Posted By: JohnH
SPEEDOMETER GEAR - 07/31/19 12:06 AM
69 B Body 440 engine,, 727 transmission.. My speedometer is running about 12 MPH slow. 355 rear, tires 26" outside diameter measurement.. According to the chart I seen, looks like the gear I need is P/N 2538936. Does this sound right? Thanks for any info...
Posted By: RapidRobert
Re: SPEEDOMETER GEAR - 07/31/19 12:49 AM
I went by the MP chart once & it was dead on. But if the speedo for instance is 12 MPH slow at say 60 MPH (shows 48 MPH) you would need 20% (12 divided by 60) less teeth on the pinion than what is in there now to speed it up 20%. For example if it has a 30 in there now you'd wanna get a 24. Jack up the car as high as you can on the dr side to minimize fluid loss & as you know clock the pinion adapter on the side of the trans to match the tooth count of your new pinion.
Posted By: John_Kunkel
Re: SPEEDOMETER GEAR - 07/31/19 05:24 PM
Actual math shows you need a 35.79 tooth pinion but I would check the odometer for accuracy first. If the odometer is correct and the speedo is off, the problem is in the speedo head.
Posted By: JohnH
Re: SPEEDOMETER GEAR - 08/04/19 09:09 PM
I had the speedo overhauled...
Posted By: lewtot184
Re: SPEEDOMETER GEAR - 08/04/19 09:55 PM
factory would have been 36 tooth.
Posted By: Magnum
Re: SPEEDOMETER GEAR - 08/05/19 04:23 AM
What is the gear in the transmission now and 12 mph off at what speed? As Kunkel mentioned the odometer is a better check because 12 off is not 12 off at 0 mph or still 12 off at a higher speed. If it was, the problem would be a bent needle.