Short 510 front springs

[LenRobertson]

After years of procrastination, I finally got 280ZX struts and brakes on the front of my '72 510. I would have been happy to go with cut stock springs but I'd done a trade for some after market springs so felt compelled to try them. They are a LOT shorter than stock 510 springs - 15" tall for stock and 9 1/4" for the short ones. Diameter of the coils I measure as 0.461" for stock and 0.505 for the new ones.

 

 

Any idea what the approximate spring rate is? It would be nice to know when I'm reading other people's posts on their suspension setups.

 

When the struts were off the car and the split collars adjusted so the lower spring perch was about the same height above the spindle as the stock 510 perch, the short springs were slightly loose between the upper and lower spring perches. I've read of other guys having this condition but does it matter? When the struts are installed and weight of the car is on the spring they aren't loose anymore. Something about the loose spring doesn't seem quite proper but what do I know?

 

With this short of a spring, do I need bump steer spacers? I've driven it on the road but have really poor tires on the front so it is a bit hard to judge by the feel what is going on. With new tires I should have the alignment checked but maybe I should obviously have bump steer spacers before I do that and I suppose they affect the alignment.

 

Len

[datzenmike]

Need the diameter of the coil through the center. Or overall width, subtract the diameter of the wire.

 

Stock coil diameter for 510 should be 5.12" and 0.472" thick wire  Assuming 6 coils on the left one 86 lb/in which is close to the 89 advertised.

 

Assuming the right is the same diameter 5.12" and 0.505 wire diameter and (really hard to count the actual coils from a picture) say 4.6 coils. I get 137 lb/in.* This is about a 60% increase. My wagon was increased 50% and we are similar age so if I enjoy this abount of increase, Len, you should be close. :lol:

 

* subject to change if measurements are not the assumed ones I used.

 

 

 

Thicker wire increases the spring rate.

Decreasing the number of coils increases the spring rate

Decreasing the coil diameter increases the spring rate.

Length of coil does not matter. If desired spring rate is achieved but ride is too low add rubber spacers.

[LenRobertson]

You have set my mind at ease. I feared someone would ID these as some sort of track spring not suitable for street use. It seems they are nothing too extreme. The little bit I've driven it, I thought it felt pretty good. Corners flatter and not horribly harsh. But then I've spent most of my life on unsprung farm tractors so my perception may be dubious at best. When I get the rear set on it will no doubt feel different too.

 

The guy I got these from got them off eBay a few years ago. They were listed as a "brand name" spring; I believe Techno Toys but I may be mistaken. TT doesn't list them on their website but then springs are passe technology. That is why I ended up with them - Reg went mad for coilovers. And he wants to go waaay low with his 510 so maybe that is a good option for him.

 

I'll measure the coil diameter tomorrow. We went to the car parts swap meet in Spokane today and I did more walking than I've done in months. I'm kind of rubber legged tonight. In a weak moment I bought a set of what I'm pretty sure are roadster SUs with manifold for $20. I figured at that price I can polish them up and use them for wall art. A guy here in town showed me an SU off his Norton bike he polished up and it is beautiful. I just hope I don't find a roadster for sale complete except missing the carbs.

 

Len

[datzenmike]

Len, you can also shorten your front springs to increase the spring rate. (number two on my list at bottom of my post) Fewer coils also lowers the ride height but you should never cut to lower as you may end up with too harsh a ride or not firm enough. 

 

It is a one way deal, so if you cut too much you can't go back. But a little multiplying and dividing you can figure out how much to cut off to get a theoretical spring rate.

 

Because the 510 has a cantilever control arm with the spring ahead of the axle, the rear spring needs to be 3.8 times stiffer to get the desired rate at the axle. For example if you want to match the front 137 lb/in the rear spring needs to be about 521 lb/in.

 

 

Roadster SUs have 4 bolts attaching them to the intake not two. 

Roadster SUs have the float chambers beside each other in the middle.

[banzai510(hainz)]

aince the 280zx is a shorter strut I would try running a longer spring to get more comfort from it as it wont bottom out. those look very short and since the strut is also short this might be a slammed down car

[datzenmike]

If the spring rate is agreeable you can just add rubber spacers to set the height.

[LenRobertson]

I think I'm just going to run these springs for awhile and see how I get along with them. Until I get the rear short ones on it will be hard to tell about how the car feels. If turns out to be too bone-jarring I can go back to stock springs with a coil or so cut.

 

I agree with hainz that these after market springs just look too short. But maybe they will be work okay. Would raising the split collars (and lower perch) an inch or so help prevent the strut bottoming out? There is something about how all these pieces interact with each other that I'm having trouble grasping.

