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Old 04-22-2008, 09:37 PM   #41
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Originally Posted by AbeFM View Post
The plastic ring, Joe, as I heard it is to give air a chance to escape. Since the bump stops are custom why would they be 8mm short just to put plastic in there? The 'ring' has a cut out of it,
Could be... I talked with Shaikh about this a while back. First off, they come in two thicknesses. We have the thin one. The thick one was something like 9mm and non-slotted, and definitely intended to increase the effective shock body length. My impression was that the primary purpose of the slot was to allow you to install it on the shaft without having to dismount the shock. The thinker one was non-slotted simply because the slot would do no good- the piece was too thick to allow you to flex it into position.

I didn't originally get them, but Shaikh sent me a set just after I got my revalves and bumpstops under the guise that they were there to protect the upper seals. Apparently he felt that when bumpstop squished and deformed against the top of the shock body, there was a possibility of the bumpstop material pinching the upper rod seal and damaging it. So I stuck 'em on and never gave it a second thought.

I can't really picture air being trapped inside the bumpstop. Mine (46mm linear) are a pretty snug fit against the rods.


Zabac, I'm really hoping that some of this is starting to make sense. Drawing those pictures in PaintShop and trying to keep them all consistant is damn tedious.
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Old 04-22-2008, 11:04 PM   #42
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I'll draw some pics as well as i believe you are simply missunderstanding me, and that's my fault, ESL FTW, lol
So here is what I'm trying to say.
We are not really disagreeing, bump stops are needed, but a bumpstop can cause damage to the shock as Shaikh shared with you and that is why you want to stay away from being on it as much as you would if you kept the stock length.
The thing i was really trying to emphasize is what is depictesd in my poorly made paint work below. Your spring height does not chance, so when you compare the examples i have made, you can see what I am trying to explain all along, i just suck at it as much as I suck at paint
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Old 04-22-2008, 11:15 PM   #43
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I realize my painting is not to scale by any means nor is it really relative to what actually happens, I really am no expert, but i firmly believe that taller tophats along with the right bumpstops (and if I understand correctly Abe does have the right bump stops, 46mm, that sounds right) will solve his problem.
Keep in mind, the springs will only compress so much, that's why you have to be very careful when setting your suspension up, especially when designing your own tophats as I plan on doing. Too tall of a tophat can lead to the springs seizing, and that's no fun at all. You have to retain proper geometry when doing this. Idealy, if I understand this correctly, you never want to fully compress the bumpstop, when at the bottom of your desired travel, you should be barely touching your bumpstop and only in extreme cases compressing it. To maintain proper handling characteristics, your bumpstops should be utilized, but not for the sole purpose of simply stopping your shock from being able to go any further.
Look at it this way, cars are equipped with 5MPH bumper covers, meaning that they will not sustain any damage at low energy impacts, but what happens to those bumpers if you hit a wall at 50MPH? Now i know this is an extreme example, but you get the point, right?
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Old 04-23-2008, 12:23 AM   #44
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Originally Posted by Zabac View Post
We are not really disagreeing, bump stops are needed, but a bumpstop can cause damage to the shock as Shaikh shared with you and that is why you want to stay away from being on it as much as you would if you kept the stock length.
I think that's the issue, we don't really agree on that. The reason a suspension designer wants to keep you off the bump stops is they will creat a high jerk, using jerk in the technical term of rate of change of acceleration. This will tend to get the whole car body moving rapidly away from the ground and overall cause uncontrol suspension happenings. :-) You want things to be linear, or at least have no step-function changes.

The issue with your drawing, your assumptions, is that something will just magically stop the car from rising. Either the spring will bottom (terms like 'sieze' and 'bind' are misleading if you asked me, at least in the case of cylindrical coil-overs. 'Bottom' would seem a better word), and keep the rod from further enterting the shock, the bump stop will do it, or the shock will internally contact. If you don't design your suspension in such a way as to prevent that last issue, you WILL destroy your shocks and have to buy new ones if you ever hit a big bump.

This is not a blown seal needing a rebuild, it's utter ruin.

