Al & JyRO:
My U. S. Gear D-Celerator brake literature says it's not meant to be used with the cruise control. The literature also says that the throttle switch is not meant to be used as an on-off switch, but rather as a safety override mechanism. That is, the driver should not arm the e-brake and let the on-off switching occur by virtue of the throttle position.
The throttle switch merely disengages (opens) the e-brake when the throttle is not fully closed.
That said, however, if you do arm the e-brake and control engagement with the throttle switch here's what will happen with the U. S. Gear D-Celerator unit. With the cruise control set at 60 mph, you start down a hill. It takes the cruise control a while before the throttle fully closes and the e-brake engages, let's say at 68 mph. The truck slows down.
As the speed approaches 60 mph, the cruise control starts to feed in a little throttle to maintain 60 mph. This disengages the e-brake, and the truck speeds back up to 68 mph where the throttle once again closes. The brake engages again, and the process is repeated.
I don't know how well the other units work, but a properly installed U. S. Gear De-Celerator will require a REALLY steep hill before it would not be able to slow the truck below the cruise control set speed. I don't turn the e-brake off under these circumstances, I turn off the cruise control.
Some other notes on the U. S. Gear De-Celerator units:
My first one was installed on my ‘95 automatic. DO NOT INSTALL ANY EXHAUST BRAKE ON A TRUCK WITH AN AUTOMATIC TRANSMISSION WITHOUT FULLY UNDERSTANDING THE CONCEPT OF A LOCKED TORQUE CONVERTER DURING DECELERATION. Discuss this with your installer. If they can't tell you about the potential for overheating your transmission, they don't understand it. Buy somewhere else. You will need a torque converter lock-up switch.
I had two problems with that unit. First was a failure to operate caused by a ground wire that was too short when installed which lead to an intermittent open wire. The second problem was a failed pull coil relay (failed closed) which caused the brake to close and open on its own. Diagnosis was not easy until the entire system was explained to me by the mechanic.
I am in the process of switching that unit from my ‘95 truck to my Y2K six-speed. I have had two problems with this installation so far, and it's not done yet. First, I had a major leak from around the front clamp. This leak was large enough to prevent the e-brake from providing meaningful deceleration. I'm told that muffler cement is the way to go to fix this, but I haven't gotten that far yet.
The second problem with the new installation was an adjustment on the brake. You can adjust the length of the rod that closes the butterfly valve to ensure that the valve is fully closed. As long as I had the brake off, I decided to shorten that rod a bit. While attempting to turn the parts that had rusted together, the rod broke.
Rather than continue to put up with an older unit, I decided to take the advice of the guy who sold me the original one and trade this one in on a new unit for $400. The original sold for $900. I haven't yet received the replacement.
I have mixed feelings about U. S. Gear and their unit. Their support has been excellent, and when everything is correct the brake works really well, but I have had some problems that probably should not have come up. I guess you pay your money and you take your choice. All in all, I'd buy another U. S. Gear.
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2000 Quad Cab, 4x4, short bed, six-speed.
1995 Standard Cab, 4x4, long bed, automatic. (soon to be sold)