First Datsun: 1973 610 Coupe

[SeparateSteve]

Hello everyone,

 

My name's Steve and I am proud to be the new owner of a 1973 610 Coupe. For a few years now I've been messing around with Nissan/Toyota/Honda cars and decided I'd like to take on the challenge of something a bit older. I say challenge because as many of you know, cars from this era are not for the faint of heart. Parts are scarce, plenty are NLA, and just about 95% of them require more than just your weekend TLC. 

 

I joined this forum this past weekend as a means to give back to the various forums that I've used to gather extremely valuable information + confidence to take on this project. In the forth coming posts, I'll try my best to document my build progress as well as my thought process, in the hopes that I too can help out a fellow car guy live out his project dreams. 

 

For privacy, I'll keep most details of my personal life/location off the site. I will admit I am paranoid with all the car jackings popping up since COVID (that could absolutely just be extreme opinion) so unless we meet personally at a car meet (which I do plan on going to a few, at least) I won't disclose too many personal details. After all, again my goal of being a member is to provide any and all knowledge I gain from performing this build.

 

On to the car: I always knew I wanted something older than 1975 for a very specific reason I'm sure most of you can guess. I knew I didn't want a Z and 510's just feel too small. Trucks were out of the question so I was really only left with one option. I got on all the marketplaces I could: ebay, offerup, craigslist, and even perused a few of these forums. Most cars during my search were either 80% complete and driving or so rusted out and without a powertrain it would be a mountain to overcome. But luck would have it that a in a few cities over someone posted a 73 610 sedan that had moderate rust in the usual spots, but at least ran and drove. I figured why not swing by and at least check it out for myself and assess what repairs need to be done - the least I could get out of the interaction was time spent around a Datsun and could learn more of what to look out for, what constitutes a 'deal' these days, and more importantly if I could really see myself building and driving one of these cars. I come from 1990+ year cars, so even though I feel comfortable wrenching, designing & machining custom parts (daytime aerospace engineer) something about dealing with a 50+ year old car seemed somewhat daunting. 

 

Obviously, I didn't end up buying that car. But I did hit a jackpot - the very awesome guy (no names/personal details) had a bunch of other similar year cars who comfortably told me everything on his lot has a price. He showed me a 610 wagon, a couple Toyotas out of my budget, and even a Z. Then he showed me something under a cover: the 73' 610 coupe with all the windows, trim, and major components neatly stored in totes. Unfortunately, the car was just about completely stripped of its powertrain and suspension - supposedly the story goes this car was always a California car and kept in a garage. The previous, previous owners took it apart in hopes of restoring it, but eventually lost the motivation. The person I bought it off of also had the same plans - restore suspension and powertrain and just drive the frickin' thing. Life happened, and he said for the right price I could take it home. A month later, after critically thinking about it for far too long, I gathered the right price, came with a truck and rented-flat bed (had to be flat bed, the car was on dollies with no suspension/wheels) and paid the man for everything he had for this car. I took the chassis, which admittedly was sketchy to load up and strap down, about 5 large totes, the entire front end assembly + L18 block, L18 head, and 4 speed manual transmission home. I finally became a classic car owner, and felt pretty good about it.

 

Earlier I mentioned cars from this era are not for the faint of heart. Personally, after seeing first hand how similar this car is to my 1990 S13, the fear of undertaking such a large project subsided and the excitement of getting this ol' girl back on the road took over. Couple that with the fact that I scoured the forums for all the information I needed to gather the right parts, I knew what I had to do. I'll dive into the details in a future post, some of you may like what I have planned for this car, others purists may dislike it. I've always told myself and others that that's the beauty of owning a car - it's yours. Do what you want to it as long as it is safe and most importantly makes you happy/brings you joy. If you believe I could do things better a different way, please wait to tell me until I ask if there's a better way I could do things. If you think I could do things cheaper/more cost effective - great, I'll note it for the next project. If you just like how I am architecting this project and feel as though I could somehow help out your project, please by all means do not hesitate and comment. Again, I joined because I feel guilty absorbing so much car knowledge without giving anything back. 

