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post #1 of 31 (permalink) Old 12-01-2004, 10:55 AM Thread Starter
 
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Driveline vibration making me insane

Okay, ever since I swapped over to a new aluminum DS and FRPP rear end I've had bad driveline vibration starting around 65-70 mph. The vibration isn't completely continuous, either, as it will come and go from time to time, but it's usually lpresent. I've torqued the bolts on the pumpkin and used urethane bushings on it. The really weird thing is that a lot of the vibration is transmitted through the steering wheel. I can't for the life of me figure out how driveline vibration could make the steering wheel shake up and down, but that's the case. I can't seem to solve this problem, so please tell me if you have any input. Here's my exact setup:

New, not used aluminum dynotech driveshaft
JustinH's FRPP pumpkin w/3.73 gears
MN12performance urethane diff bushings
Stock rubber rear diff mount, but it seems in fair condition

And here are my thoughts on what could be wrong:
Out of balance DS (seems unlikely, balancing weights are there and the thing is brand new)
Torque converter not liking the 3.73 gears
Movement in the pumpkin (seems unlikely since it's torqued to specs front and rear with brand new bushings)
Bad tranny/motor mounts causing the whole engine/trans to move (seems unlikely because the problem only popped up after the rear end/DS swap)

This thing is driving me crazy. Please help me if you can.
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post #2 of 31 (permalink) Old 12-01-2004, 11:06 AM
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what makes you think its the driveline and not something like hub runout or rotor runout in the front end. Rotor runout will cause a vibration even when you are not on the brakes.

It sounds like you have everything in the driveline covered, might want to look elsewhere.

Tire balace is good i'm sure? Wheel torque? Search vibration, the mn12 chassis is very suspect to bad vibes. I am chasing down one in my car that I will have to work on next season.

My 95 had bad vibes which turned out to be loose bolts on the subframe.


JH
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post #3 of 31 (permalink) Old 12-01-2004, 12:18 PM
 
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Quote:
Originally posted by JustinH
My 95 had bad vibes which turned out to be loose bolts on the subframe.
Good thing you found those!

If your steering wheel is shaking, chances are pretty good that it's some sort of front-end suspension or steering problem. I've never heard of a driveline vibration being transmitted through the steering column like that. The first thing I'd check is the brake rotors and tire/wheel balance.
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post #4 of 31 (permalink) Old 12-01-2004, 12:34 PM
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Either front end issues, or a tire out of round/thrown belt inside/out of balance. Had this issue on my 95, and it had a high-spot in the tire tread itself, so it kinda made a skipping noise on the highway, kinda like the sound big 4x4 tires make. Hard to explain I guess, but that's what it sounded like to me.

Jay

These are highly engineered precision vehicles, the first step in diagnosing the problem is to strike the suspected offending part sharply and repeatedly with a blunt object, then re-test.
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post #5 of 31 (permalink) Old 12-01-2004, 12:56 PM
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Here's a story to make you "think".

buddy takes his car in for a new rear end/gears/posi, etc

drives home, and has funny front end vibration.

comes to find out the shop doing the work took the car for a test drive. They got a flat tires. When they went to get his spare out, they found his can of fix-a-flat, and used it. The mechanic then stopped at the part's store and bought another can to replace his.

They never told him until later when he bought new tires. The tech at the tire shop used to work at the driveline shop, and came clean. (fix-a-flat "pools" in a different spot everytime, like water in a bucket being slung upside down.-causes vibes)

wont fix your car...but...you just never know. Have you checked with the shop that did the driveline work and ask them if they had to mess with motor mounts, tranny mounts, etc?

strange things happen to cars in shops.
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post #6 of 31 (permalink) Old 12-01-2004, 01:36 PM Thread Starter
 
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I did the work myself, so I know that no one got any flat tires or anything like that. I have obviously considered that the steering wheel vibration could be exclusive to the front end, but it would be an incredible coincidence, since I never had that problem at all before I swapped the pumpkin and DS. That's why I'm convinced there's a link, because the problem showed up immediately after that swap and with no other changes. The only real difference I've made is increased RPM between the engine and the differential. The tires, wheels and brakes themselves should see no additional forces that would cause problems, at least not that I can think of. And it's not a side to side vibration that you'd expect with an out of balance tire--it feels as if the entire steering column is shaking up and down, and I also feel vibration feels as if it's directly beneath the driver's seat. This one has me stumped, please continue with your suggestions.
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post #7 of 31 (permalink) Old 12-01-2004, 01:41 PM
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Have somone stick their head out the door and take a look while it's vibrating, Maybe they can see something out of whack

Jay

These are highly engineered precision vehicles, the first step in diagnosing the problem is to strike the suspected offending part sharply and repeatedly with a blunt object, then re-test.
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post #8 of 31 (permalink) Old 12-02-2004, 09:00 AM
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Check the K-member bolts. The steering column on a Mark VIII actually passes right next to the left exhaust manifold. if anything has moved, perhaps it is now touching SOMETHING in the steering linkage.

