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521 Manual To Auto Swap: Need New Driveshaft?


pope_face

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I tried doing a couple searches, and managed to find (I think) a bit of info, but I can't seem to confirm anything one way or another... So, I thought I'd put this up here and see what comes up.

 

I've been thinking about my 521 again, as I'd like to get it done at some point. I keep going back on engines and transmissions, but a decent offer has come up on a pair of L16's and automatic transmissions out of a couple 510's, so I'm thinking of going that route. I suspect they'll be more fuel efficient than the rotary engine I currently have sitting around, and I can still have a bit of fun with them. I don't mind taking the time to fit the transmission in and hook up the shifter and all, but I'm a little concerned about the driveshaft... I've got a stock 521 driveshaft off a '72 (with the L-series), as well as one from a '70 (with the J13), and I'll be getting a 510 auto driveshaft as well, but I'm not sure what (if any) differences there are between them... I don't know if the front of the driveshafts are the same (that go into/attach to the transmission output), I don't know if the length is the same, and I don't know if the rear (differential) end is the same. I'm willing to use any of the driveshafts, and I'm willing to try to convert them into a "hybrid" driveshaft (by using the front of the auto and rear of the manual) if that's possible (and necessary), but I'd rather avoid any heavy modifications... I don't want to have to pay a shop to cut and reweld the driveshaft, then balance it, etc.

 

As I mentioned, I've seen a bit of info regarding auto to manual swaps, but they seem to be mostly for the 510's, and there doesn't seem to be much talk of driveshafts (other than some are longer than others, due to transmission lengths). I'll try to compare the manual and auto driveshafts later this week, if I get a chance, but I was hoping here had already gone through this...

 

 

EDIT: Nevermind, I managed to find a post by Datzen that answers the question about the tranmission end of the driveshaft...

 

All the 510/610/710/ S10, S110 and 4 cylinder S12 (200sx)/A10-(HL510) 521/620/720, 240/260/280z/zx non turbo, 810 Maxima used the same spline into the transmission.

 

That's all from the post regarding yoke sizes, but it answers one question... I'll assume this applies to automatics as well. Now the only thing is to figure out the differences (if any) in length between the 3-speed automatics (I believe one is a Borg-Warner and one is a Jatco), the L-series manual transmission (on the 521), and the J13 manual (also on the 521). I guess I'll use the driveshaft from whichever is closest in length.

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Hainz,

 

Thanks for the reply... Agreed, getting a bad transmission is a concern, but by the sounds of a couple threads they are rebuildable with a little time and some knowledge... Hopefully that won't happen, but if worse comes to worst (knock on wood), I'll just dive right in and see what I can do about it. It also seems that they just about run forever, so I might not have to do anything.

 

As for going backwards... Yes, for most people it would be, but I can't drive a stick (due to medical reasons), so my only options for ever driving my Datsun are either a hand-operated clutch (potentially expensive) or an automatic. I've looked into the hand-operated clutches before, but to buy a kit would set me back over $1000... I could design and build my own, but I just want to get the truck done for the time being, then I can start toying around with other things.

 

Finally, I can't just put the L-motor back in because it never had an L-motor... The one that's getting rebuilt has a J13, which (as far as I know) never had an automatic transmission option. I do have a parts truck which had the L-series engine, but I never bought the engine or transmission with it, so no luck on that front. I do, however, have some spare parts from the L-series engine, as well as a spare driveshaft, so I can use that. If I could swap the cab from the project truck ('70) to the frame of the parts truck, I'd be able to just use all the stock motor mounts and such, but I think the VIN number is on frame, so I might run into issues with that.

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Im thinking best to find a 620 that came with a auto if you have a Med condition

I havent seen to many 521 with autos.

 

Just my opinion ,its alot of work when $1500 most likely LESS, might be ezer to get another truck as most Ratsuners dont want a auto so they should go for cheap.

 

Tana on here wanted to convert her 521 to auto and nobody wanted to help her out(even on her NWDE club). Thought it was a waist of time.