In the picture you have on the right, imagine the wheel still moving up, the little black plunger will bottom out in the tube.

For instance, not all cars have the bump stops on the shock, on some it's a rubber bumper between the a arms, or the a arm and the frame. These are obviously not bad for the seals in any way.

Quote:
Originally Posted by Zabac View Post
Idealy, if I understand this correctly, you never want to fully compress the bumpstop, when at the bottom of your desired travel, you should be barely touching your bumpstop and only in extreme cases compressing it.

To maintain proper handling characteristics, your bumpstops should be utilized, but not for the sole purpose of simply stopping your shock from being able to go any further.
The issue with flattening (and touching to a lesser extent) the bumpstops is it shocks the car and will make you lose traction in a turn. Another issue is if you raise the hat too high, the wheel can not fall, and in a dip the wheel will leave contact with the road, reducing traction you could have had, as well as causing you to hit harder when you come back down, increasing the risk of blowing the seals.

I think it's very important to understand exactly what's going on here, and the range of travel you need, before blindly raising the hats. It's mainly done to offset the shortened travel of lowering a car, but keep in mind this messes with many things, camber rates and other such things.



As an aside, one thing I'm curious about is why you don't see more offset spindles.
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Old 04-23-2008, 11:29 AM   #45
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Lets not get into the spindles yet, lol....lets agree on the konis first heh

As far as my inferior drawing goes, keep in mind that it is not to scale whatsoever.
My goal with taller tophats is to be on the safe side of things even though I may loose 1" of droop, I know too many local maita auto-x'ers who blew their rear Konis due to the lack of suspension travel. They kept bottoming them out. A good friend of mine who blew a rear shock three different times, went with FM rear mounts and never had an issues in 3-4 years since then. That says something to me, they are important, not so much up front as they are for the rear for this very reason.
When both A&B are equaly compressed, B has more room to go.
All other factors are constant, sprint rate, spring hight, shock body size, dampening rate of the shock, only thing you change is the upper mount localtion by extending it and giving the shock more safe travel.
Can we agree on that
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Old 04-23-2008, 12:04 PM   #46
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So like, my car has felt pretty crappy lately. First I thought my skills were just way deteriorating, but I started to get a sense that my shocks might not be up to snuff.

(My shocks are Koni Sports (yellow) which had the first set of "race" valving in them, which was later released as its own shock. I'm not sure my Fat Cat Motorsports bump stops and sort of prototype mounting from FCM are correct, so maybe they bottomed out. They always felt harsher when bottomed than the fronts which felt awesome since the FCM bump stops.

I bounced the corners of the car by hand, and I guess they stopped quick?

Then I turned up the stiffness, and it got much better for a couple days. Then it stopped being better. I noticed the car bottoms out a lot now where it didn't used to.

So I looked and my rear bump stops are both soaked with oil. One of the fronts is mint, the other is a little tainted.

Just recently, I noticed my rear end doesn't make the squish-squish sound it used to.

Is there any more definative test to do, or should I just send off the shocks for rebuilding? Is there any point to doing it myself?

One of the reasons (money aside) I'm wary to send them off for rebuilding is last time it took 3 months to get this done at Koni. Then I had AGX's (since sold), so now am I going to have 500 lb springs on OEM shocks? Seems a bad idea.

Lastly, I'd like to come up with a way to keep them from going boom every year and a half.

I've briefly scanned most of this thread and it seems it is mostly of bumpstop and clearance discussion. If what I am adding has already been stated, forgive me for over looking it.

I believe you've just worn out your shocks. The race valving setup is not designed for longevity. THis is primarily an issue if the vehicle sees much street time.

You've obviously had the shocks in their "race" valved state for quit a while as I've had the first set of prototype koni races for several years now, and you stated you had the current valving since before the Koni Races were availible. A rebuild would seem the most likely answer to me... and if you are having the rears done, then have the fronts done as well.

...but to simplify the matter; Koni North America 859 586 4100. The lead time is longest in the spring before racing season begins. $75ish per corner was what I had last heard a year or so ago if there is no damage.

