2002 Cadillac Escalade Crow Hops

Tiny
UUC4514
  • MEMBER
  • 2002 CADILLAC ESCALADE
  • V8
  • AWD
  • AUTOMATIC
  • 108,000 MILES
My 02 Escalade crow hops on sharp low speed turns after driving at highway speed for about 1 hr. Feel like locked in four wheel drive.
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Wednesday, April 14th, 2010 AT 7:17 PM

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Tiny
FACTORYJACK
  • EXPERT
You only have a couple possibilities, the first I would think has to be induced from an improper repair. I found this as a bulletin. I also would think it would be a concern at all times, not after an hours drive.
#PIT3026B: Tire Scrub Noise Or Crow Hop During Low Speed Turns - keywords bind front shudder steering suspension vibration wheel - (Oct 27, 2006)

Subject: Tire Scrub Noise Or Crow Hop During Low Speed Turns

Models: 2002-2006 Cadillac Escalade Models

2000-2006 Chevrolet Avalanche, Suburban, Tahoe

1999-2007 Chevrolet Silverado Classic

1999-2007 GMC Sierra Classic

2000-2006 GMC Yukon, Yukon Denali, Yukon XL, Yukon Denali XL

With Recirculating Ball Type Steering (Non-Rack & Pinion)

This PI is being updated to add models. Please discard PIT3026A.

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

Condition/Concern:
Tire scrub noise or crow hopping during low speed turns(parking lot maneuvers). It has been found that the steering rod (center link) can be installed backwards. There is a potential for this to occur on all trucks and utilities with recirculating ball type steering that does not use a steering dampener.

Recommendation/Instructions:
To qualify the correct installation of the steering rod, compare to a like vehicle. In a correct installation the steering rod should curve to the rear, outboard of idler/pitman attachment holes and inboard of the inner tie rods.

The idler and pitman attaching holes are only tapered in one direction. So that with the steering rod installed incorrectly the curved portion of the rod between the idler/pitman holes and inner tie rods would be curved toward the front of the vehicle. Remove and correctly reinstall the steering rod (center link).

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do

The second is more than likely the concern, it has to do with the viscous coupling in the transfer case being locked up. Here is some information on the coupling. There is a test procedure, it requires some special tools and a lift.


http://www.2carpros.com/forum/automotive_pictures/309872_785429_1.jpg


Transfer Case Description and Operation

The NVG 149 RPO NP3 is a single speed, single mode transfer case. The mode is full-time all wheel drive. It has a planetary differential gear set that splits the torque, normally 38 percent to the front wheels and 62 percent to the rear wheels.

The NVG 149 utilizes magnesium housings. Proper fasteners, brackets, and fill/drain plugs must be used to prevent galvanic corrosion. The planetary differential uses the carrier (6) as the input. The annulus gear (4) connects to the rear output shaft (5) and rear wheels. The sun gear (3) connects to the front output shaft (7) and front wheels through the chain (8) and sprockets. The viscous coupling (2) consists of a sealed housing filled with a high viscosity silicone fluid and thin steel plates alternately splined to the inner and outer drum. The inner drum is connected to the input shaft (1), and the outer drum to the sun gear (3). Whenever there is a speed difference between the front and rear wheels, the inner and outer plates of the viscous coupling spin relative to each other and the silicone fluid provides resistance. The resistance was tuned to be high enough to bias power quickly to the wheels with traction, and low enough to prevent binding in a tight turn on dry surfaces. This is the most common way the viscous coupling is activated, the shear mode. If the speed difference is high, the coupling can lock or hump. This "hump" occurs when the heat generated, expands the fluid inside the housing, changing the fluid dynamics between the plates. This results in pressure between the plates, forcing them into contact with each other, similar to a clutch pack. In the hump mode, the coupling can bias torque 100 percent to one axle, if required. Situations requiring this are extreme such as backing up a steep gravel grade or climbing over off-road obstacles. The viscous coupling is not serviceable; it must be replaced if defective. This is because each viscous coupling is calibrated for optimum vehicle performance for both the shear and hump modes. If the viscous coupling is in the "hump" mode too long, severe damage will occur. To prevent damage to the viscous coupling, DO NOT:

" Tow with only two wheels down

" Drive without one propshaft

" Drive with a "donut" spare tire for an extended period of time

And the test procedure, for your reference.

Viscous Coupling Test
Tools Required
J 45382 Transfer Case Tester

To determine if the viscous coupling is operating correctly, use the following test procedure. Testing the viscous coupling operation by removing a propeller shaft and driving the vehicle will cause the viscous coupling to fail. The test will determine if the viscous coupling is faulty from a totally locked up failure, or if the viscous coupling fluid has leaked out from being severely humped.

Important: The Viscous Coupling Test is very sensitive to the temperature of the transfer case. If the transfer case is very hot, the time to turn will be faster. If the transfer case is cold, the time to turn will be slower.

Operate the vehicle for 24 km (15 miles), or until normal operating temperatures are reached.
Set the parking brakes for the rear wheels.
Position the transmission in neutral.
Raise the vehicle.
Remove the front propeller shaft.
Install the J 45382 into the transfer case front output shaft.
Using a torque wrench at 11 N m (100 lb in) on the J 45382 , turn the front output shaft.
Note the length of time it takes to turn the front output shaft the 90 degrees.
" If the front output shaft turns slow, with resistance, and takes at least 10 seconds, the viscous coupling is operating correctly.

" If the front output shaft will not turn, the viscous coupling or the planetary carrier assembly could be locked-up.

" If the front output shaft turns easily, and the 11 N m (100 lb in) cannot be obtained, the viscous coupling is faulty.
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Wednesday, April 14th, 2010 AT 10:17 PM

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