Weird pulse, only in 5th....

bloopbloob

Member

Sep 27, 2006

578

4

16

Alberta

Jan 3, 2008

#1

• Jan 3, 2008

• #1

i took my first highway trip about a week ago since my 3:73 swap (~2 mos. ago). i noticed a lot of vibration in my shifter (only in 5th), and a weird humming sound (only in 5th) on the highway. whats weird is that i kind of assumed it may have been my driveshaft, but it seemed rpm independent. just the same humming pulse at different rpms, and only in 5th? i feel stupid using this to describe it , but it basically hummed to the beat of the guys head bopping on night at the roxbury........

any ideas what would cause this?

 

91 HATCH

Banned

May 17, 2007

262

0

0

illinois

Jan 3, 2008

#2

• Jan 3, 2008

• #2

my old fox done this because the bushings on upper control arms were bad

if yours are good unbolt driveshaft and spin it 180 and bolt it back up then test it again

 

bloopbloob

Member

Sep 27, 2006

578

4

16

Alberta

Jan 3, 2008

#3

• Jan 3, 2008

• #3

that sounds like a good idea to check out, but why is it only happening in 5th? in 4th at the same rpm that it happens at in 5th, the humming isn't there??? and wouldn't a driveshaft problem be rpm dependent? thats what's messing me up. i swear its the driveshaft, but it only happens in 5th gear, and the noise doesnt change with rpms........?

i dont think it's anything to do with my c/a's because it used to be smooth on the highway before the gear swap, and i havent checked lately, but they were good a couple months ago.....

 

91 HATCH

Banned

May 17, 2007

262

0

0

illinois

Jan 3, 2008

#4

• Jan 3, 2008

• #4

Do you have loctite on the driveshaft bolts at the rearend these come loose on there own if not loctited

 

Roland69

Sergeant Tangnet

Sep 17, 2005

2,867

3

58

Port Elgin, Ontario

Jan 4, 2008

#5

• Jan 4, 2008

• #5

the driveshaft is not rpm dependant just speed...try finding out what speed in 5th it does this and gear down to 4th and go the same speed if it still does it it's likely something with the driveshaft

 

ninety15.0

New Member

Mar 10, 2004

1,336

0

0

Jan 4, 2008

#6

• Jan 4, 2008

• #6

My car does the same thing. Once i get to about 80-85mph in 5th it will start this light harmonic hum. I have a new balanced DS and a balanced motor with a new harmonic balancer. I chalk it up to the 165k stock T-5. Rear control arm bushings are a good idea. i will be adressing this problem this spring/summer and i'll let you know if it fixes anything.

either way i still drive the car 350miles at a time back home to MA once a month. No problems yet.