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  • Writer's pictureJustin Schaub


Author: Ben Greene

How to Perform a Jack Test

1. Make sure your car is on a level, smooth surface. Something a jack would easily roll on without getting caught up.

2. Then, with a floor jack, raise up the rear of the car from the differential. No, this will not harm the car in any way during the ten minutes it takes to perform this test.

3. Now, start the car and slowly let off the clutch and add some gas to creep the car forward, dragging the floor jack with you.

4. Notice if the car seems to “slip” or you need to rev the car a little more than usual to creep forward. At this time, someone should also be watching from outside the car, paying attention to the speed of the rear wheels relative to the fronts on the ground.

5. You should only need to move the car forward about two feet to collect all the information you need to know.

6. Now we analyze what we saw. There are three main outcomes from the test.

  • Your front and rear wheels move at the exact same speed relative to each other and the car pulls itself forward easily.

  • The rear wheels move faster relative to the front wheels, but the car still moves forwards.

  • The rear wheels spin but the front wheels do not, the car does not move forwards.

How to Determine If It Works

  • If you saw option A, congratulations, you have a perfectly working transfercase.

  • If you saw option B, your transfer case is still functional, but is beginning to wear out and show its age.

  • If you saw option C, this means your transfer case is not operating as it should any more, effectively reverting your car to rear wheel drive only.

Of course, we could say that option B is on a sliding scale. The closer together the front and rear wheels are in terms of relative speed, the better condition your transfer case is in. The further away they are, the worse condition it’s in.

Tools Needed to Perform the Jack Test

Torin 3 Ton Car Jack -

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