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View Full Version : So...our rear ends are cheap



Tonglebeak
04-12-2008, 06:56 PM
Well, as some of you know, my subs absolutely destroy my rear end when they're blasting. Huge vibrations, lots of icky noise as a result, etc.

So today I decide to remove the rear end to figure out the priimary cause of this. I first removed the reverse light; that initially seemed like the biggest culprit to me. Removed that, had the subs going softly and still had bad vibrations. So I removed the tailights, and saw that the "metal" span above the reverse light, is bolted on behind the taililight (and two bolts behind the reverse light). So I removed that...wtf, it's plastic! Jesus christ this thing was as light as a feather, so much for having a piece of extra armor in the event of being rear ended...
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So I had the subs go again, still vibration...I narrow it down, The rear panel (back wall of the trunk) is as thin as a sheet of paper., and resonates like no ones business. Right up against the deck lid. Holding the trunk tighter reduces the vibration considerably. I adjusted the rubber stops on the trunk lid so more of the llid's weight (don't forget I have a spoiler on it too) rests, and that helped. Now I need to know how to make the deck lid hold even closer to the rear panel: this requires moving the lid just a hair towards the front end of the car. Any ideas on this?

The bad thing is that it still won't fully correct the problem. The tailights, reverse light, and the plastic span are still mounted solely to the rear wall, which resonates like no ones business, so if that shakes, everything else does as well.

P.S. Good luck if you get rear ended, you got loads of plastic and paper thin metal to save you!

LordDurock
04-12-2008, 09:04 PM
thats okay about being rear ended the car will crumble up to the rear axle.. but try putting all the tali lights back to gether with foam. and glue some rubber to the front of the trunk

Prospeeder
04-12-2008, 09:24 PM
you need to go buy some rolls of dynomat and do the entire trunk and you wont have any more rattling problems

86euro
04-13-2008, 02:21 AM
The rear of your car is built very stout compared to all newer cars. Trust me.

jinxtigr
04-13-2008, 02:28 AM
I have a wide-open air intake and glasspack muffler (soon to be a better but still high-flow design) so if I can see the guy coming I won't get rear-ended. *woosh!* ;)

85 Holiday
04-13-2008, 03:02 AM
Yep, it is pretty thin up top back there. Dynamat should help... maybe you should get your box tuned differently?

Tonglebeak
04-14-2008, 12:53 AM
Box isn't going to do anything different, the trunk just can't handle the pressure.

It really seems to me that it's so bad, any kind of sound deadener isn't going to have any effect. I just have that feeling.

85 Holiday
04-14-2008, 01:10 AM
Box isn't going to do anything different, the trunk just can't handle the pressure.

It really seems to me that it's so bad, any kind of sound deadener isn't going to have any effect. I just have that feeling.

Box could definitely make a difference. Who made yours? how is it made sealed, ported? How big? Tuned to what? etc etc etc. And no they way the panels/lights are mounted like pegs so they'll shake no matter what. All you'll really accomplish is muffling it a bit.

Tonglebeak
04-14-2008, 01:14 AM
It's a ported box, not sure what it's tuned for. The box was made by MTX for those subs, have 200w rms going to each sub, which have a 94db efficiency I believe. I had sealed pioneer premiers before, with only 89db efficiency and 350w going to each sub, and the effect was similar.

Prospeeder
04-15-2008, 07:25 AM
Box isn't going to do anything different, the trunk just can't handle the pressure.

It really seems to me that it's so bad, any kind of sound deadener isn't going to have any effect. I just have that feeling.

why wouldnt it, its MENT to deadent sound and retain the sound inside the car, theres no "pressure" your car cant deal with, its called vibrations from all the sound rattling it not pressure, try the dynomat and youll be fine.

ochy38
04-15-2008, 02:09 PM
think that rubberized undercoating works? ive been thinking about it considering dynamat is so expensive

86euro
04-16-2008, 12:45 AM
Rubberized undercoating is thick, but only compared to the paint/primer that it's intended to protect from rocks and other flying debris in wheel wells, underbodies, etc. It doesn't really deaden anything.

