Lots of vibration after changing u joints in driveshaft

ogvenom

Member
Jan 25, 2022
19
5
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USA
1996 Mustang Cobra SVT 5 speed manual, all stock except 4:10 gears, bassani x pipe and flowmaster mufflers on Eibach lowering springs.

I removed my driveshaft, took it to a local driveshaft shop and they replaced the u-joints and re-balanced the driveshaft. I put it back on and now I have vibration at any speed and it feels as if the clutch isn't fully grabbing, like my motor is working hard but it just doesn't match the amount of grab and go that it should have. Before I removed the driveshaft, i had marked it in place to re-install in the same position, but the driveshaft shop cleaned the driveshaft and wiped off the mark.

Does anyone have any ideas on what would cause that vibration and feeling of not grabbing?

Another note, the day before I removed my driveshaft, i let a friend drive and he pinned 2nd gear to above 6k and then missed and grind 3rd REALLY BAD, he's not my friend anymore, lol. Not sure if that alone would do anything but if anyone has some thoughts please let me know.

Another note, I removed my exhaust at the same time as driveshaft and then i put it back on, not sure if that is of importance but just in case!

Thank you!
 
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I feel the vibration more from the front of the car, just feel it throughout, not necessarily just in the seat. It doesn't feel driveline related because I feel it when revving in neutral.

I drove the car maybe one time after that miss shift, so honestly I couldn't really tell you if I noticed anything. I feel like I did notice it right away but it still drove so I didn't think much of it at the time.

I'm thinking of rotating the driveshaft where its bolted in the rear. I was reading that it could be the installation position, so i was going to try rotating 90 degrees and running it, until it feels best.
 

I'm thinking of rotating the driveshaft where its bolted in the rear. I was reading that it could be the installation position, so i was going to try rotating 90 degrees and running it, until it feels best.
This is not a bad idea. It will make it better, worse or do nothing, and it will not be costly to rule out a possibility.
Does it vibrate in N while not moving? What about while in N while moving?
Does RPM change the vibration?
Checking for codes for a misfire or similar issue would be my next step without more info.
 
So I turned the driveshaft 90 degrees and it may have made the drive smoother, but it did not fix the vibration issue.

I can feel the vibration slightly when in neutral, not rolling, just idling. But only because I know what i'm looking for, but the vibration seems slower.

The vibration feels the same as above, when rolling downhill in neutral, with no gas applied.

In neutral, not rolling, i give it gas and the vibration increases with RPM's, you can pretty much feel it right away.

I checked for codes and none came up.

Do you know how to tell if the harmonic balancer has slipped? Here is a photo i took...


IMG_7814.jpg
 
If you can do it yourself replace your balancer. It's probably in need anyway. I touched mine gently on the side while idling and could feel it. Plus you could look down and possibly see it off. A little off is a lot off. My car was much better after a fresh one.
 
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After the in-depth description, it’s something from the clutch forward.
The balancer is a likely suspect. Too bad there is not a cylinder balance test like OBD1.
Don’t overlook the mounts.
 
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After the in-depth description, it’s something from the clutch forward.
The balancer is a likely suspect. Too bad there is not a cylinder balance test like OBD1.
Don’t overlook the mounts.
Could a bad mis shift or a stupid burnout have caused the balancer to slip?

I'm thinking about ordering clutch, flywheel, fork, adjustable cable, along with main seal and new hardware, but its going to cost a pretty penny. Is there anything I should do first? Maybe tear it down and look at it or would you recommend just changing it all, along with the balancer?
 
Could a bad mis shift or a stupid burnout have caused the balancer to slip?

I'm thinking about ordering clutch, flywheel, fork, adjustable cable, along with main seal and new hardware, but its going to cost a pretty penny. Is there anything I should do first? Maybe tear it down and look at it or would you recommend just changing it all, along with the balancer?
I
Could a bad mis shift or a stupid burnout have caused the balancer to slip?

I'm thinking about ordering clutch, flywheel, fork, adjustable cable, along with main seal and new hardware, but its going to cost a pretty penny. Is there anything I should do first? Maybe tear it down and look at it or would you recommend just changing it all, along with the balancer?
I’m concerned that it seems off power OR the clutch is slipping, especially combined with the vibration. I’d want to narrow it down before replacing parts.
Here is how I would check my clutch. There might be a better way.

Park the car with nothing ahead of it.
Put on the parking break.
Start it, put it in second, then release the clutch and gas like a normal start. The car should die hard.
Repeat in first. If it still runs, the clutch is slipping badly. Then is it an adjustment or worn out? I hope there is an inspection spot you can get to.
 
I

I’m concerned that it seems off power OR the clutch is slipping, especially combined with the vibration. I’d want to narrow it down before replacing parts.
Here is how I would check my clutch. There might be a better way.

Park the car with nothing ahead of it.
Put on the parking break.
Start it, put it in second, then release the clutch and gas like a normal start. The car should die hard.
Repeat in first. If it still runs, the clutch is slipping badly. Then is it an adjustment or worn out? I hope there is an inspection spot you can get to.
So i tried the clutch test, here is what happened.

I started the car on a flat surface, put on the parking brake. Put it in second and released the clutch and gave a little gas, the car died. Then I tried again because I think I didn't give it as much gas as i normally would.

So I repeated the same steps, this time slightly increasing amount of gas while releasing clutch, and the car started to drive.

I then tried again in first gear and it started to drive.

I took the car for a 5 mile drive on the freeway and got up to about 70MPH. Came home and parked and noticed a slight burning smell, like something is getting hotter than normal, but couldn't pinpoint it. Not sure if I was just making that up or not, but it did seem to have a new smell.

Another thing to note, all my gears are feeling slightly more difficult to get into, like I have to notch my way into each gear, where before it would slide right in.

I'm thinking of replacing the harmonic balancer this weekend, just because it probably needs it anyway. But I don't believe that is going to resolve the issue, since I also feel like theres just not as much grab when i have the clutch fully out.
 
So i tried the clutch test, here is what happened.

I started the car on a flat surface, put on the parking brake. Put it in second and released the clutch and gave a little gas, the car died. Then I tried again because I think I didn't give it as much gas as i normally would.

So I repeated the same steps, this time slightly increasing amount of gas while releasing clutch, and the car started to drive.

I then tried again in first gear and it started to drive.

I took the car for a 5 mile drive on the freeway and got up to about 70MPH. Came home and parked and noticed a slight burning smell, like something is getting hotter than normal, but couldn't pinpoint it. Not sure if I was just making that up or not, but it did seem to have a new smell.

Another thing to note, all my gears are feeling slightly more difficult to get into, like I have to notch my way into each gear, where before it would slide right in.

I'm thinking of replacing the harmonic balancer this weekend, just because it probably needs it anyway. But I don't believe that is going to resolve the issue, since I also feel like theres just not as much grab when i have the clutch fully out.
The smell is the clutch got a bit warm doing that. I think you can rule out a slipping clutch!
You might need the parking break adjusted. Being able to drive off was not one of the expected outcomes. But that’s not the cause of your problems.