Bad Vibrations
 

I am getting some really bad vibrations in the car, it is like sitting in one of those massage chairs on high but the whole car is doing it. This started about 2 weeks ago and is getting progressively worse. I have eliminated the tires as it has done the same thing when I put a whole other set on and it still does it.
Things to note the car has had the clutch, springs, shocks, endlinks, and front swaybar replaced, the most recent was the front swaybar about a month ago. I have had my mechanic check and see if he can figure out where the vibration is coming from with no luck.
Initially the vibration would start when you hit 50 mph now it’s doing it at 40mph.
If I am decelerating in gear it does not vibrate, if I pop it into neutral it sometimes continues the vibration but I have found if I move the shifter as if to go into second it disappears.
I now of course suspect the tranny, but internals, front or back connection points, what?
The transmission mounts are in very good condition.
Anyone else gone through something like this?

Does it have the vibration on both lift throttle decel and on accel???

Is it only vehicle speed dependent, not engine speed???

Tne vibration stops totally if you take your foot off the gas with it in gear as you start to deccel but say your are in 4th and still have some momentum it will continue.Now if you put it nuetral it may or may not continue the vibration, but id does continue I found if you just nudge the shifter towards second it stops.
It is also somewhat speed sensitive, starting near 40, it seems the worst between 50 and 60.
I have ha one person say it might be the diff mounts.

it happens in my 88 tII also but i had my differential mounts checked and they are good. and have energy suspension all around. i get it mostly on the highway

Does it seem like its coming from a specific end of the car? If it is speed dependant, its not enigne related, and if it does it in neutral its not the tranny, so that pretty much leaves the axles/wheel hubs/diff. Anything I'm forgeting?

WHat year rx7 and is it turbo or not turbo? Have you checked the Driveshaft? T hey tend to go bad and shake the whole car when it reaches a certain speed.

Its a 90 GTU (non-turbo)

Check the driveshaft

What should I look for exactly?

I'm pretty sure it's not the engine because it doesn't vibrate when I deccelerate and when it's in nuetral I can rev the piss out of the engine and it doesn't vibrate.
The car is not shaking per say it's more like it's a giant buzzer.
I've also eliminated my wheels as a possibilty, as I noted in the original paragraph I had put my other set of wheels on and got the same effect.
I am leaning toward the diff mounts or the axle or possibly where they connect to each other.
I don't think its the diff itself as it would probaly vibrate wether I was in gear or not.
The main thing that worries me is my ability to stop the vibration when in nuetral by tapping second.

Your U-joints are out. that is why it only happens on acceleration.

www.rockforddriveline.com or www.arizonadriveline.com part number 430-10A You need two and it will cost you about $50 bux with freight.

Now, bookmark this post, or better yet print out and place some where safe. After you go threw the learning process you'll want to refer back to it.

A) refurb drive shaft = $250
B) new driveshaft = $380
C) not your wheels
D) not your motor mounts
E) not your tranny mounts
F) Not your differential
G) Finally, YES, the u-joints "ARE" replaceable.

$50 bux and a 4lbs hammer and two hours of time will trump all that other stuff. Don't forget your rear main oil seal before you pull out the old shaft.

after some checking I see Mazdatrix has a completely new drive shaft available with the traditional replaceable u-joints for $248 (+shipping which wont be cheap)
I'll probably taker the car down to my mechanics as I don'thave a way to safely get under my car and bang away at the driveshaft
.......
OK just got talking with my mechanic - when he had checked everything for me last week the universal joints were in great shap, the diff mounts were good, the trans mounts were good, the motor mounts were good
He and I have come to the conclusion at (least for now) that I some how bent the driveshaft

well I guess if you take the horse to the water....it is up to the horse to choose to drink or not.

Think of it this way, whilst paying out the ass for a new replacement shaft you'll be getting new u-joints. So I guess in a round a bout way.....you replaced the problem.

but I'll leave you with one thing. your drive shaft spins all the time. It is a direct drive from the differential into your tranny. IF, your driveshaft is bent, why does it only vibrate when you accelerate? I mean would'nt the vibration be a constant if the drive shaft were truley bent?? spinning all the time like that???? whether your accelertating, drving constant and slowing down?

But what do I know? I'm 3500 miles away.

