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The Hummer Knowledge Base

Maintenance and Driving Tips


--OIL LEVEL!! I think Dave could relate to this :-)

1. Slightly loose bolt holding the brake caliper bracket on the all allowing movement and clunk under light braking. Cure: disassemble the lot and slather bolt threads in Locktite 271 or 272 and reassemble with lockwashers.

2. A sloppy bushing in the lower A-Arm on the RF also adding another clunk to the voices. Cure: I'm getting a new arm next week. **Check Service Bulletin I uploaded to Bob's website regarding this matter**

3. Centerline bolt after you remove and drop the half-shafts. Known to come loose and cause a serious vibration problem; possibly ruining differential seals, retorque and locktite it. Now the half-shalft bolts to the rotor, buy the aftermarket versions. The O.E.M. Nord washer are know to come loose. -86 ćem and put the new ones on. I don't know for sure, but I believe I was told you could re-use the camlock washers. If your vehicle is a pre '96 (not sure of the manufacture date) and you haven't replaced your halfshaft bolt lock washers; you'd best do it...They are know to come loose when in abuse. BTW, there is also an AMG service bulletin on this... Dealers have in some cases, been sanctioned to install these washers. Use plenty of Locktite 271/72.

4. The CDR is the Crankcase Depression Regulator valve. I connects from the top of the right rocker arm cover to the intake manifold. As far as I have figured out, Depression refers to the pressure within the crankcase. Since we always have some blow-by, the there has to be a vent in the crankcase.

This is similar to a PCV valve on a gas motor. I am guessing that if it fails some how, you can suck oil into intake manifold and burn it up. This is why you are supposed to pull it out and see if it is dripping oil (saturated).


Scott has a method he calls "Constant-torque Modulation" which I find works even better than the standard BTM in the most extreme situations. When you approach an obstacle, set up for the climb and when ready apply FULL brakes.

Then apply throttle and run the engine up into the best-torque range AND LEAVE IT THERE. In other words, keep the throttle pressure the same throughout the climb. Then use the BRAKES to adjust speed, NOT the throttle.He has found that for the most extreme situations that this provides a much smoother climb with less slippage, bouncing, pounding or traction-breaking. He watched other drivers as they would approach, begin the climb, modulate, and then goose the gas part way up because they felt they were slipping. All this did was screw them up. The constant-torque method offers you the most available torque for the whole climb at a steady power-rate which does not fluctuate, while also ensuring that your Torsen's will be fully locked at all times so you don't spin a wheel and possibly snap a half-shaft through weak modulation pressure. The power input to the wheels is very smooth. He most especially uses constant-torque on DOWNHILLS, where it provides very precise control of your forward progress with little chance of accidentally "goosing" the pedal as you slide off the edge and bang down onto something on Nose-dive. With the brakes already fully on, you just let off a hair to creep forward as needed. Yes, it's hard on brakes and tranny, and should only be used on the severest of obstacles, using regular BTM on less demanding ones, but it's worth the effort, as it results in a smooth, finessed crawl rather than a banging, clanking kidney gut-buster.

The higher you ascend, the less oxygen you have available in your air. When you hit the accelerator, your fuel pump sprays more fuel into your engine. You will find at altitude that you only have enough O2 to burn a certain amount of fuel. Anything that you inject into your engine beyond that doesn't burn completely: it generates very little power, and comes out of your exhaust dark black with tarry, incompletely burned fuel.

To avoid this problem, keep an eye on your exhaust when climbing at altitude, and lay off the gas pedal when you see smoke. That's easy in my truck, since my exhaust emerges under the left rear wheelwell. Folks with exhausts that emerge from beneath the rear bumper may find this more difficult; they should instead accelerate even more conservatively than usual, and lay off the gas pedal when they feel that they aren't getting any more thrust.

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