03-31-2015 11:48 AM
Thanks again Dave. I replaced the brakesaver throttle switch as part of the work on the truck, not realizing that it was also the low idle adjustment bump stop. I will adjust it to 700 and hopefully that should cure it. As a practical matter, I have been using the hand throttle to run the RPMs up to about 800 to warm up the engine when starting, so it doesn't have too much time idling down at 550.
03-30-2015 06:35 PM
Hello, I have been restoring a Peterbilt 359 with a '79 Cat 3408 DITA engine in it. After many years of working on the truck, it is 95% complete, and finally on the road. I have encountered a quirk, for which I am requesting assistance. When the engine is good and warm, when I get off the throttle, usually when pulling up to a stop, the engine RPM will return to low idle (550 RPM or so). However, once in awhile the engine RPMs will dip below low RPM, and the engine can die. If I catch it in time, I can give it a little throttle for just a sec, then let off, and it won't die. If I fail to catch it, the engine will stop, but a quick bump on the starter and it is going again. The engine is not running rough (for a 3408), there is no miss, and it starts right up immediately. A friend of mine with Cat knowledge suggested that there is a spring in the governor which acts as a flexible stop for when the throttle returns to low idle, and that this spring could be worn or broken. I have studied my parts book and service manual, and see various springs on the shaft with the counterweights, as well as possibly a spring on the lever that transmits the throttle linkage motion to the governor shaft (The one with the weights and slides on it). I'm hoping someone has had this experience with a 28V 3408 (or even a 3406A) and might be able to shed some light upon which could be the culprit. I'm comfortable pulling the engine shutoff and governor off the pump, but admit I have not gotten into one before. Being a '79, the engine doesn't have the very early style governor, but has the more common type, with the engine shutoff vertically in front of the governor. Ser. 28V3098, arrangement 9N5228. If anyone has encountered this condition belore, please drop me a line. Thanks!
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