1990 Pickup 4wd Problem

[bmckee]

Hi,

I bought an old 1990 4wd pickup 4 cylinder. After I lock the hubs, when I put it in 4wd High, it is like driving with the parking brake on (which isn't). I can barely get it to 55 on the highway. This is the first time I have owned or driven a 4wd. Should I have this problem?

thanks,

BRian

[Andy]

Never ever use if fully locked on the hard stuff , this should explain it more .

Axle/Transmission Windup

When a 4WD is travelling in a straight line all four wheels rotate at the same speed, but during cornering each wheel travels at a different speed due to the radius of the turn.

All vehicles have a differential on the front and rear axles to allow the wheels on the same axle to rotate at a different speed.

Constant 4WD’s have a central differential fitted to allow for different speeds between front and back wheels, but most part-time four wheel drives do not.

When a part-time 4WD (without a centre differential) is in 4WD an attempts to corner on bitumen, all wheels need to rotate at different speeds, but without a centre differential they cannot.

This creates the phenomena called "axle windup" or "transmission windup".

High strain is placed on the drive shafts and transmission, eventually causing one of two things to happen.

Either one of the wheels slips or spins to overcome the stress

or

the drive-shaft/transmission breaks.

This is why part time 4WD’s should never select 4WD on bitumen.

Constant 4WD’s have a central differential within the transmission to overcome this problem.

However once in the dirt a constant four wheel drive can be bogged with only one wheel spinning.

This is why they have a central differential lock that stops the action of the centre diff and makes it like a part-time four wheel drive in 4WD mode.

The centre diff lock should never be used on bitumen or non-slip surfaces for the reasons mentioned above.In reality, a 4WD is only a two wheel drive with one front and one back wheel driving when traction is lost.

One wheel on each axle spins while the other receives no drive at all due to the action of the differential.

The exception to this is where a limited slip or locking differential is fitted.

A limited slip diff allows a limited amount of drive to be applied to the stationary wheel before the other wheel on the same axle spins.

A locking diff allows no slip at all and both wheels on the same axle turn at the same speed, regardless of the amount of traction.

[MuddyAlaskanToy]

one thing to keep in mind is the fact that your truck is going to drive a bit differently then it would if it was in 2wd. After driving my 1991 in 2WD all summer long except for when I go wheelin, I have to get used to how my truck drives in 4wd for the whole winter. (Winter is pretty long in ANchorage, Alaska) so there is plenty of time.

[mblogsd]

Sounds like a problem with your front differential.