521 transmission identification

[two many datsuns]

Hello,

Just bought a 71 521 today and while I was checking it out before buying it I noticed that it had a L18 swapped into it and for some reason the gearbox seems like it might have been swapped too. I'm having trouble figuring out the model number for the transmission, If any one can help out that would be great. On the top of the bell housing the numbers 1712-0621. I'll add some photos if I can figure it out. Thanks!

[NC85ST]

From the pictures, it looks like the original 4-speed. The driveshaft bolts to the transmission instead of having a slip yoke.

[banzai510(hainz)]

looks stock but if has a 4bolt flange near the rear of trans then its a stock 4 speed 521 trans. 510 one is similar.

 

just make sure oil in there.

[datzenmike]

F4W63 is the transmission 'name'.

 

That's a lot of leaked oil low down. Check oil level by removing the fill bung on the left (driver's) side just to the rear of the bell housing bulge on the waffle part of the case, about half way up. Probably protruding square shape that a crescent wrench will fit. You should be able to insert tip of finger and dip it in the oil. If down top it up with 80 or 90w GL-4 oil. NOT GL-5. Fill till it runs out. If it's down then the front seal is leaking and needs replacing, not a big job but you will need to remove the transmission and that is a big job.

 

If transmission is full or remains full after topping it up then the rear crankshaft seal is leaking and the engine as to come out. Does your clutch slip?

[two many datsuns]

Don't know, hasn't ran in years is what I was told. Last registered in 97', clutch feels good though. From what I can tell, the engine seems mint. I'm gonna try to get some spark and see if the trans is full. Rats wreaked havoc on all the wiring. Anyways, thanks for the info! I have and l20b and a 60A trans lying around, so I'm debating swapping it. 

[datzenmike]

60a won't fit the L series engine bolt pattern and if it did it wouldn't handle the power as well as the 63a. 

 

Use only NGK B6ES (L16/18) and don't buy the discount ones on Amazon. Too many counterfeits out there.

 

BPR6ES for the L20B

[two many datsuns]

Oh crap my bad, I have a 60A in my 1200 and got the number confused. I have a whole set up ripped out of a 620.

 

[datzenmike]

If it's a '73 620 the transmission is virtually the same and could be swapped in with a minor alteration to the front of your 521 driveshaft. If it's a '74 and up the transmission is a much longer, but way stronger F4W71B. You would need the shorter front drive shaft from the 620 and the 521 transmission mount sectioned and welded up.

[two many datsuns]

It came out of a king cab, so it's definitely the longer trans. Luckily I don't get rid of junk and I kept the driveshafts for it too. Just got the motor running earlier, sounded decent from the couple seconds I had it running but I definitely need a new carb. I have a 32/36 on my a14 and I'm thinking the same for this.

[datzenmike]

So it's a '76 1/2 or newer. I'm not positive the shorter 620 front drive shaft will fit the 521 and allow the longer transmission to fit but there's a good chance.

 

[banzai510(hainz)]

get it running first before worrying about a trans.

the 521 has such a lower gear ratio rear end even a 5 speed isnt going to help all that much

[two many datsuns]

Ok I'm gonna rip out the motor and trans to clean, inspect and paint. Change all the seals, hoses, and fuels lines. Clean and paint the engine bay. Redo all the wiring and rip the bed off, I plan on making a flat bed for it to use as a cool shop truck. Luckily it sat in a desert for all these years so there's not much rust. Thanks for the help! 

[banzai510(hainz)]

NO NOT A FLAT BED!!!!!!!!!!!!!!!

[two many datsuns]

35 minutes ago, banzai510(hainz) said:

NO NOT A FLAT BED!!!!!!!!!!!!!!!

 Lol. I'm a low and slow kinda guy. It'll be nice and still match the body lines. I won't massacre it, I promise 😁.

[datzenmike]

Save the bed. My 620 was a flat bed. I rebuilt it with cedar cross braces (so they won't rot) under, and real 2" x 12" fir planks from a mill. It was heavy duty.