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Well that's a disappointment... To be honest though, it shouldn't be that difficult. I'm getting an engine and transmission already mated together, so I won't need to worry about any other engine specific parts needed for the auto. The one I'll be using is from a '70 510 with a column shift, so I'm sure I can find some way to mount it up. The only real issues I can foresee are whether the driveshaft length is the same (or close enough to work), the transmission crossmember (which can be modified or custom-made), and the gearing of the final drive ratio (currently 4.88:1, IIRC), but I've got the rear diff/axle from the '72, although I'm not sure what the ratio is on that.

 

Besides, I might have to go down to Arizona or Cali to find a decent 620 auto... I doubt I'd find much here.

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The VIN number is on the frame, here.

SN521Close.jpg

Farther out picture.

SN521Far.jpg

 

I believe you either have to use the J13 frame, and change the engine mounts on the frame, or get the L16 frame legal

 

Those are your options for the engine mounts. For the transmission mount, you are going to have to fabricate something, because i do not know of any 521 trucks factory equipped with an automatic transmission. I believe some 620 trucks had an automatic, if you can find one, it might be a good thing to have, as a donor vehicle. There are a lot on similarities between the early 620 frames, and the 521 frame.

 

I have put a long tail five speed transmission into a 521 truck. It was not that difficult. Shorten the transmission mount, shorten the drive shaft, and put a slip yoke that matches the five speed transmission, move the hole in the shifter cover plate, get a longer speedometer cable.

 

I think it would be wise to get the drive line professionally done. Due to fairly small tires, and pretty low rear axle ratio, the drive line in a 521 turns pretty fast.

 

You will lose power with an automatic. You also lose a gear, but there is some torque multiplication when the torque converter is stalled. I believe the automatic 620 trucks has a different rear axle ratio to compensate for the loss of power.

 

On the bright side, once the truck has the automatic, it should be easy to fit a power brake booster, without the clutch slave cylinder in the way.

 

J-13 521 trucks had a 4.875 rear axle ratio. L-16 521 trucks had a 4.375 rear axle ratio.

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Thanks Daniel, I appreciate the photos.

 

If I can avoid it, I won't modify the driveshaft at all... I agree, I'd have to get it professionally done, and I just don't want to spend that kind of money on it. In that case I'd rather convert this to electric.

 

If the long tail required modification, then if the auto is shorter it might just work... I'll look into it some more.

 

And yes, fitting a brake booster will be easier... I'm not concerned about the speedo cable either, as I have an Autometer programmable electric speedo and the little sender unit, so I just have to mount that up and program it.

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Success! -ish, I hope...

 

Did a bit more poking around (it's amazing what kind of info is stuck into random threads), and found this:

 

Your 521 has a 26" long transmission very very similar to the 510, 710 and the early 620. Luckily, the 5 speed from a '77-'79 S10-(200sx) is the same length and will fit without having to shorten the driveshaft. This 5 speed is called a dogleg because of it's distinctive shift pattern with reverse above first.

 

From "What 5-speed tranny will fit my '71 521?"

 

Then, I took a look at the Auto Trans Picture thread, and found this:

 

The Nissan 3N71B automatic. Three piece all aluminum case with removable/interchangeable front bell housing to fit any RWD Nissan motor.

 

3N71Bs were made in two lengths 26" and 31.5" depending on vehicle. Here's a shorty bolted to a 1200 motor, note the stubby tail stock...

 

I've bolded the relevant parts... :D

 

So, assuming the auto is the short-tail version, it should (theoretically) swap right over without modification to the driveshaft... Assuming my previous assumption (in the first post) about the splines being the same is correct.

 

Thanks Datzen, for seemingly (hopefully) solving my problems without even replying once to this thread... Now that's some skill. :D

 

I will take a look at the automatic transmission on Friday (if possible), then report back on what I found. If nothing else, maybe this thread will serve as a source of info for anyone else interested in swapping their 521 from a manual over to an automatic... Although after what Hainz said I don't know if that'll happen, but a guy can dream.

 

BTW: Daniel, I didn't catch that info regarding the final drive gearing earlier... Shame the 521 L-16 gear ratio is still so high. Maybe I'll see if someone local wants to trade a 521 differential for a 620/720 with lower gearing... There's gotta be someone around that would want the extra torque.

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Thanks Datzen, for seemingly (hopefully) solving my problems without even replying once to this thread... Now that's some skill. :D

 

 

Not me, it was you mad search skills!!!

