# Can't disengage 4wd



## Deeds86 (Apr 24, 2018)

I have a truck I picked up for cheap it's a 91f150 5.0 and can't get the thing outta 4wd it is the floor shift and can switch between 2 4wd hi/low but the front axle is always locked is anyone able to tell me if there's a good place to start maybe known issues or what not? I paid $600 for the truck and plow and it's not worth much more so hubs are expensive for a wild guess I think I've read up on vacuum actuators and a solenoid in the front pumpkin I'm willing to switch from.auto hubs to manual if that will work to ignore or fix the problems but don't wanna be in the same boat if manuals cant free spin how I need... The truck won't leave my property but would like it to do farm work so 4wd has to be able to disengage


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## seville009 (Sep 9, 2002)

Can you manually unlock the front hubs using the selector on the front hub? Do you know if they are unlocked?

If the hubs are the problem, maybe pull them apart and clean them up/grease them if they’re not too far gone. If the truck is otherwise good for your purposes, a few hundred for new hubs may be worth it.


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## Randall Ave (Oct 29, 2014)

A 1991 had the auto hubs if I remember correctly. Get yourself a set of Warn manual hubs. Easy to replace.


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## Deeds86 (Apr 24, 2018)

Yeah they're the autos, I thought manual hubs would be fine maybe I've just over googled my question...I keep reading about the vacuum that actuates the hubs creating chaos or a solenoid in the axle that's way cheaper than the hubs, I'll just pick up a 
set and call it a day... Thanks for your speedy replies


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## FredG (Oct 15, 2012)

Deeds86 said:


> Yeah they're the autos, I thought manual hubs would be fine maybe I've just over googled my question...I keep reading about the vacuum that actuates the hubs creating chaos or a solenoid in the axle that's way cheaper than the hubs, I'll just pick up a
> set and call it a day... Thanks for your speedy replies


 There you go the Guys that responded know there stuff. Good luck


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## Aerospace Eng (Mar 3, 2015)

Is it the axle that is locked (i.e. the transfer case doesn't disengage) or the hubs that are locked (front axle and rear axle will move independently if off the ground but the front wheels won't turn independently). If I remember correctly the auto locking hubs from that era (my mom had a '94 that I worked on a bit) wouldn't disengage without you going into reverse for a bit. As an engineer, I much prefer manual hubs.


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## Deeds86 (Apr 24, 2018)

Everything is locked as of right now, and can switch between 4 hi and low, I can tell that from the added torque in low range, just can't get it to disengage and have given it a pretty good shot in reverse, I had read a post on another forum form that said if i replace with manual the vacuum solenoids wouldn't get a signal and the computer would try and keep the transfer case from engaging... I'll just pinch both lines and give the hubs a shot


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## FredG (Oct 15, 2012)

Aerospace Eng said:


> Is it the axle that is locked (i.e. the transfer case doesn't disengage) or the hubs that are locked (front axle and rear axle will move independently if off the ground but the front wheels won't turn independently). If I remember correctly the auto locking hubs from that era (my mom had a '94 that I worked on a bit) wouldn't disengage without you going into reverse for a bit. As an engineer, I much prefer manual hubs.


 You remembered correctly. Definitely had to go in reverse.


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## Aerospace Eng (Mar 3, 2015)

Deeds86 said:


> Everything is locked as of right now, and can switch between 4 hi and low, I can tell that from the added torque in low range, just can't get it to disengage and have given it a pretty good shot in reverse, I had read a post on another forum form that said if i replace with manual the vacuum solenoids wouldn't get a signal and the computer would try and keep the transfer case from engaging... I'll just pinch both lines and give the hubs a shot


I think you are confusing transfer case and hubs.

The transfer case has 4 modes
Neutral, where the transmission output is not connected to anything
2WH, where the transmission is connected to the rear prop shaft
4WH, where the transmission is connected to the front and rear prop shaft
4WL, where an extra reduction occurs between the transmission and the front/rear prop outputs.

If you have a floor lever, you probably have a mechanically shifted transfer case. There are no solenoids or computer, whether electric or vacuum.

Mechanical transfer cases are typically straight gears, and are very robust, but you generally have to stop when going from 2WD to 4WD.

