Performance Shock

Sure. I will be back in the workshop in a couple of days and will take some pics.
I didn't use Nitrogen, I used Argon/CO2 mix (MIG welding gas).
There are two M4 cap screws on the side of the unit. The upper one is the gas bleed/charging screw, the one 25mm or so lower is for hydraulic fluid. There is a third M4 cap screw at the top of the unit, just below the upper mounting eye, also for hydraulic fluid.
The tool was machined from Delrin and is in two halves, bored to fit to the outer diameter of the leveller unit (81mm). The two halves are clamped together with two M6 through bolts. The purpose of the tool is to permit unscrewing the upper M4 cap screw into a chamber which is connected only to the high pressure gas supply line (and not to atmosphere). When the leveller unit is charged to the required pressure (30 bar in my case), and the pressure is held at 30bar, the tool allows you to tighten the M4 cap screw without losing charging pressure.

 

OK, so I eventually found the charging tool after a long search. Nothing new in that, I spend 50% of my time in the workshop just looking for stuff.

Here's a pic of the charging tool mounted on the load leveller. At the time I first did this work, I just lashed up a Heath-Robinson arrangement connected directly to the Argon cylinder, using a bleed screw to adjust the charging pressure. I DO NOT recommend that method- I have since procured a proper nitrogen regulator adjustable up to 600 psi (but I haven't used it yet). The method does work, but it's hard on the nerves.



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The next pic above shows the charging adaptor. It's machined from Delrin- again not ideal, but it works. A bit tricky to get clean cut threads, The pressure adjusting bleed screw is on the middle left. Ignore the extra test inlet on the bottom left.

More views below
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The charging screw is the only tricky bit of the tool design. It's shown partially inserted above. The purpose of the screw assembly is to permit removal of the M4 cap screw which seals off the gas charging port on the body of the load leveller, without exposing the charging port to atmosphere. The argon gas then enters the load leveller, and when the desired pressure is obtained, the charging screw allows you to re-insert the M4 cap screw and tighten it to the desired torque.

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This is the charging screw assembly, with an M4 cap screw (not the correct one!) mounted for illustration purposes.
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The brass screw must have the same pitch as the M4 cap screw so that both move the same distance per turn. I used a 5/16-36 UNS tap and die to form the thread (works out at 0.705mm pitch). Because the housing was Delrin, I felt I had to use the steel housing shown (Tapped internally 5/16-36) to give a more secure fixing. (Tapping directly into the Delrin with a 5/16-36 tap seemed unwise).
As I'm posting this, I notice that a cross-drilling in the steel adaptor is not shown. I will take another pic to show this later.
A 3mm hex key is soldered into the end of the brass screw- this engages with the socket of the M4 cap screw in the load leveller body.

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This is the internal view of the tool showing the business end of the charging screw. The green O-ring forms a pressure seal on the load leveller body. You can just see the head of the hex key mentioned above. To use the tool, one half of the tool is offered up to the load leveller body. The brass screw is screwed inwards until it engages with the head of the M4 cap screw, but not so far as to prevent the O-ring from sealing. The second half of the Delrin tool body is then clamped over the load leveller body and tightened up. The pressure source (argon in my case) is then connected up, preferably through a proper step-down regulator. After testing for leaks, the brass screw is then turned outwards, withdrawing the M4 cap screw with it. After charging the leveller to the desired pressure, the brass screw is again screwed inwards to the required torque.

Voilá! Hope it's reasonably clear.

 

That's one certainly the coolest custom tool of this sub-forum! Thanks for sharing.

 

I need help!

So I’m looking into what next to do on my rear suspension. I find that the ride is too harsh when going over speed bumps at relatively low speeds (20 to 30mph). On exit from the speed bump, the rear suspension seems to be bottoming. In normal driving the ride is OK. Not spectacularly smooth, just OK.

The current rear suspension set up on my car (Series 1, S/N 39313) is with one original Koni load leveller plus one coil-over unit on each side. Several months ago I recharged the self-levellers with Argon and CO2 mix (MIG gas) to 450psi. The car is still a little low in the rear, as measured by the height from ground to the bottom of the weld seam at the bottom of the sills/rocker panels (187mm behind the front wheel, and 177mm in front of the rear wheel, car unloaded). I am assuming that the designer’s intent was that the car should be level under normal load, as measured by the height above ground of the weld seam at the bottom of the sills/rocker panels. The rear inner fender lip height (no load) is 620mm on the left and 610mm on the right of the car. I'm dithering about whether to increase the charge pressure in the load levellers, and/or to replace the original coilovers with new aftermarket coilovers.

I'm short of hard data on the original charging pressure for the load levellers, and on the equivalent spring rate for the leveller unit. I'm also unsure as to whether the existing damping is adequate, or indeed whether the load leveller contributes significantly to the damping.

Apart from the speed bump issue mentioned earlier, there is no indication that the dampers are not functioning. Using the oldtimers test of pushing one’s body weight onto each corner, the car goes dond as expected and rises again without any bounce whatever. Neither does the suspension bounce unduly when driving on normal road surfaces with typical imperfections.

So what’s causing the harshness/bottoming on exit from the speed ramps? Is it inadequate rebound damping, or an absence of bump stops?

There are no bump stops on my suspension. The cross-section of the Koni load leveller (see cross section diagram earlier in this thread) shows a “Bump rubber” acting on the compression stroke. My car has just a simple rubber bellows-style unit on the load leveller which would not absorb any overcompression. As far as I can see there’s no bump stop on the coilover unit either (but I did not dismantle it to see if there’s something below the upper mounting eye).

What do you guys think is the most likely cause for the harshness?