 

3N71B 26" L series automatics came in 510s after April '71. If the 510 has a floor shift, it will have a 3N71B in it. The '72-'73 620s had them also. And yes the early 620s with L16 automatics had a 4.625 rear gear but not with the L18s, also the automatic used with the L18 was longer at 31.5". This lower gearing, either 4.875, 4.625 or 4.375 was because the truck was slightly heavier and was expected to carry a half ton on the 521/620 and a ton on the 520s. A 3.90 rear end with auto should work if not carrying any loads.

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Datzen: Thanks for finally taking part... And sure, I'll accept mad research skills, but it's still all your information. :D

 

Thanks for that note on the length of the tranmissions though... I suppose that means the early BW units weren't the short tail (by which I mean 26")? I'm supposed to get two engines and transmissions from a local Ratsuner, one of which is from an early 510 ('68 or '69, I believe) with a column shift, and one from a '72 or so that has a floor shift. The column shift one has fewer kms on it, so I was hoping to install that one. If not, I'll go with the other...

 

I don't mind losing a bit of top speed with the three-speed, as I don't intend on driving it fast, but I want to be able to get on the highway and do about 90 km/h at a decent engine RPM (I'm hoping 2000 or less, although I'll accept 2,500-2,800 RPM). If it can max out at 120, I'd be more than happy. I don't want to lose too much power either... I'm not planning on hauling a lot, but I'd like to be able to put the occasional engine/furniture/brass statue of Buddha in the bed and actually be able to move. I also don't know where the shift points for the autos are... I'll have to see if I can find that and the transmission gearing info before I decide on a final drive ratio.

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The column shift is probably the B/W. I am not aware of a column shift 3N71B. I have an auto swapped in my 521, but probably won't help all that much since mine is a lockup version from a Z series. Now, the guy I bought the truck from had another 521 that also had an auto swapped in that I bought the conversion parts from since he swapped a stick into his. From what I can tell from the L series setup, it supposedly came out of a 610 wagon and was pretty much bolt in except the stock trans mount was slightly modified. As for gears, I'm running 3.70's with no issue, but I also have a KA-E in mine, which has more torque than a L16. Also, due to the slightly longer lockup trans, tunnel modifications are required. And as a final thought, the floor shifter linkage is a little tricky to hook up with the torsion bar adjusters kinda inline with where the shifter linkage wants to go. I say be the first to drop a 4N71B in there. :thumbup:

 

Mark

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Mark: Thanks for that... I'd love to put the 4-speed in there, but I need to find one first... Maybe Datzen wants to donate one to the cause... :D I'll be sure to put a blurb on the back window telling the world how nice he is (it's the least I could do for a four-speed auto).

 

I'm pretty sure the column shift is the B/W, like you said, but Datzen mentioned that the 26" autos came in the '71+ 510's, but that's the 3N71B... Not sure if that length also applies to the B/W units, but either someone will chime in, or I'll find out myself when I pick up the engine. I'm getting excited, can't wait to go get the engine and trans and start tearing into it.

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Pretty sure the 4 cylinder cars were for the most part short tail and the 6 cylinders and some trucks were the long tails. Who knows what has been put where after all these years? FWIW, the trans that was in the converted truck was a long tail, so on second thought, it was probably swapped from a 620 truck, not a 610 wagon. Maybe it was the driveshaft that was from the wagon? All I can say for sure is that is was a 1pc. driveshaft.

 

Mark

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Mark: Thanks for that... I'd love to put the 4-speed in there, but I need to find one first... Maybe Datzen wants to donate one to the cause... :D I'll be sure to put a blurb on the back window telling the world how nice he is (it's the least I could do for a four-speed auto).

 

I'm pretty sure the column shift is the B/W, like you said, but Datzen mentioned that the 26" autos came in the '71+ 510's, but that's the 3N71B... Not sure if that length also applies to the B/W units, but either someone will chime in, or I'll find out myself when I pick up the engine. I'm getting excited, can't wait to go get the engine and trans and start tearing into it.

 

 

super intrigued by this post... Im in a similar situation where I kinda have to drive an automatic. Definitely prefer the 521s to the 620 trucks overall and was hoping someone out there has done all the dirty work with swapping out trannys. were you able to make it all work out in the end?

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