...its flippin annoying. at all speeds above, say, 80mph, whenever i let off the gass i get a horrible vibration coming from under the car. it sounds like a hurricane, literally, and shakes the be-jesus out of everyone inside (even scared a couple passengers). ther is no vibration/noise whatsoever if the car is accelerating, regardless of how hard it is accel. and there is also little to none when letting off the pedal at speeds at or below 65mph. the car seems fully functional, the rear end was replaced 5k miles ago (all new internals, but stock housing), but the sound has been there is some form for at least 10k mi. LCAs def increased the amount of noise and level of vibration, and the adj panhard rod corrected the violence of it and made it just an annoying sound more than anything.

please help, as soon as my car is out of the body shop i need to get this fixed.

new rear end needed (again)?
carbon fiber driveshaft fix it?
just an adjustment error?

i assume it is the driveshaft or rear end because it is based on speed, not rpm, that the sound grows


thanks,
Geoff

 

We cant fix your problem, take it to the dealer!

-Dan

 

<div class='quotetop'>QUOTE(stkdidy @ February 7, 2006, 4:07 AM) Quoted post</div><div class='quotemain'>
...its flippin annoying. at all speeds above, say, 80mph, whenever i let off the gass i get a horrible vibration coming from under the car. it sounds like a hurricane, literally, and shakes the be-jesus out of everyone inside (even scared a couple passengers). ther is no vibration/noise whatsoever if the car is accelerating, regardless of how hard it is accel. and there is also little to none when letting off the pedal at speeds at or below 65mph. the car seems fully functional, the rear end was replaced 5k miles ago (all new internals, but stock housing), but the sound has been there is some form for at least 10k mi. LCAs def increased the amount of noise and level of vibration, and the adj panhard rod corrected the violence of it and made it just an annoying sound more than anything.

please help, as soon as my car is out of the body shop i need to get this fixed.

new rear end needed (again)?
carbon fiber driveshaft fix it?
just an adjustment error?

i assume it is the driveshaft or rear end because it is based on speed, not rpm, that the sound grows
thanks,
Geoff
[/b][/quote]

A 2 piece driveshaft should reduce vibration not increase it since the center of the shaft is supported.

Is it an auto trans or a stick?
Does it have the dampers attached to the diff on the lca brackets?
They look like a chunks of cast iron.
Was the vibration there with the stock gears?
Was it done under warranty by the dealer?
How many diff rebuilds does the person who rebuilt your diff do each year?
What brand of gears do you have?
FRPP, Motive, Richmond
It also sounds that it may be a diff adjustment such as backlash.
Was gear marking compound used to verify the contact pattern?
What was the backlash set at?

I'm just guessing but here are a couple of theories.

You said that the diff internals were replaced 5,000 ago and the problem originated 10,000 ago or more.

How long ago did you install the sportlines?

The sportlines drop the car almost 2" which would drastically change the pinion angle.
I would install an adjustable upper control arm which also has a pinion snubber.
I have a 1" drop and a Steeda adjustable UCA in mine.
You can clearly see that the diff makes contact with the snubber from time to time.
I would also install a set of lower control arm relocation brackets.
This will help bring the angle of the LCAs back to their stock angle.
BMR just released a set of bolt in lower control arm relocation brackets.
This would probably a good idea since you're not sure if the housing will be replaced in the future.

 

It is because of your gear choice, with the 4.30 gear and probably a 27ish" tall tire you have exceeded the critical speed of the stock shaft.

 

<div class='quotetop'>QUOTE(thump_rrr @ February 7, 2006, 3:29 AM) Quoted post</div><div class='quotemain'>
A 2 piece driveshaft should reduce vibration not increase it since the center of the shaft is supported.

1 Is it an auto trans or a stick?
2 Does it have the dampers attached to the diff on the lca brackets?
They look like a chunks of cast iron.
3 Was the vibration there with the stock gears?
4 Was it done under warranty by the dealer?
5 How many diff rebuilds does the person who rebuilt your diff do each year?
6 What brand of gears do you have?
FRPP, Motive, Richmond
7 It also sounds that it may be a diff adjustment such as backlash.
8 Was gear marking compound used to verify the contact pattern?
9 What was the backlash set at?

I'm just guessing but here are a couple of theories.

You said that the diff internals were replaced 5,000 ago and the problem originated 10,000 ago or more.

10 How long ago did you install the sportlines?

11 The sportlines drop the car almost 2" which would drastically change the pinion angle.
12 I would install an adjustable upper control arm which also has a pinion snubber.
I have a 1" drop and a Steeda adjustable UCA in mine.
You can clearly see that the diff makes contact with the snubber from time to time.
13 I would also install a set of lower control arm relocation brackets.
This will help bring the angle of the LCAs back to their stock angle.
BMR just released a set of bolt in lower control arm relocation brackets.
This would probably a good idea since you're not sure if the housing will be replaced in the future.
[/b][/quote]
1 stick
2 no
3 no
4 no, dealership would do it (for 2x the price of any other good shop) but wouldn honor warranty on it
5 MANY
6 frpp
7 what is that?
8 i believe so
9 no idea
10 15-20k miles ago, no wobble til relatively recently tho
11 drop is well over 2in (almost 2.5)
12 what is a pinion snubber?
13 this is on the short list, but car is in the shop for body repair


btw, ill have a dealership look at it, but 80-100$ per hr labor is rediculous considering there is no warranty on my rear

<div class='quotetop'>QUOTE(Mike@PowerHouse @ February 7, 2006, 6:49 AM) Quoted post</div><div class='quotemain'>
It is because of your gear choice, with the 4.30 gear and probably a 27ish" tall tire you have exceeded the critical speed of the stock shaft.
[/b][/quote]

80mph with 4.30s is like 95 with 3.55 when it comes to shaft speed...stock it didn wobble at all, even at 130

 

It is because of the drop.Under load it is fine, but when you let off, The drive shaft is to straight and will float slightly causing your vibration.You have to adjust the pinnion angle to correct this.

 

Stkdidy If you PM me your email address I'll send you the driveline pdf files. It won't allow me to post them for some reason.



If you look at the pic above the rubber piece you see pointing downward is the pinion snubber. The picture is of the CHE Performance adjustable upper control arm.

With the amount of drop the sportlines provide an adjustable upper control arm and a set of lower control arm relocation brackets would be my first investments.

If you still have the same problems i'd then remove the diff cover and check the gear contact patern.
Backlash is a little harder to check if you don't have the proper tools for it.