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Re:How do vacuum hubs work?

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17 Apr 2022 17:53 #242945 by X8GGY
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.


 

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17 Apr 2022 18:02 #242946 by Lambert
Replied by Lambert on topic How do vacuum hubs work?
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.

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17 Apr 2022 19:09 - 17 Apr 2022 19:13 #242948 by X8GGY
Replied by X8GGY on topic How do vacuum hubs work?

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…
Last edit: 17 Apr 2022 19:13 by X8GGY.

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17 Apr 2022 19:18 #242949 by Lambert
Replied by Lambert on topic How do vacuum hubs work?
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.

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17 Apr 2022 19:28 #242950 by LesNewell
Replied by LesNewell on topic How do vacuum hubs work?
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.
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17 Apr 2022 19:38 - 17 Apr 2022 19:47 #242951 by X8GGY
Replied by X8GGY on topic How do vacuum hubs work?
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…
 
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Last edit: 17 Apr 2022 19:47 by X8GGY.

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17 Apr 2022 19:41 #242952 by X8GGY
Replied by X8GGY on topic How do vacuum hubs work?
Looks like Les has already answered my question whilst I was typing… 

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17 Apr 2022 23:03 #242960 by Busta
Replied by Busta on topic How do vacuum hubs work?
Welded front diff? That's a crazy idea! 

I've been running a welded front diff for over a year now in my daily driven Jimny. From my experience I can tell you you don't need to switch the hubs individually to achieve what you want to do.
In a cross axle situation drive will already be going to the wheel that's on the ground. When you want to turn, both front wheels will be actively pulling the car in the direction they are pointing so the car has no to choice to do anything but turn. And obviously in a straight line it will go straight. Combined with fiddle brakes on the rear axle you will have a very capable and highly manoeuvrable jimny. It's only when you lock the rear diff that you lose manoeuvrability.
The only accompanying mod I've done is to bypass the 4wd switch on the transfer case, instead operating that circuit from a simple on-off switch inside the car. This gives me control over when the hubs engage and disengage which is obviously very important for quick disengagement when you transition onto high grip surfaces or any other time where drive to the front wheels is not required.

It's also worth noting that the hubs work just as well with pressure as they do a vacuum. 5-10psi is enough to operate them (the engine vacuum is within that range). Just be aware that the hub seals (specifically the one behind the wheel bearing and the one in front of the CV joint) are critical to the system working and aren't designed to work with pressure. It may be prudent to glue them into place.  A cheap 12v compressor with a pressure cut-off would be more than sufficient for operating the hubs in this manner. 
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18 Apr 2022 09:55 #242970 by X8GGY
Replied by X8GGY on topic How do vacuum hubs work?
Thanks Busta!

I’ll weld the Diff up before rebuilding the front axle then… cheapest traction mod available! 

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18 Apr 2022 10:30 #242972 by mlines
Replied by mlines on topic Re:How do vacuum hubs work?
The vacuum is not required once the hub is engaged as magnets normally hold the position ( subject to grease, dirt and sods law)

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18 Apr 2022 10:58 #242974 by X8GGY

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24 Apr 2022 15:55 #243127 by X8GGY
Replied by X8GGY on topic Re:How do vacuum hubs work?
Been giving this lots of thought today…

Decided after looking at all the very expensive options for front drivetrain upgrades, to indeed weld up the front Diff, and use standard front shafts, albeit with new CVs as they seem reasonably priced…

So I’ll order a couple of them for when I get parroted and can get on with finishing and rebuilding the two narrowed front axles… so 26 spline TG shafts in the back with an open Diff and fiddle brakes, and the above in the front with a 12v vacuum pump(s).

THANKS for all your valued input!

Dave
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