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DreamcastERA

DreamcastERA

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Well, I have installed the replacement solenoid and check valve.

I test drove it around and didn't think I heard anything. I popped it into 4WD and then back into 2WD to test that out - and shortly after going back into 2WD it made the sound again.

I came to a stop and then set off again. Sound was gone once more.

After that I tried to put a little bit of load on the engine by manually locking into 5th and 6th gear at ~40 mph and giving it maybe 3/4 to full throttle - which did cause the sound to occur aggressively and repeatably. I had to entire a round about and upon coming out the other side I tried again, and was not able to replicate the noise.

If anything it seems to be happening less consistently, but it's really starting to drive me a bit insane

After letting the truck sit, I checked the reservior for vacuum, and it had none in it - seems like bad check valve again.

UPDATE:

I have since driven the truck again after letting it sit for ~20 minutes. I tried locking into 5th / 6th gear again and was unable to reproduce the issue. In-fact no matter what I did I could not reproduce the issue on this drive. Quick note: My vacuum reservoir now seems to hold its vacuum - but as soon as I shut the truck off, my hubs engage and they lose vacuum. The hubs lose vacuum, despite the fact that the reservoir still has vacuum in it. SO seems like that means I have a break in my lines somewhere.

Once I turned the truck on , I ofc had no issue and was not able to replicate the problem.

UPDATE 2:

I pulled the skid plate off and discovered that you can pull enough vacuum to disengage the hubs with your mouth, so thats something! I went ahead and tested the flexible hose on both hubs and they each worked and held. However, the passenger side looked like it had bee repaired before by some electrical tape so I removed all of the tape and tested each piece individually, zip tying a couple suspect areas. They held just fine afterwards. I then tested the plastic line that links both hubs together and connects them to the solenoid (I disconnected the driver's side from the hub and tested from there), but it did not hold. I then pulled my skid plate and checked the plastic line that runs across the frame and found no issues. After I was satisficed, I checked the last spot - the connection to the solenoid. The plastic line that connects the hubs to the solenoid broke off as soon I removed it - so that was a potential leak point as well. I repaired that and then I noticed something interesting (which may be common knowledge): the solenoid dumps all vacuum to the hubs after maybe 10 seconds after turning off the truck. I tried the old one and it has the same behavior. Not knowing that this was normal has made diagnosing this issue very difficult, because I expected the truck's hubs to stay UNLOCKED when the vehicle was turned off in 2WD IF the vacuum reservoir still had vacuum. Regardless - the issue has not returned! I even marked the front axle and the hub to see if they moved at all during my drive, and they were in the same spot when I get home as when I left. My truck does make a sort of moaning/groaning sound when coming to s top but that seems to be brake related. It may have been making this sound for a long time, but I haven't had a reason to pay such close attention until recently. Perhaps I fixed a leak somewhere along the way, or maybe the new check valve had an intermittent failure (maybe once it actuated a few times it worked itself out. If it did have intermittent failure, that would explain why there was no vacuum in the reservoir after my initial test drive, and potentially also the sound.)

Point is, it appears to be fixed now! The lines are all brittle feeling, so I'm likely gonna replace them all with something less failure prone when I get home. I still appreciate all of y'all's help! The real test will be on the highway when I head home, but so far it seems to be in working order.
 
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CoronaRaptor

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Yeah, the hubs are suppose to engage when the truck is off, been that way for years. That's why these trucks are suppose to be flatbed towed if they break down. Glad you found the source of your problem, happy motoring now!
 
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