avu3

82 GSL 5 sp rear drum open axle. All stock. 135k on the chassis, 60k on the motor. trans unknown, assume original.

In 4th gear at ANY RPM I get a huge driveline vibration. It doesn't seem speed related, as I can be going to same speed in 3rd (at a higher rpm obviously) and it does not vibrate.

Would the gear IN the transmission have a problem causing this?

The only other thought I am having is u-joints (them seem a touch loose, but not bad) or a trans mount (haven't really checked it). Maybe the motor RPM in 3rd is enough preload that it doesn't have the harmonic that causes this horrible vibration.

Don't have a problem with 5th, or didn't last time I used it, but am currently afraid to get the car going fast enough to use it till I get 4th sorted out.

Thoughts? Opinions? car has been such a basket case I'm hesititant to drop another $60 in parts to find I have a bum gear box.

Scott

Rx-7Doctor

iTrader: (13)

Strange. In most cases if it is either the front or rear u-joint there are other symptons.
One being when just taking off thier is a vibration usually caused by the front u-joint.
Vibration as you go faster is usually the rear. The trans mount usually causes vibration when in neutral and revving. Because the trans and engine are turning at the same speed only in 4th which would give the most amount of torque. It could be that the driveline is just out of balance or is slightly bent somewhere. Try repositioing the shaft. thats all you have to do is removee the 4 bolts at the diff. pull the shaft slightly away from the diff and turn it so it aligns with the next corresponding whole. See if this changes anything. But inspect the driveline for damage also. Also check to make sure the trans is not shifted to one side from a broken or loose trans mount.

avu3

Interesting. Just tonight I noticed a bit of "bucking" when starting off, but I attributed it to being cold and me not giving it much gas. Potentially check.

More vibe when going faster, check.

No vibration in neutral. Smooth, unless I tug the gear shift into neutral without using the clutch. If I do this, the vibration stays. Discovered this when I "knocked" the car into neutral changing stations. Once "knocked" into neutral, activating the clutch makes it smooth again. Never really thought much about it till you mentioned it.

Before you think me an idiot, we have two 85 RX7 race cars (pro7, ita), and this is a parts car, which happens to run well enough to be driven around, so I do, because I enjoy it. I don't spend a lot of time on this car, becuase I have the wife's car, both race cars, the tow vehicle, and my driver to maintain already.

I believe, Doc, you have convinced me to drop the coin into the parts. Heck, if nothing else, they are usable spares for the race car.

Scott

avu3

After further inspection it appears I've damaged the rear end. The drive shaft is solid, the trans mount is solid, but the rear pinion has an abnormal amount of play in it. I have to decide now if its worth the time and effort to keep it on the road.

It runs ok, I know the motor is toast (leaking water jacket next to spark plug temporarily fixed using the aluma seal method), but I have to wonder, WHAT NEXT?

I enjoy the car a lot, its fun to toss around on the roads by my house, but its not a daily driver and I have two other suitable cars.

I have a spare rear end, its just a question of it I want to spend the time.

Thanks again, Doc, for the help.

Scott