u joint and hub problems

hi, i had the front drivers side u- joint replaced exactly one week ago, and now it seems to be broken again.
now when i brought it to the shop they pointed out that the hub was locked in 4wd and would need new hubs to fix that.
they did not say it was necessary in anyway, they actually persuaded me that it wasnt worth the money for an 92 explorer.
the only thing they entailed was that i could only drive in 4wd. is this true? or is it because of the hub being locked up that the u joint keeps breaking? im at my wits end, and at the bottom of my wallet here.

The locked hub is very possibly contributing to the failing u-joints. Since your Explorer has 4WD rather than AWD, there is no center differential which means when you are turning shaply such as in to parking spots, around downtown street corners, etc., the transfer case is forcing the front wheels to turn at the same speed as the back wheels. This is hard on drivetrain components.

I suspect that if you read an owner's manual for your truck, it will state to only use 4WD when necessary on slippery surfaces such as snow and mud. It probably says something about "NEVER use 4WD on dry pavement...."

Your thought is probably correct, you should fix the locked hub or your truck will continue to eat u-joints.

-Rod