Speed Pinion Gear Tooth size explanation

[Dean Prevolos]

I don't know enough about these A833 transmissions, so I'm asking the question. How do I calculate or find out what size speedometer Pinion Tooth size I need to buy for my A833 transmission? I have a 67 A833 trans, 18 spline installed on my 426 Hemi with a stock Dana 60 rear end (3:54). I looked at Brewars website and see many used speed pinion gear sizes for sale but nothing new(currently out of stock). Any advise is appreciated.

 

[toolmanmike]

I don't know enough about these A833 transmissions, so I'm asking the question. How do I calculate or find out what size speedometer Pinion Tooth size I need to buy for my A833 transmission? I have a 67 A833 trans, 18 spline installed on my 426 Hemi with a stock Dana 60 rear end (3:54). I looked at Brewars website and see many used speed pinion gear sizes for sale but nothing new(currently out of stock). Any advise is appreciated.

You'll need tire diameter as well. There are charts on the internet. Do a little searching and you will find the.

 

[Fran Blacker]

If you use stock tire size service manual has info.

 

[66Satellite47]

A factory service manual has the chart that tells which tire diameter and gear ratio to use for each speedo pinion.

 

[Fran Blacker]

 

[66Satellite47]

Too bad we all can't convert the tire size to diameter. Something that always pissed me off about the FSM.

 

[moparmarks]

I just bought 6 gears from these guys on Ebay. Haven't used one yet but will probably install one this week. By far the best price out there.
https://www.ebay.com/itm/154412095893

 

[moparmarks]

 

[moparmarks]

I'm doing a car with 33" tires and 4.10 gears so I'm using the SWAG method.

 

[Nate S]

The speedos tend to be wrong to begin with. The charts can be sorta close. Quick rule of thumb is that for factory-ish size tires us the rear gear ratio. 3.23, use 32, 3.91, use 39 etc. that’ll get you in the ballpark.

Important part after that… put it in and use a gps app to measure some speed, say 60. Then look at the speedo. If the speedo is too high you need more teeth, too low, fewer. Make a ratio between gps and speedo, say you read 65 and gps was 60. 65/60=1.08. And let’s say you have a 35 tooth gear in there to start. 35 x 1.08 = 37.9 so use a 38. I’ve done this and it makes a super accurate speedo.

**special note** when the speedo is right on, the odometer might not be! Use an odometer app for the same thing. Can only have one right though. I do the speedo.

Edit: a couple other thoughts: 65 and before use different gears. The “lookup charts” can be very wrong. My ‘64 by the chart and factory spec had a 19 tooth. With factory dia tires I need a 21 for the speed to be right and a 20 for the odo to be right.

 

[Dave6T4]

BFG used to have a chart of tire diameter by tire size. It can likely still be found on internet.

 

[Fran Blacker]

Just googled 775 x 14 = 27.02" dia. Go to Coker tire and look up tire size and it give diameter. 4- 775 x 14 tires $1,189!!

 

[Beekeeper]

Brewer’s has a chart on their website

 

[Kern Dog]

**special note** when the speedo is right on, the odometer might not be!

Say Whuuuuut?
Really???

 

[steve817]

Correct mph readings is based off of a multitude of mechanical and electrical (eddy currents) that happen from the gear in the tranny, cable core, connections, and speedo function. Just because the speed is accurate, that does NOT mean the odometer is correct (and vise versa).
That is a very true statement.

 

[RemCharger]

Would it make sense that if the odo is calibrated, the speedo might be off.

 

[Dean Prevolos]

View attachment 1268774

Thank you Fran, I see it on page 21-15.

 

[Dean Prevolos]

The speedos tend to be wrong to begin with. The charts can be sorta close. Quick rule of thumb is that for factory-ish size tires us the rear gear ratio. 3.23, use 32, 3.91, use 39 etc. that’ll get you in the ballpark.

Important part after that… put it in and use a gps app to measure some speed, say 60. Then look at the speedo. If the speedo is too high you need more teeth, too low, fewer. Make a ratio between gps and speedo, say you read 65 and gps was 60. 65/60=1.08. And let’s say you have a 35 tooth gear in there to start. 35 x 1.08 = 37.9 so use a 38. I’ve done this and it makes a super accurate speedo.

**special note** when the speedo is right on, the odometer might not be! Use an odometer app for the same thing. Can only have one right though. I do the speedo.

Edit: a couple other thoughts: 65 and before use different gears. The “lookup charts” can be very wrong. My ‘64 by the chart and factory spec had a 19 tooth. With factory dia tires I need a 21 for the speed to be right and a 20 for the odo to be right.

Thanks for that explanation Nate.