Electrically shifted transfer cases usually use planetary gear sets and clutches, and can be shifted on the fly. However, they are not nearly as robust as the mechanical type.

Regardless of the type of transfer case, it only controls the output to the front and rear prop shafts.

The front prop shaft turns the front differential and axles. If the hubs are not engaged (only possible with manual hubs) the axles turn independently of the wheels. If the hubs are engaged, the wheels are locked to their respective axles.

The mechanical auto locking hubs I am familiar with basically used a ball and ramp setup to lock the hubs, and would only stay engaged when driving forward (hence the "lock" position on them in addition to the "auto"). This is useful if you are in 2WD, start to get stuck, and want to power out of the hole, or get off the ice. You shift into 4WD, drive out, shift back to 2WD, back up until the hubs unlock, and go on your way without getting your dress shoes muddy or wet. Other than that, if you are ever going to go into reverse, you still have to get out to put the auto hubs into lock.

You need to figure out if you have a transfer case problem or a hub problem, although I'd go to manual hubs anyway.


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## BUFF (Dec 24, 2009)

As long as the transfer case can be shifted between 4hi/lo and 2wd what's the big deal about the hubs not disengaging / unlocking, it's a $600.00 yard truck.
Even if the truck was to go on the road having the hubs locked is not a big deal unless the front diff was a spool or locker which I highly doubt it is.
For decades I've been locking my hubs in and leaving them locked during winter months. The only negative is a drop in fuel mileage.


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## EWSplow (Dec 4, 2012)

If the hubs are locked and won't disengage, it could be something as simple as a vacuum hose that's cracked, or came off.
I'd also go with Randall's advice, get some Warn hubs.


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## Deeds86 (Apr 24, 2018)

I've got the manual hubs on my SD and feel their way more reliable, but the plow truck has the auto hubs when I put the transfer case in 2wd the 4x4 light stays on and the front driveshaft is not able to be turned, but when I switch between 4 hi and low I can definitely notice a difference in torque and how it operates their just is constant drag on the the front axle once in 2wd (with 4x4light on) so I didn't know if switching it into 2 would cause the vacuum solenoids to release the hubs or what? I'll just pull them and switch them to manual hubs that seems like the best method since I'm not worried about drivetrain spinning the front with the hubs disengaged I figured it wouldn't be a problem but thought I'd ask because when looking for hubs online a few posts came up saying it wouldn't release the front diff but now that I think about it even if that was the case it doesn't affect anything if the front is freewheeling


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## Randall Ave (Oct 29, 2014)

I can't remember back that far good, but I don't remember the hubs working on any vacuum back then. And the hub kit for that is not expensive.


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## BUFF (Dec 24, 2009)

Randall Ave said:


> I can't remember back that far good, but I don't remember the hubs working on any vacuum back then. And the hub kit for that is not expensive.


Back then after you engaged the transfer case the front tires had to make a couple forward revolutions to engage the hubs, to disengage the hubs you had to disengage the transfer case and back up to reverses the process.
Everyone I knew that had those hubs changed over to manual hubs. Ford stopped this design in '97 and went to a vacuum operated hub for auto locking on vehicles with electronic 4X4 which still suck but you don't have to go forward and backwards to engage/disengage.


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## Randall Ave (Oct 29, 2014)

BUFF said:


> Back then after you engaged the transfer case the front tires had to make a couple forward revolutions to engage the hubs, to disengage the hubs you had to disengage the transfer case and back up to reverses the process.
> Everyone I knew that had those hubs changed over to manual hubs. Ford stopped this design in '97 and went to a vacuum operated hub for auto locking on vehicles with electronic 4X4 which still suck but you don't have to go forward and backwards to engage/disengage.


That's what I thought, back then Ford no vacuum. It was mechanical, and the auto hubs sucked.


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## EWSplow (Dec 4, 2012)

Randall Ave said:


> That's what I thought, back then Ford no vacuum. It was mechanical, and the auto hubs sucked.


You and Buff know far more than I. I thought they were vacuum assist.
OP, listen to these guys.


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## Randall Ave (Oct 29, 2014)

EWSplow said:


> You and Buff know far more than I. I thought they were vacuum assist.
> OP, listen to these guys.


