Rear axle swap

[Bryant]

I am considering a real axle swap for my 1970 Datsun 521. What would be good options to pair with the KA24 and 5speed? Any info would help 

[carterb]

I had a Mazda RX7 rear axle with disk brakes and LSD built for my 620.  John Wallum in OR made it for me.

[datzenmike]

There's nothing wrong with the H-190 that's in your truck. It's good for 280 ft lbs of torque, more than strong enough for a KA. Gearing is a little low at 4.375 but there are plenty of ratios available from later trucks. Maybe a 3.70 or 3.889 from a 720 truck? The differentials are a bolt in third member and easy enough to swap.

 

It's not like the KA makes so much power you spin the tires in every gear that you would need an LSD. As far as brakes, the 10" drums will stop you just as well as disc, it's just that disc are way less maintenance.

[thisismatt]

Keeping it 6 lug, an early 79-84(?) 4wd Toyota axle will get you way more LSD & gear options, but no good disc brake options from what I've found.

[Bryant]

Datzmike yeah I agree I don’t necessarily need to upgrade for the power that the KA will be putting out but I don’t want to deal with drums brakes and so far I have had a really hard time finding any parts in general for that rear axle. 

[Stoffregen Motorsports]

X2 on the Toyota axles. 4x4 truck axles have the six lug bolt pattern and the 8" diffs are very strong with tons of aftermarket support. Gearsets are $225, bearing kits $100, LSD units $650. Try that with a Nissan diff. It will be three times the cost if you can even find those parts.

[datzenmike]

2 hours ago, Bryant said:

Datzmike yeah I agree I don’t necessarily need to upgrade for the power that the KA will be putting out but I don’t want to deal with drums brakes and so far I have had a really hard time finding any parts in general for that rear axle. 

 

The Toyota axle is a bit wider.

 

The Isuzu Trooper rear caliper and 6 bolt rotor can be fitted by making caliper mounts for the axles.

[greenthumb]

There is another way. 
I used a Honda Passport axle. Factory LSD with disc brakes and internal e brake which is adapatable to the 521 linkage. Ratio is 4.30. The early Passports were built with cooperation from Isuzu. Turns out they used a Dana 44. 
It’s not a boltin however. I had to shorten and respline my axles, but the win of factory discs was worth it to me along with a properly functional e brake 

[greenthumb]

Also 6 lug

[Stoffregen Motorsports]

Narrowing an axle is not a bad way to go.

 

The early Toyota 4x4 pickup axles were 55." wide. How wide are the 320, 521, 620 axles?

[Stoffregen Motorsports]

Oh yeah, and Toyota drum brakes work awesome. No need to upgrade to discs.

[Stoffregen Motorsports]

Also -  disc vs disk. Brakes are disc. Floppy drives are disk.

[thisismatt]

20 minutes ago, Stoffregen Motorsports said:

Narrowing an axle is not a bad way to go.

 

The early Toyota 4x4 pickup axles were 55." wide. How wide are the 320, 521, 620 axles?

 

521, according to internet/ratsun sources, is...

 

53"

52-7/8"

52-9/16"

 

[Stoffregen Motorsports]

So an inch per side. Nobody would ever notice.

[thisismatt]

3 hours ago, Stoffregen Motorsports said:

So an inch per side. Nobody would ever notice.

Yep, and I need that inch for my rays/nismo wheels 👍

[gene knight]

On 3/27/2022 at 6:53 PM, greenthumb said:

There is another way. 
I used a Honda Passport axle. Factory LSD with disc brakes and internal e brake which is adapatable to the 521 linkage. Ratio is 4.30. The early Passports were built with cooperation from Isuzu. Turns out they used a Dana 44. 
It’s not a boltin however. I had to shorten and respline my axles, but the win of factory discs was worth it to me along with a properly functional e brake 

what year of passport?  how much did you have to shorten the axles? did you use honda axles or datsun axles

[greenthumb]

Not exactly sure what year. It would have been one of the earliest years when they were built with cooperation and parts from Isuzu. I removed the Honda axles and had Dutchman shorten and respline them. I can’t recall exactly how much we narrowed it. Maybe 1 1/2” -2” on each side? 

[Oilspot]

So on the Toyota 4x4 rear end swap.....

 

I've got a 83' Toyota 4x4 parts truck. That would be a 4.10 r&p which would be a great mild improvement from the stock 4.375 with my stock L16.

Things I'd have to address.... Standard to metric on the brake lines, but I could do that at the rear T easy enough. 

As far as drive shaft issues? Anybody happen to know the difference in third member snout lengths??? If the Toyota unit is longer I can get the stock Datsun driveshaft shortened locally easy enough. 

If it's shorter I'm looking at a bit more of a problem. 

 

[datzenmike]

Mild improvement??? Depends what you want. 4:10 will have less torque multiplication in all gears. Engine RPMs will be slightly lower at all speeds and all gears, not much and an L16 should be able to handle it.

 

I should imagine Toyotas use metric too.

[Oilspot]

10 minutes ago, datzenmike said:

Mild improvement??? Depends what you want. 4:10 will have less torque multiplication in all gears. Engine RPMs will be slightly lower at all speeds and all gears, not much and an L16 should be able to handle it.

 

I should imagine Toyotas use metric too.

Isn't 521 sae!?!? 

 

Trucks got more than enough torque for a little truck!!! The 4.10 would give me +4mph at 4000 in 4th gear.

I feel like I just said 4 way to many times in a sentence! 

 

 

Edited April 10, 2022 by Oilspot

[Stoffregen Motorsports]

I always thought the 521 was the introduction to metric. Maybe I'm wrong.

 

The diff lengths are similar. You do understand it is vital to get accurate measurements, right? If the shaft is too long, it can damage the trans, diff or both. If the shaft is too short, it can slip out and cause a very bad day.

[greenthumb]

Mechanically they are metric. All the body fasteners are SAE NF

[Oilspot]

2 hours ago, Stoffregen Motorsports said:

I always thought the 521 was the introduction to metric. Maybe I'm wrong.

 

The diff lengths are similar. You do understand it is vital to get accurate measurements, right? If the shaft is too long, it can damage the trans, diff or both. If the shaft is too short, it can slip out and cause a very bad day.

A lot on the 521 is SAE!!! 

I've had to have a driveshaft shortened so Ill get the length in spec. Thank you for looking out though!!!!! 

[the510]

Anyone have John Wallums contact info? 

[mainer311]

DP and I just did disc brake conversions on the stock rear axle, so I’m not sure what this “can’t find parts” business is about.

Edited May 14, 2023 by mainer311