setting Speedo switches

There's always Canada Post unless you need it right right now.

I know how you feel though. Having kilos on the guage was bothering me untill I looked on eBay and saw what it would cost to replace it.

 

HeavyD,

I was reading your reply about speedo switches.

Hope you can assist with this issue I have. Please let me know. Took it to a shop to request a speedo adjustment, but not sure if it was executed properly.

Vehicle -
1999 Peterbilt 379
ISX 565
Tires - Toyo M506Z Off Road, Size - 11R24.5, Inflated Dia 44.3, Rear End Ratio 3.58, 469 Revs per mile

The mechanic didn't record the original settings. Not sure why, but oh well. Here we are.

Switch set points by the mechanic, not sure how he got to these setting numbers. I believe he used a formula.
1st try - 3 6 9 10 speedo was very slow. gauge showed 25 mph, gps was 55 mph
2nd try - 1 2 4 5 7 8, still way off
3rd try - 2 4 6 this setting actually placed it very very close, if not right on. It worked and I was happy with it.
BUT........., when I left the shop, it resorted to being real slow again.

Any suggestions?

The mechanic mentioned to check the speed sensor on the trans. I am unsure how to proceed.

Any input would be great.

Thank you sir.

 

I am an International Truck tech. I don't have access to Pete stuff. I would ask this question in the Peterbilt section and hopefully one of the guys there can help you better.

 

The amerek guide should work. I recently replaced my 2000 Freightliner’s speedo with the ametek. I set switches the same. It was always off about 3 mph. Now the miles are off about 5%. The formula includes measuring tire height, first, then a bunch of math. I’m going to fine tune mine, simply by going to the next settings on the scale. It should work. Other newer type Speedo’s use gps, and can be calibrated to work, also.

 

Pete used a different Speedo 98 00, mine is LP 24.5 w/3.70, should be real close. Closed 2,4,5,7,8,9. Pushbroom is the guy to confirm.

 

I wonder if the final drive ratio is the same on an 18 & a 13 speed trans. .73 I believe on my 13.