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Discussion Starter #1
Hey,

The front axle on my Case MB4/94 doesn't seem to lock. The knob is also hard to turn when shifting from 4x4 to 4 lock. I have about 100psi in the tank and the rear axle is locking.

Any thoughts?

Mark
 

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I have had trucks that have been sitting for a long time have the piston seize up and will not lock. Had to remove the axle and take it all apart to free up the piston and replace the seals. Worked fine after that.
 

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It's pretty common for the locking mechanism to gum up without regular use. Disconnect the air line from the axle to make sure you can get pressure there. If you have air at the end of the line, try shooting some light oil into the axle fitting and letting it soak for a while. Sometimes that will free it up - if it doesn't and the air system is working properly, you're probably looking at pulling the axle apart.

If you DON'T have air at the fitting, start by finding where there IS air.

{edit} I just noticed you're in MN. Do you have ice in your air system ? ?
 

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After confirming air is reaching the locker fitting on the axle, try several applications of light oil into the port. The locker might free up. Drain it too (plug under the axle).

Could be the pressure through the overflow valve (looks like a regulator, but isn't) is low. You should confirm full tank pressure is reaching the lockers. The rear locker might be operational at low pressure, but not the front.

Bob


Hey,

The front axle on my Case MB4/94 doesn't seem to lock. The knob is also hard to turn when shifting from 4x4 to 4 lock. I have about 100psi in the tank and the rear axle is locking.

Any thoughts?

Mark
 

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After confirming air is reaching the locker fitting on the axle, try several applications of light oil into the port. The locker might free up. Drain it too (plug under the axle).

Could be the pressure through the overflow valve (looks like a regulator, but isn't) is low. You should confirm full tank pressure is reaching the lockers. The rear locker might be operational at low pressure, but not the front.

Bob
Bob, It's been a while since I pondered the manual, but my recollection is that the pressure to the locker switch and lockers is regulated to around 15-30 psi or so. The tube connections from the locker switch to the lockers don't seem to be designed to handle high PSI. However, some solvent and a few blasts of high pressure would be my last best effort to free it up before splitting the axle. Remember to drain the locker (small bolt on underside) as whatever oil/ water/ grit that comes out will be some indication as to what you're dealing with.
 

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Discussion Starter #7
I've only owned the truck for about 6 months now, and have no idea of how it was maintained. I recently changed the fluid in the axles and the old oil looked OK, but I didn't drain the lockers...the small bolt on the under side. Any ideas on the shift knob being hard to turn from 4x4 to 4 lock?
 

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Discussion Starter #8
It's pretty common for the locking mechanism to gum up without regular use. Disconnect the air line from the axle to make sure you can get pressure there. If you have air at the end of the line, try shooting some light oil into the axle fitting and letting it soak for a while. Sometimes that will free it up - if it doesn't and the air system is working properly, you're probably looking at pulling the axle apart.

If you DON'T have air at the fitting, start by finding where there IS air.

{edit} I just noticed you're in MN. Do you have ice in your air system ? ?
Not sure if there could be ice in the system...is there a fix for it or preventive for it?
 

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Not sure if there could be ice in the system...is there a fix for it or preventive for it?
The MB4/94 should have a alcohol injection system. Search the archives for recent pix and descriptions - there was a thread in the last two weeks about it. Ensure it's filled with the proper fluid and in the 'on' position. Work the brakes and activate the 4X4 engage/locked switch a bunch of times to get the vapor distributed.

This time of the year in MN, you'll soon not have air-assist for your brakes if the system is not working.
 

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Actually, full system pressure is placed on the lockers when the manual locker actuating valve is open. But, the overflow valve has to have opened to provide that pressure. There can be full pressure showing on the air gauge but pressure might not exist on the locker system.

Understanding the purpose of the overflow valve helps to understand locker operation, or failure. It is a safety device, not a regulator. The overflow valve is designed to stay closed until air system pressure builds up to at least 50 or 60 psi. Yhen the valve opens to supply 'non-critical' circuits. This ensures that pressure is available for the brakes. Other systems, including the lockers, are not of primary importance for safety and are located beyond the overflow valve.

If the overflow valve does not open, but leaks a little, there could be some pressure on the locker system at first, then any leakage at the locker pistons would dump the pressure. The pressure loss on the lockers will NOT show up on the dash pressure gauge below 50-60 psi because that is measured BEFORE the overflow valve. Any time the system pressure dumps to 50-60 PSI there is a leak beyond the overflow valve.

So, full pressure (100-110 psi) is supposed to hit the locker pistons. You can test the lockers with shop air. Shop air is handy to force light lube oil through the lines to the lockers, too.

The simple rubber flex lines carrying locker air across the thrust tube ends have to handle full system pressure. I had one blow at last SE Mogfest because I had not recently replaced it. I upgrade these hoses with single wire hydraulic hose, because blowing one will render lockers unusable.

When the lockers are actuated there should be no air moving continuously moving through the diffs, but often there is. Worst case, high air flow into the transmission can be heard, or the dipstick can even blow out!

Bob





Bob, It's been a while since I pondered the manual, but my recollection is that the pressure to the locker switch and lockers is regulated to around 15-30 psi or so. The tube connections from the locker switch to the lockers don't seem to be designed to handle high PSI. However, some solvent and a few blasts of high pressure would be my last best effort to free it up before splitting the axle. Remember to drain the locker (small bolt on underside) as whatever oil/ water/ grit that comes out will be some indication as to what you're dealing with.
 

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Discussion Starter #11
I'm afraid I don't have the alcohol injection system, but it's very possible I had this problem over the summer. I'll keep my eyes open for the parts, are there any aftermarket kits that someone could recommend?
 

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The problem is most likely in the axle - crud block or rusty locker. If you don't loose air rapidly when you engage, it's probably not the seals.

However, from experience, I can predict you will have some problems in the winter without some sort of air antifreeze. When it's super cold and dry, maybe not, but when it's all damp and 20-30 F, you WILL get airline icing without some 'help'. But that's off topic to your locker problem.
 
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