Questions and Answers
Clunking Mazda RX-7
Q. I have a 1985 Mazda RX-7 with a carbureted 12A rotary engine, 5 speed manual transmission. It has 218,000 miles on it. I'm getting clunking noises, rough shifting, and vibration. When driving at a steady speed, if I push in the clutch the vibration goes away.
I never noticed any of this until I had the transmission overhauled. They replaced the "soft parts"( synchronizers ) and the clutch assembly. The flywheel was resurfaced.
How much play is allowed at the differential when turning the drive shaft by hand? Mine has about 1/8-3/16 of play. If U-joints were too worn would it be visible when turning the drive shaft back and forth? With the amount of free play I have and no visible movement in the U-joints, could either of these cause any of my problems?
A. That amount of play in the drive shaft is allowable. There will always be some slack due to the way the gears in the differential ride on one another.
If none of the universal joints are bad, then the vibration problem could be an unbalanced drive shaft. Look at the drive shaft and see if there are any spots where a weight used to be. If they all seem to be there then unbolt the drive shaft from the differential and turn it 180 degrees and rebolt it. I have found that if you do not mark the drive shaft to the differential you will, sometimes, get the problem you describe.
This, of course, will not be the cause of the rough shifting or the clunking noise. If this started after the transmission rebuild, then I would take it back to the shop that did the work and tell them that. You can also take it to a different shop, play dumb and see what they diagnose it as. This will give you a second opinion as to what the problem is.
