Daveydave

Hey guys, I've been getting this weird "knock" sound when I drive over bumps. It literally sounds like there's something loose in the trunk that's hitting the hatch, but I've emptied the trunk out to be certain. Also I made sure that the jack is braced tight so it's not rattling around back there. So in doing some searching here, I've found a few threads that seem similar, relating to the suspension, but are coming from the front, not rear. Might not matter though, maybe the same parts either way. This thread:

https://www.rx8club.com/series-i-trouble-shooting-95/suspension-buckling-after-poor-alignment-autox-219251/

talks about possibly being one of the locking nuts on one or several of the front suspension adjustment points. Or maybe stabilizer bar end link, but I don't know if that is in the rear (as they were diagnosing a front noise).

Also, last time I had the car up on a lift, the guy noticed some dried grease coming from the rear left strut. Not fresh at all, but very thick when we scraped it off on our fingers, so it's nothing new apparently. But, could it be as simple as the strut needing replacement? Would that knocking noise happen? Can I verify that before just taking it somewhere to have it replaced?

I was hoping this weekend to jack up the rear of the car and look around the suspension and see if I can find anything loose or rusted out. If anyone knows what specific bolts I should be looking for, I'll search out pictures on the site or in the service manual PDFs.

Thanks guys.

paimon.soror

iTrader: (15)

I swear I have dealt with so many knocks in the car that I can attest that knocks can really come from anywhere if you arent meticulous about your modifications and making sure that you cover all bases when assembling everything! lol... anyway ... check the following

1. So you say your strut had some grease and possibly it bled. One easy (yet not always reliable) test is to open your trunk, bounce it up and down. Do you hear squeaking? Clunking? Binding? ... your strut is most likely shot. Do the same for the front, open the hood, place your hands on the front frame rail behind the radiator, bounce.

2. Check your front and rear swaybar endlinks. Are they stock? Aftermarket? Either way, make sure to get them good and tight. The swaybar has a good amount of play in its link holes, if you do not have the endlinks tight, you will get a knocking noise. Best bet is to go to the hardware store, grab some nice new nylock nuts, and torque them down to about 45ftlbs. This one is by far the most common source of knocks when going over small slow bumps.

3. This one was the most recent finding I had, and as stupid as it sounds, caused some crazy knocks in my car. The sump guard underneath the oilpan is held on by 5 bolts. Make sure they are tight to 20ftlbs. As strange as it sounds it does provide some structural benefits.

Start there.

Daveydave

Thanks for the quick reply! I should have noted that everything is stock on the car. I did try pushing up and down on the trunk to try and recreate the knocking, but no dice. I don't think I remember any excessive squeaking, but just "normal" shock noise. Good call on the endlinks. I'll scrounge up a good picture of those so I can zero in as soon as I get under this beast. And yes, it happens almost randomly over either small slow bumps, big ones, or sometimes just accelerating or turning. Getting worse (or more prevailant) so I need to get this situated quick.

Thanks for the great start!

PS. the sump guard would be in the front of the car, right? I'll check it though.

maskedferret

iTrader: (1)

I had something like this but in the front of the car and discovered it to be a loose alignment bolt or two. I don't know if the rear alignment bolts would have the potential to behave like this when loose, but it's worth a shot checking those.

paimon.soror

iTrader: (15)

Ah for some reason i thought this was in the S2 section, I dont believe your generation RX8 has the sump guard so that is one less thing to check.

Daveydave

I'll have to look those up as well. The endlinks in the rear look almost like those could be reached and tightened without even having to lift the car. At least in the photos (I'm at work, so I haven't tried looking under the car yet).

paimon.soror

iTrader: (15)

You can def get to them without lifting the car up. The front you can get if you turn the wheels to full lock, assuming that the endlink bolt doesn't turn when tightening (and you have smaller arms lol)

Also for what it's worth you might want to check the brackets that hold the sway bars in place as well. The rears should be at about 19ftlbs while the fronts should be at 30ftlbs.

Daveydave

Awesome, thanks. Based on what you've said, and what I'm picking up from symptoms in similar threads, I'm pretty sure this is what's happening. I'll keep you posted.

Daveydave

Well, I got underneath the back and checked the endlinks. Those guys are definitely bolted on tight! I decided to really jump up and down on the back just to see if I could re-create it, and I did hear a pop from the left side, but not quite the "knocking" that I hear when driving. I wonder if it's the strut that showed leakage?

paimon.soror

iTrader: (15)

By tight do you mean hand tight or checked-with-a-torque-wrench tight?

