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72 510 questions


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New to the 510 world, and hoping for some solid advice.

I would like to lower the car (who wouldn't?) but don't need to adjust the ride height. So not looking for the expense of coil overs since this will just be a weekend car. I have read about the advantages of using some 280zx fronts and a bit about using roadster springs in the rear. I have also seen write-ups about cutting the perch off and using a collar, so I have some ideas about where to start, but I guess I am just looking for a simple way to get the car a bit lower without mucking with the whole suspension? Is there a quick and dirty/clean way to do this?

Thanks for any new info you guys can provide!


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Roadster springs are leaf springs and solid axle (IIRC) so you must have a wagon? If so, you can use lowering blocks for the rear 2"-3" or any size to your taste and leave the stock springs as they are. That's the cheapest way to lower the rear. I have 2" blocks on my '72 goon.


In the photo below It's the aluminum block sitting on top of the spring with long u-bolt to clamp it.


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He might mean front springs from a Roadster in the rear.



The trouble with lowering an IRS is the retarded looking camber it causes.


The Dodge D50 front coils can also be used in the back. If you cut them to 5.5 active coils this gives a spring rate of 132 lb/in.  Reducing the coils to 5 produces 170 lb/in. I don't know what the ride height would be but if too low you can add rubber spacers.


The front coil should be a similar rate to the rears. The stock 510 front coil is only 89-90 lb/in. If you go to split collars you can trim the stock front spring to increase the rate to match what ever you choose for the rears. There is a mathematical formula for working out a coil spring's rate this using only multiply and divide and some careful measurements of the coil spring. You can use this for determining the rear spring rate also.Over all you can't adjust your ride height indiscriminately. There are limits to how low your ride height can go without bottoming out. The lower you go the stiffer you need the springs to be. You can go 2" maybe 3" but not on the stock front spring.... it's way too soft. 

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will upload pictures soon. Mike is correct (as usual) roadster springs in the rear. 

Banzai, are you sure about just cutting a coil off? I heard (on roadsters anyway) that this is not a great idea due to geometry issues. Maybe mike can confirm or deny?

I dont need to go too low, maybe an inch or two max...

I'll keep studying up and in the meantime I will work on the dog leg 5 speed I just got in today.


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Be cautious, lowering the 510 suspension alters the steering geometry (bump steer) and rear camber/toe (loss of traction and funky tire ware). You might get away with an inch or two, but any more and you'll need to address these issues that arise. Not unsurmountable or crazy expensive, just needs to be part of your plan. 

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When a coil spring is shortened the spring that's left becomes stiffer. So... if you shorten a coil in order to lower the car you may end up with an impossibly stiff kidney jarring ride. If you trim it to achieve a particular spring rate or stiffness you may not be as low as you would like. 


Know what you have first and you can work out the stiffness you want to get to. Blindly cutting a coil because a buddy did this to his will get you what he likes.


Front strut coil 7 active coils, center to center diameter 4.648" and the wire thickness is .472" The formula is 11,250,000 (a constant for steel) X wire / 8 X number of coils (7) X spring diameter 4.648 4


Multiply and divide and the stock spring rate is 99  lb./in. ( pound per inch)


Rear coil is 2.983 center to center coil diameter and 0.56" wire thickness. I don't have the number of coils not touching anything. Called number of active coils. Does this sound about right??? If you can confirm my numbers and the active coils I can work out the spring rate for the rear coil. I should guess around just under 400 lb/in

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I have all the stock suspension so i can get a count. I have read your write up about cutting the perch and maybe taking one coil off then using a split collar and thinking about that way to go. I may wait on this project until I have the car back together. Much work to do before it is back on the road.

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10 hours ago, woton121 said:

I have all the stock suspension so i can get a count. I have read your write up about cutting the perch and maybe taking one coil off then using a split collar and thinking about that way to go. I may wait on this project until I have the car back together. Much work to do before it is back on the road.


All measurements must be as accurate as possible. Thicker wire makes it stiffer, thinner, softer... smaller coil diameter makes it stiffer larger softer...and fewer coils makes it stiffer while more coils makes it softer. To get the coil diameter measure the outside to outside then subtract the wire thickness and this will give you center to center diameter. Free coils are coils free to compress and not touching the top hat, spring perch or themselves.




For example in the picture above the top right where the cut end is touching begin there and count down 1, 2,  and just a hair over 6.5 free coils where it touches the other end. 



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Points to add....

1, The stiffer Roadster front springs were the competition ones. They were never common and are greatly over rated. The normal Roadster front springs are basically the same as the 510 rear springs.