Ok, I won't leave you in a lurch. You indicated that you may not have the tools or a way to get under there. Let me let you in on a secret. You may have to familiarize yourself with the exhaust and how it works or bettrer yet how to un hook it so it drops in the rear. This is accomplished without tools....well maybe a large screwdriver to pry the rubbers off the hooks. You'll have to learn about the heat sheilds and how a 10mm turned counter clockwize loosen the screws so the heat shield comes off. You'll also need to get used to pulling on a 12mm wrench to get the 4 bolts loose that actually hold the shaft to the differential. Once you familiarize yourself with those three things, you see that your mechanic is dancing around going ChaChing after your last phone convo with him....

One final thing, Your mechanic dropped your exhaust and took your heat shields out to inspect that front u-joint.....right??? well........right?? That's what I thought

this is happening to me also like i posted. i have a 6 puck racing clutch and a hd pressure plate would it cause a thud from the rear if i shift. not completely letting go but a firm release? my question is would this happen (vibration and thud) with just the drive shaft?

Wha??

Start a thread with a few more details

Yes actually.

Actually my mechanic recommended that I see if I can find a "donor" shaft to see if it's bent at no point has he told me to bring it in so he can fix it. I think he'd rather have me do it, there has been a number of occasions where told me I can do the work and don't need him to do it. He has plenty of business and doesn't need me to bring every problem his way. Also he is a Porsche certified mechanic and has had a decent local racing career. He has been nothing but honest with me for the last 5 years, if he doesn't know what the problem is or can't fix it he tells me so.
Now as to the car:
The driveshaft maybe need rebalancing, it may be flexing under load - which would explain the vibration because of the torque being applied, it may be bent, I don't know because I'm not a harmonics engineer.
Again I cannot getunder the car safely, I probably have all the tools I need but I am not going to crawl under the car while its up on jackstands as it slowly sinks into my gravel driveway.
I am talking to another shop about get the shaft rebalanced they said $30, I need to work out the details with them.

Anyway can we all agree I probably need to pull the driveshaft?
The how I'll have to figure out later, for now though I've got a Miata I can use as a daily driver, 325is (E36) that needs a new steering wheel so I can get inspected and sell it, and the FD is getting close being to road worthy now.
I've got too many damn cars.

Weather you realize it or not I am trying to get you to think critically about this whole thing and save yourself a lot of money........which would be synonymous with "helping" you.

But, if you want to take it to a Mechanic, it is your call.

After all that, I am not sure what the point to the thread is. You asked us for our input and when we give it....you argue and then say your mechanic knows what it is and has already diagnosed the problem and we're all wrong and he's the reputable one and isn't going to charge you a dime extra...........

Not trying to bag on you, but do you realize that after this little excersize you basically are going to do what ever it is you wanna do regardless of the "help" we have given? Has anyone ever pointed this behaviour out to you before or am I the first?

Somehow you missed the point about me not being able to get under the car safely, hence I cannot do alot of what you recommended.
Then you you started ragging on my mechanic like he was some sort of greedy bastard.
It still may be the U-joints, maybe they are missaligned or something along those line.
I was trying to get a bunch of ideas, opinions etc on what it could be and I also voiced what mechanics view was.
I am sorry I don't have garage or even a concrete slab to put the car up on.
Again I cannot get under the car without seriously risking my life, so I'm not gonna do that.
And for the record people usually do what they want to, so no, I won't be following your commands to go forth and fix my car myself your majesty.

hahahaah. I like the "your majesty" thing....I could get used to it.

I just thought it rather odd, and felt like it should be pointed out for further reference.....on your part.

You're right, getting under that car is a bitch. You really have to get it high in the air to do any real work. I have to jack it up all the way on each corner, put the jack stand under it (on the lowest setting) and then get a block of wood in order to "jack" up the jack and lift the car a bit higher. takes a good half hour to get it all the way up on the jack stands. And to boot I'm a fat boy so it is tight under there........don't like it too much myself.

I wouldn't mind squeezing under it but after changinng the spring and shocks out and watching a pair of jackstands sinking into the gravel with just one tire off I am not about to put the whole thing up in the air sitting on gravel dirt, plus there's all the damn mosquitos still out. Mid-October and I still have f'n mosquitos, what are they starting to grow fur.

damn double posting

update:
well it was the u-joints sorta - I took the car to a local 7 specialist and he found that where the u-joint is mated to the driveshaft is where the problem was. The u-joint itself was in good shape but there was a hair line crack that under load allowed everything to get out of line enough to vibrate. So he has gotten hold of a low mileage shaft (20K miles on it) and swapped it in . Tommorrow I pick her up at a cost $250

I've been trying not to do this every time I see this thread, it's just so hard...

Doo doo doooo bad vibrations
She's givin me excitations...

I've been waitin for that