Cordt

K this is really weird and I can't think of anything that could possibly cause this....

My car (86 base model) has a small rapid vibration in pretty much every gear, which usually gets much much worse on deceleration....the only way I can get it to stop is by shifting into forth and having the engine not quite revved up enough, or revved up too much to match the speed of the transmission, and let the drivetrain "pull" the engine to match the speed. I can then go through the entire rev range with no (abnormal) vibration.

In 5th cruising on the highway if i let off it will start to vibrate worse.
If I downshift, rev match perfectly and then proceed to decelerate in 4th it will vibrate like all hell. The rest of the gears do not do this, they vibrate all the time but not as much as 4th does when decelerating like that.

Also when transitioning between 4th and 5th gears going highway speed, while I have the clutch depressed there is a loud pulsing vibration, like it will go VVVV pause VVVVV pause VVVVVV pause and it speeds up/slows down with the engine speed, but it will only do this when the car is rolling at a decent speed. Also (this is regarding 4th gear ONLY) it seems like if I re-engage the clutch mid-vibration it will stay that way and vibrate like crazy while im driving, but if I just push the clutch again and let it re-engage slowly or re-engage it just at the right time between the vibration pulses it won't vibrate.

What the hell is vibrating here? I have a brand new clutch kit and brand new pilot and release bearings, and it was doing this before I replaced these things. I also replaced the transmission because the old one was doing this and also had some bearing noise and the new one is EXACTLY the same, what the hell???

-Crash-

check to see if your front diff mount if broken, i have the same type of problem (lots of vibration while in 5th gear at low speeds, 1500~1800rpm) and i believe that is the cause, as soon as i change mine out i'll let you know.

to check it, get under the back of your back with a bright light and look for big rips in the rubber, the front diff mount is located at the nose of the diff.

Mazdatrix link to the diff mount:
http://www.mazdatrix.com/G8DiffMnt.HTM

Cordt

the rear end is a suspect so i actually have a whole new diff i was planning on putting in today but when i got under there i realized my exhaust is ONE piece...meaning i would have to remove the manifold to get it off...think im going to have a connector inserted in there before i do anything so i can remove just the pipe instead..

but i dont see why if this was the problem, i can make it go away in 4th gear by engaging the clutch a certain way? thats the really weird part.

jgrewe

iTrader: (1)

Could be U joints getting out of phase. A bad front diff mount will do this to you sometimes. Get under the car and wiggle the driveshaft around to check the u joints to see if either of them is going bad. Next pry on the diff housing to see if you can lift the nose of it.

Remember, the drive shaft spins in constant ratio to the wheel speed(road speed), variable from the tranny/engine. If the vibration is faster at higher road speeds it's all from the front u joint back. If engine rpm effects it, its from the tranny forward.