Vibration when decelerating
 

Hello everyone. I am trying to figure out possible points of failure on my 84 GSL. When I am traveling above 30mph, I get a vibration when I let off the gas. The fast I am traveling the worse the vibration when letting off the gas. There is no vibration when I accelerate. The car is stock, so no special mods to take in to consideration. I think I may have a bad u-joint on the drive shaft, but was wondering if anyone might have other ideas.

Thanks for any help.

I get this when I let off the gas completely while in first - third gear as well (no matter how smoothly, although its way worse if I let off abruptly). I thought it was just what happens when you do that in a manual car, as it's my first. I am curious now to know if it is normal. Sorry I am not really answering your question, I just thought it was a normal occurrence.


EDIT: I just realized I have a different car than you, so my post is even worse than before. Can't figure out how to delete it though. Sorry again.

check the drivetrain mounts.
engine,transmission,differential mounts.

Mounts would also be my guess. General transmission/diff trouble shooting: http://www.mazdatrix.com/g2.htm.

Thanks for the suggestions guys. I'll have a chance to get under the car this weekend, and check everything out.

@RotaryRocket88 - Thanks for the link to the MazdaTrix site, I completely missed that page when I was looking over parts on their website earlier.

If you find all your mounts etc. are in reasonable condition you might want to check you cars curb height .. What happens in most vehicles is when the car bags out and looses it's curb height or has been altered buy the owners you will find that the output shaft on the trans and the input shaft at the diff are almost lined up perfectly .. A drive shaft is intended to run on an angle from front to rear so the u joints can work .. When a u joint is lined up with the apposing u joint on the other end weather they are in good condition or not , (you will notice this more with good U joints than with poor ) they will fight each other and cause a vibration on deceleration .. Same thing happens with the worn parts .. If all else fails it might be something you will want to check .. :)

pull the shaft and check for hard spots when rotating the u-joints. if not check your front diff mount. i had a vibration and it was that my shaft was only on by 2 bolt and one was loose. so it had room to clunk around, luckily i had noticed before it rip out of it and tore some shit up.

Well, it looks like it's the driveshaft. I was driving it over to my father in laws to get ready to work on it, and a loud "Kachunk" later and the rear u-joint went, and so did the shaft. Doesn't appear to have done any additional damage, but I won't know for sure until tonight. Thanks for the help guys.