drive shaft install question....
 

I'm in the process of installing a clutch which is already out of the car.
Directions said to mark the drive shaft at the rear end before removing...which I did not. What is the reason for doing this, and what problems could I run in to?what can I do now?

In theory your driveshaft could be out of balance. I imagine that if there was anything wrong, you'd hear/feel vibration at a particular speed.

Carefully wipe down the coupling ends and look for original paint marks. If you can find those you're in good shape.

Dave

Thanks for the quick response.

bump

has anyone not marked the shaft and then had problems?

I just cant see why marking it would be a big deal. if the shaft was that out of balance to begin with it shouldnt be on a car

Marking the drive shaft is a common procedure. If it wasn't out of balance where it was, it won't be out of balance if you put it back on in the same position. Theoretically, it should be in balance in any position. However, that is not always the case. Better to mark it, and insure that you don't have a balance problem later.

Well if it goes together and vibrates, take it off, turn in 90 degrees, and try again. Just don't let it run vibrating like that for long.

It is common practice for ANY rotating mass to be marked prior to disassembly, then put back the same way. Sometimes one is only talking a few grams per millimeter out of balance that can make a big difference on how long bearings and the like live. What you are wanting to avoid is when the mass centerline does not coincide with the geometric centerline and the ensuing attenuation.
Pardon me if I wax poetic here a bit, but balancing machine tools is something I have pretty good experience with in my line of work. Let me give you an example of what can happen in even a slight out of balance situation. We balance our tools to less than 5 grams per millimeter, this is a world class standard. Often time brand new tools will come with up to 200 grams per millimeter of unbalance. At 3000 rpm you will have 85 ft-lbs of force being generated axially, at 6000 rpm this jumps to 350 ft-lbs. That is like hitting the bearings with a 60 pound ball peen hammer, 60 times a second.

I have pulled my drive shaft at least 6 times with no marking. I think marking would be a great thing to do as a standard practice but if you forgot there is nothing you can do once it is off but put it back on.

All 6 times I had no problems with mine when reassembled in random fashion.

Im thinking about mounting a plaque on the bottom off my car that says "Mark Drive shaft" although it appears it doesnt really matter on my car...

Like Baja said, mark it as a matter of practice. It's foolish not to, if you have a choice.

Once those balancing marks are lost or forgotten, IMHO it's not a big deal. People buy/sell driveshafts all the time, and I've not heard much discussion about balancing the final assembly. But Baja is right - it will put extra load on the bearings in the differential and perhaps fail them prematurely.

Dave

If the driveshaft is unbalanced it will be unbalanced no matter how you connect it to the diff. If it is balanced the same is also true.

Marking it before removal is just good practice but 999 times out of 1000 it's not going to make a bit of difference since the driveshaft is balanced alone, not as a unit with the diff. Cars or trucks with two piece driveshafts are a different story however. ALWAYS mark those.

I agree - it's a good habit to be in (marking the driveshaft), however I've yet to see a problem with mounting the driveshaft on ANY RX-7. They're balanced by themselves.

I wouldn't sweat it.

Dale

That was exactly my thinking.