Another Driveshaft Question

Rockin302 · Oct 27, 2004

I've been reading some old posts regarding vibration at highway speeds and want to confirm that it's my driveshaft that needs replacing/rebalancing and not anything else like the harmonic balancer, motor mounts, etc..

-At highway speeds I can feel the car vibrate and I also notice the rearview mirror vibrate like a pager.

-When I let off the throttle and let the car coast (at highway speeds) the car shakes a bit more.

-I haven't tried putting the car in neutral at those speeds but will do so tomorrow and see what I find.

-I've also read that if I'm at a standstill with the car in neutral it shouldn't shake and if it does, it might mean that my Harmonic balancer is out of balance or I have worn/damaged motor mounts. I don't have this problem at a standstill which makes me think it's the driveshaft.

Can anyone confirm that my problem is the driveshaft? Or is there another possible culprit to the vibrations??

BTW, the tires are fairly new so I don't think an out of balance tire is an issue. It's a 1990 lx 5.0 5-speed notchback with 116,xxx miles.

Thanks in advance for any help!!!

HISSIN50 · Oct 27, 2004

to add (to what i think you meant): in neutral while stationary, rev the motor to see if you get vibes (just wanted to clarify that point - being at idle while stationary does not show much).

you are on the right track. have you recently had the DS removed? it could be out of phase. more than one guy has had luck simply rotating the DS 90* and trying again. the bolts which secure it are 12mm, 12 points. use threadlock upon refastening them.

otherwise, an alum DS has helped many. do you have stock gears?

one can swap wheels/tires front to back if in doubt. the clutch or trans can also cause vibes.

good luck.

Rockin302 · Oct 27, 2004

While stationary and in neutral I can rev the engine with no vibrations whatsoever.

I have stock gears on the car and I don't believe the driveshaft has ever been removed although I'm not completely certain because I recently bought the car used.

It seems though, that the aluminum driveshaft has been quite a problem solver for most vibration issues.

Thanks for the help Hissin50!

HISSIN50 · Oct 27, 2004

Rockin302 said:
While stationary and in neutral I can rev the engine with no vibrations whatsoever.

I have stock gears on the car and I don't believe the driveshaft has ever been removed although I'm not completely certain because I recently bought the car used.

It seems though, that the aluminum driveshaft has been quite a problem solver for most vibration issues.

Thanks for the help Hissin50!

you have done your homework and i concur with your thoughts. though sometimes hard to find, a driveline shop should be able to dynamically balance your existing drivetrain - something to consider with the prices of alum DS's as they are (and perhaps more of a guaranteed fix).

the last thing ill toss out. i would check your undercarriage clearances. the alum DS's are a smidge larger in diameter. be sure there wont be any muffler clearance issues if goin the alum DS route.

good luck and let us know what you decide and how it works out for ya.

Rockin302 · Oct 27, 2004

Thanks for the info Hissin!

Opps, I didn't consider clearance issues if I was going to have an FMS aluminum driveshaft installed. If the exhaust is stock do you think it will have any clearance issues?

On that note, how difficult is the R&R on the drive shaft? Does it just slip right out after unbolting the 12mm nuts and a few other bolts or is it best left to someone who knows what they're doing?

I think those should be my last questions. Thanks again Hissin and I will keep you posted when I get the problem fixed.

HISSIN50 · Oct 27, 2004

Rockin302 said:
Thanks for the info Hissin!

Opps, I didn't consider clearance issues if I was going to have an FMS aluminum driveshaft installed. If the exhaust is stock do you think it will have any clearance issues?

On that note, how difficult is the R&R on the drive shaft? Does it just slip right out after unbolting the 12mm nuts and a few other bolts or is it best left to someone who knows what they're doing?

I think those should be my last questions. Thanks again Hissin and I will keep you posted when I get the problem fixed.

hey no problem. nice to have someone else on here late at night.

i think doing a DS is one of the easier things to do. i have huge mufflers compared to most folks (they rub the stock DS!) so im not sure what others have had to do to R/R the DS. i think one can remove the DS w/o having to do anything else (i would have to remove part of the exhaust on mine, but i dont think that is normal). the DS slides into the trans tail shaft. so once the shaft is free from the pumpkin (the 4 bolts), it should slide out (confirm with others before assuming i know what im talkin about because, like i said, im not sure how normal cars are. i do try to say when im not positive on something so as to remove ambiguity)

IIRC, the alum DS is ~0.5" larger in diameter than the stocker (again, get confirmation on this). most guys seem to be just fine clearance wise.

have a plastic bag handy to toss over the trans tail shaft - fluid will leak out. you will need to top off the trans fluid afterwards. and i think i mentioned to use threadlock on the 4 bolts at the pumpkin - they very likely will back out if you dont (factory uses threadlock on them).

good luck with it all. most guys love their alum DS's.