Your exhaust, something has to be touching the front end.

motor mount, trans mount, something.

The only other thing I can recommend is to try rotating your tires. front to rear, if only for a day.

typically, if a vibration is in the steering-wheel, it is from the seat-forward if it is in the seat, it is from the seat-back

so, draw an imaginary line(cut your car in half), and check everything from the seat to the front of the motor. it doesnt take much...
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post #9 of 31 (permalink) Old 12-02-2004, 10:33 AM Thread Starter
 
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Thanks, I'll see if I can figure something out that way. I do have a new trans mount and crossmember bushings awaiting installation, so we'll see if that helps any, too.
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post #10 of 31 (permalink) Old 12-02-2004, 06:27 PM
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Possibly a couple of things..
Bad setup in the FRPP diff-mine had it,and I've got the bearing races to prove it.
Bad wheel bearings...
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post #11 of 31 (permalink) Old 12-02-2004, 06:43 PM Thread Starter
 
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Thanks JL, I was hoping you'd have a thought on this one. It is possible the diff isn't set up correctly. That's something I didn't check, and I let one aftermarket company test fit one of their differentials in the housing, so I can only hope they installed the TL diff correctly. The rear wheel bearings are roughly 30,000 miles old, what's the life expectancy on them?
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post #12 of 31 (permalink) Old 12-02-2004, 06:48 PM
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Quote:
Originally posted by mercutio
Thanks JL, I was hoping you'd have a thought on this one. It is possible the diff isn't set up correctly. That's something I didn't check, and I let one aftermarket company test fit one of their differentials in the housing, so I can only hope they installed the TL diff correctly. The rear wheel bearings are roughly 30,000 miles old, what's the life expectancy on them?
The rear bearings..I've seen them go for 220K miles on my car(really due for a change now),and others have them fail with 20-30K miles on them.
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post #13 of 31 (permalink) Old 12-02-2004, 06:49 PM
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I'll bet you're still running 15" rims with some combo. 17" rims with Z rated tires and ecentric rings are the way to go if you want smooth highway rides with the driveshaft/ rearend combo's. Take two in the morning and call me about noon. Ed.
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post #14 of 31 (permalink) Old 12-02-2004, 06:53 PM
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Quote:
Originally posted by Hollywood Ed
I'll bet you're still running 15" rims with some combo. 17" rims with Z rated tires and ecentric rings are the way to go if you want smooth highway rides with the driveshaft/ rearend combo's. Take two in the morning and call me about noon. Ed.
Aftermarket wheels and hubcentric rings are a piss-poor idea to cure vibration.
I never had a problem with 3.73's/dynotech shaft,and the stock 15" wheels on my car-that's absurd.
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post #15 of 31 (permalink) Old 12-02-2004, 07:18 PM Thread Starter
 
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I'm with JL on the wheel issue, but I am running 17x9 wheels with 275/40s in back and 255/45s in front. Other specs, just in case anyone is wondering:

rear disc swap
front UCA's replaced under a year ago
front upper shock mounts replaced under two months ago
originally used Steeda diff bushings but replaced them with MN12perf. bushings after the vibration destroyed one of them. Will post pics of that whole situation. Basically, if you look at the way the Steeda bushings work, the middle bushing tried to suck its way out past the lower bushing. I assumed that CAUSED the vibration, but apparently not, since those parts are gone but the vibration is still there.
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post #16 of 31 (permalink) Old 12-02-2004, 08:42 PM
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I'm chasing a vibration too................keep us updated. I haven't made anyprogress with mine............

95 LSC- Mods: 2.5 dual exhaust, 3.73s, 17x9 cobra R Rims, SCT dyno tune, MM driveshaft, 249 rwhp/ 268 ft lb tq
97 Base- Mods: Forged motor, Eaton m112, 2.76 pully, too many mods to list..........
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post #17 of 31 (permalink) Old 12-02-2004, 09:32 PM
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I have the same symptoms. Ever since I installed the FRPP pumpkin, there has been vibration at highway speeds. I haven't even begun to try to identify the problem. But from what was said here, it looks like I paid $600 for a diff that wasn't set right?

