heinzboehmer's 2002 Topaz 6MT Coupe

[heinzboehmer]

Over the past few months, a rattle/clunk started to develop in the rear of the car. It was only audible when there was significant and quick compression/decompression of the rear suspension. I took stuff apart and tried to replicate it, but was unable to.

I don't drive the car on the street too much, so I would kinda forget about it, but one day I got sick of it and decided to try and track it down. Had a friend drive the car while I rolled around in the trunk and tried to pinpoint it. It was super hard to do, as the noise sounded like it was coming from a bunch of different spots. Figured it was coming from something solidly mounted to the chassis and the sound would reverberate in the trunk. So instead, I got back under the car and started putting a wrench on everything. I do paint mark all the bolts that I torque, but after talking to another friend about having stuff rattle loose on track, I decided to do a torque check instead of just a visual one.

This is what I found:

That's the lower wishbone to subframe bolt. Both sides were like this and I have no idea how they got loose. When torquing them back up, I tried going up in small increments to see approximately how tight the things were. Started by setting the torque wrench to 25 ft-lbs and it didn't even click there. Sketch.

I'm thinking the bolts must have been loose for a while, but only recently did they get loose enough to start making noise. Unfortunately, it does look like they were moving around a good amount:



So far haven't heard them clunk again, but I'll probably need to add some mending plates to the subframe, as I'm expecting the bolt hole to be slotted now. Oh well, I'll do that whenever I stop being lazy and install some camber arms.

[heinzboehmer]

Well, he hasn't taken advantage of moving the shaft up yet with that 7mm thick tms spacer in there still right? I'll be interested to see what you do Heinz. I'm using a 2mm thick washer, though my setup is obv different (I have tms street plates too though). I saw Kdawg's thread, so even with that thick spacer in there, TMS plates are still considerably shorter than stock. Probably why I was so happy with TMS plates with NO spacer on my bilstein b6 converted into coilovers with GC, lot's of travel, free lowering, and stiffer rate (325lb). So maybe you don't plan to replace that 7mm tall tms spacer?

Turner street plates move the shaft up 5.5mm compared to the stock ones, with the spacer installed how it's shown in that diagram a couple comments up. So I've gained that at least. Spacer I'm going to make is going to be 5mm thick (to compensate for the loss in ride height), so a total of 10.5mm shock shaft travel gained.

I don't plan to replace the Turner spacer. Shock washer ended up being too close to the bottom of the camber plate for my liking. Don't want it to bind during driving so will leave it how it is in that diagram.

Did you contemplate getting a shorter but stiffer bumpstop ever? If so, why not? Seems cheaper than plates.

I thought about it, but decided I don't know enough about suspension tuning to make an accurate call about what to replace it with . Shorter + stiffer sounds like if I do contact the bump stop, the crash will be much harsher. Think I'd rather keep the longer, less stiff, more progressive ones for that reason. But once again, I'm no suspension engineer so no idea if my intuition is correct or not.

Also, sendcutsend quoted the two spacers (using rough measurements) at ~$15, so super cheap. This is with them made out of aluminum. They don't have 5mm thick delrin in stock, only 3.6mm, which was only a couple bucks more.

[Tbonem3]

Ya, I suppose it is dubious that the mild increase in rate is enough for the half inch+ drop on eibachs or Dinan, much less h&r or God forbid tein.

Well, he hasn't taken advantage of moving the shaft up yet with that 7mm thick tms spacer in there still right? I'll be interested to see what you do Heinz. I'm using a 2mm thick washer, though my setup is obv different (I have tms street plates too though). I saw Kdawg's thread, so even with that thick spacer in there, TMS plates are still considerably shorter than stock. Probably why I was so happy with TMS plates with NO spacer on my bilstein b6 converted into coilovers with GC, lot's of travel, free lowering, and stiffer rate (325lb). So maybe you don't plan to replace that 7mm tall tms spacer?