 

That's my intro, for now. You'll have to excuse this next unfortunate bit: I currently live over 300 miles away from where the car is being stored, so I really am only available to wrench on it a few times out of the year. I do plan on moving it closer to me, but that's after I can get it rolling and steering - so that's my first task at hand. This does give me time to plan out and research what parts I need and what I want to immediately upgrade from stock OEM. For a sneak peak, I plan of upgrading the front suspension to S13, keep the rear OEM, and again go with a S13 steering setup. Datzenmike, since I know you will probably come across this (yes, your reputation precedes you - thank you for all your contributions to these forums) I promise I will study and most importantly test out any upgrades I plan on doing before letting any passengers ride along. For me, safety supersedes everything else - no point in driving a car that has the potential to break a steering linkage/ball joint/brake line and hurt someone.

 

Stay tuned. I'll leave you with a picture of the chassis, once I brought it to the storage location:

Datsun1 by SeparateSteve, on Flickr

[Mrbookends]

My man, you're living the dream with this one! I'll be curious to see how your project develops over the coming year! I have a '77 620 King Cab (ha!) that's under the knife in my garage; running and driving, but I'm at the point where a crucial decision needs to be made: rebuild the L20B or swap in a KA24DE? As I'm sure you'll quickly realize, once you start working on one aspect of your build, two, three (or more) things will pop up and then it's back to the rabbit hole of late night research!!

 

Good luck and thanks so much for sharing!! 

[Pounding Rox Truck Shop]

My favorite Datsun!! Such a sexy car!

[Rustbin]

Oh nostalgia! My first car was a '73 610 coupe like yours, well not exactly. I got mine with over 100k, dented rear quarters, a chunk missing from the front right fender, a noisy throughout baring and a bent rim that caused a vibration at 50mph but I drove it like that till the alternator crapped out, then I started to learn how to fix cars. The S13 strut idea seem like a good idea. The L18 might be a bit lame, if your used to newer car performance so a KA24DE would keep up to traffic. Being a longer wheelbase it is a bit more stable at 80mph than the 510, which was my second car, so it can handle the horse power. Wishing you good luck and I will follow your build.

[SeparateSteve]

Back for post #2, this one's all about getting the chassis rolling!

 

In the original post I hinted at trying to upgrade the front end of the car using S13 suspension, at least as much as I can. Well turns out with a lot of research and a little bit of luck from friends throwing away parts, you can get pretty far. Taking into consideration how hard it is to get replacement parts for specific components (for example original '73 610 Tension Rods... virtually just don't exist on earth anymore), I really wanted to make this work out.

 

I started off with the subframe: 

 

It's a front subframe off of a 240Z that has had its motor mount brackets cut-off (it was free - custom mounts will be welded back on later), and I read online somewhere that these fit 510s. So if they fit 510s I knew it had good chances of fitting a 610. Not only that, but I was told by my buddy who gave me this that he can confirm S13 lower control arms fit the subframe. So first I measured the hole patterns to be pretty damn close to the hole patterns of a 510 but noticed something interesting. The front-most holes on the subframe are slightly closer to each other than the rear-most holes. This normally wouldn't be a problem since the the chassis-side threaded holes line up perfectly. However I already had the idea since this subframe can accept a manual steering rack, why not go above and beyond and attempt to fit a power steering rack from, you guessed it, a S13.

 

My first problem with this became apparent: Since the Z cars use a front-steer manual rack, simply flipping the subframe around for a powered rear-steer rack would throw off the alignment of the previously mentioned asymmetric hole pattern. Since the holes were really only about 1/16" off (it was so close I could get the screws started to the chassis, but the screws rubbed on the ID of the holes on the subframe and I didn't like that) I ended up just drilling out each of the holes to a slightly bigger ID. The flanged screws I used had more than enough meat to grab onto under the heads, and with Class 12.9s I knew I can safely smoke these down. I ordered a resealed S13 power steering rack + the u-joint + inner/outer tie rods, slapped that onto the subframe, and got everything bolted up using some custom bent 3/16" steel hold down brackets I designed up:

 

