Mustang guys....help w/ vibration problem

[Nitrousbird]

Not for me, of course. smile.gif My roomate's daily beater is a 94 GT, 5-speed. Has around 145k miles on it. Other than it burns a little oil, the car runs great. He is pretty easy on it, and has owned it since about 90k miles.

 

Very recently, the car developed a vibration problem. There is a noticable, but not insanlely bad, vibration in 2nd and 3rd gears above 2000 RPM. Does not vibrate in 1st, 4th or 5th.

 

I had him go up to speeds his car would have been in at second @ 2500 RPM, but in 1st gear, no vibration. Had him take it out of gear at the speeds it was vibrating in 2nd & 3rd, and the vibration imediately goes away. Same as when he just pushes the clutch in. Also, going those speeds out of gear, and reving the motor up to 3000 RPM, no vibration.

 

My guess is that something is out of whack in the tranny. The car shifts fine (has a B&M shifter), and he is always easy on this car. Clutch may be original; he has never replaced it at least.

 

For now, he is just going to drive it. We are guessing it WILL get worse, and probably sooner than later. A cheap, stock T-5's out there to swap in. He is not really into modding this car much (that's what his SS is for), so the need for a heavily built tranny just isn't there. Of course, if he could get a built up tranny for nearly the same price, he would of course do that.

 

Or maybe it isn't the tranny at all, but I'm not sure how it wouldn't be.

[flyinbrian]

Check the U-joints.

[20G TSi]

ok, thats a hard one. Here's my guess:

 

The engine is missing ONLY when a load is placed on it at lower rpms. Check the basic tune-up stuff, but I would also check the motor and tranny mounts.

 

I say ONLY with a load on it, since 2nd and 3rd gears accelerate in RPM quickly (but not as quick as 1st, where it probably goes past the rpm where the vibration is prevailant, so it goes un-noticed). 4th and 5th, you may be going too fast (causing road/tire vibration) which drowns out the vibration.

 

I have a seriously hard time believing its anything inside of the tranny, since its basically just gears/shafts in there, what could have come un-balanced to the point you would be able to notice a vibration, ya know? T-5's usually break gears/input shafts, strip synchros, break shift forks (ok, maybe I'm the only one who breaks shift forks) smile.gif

[20G TSi]

Originally posted by flyinbrian:

Check the U-joints.

and what he said

[flyinbrian]

Originally posted by Nitrousbird:

Or maybe it isn't the tranny at all, but I'm not sure how it wouldn't be.

The driveshaft is spinning at higher RPM's through each gear from first to fifth. It is the harmonics of certain RPMs that is causing the vibration under a load. You don't always feel the effects of a bad u-joint or u-joints in ever gear.

 

I am not saying it can't be the tranny, but 145K on u-joints and those symptoms would have me checking u-joints before I did anything else.

 

Cheap fix too!

[Nitrousbird]

Hmmmm....never really considered U-joints. The only vehicles I've ever been in w/ bad U-joints have normally been noticable at almost all speeds/gears. But sure sounds like something to consider!

 

Never really looked under a Mustang to see how the tranny mount attaches/works; but I know on my car (I broke 2 stockers before finally upgrading to a improved factory unit, and now a poly one), I didn't get any vibrations from it, just the damn tranny pulling up and clunking loudly under the car (THAT is annoying I might add). I'll have him take a look at the motor mounts as well.

 

I highly doubt it is a motor-missing type problem. I've driven the car before, and it runs pretty smoothly....and the motor still runs smoothly even when there is a vibration.

 

Thanks for all the ideas; I'll let him know. Not sure when he will actually get to fixing the problem.

[Boost-n-Juice]

My .02 says it's the tranny. My Mustang vibrates in 2 and 3rd only as well. Nothing REALLY major, just enough to annoy you.

 

A T-5 rebuild kit is like $150. I hear they're easy to rebuild. I have a friend that might rebuild it for him, for a small fee.

 

BC