Speedometer gear question

[island45]

Just finishing up a transfer case rebuild. I rebuilt a '78 case from an Fj55 to swap into my '79 Fj55. My '79 has 3.70 gears and the '78 had 4.11. The '79 has 33" tires. My question is should I use the speedo gears from the '78 or the '79? I think this is the time to decide as I'm ready to button up the output with the parking brake etc , Thanks

 

[charliemeyer007]

Its hard to follow your question as written, I'm sure it makes sense to you.

Gear from 3.70 to 4.11 means the engine turns over more for any speed
Taller tires means the engine will turn over less at any speed

I doubt that with both changes it will cancel out. I would just put some sticker's on the speedo for like actual 15, 25, 35, 45, 55, 65, 75 mph.

Perhaps someone has done such a swap and will have a better clue about which of the 2 speedo gears provides the better result.

 

[Green Bean]

Sorry, I can't answer your question regarding the proper speedo gears for the different axle ratios. But make sure that the speedo driven gear matches the drive gear. They should both be marked. For example an 18 drive gear must us an 18 tooth driven gear. More info Here.

 

[pb4ugo]

So using an rpm calculator and figiuring a stk land cruiser had some where around 29" tires 1:1 final drive (4th gear). with 3.70 gears 29" tires traveling 60 mph your rpms will be 2572.
Using 4.11 gears with 33" tires going 60 mph your rpms will be 2511 rpms. I would try using the 78 speedo gears. It will be closer to right, I think. 33" tires 3.70 gears and 60mph your rpms will be much less at 2260 rpms.

 

[island45]

Thanks, will go with the set from the '78. as you can imagine, this vehicle is pretty high geared with it's 3.70s and 33"s.