okay, heres a question...

MustangChris · Mar 2, 2009

alright everyone.. after doing my suspension i feel alot more of the road and whatnot... anyways. when im on the highway and i get up to a pretty good speed (70+) i hear a vibration run through my car. its VERY noticeable. it happens about every 4 seconds, and it feels like its "rolling" through the chasis...

I will first feel it in the steering wheel (heavy vibration) and then it will make my rear view mirror vibrate (like my subs are bumpin') and i dont feel it in the wheel anymore... then i feel it in the butt of my seat and it goes away... 4 seconds or so later, it starts at the front and rolls on back... i drove on multiple pavements, so i know it wasnt the road i was on...

heres a list of junk i did to my car:
99 cobra steering rack
03 cobra a arms
bbk gripp springs
used tokico shocks/struts
prothyne bushings all around (front and rear)
aluminum rack and pinion bushings
bump stop kit
solid motor mounts
new end links (for a dropped car)
caster camber plates
used screamin deamon coils
used thomson wires
new NGK plugs
full tune up
drilled front rotors
new front brake pads
new yokohoma all season tires
professionally aligned
solid steering shaft

and thats all the major stuff... i wont mention junk like "a/f gauge"

....

anyways, the reason im asking is because its VERY noticalbe. and it doesnt speed up or slow down with the car... (i go 80, it still goes through the car every 4 seconds or so... i got 70 it still goes every 4 seconds) im at 3,000 RPM at 70 MPH (4.10s) so, does that have something to do with it? when i speed up or slow down (in turn, changing the RPMs) it still happens...

it drives me crazy! >.<

anyways, any thoughts, or anywhere to start looking?

thanks,
Chris

CC'S95GT · Mar 2, 2009

i thinking it's something with the bump steer kit or cc plates.

MustangChris · Mar 2, 2009

how would i inspect those for improper install and/or malfunctioning?

CC'S95GT · Mar 2, 2009

why did you use a bump steer kit. those are usually for slammed rides or full race applications. they should have come with destructions on how to set them up. i don't think they're as easy as bolt on and go. there is some tweeking with the spacers for those.

Codycougar91 · Mar 2, 2009

check the driveshaft u joints just in case, they can cause lots of vibration if theyre on their last leg

MustangChris · Mar 3, 2009

Codycougar91 said:
check the driveshaft u joints just in case, they can cause lots of vibration if theyre on their last leg

i do hear a loud "thud" when i shift... whether soft shifting or hard shifting... i assumed it was my u joints...

how do i inspect them to see if they are bad?

DESERTCOX05 said:
why did you use a bump steer kit. those are usually for slammed rides or full race applications. they should have come with destructions on how to set them up. i don't think they're as easy as bolt on and go. there is some tweeking with the spacers for those.

i lowered my car and was told it was a good idea to put them on... i let my friend (who has more experience with suspension work than i do) install those. it holds an alignment okay and stearing is fine. so, i dont know how else to check the bump steer kit...

CC'S95GT · Mar 3, 2009

mine is lowered on sportlines and all my suspension is still stock. i feel i need cc plates. but not a bump kit because my car is not darty when i'm cornering or going over bumps. the bump kit is supposed to correct the steering angle of your tie rods by putting them back to level after lowering the suspension. i am by far no expert on this. i know only what i've read at other sites. for as many people who have lowered their stangs the number who have bump steer kits is very low. ck your u-joints for slop. and do more reasearch on the bump kit

MustangChris · Mar 3, 2009

how do i check my u joints for wear and tear?

Dalamar · Mar 3, 2009

That is strange.
vibration is typically associated with the transmission/driveline.
did you change your pinion angles?
since you didn't do your driveline, are your wheels possibly out of balance?

could it be something with your motor mounts?

MustangChris · Mar 3, 2009

i dont even know what a pinion angle is

although i can guess

lol.

tranny is clearly getting tired and old... 114k miles... it has alot of play in the gears, and grinds into every gear if i drive it when its cold...

the wheels were just mounted and balanced, should i take them back and have them checked?

the motor mounts were my first guess, but i dont know why it would stay about the same pattern (which happens to be very long and drawn out... lasting roughly 1 second and taking roughly 4 seconds to reoccur) when i speed up or slow down (or change engine RPMs.)

drivetrain modifications:
stock flywheel (machined down 1 time)
spec stage 2
hurst short throw
cobra bob shifter gasket
driveshaft safety loop
FRPP aluminum driveshaft
FRPP 4.10s
eaton LSD 8.8 diffy
moser 31 spine axles
FRPP axle girdle
Royal Purple ATF in tranny
Royal Purple 70w90 diffy fluid
Filtermag Magnet in the diffy

the only thing new to my set up (drivetrain wise) is the shifter gasket, the diffy cover, and the diffy magnet... everything else has been on the car, and none of that should make that vibration...

im leaning towards getting the tires re-balanced... :-(

2slo95fiveoh · Mar 3, 2009

MustangChris said:
i dont even know what a pinion angle is

although i can guess lol.

tranny is clearly getting tired and old... 114k miles... it has alot of play in the gears, and grinds into every gear if i drive it when its cold...

the wheels were just mounted and balanced, should i take them back and have them checked?

the motor mounts were my first guess, but i dont know why it would stay about the same pattern (which happens to be very long and drawn out... lasting roughly 1 second and taking roughly 4 seconds to reoccur) when i speed up or slow down (or change engine RPMs.)

drivetrain modifications:
stock flywheel (machined down 1 time)
spec stage 2
hurst short throw
cobra bob shifter gasket
driveshaft safety loop
FRPP aluminum driveshaft
FRPP 4.10s
eaton LSD 8.8 diffy
moser 31 spine axles
FRPP axle girdle
Royal Purple ATF in tranny
Royal Purple 70w90 diffy fluid
Filtermag Magnet in the diffy

the only thing new to my set up (drivetrain wise) is the shifter gasket, the diffy cover, and the diffy magnet... everything else has been on the car, and none of that should make that vibration...

im leaning towards getting the tires re-balanced... :-(

A Tire imbalance wouldn't fade in and out at the same speed/rpms. It would be more of a constant vibration..
A on/off issue like this would be something more along the lines of a transmission or driveshaft issue..
My car used to do something similar to this.. It sort of felt/sounded like i was going over rumble strips every 4-5 seconds.
I since then have replaced both my transmission (with a TKO) and my stock driveshaft (with an Alum. one).
Now i no longer have that symptom, and those are mainly the only modifications to the driveline (other than the engine)

uncltrvlnmatt · Mar 4, 2009

The type of vibration you are talking about sounds like its in the drive line. But you should go over all the suspension mods just for safety.

To check the u-joints jack up the back of the car. (USE JACK STANDS) crawl underneeth and lift on the u-joints, twist the drive shaft, and if you want you can put a bar between the u-joint and yoke for some extra leverage. You are looking for play at the caps where the u-joint goes into the yoke.

When you are twisting and turning the drive shaft try and feel or listen for binding in the needle bearings. If there is any binding replace them. If you hear anything replace them. If you hear something it may have a crunching sound, most likely it will be very faint and hard to hear.