2. The arithmetic for calculating stiffness looks hard, but since when cutting the springs you aren't changing the wire diameter nor coil diameter, only the length of the wire, you may just do a simple ratio calculation. If you cut one coil from 10 coils you are 10% stiffer. 

3. Changing wire thickness gains stiffness more than you think. That's the D cubed part of the equation. Pretty much each gauge of wire is triple the previous gauge. That's why the old Dodge mini truck and aero Tbird front springs work for the back.

4. While the cut springs are shorter and stiffer, the total load capacity is reduced and the car runs out of suspension creating lots of problems and often is considered too stiff but is really just crashing into its stops.

5. If you want to lower the car by half of it's suspension travel, you want to double the spring rate, maybe more if you want to increase to transition handling. Usually these goals are in common. 

6. Lowering the rear of a 510 by 2" changes the rear toe alignment by 1/4" or more. Toe out not toe in. This is bad unless you really like steering a shopping cart at 60mph. This is not adjustable with factory parts. It is not obvious by looking at the car, but if your camber is visibly changed you can bet the toe out is there too.

7. Easily adjustable rear coil over conversions are great for playing with different spring rates and terrible for accidentally getting the rear toe settings all screwed up. the lower mounts at the control arms are not strong enough for the load either.


So, for a quick and cheap handling improvement, stiffer springs that do not lower the rear are the best deal. Stiffer front springs with shorter '69 or 280ZX front springs are also the cheap and effective solution. Stock wheel rates on the 510 are about 90#/" all around and the balance is so good we all became interested in the car. You probably want to keep that ratio rather than become a chassis engineer and "improve" that.

The rear suspension leverage is almost 4:1 spring rate to wheel rate while the front is almost 1:1.

I hope the helps..



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The cantilever rear control arms have a 3.8 to one mechanical advantage. A 500 pound per inch rear coil will feel like 131lb/in at the axle. The Dodge D-50 front coils are about 500 lb/in.


If going to coil overs on the rear shocks then the amount is almost 1 to 1. Agree with 7, the shock mounts were not intended to hold up the rear of the 510.


You can raise the attachment points of the control arms on the 510's rear cross member to reduce lowering induced camber, and provisions can be made for toe adjustment at the same time.

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Pay attention to DHale_510.  He knows of which he speaks.  ? 


You have a '72 so if it still has stock struts, it has mid-length struts. Finding some '68-'69 510 struts (easier said than done these days) will get you 1/2" lower.  You can also modify the strut insulators to get another inch lower, as shown in the How To Modify book:



You can also use modified 280ZX strut insulators to get that same effect as FAR's mod. The mounting stud spacing matches the 510. Just turn down the OD to match the 510 insulator OD so they fit inside the strut towers.  ZX insulator on left, 510 on right:





Neither of these mods affect suspension travel and are compatible with stock springs. 


280ZX strut tubes are about 1" shorter than your '72 struts, but you'll have to shave off the spring perches and use 510 perches. You could just have your 510 struts shortened to fit 280zx inserts.  You can get ~ 1.5" - 2" lower in front using 280ZX insulators and shortening your 510 struts to fit 280ZX inserts. 


In the rear, you can cut your stock springs or install shorter, stiffer springs, but camber and toe are adversely affected as pointed out by others above. To do it right, the semi-trailing arm pickup points on the crossmember need to be slotted to compensate for the excessive neg. camber and toe out introduced by the shorter springs. Cheapest way to do this is a "street slot".  See Dime Quarterly Vol. 2 Issue 4.



Use bump stops!  You don't want your spring rate to suddenly jump to infinity in the middle of a corner. You can shorten the stock rubber bumpstops, but conical bumpstops offer a more progressive rate.  The urethane ones shown below are available from Top End Performance. Energy Suspension also makes them. 






Edited by Tedman
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Furthermore you can source 210 strut insulators and do the mod that tedman posted to get an additional drop. Memory isn’t what it used to be but I recall it to be over an inch more drop without Further stiffening ride quality. I have done this many times over the past 20 years. 

Another thing to consider, the difference between a 69 and a 70 strut tube is 2 cuts and a weld. for me personally I cut all tubes no matter if I’m doing coil overs or not, they all get shorter strut cartridges and the tube is matched to it. The reasoning behind this is about cartridge valving. If you reduce spring height you’ve now compressed the cartridge and it will be working in a different internal position and often times more prone to full compression which inevitably  blows them out...oily mess, bouncy, tire cupping and general discontent will be the final result.

Edited by jbirds510
Moar info
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