Don't mind the dusty engine bay, nor the the rat's nest of wiring. I'll save those for a later day. Note the two lines loop the power steering ports on the rack - I'll be turning the wheels a lot throughout this build so I at least wanted to get some lubrication to the seals inside. I made a soft line with two AN fittings, filled as much auto trans fluid as I could, and tightened them down to the rack. Subframe and steering are in:

 

The next step was to figure out coil overs. I plan on dialing in ride height and shock dampening, so 2 way adjustable coils were a must. Once again, I scoured the internet and came across a post that claimed S13 coil over top hats straight up fit into 510 (and therefore 610) shock towers. So I dusted off some cheapo coil overs I had saved from my drift S13 build and test fit them. Shout out to that post, because these top hats fit perfectly with zero issue! Somethings I have saved in my notes for the future: 1. These coil overs currently are rated for a much heavier chassis with a much heavier power plant, so I'll swap these cheap units for more reputable ones & will replace the springs out for some softer Swift springs (waiting to see how heavy the front end will up at). 2. I'm not exactly certain of the strength about these 1973 shock tower mounts, but odds are they will be reinforced to help distributed the loads from rougher driving conditions. 

 

With a subframe, steering rack, and coil over setup complete all that was left to do was to connect them all together. I had some spare S13 FLCAs that were extended about 1" and already had Moog ball joints, spare unmodified S13 knuckles with 4-lug wheel bearings, and spare ISR adjustable tension arms all that were donated to this project. The 1" extension on the FLCAs will probably have to be reduced if the wheel poke becomes too egregious. Fortunately there is enough adjustment on the inner/outer tie rods to safely reach the knuckles on both driver and passenger sides. The adjustable tension rods will have to be shortened by a considerable amount, since I would like to re-use the original 610 tension rod brackets that came with the car. I designed up some adapter pieces that serve to connect the rod-end of the S13 rods to the thru-hole of the 610 brackets. Unfortunately, this will become a mini-project of its own, so I just loosely mounted the tension rod and left it for another day. 

 

Another reason I chose to forego the original setup in the front were because of brakes - or rather the lack of readily available and reasonably priced brakes. Since I can mount S13 knuckles, a whole new batch of brake rotors and calipers became available - I wouldn't have to rely on some expensive kit that bolts onto the original spindle/hub. There's absolutely nothing wrong with those kits, but I'd rather try to maximize my braking power-to-price ratio and also keep a healthy aftermarket (Rockauto) at my disposal. I happen to pick up some 93 TT 300ZX brakes which, if I'm being honest, are completely overkill. The price was good, they came with pads + rotors, and I'm familiar with their braking forces in a proper setup. I will have to run the stock brake booster/master cylinder combo until I find a way to adapt a larger bored cylinder. It'll probably feel horrendous, or maybe it won't - but it probably will. At least 16" wheels will clear these brakes, so that's another bonus.

 

Anyways, all that being said and I'm left with this. I won't lie, it put a smile to my face when everything got hand-tightened up:

 

 

Some keened-eye readers will see an unfortunate issue with the position of the wheel with respect to the fender arch. Because this subframe pushes the FLCA mounting flange 2" towards the front of the car, the center of the wheel gets pushed 2" also. That sucks, because a quick fitment of the wheels proves this setup needs to be pushed back 2". There's no going back to OG suspension now, and I would hate to have to do custom fabrication on this expensive (free) subframe. I'm going to purchase some FLCAs that have a spherical bearing on the subframe mount to gain that degree of freedom to rotate the arm ~7 degrees to the rear of the car. I used the adjustable tension rod to 'push' the FLCA to about where it looked correct and re-mounted the wheel to check for interference. Sure enough they clear, so I'm fairly confident the spherical bearings are the way to go. My caster will be gone, so self steering will pretty much not exist - but at least I'll be able to drive a cool car.

Don't mind the torn up tire, this wheel/tire combo are just to roll around on. The final shoes will be ordered closer to the end of the build.