Also, take a look at your shock bodies ... any dried up grease on there? If it was leaking it would sure still be leaking unless all the fluid is gone, and that would be obvious as you would see some sagging.

Daveydave

Well, I tried loosening it with a socket wrench and it wouldn't budge... though I didn't throw all my strength in, I figured if it was that hard to loosen, it was tight. Maybe I should loosen them and screw them back to the recommended 45 ft lbs just to be sure.

There is dried grease on the body of the left rear shock (the same I had mentioned above). It didn't start this knocking until I had it in to Mazda to have the cat replaced. After that I heard it on the highway I brought it back to Mazda. That's when they had it up on the lift and he pointed out that there was dried up grease on the rear left strut and that might be where the sound was coming from. I thought it was strange that the noise wasn't there previously, and a little suspect, but who knows, maybe it was a coincidence that it showed up then. He said that because the grease was thick and dried up, it had been there for a while.

You mentioned sagging. Would the car be sagging to one side noticeably when looking at it from the rear? I'll look, but if it is, it's definitely not obvious.

paimon.soror

iTrader: (15)

Well if you heard it on the highway chances are then it isn't your endlinks. In my experience the endlink noises were audible only at very low speeds and uneven/crappy roads.

The sagging would be somewhat noticable ... i suppose you could just get your car on level ground and measure the distance from the center of the wheel to the quarterpanel. Shouldn't be too much of a difference.

Maybe you could grab a video/sound clip of the noise just to see what we are dealing with?

Daveydave

Interesting, ok. The knock is so random. It definitely happens during all speeds, but sometimes over large bumps it won't occur, and sometimes it knocks when I barely feel any bum at all (or none even). I would figure that if it was the strut bottoming out, it would only occur on larger bumps, and be louder the larger the bump was, but that could be just me. I was going to have my wife drive while I crawl back and open the divider from the back seat into the trunk and really listen to where it is. When I do that I'll take an audio clip. I'll measure the space from the wheel center to the quarterpanel tonight too, good idea.

Daveydave

Well, it's been a while since I posted, but here's what I found. I measured from the center of the hub to the bottom of the quarter panel on each side, and the side (left) that has the suspected leaky shock is 1/2" higher, which is kinda the opposite from what I would have suspected. I just found a thread on here that is someone having the exact same issue (https://www.rx8club.com/canada-forum-35/clunking-sound-rear-suspension-172674/) and am reading through it as we speak to see if there was resolve. One suggestion there was a loose/missing caliper bolt, so I'll need to check that.

More info about the knocking though. It really isn't JUST bumps, but also side-to-side movement (like sharp cornering). It really sounds like someone left a socket under the trunk lining and is just bouncing around back there with any g forces that push it!

USAFPilot11

iTrader: (5)

Hey all, I think I have a similar problem. My problem is when the weather is really cold. Say +/- 35 degrees.

When its that cold there seems to be a cracking/knocking noise coming from my rear windshield area. Once the car warms up, say 10 min of driving, the noise stops. The noise is also aggravated by torquing the suspension, like going over a speed bump or going over unlevel ground (my driveway is on a hill and doesn't meet the road very well).

My initial thoughts are that the glass is contracted because of the cold and isn't sitting in the frame well. But I just think that's a stretch.

After reading these posts, maybe its the struts? Idk. It's just annoying but liveable because it only happens when the car sits in cold weather for a long time.

I appreciate you guy's help.

Bladecutter

Have someone drive your car for you when its cold, while you sit in your back seat and look for the source of the noise. Have the center pass through to the back seats out, to help you hear if the noise is in the trunk somewhere.

If it is the window, take the car to a window shop, and pay them to remove, and reinstall the window. They usually use much better sealant than the factory does, just to prevent noise complaints from clients.

BC.

USAFPilot11

iTrader: (5)

Thanks BC. Yeah I will probably take it to a window place for them to check it out.

As for someone sitting in my car, I've done that with a non-expert friend. We determined it is not in the trunk but somewhere around the window area, but its very hard to determine the source.

