Front Hub Vacuum Route ?

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bryn

The job is progressing. We had a look at the front wheel bearing today and it was absolutely goosed. Smartly pulled it apart and fitted a new one with one or two observations on the way. The old bearing was a two part double row ball bearing whereas the new one is a double taper roller type. The retaining nut came off ok but the sealing flange was quite corroded and although it cleaned up will be replaced. Finally,,because of the wear to the sealing flange I wondered if the seal in the vacuum hub was a bit worn too but I cannot seem to find a replacement. Has anyone any idea where to source one please ? There was so much slack in the wheel bearing that it may be the suggested source of the vacuum leak.

Today I stripped the vacuum hub into its component parts. The first seal is fairly easy to prise out from one of the three recesses around the edge of the unit,followed by the engaging sprocket. The sliding collar assembly comes out in one piece after a bit of clouting with a rubber mallet on the outside of the hub. It engages in three slots which I think may have been part of the problem I had and some of the information I sought. These slots were solid with a mixture of grease and corrosion and I think seriously reduced the chance of the unlock part of the operation operating correctly. Opening the sliding collar unit was quite tricky as there is nowhere to get a lever in to prise the two halves apart. As there is a big spring inside giving a bit of assistance I gently nipped the lower steel part in the vise,the rotated it a few degrees and did it again all the way round,hearing a few clicks as I did it and found that the two halves had begun to separate giving me a chance to pry them apart. All becomes clear once inside as to how the hubs operate. Fixed to the back of sliding collar is a diaphragm which provides an airtight seal to the unlocking chamber. Vacuum is directed down the three slots mentioned earlier into the chamber and pulls the collar back to the retaining magnet. Back to the start,,the large seal I removed from the hub at the outset forms,together with the new wheel bearing seal,forms the locking chamber which operates on the sliding collar in the opposite direction and pulls it into engagement. The exact route the vacuum takes from the incoming pipes to all this is still a mystery but will be resolved tomorrow.
The upshot of all this is that when I put it all back together and went for a swift test,,IT WORKED !

That's a really good result, well done. I have been reading this with interest as finding information on the way hub works has proven elusive, so well done on just going for it. I plan to keep my hubs vacuum operated and fix any problems, but so far everything is working so not seen inside.
If you feel like it or get chance a photo of a simple sketch of how it works will help my simple mind understand your description better.
No problem if you can't, sure one day I'll have a chance to follow in your footsteps.

This level of intricate design complexity is why most people opt for the manual hub option and the greater reliability it brings.

Can't disagree that manual hubs are going to be more reliable in the long term, but I suspect they are just more tolerant of abuse and lack of maintenance (thick set rusty grease etc).
But I also feel the trend is to bin the vacuum system straight away in favour of manual hubs as it's seen as complex to fix, this mainly due to lack of detailed information on what is actually happening when you press the button. I don't want to bin mine, so just trying to gather as much information as I can before it goes wrong, and the movement within the hub is one area I don't fully understand at the moment.
It can't be that complex can it? after all it's a mechanical "Steam punk" system in operation.:laugh:
So any info or drawings of what's inside appreciated.