 

Let's move onto the rear: it's all stock. I spent so much time and energy on the front setup, which I can't even claim completion on, that I told myself upgrading the rear will have to be another sub-project in the future. I felt as though the rear arms are built like tanks, and I like the simplicity of just ordering a new strut/spring combo. Unfortunately for me, the spare S13 rear coil overs I have do not bolt right into the rear strut mount (coil over top hat has two screws, 610 chassis only has 1 thru hole). I decided to buy some Koyo shocks off of Rockauto and found a forum post somewhere that claimed I could cut Eibach PN: 1800.300.0400S exactly in half to get two somewhat properly rated springs for these cars. Since the Eibach spring comes with a flat top and bottom, both driver and passenger sides got one flat surface. The cut ends were somewhat flattened with a belt sander. All of that mounted to the car looks like this:

Those ridiculous spacers aren't permanent. They are just used to mount the spare 5 lug wheels that a friend let me borrow. These will be tossed when the final 4 lug wheels get purchased.

 

With the rear mustache bar, original R160 diff, diff support bar, and axles installed I finally got this shell rolling around and decided to give it its first wash in who knows how many years:

 

That's probably enough for the second post. I hope these long-form posts aren't too annoying for you guys. I figure if I spend the time to do a write up, might as well dump as much information as possible. That being said, as part of me giving back to this awesome community, I want to make the next paragraph a summary of facts to help out future 510/610 builders quickly find some relevant info. 

 

-Will a 240z subframe bolt up to a 510/610? Yes, but the motor mounts and the lower control arm mounts are different. Simply bolting up a Z subframe will not be the only thing you need to do to get rolling.

-Will S13 FRONT coil overs fit a 510/610? The top hats definitely bolt on. The lower interface will not fit the original spindle/hub. If you want to use S13 front coil overs, you will have to swap over to S13 knuckles, which in turn will force you to replace a lot more components.

-Will S13 REAR coil overs fit a 510/610? No. S13 top hats use two screws to mount, while the 510/610 chassis only have 1 thru-hole per side. On the plus side, if you can figure out the top hat issue (such as a custom top hat), the lower mount will just require a bushing to go from the larger S13 mounting hole to the smaller 510/610 threaded stud.

-How can I add power steering to a 510/610? Among the different ways people have integrated modern power steering systems to their classic cars, I managed to use a 240z subframe mounted in reverse (so that the steering rack sits towards the rear of the car, Z's are front steer cars) and made custom rack brackets with energy suspension bushings to install a power steering rack from a S13. While I haven't officially tested the system, it all bolts up and I can articulate the wheels from lock-to-lock without any issues of binding. So my suspicion as of this post is this particular mod will work.

-Will S13 tension rods fit a 510/610? Absolutely not. The mount to the FLCA side requires a S13 bolt pattern, and the 510/610 tension rod bracket will not accept the rod-end style of the 240sx arm. Since my build includes a S13 FLCA, I will simply modify the arm to safely mount to the original 610 tension rod bracket.

 

If anyone has any specific questions, or if you're thinking about doing something similar for you build, by all means reply! I'm not on here very much, but I'll do my best to provide any and all helpful info to my fellow builders. I'd also appreciate any advice for the issues I highlighted in this write-up.

 

Stay tuned for the next post.

 

 

 

[ggzilla]

what does FLCA stand for? something Lower Control Arm?

 

15 minutes ago, SeparateSteve said:

The mount to the FLCA side

[SeparateSteve]

4 minutes ago, ggzilla said:

what does FLCA stand for? something Lower Control Arm?

 

Yep you got it - Front Lower Control Arm!

[datzenmike]

Eibach PN: 1800.300.0400S  cut into two should work out to 300 lb./in. spring rate at the rear axle. Is that what you are after?

[Rustbin]

Depending on wheel fitment, maybe flared wheel arches or if you can tuck the tires into the stock width, cut and weld the front arches back on 2" forward? Just thoughts.

[SeparateSteve]

14 hours ago, datzenmike said:

Eibach PN: 1800.300.0400S  cut into two should work out to 250 lb./in. spring rate at the rear axle. Is that what you are after?