 

As for the carb set I bought Sunday, I went to http://www.ztherapy.com/and looked under "Spotters' Guides" for the Roadster. The carbs shown for 1500 and 1600 Roadsters look like what I bought. The text for the 1600 carb says "Same carb body is used front and rear (not mirror image)". I think the 2000 Roadster carbs had float bowls on opposite sides (mirror image bodies).

 

My real concern is there is a local guy with a couple of basket case 1600 Roadsters he isn't doing anything with. I live in fear he is going to foist them off on me somehow. Not that I don't like Roadsters but I already have too many projects. Could buying a set of Roadster carbs be the start of something?

 

Len

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

[datzenmike]

Front

The coil spring is what carries the weight of the car. It compresses the spring until it equalizes. If your ride height is too high or low you adjust the bottom spring perch down or up and lock in place with split collars. I would say it is not advisable to lower much on stock springs, as they are bouncy and have more travel. If adding firmness there is less likelihood of any bottoming out.

 

Rears

Cutting the spring will increase the stiffness but will likely lower the ride eight. There is no lower perch and split collar to adjust this. The chance of getting the right firmness and ride height is very unlikely. If too low slip rubber spacers under the spring.  

[DHale_510]

Bump steer spacers allow you to level the front control arm so the steering is in better alignment. A car with the steering arms at different angles from the control arms will have less accurate steering and less predictable handling. Maybe we really should have called them roll center correctors from the start.... but here we are. They also are needed to clear ZX calipers at half pad wear.

The unsung problem with the rear end is toe correction. Any lowering of the rear ride height will cause toe out which will greatly affect the way the car handles, usually in a "bad" way. It will swing the back out much more quickly and wear tires much more quickly. It is hard to see and harder to correct and always there when the visible negative camber angles are there. This has destroyed more 510s than any other thing methinks....

The other problem with cutting springs is while the stiffness increases linearly with length [half a spring is twice as stiff]. the loss of load capacity is about twice as much. The car will bottom out much easier even though it is stiffer. Bottoming out just happens at the wrong time too, when you are going hard. Bottoming will overload the tire at this critical time and you will slide, skid, need a quick recovery. Bottoming is not too stiff, it is too soft. Most parts of the car are as unhappy about it as your passenger, and will leave you about as quickly.

Dennis

[LenRobertson]

Dennis - Thanks for taking time to post all the information. I'm starting to think I probably will need to get bump steer spacers but will wait until I get the custom rear springs installed and see how it drives. I noticed when I drove the 510 at road speed with the short front springs on, the steering seemed to want to dart slightly to one side or the other. Maybe when I hit a slight bump, maybe at random. But that could be front end alignment too I suppose.

 

So when lowering the rear of a 510, is there a cure for the toe out problem? I'm just starting to study suspension mods and haven't gotten to that one yet. The custom rear springs I'm going to use are currently installed on a 510 and while it looks noticeably lower that stock height, it doesn't look drastically lower. Or does any amount of lowering produce toe out issues? I've obviously got lots to learn.

 

Len

[datzenmike]

Len, any time ride height is altered, the toe changes. It's unavoidable. I made my own bump steer spacers out of 1/4" aluminum stock. Two of them each side fixed it. Corners better now but the tow was now way out. Had to do my own alignment but it's on track now. 

[LenRobertson]

Len, any time ride height is altered, the toe changes. It's unavoidable. I made my own bump steer spacers out of 1/4" aluminum stock. Two of them each side fixed it. Corners better now but the tow was now way out. Had to do my own alignment but it's on track now. 

 

I've considered making my own spacers. I've got both lathe and mill out in the shed, waiting to be used. It would probably be a fun project. I need to dig through my aluminum stock and see what I have that might be thick enough.

 

So you ended up with 1/2" spacer height? It looks like the store bought spacers are mostly 1" height but I haven't looked a lot. Maybe various height are available.

 

Len

[datzenmike]

What happens Len, is the tie rods are joined to the idler arm (and the pitman arm) which are solidly mounted to the vehicle, and sits lower when the vehicle is lowered, but the other end attached to the steering knuckle remains in the same position. Now as the tie rod end swings upward, it becomes shorter horizontally and pulls both steering knuckles inward toeing out the front of both tires. Normally the tie rods should sit level so that up and down bumps alter the length as little as possible.  When the toe is adjusted to compensate everything is fine until you hit a bump. As the toe rod is already sloping upwards the bump moves it even higher, excessively shortening the length. This will toe out one (or both) wheels and you will feel it pull on the steering wheel. If you are turning a corner the car will feel squirrelly and try to steer itself. A spacer between the steering knuckle and below the strut will lower the outer ends to the horizontal and return the steering to normal.

 

You will need to look at the tie rods with the car sitting level. I used a level bubble and tape measure to determine that about 1/2" lower on the steering knuckle was about right. I fit them and 1/2" longer bolts and because I had aligned my steering had to undo this. If you lower and use proper bump steer spacing, the steering should not change.