Did you contemplate getting a shorter but stiffer bumpstop ever? If so, why not? Seems cheaper than plates.

[Bry5on]

I personally don’t buy that the eibach setup is optimized correctly. I spaced my Dinan setup up 1/2” inch in front (similar rates and drop) and preferred the balance mid corner. It seems to be a balance of performance and aesthetics, where performance took a hit to manage aesthetics.

The strut moves up with the inner bearing/bushing, the spring mount moves with the outer bearing. Travel is dictated by the strut position, height is dictated by the spring position. Heinz is taking advantage of the fact that you can tune those locations/heights independently.

[heinzboehmer]

Tbonem3 I see what you're getting at. Worth noting that the relative positions of the surfaces that the shock shaft and spring sit against on a specific camber plate will dictate shock travel and ride height. So it's possible to get thinner camber plates (spring to body), lower ride height and also increase shock shaft travel, as is the case with the Turner street ones. Look at the measurements in this thread to compare against stock: https://nam3forum.com/forums/forum/m...ate-comparison

My car is modestly lowered (on eibach pro kit springs) and I was concerned by the measurements in this post: https://nam3forum.com/forums/forum/m...742#post181742. Admittedly, I haven't measured myself, but it looks like basically any modest bump would put me in the bump stops. Like Bry5on said, these camber plates give me more shock shaft travel, which results in me staying out of the bump stops more often and an improved ride. This effect will be even greater with the spacer I'm gonna have made.

[Tbonem3]

How will he move the strut top upwards other than not include the TMS spacer? Unless he finds a smaller spacer like I had suggested.

Also bump stops are part of suspension tuning. Eibach increased spring rate by 8%, and only lowered the spring height by .6". They would have taken all of this into consideration. You're only "on the bumpstops" too much when you lower the car, but don't increase spring rate, comensurately. The eibach springs have a slight increase to match the slight drop.

Increasing bump travel to stay farther away from the bumpstops will only mean his wheel will come closer into contact with the wheel well before bump stop is engaged and spring rate is exponentially increased. Might make the car more confortable up front (since spring rate won't increase as much), but he could also slow the rebound on the konis to match increased rate from slight contact with bumpstops.

[Bry5on]

Heinz you’ve got it right. Keeping the ride height (effective upper spring perch) fixed and moving the strut top upward will increase travel as long as there is no coil bind, which in your case there is not. Your calcs are right and you’re gaining about a half inch of travel, which should improve your ride quality by keeping you off the bump stops in more situations.

The rubber spring perch is on the bottom of the little grooves and would not aid/hinder drainage there, and at least in my car, there was dirt around the upper strut bearing that was able to get there between that small gap from the upper strut bearing aluminum and the rubber splash shield. It’s worth noting that spacing the spring perch down opens up this gap and makes drainage a more relevant topic.

[Tbonem3]

Here's another thought - If you don't want to lower the car (at all or much at all), why bother wanting more travel? Travel is sufficient (barely) at stock ride height with soft (143lb) front springs.

Generally, you'd want more bump travel because you want to lower the car (for looks, for lower COG) without severly ramping up the spring rate. So if you keep the 143lb front spring rate or similar comfortable amount (like158lb eibach springs, for example), but you also want to lower the car a full 1" like people usually do, you'll run into problems. If you're moving up to a stiff spring like 400lb, travel doesn't matter so much because that stiff of a spring won't be that compressed (without aero and very high speeds) so you can lower the car significantly and not worry about travel. Your worry will be finding dampers that can adequetly control rebound from 400lb springs (FCM, ohlins, jrz, mcs).

[Tbonem3]

Yes, I should have clarified that it depends on the setup - is top perch above or below the point where you're removing stack?

So in your example, you'll gain a little bump travel (shaft travel) without affecting ride height. Or, they way I looked at it always wanteing to lower the car: maintain the same travel, but still get to lower the car for "free."