And a second related question-
Elsewhere on Fchat AlCampbell talks about replacing the load leveller with Koni coilover units from Turner Motorsport. He mentions using spring rates of 150lbs/in. And 10 inch spring length. On my car the coilover spring is 102mm OD with 11mm wire diameter, total 12 coils, with a fully extended spring length of 300mm (with the coilover assembled, on full extension, 460mm eye-to-eye dimension). By my calculation this works out at 102 lb/inch spring rate. I would have assumed that the steel coil spring rate would have been chosen as the same value as the load leveller, so if one was setting out to replace the leveller with a coilover unit, the first guess would be to go for a rate of 102 lb/inch approximately.

Anyone got any thoughts or hard data on this?

 

Good day Pat,

How old are the shocks on your car? I ask, as regardless of how they "look" or feel under static conditions, the internal passageways become plugged with the age related decay and breakdown of the internal seals. If your shocks have not been rebuilt or replaced over the past few years, I would rebuild/replace them as a first step.

My shocks had no visible issues and appeared to function normally under a static test... when I opened them up, I was shocked at what I found. Some passageways were so blocked, that it it looked like it was purposely done. Here is a thread I created along with pictures of what I refer to.

https://www.ferrarichat.com/forum/threads/365-gt4-2-2-shock-rebuild.622534/

Cheers,

Sam

 

Brilliant thread Sam!.
And you have answered one of my queries which is the free length of the spring- I can measure it from the pic you posted.
To answer your question- I suspect my coilovers may well be original. So your suggestion that they are, to say the least, likely to be compromised makes sense.
I'm tempted to purchase a pair of coilovers with adjustable dampers and springs of the same spring rate and free length as the originals. That would help identify whether additional damping would reduce the banging noise/ harshness on exit from these speed ramps, and would also allow me to recondition the originals following your very detailed guide at my leisure, and still have a driveable car. And the aftermarket units would be then available as spares in case the load levellers give trouble in the future.
You have also partially answered another of my queries- your coilovers have a bump stop fitted for the compression stroke on top of the pin nut.
Have you identified any other form of bump stop anywhere on the suspension, to deal with a full rebound situation?

As regards the damping characteristics, if any, of the load levellers- I have read the Koni technical manual posted by Raemin but I have to confess I am none the wiser. Can't make head nor tail of it. Logically though, based on what you found when you stripped down your shocks, and looking at the plethora of bits and pieces inside the leveller, and assuming the materials and construction techniques used by Koni would be very similar, the chances of finding the same blockages seem very high. Another reason for having a couple of spares on hand!

 

Good day Pat,

I am glad that you enjoyed the read/adventure!

As for additional bump stops... nope, all that you see is all that was on my car, which matches the original parts manual. That is not to say that Ferrari may have added things later, but in my case I found no evidence of this.

As mentioned and shown in my thread, the internal rubber seals do break down over time and the resulting bits cause all sorts of issues. My shocks appeared to work, but once the spring was removed, the shock would compress, but would not return on its own. The spring clearly forced the shock return and so the entire damping characteristics were not what was originally designed/intended.

Koni and their official rebuilders will not sell you any bits that you may need and so you have to source many of the items. That said, many of the koni shock core metal parts are shared between shock models and so you can salvage parts from used Koni shocks sold on places like ebay. Also, as you surmised, the overall shock assembly and design is the same. In most cases the mechanical bits do not fail or even wear... just the seals with the seal bits plugging up the internal valving. As a precaution, I bought a pair of used "not working" Koni shocks with no signs of physical damage for around $50. I could have sent my shocks to be rebuilt, but the 365 shocks are NLA and so I was worried about transport damage or loss. Secondly, not all rebuilders share the same quality of work. Thirdly, by doing it myself I could ensure that the result was as close to looking like original as possible (e.g. paint color, decal type/placement).

All in all, rebuilding the shocks is not that complicated, but a person does need to be both resourceful and confident in one's skills to have a successful result.

Cheers,

Sam

 

The levelers do not provide any type of damping,

The pressure for the leveler is 500psi (as per my notes taken on a 365gtc4 discussion, that I cannot find anymore).

 

Thanks for this. By coincidence today I came across a photographic description of recharging the levellers on a 365GTC/4, which also showed a recharge pressure of 500psi. (I can't remember where I got this info from). So it looks like I was excessively cautious in limiting the charging pressure to 450psi. I have just acquired a "proper" pressure regulator so I intend to charge the units again, this time to 500psi which should increase the ride height by some few mm at least.

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I'm still trying to understand how the suspension on our cars absorbs the shock of a full rebound such as will occur coming off a speed bump, because I cannot see any rebound bump stop other than the metal-to-metal contact when the load levellers and the coilovers hit full stroke.
Anyone got any theories- or physical proof?

 

Just discovered where that info came from....
Ferrari 365 GTC/4 Rear suspension self levelling - www.tomyang.net

 

My load levelers failed. I had them rebuild for a lot of money. The rebuild lasted about a year and then failed again. I went with the aftermarket set up. It works well. If I could buy new Komi self levelers I’d do that.
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What was your aftermarket solution? Brand/Part#? Is good to have that stuff recorded for when later folks come perusing the threads.

 

I’m on a trip now. When I get home I’ll see if I can find more info on it. I don’t remember without looking it up.

 

Looked it up. This is what I got. The kit was originally sold by Ricambi but it looks like this other company is now selling the replacement. Remember that this replacement is not a load leveler like the original but it is a workable solution.

https://www.performanceshock.com/product/ferrari-73-75-365-gt4-22-400-load-leveling-rear-replace/

 

We have never sold that kit (or any variant of it) at Ricambi America.

 

Thx for the correction. I knew I should have waited until I got home to post.