Driveline Vibration

[SteveWK]

Been a while since I posted, but I read nearly every post here. I should write up all the mods that have worked for me and those that haven't, but time has been an issue. The list is long.

Here is my problem: Under acceleration the car vibrates very noticeably starting around 5,800 RPMs to redline. I can feel it in the shifter and feel it through the seat. It is completely RPM dependent. Speed does not matter nor does the gear, just RPM. It is worse under load. I noticed this problem several years ago when I had a BMR K member installed. I chalked it up to the near lack of motor mounts on the K member. It was bad enough that I had the stock K member put back on which greatly improved the situation. But now it seems to be getting worse. The car has 21K miles and the stock clutch.

I have performed the following troubleshooting:

1) With the transmission in neutral and the clutch depressed (disengaged), increasing the RPMs to about 6,500 yields no unusual vibration. Silky smooth for the most part.

2) With the transmission in neutral and the clutch engaged, increasing the RPMs to about 6,500 yields very noticeable vibration starting about 5,800 and can be felt in the shifter and resonates through the seats. It is worse under load.

I'm thinking either the clutch has increasingly gone out of balance or the the input shaft to the transmission is hosed in some fashion or the trans mount is bad. I have open tracked the car. It has been driven hard but never abused. The fact that I still have the stock clutch at 21K miles and Vans 13-6 kit on the car is testament to that.

Any ideas?

Steve

 

[MastaAce03]

Exhaust leak or your exhaust touching something underneath? I had a similar issue and found my exhaust had marks of rubbing against my torque arm. You may not have a torque arm but definitely something I’d check.


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[SteveWK]

I do have a Griggs torque arm. Actually it is the Griggs gr40ss setup. The torque arm and watts link are the best mods yet. I will double check the exhaust.

 

[SteveWK]

Hmmm, something else I should check out. See attachment.

 

[MastaAce03]

I also have the same Griggs set up. I had to get some custom exhaust work done to keep the piping away from the torque arm.


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[Catmonkey]

Based on your description, I'm guessing the pilot shaft bushing is toast.

 

[SteveWK]

Thanks for the input. I'm going to get the exhaust straightened out, but I do think in the end the transmission will be coming out. I don't know of anyone else having a trans problem or a pilot bearing failure ... sigh.

 

[Snoopy49]

I sounds like something went south with one of your clutch plates. The only time you have no vibration is when the clutch plates and input shaft are not spinning.

 

[Snoopy49]

Based on your description, I'm guessing the pilot shaft bushing is toast.

If it were bad enough, it could throw off the input shaft alignment enough to cause the clutch plates to be off center when they engage. That would shake things up.

 

[tomshep]

Out of pure simplicity, I would look at the balancer and mark the outer ring to inner ring with a line of paint, if these use a two-piece design.

After that, I am in agreement with a pilot bearing. Maybe the front bearing on the input shaft. Clutch somehow out of balance. Those would be my focus.

Tom

 

[SteveWK]

Based on your description, I'm guessing the pilot shaft bushing is toast.

I have the Ford maintenance manuals on CD and replacing the pilot bearing looks pretty easy to me. I will get the correct tools to do it.

I sounds like something went south with one of your clutch plates. The only time you have no vibration is when the clutch plates and input shaft are not spinning.

This is what I am hoping. Don't know if I should replace the stock unit with another stock unit or an aftermarket. Given I don't know what has failed, I might wait until I get it apart.

If it were bad enough, it could throw off the input shaft alignment enough to cause the clutch plates to be off center when they engage. That would shake things up.

Love this information. This is what I don't know. Would like to learn more about this kind of thing.

Out of pure simplicity, I would look at the balancer and mark the outer ring to inner ring with a line of paint, if these use a two-piece design.

After that, I am in agreement with a pilot bearing. Maybe the front bearing on the input shaft. Clutch somehow out of balance. Those would be my focus.

Tom

I have an ATI 10% balancer on the car now. Not sure what I should be looking for with the paint marks, but I'm assuming to see if they are split in some fashion. Incidentally, the 10% overdrive is going to come off at some point and a stock ATI is going on. Too much boost with stock exhaust on 91 octane, imho.