But replacing the stock mounts for thinner camber plates will lower the car rather than simply give you more travel because you've change the top spring perch's location relative to the strut housing. If you had adjustable coilovers, you could then scoot up the bottom perch or put in taller springs.

So pairing thinner camber plates, and not using a spacer like TMS', with stock style spring and strut, is something to do if you wish to get the car a little lower (good for B12 which is gas pressurized) without compromising travel.

[heinzboehmer]

Okay maybe I've been using the word "travel" too broadly, I'll try to be more specific. I don't care about more total wheel travel (before coil bind), I have enough of that. Goal of this is to stay out of the bump stops by gaining more shock shaft travel.

Still unclear as to why raising the car is necessary to gain shock shaft travel. Here's a cross section of the camber plate:



If the "Nickel Coated Shock Spacer" is removed, the shock shaft extends further up, moving the bump stop away from the shock body. This should not affect ride height as the top and bottom surfaces that the spring sits against have not moved, nor has the relative position of the "Camber Plate Assembley (lol)" or "Stock Spring Perch" to the body changed.

With a spacer between the "Stock Bearing" and the "Stock Spring Perch", the dimension between the top and bottom surfaces that the spring sits against will not have changed, but the "Camber Plate Assembley" will have moved up (in relation to the "Stock Spring Perch"), resulting in a higher ride height AND more extension of the shock shaft, thus moving the bump stop away from the shock body. This should result in more bump travel, right? (but only due to the extra extension of the shock shaft)

[Tbonem3]

Just removing stack height (thinner plates or removing the turner spacer, for example) will retain the exact same bump travel, but shorten droop aka lower ride height

You can only gain travel by raising the car i.e., putting in a taller spring or raising the bottom perch (on adjustable coilovers). If you increase travel by putting in a taller spring, or moving that bottom perch up AND you reduce stack height, only then will you have increased travel, but maintained current ride height.

[heinzboehmer]

Hmm, I'm still not sure why a longer/raised spring is strictly necessary. The Turner plates change the location of the spring seat and shaft seat independently, so even with the same effective length for the spring, there is gain in shaft travel.

The idea of swapping to camber plates got into my mind because of this post: https://nam3forum.com/forums/forum/m...742#post181742. The Koni travel up front is extremely limited, so any gain in travel is welcome. I don't need more camber (as of right now) and didn't want to go any lower. Thought that 5mm would be okay but the occasional scrape if I don't get the angle into the driveway perfect is annoying me, so I'm going to get the spacer made (which is serving the same purpose of making the effective spring length longer).

I considered swapping out my suspension for something else (which will probably end up happening in the future), but everything I looked at involved also swapping top mounts, so I decided to start with that.

[Tbonem3]

I look at shorter stack height as a way of gaining free lowering, not so much gaining travel, but retaining travel while being able to lower the car a bit (having my cake and eating it too so to speak).

I can see why you were reluctant to not use the turner supplied bearing/washer under the poly bushing (I don't have that issue with my setup which is why I put mine up top [also to take up some of the now unnecessarily long shaft threads]). I would suggest finding a spacer that will give you the clearance you want, but is shorter than the 7mm tall turner piece.

Gizmo's right about there being the need to raise the spring or get a taller spring, but like I said at first, I look at it as "travel is fine as-is, I just want to lower the car a little more (1/4" less say) for looks and not compromise the already limited travel. This is in regards to b12 kit or similar stock style.

[heinzboehmer]

Huh, never crossed my mind that those could be there for draining water. Upper rubber spring pad has them too, so I assumed they were there to clock the two parts, but I guess that doesn't really matter when they're radially symmetrical. Water drainage makes more sense. I'll remove them from the final piece then.

Wasn't planning on 3D printing these. Realized they might be a pain to machine, but decided I'd deal with that later if I got any pushback from the manufacturer

[Bry5on]

You’ll want to get rid of those form keys, they’re likely for draining water so you don’t rust those bearings.

Are you planning to 3D print them? The geometry as is would be difficult to machine, but no problem if you eliminate the keys