radioactive

It sometimes will lock in, but more frequently will not. Is not the vacuum issue they are noted for and can hear the TC motor click when the ESOF switch is flipped. It has the mickey Mouse factory lockout hubs, but even when engaged, 4wd is intermittent.

The rear wheel(s) will spin, then 4wd will kick in with a helluva bang, then usually kick out again. Been investigating a set of Warn manual hubs, but not certain the hubs are the problem. Any other diagnostics I can do to narrow down the problem?

PerryB

Does this still happen with the hubs manually engaged ? It SOUNDS like you have a vacuum leak and the hubs are only marginally engaging. If I remember correctly the SD is opposite from the 150 in that the SD uses vacuum to engage the hubs, the 150 uses vacuum to DIS-engage.

radioactive

Yes, still happens with hubs manually locked.

I need to use a vacuum pump with gauge and double check the system, but the heater blower does not default to defrost when I engage 4wd like all the diagnostics says it will do if it is a vacuum issue.

radioactive

Had a couple of seriously steep hills to climb this morning on grass wet with dew and the 4wd worked flawlessly. As a precaution, I manually locked the hubs, but in the past that didn't keep it from disengaging at random.
I'm wondering if the issue isn't gummed up hubs not allowing them to fully lock and the increased use of 4wd has loosened up the crud???

whitescrew77

Might have to actually take it to a mechanic or 4wd shop.

PerryB

If its still happening when manually engaged, don't bother with the vacuum pump. You'll have the defroster issue if its a loss of vacuum issue. Can you tell, does it sound like the bang is coming from the T-case or the hubs? You either have a faulty T-case actuator or a stripped hub. Usually once a hub goes, its gone and there is no more front axle drive. I suspect the actuator.

radioactive

It sounds like the T case, but the truck exhaust is so darned loud it's difficult to pinpoint. With the key in the on position, but engine NOT running, I can hear the TC actuator click when the ESOF selector is switched to 4 high. I know that's no guarantee the TC case is engaging though.

I engaged the 4wd well before the base of the hills and it worked flawlessly today for a change.
In the past I have had a helluva time getting it to engage at the actual time it was needed even when the hubs were locked manually. I'm still thinking maybe the grease in the hubs is gummy and not allowing free movement to engage and the recent engage/disengage activity loosened them up a bit.

There is no audible "click" when turning the hub, or "feel" that turning the hub has had any effect. These are the plastic factory hubs and not aftermarket such as Warn or Superwinch. I bought the truck used and the first time I turned the hubs to lock, I had to use pliers to get them to move.

Probably going to take it to my mechanic for a bearing pack and general inspection of the front end. The truck has almost 350,000 on it

radioactive

Thanks for the input guys. I bought a set of the Warn premium lockout hubs and that cured the problem