If you were happy with the koni races, then you need to find a way to keep them because there really isn't anything out there in there league for what you are doing.

/twocents
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Old 04-23-2008, 12:18 PM   #47
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Peanut, he had his Konis re-valved several times, he is trying to figure out how to get more life out of them. That is why I am suggesting he gets some tophats that give more travel.
Since you have the actualy race shocks, you do not have this problem as those are much shorter as is.
Thanks for chiming in, seems you know the Konis pretty well. Can you tell me what you think about re-valving the front only to race spec and leave the rear as sport?
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Old 04-23-2008, 12:37 PM   #48
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Gotcha

I hate to keep adding on and risking being a repeatative know-it-all (especially if i'm wrong), but, ... I think the longevity issue is the price to pay with the "race" valving. Koni may be able to offer a stiffer "sport" valving that has the longevity Abe is looking for. I don't know the design of the valvings and build materials to comment with any detail.

As far as mis-matched valving, It seems I vaguely remember someone on miata.net or rr-ax.com doing that with reasonable success and a local was looking to do the same. I can certainly imagine circumstances where that is a legitamate option.
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Old 04-23-2008, 12:45 PM   #49
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Reason I want to do this is because I am very happy with the way my rear behaves.
Up front however, i feel strongly that i need more spring, but at 650 I am already pushing the Sprots to their limit, i feel it. I am no expert, and when i say i feel it, it could simply be the placebo effect, lol.
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Old 04-23-2008, 01:24 PM   #50
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Peanut, he had his Konis re-valved several times, he is trying to figure out how to get more life out of them. That is why I am suggesting he gets some tophats that give more travel.
I don't see how installing tophats with more travel is going to make one bit of different in the lifespan of his shocks.

I think we've clearly identified that we disagree as to the purpose of the bumpstops. To me, it seems perfectly obvious that the Miata was designed to use them as a part of the "normal" suspension process, albeit the design of them sucked on the NA. The "average" Miata owner, who is running "average" springs (200-400 range, for example) simply cannot stay off them. Simply raising them up doesn't change the fact that the shock will come into contact with them during normal operation.

Again, I'm not arguing against raised tophats in general. I like them, I use them, and I agree that more travel is generally better. I simply don't see how it will make one bit of difference as to the longevity of Abe's Konis. His shocks are dead because they are old and they have had a hard life, not because they touched the bumpstops.
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Old 04-23-2008, 02:56 PM   #51
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Peanut,
I think you called it 100%. I've only had these rebuilt once, when I first got them. The price seems right, etc, as well.

I guess I must have had them on the car much longer than I realized, I think that's all I can say. I'm not as gentle on the car as I could be, and if you've had yours for years then I am sure that's my issue.

Now all I'm worried about is getting them back in time.

Top hats might help with the hard bottoming in the rear, as might taller, slower bump stops.

It's great to know it's the worst time to get them sent out. Perhaps I'll just do it in summer, and deal with the crappy handling in the meantime.
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Old 04-23-2008, 03:18 PM   #52
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I don't see how installing tophats with more travel is going to make one bit of different in the lifespan of his shocks.

I guess we can agree to dissagree on this subject.
I don't think the bumpstops alone are what killed his Konis, I still think it's bottoming out because bumpstops alone are not enough as a solution. OEM bump stops would have killed them sooner. Don't get me wrong, I believe in bumpstops, just not as the answer to this problem, again, proper bumpstops are important, but our rear suspension geometry needs more help than bs can offer, no matter what bs you use.
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Old 04-23-2008, 03:26 PM   #53
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The simple question is:
What is the physical mechanism by which oil has managed to leak out of my shocks, why have they stopped working?

My theory is the valve inside is bad, though I don't see how that makes oil come out of the top. That would make them stop working, but shouldn't make them leak.

So I imagine BOTH the valving is blown, and the oil seal is blown.


I can imagine the valving wearing out through much hard use (high internal pressures and flows).

I could potentially seeing the upper seal bad from the shaft going through it all the time. Perhaps it's worsened by the valving not working.
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