Lots of vibration from my newly purchased fastback (3000-4000rpm)

DarkoStoj

DarkoStoj

Founding Member
Sep 4, 2002
929
13
39
Detroit
#1
I just bought a decently built 66 fastback. I am having some pretty bad vibrations between 3000 and 4000 rpm.

It has a built 351cleveland
toploader 4 speed (the shifter rattles like mad)
narrowed 9" rear with 3.89 gear and detroit locker
subframe connectors.
and it has this crazy ladder bar setup.

It still has leaf springs, but the PO also put on these ladderbars that are bolted onto both sides of the axle then bolt to the frame of the mustang. I've never seen a setup like this.

The shifter also rattles like mad and is driving me CRAZY!

any ideas? :)
 
#2
need more info.

You say it vibrates at that rpm, but in gear or out of gear? Will it vibrate while sitting still.....by just revving the engine up? If so have you tried pulling spark plug wires one at a time and found one that does not change the way it runs? Any plugs fouled? tried jacking on the engine (with a jack) to confirm all your motor/transmission mounts are good?

Just a start for you!
 
#3
it is driveline vibration.

If I'm driving in any gear I get vibes starting at 3k rpm, and they go away after 4k rpm.

I had a 2hr drive on the expressway and I could either drive at 60mph and 3000 rpm or 80mph and 4k rpm. Anything between that there was a lot of vibration...I could feel it through the car and expecially through the shifter handle (and it was also rattling along with vibrating)
 
#7
does it still have the original 2 piece driveshaft, the tube in a tube surrounded by rubber kind? if so the the tubes have probably slipped causing the yokes to be out of phase, could also just be that if it is a one piece replacement shaft that the tokes were welded out of phase. either way it sounds to me like that is the problem, yokes out of phase.
 
#10
i idled it while in neutral sitting still and it seemed like any rpm past 2,000 the car would vibe. Now this didn't seem all that bad, but there was some I noticed.

I would think that since it happens between a certain rpm it has to be something with the driveline angle, but i'm not really sure.
 
#14
alright so I took it out for a long drive today and I think i've ruled out it being a driveline vibe.

Considering it vibes at certain RPM's and not certain speeds should rule out the fact that the vibration is coming from the driveshaft angle, or bad ujoint, etc.

I was revving it while parked and I did get some vibes. Then I revved it while driving with the car in neutral and i got the bad vibes again.

I guess I just didnt want it to be a flywheel problem so I was trying to rule it out because I REALLY don't want to pull the trans.

Now I am going to check the motor mounts, then the harmonic balancer....and lastly the flywheel.

How would I be able to check whether my balancer and flywheel are for the right balance.

And how hard would pulling a toploader/4speed be with a cleveland and long tube headers (full 3" exaust) in a 66 :(
 
#15
I have had the same problem three times with different clevelands. The first one either the flywheel or bolts on the pressure plates were off balance. By that I mean the bolts were different resulting in an imbalance present whether the clutch is in or out or whether your car is in neutral. I replaced both bolts and flywheel and it was fixed.

The second time it was the aftermarket bellhousing that was slightly misaligned. Whenever you install an aftermarket bellhousing you must align it within 3thousands of an inch dead center. Another symptom is the trans sometimes is hard to enter a gear or pops out of gear.

The third time, which is now, has proven more elusive. I have an aftermarket bellhousing, aftermarket March pulleys, and new clutch and pressure plate.
I am going to first remove the belts to see if some of the pulleys are the source. Next I will check the dampener. If not, next I will remove the pressure plate, clutch and flywheel and reinstall the trans to see if the vibration is there. If its gone, through process of elimination I will install the items to see when it returns. Hard job to do, but it has to be done. I will have the pressure plate zero balanced and the flywheel checked.
 
#17
may be a shot in the dark, but if you pull the flywheel make sure its for a 351. My car when it originally was restored had a 351 put in by the original owner, and he had put the BOSS 302 flywheel back in which caused some pretty wild vibration. Just something to think about.

Good luck.
 
#18
BADBOSS said:
may be a shot in the dark, but if you pull the flywheel make sure its for a 351. My car when it originally was restored had a 351 put in by the original owner, and he had put the BOSS 302 flywheel back in which caused some pretty wild vibration. Just something to think about.

Good luck.
Click to expand...
what kind of vibration was it? Similar to what I'm experiencing?
 
#19
DarkoStoj said:
what kind of vibration was it? Similar to what I'm experiencing?
Click to expand...


sorry, wish i could be more helpful on your question. My car was restored back to show quality in 1983, and the previous owner really messed it up. The guy who restored the car made the statement in an article on the car and the problems it had in the MAY issue of Mustang Monthly 1983. I have spoken to this guy on the phone, but didn't ask about this detail.

Just figured it might be something to check. Dont cut any corners with that baby. They are precious.
 
You must log in or register to reply here.

Similar threads

R
  • Locked
66 Mustang Fastback Pro Touring/Street
Replies
10
Views
9K
Classic Mustangs For Sale
raw23062
R
dodgestang
  • Locked
1965 Mustang Fastback
Replies
0
Views
8K
Classic Mustangs For Sale
dodgestang
dodgestang
DarkoStoj
How much is my built A code 66 fastback worth?
Replies
16
Views
1K
Classic Mustang Specific Tech
nmk_61802
N
DarkoStoj
my built 4v 351c is a dog
Replies
32
Views
8K
Classic Mustang Specific Tech
Hack
Hack
Top Bottom
Back
Forums
Menu