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Vacuum hubs

  • Baloo
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31 Oct 2021 13:39 #239761 by Baloo
Vacuum hubs was created by Baloo
so can some one explain the front hubs to me,  why is there 2 pipes to each hub, i assumed  it was using a vacuum to over come the spring in the front hub  there by allowing drive from the halfshaft to be transmitted  to the hub?wheels,   i assume the vacuum  originates in the inlet manifold ?,  where is the valve that opens the hub to vacuum and what operates it ?    i was just going to convert the fixed hubs all the time as it wont be on the road , but i was just pondering welding up the front diff which destroys  the turning ability as the front axle will try to push on  so could i retain the vacuum engagement of the front hubs and have 2 separate valves on the dash board and lock/unlock the front hubs individually as required ? 
thanks Andy

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31 Oct 2021 13:57 - 31 Oct 2021 14:04 #239762 by Busta
Replied by Busta on topic Vacuum hubs
There is a diaphragm in the hubs which moves the engagement collar back and forth. It requires a vacuum to move either way. A vacuum line from the inlet manifold runs to 2 solenoids under the battery. One opens to lock the hubs, the other to unlock them. They are 2-way solenoids, so when one solenoid is in the vacuum position the other is venting to atmosphere via the little blue filter thing. That's what the 2 hoses are for. It's a fairly simple system.

If you have a manual transfer case, the easiest way to gain manual control of the hubs is to disconnect the 2 wire connector from the transfer case and run 2 wires from it to a switch on the dash. This is what I have done. The switch then allows you to operate the hubs completely independently of the transfer case. The 4wd light on the dash will then light up whenever the hubs are locked. There is probably a similar way of doing it with the electric transfer case models but I'm not aware what it is.

If you weld the front diff (as I have done) you definitely need a means to lock and unlock the hubs, and for me the vacuum system is far more convenient than manual lockers. A welded front diff won't limit your turning circle off-road as I have demonstrated on here previously, but it will put huge amounts of stress on the driveline if you have the hubs engaged when driving on grippy surfaces.

For extra reliability I have replaced my vacuum hoses with new PVC pipe and routed them up the brake hoses and into the engine bay, rather than along the axle and radius arm where they are quite exposed. You will also need to make sure the hub seals- one behind the wheel bearing and one where the CV enters the hub are both in good condition as the are critical to the system holding a vacuum.

Edit to add: You can also operate the hubs via pressure rather than vacuum. Applying pressure to either of the hoses under the battery you can make the hubs click in and out. This obviously uses the opposite hose to the vacuum system. Just be careful not to over-pressurise it- the vacuum system only runs at 5-10 psi.
Last edit: 31 Oct 2021 14:04 by Busta.

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31 Oct 2021 14:13 #239764 by Baloo
Replied by Baloo on topic Vacuum hubs
perfect excellent explanation thank you its the way i think im going

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01 Nov 2021 21:09 #239799 by Baloo
Replied by Baloo on topic Vacuum hubs
Busta so you run a welded front diff ? does it improve traction significantly off road ? have you got the rear welded as well ?

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01 Nov 2021 22:14 #239803 by Busta
Replied by Busta on topic Vacuum hubs
I run a welded front diff and a Quaife LSD rear.

Yes it improves traction significantly offroad. Most importantly it does so in a controlled manner without any of the loss of agility you get when you lock the rear diff. So rather than trying to push straight ahead all the time it simply goes wherever the front wheels are pointing, which is something a lot of people struggle to get their head around. For example if I get into some ruts that I don't fancy following I just steer out of them and it climbs out without any fuss. And if one front wheel is up against an obstacle such as a rock, rather than than the other 3 wheels spinning and the car pivoting around the obstacle it just climbs up it without fuss.

And obviously as soon as you flick the switch to unlock the hubs the diff is disconnected from the drive wheels, the car is in 2wd and it drives completely normally.

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02 Nov 2021 12:05 #239808 by Baloo
Replied by Baloo on topic Vacuum hubs
sounds good to me, i am going to try it 

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