Axle skool?- 5.125:1 huh?

[fisch]

Ok, so the '59 Datsun I bought comes with a 5.125:1 rear axle. I know this means that the wheel with stock tires turns once for every 5.125 revolutions of the engine/shaft. I am sure this was to compensate for the massive 37 hp C-engine it comes with.

 

More than likely the axle will be replaced. There are options. Purple has a Ford Courier in his and I hear the 720 is close, as well as the Roadster.

 

But for the sake of discussion...

 

I think higher ratios are bad for MPG, but good for towing. But what does this mean for real world driving if you put a L18 or L20 in it. W/ triple the HP as the stock mill. How would it launch at the stop light? Would it sound like it was going to explode at highway speeds?

 

Anyone have experience with axles geared this high? Do they have any use with today's engines?

[fastdadd]

numerical higher the numbers the lower the gear is....5.125 is a really low gearing....giving better torque but the motor will be at high rpm at speed...my 620 with an l20 has 4.11 and at 70 mph i am at 4000 rpms

[Dime Dave]

There may be a chance that you can swap center sections with another vehicle and change gear ratios rather that replacing the whole rearend assembly. The 320 lists a 5.12 ratio in the parts catalog, but no one to my knowledge has ever found one installed in a 320 truck. Could it be it was out of a Bluebird like you have and listed as a 320 option? I actually have a NOS 5.12 that has the listed P/N.

 

It could be possible that the rear in your Bluebird is an early H190. Start by seeing if the axle has a bolt-in aluminum center section, if yes count the number of bolts, the H190 has 10. If there are 10 bolts then it may be worth some additional measurements and possible removal to compare it to an H190 center. If it is the same as a 320, 520, 521 & 620 aluminum centers then a 510 wagon center (or Roadster) with 3.89 ratio could be installed by just swapping the side & spider gears.

 

I purchased a 320 center with 4.88 gears for my H190 equipped 1200 racecar. I took the spider & side gears from a 510 wagon H190 center and installed them into the 320 center. Fit like a glove and works fine in the H190 510 Wagon rearend.

 

Now I also have a 3.89 ratio center that will fit a 320 P/U (it

[Farmer Joe]

ive got 4.37s in the 620 and even with the five speed with the .82 overdrive, im still revvin about 3800rpms on the freeway just to kinda keep up with traffic.

[kennysgreen280z]

Fisch, Im pretty excited to see this project happen. 5.xxx gear is going to be pretty low for any L series transmission. Here is a handy calculator you can use to see RPM and whatever speed you feel like. Its based on most of the Z transmissions, but you can put in whatever ratios, tire size, and engine redline you feel like. I dont know how the L18/20 is at freeway speeds, but I generally like to be around 3000 rpm at 65-70mph.

 

http://www.geocities.com/z_design_studio/transmission.html

[fisch]

Great info here guys. All hail Ratsun! Heh all I can do till this lil thing gets delivered is speculate and run through 'what if' scenerios on google and Ratsun!

 

That is a fun calculator!

[Bleach]

Just keep it below 40mph and you'll be fine. :)

[datzenmike]

How much does the '59 weigh?

 

I should imagine 4.11 would work just fine for an L20B and a tiny truck like that. If not hauling any loads a 3.889 or 3.70 from a 720 would work too.

 

IIRC early H-190s used non metric fasteners in/on them. If changing the diff the mounting bolts may be standard thread?

[fisch]

How much does the '59 weigh?

 

I should imagine 4.11 would work just fine for an L20B and a tiny truck like that. If not hauling any loads a 3.889 or 3.70 from a 720 would work too.

 

IIRC early H-190s used non metric fasteners in/on them. If changing the diff the mounting bolts may be standard thread?

 

This is the 59 sedan Mike, so no loads other than me and the fam! It only weighs 2039 pounds. I am curious if the will be mostly metric?

[datzenmike]

Don't know if metric or a mix. Datsunaholic mentioned non metric fasteners in an early rear end. Maybe it was a 320? I could be wrong, Doug?

[Dime Dave]

The 3.89 510 Wagon/Roadster ring gear uses the same bolts as the 4.88 320 ring gear. I don't know if they are imperial or metric, but the bolts are the same and will physically interchange between the two. I actually tried it while I had the two centers on the bench changing spider and side gears.

[DRIVEN]

My brother's 521 has L20b and 1980 720 5-speed. I can't remember exactly what the gearing was though (mid 4's?). He is running stock sized tires - tall and skinny, like yours. It has no problems running 70-80 on the freeway, doesn't lug from a stop, and still gets around 30mpg. If I get a chance I'll check the exact ratio next time it's on the rack. Maybe someone else might know what the ratio is. DATZENMIKE?

[mnementh666]

Just for reference, I have a 3.70 rear and a '79(?) Z-car 5spd (not the tall 5th) in my 521, and I *think* it pulls 3k rpms at 65. I'd have to verify.

It's not a bad setup for freeway cruising, without being too much of a pile of azz off the line.

I have the L20B in it though :D

[datzenmike]

My brother's 521 has L20b and 1980 720 5-speed. I can't remember exactly what the gearing was though (mid 4's?). ... Maybe someone else might know what the ratio is. DATZENMIKE?

 

If the engine code is PL521 (from 07 '69) then it came with an L16... and those all were 4.375 ratio.

 

If the engine code is L521 (to 06 '69) then it came with an J13... and those all were 4.875 ratio.

[DRIVEN]

4.375 it is.