HELP! Rear axle/hub problem

[Steve Davis]

I'm at a loss (after over 30 years of FV). I stripped the splines from a hub in the second race of the Atlanta major - I thought it might have been NOT tightened enough. Got the old one off, no problem. Put on a new one and it won't "snug up" as it seats on the axle. Inspected axle - no noticeable wear on the splines - looks good. Tried again -- drum still rocks slightly when all the way up. I figure, it's somehow not seated enough and the axle hasn't pulled fully through the bearing, so tried tightening again to full torque - loosened nut and hub still rocks. Checked against another trans - pulled nut and found what I expected - hub fully seats without nut and doesn't rock AT ALL. Pulled backing plate assembly - got main bearing off - all looks good - checked spacer for measurement against several others and I already had the thinnest one. Pulled the spacer behind the bearing and inspected it .. obvious damage, but not TERRIBLE - but needed replaced. Put in new one - tightened, loosened and same thing. Finally measured splines sticking out from inner hub cover. I find that the splines on the "good" trans stick out about 1/8 MORE than the ones on the suspect trans. (not surprising). Swapped drums between good and bad, and found what I expected.. the bad one won't seat on the splines, no matter how much torque is applied. Went back and pulled the VW washer that's outside the spacer to pick up a few thou' of space .. still same thing.

At this point, I have no idea where to go except to remove the axle tube and axle - but I can't imagine what I might find there. The axle is free to move in/out as expected (carefully, so as to not loose the fulcrum plates behind the paddle). Putting on new drum (tried several hubs - all same result) is a worthless effort since it's obvious that the drum is not properly seated on the splines and will just wobble loose quickly, destroying another drum in the process.

Can any of you out there think of anything I haven't considered?? It just seems that the axle MUST be "mis-manfactured" and have the wrong length from that inner spacer behind the wheel bearing to the end of the splines.

Ideas??

Steve, FV80
(also posted to the interchange)

[problemchild]

The axle tube assembly has way more chance of being incorrect length than the axle itself. The pin can also interfere with the relationship between the tube assembly and axle, particularily if the the axle tube assemmbly is odd.

[Daryl DeArman]

I'm not certain that I understood exactly what you are describing...

Cracked axle between rear facing of inner hub spacer and end of threads? Torquing nut causing that dimension to grow?

[Steve Davis]

More info... Greg - you are right, but wrong (I think). I don't see the axle tube length to the casting being in play here (but I'll look again in a minute).
Daryl - not sure where you are.. there is no cracked axle - the axle seems perfect .. except about 1/8" too short.

Additional - posted on Interchange...

BLS wrote:Maybe a dumb answer, but wouldn't it be more likely the axle tube length than the axle? The position of the bearing housing etc. is determined by the axle tube, pressed on to the tube IIRC.

Yes - it would be .. however, the hub on the spline position is determined by the items in order..
1). axle - free floats in the diff regardless of the tube length (within reason)
2). the outer axle flange near the splines
3). The beveled spacer that matches the radius'd flange in item 2
4). The main axle bearing that rides again said spacer in item 3
5). The outer spacer that rides the outer surface of the main bearing (encapsulates the small o-ring)
6). The (somewhat questionable) spacer washer .. that is usually worthless and destroys itself in aftermarket axle seal kits .. and is often left out .. successfully
7). The hub/drum itself which seats on the splines.. usually FULLY when all said items above are tightened.

I did check and make sure that a hub WOULD seat on the axle without the outer spacer in place. The drum seats nicely.. just as it should. And that ~1/8" of missing length from the outer spacer to the end of the splines seems about what it would take to get it to work...

Steve, FV80

[S Lathrop]

Ware on the splines is very hard to detect.

The FV splines and the cast iron drum are the same dimensions as the parts on the Zink Z10 FF and Z11/Z14 FSV.

I found that the quality of the flanges we used were so bad that I started to make my own flanges by machining them from German made rear drums for other model VWs.

I have had success assembling the drum on the axel using Hysol or Scotch Weld structural adhesives. This was necessary when we started racing the FSVs on ovals. It works well and lasted for a season on FSVs.

Down side is that you will have to use heat to take the parts apart. You can wax the splines to make disassembly easier.

You might have a bad inner spacer. I have never found this to be a problem but you might check.

[problemchild]

I regularily see 1/8" difference in the length of what I consider serviceable tube assemblies and have seen 1/4" on some that looked normal. Erratic QC of axle tubes and improper assembly (including flattened bells) seem to be contributing factors.

[Daryl DeArman]

Daryl - not sure where you are.. there is no cracked axle - the axle seems perfect .. except about 1/8" too short.

...misunderstood, as I suspected, what you were describing. When you said you couldn't get it to "Snug Up when it seated on the axle" I missunderstood that to mean you got the drum to seat but couldn't get the axle nut to torque.

[Bob Neumeister]

Steve, Can you enlighten all of us on what you found the problem was? thanks

[Steve Davis]

I finally got it "solved", by trial and error. I changed the axle and the drum still wouldn't seat to my satisfaction. I sorted through several drums I had on hand and FINALLY found one that would seat "properly" (in my estimation -> no rock in drum after torquing nut and then removing nut).

As I tried to explain earlier, the axle tube has NOTHING to do with the issue. The tightness of the drum on the splines is determined by the stack of spacer/bearing/spacer/[washer]/drum - from the axle flange out to the drum. I took the axle completely out of the car and did this testing on the bench with ONLY the axle, the parts and the drum. The axle tube was laying elsewhere.

Maybe I'm expecting too much. I talked to Bob Lybarger at the 50th and he said that all drums do NOT necessarily 'seat' to the point that they don't rock AT ALL. Maybe it's one of those things where, when there's no problem, you don't notice a little movement in the drum, but when things are questionable, I start looking for problems and look a LOT more closely at specific things that I don't normally pay much attention to. Still strange though, I tested several combinations and most seated as I expected ... including all of the trans (3) that I personally own. Maybe I've just been lucky up till now.

Steve, FV80

[gegar]

Hello Steve,

I have experienced the same issue that you are dealing with many years ago. What I found in my case was not an issue with spline fit/clearance, but instead a "squareness issue" with the stack up the following items: inner spacer, outer spacer, axel portion that mates with inner spacer, ball bearing, the inner contacting surface of the drum (most common culprit), and lastly the outer nut contact surface. If any of these items is not absolutely uniform in thickness, there will be point contact somewhere in the stack up after you apply the torque. I found this to be the main reason that rear drums would "loosen up" after some track time, the point contact wears away due to fretting, which then results in looseness. All the items in the above mentioned stack up should be measured in order to gage for uniform thickness. The axel should be placed between centers, and the inner ring seating surface checked for run out. I would often take a light lathe cut on the inner and outer drum contacting surfaces in order to true them up, I would use the drum's wheel mating surface as my reference datum. Lastly, I used a flanged outer nut to increase the outer compression contact area.

Hope this helps, Al

[sabre1fv]

Steve,

I'll second Al's comments though I have yet to run into this problem. I have a box of the inner and outer spacers that are no longer of uniform thickness that I have accumulated over the years - I have been hoping to get access to a surface grinder to true these up. Perhaps these could be trued with a lathe as well, but it seems to me that they were too hard to cut with lathe tools.

-Jim