Speedo calibration dip switches

Good info Hammer! In the old days when we swapped stuff around we removed the driveshaft from the transmission. Used to remember a formula to figure road speed by tire R.P.M. gear ratio, engine RPM etc. There is an Eaton sight for that now. Then flipped the dips intell speedo read max speed.

 

On a Peterbilt, if you call your friendly dealer, they can email you the chart for figuring it out. The proper way to do it is shown on the chart, but includes measuring tire circumference and plugging it into a formula. Also note that the older analog gauges, and the new digital gauges use different settings.

 

my peterbilt dealer in Phoenix gave me serious run around.

 

There is a formula for 379 Peterbilt Speedo's built by AMETEK, I just replaced mine in an '05. You need to know your tire diameter and diff. gear ratio, I've got 40" tires (Michelin XDN2 low-profile 22.5's) and 3.36 rears. If the gear ratio isn't on a sticker in the glove box, any dealer can look it up from your VIN. Put the numbers in the formula, then look on the table (I only sent the page closest to my tire size, PM me if you have tall rubber and I'll send the page with the right numbers.) It will tell you what position to put the switches in. Good luck

 

I was wondering if I could get some help with these dip switch settings?

I have a 1996 Western Star, speedometer is factory.
Factory 15 speed O.D., 3:36 rears and 11R/24.5 tires (tall rubber).
I've tried different settings but keep coming up about 4 mph slow on the actual speedometer reading (checked against 2 different gps).
I know it is the dip settings...please help.

Thanks,
John

 

Give this thread a read. There's a few attachments posted in it showing how to set the switches.

http://www.thetruckersreport.com/truckingindustryforum/threads/dip-switch-settings-on-a-379.322298/

 

Dummy harness that reaches the passenger seat and a gps

 

Thanks NorthernMechanic for the helpful response. I've read several already but keep getting something a bit off. I'll read through the thread you posted.

 

Google AMETEK they have a tech #. The guy told me they have a generic setting for trks with Cat Engines.
(1998 Any way).

 

Ok, I'll look into that also. I been working on the formula; I'm getting closer to fixing this I think.
Thanks for the help ironmule.