So what's this all about?

Jeb_Bush_2000 · 05-02-2002, 11:44 AM

I have a driveline vibration that I attributed to a bad rear U-joint.

At highway speeds, between 60 and 80mph, when I let off the gas, my car shudders violently. Putting the clutch in makes no difference. When the throttle is open, the vibration ceases, and it stops completely at WOT or near-WOT. Those are the symptoms of a bad U-joint, right?

Well I dropped the car off the other day to get some work done, along with replacing the rear U-joint. My mechanic took it apart, and was going to replace it, but he told me it "looked perfect" and it would be a waste of money to replace. So my question is, what else could cause a vibration like that? I would assume it's the driveshaft, but wouldn't it vibrate all the time if it was out of balance? I always thought the bad U-joint caused that vibration because when you applied torque to it (opened the throttle), it shifted back into position and remained relatively balanced.

I know it's not the rear-end. I know it's not the tires. I know it's not a steering problem. I know it's not a transmission problem. I know it's not engine-related.

I am totally stumped.

HiFlow5 0 · 05-02-2002, 12:00 PM

I'd go and get rid of that junk stock driveshaft and get a nice aluminum one. What are you running for gears? I just had 3.73's installed and there was a whole lot more vibration in the driveshaft area cause the driveshaft is spinning more then with stock gears, especially at higher rpms and highway driving. Go with an aluminum driveshaft and you'll be happy, I was!

Jeb_Bush_2000 · 05-02-2002, 12:06 PM

Stock driveshaft, stock 2.73's. Hell, I even have that 20lbs weight attached to the pumpkin.

And the funny thing is, above 80mph, it doesn't vibrate at all. I guess it could be related to harmonics, maybe?

USMC302 · 05-02-2002, 12:33 PM

harmonic balancer may be a possibilty but most likely the driveshaft, they do get out of balance and more commonly with gear installs. Ford recommends upgrading to the aluminum ds when gear changing. Good luck and let us know the outcome.

Jeb_Bush_2000 · 05-02-2002, 03:05 PM

It's not the harmonic balancer.

Falcons Talon · 05-02-2002, 03:16 PM

When I had my '84, and I would hit between 60 and 80, the car would shake as well, and after 80, I was ok...In my case, it was the front tire and alignment....more blame to the tire.
On my '92, when I would hit 80, the car would rattle to hell, and I couldn't go any higher without fear of shaking my car to pieces...Ticked me off everythime this stupid little prsim gsi would pass me screaming at 85 after work. IN this case, it was the forward U joint. smiling slyly After I fixed it, I cruised at 80 until the turd burglar passed me, and then I flew right by him. He now takes an alternate route home. Check your tires again. Mine didn't look bad, but they were.

Good luck...hope this helped.

Jeb_Bush_2000 · 05-02-2002, 04:12 PM

I just got the car back a few minutes ago, and I'll double-check the front tires. All four are probably going to get replaced in a year anyway.

As a side note, my car sounds very strange with the Summit cat-back. Between the roaring of the police fan clutch and the whistling of the cold-air kit, it has sort of an exotic sound to it. Weird.

QKHORSE · 05-02-2002, 06:40 PM

well i had a similar problem like u do and it was the muffler touching the driveshaft. When i hit around 70-80 the muffler vibartion would cause the muffler to touch against the driveshaft.

Ian

Jeb_Bush_2000 · 05-02-2002, 09:48 PM

Well, the vibration's gone. Go figure.

Falcons Talon · 05-02-2002, 10:23 PM

Did you find any fur in the engine compartment?

Jeb_Bush_2000 · 05-02-2002, 11:25 PM

LOL. No, I didn't. Why?

Coupe5oh · 05-03-2002, 12:02 AM

Same exact thing happened to me, it was my driveshaft bolts loose, they were so loose that they were about to fall out, i posted about this, and it did the same thing you described, ask the mechanic if he removed the d/s and reinstalled it when he looked into your u-joints, i also recomend the alum d/s it was worth 169$

btw the police clutch fan failed me, just my experience with it, it may have just been old and worn out, but it came apart at a low speed and smashed through my radiator.

Jeb_Bush_2000 · 05-03-2002, 12:31 AM

Did yours make a really loud whooshing noise when it was cold, too?

Aww, crap, I forgot about the driveshaft bolts. That must've been it. He said he took the U-joint out and decided it was in fine condition.

05-02-2002, 11:44 AM	#1
Jeb_Bush_2000 Registered Member Join Date: Jul 2001 Location: Taxachusetts Posts: 374	So what's this all about? I have a driveline vibration that I attributed to a bad rear U-joint. At highway speeds, between 60 and 80mph, when I let off the gas, my car shudders violently. Putting the clutch in makes no difference. When the throttle is open, the vibration ceases, and it stops completely at WOT or near-WOT. Those are the symptoms of a bad U-joint, right? Well I dropped the car off the other day to get some work done, along with replacing the rear U-joint. My mechanic took it apart, and was going to replace it, but he told me it "looked perfect" and it would be a waste of money to replace. So my question is, what else could cause a vibration like that? I would assume it's the driveshaft, but wouldn't it vibrate all the time if it was out of balance? I always thought the bad U-joint caused that vibration because when you applied torque to it (opened the throttle), it shifted back into position and remained relatively balanced. I know it's not the rear-end. I know it's not the tires. I know it's not a steering problem. I know it's not a transmission problem. I know it's not engine-related. I am totally stumped. __________________ Stripped-down '93 LX Coupe -- "Danielle" R.I.P. 05/30/02 "I've seen some crazy stuff in my life, but that...was...AWESOME!!! Oh, sorry about your car, man."