What you trying to say, were OLD?, Actually Buff's not, just me and Fred.


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## BUFF (Dec 24, 2009)

Randall Ave said:


> What you trying to say, were OLD?


You have me by 4yrs....... Old timer....


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## EWSplow (Dec 4, 2012)

Randall Ave said:


> What you trying to say, were OLD?


LOL You're older, Buff's younger. Guess I'm just all that knowledgeable.
I was a little surprised they weren't vacuum. Other manufacturers have been using vacuum for decades. I think.


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## BUFF (Dec 24, 2009)

EWSplow said:


> LOL You're older, Buff's younger. Guess I'm just all that knowledgeable.
> I was a little surprised they weren't vacuum. Other manufacturers have been using vacuum for decades. I think.


1st is was GM when they stopped square bodys, then Dodge in '94 when they stopped the W series. Ford was the hold oot but still offers locking hubs and floor shift 4WD.


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## EWSplow (Dec 4, 2012)

BUFF said:


> 1st is was GM when they stopped square bodys, then Dodge in '94 when they stopped the W series. Ford was the hold oot but still offers locking hubs and floor shift 4WD.


Let me check, but I believe my 85 Cherokee has vacuum.


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## BUFF (Dec 24, 2009)

EWSplow said:


> Let me check, but I believe my 85 Cherokee has vacuum.


Hmmmmm..... A f-150 is barely a "truck" a Cherrykey is a car and this discussion is in the Truck and Equip thread......:laughing:
But you are corect


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## Mark Oomkes (Dec 10, 2000)

Vacuum hubs in the early days sucked. And not just because they were vacuum activated. 

I remember them going bad in my '00 F350, they wanted some stupid amount to replace them...$800 or something because the seal was bad. Screw that, I can turn them manually twice a year for a lot less than that.


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## EWSplow (Dec 4, 2012)

Mark Oomkes said:


> Vacuum hubs in the early days sucked. And not just because they were vacuum activated.
> 
> I remember them going bad in my '00 F350, they wanted some stupid amount to replace them...$800 or something because the seal was bad. Screw that, I can turn them manually twice a year for a lot less than that.


As did the stock hubs.


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## BossPlow2010 (Sep 29, 2010)

Mark Oomkes said:


> Vacuum hubs in the early days sucked. And not just because they were vacuum activated.
> 
> I remember them going bad in my '00 F350, they wanted some stupid amount to replace them...$800 or something because the seal was bad. Screw that, I can turn them manually twice a year for a lot less than that.


Didn't the vacuum control the direction of air/ defrost vents as well?
I recal my 04 had a vacuum go bad


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## Mark Oomkes (Dec 10, 2000)

EWSplow said:


> As did the stock hubs.


True enough...the hubs on that truck were the vacuum or manual. So I still could have 4WD, just had to manually lock them in. They lasted for a long time before we replaced with Warns.


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## Mark Oomkes (Dec 10, 2000)

BossPlow2010 said:


> Didn't the vacuum control the direction of air/ defrost vents as well?


LOL...that's right, if it went bad you ended up with only one, can't remember which...all defrost or all heat.

Don't forget the hydroboost brake\steering. That pump went out and you lost power brakes AND steering.


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## Randall Ave (Oct 29, 2014)

Mark Oomkes said:


> LOL...that's right, if it went bad you ended up with only one, can't remember which...all defrost or all heat.
> 
> Don't forget the hydroboost brake\steering. That pump went out and you lost power brakes AND steering.


Hey, if you're gonna crash, crash big.


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## Philbilly2 (Aug 25, 2007)

Randall Ave said:


> Hey, if you're gonna crash, *make it* *EPIC*.


Fixer'


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## BUFF (Dec 24, 2009)

Mark Oomkes said:


> LOL...that's right, if it went bad you ended up with only one, can't remember which...all defrost or all heat.
> 
> Don't forget the hydroboost brake\steering. That pump went out and you lost power brakes AND steering.


I lost my vacuum pump in my '00 while at Togowtee, drove 450<> miles pulling a 30ft enclosed sled trailer. Got to love a manual trans and trailer breaks.


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