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4WD not working....

James86

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We finally got our snow in Minnesota, and low and behold, for the first time since I've owned my truck the 4WD will not work. The front makes the same clunk as usual, but apart from that, I don't feel the 4WD working. I crawled under and both hubs are engaging as far as I can tell (the CV axles do not spin by hand like they usually due, suggesting they're engaged) and I can shift into low range (light shows 4 LOW) and the gearing definitely drops, suggesting the shift motor works, but if I gun it on a loose surface, only the rear tires spit snow/dirt and the ass end crabs out, but the front wheels don't pull and don't leave a mark like they always have. I cannot figure out why the transfer case would be able to change gear ranges, but seemingly not send power to the front axle. I've had this truck over 7 years so I know that it did work and how it handled and felt (I could always sense that driveline hum beneath my feet when the front axle was engaged.) Odder still, it seems like sometimes the 4WD will engage if I shift from 2WD to 4WD in reverse, but if I go forwards, it's back to 2WD. All dash lights seem to work as normal as well.

Sorry for the wall of text, but figured I'd explain best I could.
 


bmerr98

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Just a shot in the dark, but are you still rocking the PVH hubs? I had a situation where only one engaged, and with open gears, had no 4WD, since all the power went to the side that did not engage.

I eventually went with AVM manual hubs, but for the short term there's a quick fix that'll let you manually engage/disengage your PVH hubs. I don't recall where it is online, but IIRC you can cut out the little screen piece in the center of the hub and just push the locking mechanism with your finger. Works alot like a ball point pen with the push button thing. Push in and it comes out half way (locked), push in again and it comes out to the original position (unlocked).

You'll want to disconnect and plug the vacuum hoses going to the hubs as well, since the solenoid will still operate. If you lock both sides manually and then turn the switch and one hose is still good, it'll undo by vacuum what you did manually, and you'll be in the same spot with no 4WD.

BEFORE ANY OF THIS HOWEVER, you should do whatever troubleshooting you deem necessary to pinpoint the problem. If the problem is that only one hub is engaging like my truck was doing, this may get you by til warmer weather comes along.
 

James86

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Yep, I remember that work around. I have the Crown Vic police cruiser center caps, so I can get at my hubs easily if I choose to go that route, but I'm thinking it a transfer case issue. I checked both axles (truck sits just high enough) and they do not freely spin as in 2WD mode which suggests to me the hubs are in fact engaged. I know they can get "out of sync" after I kick back to 2WD sometimes and one stays locked in, and I can reach under and tell which side is still locked. So both hubs seem to be engaging, but I don't feel that good old 4WD hum under my feet from the front drivetrain turning. It's odd to try and explain I guess.
 

James86

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The hubs are locking. I'm just not getting power to the front axle. I talked to my mechanic and it sounds like an issue with the transfer case but aside from the chain failing or something internal breaking, we weren't sure how it's still going into low range without at least engaging the front drive shaft. The hubs appear to be functioning properly and diff and transfer case fluids have been properly serviced since I've owned the truck and this is the first time in almost a decade of ownership the 4WD has not worked.
 

don4331

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James86:

By something internal breaking; you are including one of the parts of the transfer case?

There are 2 forks in the transfer case, one for engaging the chain/front sprocket/axle; and one for low range.

It is possible for the fork for front axle engagement fork to pop off cam/roll pin activating it shear/fall out, while the low range fork is still connected.

I would try putting front end of truck up on jack stands to see if driveshaft to front axle is engaged. Then at least you know if problem is transfer case or front axle.
 

James86

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James86:

By something internal breaking; you are including one of the parts of the transfer case?

There are 2 forks in the transfer case, one for engaging the chain/front sprocket/axle; and one for low range.

It is possible for the fork for front axle engagement fork to pop off cam/roll pin activating it shear/fall out, while the low range fork is still connected.

I would try putting front end of truck up on jack stands to see if driveshaft to front axle is engaged. Then at least you know if problem is transfer case or front axle.
That's what I was leaning towards. Been a little cold out for crawling around under the vehicle since I live in an apartment, but I am leaning towards TC - just wasn't sure what's in there that could fail. I tried looking at the diagrams in the Tech Library but didn't really know what to look for. I hear both hubs engaging and disengaging, but while the indicator lights behave as normal and I can drop into low range, I don't really hear much going on from the transfer case. If the hubs acted funny in the past usually it'd start working after a cycle or two, but this time it's a whole lot of nothing.
 

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J
I would try putting front end of truck up on jack stands to see if driveshaft to front axle is engaged. Then at least you know if problem is transfer case or front axle.
I 2nd this before you do anything else.
If you tried to turn your axle CVs (checking for an unlocked hub) with both front wheels on the ground, it still won't turn freely because you still have one locked hub holding one side, AND the t-case is infact engaged. With one or both front wheels off the ground, a hub that failed to lock will be much more obvious.
 

James86

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The irritating thing is the other day, 4WD engaged on the first try without a sound. Usually I hear some sort of a ratchet sound or something but this time it just worked - all4 wheels pulled me up a sloppy gravel hill and I could feel it engage. I'm hoping that alleged warm spell comes soon and I can at least get it on stands. From what I understand, if I engage the 4WD and shut the vehicle off, the hubs should stay engaged, so if the front end is in the air and the vehicle is off everything SHOULD stay locked in and I can trouble shoot this, because I don't want to crawl around under a running vehicle on stands. I get what you mean 4x4junkie, I guess I was thinking a bit in reverse since when in 2WD, I can see if one hub is still engaged to the wheel by spinning the CVs, whereas if its in 4WD even if one hub is not enaged, the halfshafts are always connected to the front driveshaft so if the 4WD is engaged in the transfer case, neither shaft will turn and I need the wheels off the ground to see if the issue is at the hub.

Why couldn't this happen when it was WARM out....:icon_twisted:

Am I understanding this correctly?
 

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Unless you have a locker up front, you will still be able to spin one shaft with the transfer case engaged when both tires are off the ground. The other shaft will just spin in the opposite direction with an open differential. If you keep one shaft from turning with the transfer case engaged, you should not be able to turn the other shaft.
 

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As the hubs are vacuum activated; they only stay engaged while there is vacuum from the engine. There is a reservoir, but you are working on borrowed time from when you turn engine off; until the hubs release. But, I was thinking the TC doesn't disengage when engine is turned off (being electric) so you would be able to try to turn the drive shaft to the front axle and confirm if TC or not.

Just thinking out loud, assuming you don't have locker in front, if you only jack up one corner; engage 4x4, you shouldn't be able to manually turn the raised wheel. If you do driver's side; you should be able to see if the front prop shaft is turning. If the front shaft is turning; you have TC issues.

We had some nice weather on weekend, almost enough to melt all the ice in the subdivisions, so it should be headed SE to you in next couple days.
 

James86

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I thought the hubs were glorifies click pens, so the hubs engage with a brief application of vacuum to click them in, then to disengage another application of vacuum unclicks them, so I should be able to engage them with the engine on, then shut the truck off and they stay engaged until I start it again and switch back to 2WD. I've parked it in 4WD before.
 

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That's correct, they don't need vacuum to stay engaged (they are called "Pulsed Vacuum Hubs" because the vacuum is applied (pulsed) for only a moment to lock them in, and then vacuum is applied again to unlock them).
 

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Not sure if you pulled your hub caps, but I had a hub crack just enough so it didn't work.
 

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