05-02-2002, 12:00 PM	#2
HiFlow5 0 Registered Member Join Date: Mar 2000 Location: Springfield, Ma, usa Posts: 706	I'd go and get rid of that junk stock driveshaft and get a nice aluminum one. What are you running for gears? I just had 3.73's installed and there was a whole lot more vibration in the driveshaft area cause the driveshaft is spinning more then with stock gears, especially at higher rpms and highway driving. Go with an aluminum driveshaft and you'll be happy, I was! __________________ NewEngland Auto www.baystategearheads.com -91 Mustang Coupe, ex 4cyl (sold) -99 F150, 3" lift, 35" Procomps, Magnaflow exhaust

05-02-2002, 12:33 PM	#4
USMC302 Registered Member Join Date: Apr 2001 Location: Gallatin, Tn Posts: 1,326	harmonic balancer may be a possibilty but most likely the driveshaft, they do get out of balance and more commonly with gear installs. Ford recommends upgrading to the aluminum ds when gear changing. Good luck and let us know the outcome. __________________

05-03-2002, 12:02 AM	#12
Coupe5oh Registered Member Join Date: Nov 2001 Location: SanAntonio, Tx Posts: 734	Same exact thing happened to me, it was my driveshaft bolts loose, they were so loose that they were about to fall out, i posted about this, and it did the same thing you described, ask the mechanic if he removed the d/s and reinstalled it when he looked into your u-joints, i also recomend the alum d/s it was worth 169$ btw the police clutch fan failed me, just my experience with it, it may have just been old and worn out, but it came apart at a low speed and smashed through my radiator. __________________ Police package 5spd 90 Lx, Stock original motor, 3.27grs, BM fan, fms 10.5 clutch, D&D quadrant, and adjuster, ADS chip, 180 stat, mac cai, mac h-pipe, mac subframe connectors, ASP crank pulley, ripper shifter, 26x10.5 M/T sport pros welds. 246 hp according to analyzer Race weight: 3,120 E.t-13.57 with 26x10.50's e.t. streets. 1.88 60' mph- 99.92 mph

05-02-2002, 12:06 PM	#3
Jeb_Bush_2000 Registered Member Join Date: Jul 2001 Location: Taxachusetts Posts: 374	Stock driveshaft, stock 2.73's. Hell, I even have that 20lbs weight attached to the pumpkin. And the funny thing is, above 80mph, it doesn't vibrate at all. I guess it could be related to harmonics, maybe?

05-02-2002, 03:05 PM	#5
Jeb_Bush_2000 Registered Member Join Date: Jul 2001 Location: Taxachusetts Posts: 374	It's not the harmonic balancer.

05-02-2002, 03:16 PM	#6
Falcons Talon T.P.M. President Join Date: May 2002 Location: Brownsville Posts: 265	When I had my '84, and I would hit between 60 and 80, the car would shake as well, and after 80, I was ok...In my case, it was the front tire and alignment....more blame to the tire. On my '92, when I would hit 80, the car would rattle to hell, and I couldn't go any higher without fear of shaking my car to pieces...Ticked me off everythime this stupid little prsim gsi would pass me screaming at 85 after work. IN this case, it was the forward U joint. smiling slyly After I fixed it, I cruised at 80 until the turd burglar passed me, and then I flew right by him. He now takes an alternate route home. Check your tires again. Mine didn't look bad, but they were. Good luck...hope this helped.

05-02-2002, 04:12 PM	#7
Jeb_Bush_2000 Registered Member Join Date: Jul 2001 Location: Taxachusetts Posts: 374	I just got the car back a few minutes ago, and I'll double-check the front tires. All four are probably going to get replaced in a year anyway. As a side note, my car sounds very strange with the Summit cat-back. Between the roaring of the police fan clutch and the whistling of the cold-air kit, it has sort of an exotic sound to it. Weird.

05-02-2002, 06:40 PM	#8
QKHORSE Registered Member Join Date: Apr 2002 Location: Ottawa,ONT Posts: 12	well i had a similar problem like u do and it was the muffler touching the driveshaft. When i hit around 70-80 the muffler vibartion would cause the muffler to touch against the driveshaft. Ian

05-02-2002, 09:48 PM	#9
Jeb_Bush_2000 Registered Member Join Date: Jul 2001 Location: Taxachusetts Posts: 374	Well, the vibration's gone. Go figure.

05-02-2002, 10:23 PM	#10
Falcons Talon T.P.M. President Join Date: May 2002 Location: Brownsville Posts: 265	Did you find any fur in the engine compartment?

05-02-2002, 11:25 PM	#11
Jeb_Bush_2000 Registered Member Join Date: Jul 2001 Location: Taxachusetts Posts: 374	LOL. No, I didn't. Why?

05-03-2002, 12:31 AM	#13
Jeb_Bush_2000 Registered Member Join Date: Jul 2001 Location: Taxachusetts Posts: 374	Did yours make a really loud whooshing noise when it was cold, too? Aww, crap, I forgot about the driveshaft bolts. That must've been it. He said he took the U-joint out and decided it was in fine condition.