The small bleed plug for the diff lock is easily missed. It's not at the bottom of the diff housing but is up higher near the bottom of the axle tube on the side where the air line enters. Good luck finding it.
Could you verify full pressure is being delivered to the lockers? Only a few psi is required to feel air flow. The lockers should see full system air pressure after the overflow valve opens at about 5 bar. BTW, Until the overflow valve opens there should be no air available for the diff locks.
What pressure does your system hold? (yes, I remember your front locker works ok, just trying to work through this with you)
yep i understand, in the cab on the dash is the meter, when it reaches 8 on the mtr the blow off valve is released, there are no air leaks to the system, so i have shut of the engine, gone round the back of mog un done the air suply to the top of the diff casing, an then pulled diff engage lever, air is flying out, i am guessing that if the front diff is engaged an working that the rear should also.. Am thinking that am going to have to take it apart an see the condition of the diff seals!was hoping not to have to do this, is there anything i should do before this is the nxt step. I also do not have a drain plug on axle diff casing for draining condensation, front or rear, have crawled all round an its just not there.. My machine is a 1968,ish model 406, u900..
Sure sounds like you have all the bases covered. One thing I might point out is that the pressures seen on the dash gauges do not necessarily show the pressure applied to the diff locks. There is a device called the overflow valve which does not pass air to the diff lock valve until system pressure passes the setting of the overflow valve, usually around 5 bars.
The purpose is to safeguard air pressure for the brakes. No other "auxiliary" circuits (like diff locks) will get air until the overflow valve is satisfied the brakes are taken care of.
From your good descriptions, I do not think you have a problem with the overflow valve because your front diff is getting sufficient air, and the rear must be also. Just wanted to point out that if the overflow valve fails, the truck air gauges will show normal, you'll hear the normal 'pop-off', and all will seem well, but no (or partial) pressure could be applied to the diff-lock system.
One final test would be to use a shop air supply to put pressure on the rear diff lock. If shop air is applied directly to the diff lock port and it still does not move, then I'd be ready to give up too!! If there is any way to avoid the rear axle tear-down, you'll certainly want to find the way.
Chunker, I'm not an expert on Mogs so I don't know if any came from the factory without drain plugs for the locker, but I can send you a pdf from my manual showing where it is in relation to the air connection. Shoot me an email with your addy if you're interested.
RMontez rmontez@yahoo.com
Thanks RMontez, i have managed to get a workshop manual, i have a sneeky feeling that mine is a early 406 mog as the cab has a different bit of grill mesh. YOU KONW ON A 406 THE GRILL IS just between the head lights well mine is also the other side of the head lights an goes round the corner of the cab a little bit, i have no vent drivers side of the cab just behind of the indicator, i saw one on ebay in germany the other day an it was advertised as a 1964/65 model, so this has got me wondering if mine is an early model, with out diff drains on the axle tube just under the air locker. newer 406 models have drain plugs. So iam thinking i will drill an tap a bolt on the under side as a drain .
thanks ham mogger, i have thought about using my workshop air comp to give it a quick blast, only one thought is what happens if it locks in, an will not return to out of diff?? STUCK IN, does it then require that i split it, i have ordered new seals today just incase, is there anything i need to know about in the strip down which is awkward, is putting it back together fairly straight forward to?
I have done the rear locker seals in my 1200. I made a dolly on wheels to put my jack stands on. With a couple of well place straps the half of the axle just slid out from under the truck, I changed the seals and slid it right back in. If you get the axle well supported it is just a matter of undoing the bolts around the diff and pulling. You want to make sure the axle is supported so it dose not shift, otherwise it will be hard to line it back up.
I did the job in about 6 hours, working by my self in the garage. The only thing I needed help with was bleeding the brakes.
The breakdown-replacement has been covered here within the last few months. Steve in Co if I recall, and he had alot of pics to boot. Good luck!
I did the front lockers on my 79 Case Mb94/4 a few months ago. It was actually very easy except I missed one of the rubber seals and had to disassemble twice. Much faster the second time. I am not sure how difficult the rears would be. The hardest part was safely supporting the mog before crawling underneath.
BTW, make sure your breather tubes are clear and not packed with mud.
Thanks RMontez, i have managed to get a workshop manual, i have a sneeky feeling that mine is a early 406 mog as the cab has a different bit of grill mesh. YOU KONW ON A 406 THE GRILL IS just between the head lights well mine is also the other side of the head lights an goes round the corner of the cab a little bit, i have no vent drivers side of the cab just behind of the indicator, i saw one on ebay in germany the other day an it was advertised as a 1964/65 model, so this has got me wondering if mine is an early model, with out diff drains on the axle tube just under the air locker. newer 406 models have drain plugs. So iam thinking i will drill an tap a bolt on the under side as a drain .
The early mogs don't have the same drain plug as the later mogs do. Plus it used different seals as well for the locker piston. I have photos somewhere of the early set up. I had one set of axles that sat for so long that the piston would not move out no matter how much air pressure was behind them. Had to use a puller to get the piston out once the axles were apart. I have also seen seals leak so bad that they would pop the dipstick out of the tranny! Best thing to do is just split the axles and replace the seals.
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