Knock in the rear end.

I bought this car over a month ago and I haven't been able to drive it because of a coolant issue that I couldn't fix because of an injury at work. This weekend I took care of the coolant issue. So I drove it to work today for the first time and it's making a knocking sound in the rear of car. It is rotational, if I speed up the speed of the knock increases as well. However, it doesn't always make it. On the way to work there were times it was very pronounced and then there were times you couldn't here it at all. There aren't any vibrations either. Also, when I puch the brakes the knock stops.

Yesterday I did find out that some of the wheels were missing a lug nut. So I am going to go get some lug nuts on the way home and re-torque all the lugs to spec when I get home. I just wanted some ideas of what other things I should check.

Thanks,
Clint

Sound like your exhaust is loose...

If the exhaust is aftermarket the exhaust might be bumping up against the body due to lack of clearance. A couple things to check for:

Is it more prominant when the car is warm?
Does it happen when you first give the car gas?

I would suggest you go under and take a look... The engine will torque the exhaust upwards when you give it gas... Also check to see that your engine mounts are still good.

The exhaust is stock and it does it regardless of whether the car is warm or not. It doesn't seem more prominent under acceleration. Someone else suggested I check the exhaust. I hope that is all it is. I'll get under there tonight and check it.

if you can make a vid and record the sound, then we can give you a better diagnostic.

I don't have access to a video camera.

Sorry... I missed the rotational...

If you are TT I would check the joints on the driveshaft...

[Edit: actually I would say it's too hard to say at this point... There are too many things it could be... I would first look at the exhaust because that is easy, but it could be anything from suspention to drivetrain)

Someone has suggested warped rotors, which is a possiblity considering that the wheel is missing a lug nut. I guess I'll have to pull the rotor tonight and check it as well.

Someone has suggested warped rotors, which is a possiblity considering that the wheel is missing a lug nut. I guess I'll have to pull the rotor tonight and check it as well.

well you said it happend when you accelerated the engine.....Right?

well you said it happend when you accelerated the engine.....Right?

That depends on what you mean. It only makes the sound when the car is in motion. As I speed up the knock speeds up, as I slow down the knock slows down, and if I push the brakes the knock stops.

can it be that your brake pads have no hardware on them? they might just be loose. have you used y0ur ebrake and has the rattel gone away?

it really could be anything, i had that happen to me once, come to find out, i had a fat pice of metal stuck on the side of my tire on the inside. whenever i moved it just clunked on the ground.
just gotta lift her up and check it out

Yeah, tough to say, at first I thought driveshaft u-joints or carrier bearings, but the fact that it stopped when you apply the brakes would lead me to check the brakes first. A missing lugnut could technically have caused a warped rotor, something could be interfering with the caliper. Also might not hurt to check the wheel bearings, and make sure your wheels are balanced. But check the brakes first.

Yeah, sadly Checker can't get the rotors, AutoZone is trying to sell me their cheap brand, and PepBoys wants $107 per rotor. :screwy:

I think I am just going to find some good blanks from a 3S vendor.

Yeah, sadly Checker can't get the rotors, AutoZone is trying to sell me their cheap brand, and PepBoys wants $107 per rotor. :screwy:

I think I am just going to find some good blanks from a 3S vendor.

HOw did you come to the conclusion that it was indeed your rotors?and if it is your rotors, ive seen some for 60 each online from brembo.

if you can't find anything cheaper, this (http://www.3si.org/forum/showthread.php?t=305809) might still be going on

HOw did you come to the conclusion that it was indeed your rotors?and if it is your rotors, ive seen some for 60 each online from brembo.

Well, first off. All the wheels are missing one lug nut. This causes improper torque distribution which causes warped rotors. Also, a friend of mine that has owned a few Stealths had a problem pretty much identical to mine and said that his rotors were warped.

if you can't find anything cheaper, this (http://www.3si.org/forum/showthread.php?t=305809) might still be going on

Nope, closed, bummer. :frown:

Anyhow, last night I picked up some lug nuts on the way home and put them on. This morning on the way to work I almost couldn't hear it. It made the noise briefly, two maybe three times on the way and it was pretty quite. So I am going to replace the rear rotors, looks like I get to brake shopping. I would just get the ones at AutoZone, but I don't know how much I would trust Duralast.

Also, I wasn't sure how much to torque the lug nuts last night so I went with what all my other cars have been which is 95 ft/lbs. Is that the correct amount for the 3S?

Thanks for all the help guys,
Clint

Yeah, sadly Checker can't get the rotors, AutoZone is trying to sell me their cheap brand, and PepBoys wants $107 per rotor.

I think I am just going to find some good blanks from a 3S vendor.



c'mon now. this opportunity is rife with "forced upgrade" !!! how bout some cross drilled/slotted rotors? :iceslolan

Also, I wasn't sure how much to torque the lug nuts last night so I went with what all my other cars have been which is 95 ft/lbs. Is that the correct amount for the 3S?

Thanks for all the help guys,
Clint

i don't think anyone torque their lug nuts to spec. i just tighten them with an impact wrench. but if you're really curious about the torque spec, i can look it up in the service manual.

