Foxbody Vibration At High Speed

[Wetblanket]

Where do you feel it the most...center console...rear of car...steering wheel ? I've seen some weird stuff in my years as a technician. Sometimes tires can have imperfections in the radial belt that can cause vibrations at speeds over 45mph. The only way to find out is with a road force balance. All shops don't have that type of balancer but it is the best. I've had instances where the tires have balanced to zero with a conventional balance but the customer still had vibration issues. Once we put it on the road force balancer we found we had to rotate the tire on the rim in order to counter out of roundness in the tire.

The issue with conventional tire balancers is they don't simulate load on the wheel. The road force machines actually put a load on the rim and tire and measure the weight and how far out of round the wheel tire combo is.

Like every one else has said...including you. If it started when the clutch was done then it probably has something to do with that. If it doesn't change in or out of gear...or on or off the gas...then you can almost cancel out the trans and rear. Axles and flanges can also bend causing vibrations that don't change except for speed.

at 50mph you're not spinning the motor at 5000rpm. at 50mph you should be somewhere around 2000rpm. Load is load and rpm is rpm. So, 2000 rpm in 3rd gear is like 2000rpm in 4th and 5th. The wrong flywheel will shake the teeth out of your mouth at the same rpm.

I had a car that had a broken factory plastic fan blade. That thing shook worse than a misfire and solid motor mounts. Check the fan blades. While jacking letting the motor tilt back to remove the trans its pretty easy to hit the shroud and crack a fan blade... Trust me...I've been there and done that.

Tires brand new and brand new roadforce balance. I don't have a factory fan but the vibration is really the mid to rear of the car you feel it on your butt more than anything but the mirror will be shaking bad so it runs through the whole car

 

[Wetblanket]

Where do you feel it the most...center console...rear of car...steering wheel ? I've seen some weird stuff in my years as a technician. Sometimes tires can have imperfections in the radial belt that can cause vibrations at speeds over 45mph. The only way to find out is with a road force balance. All shops don't have that type of balancer but it is the best. I've had instances where the tires have balanced to zero with a conventional balance but the customer still had vibration issues. Once we put it on the road force balancer we found we had to rotate the tire on the rim in order to counter out of roundness in the tire.

The issue with conventional tire balancers is they don't simulate load on the wheel. The road force machines actually put a load on the rim and tire and measure the weight and how far out of round the wheel tire combo is.

Like every one else has said...including you. If it started when the clutch was done then it probably has something to do with that. If it doesn't change in or out of gear...or on or off the gas...then you can almost cancel out the trans and rear. Axles and flanges can also bend causing vibrations that don't change except for speed.

at 50mph you're not spinning the motor at 5000rpm. at 50mph you should be somewhere around 2000rpm. Load is load and rpm is rpm. So, 2000 rpm in 3rd gear is like 2000rpm in 4th and 5th. The wrong flywheel will shake the teeth out of your mouth at the same rpm.

I had a car that had a broken factory plastic fan blade. That thing shook worse than a misfire and solid motor mounts. Check the fan blades. While jacking letting the motor tilt back to remove the trans its pretty easy to hit the shroud and crack a fan blade... Trust me...I've been there and done that.

Tires brand new and brand new roadforce balance. I don't have a factory fan but the vibration is really the mid to rear of the car you feel it on your butt more than anything but the mirror will be shaking bad so it runs through the whole car

 

[90sickfox]

Does your trans leak at the rear seal ? A tail shaft bushing can cause a vibration, too. Usually, that would change with load also...ie. on and off the gas in gear. It might be worth bit to pull the trans and check the flywheel and clutch. If you know someone that knows how to use a dial indicator you could have them check axle run out.

What happened when the clutch was replaced ? Was it worn out ?

 

[Wetblanket]

Does your trans leak at the rear seal ? A tail shaft bushing can cause a vibration, too. Usually, that would change with load also...ie. on and off the gas in gear. It might be worth bit to pull the trans and check the flywheel and clutch. If you know someone that knows how to use a dial indicator you could have them check axle run out.

What happened when the clutch was replaced ? Was it worn out ?

It was real work out like it went out on me while driving

 

[General karthief]

You need to pull the trans and check the clutch assembly and flywheel.
Can you check your receipt and confirm what flywheel you got?
Like I said before there are 2 302's and 2 flywheels and they are balanced different.

 

[Davedacarpainter]

Honestly though, wouldn't a 28oz flywheel shake the crap out of the poor engine?

It wouldn't matter if it was idling or running at 5k (not that it would rev that high at all with a 28oz instead of the 50oz).

@mikestang63 ?

 

[General karthief]

I worked on a older stang that had a roller engine in it with the wrong flywheel it idled ok but anything above it felt almost like a miss, it did shake badly, when you put it in gear (automatic trans) it would vibrate, again kinda like a miss, I imagine a stick would be worse? Heavier flywheel.
I think he has eliminated common things, it started after clutch change, new flywheel from O'Reillys I think. I also suspect he didn't mark the driveshaft when he removed it, been there did that once.

 

[mikestang63]

Honestly though, wouldn't a 28oz flywheel shake the crap out of the poor engine?

It wouldn't matter if it was idling or running at 5k (not that it would rev that high at all with a 28oz instead of the 50oz).

@mikestang63 ?

He couldnt rev that thing up with the wrong balanced flywheel. It would shake like a paint can at Home Depot.

