Cheap suspension mods

[afbrian13]

Awhile back (year or two?) I was reading about a guy on here who stiffened and lowered his car on the cheap. Basically he refilled the struts with 20w fork oil and cut the springs.

 

Theres a formula for cutting springs "the right way" so you get the rate you want. I guess the 20w is a good middle weight oil for it.

 

The guy cut the spring perches and used shaft collars to set the ride height.

 

Like I said, suspension mods on the cheap, not for racing, just spirited driving.

 

I was wondering how this was holding up? Anyone else do a suspension like this? I have a 280z, and an extra suspension, so I think I'm going to give it a shot.

 

I was going to buy a tokico blue w/spring setup, but it seems I waited a couple years to long.

 

Thanks for any info, options, or opinions.

 

Brian

[datzenmike]

I've done this too. But you need the original strut dampers. If they have been replaced by the cheaper inserts then the best thing is just keep replacing the insert. I used motorcycle fork oil as it comes in many different weights. I chose 20W but just recently was told by the guy I got the idea from that he runs 30W with no problems. Fork oil has anti foaming agents (not that it should need them) and also rust-inhibitors.

 

I worked out my stock spring rate and then worked out how much to remove to increase by 50%. So roughly from 100 lb/in. to 150 lbs/in. It's firmer ride, it's nice, well damped, lower for sure without being insane but if I ever take the struts out gain it's 30W and maybe 175 lbs/in. That will probably max out my interest in stiffness. Some 510 owners go 250 and 300 lbs/in.!!! Well it's not a track car and I'm not young any more and like my comfort too much.

 

Spring rate is calculated with this formula...

 

11,250,000 X wire thickness⁴ (wire thickness x wire thickness x wire thickness x wire thickness)

________________________________________________________________________________

8 X number of free coils X coil diameter³ (diameter x diameter x diameter)

 

All measurements in inches. Coil diameter is measured from center of wire across the coil to the center of the wire. You can also measure across outside to outside and subtract the width or one wire.

 

Example

710 coil spring... coil diameter 5.0625", wire thickness 0.5", coils 6.5

 

 

11.250,000 X 0.5 x 0.5 x 0.5 x 0.5

___________________________________=

 

8 X 6.5 X 5.0625 X 5.0625 x 5.0625

 

 

 

11,250.000 X 0.0625

_________________=

 

52 X 129.74633

 

 

 

703125

____________=

6746.8095

 

 

 

104.21592 lbs/in. Give or take about 100 lbs/in.

 

 

I imagine your 280z car is around 150 lbs/in. 

 

To make the ride height adjustable I trimmed the lower spring perches off, ground away the weld so the strut tube is smooth, and installed a 2" split collar.

 

Just a light nick all round with a metal cutting blade and a 6" angle grinder...

 

Tap it loose...

 

 

 

 

Grind smooth ...

 

 

Split collar can now slide up and down for ride height adjustments...

 

 

 

Face it, $400 to $1,200 for coil overs that you adjust once or twice until you get your ride height where you want it is ridiculous. Mine cost me $30 for both sides, this includes the metal cutting blade.

 

 

I was actually swapping '84 Maxima wagon struts on but the above applies to the stock strut and spring too. I swapped my 710 cut spring and lower spring perch onto the Maxima strut. The Maxima springs were way to wide to fit up into the 710's strut towers anyway.

 

While the struts were out the gland nut was loosened, removed and the piss thin old oil dumped out and the damper mechanism inside removed.

 

 

 

 Gland nut removed.

 

Take care removing this O ring and you can re-use it. Dental picks are $3-$4 so get one. The O ring HAS to be removed to get the dampers out of the strut.

 

 

 

 

You can rinse them off but not really needed. Just put back in with about 300mm of new oil. Instal O ring and gland nut.  Hold right side up and extend the piston rod fully upward. Turn upside down and fully compress the piston rod into the strut. Do several time to expel any trapped air in the valves. Open and top up the fluid leaving 1/2" for heat expansion.

 

The Belray 20W fork oil was $17 / liter CDN, for enough to do 3 struts.

 

I did my other 710 sedan that my wife drives. Trimmed the spring a little less and used ATF instead. It's somewhere between 7 W and 12 W and really has no standard viscosity rating. It works fine. Hydraulic jack oil will also use if you can find the viscosity. Fork oil is just the easiest.

 

 

I drove my goon for almost two years before I got tired of fender rub when turning off the street and up into parking lots, so I raised both sides about an inch and it was perfect. However the split collar probably wasn't as new, or I didn't clean the strut tube for good grip or maybe several things, but it did slip on a bad bump later and freaked me out. So I got out my MIG and put a small tack on the strut that the collar can't possibly slip down over. Did both cars. easy enough to grind away if I choose to do so later.

 

 

BTW... the 2" split collar when properly tightened is rated to support 3,000 pounds. Two will support 2 3/4 510s. Probably 2 1/2 710 goons.

.

[tr8er]

Has anyone sourced this O-Ring shown above.