Techfizzle
04-16-2008, 02:15 AM
I hate the bottom of floors rusting on cars. Would putting truck bed liner on the under side of the car help?

collegiate89
01-20-2009, 07:31 AM
So I know this is an old thread, but if anyone is looking for some cheap sound deadener, there is B-Quiet which is about 100 bucks for 50sq feet.
http://www.b-quiet.com/extreme.html (B-Quiet)

bubblebob88
01-20-2009, 09:00 AM
I had a friend that had some real hard beating subs, around his trunk keyhole was all sunk in and looked wrinkled on the bottom of his trunk keyhole. He put about three trunk lids on that Cutlass, his lastest setup just warped everything. I believe he never used dynomat, until recently and his trunk hasn't gotten any worse.

dcjredline
01-20-2009, 12:19 PM
Dont bother your not going to teach him anything he knows it all. Why ask Tongle if when people give you suggestions you just shut them down? All the suggestions are good ones here (well the sound deadening one is about the only one) I have been doing mobile electronics for over 15 years now most of that proffessionally. I even went to school for it and got certified 10 years ago. Your on the right track finding things that are rattling and stopping them. Using dynamat or the other stuff suggested is what you should use when you find a rattling panel.

Resonant Frequency is the reason your car is rattling. Look up the deffinition and you will see what I mean I am not going into the whole deff here. Your cars resonant frequency is prolly similar to most of the notes in the music you listen to and thats why its soo bad. Stop most of the rattling and youll be much happier.

CamoDeafie
01-20-2009, 03:45 PM
what about cutting a piece of plywood board to perfectly fit the trunk walls, and putting deadening on the inside of it, and putting a sort of soft foam between it and the trunk wall, and then having a custom made trunk box that'll tidy up the trunk appearance-wise, and lots of deadening, and then that should help? its an idea i've seen somewhat similar in most of the highly modified trunks for music and entertainment....

Tonglebeak
01-20-2009, 11:23 PM
Holy shit this thread is old...anyways I have a hundred square feet of fatmat. Have had it for a while, just waiting to install it.

And since when do I shoot down everyone's suggestions?

02GTP
01-21-2009, 03:18 AM
its a late 80's/early 90's GM, what do u expect of build quality?

CamoDeafie
01-21-2009, 04:06 AM
its a late 80's/early 90's GM, what do u expect of build quality?

better than the same generation Japanese imports ;) :P lol. i know.... the mid 90s was a milestone for japanese car quality.....and then right after GM axed the A-body platform, GM quality goes down.....coincident? (i'm aware, they went up ding the 2000.....in fact, from my observation, the GM vehicles of 2000-current are far more reliable than Mopar's....)

02GTP
01-21-2009, 04:18 AM
here is the low down. Japanese>Ford>GM>Mopar. that is y gm is down the shitter because they built complete garbage from the late 70's till late 90's/early 2000 even though some of their cars are still questionable. i work for ford but am a gm guy. i dont care for fords build quality but their reliability is actually pretty good. i think the 2007+ gms are great but i fear its too late for the public to catch on. u should see some of the tsb's for GM. "porous engine blocks" 3.1's with 4 pistons of one kind and two of the other. how the hell does that happen?

performance cars, GM still rules. ZR1>All.

Tonglebeak
01-21-2009, 04:27 AM
Times like these I wish we could lock our own threads. This thread is old news and doesn't apply to squat anymore.

dcjredline
01-21-2009, 03:11 PM
performance cars, GM still rules. ZR1>All.

Much as I hate to admit it, the Viper ACR stomps on the ZR1 all day.

LordDurock
01-21-2009, 03:34 PM
yea the viper is one sick driving mechien no fluff to it

02GTP
01-21-2009, 04:40 PM
not really, the viper is faster by .4 seconds around a 13 mile track. the zr1 has a higher top speed, accelerates faster, and brakes better. it is also far more liveable and comfortable, not a track toy like the acr. the acr also has stickier tires than the zr1 and i would venture to say that a zr1 with equal tires would be just as fast or faster.