I have my propshaft off while I try and track down my transmission noise (see previous post). Some helpful syncro owners over on the IG16 forum suggested that I look at my propshaft as the source of the noise. Well why not eh?
This is a story of mistakes and ignorance. When I compared my two propshafts in this post, I mistakenly concluded that one shaft had thinner walled bushings than the other. Well it did look that way and both assemblies felt equally tight – ie acceptable fit of shaft into bushings. But I think I must have been wrong for when I examined the “thin walled bushing” propshaft (the one I just removed from van), I could detect play in the bushings. The rubber giubo and the internal O-ring have been removed and dial indicator set up to measure movement as I lifted U-joint yoke up (trying not to rotate joint as I did it).
Here is diagram of that end of the propshaft just to refresh memories.
And my measurement set-up.
And short movie showing movement.
I admit to this being not an extremely accurate way of measuring the radial play, was hard to just move the yoke up and down and not rotate it. But I could feel the play and it was more than I think it should be.
So it comes down to replacing the bushings. The outer one would be relatively easy, but the inner one is a different story. And I think the inner one is important to be snug as it is at the end of the shaft and would limit shaft movement more than the outer bushing. That was a convoluted sentence, I hope you get the idea.
On the Yahoo Vanagon Syncro mailing list, the bushings have been discussed a few times. One list member wrote (a year ago?) that the inner bearing could not be replaced as it sits in a recess in the tube and was probably installed before that end was welded onto the propshaft. The drawing at top of this post does not really show the recess (drawing too small), and I had forgotten all about it.
Foolhardy is a useful adverb to use whenever I get it into my head to fix something. I kid myself that I know what I am doing, ha!
I pondered how to remove the inner bushing and came up with chiseling it out. I have this neat little 1/4″ chisel that looked like it would work.
And off I went, chiseling a groove down the inner bushing. It took a couple of groove before I could break out the bushing. I found it difficult to get a good pic of what was going on deep in there, but in this pic you can see a section of the bushing folded inwards. Sharp eyed readers will be able to see that there is a lip in the tube which locates the bushing. Bushing was pressed in from other side, then that end cap inserted (portion of bushing is obscuring the hole in the center of that end cap), and then assembly welded to propshaft. Even sharper eyed readers will notice another, smaller lip about halfway between inner and outer bushings. I overlooked this, I have no excuses why and it bit me on the ass later on.
Bits and pieces of the bushing. After I knocked the fragments out I could see the aforementioned lip. I didn’t feel very happy at that point.
I really had no choice but to go on and cut out the outer bushing. This pic shows how well the chisel cuts the bushing and the underlying steel – doh!
Note the fretting or corrosion on the surface of the bushing. Here is a close up of a fragment, looks a bit like sintered bronze, like an “Oilite” plain bearing.
So alright then, what to do about the inner bushing problem? I wasn’t about to cut the end off the propshaft. I settled on the idea of turning down the diameter of the end of shaft a tad, to about 23 mm from 25 mm (diameter at end where shaft inserts into bushing) and making that reduced diameter area about twice as long as the original bearing surface. I reasoned that a Delrin bushing could be made to fit into tube, be supported by the tube and extending on unsupported over the original bushing spot. Jeez, I need a diagram to explain.
Here is a cartoon cross-section of the end of propshaft that houses the bushings.
And with shaft in place.
And assembled with new bushings.
The drawings are not to scale and are meant just as sketches to get my idea across. Important thing to note is the new internal bushing will come further up the shaft, and be unsupported in old bushing area.
Off to the lathe!
Mounted yoke shaft between centers, was lucky and set up resulted in less than 0.001″ run out at end (inner bushing area).
Then turned the end down to 23.00 mm. I found it hard to get a nice surface finish even with very light cuts. I was using a round nosed HSS tool bit (has given me nice finish on other jobs), but this time I had problems. So, a less than perfect finish.
Chamfered the end and gave it a quick polish. I think it will be good enough.
Next step is to make the Delrin bushings. Whoa, slow down sonny! Have another look inside the propshaft, it is not quite the same as you describe in your sketches. Go on, look at that picture you took of the bore. What? No! Really? , let me… well gosh darn it.
I missed this before I thoroughly cleaned out the bore – the bore is machined out slightly for a little way, above the machined out area for the internal bushing. Illustrated, but exaggerated and not to scale, the slightly bored out region is not as large a diameter as illustrated, but it still screws things up for me.
So my original plan of a longer internal bushing will not work, see?
I decided to make the outer bushing, classic avoidance behaviour. I actually made 2 outer bushings, first one really as a practice piece, second one with a lip. I also went ahead and, again for practice, made the now discarded inner bushing concept.
Delrin rod (1.5″ diameter but turned down a tad before this shot) and boring out to fit yoke shaft. Gotta love that chipped cutter I am using, funny thing is that it does a nice job on this plastic.
Bored out to size, 25.00 mm.
I made a quick and dirty mandrel to mount bushing so that the outside diameter could be turned to size.
Then to get the bushing off the mandrel, I bored out the end of the mandrel.
To make the “practice” inner bushing, I first bored out Delrin to size, parted off, then mounted oversized bushing to yoke shaft to machine down to size. Note the outer bearing installed first. Makes you wonder if I hadn’t realized the issue with the propshaft bore yet, doesn’t it?
As I mentioned before, I went on to make another outer bushing and gave up for the evening.
Back to the problem of, in essence, installing a bushing from the wrong end. How about making the bushing the squeezing it to deform enough to be pushed in the bore and end up in position, then use a tool to form it back into shape, against wall of bore? Nope, daft. Well how about taking propshaft to machinist to bore out? Well, that might be the fall back solution. Ok, how about a split bushing? Would that allow the bushing OD to be reduced enough to be pushed in and then expand in correct place? Mmm, maybe, worth a try?
Something like the Iglide Clip2 plastic bushing (but without the end flange)?
The nominal diameter of the bore is 26 mm, and where the internal bushing is located, 28 mm. Circumference of bushing should be (pi X 28) 87.96 mm, and to fit in through 26 mm bore, 81.68 mm. So slot in bushing needs to be at least (87.96 – 81.68) 6.28 mm. Seems like a large slot to be cut. One thing in my favour is that the yoke shaft does not fully rotate in the bushing, just a few degrees allowed by the flex in the Giubo. A diagonal slot as shown in the Iglide bushing above would provide better support of the shaft so it is worth a try cutting the slot that way.
This post is getting rather long and rambling and I have other work to do, I’ll try making the split bushing later and report back in another blog entry. Feel free to give me a hard time in the comments section, I deserve it 🙂