Grinding noise from front wheels

Hey everyone!
Mechanical question here.
2010 Gen 3 Jimny with air lockers.
Everytime I go over corrugation on a dirt road or over a cattle grid, I get a nasty rotational grinding sound in the front end.
The sound changes slightly if turning, and also changes with speed.
I'm pretty sure it's got something to do with the vaccum hubs because if I restart the engine it stops.
I haven't had it happen when in 4wd, only in 2wd.
I'd prefer not to do a manual hub conversion at this stage.
Any suggestions on how to fix it myself or where to take it near Brisbane QLD would be greatly appreciated.
My local 4wd mechanic hasn't had much to do with vaccum hubs.
Cheers,

This kind of issue is commonly caused by a leaky vacuum solenoid. The solenoids are below the battery and are straighforward to disassemble and clean.
The vacuum system is very simple and nothing to be scared of. It uses the engine's vacuum to simply suck the hubs into position. There are 2 solenoids, a vacuum switch that "checks" everything is working, some hoses and the hubs.

The simplest possible cause is something caught between the dust shield/backplate and a brake disc, or the backplate/dust shield is touching the disc - just bend it away from the disc. this produces a sort of scraping noise that gets worse when you turn the steering one way.

It could be that one of the vacuum hubs is partially engaged, although this is difficult as they are magnet locked disengaged. I'd expect a brrrr! noise like gears grinding.

I suppose the easiest test is to get it making the noise, and then jack up the front wheels and turn them by hand to try and locate or feel the problem



 

I agree with facade 
Also you could remove the vac hubs and drive it 
This will be part of the elimination game 

Thanks for the help.

I'm thinking its a leaky solenoid or broken hub magnet which is allowing the hubs to partially engage when travelling over rough corrugation. Definitely a Brrrr! gears grinding sound.
Seems like the noise is from both wheels though so i'm leaning toward the leaky solenoid. Haven't had the time to look into it yet, but planning on pulling the battery and fuse box out and having a go at cleaning the vacuum solenoids on the weekend.
Any thing I should know before I give it a go?

Cheers,

Photograph the pipework and pull the panel with the solenoids on.

They each have 3 ports, one to the vacuum tank (these join with rubber and go out under the wing), one to the hub, and one to fresh air (with a little filter on)

When they are powered off the vacuum tank port is sealed off (so a vacuum can build up in the tank with the engine running) and the hub port joins to the fresh air one.

When they are powered on the vacuum port joins to the hub port.


So, how they work is

Normally the vacuum tank is sealed off and air gets to both sides of the hub.
When you engage 4wd the controller switches on the engage solenoid for 5 seconds. This applies vacuum to the engage side of the diaphragm and air still gets to the other and pushes the hub over. Because everything is sealed, the vacuum switch activates, the light comes on solid, and the solenoid switches off. Now air gets to both sides of the diaphragm again, but the hub won't move.

When you disengage 4wd, the controller switches on the disengage solenoid for a few seconds, vacuum reaches the diaphragm, and the air on the other side pushes it over and it locks against the magnet. (there is no vacuum switch in this line, as the ecu doesn't really care if the hubs don't disengage)


What usually happens is people go through water which gets to the filter, and the damp causes the solenoid to stick part open, so vacuum permanently leaks through to atmosphere, the tank never fills (empties!) and the hubs won't work properly as the vacuum is low.

After that long winded explanation, use wires to apply 12V to the terminals, and the solenoids should merrily click, squirt some GT-85 down the ports and keep cycling them on & off to free them up.

Then check that you can't blow into the vacuum port when they are off, and when they are on you blow through to the hub port.

Thanks for the detailed explanation.

I ended up pulling the solenoids apart and cleaning them out with MAF cleaner, followed with some gt-85.
The red one seemed to have a little moisture in it.. could have been the issue? Although not entirely certain.
The mesh part of the filters was completely worn away on both solenoids and the switch. Have put them back in as is for now and planning on ordering some new ones to replace them with.

I also bought an etorx set and took the vacuum hubs off for a little look and couldn't find any evidence of grinding between the hub and spindle.
I wonder if its possible that the issue could be with the front air locker?

Now I just need to go find a cattle grid to drive over and hope this is the end of it.. only time will tell.

Thanks for the help!