Re:How do vacuum hubs work?

Sorry, I know how they work, but more specifically…

When you engage four wheel drive and all the electrical gubbins decide to (hopefully) engage the vacuum hubs… I understand they are “sucked” in to engage them, when they subsequently go “off” are they just lightly sprung to go back out, or does the vacuum system swap from suck to blow…? (No sniggering there chaps!)

I’m still in hospital and have far too much time to think about stuff… the next buggy I’m building… traction aids are so expensive, so I was considering welding up the front Diff and as I’m only using Jimny parts for the ground-up build (i.e. not the electrical systems) I’m considering just buying a 12v vacuum pump to suck the hubs on and off at will… Infact, the more I think about it I’m considering having two vacuum pumps so I can control them separately?! No, think about it before you all shout at me… in a four wheel drive system you’ve only ever really got drive to one wheel on each axle due to the diffs being open (ie no traction aids in the Diff). So power passes to the wheel with the least path of resistance… hence if you’re cross-axled the one in the air spins fast and the one on the ground just sits there maybe twitching a bit  … So imagine in a small one seater crawler (style) buggy if  you could decide where the power goes?! i.e. the Diff is welded up and I could switch one vacuum hub or the other on? And for full traction situations where steering isn’t an issue, BOTH.


 

The solenoid valves vacuum in both directions. So yeah with multiple manually controlled valves from the same vacuum it would be possible to have the precise control you want.

wrote:

The solenoid valves vacuum in both directions. So yeah with multiple manually controlled valves from the same vacuum it would be possible to have the precise control you want.

Oh blimey! 

Explain “The solenoid valves vacuum in both directions” to me?!

Does that mean, now that I remember that there are two ports on each hub, that one port sucks on, and excuse the expression, the other port then sucks off (?!), hmm, ok thanks Lambert, that’s going to take some more thought to make quick switching to work effectively…

Yes 2 ports per hub. One for in one for out.. essentially you need a pair of 2 position valves with one position feeding the on port of the left hub the other position feeding the off port same for the right hub. You would only have separate vacuum sources for redundancy but in reality you only need a manifold vacuum as without the engine running you wouldn't have drive anyway.

Don't bother with vac pumps unless you are using a diesel. With a petrol you just use manifold vacuum. Misubishi L200/Pajero hub valves are pretty cheap. That's what I'm using on my Jimny. The connectors aren't compatible with the Jimny but that's not a problem in your case. Another option is to do it fully mechanical with push button valves . P goes to vacuum, T vents to the atmosphere, A goes to the hub. It's easy to get 1/8" to 4mm push fit connectors. 4mm pneumatic hose fits the rubber connector pipes on the hubs.


The hubs just need vacuum for a couple of seconds. Vacuum one way to engage, the other way to disengage.

I don't see why your idea would not work. If you want to turn tight, just apply power to the outside wheels. If you want to turn really tight, brake the inside wheels as well.

Thanks again!

I’m thinking it will - eventually - be powered by a motorcycle engine (a Suzuki of course) so I’d need a 12v vacuum pump at some point too…

Last question (for tonight  ) then, are these vacuums short bursts or constant then? i.e. a quick burst to just move the drive cog in the hub one way or the other, or continuous so the drive cog is ‘held’ either on or off?

I’m just trying to get my head round everything to fill time incarcerated in hospital(s), and to know how to rebuild the two narrowed axles when I eventually escape…

 

I know the back (front axle) is going to be an open Diff and have already rebuilt the rear Diff with 26 spline side gears to suit a pair of the shorter side TrailGear HD shafts and CVS, with fiddle brakes -


 

So I’m trying to decide about the front axle…