Would changing my diff ratio alter my speedo reading ?

[71 Bee Man]

G'day guys,

took the Bee out for a long drive today - in the beautiful summer sunshine we are experiencing here....gee it was hot - and I couldn't help but notice that I seemed to be the only one doing the speed limit. When i asked a friend who was following what speed we were doing, it seems that when I was doing 49 mph, I was actually only doing about 43 mph. At about 70 it was more like 59/60.

Recently I changed from a 3.23 diff ratio, to a 3.55. Would that be the reason, or could it be as simple as a worn speedo cable ? Earlier in the year my speedo - at about 70 mph - decided to get the jitters and bounce backwards and forwards about an inch, and then decided to fix itself.

Any ideas ? It's a 383 / 727 / 3.55 car

Peter
Sydney, Australia.

[charger Downunder]

Hi Peter diff ratio and tire size will change it their is a few charts around
http://www.moparts.com/Tech/tech/pages/speedo.html

[firefighter3931]

Yes, swapping rear end ratios will alter the speedo calibration. Taller tires will also affect it as well. You need to use the correct tire height and axle ratio when selecting a speedo gear. 


Ron

[dukeboy_318]

yep itll affect it, ive got to fix the one in my ram 2500 because i went up a couple of sizes and my speedo is now off by 4 miles an hour

[71 Bee Man]

Yes, swapping rear end ratios will alter the speedo calibration. Taller tires will also affect it as well. You need to use the correct tire height and axle ratio when selecting a speedo gear. 


Ron

Thanks very much guys.

I wasn't sure that it would make that much difference, but apparently it has. I've looked at the charts (provided by the links) and am now looking to get a new speedo pinion.

Regards,

Peter

[Ghoste]

See if the Aussie Chrysler dealer can get it.  It may be available locally.
What size did you determine you need?

[71 Bee Man]

See if the Aussie Chrysler dealer can get it.  It may be available locally.
What size did you determine you need?

We actually don't really have any Chrysler dealers here that would sell the stuff. Chrysler pulled out of Australia in 1981 and didn't come back till 1996, and they aren't really interested in the older stuff.

I figured out I need one with 36 teeth.....a red one. I have the part number at home. Looks like I have a 33 tooth one in at the moment.

Peter

[Ghoste]

If it isn't available locally, let me know as I probably have one somewhere.

[charger Downunder]

Peter try these guys their local.
http://www.bluestarspares.com.au/store/viewItem.asp?idProduct=8795

[71 Bee Man]

Peter try these guys their local.
http://www.bluestarspares.com.au/store/viewItem.asp?idProduct=8795

G'day Steve,

The funny thing is I reckon I can pick one of these up NEW in the States for about $15 US and probably $5 postage. I'll just see what pops up - I may even get 2 ....one for now and one for if I decide to get 15 inch rims.

Peter

[kamkuda]

It is a pretty easy install too.  I had to do the same when I changed gear sets.