How much run-out do you think is acceptable? Yesterday we were prepping a driveshaft in the lathe and we noticed it has about .052" of run-out. The more I have thought about this, my mind keeps swaying back and forth about what is acceptable vs. how much would create a driveline vibration.

I might add that we had the U-Joint end in a four-jaw that was indexed within .0005", --and the other end was in a steady rest in the bearing area with about .001"-.0015". I can see this turning into a 2-3 hour process just trying to straighten it, then re-index it into the lathe to re-check progress, then removing to straighten .010" again. Have any of you checked your driveshafts to see what the run-out is?

Is this an old or new driveshaft? Is it bent with close to zero run-out at both ends, straight and off-center, or a combination?

Hey David. It is a used driveshaft that was in a "restored" car. I'm sorry but I am not following you on the run-out question. My bed on my lathe is not quite long enough to use a live center, so we had the square end indicated in at .0005+/- on that end in the chuck, and using a steady rest on the pinion end, we picked up in the bearing area and he indicated it at around .001", ...again +/- (probably more on the plus). Therefore it has around .050 +/- of run-out around the center distance of the shaft. Is this clearer?

Brent I don't quite follow you. Are you saying you estimated the runout in the center of the driveshaft to be .050 from the .001 run out in the bearing area?
Or did you actually measure the run out in the center? I know driveshafts are only finished on the bearing surfaces and its difficult to get an accurate measurement in the middle.

If you have a longer straight edge check the length for bends. Make sure to check at several positions around the circumfrence. If you don't find an appreciable bend I'd put it back in unless there were symptons which suggest a problem. Then I'd suggest a new one might be the most cost effective solution.

See, that is exactly what I am speaking of.

The main purpose for chucking up the shaft in the first place was to dress down the front bushing area. Hence the reason for indicating the front end that closely. We were not as worried with the tail so he only indicated it in at around .001". Since the center section of the shaft is unmachined, all we can do is get a rough measurement but it was around .050" of run-out while the front and rear ends of the shaft are indicated in pretty tight. Bottom line is the shaft has about .050" of bend in it.

My question is, what is acceptable by your standards?? If we are still unclear, I will post some pix tomorrow when I get to the shop.

Brent:

I have seen original drive shafts that basically were "true" at each end with the center unmachined area so far "off-center" as to make me wonder if the whole car would not have done a "bunny hop" going down the road but the ends were basically near perfectly true machine wise but likely a mile off in terms of weight balance over all.

One advantage of the repro drive shafts that I have seen is they are turned from a solid piece of shafting and are thus inherently balanced much better than most originals. I am pretty sure there is more than one drive shaft maker and at least one of them has or had a problem of missing the correct location on the ujoint pin hole which tells me they either didn't have the factory drawing or didn't care enough to bother to check their work. Either way I wouldn't touch the thing since it would seem to indicate that other areas might also be incorrect.

Hummm, ...now I am up against trying to decide if I should just buy a new driveshaft to replace this one, --and if the one that Snyder's sells is one of the good ones or bad ones.

Thanks John. Also, check your voice mail if you haven't already.

I can't get my cell phone voice mail until I leave the area. My house/shop is a cell phone dead zone. I cannot use my cell phone unless I am on the road somewhere. It is the price one pays to live away from the herd. I will indeed retrieve your voice mail but often I don't even get them for days after they are sent. Tried all of the various services - none work here. I figure to the right buyer - it might ADD value to my house ha ha.

Reminds me of the time in the late 1970s when I met a salesman for Rockwell truck axle division. They were trying to sell fiberglass driveshafts for Mavericks or something. Nobody at Ford could tell him how strong a driveshaft had to be. I'll bet they didn't have specs on runout, either, as long as warranty costs weren't too high.

John, it's prbably your Strobospark and other sparking devices messing with your celfone reception..

rdr

Brent,

Your axle does not sound like it's bent at all. It's just that the unmachined area has runout.

How fast can that lathe turn? 1500 RPM? Run it up as fast as you can and you'll get some idea just how much vibration it will cause.

Here's the math, I believe.

If the runout is 0.050", I assume you mean total indicator reading. If so, this means the mass of the center of the driveshaft is running 0.025" off-center.

If it is turning 2100 rpm, or 35 revolutions per second, that's 220 radians per second.

Acceleration in feet/sec2 is equal to the speed in radians per second, squared, times the radius in feet (0.002 feet in this case).

So, the acceleration on the off-center mass is just less than 100 ft/sec2, or about 3 "gees".

I have no clue how much mass is off-center on that driveshaft. If it's a huge 5 pounds, though it is probably less, the shaft will add some 15 pounds of load to its bearings as it spins around.

I rather doubt you'd ever feel it.

Seth

I installed a drive shaft from Snyder's last year with no problems. The hole for the u-joint pin lined up with the holes in the tube and u-joint.

Thanks guys. I ordered a new one this afternoon from Snyders. This is a personal vehicle that I just don't want "issues" with so I erred on the side of "don't want no vibrations".