to paint it black for fear I would get some on the paint, what I will do though is take some machinest bluieng and spear it on the fender, go for a ride and I should no pretty quick if my suspect area is for real.

All bolts, axles half shafts etc look perfect. How important is it to detach the sway bar when adjusting the height, I did not do that when I went from 26.5 to 27".

Once again these are some pretty healthy dips which cause the noise.

Blas · #11 (**permalink**) 11-17-2008, 04:06 PM

use a black magic marker. All you really want to do is to see if it rubs off again. No real need to undo the sway bar for that small an adjustment.

Poolw · #12 (**permalink**) 11-17-2008, 04:11 PM

You could use some chalk and see if it gets rubbed off.

Jerry Clayton · #13 (**permalink**) 11-17-2008, 04:19 PM

Or white shoe polish

madmaxx · #14 (**permalink**) 11-17-2008, 04:58 PM

Thanks everyone, I used some turtle wax and let it dry, did the trick. Went and did some 4x4 ing heard the noise and went home. Looked with a flashlight and sure enough at the top it was rubbed away, about 3/16 of an inch. I am currently at 27" with a full tank of gas, and not much adjustment left on the spring probably 1/2". I have to admit you really have to hit some substantial dips so I may just let it ride and least I know it is not a bushing or something else. The real solution is to machine the wheel adapter that has the drive pins to make a 1/4" thinner, this would pull the wheel assembly in and you could probably have the ride heigth at 26". I am glad I do not have the p295.

Madmiles442 · #15 (**permalink**) 11-25-2008, 08:53 PM

My shocks are adjustable in stiffness and if I have mine set too soft, they rub on larger dips. If I want the softer ride, I am more careful, or just stiffen the shock a couple of clicks.

madmaxx · #16 (**permalink**) 11-26-2008, 08:51 AM

At a wheel height of 27 3/16" of an inch zero rub on any dip regardless of severity. I found this out after the gas tank got to 1/2 full by gauge, probably 3/4 empty by volume since the tank is not a perfect box. Full tank of fuel drops it from 27 3/16" to 26 7/8" and only on the most severe dips and 45 mph will a slight noise be heard. Surprisingly I did not perceive a decrease in ride quality and for all practical purposes it feels better.

cdog · #17 (**permalink**) 11-28-2008, 11:46 AM

My 305's rubbed a little for years, especially with a full tank. Over big dips "zzzip". As long as it's minor, it won't cause any problems like paint spidering/blistering, etc. so long as it's MINOR and doesn't happen often.

I now have 295's with no issues.

Seagull81 · #18 (**permalink**) 11-29-2008, 10:27 AM

Madmaxx,
You are supposed to raise the tail hook before leaving the hanger!
Steve

madmaxx · #19 (**permalink**) 11-29-2008, 01:19 PM

LOL, with this cooler weather I know what you mean. Since I raised the height to 27 3/16 with a full tank of gas I almost forgot about this thread, not a whisper of the noise anymore.

PurpleVenom · #20 (**permalink**) 11-30-2008, 08:13 AM

Not being a superformance owner, I have a question. Where/how do you measure the ride height? Trying to imagine where you would measure 27".