I tried asking the dealer about it during my last oil change but they are usually douchebags about it and just blow me off. I have to say I love my RX8 but I haven't have very good dealings with Mazda Customer Service.

zoom44

well you should have your differential checked and probably have it serviced/fluid replaced.

and you should have the exhaust checked front to back to ensure its been properly mounted.

and you should ensure that the PPF has been properly secured. it must be loosened and then tightened following the correct procedure

zoom44

read this pdf about power plant frame installtion. it starts partway down the first page

AngelKiha31

Davey, I'd suspect your strut. Mine did the same last year. Sounds like a semi-random clunk, that usually happens on small bumps. Do a push and lift test on your rear bumper. Listen for the clunk and a bubbling hiss. If you hear either, it's most likely a strut.

Usaf, it's something to do with the rear window. Mine is the same. I think there was something mentioned in the main rattles thread in this forum that covers what it is. If I remember right, it's something to do with a mount, usually on the passenger side of the rear window, hidden by the head liner.

(COMBINED
Forgot to add that mine also happened while accelerating and some corners. It sounded like my jack was rolling around in the trunk. Checked the car at work, heard the bubbling hiss, but could never get it to clunk. Saw oil on my spring, determined it was the strut. Replaced the rear struts. No more clunk.

((EDIT: I admittedly had a little too much to drink and had struts on the brain when I was thinking shocks.))

Daveydave

I'm beginning to think that is it too. I've done the push test, but not the pull test too. I heard one faint clunk when I pushed with all my weight, but I don't remember hearing bubbling. I probably wasn't listening that close.

Did you replace the strut yourself, or have it done? If you had it done, about how much did it run?

Oh, if I just pick up a Monroe strut online, is it fine to just replace the offending strut, or is it something that needs to be in pairs?

Daveydave

Thanks for posting this... I'll take a look at the PPF to make sure it's secured properly.

USAFPilot11

iTrader: (5)

Thanks AngelKiha. I'll try to find that thread.

AngelKiha31

Ok... now that i'm totally sober and not posting on my damned cell phone, i'll expand and correct my previous posts... heh.

Turned out the clunking was just one of my shocks being blown. The hissing/bubbling was the noise the shock was making, as it had failed and the oil was mixing with air wherever it was leaking. The strut was totally fine, except the shock. I did catch it fairly soon after it failed, within an hour, so I did notice that there was l lot of fresh oil on my strut/springs/rims/tires. I don't know if you'll hear any bubbling, especially since the oil may have totally leaked out, but it'll be worth a try. If you don't hear anything, look up and feel up around the springs surrounding the shock. They should be relatively clean, and oil-free. If a spring is caked with oil/oily dirt, I'd bet you just blew a shock and the rest of the strut is in good condition. If that's the case, it's an easy fix to do. There are manuals online, but I lucked into a post that had the link to the following website, which is basically a step-by-step guide to replacing the shocks: http://www.hi-impact.org/ryang/modif...hock_rear.html

I'm honestly no mechanic, so don't take my thoughts as truth. I'd take it to a tire/suspension shop that you trust and have them inspect it. Also it'd be a good chance to get a quote. If I remember right, I was quoted $250 for a single shock replacement at the local shop. Honestly, I don't know if this was fair or not, but being about 250 miles from the nearest Mazda dealer, it seemed at least reasonable.

I replaced my own shocks, just a couple hours, a spring compressor, and parts. I think the total came to somewhere around $250 US for both rear shocks, and the compressor.

USAF:
Found it!!! Forgot that it was called: "Rattle Hunt"
https://www.rx8club.com/series-i-do-yourself-forum-73/diy-rattle-hunt-79235/page2/
You'll find the post you need at like 28 or 29.

Daveydave

Angel! You rock! Thank you for the link to the DIY! I'm really thinking this is it since the left rear shock is caked with oil. Old and dried, so it's been this way for a while I guess. I just bought the car 2 months ago 2nd hand, so who knows what potholes were hit to do that. Anyway, does that mean my car has been only supported by one shock absorber in the rear? Do I automatically need to swap them both out? Or is replacing the bad one is sufficient?

Also, I don't do any racing or anything, so just stock or equivalent would be fine for me. I have an 07 Sport model (I guess bottom of the line, no sunroof, cloth seats, etc). I was wondering which shocks I need though looking at this site: http://www.partsgeek.com/catalog/200..._absorber.html

They have normal suspension, sport suspension, and Special Tuned Suspension. All roughly the same price.