hi guys, i had install 5 speed into my sedan 1200. my tailshaft had been cut n joint to accomodate longer gearbox. i notice when running past 100kmh i could feel vibration from my floor. is it from my tail shaft modification? is it possible the tail shaft to be balance? thanks

If a professional has done the tailshaft then it should be balanced already. Try turning the tailshaft 180 degrees ahd see if that changes it. Also note if the vibe is in both 4th and 5th gears or just 5th. These trivial details are very important when diagnosing a gearbox problem.

thanks for the advice. there is a lot of vibe in 5th gear compared with 4th gear.. i'll try to turn it 180 degrees.

turning it around 180deg will make no difference.

Either the shaft wasn't balanced, not balanced well enough, or the 5speed you have just installed has some worn bearings.

It's also possible that the tailshaft guy didn't replace the universal joints, and one is worn out, as they don't last forever..

sometimes when i suddenly release the clutch paddle, a 'ktang' sound heard from underneath the floor board. is it the sign of worn universal joint. maybe i should replace the universal joint first than try if there are any sign of vibe before rebalance the tail shaft. what do you think?

update, i've just return from 100 km plus journey, during the last 20 km, the vibration became more noticeable even at speed below 100kmh. During my trip i speed up my car up to 140kmh ignoring the vibration. i think maybe my universal joint had worn out... but must check n confirm.

dont go too far too fast if you suspect a uni-joint, if it fail at any sort of speed you can expect serious damage to everything around it, including yourself. jump under the car, grab the shaft at each end and check for movement in the joints.

another things i notice, the vibe even higher when at speed i free the gear or press the clutch..

Sounds like the front uni is worn. If you didn't ask the Tailshaft Balancer to check the uni's it's unlikely he would have, or he would have told you & charged you extra. I've had a front uni fail twice, both times when leaving traffic lights, so no pogo'ing, but it made a godawful bang. Changing Uni's isn't that hard, so it might be worth doing just to see if it cures the problem. Hopefully the uni's aren't peined in, which makes it a machining job to remove them. Most people just throw these style tailshafts away & start again. Lots of late Nissans have this feature (Sunny's, Late 1200 utes, etc).

U-joint usually smooths at as you lift the throttle.

It might be a bad tire or even wheel balance. That happened to me last year. On one long trip it got worse.