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The top attachment piece will be cut off the OE mount, trimmed to fit, then welded in place on the new top so that it all bolts up just like the original design.
The modified mount will be a little bit heavier than OE, but more rigid. The OE mount is thin-wall up to the top bell piece that’s welded on (you can see this in the earlier picture where I cut the section out of it to see the gas bolt interference position). That OE top bell piece is twice as thick as the lower body part to handle the shock force loading and also transfer the spring deflection load at the shock mount base up into the bolt-on chassis bracket.
In the photo above, the new upper piece is all the same thicker wall as the OE top bell piece and then the flat top on it that the bearing carrier bolts to will be thicker still. Because both the higher rate spring and shock valving loads of the inverted MCS setup will all be applied directly at the top now.
A Mazdaspeed strut brace will also be tying both bracket mounts together to further minimize defection. The mounting brackets on it will also be modified to provide additional rigidity as a unified structure.
Since is 2 mo before my Rx8's event
Decide to switch my roller wheel to my 8
And clean my MCS damper, forget to zip tide the rod to measure stroke
But by look on the dust on shaft and on track photo, I could use some more front damping
looks more like you need a shorter rear spring and possibly higher rates. Possibly a longer front spring, but I can’t tell if you have the helper in coil bind because the rear is sitting so high that you have to have the front spring perch wound up to avoid additional rake. Knowing your ride heights would help ...
looks more like you need a shorter rear spring and possibly higher rates. Possibly a longer front spring, but I can’t tell if you have the helper in coil bind because the rear is sitting so high that you have to have the front spring perch wound up to avoid additional rake. Knowing your ride heights would help ...
I will do the mount first to get proper ride high on rear
The swift helper spring is design to compress on 1G of load
In the two front shock pictures above the the helper spring is fully compressed even though the shock is in full droop. The perch is also very high above the UCA. That tells me that either the spring is too short or you don’t want the front to be any lower since the rear is too high. It’s just being a spring spacer, not a helper spring.
on the rear shock pictures it looks to me that there is enough spacing between the spring coils at full droop for the spring to be shorter without it coil binding at full compression. So I’m not sure that the rear shock mounts really need to be modified.
In the two front shock pictures above the the helper spring is fully compressed even though the shock is in full droop. The perch is also very high above the UCA. That tells me that either the spring is too short or you don’t want the front to be any lower since the rear is too high. It’s just being a spring spacer, not a helper spring.
on the rear shock pictures it looks to me that there is enough spacing between the spring coils at full droop for the spring to be shorter without it coil binding at full compression. So I’m not sure that the rear shock mounts really need to be modified.
Let's right ~
Since rear sit too high
Let's in order to make ride high rack ratio right
I have to adjust front ride high up !!!
I was think to build the rear mount at first
But want to run 295 on 18x10.5j et 35 wheel
So I might keep this ride high ,
Next season will be focus on fine tune front end alignment, like add offset bushing to gain more camber
As much as I would have preferred to have a 3/4” bearing on the rear shock mount, it was proving to be a bit too much trouble and cost compared to a readily available 5/8” bearing carrier. So I ordered a pair of those today instead. Hard to get anything done this last few weeks with all the holiday vacations and activities. Hoping to get back up to speed going into the New Year.
I don’t mind sharing the info, but would prefer to verify it first before steering anyone wrong. Didn’t make it out there this past weekend, but the bearing carriers arrived. Shouldn’t be too much longer.
Had the top plates laser cut from stainless arrive today and was impressed with how precise they are. Saved me from doing a hack job or having them fully machined. They do need some partial machining for a center register because the bearing protrudes about 2mm from the carrier on the mounting face side, but that’s easy work in a small lathe. So I’m going to build 4 or 5 sets of mounts. This is going to take a bit longer because that forces me to build jigs for aligning the top mounting bracket. If I was doing only a pair for myself I’d just go ahead and wing it.
This is something I need to figure out now also.
I don't quite get how yours it's going to work. How does your top bearing part secure to the tube? Are you just adding a clevis to the shock eye? Why not just make a tab that keeps the clevis from rotating if that is a concern.
i may try this but with 7500da or 8300 Penskes, I have an opportunity to get them at the dealers cost.
Team, why did you go with the MCs instead of Penske 7500da's?
Funny you say that, my pre edit post had some other things in it and said that I was going to probably get told to go read the thread. I skimmed the thread and answered my own questions and edited it out. Guess I missed some things. =)
If you want to use a clevis mount then it’d be better to replace the entire top section with a bird cage like the old Eibach/Mazdaspeed rear coilover mount. However, being an open design it will allow water, dirt, dust, etc up inside the trunk area. It can also subtract more from the bump travel range relative to shock length depending on how you design it. If you just slap a clevis inside an OEM housing it will lose potential compression travel, but some of these companies are selling the NC MX5 length for the RX8, which tends to be a lot shorter. So you end up losing extension travel instead.
see post #51 and the middle modifed shock mount (previous version) in the picture above. Proposed new version on the left, OEM on the right.
looking good Mark. thanks for putting in the work and posting the info. im still trying to chase ohlins for a set of TTX but if that doesn't work out, i'll be buying a set of top hat from you for MCS.
A bit more progress, but slow going due to my personal situation. Tight fit, just does clear at the top. The height is fine, the curving wall piece on the inside trunk sheet metal at the top is a double thickness stiffener and the is right at the side of the bearing carrier. It may even rub some.
It’s not your fault. The whole thing has drug out 6 months longer than it should. The inverted rear shock orientation along with the MCS gas bolt design/protrusion and lack of sufficient clearance within the OE mount top is what’s driving this.
I ended up using 3.25” x 0.125” wall DOM tubing. You’ll need at least 3” ID clearance, but about the largest OD you can use to get up into chassis opening where the two studs are is about 3.375” or so. It’d have to be perfectly positioned to slide up in there too. The lower wall thickness on the OE mount is approx. 0.075”. Per the picture above though, the add-on top piece welded on the OE mount for the chassis tie-in bracket and bushing mount is thicker, around 1/8” or a bit more.
The tubular piece coming up through the lower mounting plate is somewhat concentric/straight along it’s centerline, but passes through the plate at a slight angle. Without having a welding machine and being able to tack it in place on the chassis adds some challenge to it. It might seem as easy as just making a new plate and sticking a tube up through it, but not without either doing it in place or getting the exact alignment plotted out.
I debated going thinner wall on the new top tube piece to save weight, but in the end decided it being stout was more important. The OE mount top end would normally only see the shock force loading. But now as a true coilover both the spring and shock force is concentrated on the top. So having the mount stiffer, tying the chassis bracket in at the top just like OE, along with a strut bar between the two sides seemed more prudent over a pound or two.
I bought the bolt-on aluminum bearing carrier with 5/8” FK bearing from DifTech for about $50 each. They use them on their rear Nissan Z car shock mounts. However, the bearing is not fully flush. The mounting plate has to be machined for the bearing OD counterbore to fit in flush with and then the proper centerhole. I had four extra sets of top plates made in 3/16” thick T304 stainless. This requires 308, 309, or 310 wire/weld rod when welding it to the steel top tube. Still debating whether to build more mounts than I need. Which I have several sets of used OE mounts that can be converted.
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12-27-2019, 11:04 AM