 

[Wetblanket]

He couldnt rev that thing up with the wrong balanced flywheel. It would shake like a paint can at Home Depot.

It doesn't happen with rpms at all it's all speed related

 

[Davedacarpainter]

It doesn't happen with rpms at all it's all speed related

That's what i thought you were saying.

that doesn't leave a lot for it to be. You have your wheels and tires balanced properly. It does the vibration no matter what gear your in starting at a certain speed, not engine rpm, that kind of takes out the worry of the pilot bearing. So transmission forward is ok and your wheels are ok. Not much left between those two points.

You have a tailshaft housing with its bushing and seal, the driveshaft with u-joints, and if you screwed with it, the pinion flange/pinion nut/crush sleeve and pinion gear. Did you take the pinion flange off for some reason?

As far as that goes, did you leave the rear end on the car during this?

When you dropped the transmission, did you install a new tailshaft housing seal and bushing? Like @90sickfox mentioned, this could produce a nice amount of vibration that would travel right through the new crossmember.

You said you had the driveshaft balanced and runout checked, right?

We really are getting past my limits knowledge here with this one. I suppose it's possible that some other thing just had bad timing to go out on you too, but i doubt it.

It just sounds like this would be in the driveshaft area of the driveline, from the ts housing to the pinion gear.

I'm going to invite a couple more people to your thread to see what they might know. @madmike1157 @Boosted92LX @hoopty5.0 @RangerJoe

 

[General karthief]

Did you try moving your driveshaft around to the next bolt hole?
If it's speed related it will likely be driveshaft tires/wheels bent axle or drums/rotors
I only talk about the clutch assembly and flywheel because you said that it started after you changed it.

 

[General karthief]

Ok let me ask this, does it oscillate or is it constant, does it get more pronounced the faster you go?

 

[Boosted92LX]

If it's a speed related vibration, especially on a car with a factory driveshaft, it's a 98% chance that driveshaft is the culprit. The balance on them from the factory was terrible, and they are terrible about throwing weights, resulting in an enormous buzzing vibration. I tried three different factory driveshafts in my car before giving up and buying a new aluminum ford racing unit. They are worth every penny. Installed it and the vibration went away and never returned. Time to bit the bullet it sounds like.

 

[Davedacarpainter]

If it's a speed related vibration, especially on a car with a factory driveshaft, it's a 98% chance that driveshaft is the culprit. The balance on them from the factory was terrible, and they are terrible about throwing weights, resulting in an enormous buzzing vibration. I tried three different factory driveshafts in my car before giving up and buying a new aluminum ford racing unit. They are worth every penny. Installed it and the vibration went away and never returned. Time to bit the bullet it sounds like.

He already has an aluminum ds that he had balanced.

 

[General karthief]

He says he got new ujoints and a rebalance on a aluminium driveshaft.
Trans bushing?
Bent axle?
I suggested to start with reindexing the driveshaft.
Maybe jack up the rear off the ground and put it gear and spin the drivetrain. see if anything looks out of wack

 

[Boosted92LX]

He already has an aluminum ds that he had balanced.

"An aluminum driveshaft" that someone "had balanced" is not the same as a new ford racing driveshaft. I've paid shops to balance things for me that were waaaay out of spec because the shop sucked. That's typically the first thing to check. It could be a separated tire, balanced or not, will still raise heck going down the road.. and tire shop guys aren't all rocket scientists.. the flywheel can cause a vibration, but the car will be way diwn on power, and the vibration will be rpm related, not speed.

 

[hoopty5.0]

Re-clock it 90 degrees at a time until it goes away

 

[General karthief]

I agree with the balancing act, lucky we have a good local shop, I mentioned the driveshaft move earlier, hopefully he's in a warm climate to work on it and his hands are not frozen to the driveshaft, that will cause a vibration.

 

[Wetblanket]

Ok let me ask this, does it oscillate or is it constant, does it get more pronounced the faster you go?

It gets worse the faster. And it started after the clutch job so I would take the bent acle out of the picture cause it didn't bend an axle in between that time. I'm wondering if I should just go head and buy a brand new aluminum driveshaft but I'm worried I'll pay 300$ and still have the same exact problem and I never took the pinion thing off I'm sorry I really have no clue about rear ends the pinion is the thing the ds connects to? Am I right I don't mean to sound like an idiot but I'm still learning the more I learn the better and thanks for all the replys I've been working a lot lately and haven't had enough time to get under the car. But should I go ahead and buy a new ds if clocking it doesn't work

 

[Davedacarpainter]

It gets worse the faster. And it started after the clutch job so I would take the bent acle out of the picture cause it didn't bend an axle in between that time. I'm wondering if I should just go head and buy a brand new aluminum driveshaft but I'm worried I'll pay 300$ and still have the same exact problem and I never took the pinion thing off I'm sorry I really have no clue about rear ends the pinion is the thing the ds connects to? Am I right I don't mean to sound like an idiot but I'm still learning the more I learn the better and thanks for all the replys I've been working a lot lately and haven't had enough time to get under the car. But should I go ahead and buy a new ds if clocking it doesn't work

Yeah, the pinion flange is that disc on the rear end that the drive shaft bolts too.

Your questions aren't stupid, everyone learned about these things at one time or another, this is just your time.

I'm going with the ds being the problem. Do like suggested and try clocking it first.