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 🙂
#1 by Bill on June 7, 2012 - 3:43 am
This is super-useful even if you haven’t found the solution yet. I’d be very tempted to simply bore the whole thing out to a single diameter and be done with it — although I think the split delrin bushing would work fine.
#2 by albell on June 7, 2012 - 5:44 am
I would have bored it out if I could have, but my lathe is not large enough to hold the propshaft, and I don’t have any hand reamers that would work. I really couldn’t think of any other way of boring out the housing accurately. I was thinking I would take propshaft to local machinist if the split bushing did not work.
#3 by Alan on June 7, 2012 - 10:56 am
That is not at all how I found my ’86 shaft. For starters, the bronze bearing found in mine was already a split design, sintered, but with embossed grease-retaining diamonds. Secondly, the annoying inner lip you found all too late was not present in the female ID of my shaft. This may reflect running production changes in a low-volume part at SDP, and finally brings some truth to the (non-cost-effective and) non-rebuildable rumors. I knocked out the end plug on mine and withdrew both sleeves from the outer end with a bearing puller. I further creased the end plug (now trapped in the shaft) with the use of a long bar before removing the pretzeled-thing with a magnet…the toughest part of the task. Two commercial un-flanged metric polymer sleeves were reinserted to the factory depths. If I can offer anything, it is that the plastic sleeves I think were a good choice, and your replacements should work well and perform more quietly when “lugging” the engine than even new originals. Be aware however that all Delrin is not created equally, especially with regards to creep and water resistance. Pay attention also to u-joint phasing when reassembling the shaft. If your split bushing gives you problems, it might be simpler to find a driveline shop to cut off the tube, allowing you to perform your work before it is re-welded. Certainly a rebalance will be required in either case, as boring the shaft by chucking its ID cannot assure original centers even with a practiced machinist using a four-jaw. I re-balanced the shaft in situ myself running the car on a lift with the cruise control and using a strobe and hose clamps and it has run smoothly at all speeds now for several years. Good luck and have fun!
#4 by albell on June 7, 2012 - 11:14 am
great info, thank you. I wasn’t specific, nor was I offered any choices, when I bought the Delrin. I hope what I got will work out. This particular propshaft is from a post ’86 van (specific year unknown, perhaps ’89). I should take a closer look at my ’86 shaft and see if it is similar to yours. The embossing to hold grease seems like a good idea, I applied a bit of grease even with the Delrin bushes, but I bet only a layer a few molecules thick remains on the bearing surfaces after I pressed assembly together (it is snug fit). I wonder just what the range of
radialrotational motion is? Can’t be much eh?
I’m very interested in your in-situ rebalancing method. One thing that springs to mind is the droop of the wheels when on the lift. Is this, and the resulting cv joint angles, anything to be concerned about?
Harry Mann, mod. on the 80-90 forum, experimented with stick on roofing material on shaft to dampen resonances. http://wiki.club8090.co.uk/index.php/Syncro_links_page#Prop-shaft_sound_damping
I’m curious about this, and mindful of his experience of the strips coming off. Any thoughts?
Thanks again for commenting,
PS you knocked out the end plug and got it back using magnet – I can visualize that fishing trip 🙂
#5 by alistair on June 8, 2012 - 7:06 am
I had another look at the bushings in the ’86 propshaft. Inner end bushing is one piece, not split as you found. Annoying inner lip is not present.
#6 by Alan on June 8, 2012 - 4:41 pm
Glad you got it back together alright.
I greased my plastic bushings too as I had read they were compatible with grease and even the few molecules that remain should help protect the steel against the formation of some rust. I was fascinated to see that the harder surface of the piston had suffered a fair share of the wear and the bronze material looked comparably new. I have seen this before (the lip of a seal often wears the shaft faster than the rubber). The steel discoloration looked more like the type of “coffee table ring” you might get between longstanding contact points of dissimilar metals. I think the assembly only moves a few degrees…ever. If the shaft has to come apart again and shows any further wear I may have the shaft hard-chromed to restore it and protect it from rusting. The whole exercise was kind of a “nothing to lose” experiment. I wish I had found this first and might have felt less alone and not put it off.
