DIY Guides › 4WD
Some setups rely on vacuum to engage the front axle. Leaks can leave you in 2WD.
When to use this guide: Transfer case seems to shift but the front wheels do not pull.
On 1984–1991 Cherokees, the front axle has a vacuum-operated disconnect. When you shift into 4WD, vacuum is supposed to physically lock the axle in. If the vacuum lines going to that disconnect are cracked, disconnected, or rotted, which they often are on older rigs, the front axle never locks in, even though the transfer case shifted correctly. Check the vacuum lines before assuming the transfer case is the problem.
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