OT: Street Rod Speedometer

[Jason1(Pa.)]

I have a street rod I got last summer. I notice that the speedometer reads 10mph faster then what you are going. How can I solve this problem. Anyway to get the calibration right? Thanks

 

[Bob]

It would help to know WHAT you have...


If it is a mechanical speedometer, you can change the speedometer drive gear(s) in the transmission, or there are speedometer drive adapter gearboxes with different available gear ratios to correct the error.

If it is an electronic speedometer, there are electronic units available to make the correction (DRAC's)

 

[Jason1(Pa.)]

Sorry. I didn't say that it is a mechanical speedometer. Where would be the best place to look into for new gear(s)? thank you

 

[Bob]

What is the transmission make???

Knowing that, GOOGLE speedometer gears (make).

 

[Anonymous-0]

First you have to find out what driven gear you have. And who made the transmission where that gear rides. Then you have to do the math to find out how many more teeth you need. Then you can start with the parts room at the nearest dealer for the make of transmission. Sometimes its hard to get enough teeth on the driven gear and you have to change the driver and the driven. I know Ford parts counters have a book of speedometer gears.

I changed my F-150 from 3.08 to 4.10 gears. It had an 18 tooth driven gear, and I computed I needed a 24 tooth driven gear for the same driver. I had to go to a couple dealers who customized Mustangs to find a 23 tooth driven gear (6 months later truck and it would have been a computer setting). Since the teeth on that gear are very thin, I bought a spare. So far in 80,000 miles I've not needed the spare.

It should be that hot rod shops that sell rear axle gears carried the speedometer gears, but I've not found that to be the case.

Gerald J.

 

[JDemaris]

You don't need to change gears unless it winds up being the cheapest/easiest fix. There are all kinds of "correction" gearboxes for mechancial speedos - and also electronic correction boxes for electronic speedos. Some companies use them as original equipment - like Dodge diesel trucks.

I just put a different one on my truck to because it was off by 9%. You can calculate exactly what you need - and the little gearbox hooks between your trans speedo cable.

Many places sell them - one is:
http://www.transmissioncenter.net/727Transmission.htm

 

[Anonymous-0]

I'm sure there are more places out there, but this one poped up when I googled.

http://www.speedometershop.com/ratio.html
http://www.speedometershop.com/ratio.html

 

[JDemaris]

Here's a more specific link for speedo correction stuff:

http://www.transmissionsone.com/speedometer_gear.htm

 

[big fred]

If it's an aftermarket speedo, your best bet is to contact the company that made it. Tell them your tire size, rear end ratio and transmission type, and they should be able to point you in the right direction.

 

[Anonymous-0]

Leave it the way it is. It will look more impressive to a passenger. As long as you know how far off it is, you can avoid tickets.

 

[Fixer]

Could go to larger diameter rear tires. Bernie Steffen

 

[dave guest]

Dealer's parts man used to ask you the tire size and give you the right gear. Easy enough then.

 

[dave guest]

Dealer's parts man used to ask you the tire size and give you the right gear. Easy enough then.