Speedometer gear selection

As some of you know I’m swapping my 318/904 to a 440/727. The 727 trans came out of a truck/mobile home. How do I go about selecting the right speedometer gear for my 70 b body?

Hey Sonny, there are charts which plot your rear end gear ratio, against your rear tire size. Find the two, and pick out the correct one for your set up. I found one in the Year One Catalog...

I'm not sure if the gears are the same style but I think they are. You need to know your rear end gear ratio and your rear tires size (height). There is a chart for how many teeth gear you need in the SRM. There are several venders to get the gears from. When I went on line they wanted to know what drive gear you have,(inside the trans) also. Ford and GM had listings for those that you needed to know as well but there was no listing for Chrysler. That's when I found out that Mopar gears drive directly off the shaft and don't use another inner drive gear. The shafts have 13 teeth if I recall. Beware of listed tire heights listed by the tire manufacturers. I bought Mickey Thompson rear tires that listed the diameter as 28" which was bullshit. I measured mine mounted and inflated at 26". I ordered the gear based on (my) measurement and the 3.91 gears I had in the rear of the car and came out spot-on as proven by a roadside speed detector, which could be off a little I suppose. I wish I could remember who the vender was but senility has removed it from my head. If you really need to know I can search my receipts for that info but I'm sure someone here will most likely chime in before I can find it! Good Luck!

Sonny said:

As some of you know I’m swapping my 318/904 to a 440/727. The 727 trans came out of a truck/mobile home. How do I go about selecting the right speedometer gear for my 70 b body?

Click to expand...

the height of your rear tire.

Sonny said:

As some of you know I’m swapping my 318/904 to a 440/727. The 727 trans came out of a truck/mobile home. How do I go about selecting the right speedometer gear for my 70 b body?

Click to expand...

Yes, as these guys say..... you need to know your rear end gear ratio + the DIAMETER (height) of your rear tires. You might check brewer's performance for a calculator/cheat sheet. What you need to know is the number of teeth for your transmission speedometer gear. Brewer's sells new & used ones or you can search wherever you like. The gear is REALLY easy to install (though you'll spill a little transmission fluid if the transmission is already in the car).

If your speedo was right before the swap, just put the 904 gear into the 727.

R/T Boy 67 said:

If your speedo was right before the swap, just put the 904 gear into the 727.

Click to expand...

I Shoulda thought about that prior to selling it