Thread: ARB Locker Question

[QUOTE=LOVEMYRANGIE;1424804]Most solenoid seals are NBR so will react with oils.
As ARB supply an oilless compressor when fitting Airlockers, you wont get this problem unless its the actuator seal flooding oil back hence NBR standard rubber solenoid internals.
Back in my automation days, some pneumatic controls required solenoids spec'd with Viton seals to stop this happening.
Just pull the solenoid off and unscrew the plunger unit presuming it's an industrial mini type solenoid and have a look. Pretty evident when they are stuffed.
Try Braeco for something if it's oil doing it.

A lot of pneumatic manufacturers use NBR for valve & piston seals, they are used with lubricating oil (ISO22) with no problems. I just checked the link below and oil resistance is listed as good to excellent.

http://www.robinsonrubber.com/pdfs/NitrileRubber.pdf

Temperature can be a problem. I've supplied pneumatic blanking plugs for use on 200 & 300Tdi cooling systems and the first job is to replace the NBR seal with a Viton one, althought the above link lists it as 120C. We only rate cylinders with NBR seals to 70C.

Colin

Hi guys,

Just wanted to offer my .02 on some of this.

1 - NBR (aka Nitrile) is one of the most oil resistive elastomers available. It is used throughout your vehicle wherever mineral based oils will come in contact with lubricants. We use FKM (aka Viton) over NBR wherever extreme temperature resistance is required, or wherever high surface running speeds are expected.

2 - Leaking air during a hard climb (you said the compressor was running) is generally the result of a pre-load problem. To test this - try locking your diff and gently driving against your parking brake to torque up the diff and see if your compressor comes on. Basically the problem is that your diff is under torque and so it wants to push the carrier bearings away from centre. If too little bearing pre-load is used it succeeds and the bearing very slightly disconnects and allows your seal housing to run inconcentric to the Air Locker while it is. This pinches the O-ring seals on one side and potentially opens an air gap on the other - causing a leak. In extreme cases of this you can cause damage to the sealing surfaces when the concentricity gets so out of whack that the seal housing can make physical metal to metal contact with the diff.

3 - To check your pre-load on a banjo style assembly:
- remove the third member
- mark a texter line showing how far your adjuster nut has been tightened (i.e., a little on the nut and a little on the bearing cap at the same point. Marking just one side is fine.
- remove the locking tab from the marked side.
- unscrew your adjuster nut a full turn. You may need to loosten the bearing cap bolts to do this.
- screw the adjuster nut back in but only until you feel that it has just touched the bearing. Do not tighten it at all. You just want to feel the contact of what you would call neutral pre-load.
- Look at where your mark is compared to the position your adjuster nut is in now.
- If your pre-load is correct then there should be almost exactly 90 degrees (one quarter turn) in the adjuster nut to put it back to where you started. If not then the pre-load is insufficient. Don't strangle your mechanic, this could have occurred from bearing wear over the years.
- Tighten the nut the correct 1 quarter turn and reinstall the locking tab, tighten bearing cap bolts, etc.
- If you found significantly too little pre-load then examine the O-ring sealing surface for possible signs of damage.

4 - To check your pre-load on a Salisbury style D60 assembly:
- Remove both bearing caps.
- Remove the diff.
- If you didn't need to pull really hard or pry the diff out of the housing then you should already suspect too little pre-load.
- On a Land Rover Salisbury axle I would put 0.30mm [0.012"] worth of pre-load shim into the set-up (i.e., I would put that amount more shim than what the housing wants to accept.
- To do this you will need to remove some shim from the diff
- Reinsert the diff and measure the gap you have created.
- Add that gap measurement to the pre-load amount above to find out how much shim you are putting back into the car.
- Spread the differential using a differential spreader. We sell these or you can get one / borrow one from any good diff mechanic. (follow your service manual for this procedure)
- Insert the diff with the preload shim back in.
- Remove the spreader.
- Again, if the diff basically fell out then you will want to look for damaged pneumatic surfaces before you re-assemble.

Carrier bearing pre-load is a set-up process not to be taken lightly. Too little will result in carrier bearing wear and damage, and severely weakened ring and pinion strength due to shifting tooth mesh geometry. Too much pre-load can result in carrier bearing wear also. Your carrier bearings will tell you how they have been running. Look for smooth uniform wear bands around the entire inside of the cup. If this band is uneven or shifts from top to bottom then things aren't 100% in there.

Hope that helps.

PS - Thanks yet again for passing me these links (you know who you are).

-daniel
AIR LOCKER