Thanks for all the great info.

Steve

 

[Snoopy49]

This is a picture of a 426 Hemi harmonic balancer. Notice the alignment mark, if the line doesn't line up with the notch in the center hub, the outer ring has shifted its position and the balancer needs to be replaced or repaired.

 

[Catmonkey]

I have the Ford maintenance manuals on CD and replacing the pilot bearing looks pretty easy to me. I will get the correct tools to do it.

Yeah, the hard part is removing the transmission. It's a tight squeeze and has to be chocked just right to pull it out. It could be clutch discs like Snoopy points out too. Read that shop manual carefully. Temporarily installing longer bolts for the k-member at the struts can only help removal.

 

[SteveWK]

Yeah, the hard part is removing the transmission. It's a tight squeeze and has to be chocked just right to pull it out. It could be clutch discs like Snoopy points out too. Read that shop manual carefully. Temporarily installing longer bolts for the k-member at the struts can only help removal.

Well dang, the K member and engine needs to be dropped. I'll have to discuss this with a fellow GT500 owner. He does a lot of wrenching and has no problem dropping the K member. I want to do this at home. If the problem is with the transmission, I don't want the car sitting in somebody's shop for weeks while it gets fixed, plus I want to know how it was put back together. There is a whole saga with the Griggs install and I don't want a repeat of that.

I do have wrenching experience. Back in the early 90's I put a Paxton ball drive on my '88 GT and replaced several sets of head gaskets on that engine. I'm 27 years older now and just don't have the get up and go I did back then.

I'll check out the balancer and get the exhaust fixed. I do think the exhaust is vibrating against the body some, but I don't think it is the whole problem. I will keep you up to date on the progress.

Thanks,
Steve

 

[tomshep]

By marking the balancer I mean putting a painted line from the inner ring to the outer ring. That way, you will be able to see if the outer ring slips in relation to the inner ring. This may not help if it has already moved unless you can find some sort of a line from the original assembly. It will help you for future slipping.

Tom

 

[SteveWK]

Thanks for the additional info. I was scheduled with an independent exhaust guy to have the car looked at Sunday, but I was laid out with the flu. I was planning to inspect the balancer while we went over the exhaust. Hopefully this weekend I can get to it.

BTW, here's the exhaust guys FB page. He looks like he has some skills to me, and seemed really congenial on the phone. I'm wondering if he could fabricate some shortys.

https://www.facebook.com/PerformanceWeldingSolutions/

 

[Beercules]

Sounds like plugs, other than vibration with trans in neutral and clutch engaged.
When's the last time you changed them? My 3 valve started acting like crap, plugs looked good... changed plugs and fixed it.

Not too expensive and lots easier than pulling the trans. If it's not the problem, you'll have an extra set of plugs.

 

[SteveWK]

Sorry I haven't updated recently. The flu kicked my butt.

I recently changed the plugs to NGK TR7IXs gapped at 0.028. So that shouldn't be the problem.

I did get the car on the lift with the "exhaust guy" and he pointed out where it was vibrating against the Griggs front torque arm mount. I should have all of the exhaust fixed within the next week and shall see how it performs.

I'm also hoping the + 0.75 (max) knock sensor output I have seen while data logging will be fixed with the exhaust vibration too.

Steve

 

[SteveWK]

Just thought I would check in with this issue. The car finally goes to the exhaust guy this Saturday. I bought a grinder and got underneath the car to modify the torque arm's cross member and decided it was too close to the exhaust to not potentially put a hole in the pipe without removing it. It will have to wait.

As much as I would like to do all of this work myself, I'm going to farm it out. I've got a shop installing 3.73s this week, and if that goes well they can install a new clutch.

Steve

 

[SteveWK]

Got the exhaust straightened out. He found several places it was touching, and lo and behold, less vibration everywhere. I guess I let my imagination run a bit wild on this one.

For anyone in the Wichita, KS area, I highly recommend Performance Welding Solutions. He did a great job finding trouble spots and fixing them. See photo.