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FLU419 stuck in 4-wheel mode, not engaging in differential lock

RoJoGro

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Update:
today I got the grease-nipples from Grainger. I also fabricated a small angled tool out of a nail which I used to push the piston a bit (but not sure if it actually moved).
The larger opening when removing the air-intake nipple allowed using this 'L' shaped tool to be inserted.
After that I closed it all up and used the M10 grease-nipple and after a few pumps the lock snapped in place. I moved the wheel after each 1/2 pump or so.
However I have no idea what pressure was actually applied.
If I get to it, I'll use air-pressure first, shut off the air line and continue with the grease-gun while having a gage connected.
That was all on the rear axle.
 

RoJoGro

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I just thanked tennmogger for the greas-gun tip.
However today I added a pressure gage, started with air-pressure, turned off the air-line (so not to fill with extra pressure and grease) and started pumping the grease-gun. it did lock somewhere between 250-300psi. but now it's no longer unlocking - even with all pressure gone.
I hope the spring does it's magic the next time I work on it in 2 days.
My plan was to monitor the pressure when it locks and when it unlocks and I should be seeing a decrease in the locking pressure the more it gets moving - I suppose.
There is also the front differential I have to get moving again.

On a side-note: I am using 1/4" poly lines I bought from Lowes with quick connects and am surprised that they hold the pressure.
 
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alpine44

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I have a NOS hydraulic handpump from a mobilizer dolly laying around that would make a nice setup for freeing stuck lockers. What are the thread dimensions on both (top/bottom) ports?
 
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tennmogger

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There must be some corrosion in the differential. Have you drained the diff to see what is in there?

Loosening that locker might be facilitated by driving in a straight line, wobbling left and right to load the locker one way then the other. The spring pushes back on the locker so wiggling it this way might help.

Or, with one tire off the ground and transmission in gear (to hold the pinion) slam the tire and​ wheel to it's limit ccw and cw to 'work' that locker. Warning, more WORK involved than just driving!

No matter how much effort you expend it's easier than pulling an axle housing!
 

RoJoGro

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I did wiggle the wheel, since it is in the air. I have the gear in neutral, but the other wheel is on the ground and with the differential locked it would be the same, right?
And you are right, it's work! I may just drive it a bit.
The drainage has a M10 threat (not M10-1.5) I think M10 is the same as M10-1.0 designation. That's what I bought the grease-nipple from Grainger, it had M10 and placing both threats together it was a match - although I could not screw it in by hand all the way, I could do with the drain screw.
I'll try to measure the top screw.
I am not familiar with a NOS hydraulic handpump, but not sure if it would work, since both holes (top and bottom) are the same chamber which is pushing the piston - I guess one would need to connect the other line to the differential-box to push from the other side to assist the spring (but this may have other implications).
I would need a 'one-hose' pump/sucker type gismo,... Hmm a vacuum-pump perhaps could pull it back.
 

The FLU farm

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it did lock somewhere between 250-300psi. but now it's no longer unlocking - even with all pressure gone.
Hey, you got it moving. Now it's "only" a matter of making it move freely.
That'll probably take several on/off cycles. I would begin with doing it with one wheel up, then once the locker seems to work somewhat predictably, take it out and drive.
It'd probably help to get in the habit of switching the lockers on and off a lot , like every couple of feet. And if you're lucky, the front may loosen up in the process.

Next would be finding out why they stopped working in the first place. Some FLUs seem to produce more water/crud from their air system than others. Also, as tennmogger pointed out, did any of it make it into the diffs? Let's hope not.

Just read your latest post. A vacuum pump may well do the trick. Worth a try, I think.
 
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alpine44

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I did wiggle the wheel, since it is in the air. I have the gear in neutral, but the other wheel is on the ground and with the differential locked it would be the same, right?
And you are right, it's work! I may just drive it a bit.
The drainage has a M10 threat (not M10-1.5) I think M10 is the same as M10-1.0 designation. That's what I bought the grease-nipple from Grainger, it had M10 and placing both threats together it was a match - although I could not screw it in by hand all the way, I could do with the drain screw.
I'll try to measure the top screw.
I am not familiar with a NOS hydraulic handpump, but not sure if it would work, since both holes (top and bottom) are the same chamber which is pushing the piston - I guess one would need to connect the other line to the differential-box to push from the other side to assist the spring (but this may have other implications).
I would need a 'one-hose' pump/sucker type gismo,... Hmm a vacuum-pump perhaps could pull it back.
"Pushing" with significant pressure from the differential side is not an option due to the risk of blowing out the seals towards the central tube or axle housings.