So after I read that forum post I did some quick hand calcs which probably had some errors in it - I made some assumptions on the cantilever lengths in my moment free body diagram. These cut springs are a little on the softer side, I think. That being said in the post I read the driver noted a smooth ride with a safe amount of compression (no bottoming out, or tires hitting the fender). If in the future I decide I want to go firmer (to match the fronts) it will just be a quick search of the Eibach catalog for a stiffer 18" spring. What in your experience is the sweet spot for sporty, yet soft enough for longer cruises? 

[SeparateSteve]

2 hours ago, Rustbin said:

Depending on wheel fitment, maybe flared wheel arches or if you can tuck the tires into the stock width, cut and weld the front arches back on 2" forward? Just thoughts.

Yeah good thoughts, I came up with similar ideas in the moment. I'm a little afraid to do any chopping and welding without the final wheel/arms/spacers combo finalized, but I definitely thought about that. I also thought about asking around to see if anyone can do custom fiberglass fenders near me. The latter would be way pricier, though. 

 

We'll see where the wheel ends up with the adjustable lower control arms. Then I'll plan out what will look the best, without burning a hole in the pocket.

[ggzilla]

My notebook says that 300 lbs is stock for the rear springs and racers like 1200 lbs

It also says if you cut the spring in half it doubles the spring rate or linear-rate springs

Dunno is that is correct

 

Eibach 1800.300.0400S is 400lbs springs so cut in half would be 800 lbs each

And that it shouldn't match the front rate, because the rear springs are on a lever, so they need to be stiffer rate then the front

[datzenmike]

300 sounds very close and would work out to just over 100 lb./in. at the axle. I calculated one out once and it was 98 lb./

in. 

 

What is the spring rate on your front coil overs??? This will dictate (more or less) what you put in the rear. 

 

 

400 cut in half makes two 800 pound per inch springs. As the rear control arms are cantilevered and based on the 510 which had a 2.8 ratio then 800/2.8 = 285 lb./in. at the axle. This is getting into race territory spring rates. You're not drifting around corners at 90 MPH, build some comfort into your car.

 

Stock rear springs on the 510 are around 100 lb./in. I believe, so a roughly 300% increase. 

 

The only thing not addressed is the length of the cut spring. Eiebach says 18" so two 9". How long are the 510 rear springs???  The chance of getting the spring rate AND the length (ride height) you want, is extremely unlikely. Car may sit too high if stiffer and the same length as stock. If it sits lower you can use rubber shims to lift it. The 510/610 sedan rear springs sat on round rubber seats... 55036-21000

[SeparateSteve]

My research on rear spring rate ranges that datsun owners like agree with ggzilla (300-1200 lbs/in, comfort-race application respectively).

 

My initial plan for the front springs is to be somewhere right in the 200-300 lb/in range. The powerplant will be a larger chunk of iron, and I want a little better response from each corner. My thought would be to fine tune the preload on the front coil overs to dial this in.

 

I found a couple of replies between you DM and DimeDave, where you guys agreed that :

"I have always used 3.8 x wheel rate for calculating the spring rate of stock position 510 rear springs . If you are looking for a 200# wheel rate you would need a 760# spring in stock position. (200# x 3.8)"

 

To be fair, this was back in 2013. So if the math was revised then disregard. But i saw this and used 3.8 for my cantilever ratio. So my calcs went like:

 

400 lb/in spring cut in half turns it into a 800 lb/spring. Assume a pefect cut.

 

(800 lb/in) / 3.8 ratio of moments between wheel and center axis of spring, both relative to the pivot points on the rear subframe: 210 lb/in resolved over the wheel. 

 

If the above is still true (I don't have the rear arm to measure near me), then its on the softer side of what I want to run in the front. These numbers are still above the maximum comfort, less sporty range - but puts me in the <30 age range.

 

To address the rear height, I'll be frank. I just shot in the dark, and hoped it would sit nicely. And yes to confirm I have those same rubber spring lands you pointed out, and also thought while I was installing them: why doesn't anyone make flat, modular shims here? The rubber land already has a piloting feature molded into it. 

