Ok I am running a 04 379. The speedo and odo are consistantly off. Meaning that my speedo reads more then 3 mph faster then my actual speed even with new drives installed. As the tires wear then the speed goes even farther off kilter.
I have had it into Cat and Pete and they both say that the proper coding is in the computer for the axle ratio, transmission and tire size.
I had the dash apart the other day to put in a bulb in the speedo and noted the switches on the back of the speedo. I heard it had them but I never seen them since this was the first time I had the dash pulled down.
Is there someplace I can look to find the settings of these switches and can they be adjusted to bring the speedo down closer to my actual speed?
04 379 pete, deciphering the switches on the back of the speedo
Discussion in 'Trucks [ Eighteen Wheelers ]' started by Rat, Dec 3, 2011.
-
-
Trucking Jobs in 30 seconds
Every month 400 people find a job with the help of TruckersReport.
-
I don't know why cat would even have a clue about the dip switches on the speedo, maybe the tach. I always just call Peterbilt. they will need the revs per mile on the drive tires you are running and the rear end ratio, then they should be able to tell you which switches are ''open'' and which one should be set as ''closed''. My speedo is right on the money set that way.
Also found this http://new.ametek.com/content-manager/files/DIX/51536-b.pdfRat Thanks this. -
I have fine tuned them with the dip switches. I first note the switches original positions, I then leave the clamp off the speedo head for access while driving. I've used mile markers to monitor adjustments and sometimes a radar gun with an assistant. Trial and error but it works. Some of the switches will cause a larger change than others, you just find the right combo.
Rat Thanks this. -
-
Got it figured out today. I pulled the speedo strap so that I could get to the speedo.
I picked a deserted road and flipped the far right switch to see what happend. Speedo needle dropped about 20 mph. I flipped the far left switch and it hardly moved at all. maybe a tenth of a mph. It took me three trys to get the speedo almost dead on. At 65 on the gps the speedo needle sits directly over the 65 mph line. At 68 on the gps the needle is just slightly below 70. At 25 on gps the needle is directly on the 25 mark.
Before with my foot on the floor the needle would run right between 70 and 75. Now it just barely touches the 70 mark which is GPS indicated 69.4.
Thanks for the comebacks on this. -
Good to hear you got it worked out.
-
I have 98 Pete with 390 with 24.5 in to witch to 22.5 the speedometer perfect now for 24.5 so switch do I move on the back of the speedometer I put the 22.5 on if anybody can help that would be great thanks
-
This document explains the process in calculating and adjusting the dip switches,
Attached Files:
Oxbow, RocketScott and spsauerland Thank this. -
Trucking Jobs in 30 seconds
Every month 400 people find a job with the help of TruckersReport.