My 68 is noisy as heck going down the road. I mean, yell over the noise loud. It's not just engine noise from the squirrels in the J13 either. I've coasted down a long hill with the rig in neutral and the engine off at about 50MPH and it's really, really loud.

So, I suspect a rear end replacement/rebuild is in order. What is my best option? Is there something newer that will bolt in and give me some more 'legs' for traveling at 60MPH?

Thank you in advance for any help you can provide.

i'm not 100% sure that all of the datsun rear ends match up... but i do believe they do and there are a fair bit of 2wd 720's that use 3.70 rear gears that should do ya good with the J13 up to 70 or so

The 510 Wagon used the same ring and pinion, but different carrier. All of those were 3.90. I fear that 3.70's would be a bit too tall behind a j-13, but if it's a drop in ordeal, you could just go with smaller tires. I just went with 245/40/17's to get myself some freeway gears... There's a guy in Albany who works at B&R auto wrecking that could find you a diff. 541-926-2300, ask for Kevin.

521ofdoom, Thanks for the info. I was just in Albany today. I'll ring him up and see what we can put together.

The side gears of the wagon will not fit the truck axle splines.

i have a 620 diff in my 69 521 it droppeed right in.dont forget to change the wheel bearings while you have the axles outthe gear housing on the 620 is cast iron and a little stronger(not that a 1300 needs it)pay attention to the gear ratios, my recomendation is stay as close to stock as you can too tall and the engine wont have the powertoo short and you will loose top end speed and wind the engine out

Stock gears in the old trucks tend to be really low, the idea was to make the them capable of carrying heavy loads, hence the way a 521 rides so poorly. if you're not loading the thing down, a set of 3.90's or 3.73's if you can find them will detract from the taking off in second gear, but you'll be in the 3,000 rpm range at 70mph. Much nicer than before. I have the stock 4.11's in my 69, with 245/40/17's and I am in the 4,000 rpm range when I'm in traffic on I-80... Looking for 3.90's here....