 

So the picture above shows the car sitting with no fuel, no driver, and no drivetrain. It's close for my liking. Odds are if keeping these springs I may have to space the springs ever so slightly. Only time will tell - meaning either i fine tune it in its current config or install coil overs.

 

[fiveoneO]

I used a 3in inside diameter 400lb Eibach spring cut in half for the rear of a 510 and I was happy with it. Not too stiff not too soft, perfect for daily driving. Sadly I don't remember the length. It did end up lower than I wanted, so I bought some 1/2in thick polyurethane spring isolators from Summit Racing and got the ride height where I wanted. 

[Rustbin]

I have two uncut 510 rear springs, they are 300mm or just under 12" long and just under 3" inside diameter, if that is helpful. You could go with coil overs as another option, T3 has ones that would just bolt in. 

 

[SeparateSteve]

10 hours ago, fiveoneO said:

I used a 3in inside diameter 400lb Eibach spring cut in half for the rear of a 510 and I was happy with it. Not too stiff not too soft, perfect for daily driving. Sadly I don't remember the length. It did end up lower than I wanted, so I bought some 1/2in thick polyurethane spring isolators from Summit Racing and got the ride height where I wanted. 

Good to hear some testimony, definitely makes me feel better about the purchase. I can't remember if you had shared this info somewhere else on Ratsun, but I found the comment by 'Akara' on the 510Realm back in 2011. Same set up, same testimony. I like my odds!

[SeparateSteve]

17 minutes ago, Rustbin said:

I have two uncut 510 rear springs, they are 300mm or just under 12" long and just under 3" inside diameter, if that is helpful. You could go with coil overs as another option, T3 has ones that would just bolt in. 

 

So I'm over 3" shorter when comparing my setup and OEM uncompressed springs. Good to know - and I agree, the T3s seem to be the end all if say I don't like the proposed Eibach springs.

[datzenmike]

It's 3.8 not 2.8? Well that's memory for you. 800/3.8= 210 lb./in. I would go with this and see how it handles first. You can raise the spring rate by shortening it further. 

 

 

 

Well you can always shim a short spring.

[SeparateSteve]

On 6/20/2025 at 8:27 PM, datzenmike said:

It's 3.8 not 2.8? Well that's memory for you. 800/3.8= 210 lb./in. I would go with this and see how it handles first. You can raise the spring rate by shortening it further. 

 

 

 

Well you can always shim a short spring.

That's the near-term plan. See how it rides, then cut or buy some 3" ID shims under the top hat.

 

I did have a question about the conversion coil overs. Has anyone ever report shearing off the little mount on the rear arms? I wondered how strong those tabs are, since now the force from the wheel goes directly thru that mount, which was never meant to carry the spring force..

[ggzilla]

44 minutes ago, SeparateSteve said:

I wondered how strong those tabs are, since now the force from the wheel goes directly thru that mount, which was never meant to spring the spring force..

The aftermarket coilovers bolt to the shock mounts

* The bottom shock mount is a tubular bracket in the lower control arm

* upper shock mount is the body sheet metal

* Neither were designed to take the full weight of the vehicle, that's the job of the bump stop. However, both are reinforced parts

 

 

[datzenmike]

This is true but have never heard of a failure. Weld in some strength if for nothing but some peace of mind.

 

 

Got any numbers? I see the mechanical advantage squeezing the spring but not the 3.8

[ggzilla]

Is 3.8 the ratio you heard? I heard 2:1, but i've never seen any numbers, and the photo looks bigger than 2:1. Somebody should measure the two distances

[datzenmike]

I posted 2.8 from memory but it turned out to be 3.8, I guess. 

 

If the distance from the hinge point is 6" then it's 1 to 1. If increased to 12" it would double to 2X. Could the longer red line be 1.4 times the shorter line? That would make it 2.8 X.  

[Rustbin]

In all my looking I haven't seen anything about the suspension breaking but I have added a support to tie into the ridge in the parcel tray and will be re-enforcing the rear trialing arms as per the "How to hotrod and race your Datsun" a Steve Smith autosports publication, page 114, for my 510. I have bent a trailing arm before and my Datsun is kind of rusty so I think extra strength will give me peace of mind.