I was completely unable to see the split in either of my bushings. I had fabricated a puller from all-thread and a thick, hard, air-cooled VW cylinder head washer (I think). I cut two sides of the washer to pass through the ID of the bushing, and beveled the remaining outer radius like a throttle’s butterfly to make a toggle-washer. Since I had first tried cutting the outer bearing with a modified cold-chisel in my air hammer and didn’t like what it was doing, I thought I might have cracked the outer bronze sleeve. It was only when the inner bushing was removed without violence that I noticed the hairline factory bushing split and cursed my chisel marks outboard on the housing. It was this puller I then converted into a driver by double nutting on each side to install the poly bushes. I was surprised by both the interference fit, and the compression of the plastic material, compared to its clearance when unpressed.
I mucked about for some time with the strobe. The magnets and electric guitar pickup and electret microphone I thought should have both made good mechanical vibration pickups as a flash trigger, in theory, for the disposable camera flash circuit I had modified. In theory only! I ended up with a rheostat and a timer circuit to try and “freeze” the motion of the shaft as it oscillates about in space…much like the neon strobes we used to use to adjust the speed of our turntables with (but the cruise control does cycle the engine speed a bit with no load). I had used a white paint pen to mark the shaft around its circumference with numbers so I could find the side that was getting thrown outward at the peak vibrational speed. In the end I trusted my eyes to the paint pen markings as much as the changes I could see with my weaker than commercial strobe! You see, it turns out the obsessive Germans made such damn-round driveline tubing that what I found was the paint pen could be used to always mark the heavy side of the spinning shaft as opposed to the same high point in the tubing each time. You probably wouldn’t even need a strobe. Don’t wear loose sleeves and just use the driveshaft protection bars as you would a lathe tool rest until the pen “just” touches the shaft. Amazingly, the weight of the worm-drive mechanism of two stainless-steel hose clamps was Way more than enough to get rid of my vibration. Put the hose clamp tensioners both directly across from the center of the paint mark on the shaft, and try again. Too much, separate them and try again. No more vibration…good. Try a full range of speeds and confirm with the pen. My clamps ended up at, like, ten and two o’clock, if the heavy spot was six…so you have a lot more balancing-mass than you’ll likely need. When it is right, the slightest touch of the pen on the spinning shaft will make a full radius marking of the same width. I was glad I had freshly painted everything a glossy black. You may have to do both ends of more than once for the best result. I only ended up changing the balance on the rubber guibo end.
I did feel the CV’s to see if they were warm, and “steered” the fronts while spinning to listen for changes that could indicate wear or looseness in the front outer CV’s. My Syncro is at stock ride height with factory CV’s, suspension, and shocks, so the running angles of the CV’s are within the factory limits of the design. If you have a lifted rig in which modified trailing arms have been installed, or longer shocks, this could be a concern. If you have tight CV’s…those that are less than 200 miles old…I think it might be better to wear them in a bit at lower operating angles on the street first or they might warm up. If unsure, I would rotate the wheels by hand with the transmission in neutral and feel, listen, and look for any binding. If you find it, your car will most likely be in this same situation every time the suspension gets to full droop, and it would be a good time to consider some limiting straps, a shorter shock, or different CV’s (or those modified) for more angular travel.
It was my experience with the surprisingly small mass needed to effect a major vibration that would steer me away from adding dynamat or other dampening materials. If I ever have a sudden vibration after driving off road, I’m first checking the shaft for a mud-spatter buildup! If you clamped a strip of rubber under the hose clamp I bet it would dampen much of any remaining sound like a harmonic balancer. While the shaft is out of the car you could quantify this effect by hanging it from wire and “pinging” it slightly with a hammer. My plastic bushing equipped shaft makes none of the bell-ringing noises it did when lugging previously. If you stall the engine, you can hear what I think is growing lash in the front ring gear at the moment when the motor dies…I don’t do this much, and it doesn’t concern me yet. Take out the electronics experiment, and I like the smooth, cheap, quiet home-brew rebuild just fine.
Oh, and let’s keep this early-shaft thing to ourselves, I don’t want to put a price run-up on early shafts unless I’m ready to sell mine as rebuildable 😉