'NOS" means "New, old stock" basically stuff that has never been used but sitting around forever. The pump I was referring to is a rectangular oil reservoir with built in hand pump. I will order the fittings and motorcycle brake line together with other stuff from Belmetric and then try this pump for pushing my locks in. I do not know whether they are stuck since my plastic line from the valve is broken but considering how long these vehicles have been sitting around I would not be surprise if I have the same problem.

As far as vacuum is concerned, keep in mind that 14 PSI from the other side is the max on this planet no matter how much you suck out.
 

The FLU farm

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As far as vacuum is concerned, keep in mind that 14 PSI from the other side is the max on this planet no matter how much you suck out.
True, but on the other hand, when applying pressure, it's working against those 14.7 psi. With vacuum at least it works for us.
To what degree it matters when it took a few hundred psi to to push the piston in is debatable.
 

RoJoGro

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[Alpine44]
I recommend to also add a pressure gage so you have an idea. and it allows you to check if the pressure needed the 2nd, 3rd, 4th time is decreasing...
if the plastic tubing is still somewhat good from the axle, you can cut it at about 12"-18" (clear area) and use a 1/4" quick connect to attach you pump.
The tubing originally is a 6mm OD and 4mm ID. I do not know - however - if the 1/4 tubing would fit into the nipple (it may), but the other way works.
 
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RoJoGro

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the treat is a M14-1.5 for the nipple screwed into the axle and M12-1.5 for the air-compression fitting.
the M12 also happen to fit a 1/4" SAE adapter, but you have to use a flat washer.
The first picture shows the part as I took it out of the axle with the copper ring FLU419_DiffLock_Air1.jpg the side with the ring is M14-1.5
This shows the same part with an adapter 1/4" to 1/4" compression. FLU419_DiffLock_Air2.jpg

Today I tried using a vacuum pump, but I think the pump was no good (a 'rental' from Autozone) unfortunately there was no gauge on the pump.
I also drove it a bit and made some turns (on soft ground), but nothing unlocked the differential.
 

The FLU farm

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I also drove it a bit and made some turns (on soft ground), but nothing unlocked the differential.
There are times when we need to be careful about what we ask for. But better an eternally locked diff than open, I think. Other than tearing up the ground a bit, there's no real drawback that I can think of.
Unless ...the dog clutch is only partially engaged. You may want to measure the distance that the piston is pushed in, compared to where it should be when fully engaged.
 

alpine44

Member
397
15
18
Location
Asheville, NC - Elkton, MD
[Alpine44]
I recommend to also add a pressure gage so you have an idea. and it allows you to check if the pressure needed the 2nd, 3rd, 4th time is decreasing...
if the plastic tubing is still somewhat good from the axle, you can cut it at about 12"-18" (clear area) and use a 1/4" quick connect to attach you pump.
The tubing originally is a 6mm OD and 4mm ID. I do not know - however - if the 1/4 tubing would fit into the nipple (it may), but the other way works.
Thanks for the dimensions. I will put a pump kit, including pressure gauge, together in the next couple of weeks and will add it to the loaner tool thread. The square hydraulic pump (fluid drained) and the connections will fit easily in a flat rate box.
 
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RoJoGro

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There is a listing on eBay right now for the piston (#13 on Figure 139) for $25. I bought 2 and there are 4 left. Search for 4163350250
Although one could probably clean the original, for this price I save some time.
The picture on the listing shows it without the packing ring (#14) does this ring 'stretch' and be slipped into the groove?
 

The FLU farm

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Being that the sealing qualities of the O-ring are important, I hope you're not planning on reusing it. Of course, I also hope that you won't need to tear into the axle in the first place, but if you do...
Since you'll be able to get the ID, OD, and width of the parts the O-ring should fit, I'd go in search of quality O-rings based on those measurements.
And, yes, you would normally slip or roll an O-ring into position, using the appropriate lubricant in the process.
 
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