^ If you get rotors that are vented through slots and holes don't you want them cast that way? (rhetorical question) I think there was recently a discussion about this on AF.

c'mon now. this opportunity is rife with "forced upgrade" !!! how bout some cross drilled/slotted rotors? :iceslolan

.

Dont they just collect brake dust?

Huh? Are you referring to drilled/slotted rotors? Because they work great.

the purpose of drilling holes and cutting "slots" or grooves into a brake rotor is to increase the surface area of the object and thus allowing is to cool more effectively and efficiently. think of it like a heat sink for a computer.

the purpose of drilling holes and cutting "slots" or grooves into a brake rotor is to increase the surface area of the object and thus allowing is to cool more effectively and efficiently. think of it like a heat sink for a computer.

^This statement is wrong^. How is surface area increased when you make holes and there is less for the pad to grab on to? Your statement will fit great if we were talking about BIGGER ROTORS, then you will have GREATER SURFACE AREA (http://www.math.com/tables/geometry/surfareas.htm). I rest my case:licka:

No the assertation is correct... Linebckr is refering to "surface to air" and not "swept area".

The problem is not the increase in surface area but the decrease is mass and therefore easier to "heat soak" as well as "heat cycling" which can cause the holes to aggrigate stress and cause fractures.

This is primarily why competition race cars have moved to slotted over cross-drilled.

Cross drilling and/or slotting reduces out-gassing and cleans the pad from debree which actually increases the quality of pad to calibre contact. But it comes at the expense of pad and rotor life.

The reason there is a debate is that the effect is very small compared to SS lines, bigger rotors and better pads.

I know that they can work better (at the expense of quickly worn pads) but I was just saying don't you want them to be cast like that (the holes) instead of drilled like some of the cheap ones. But no, I never said they didn't work well.

^This statement is wrong^. How is surface area increased when you make holes and there is less for the pad to grab on to? Your statement will fit great if we were talking about BIGGER ROTORS, then you will have GREATER SURFACE AREA (http://www.math.com/tables/geometry/surfareas.htm). I rest my case:licka:

hey, genius. next time you call me out, make sure you're right and not making a fool of yourself. i know my stuff, and so does 2old. we're still waiting to see what you know :rolleyes:.

i never said anything about area for the pad to grab. that's common sense, and any moron knows that. the issue at hand is cooling and the escaping of gases produced by pad-to-rotor friction during braking. that's why cross drilled/slotted rotors were created.

now if you want to significantly increase stopping capability, then you increase the size of your rotors, but most importantly increase the size and/or number of pistons in the brake caliper.

No the assertation is correct... Linebckr is refering to "surface to air" and not "swept area".

The problem is not the increase in surface area but the decrease is mass and therefore easier to "heat soak" as well as "heat cycling" which can cause the holes to aggrigate stress and cause fractures.

This is primarily why competition race cars have moved to slotted over cross-drilled.

Cross drilling and/or slotting reduces out-gassing and cleans the pad from debree which actually increases the quality of pad to calibre contact. But it comes at the expense of pad and rotor life.

The reason there is a debate is that the effect is very small compared to SS lines, bigger rotors and better pads.

thanks, 2old :).

yes, the debate rages, but i've heard from several people that by adding SS braided brake lines and high performance pads (EBC green/red or some other pad), they notice a decrease in distance travelled (vehicle) when braking and less brake fade. of course, this is a good way to increase performance on a budget.

if you have no budget, then upgrading rotors and calipers is the way to go.

:meant: :comprage1 I dont think i made a fool out of my self, but i was right and so was 2old. im going to stop the this hijack:nono: And you said was

c'mon now. this opportunity is rife with "forced upgrade" !!! how bout some cross drilled/slotted rotors? :iceslolan no more HIJACK

c'mon now. this opportunity is rife with "forced upgrade" !!! how bout some cross drilled/slotted rotors? :iceslolan

i don't think anyone torque their lug nuts to spec. i just tighten them with an impact wrench. but if you're really curious about the torque spec, i can look it up in the service manual.
Man, I need a "forced upgrade" like I need a hole in my head. I don't have to money for that right now. I just put the exhaust on the GTC and I need to take it back to get the downpipe welded on then the correct donut gets here, plus I need to get my SS brake lines put on the GTC and I need to get the 60k done on the Stealth. Besides, I don't want crossdrilled rotors. In my opinion they are a marketing ploy. Outgassing isn't really a problem on newer pads unless you are buying crappy ones. Crossdrilling reduces the contact patch between the pad and the rotor. Also, since you have removed material it reduces the rotors ability to hold heat so that heat is transferred to the pad, then the caliper, then the brake lines, and then the fluid. This can cause the lines to balloon and the fluid to boil and then you have brake fade. I think you're better off getting bigger "blank" rotors, SS flex lines, some performance pads, and some good DOT3 or DOT4 fluid. Slotting is useful, but being my DD I'd rather not be replacing pads that often.

As for the lug nuts, could you check your manual? I don't have one and I would like to make sure they are all torqued to spec so I don't warp the new rotors when I put them on.


As of this morning it seemed to only make the noise at around 40MPH. I think I am just going to wait for Checker to get the rear ones in. They weren't expensive and they were a good brand, otherwise I'll just get some Brembo blanks for $100 from IPS.

Thanks,
Clint

i checked the manual. lug nut torque spec is 87-101 ft-lbs.