There is another problem on my 'Bird...whenever I reverse, there is a noise about every 1/4 revolution of the wheel. I wonder if it's a symptom of the same problem.

When I get ready, I'm gonna have the diff fluid checked/changed and finally get that custom driveshaft. I hope that will fix the problem, but from reading this topic, it doesn't sound as promising.

I come from a dusty place.
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post #18 of 31 (permalink) Old 12-02-2004, 09:49 PM
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i have a frpp diff too, checked it before installation, well within spec. I also checked the driveline while everything was spinning up to 80+ mph, no vibs there........

95 LSC- Mods: 2.5 dual exhaust, 3.73s, 17x9 cobra R Rims, SCT dyno tune, MM driveshaft, 249 rwhp/ 268 ft lb tq
97 Base- Mods: Forged motor, Eaton m112, 2.76 pully, too many mods to list..........
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post #19 of 31 (permalink) Old 12-04-2004, 10:44 AM
 
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Put the car in the air ( Carefully !! ) and gently take it up to 60mph that will
rule out the front wheels then take the rears off and install the bolts with
some spacers to keep the rear rotors snug. If it still does it then it's the drive train.

Do you have mags ? If so do you have wheel centering rings ?

They do help, or they did for me.
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post #20 of 31 (permalink) Old 12-04-2004, 11:04 AM
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In addition, I think that you need to raise the wheels up too so that the CV joints don't fail too quickly.
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post #21 of 31 (permalink) Old 12-04-2004, 01:26 PM
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Did you install your driveshaft correctly. I've never worked on the driveline of a thunderbird, but i've seen a Z28 camaro witht the driveshaft installed 180* off, and it caused vibrations at highway speeds.

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post #22 of 31 (permalink) Old 12-04-2004, 06:36 PM
 
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Quote:
Originally posted by Grasshopper
In addition, I think that you need to raise the wheels up too so that the CV joints don't fail too quickly.

15 seconds at 60mph won't be a problem but when I did it I put some extra
jack stands under the lower control arms just te safe rather than sorry.
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post #23 of 31 (permalink) Old 12-06-2004, 10:52 AM Thread Starter
 
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Quote:
Originally posted by Primalzer1995
Did you install your driveshaft correctly. I've never worked on the driveline of a thunderbird, but i've seen a Z28 camaro witht the driveshaft installed 180* off, and it caused vibrations at highway speeds.
It's possible, I'll check that out.
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post #24 of 31 (permalink) Old 12-06-2004, 03:17 PM
 
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Quote:
Originally posted by mercutio


It's possible, I'll check that out.

www.flash.net/~ivc1/cobra/irsvibes.html


Hope this helps - Let us know
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post #25 of 31 (permalink) Old 12-06-2004, 04:25 PM
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Interesting find LST.
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post #26 of 31 (permalink) Old 12-29-2004, 06:35 PM Thread Starter
 
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Never posted the pic of what happened to my diff bushings, so here it is. Notice the middle bushing tried to force its way through the washer and inside the lower red bushing.
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post #27 of 31 (permalink) Old 12-29-2004, 10:03 PM
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Was that what was causing your vibes???
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post #28 of 31 (permalink) Old 12-30-2004, 11:08 AM
 
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I highly doubt that your looking at a driveline vibration issue. When I did the 4.10/MMX/MN12 diff bushing install, that curred my driveline vibration issues (Except when I get the car "up to speed" ). As I'm sure you know, Mark VIII's are notorious for driveline issues. I would get severe vibration at 65-70, not to mention the car was damn near undriveable by the end of the 1/4 mile. Mine was bad enough it actually transmitted to the steering wheel, and if you looked in the rear view mirror, you would get a headache if you watched it to long.

Now I am chasing something else, but I believe it's in my mounts since my vibration was as bad as it was.
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post #29 of 31 (permalink) Old 12-30-2004, 11:22 AM
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also remember putting poly mounts in any car will increase vibration by taking out the damping force of the rubber

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post #30 of 31 (permalink) Old 12-30-2004, 06:45 PM
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Another thing to consider. Just because the driveshaft is new, that doesn't mean that it couldn't be out of balance. It could also be that it is not true, meaning perfectly straight. It is a remote possability, but is worth considering. Remember, anything mechanical built either buy machine or hand, is still subject to human error. I hope you find the problem. Good Luck!!
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