Is there a fifth gear for a 66 520?

[Stevedawg]

So I have a 66 datsun 520 it's a 4 speed and I was wondering is there a way to get a fifth gear for highway driving? I live on an island so the 4 speed is no problem, but when I go off island I don't want to over rev my motor.

[wayno]

The engine is made to rev, if you want to lower your hiway rpms, then change your rearend gearing from 488s to 437s, 411s, or 390s, but you lose your starting out power, 437s would help quite a bit though.

To put a 5 speed behind your J13, you would have to make a custom plate and figure out the starter.

[ggzilla]

There is no fifth gear for a 1966 520.

[datzenmike]

Nissan didn't design it so it would over rev. It only sounds like it. Tens of thousands were built and they ran just fine. As wayno said a lower differential gear is cheap and easy.

[ggzilla]

A lower ratio differential gear will result in slower acceleration.

 

If you want to lower revs without any side effects, drive slower. Otherwise put your foot down and do 60 MPH.

[140ypower]

The engine is made to rev, if you want to lower your hiway rpms, then change your rearend gearing from 488s to 437s, 411s, or 390s, but you lose your starting out power, 437s would help quite a bit though.

To put a 5 speed behind your J13, you would have to make a custom plate and figure out the starter.

 

fits 410/411 gear that or what? :)

[datzenmike]

The 520 uses an H-190 differential. The '190' is the diameter in millimeters or 7.48" The 520 uses a 4.88 ratio so that for very turn of the rear wheels the engine turns 4.88 times in 4th gear. With 6:00 x 14" tires this means that at 60 MPH the engine is turning only 4,159 RPMs. At 70 it would be 4,853 and so on.

 

Keep in mind that Nissan selected this gear ratio so the truck could be revved enough to carry a full load at freeway speeds with a tiny 1.3 liter motor. If you are never going to carry up to a ton of cargo you can, with some restraint, lower the ratio somewhat. Again, keep in mind the J13 doesn't make a lot of power and dropping the RPMs too much will result in a very sluggish vehicle that may not reach freeway speeds on windy days or climb hill well. 

 

There are other trucks with the same rear end and lower ratios that can be swapped into the 520. Most all 620 standards were 4.375. The '79 620 and some later 720s were 4.11. Some 720s were 3.889 and the great thing about the 720 is there is an engine tag with the installed gear ratio stamped on it. A 3.889 at 60MPH is 3,315 RPMs... close to a thousand RPM drop.

 

Five speeds are expensive and lots of work to swap and if most of your driving is around home, not even needed. A differential swap can take just a few hours.

[ggzilla]

I recommend the 4.375 if you do not use it for hauling loads.

 

4.11 only if using it mostly for highway

 

3.889 never. Remember a 520 already has large tires, which reduce acceleration compared to small diameter tires.

[datzenmike]

Came with 6:00 x 14s or 175/70R14 equivalent. About 23.65" diameter. This is what I used for RPM calculations.

[ggzilla]

Or get a larger engine which will be faster AND more fuel efficient with high gear ratio. For example an L16 with 5-speed. Not an easy swap, but easier than putting a 5-speed behind the J13.