Rockin302 · Oct 27, 2004

Awesome!! I'll probably wait a month or so before I get the driveshaft so I can save up for it (have other bills that are getting in the way). If it works like it should and solves my problem (crossing fingers), I think a good set of weld on subframe connectors may be my next purchase.

Mustangs = money pit (it's ok though, it's for a good cause!!)

Michael Yount · Oct 27, 2004

Driveshafts don't usually just 'go out of balance'. Occasionally they'll throw a balance weight or you'll bang the underside of the car and slightly bend one (only takes a few thousandths to throw one out). But unless something has happend, they don't just start vibrating.

Given what you're describing as symptoms, I'd check your ujoints. When they start to go, they'll make a helluva vibration especially under no/low load. If that's it, get 'em changed, cause the vibration will break other things too.

Rockin302 · Oct 27, 2004

If I'm not mistaken, I think the FMS aluminum driveshafts come with new u-joints which will hopefully take care of the problem.

If the joints are bad can I get under the car and try to move the shaft up and down and side to side to see if there's any play?

Goldmember · Oct 27, 2004

its definately your driveshaft. get an fms and your problem should be cured. i had the same problem and now i can do 120 and its as smooth as an airplane.

Michael Yount · Oct 27, 2004

To properly check the ujoints - you need to take the shaft out. Then you can check each end. If you want/are getting an aluminum shaft anyway - you're right - they come with new joints. But if you're just trying to solve the vibration, new ujoints are WAY cheaper than replacing the whole driveshaft.

Meangene21 · Oct 27, 2004

I had that the noise at had speeds only. Turned out my exhaust was loose.

QDRHRSE · Oct 27, 2004

Rockin302-

Where are you in California? I have an extra FMS driveshaft thats almost new. I'll sell it to you and put it in for $150...actually I'll put it in for free. Other than getting the bolts off, they're a pain sometimes, its the easiest job ever!!

Michael Yount · Oct 27, 2004

Now there's an offer you can't refuse!!!!

dastang2 · Oct 27, 2004

are your front tires wearing on the inside more, you may have a bad ball joint. mine has that and it shakes exactly like yours. of course the front tire has a flat spot and the inside of it is bad along with both bald rear tires and motor mounts are bad too. i have some suspision about the balancer also. what a piece of crap these 3.8 liters are.

Rockin302 · Oct 28, 2004

I'm actually going to have the whole driveshaft replaced so going with the FMS driveshaft looks like my best bet.

The tires aren't wearing unevenly and are fairly new so I can't tell yet but they were balanced and all.

Sorry QDRHRSE, I live in the SF area so it would sort of a pain but thanks for the offer and thanks everyone for your input.

Seems Goldmember swears by the FMS shaft so I hope it does the same for me!!

Rockin302 · Oct 29, 2004

Ok, so I drive the car today on the highway and I'm cruising at about 65-70 mph and I drop the car in neutral and the car starts shaking like crazy as if it's going to fall apart. I also have the clutch pedal depressed (meaning I have the clutch pedal to the floor) at the same time. So does this rule everything out and my drive shaft/u-joints are completely jacked??

Remember, I have also had the car idle and stationary and rev the engine with no vibrations so I'm thinking the Harmonic balancer is still good.

Thanks for the help guys!!!!

cjman15 · Oct 29, 2004

Do you get ALOT of vibration through your pedal too? I have this same problem with my stock shaft in my '89. I had to U-joints replaced about 5 or 6 months ago and it still vibrates as much as the day I got it. Shifter, pedal, whole car shakes. I know how crappy it is. I'll probably end up getting a FMS Shaft also....

Rockin302 · Oct 30, 2004

cjman15 said:
Do you get ALOT of vibration through your pedal too? I have this same problem with my stock shaft in my '89. I had to U-joints replaced about 5 or 6 months ago and it still vibrates as much as the day I got it. Shifter, pedal, whole car shakes. I know how crappy it is. I'll probably end up getting a FMS Shaft also....

I don't get any pedal vibration but the car shakes quite a bit when I drop it into neutral with the clutch disengaged ( clutch pedal to the floor). I feel it through the seat a if I had a built it massage chair. The window vibrates which makes the rear view mirror act like a buzzing pager.

And to bring anyone reading this up to speed, the car does not shake at idle, like at a stop light. I can rev the motor and it's real smooth so it's not a bad balancer. Also, it isn't real noticeable in the city just highway speeds.

If anyone can help with any other suggestions that would be great!!! Thanks to those that have contributed!!

Rockin302 · Oct 30, 2004

Oh yeah, to add to my previous post, the car feels real solid in city driving where the roads have potholes, cracks, etc. Doesn't seem like anything feels loose.

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