I am looking for upper shock mounting plates for my 1995 RX-7, with Penske 8300 coilovers. Those have a 10mm shaft diameter. I found a few but they are meant to be installed on smaller diameter shock shafts such as stock-size shocks.

General searching on the internet turned up 3 possibilities:

1. Apexi 256AZ02R (I think the R in the part number is rear?)
2. Cusco 422 411 A (I think there should be a number after the A but that depends on the usage? Or it might be front vs rear?)
3. Tein. Their main (Japanese) site referred me to their US site, but they didn't reply. I emailed Touge Factory seemed to be an authorized vendor, who said they didn't have any info on the Teins.
4. Stance: Touge Factory said this is their own brand and they recommended these instead of Tein. The issue is their pillowball ID is only slightly larger than the Penske shaft OD. I don't think machining a bushing of 0.08" size wall will work very well, since it would likely get mashed to nothing in fairly short order and lead to the shock rattling inside the pillowball

So looking like Apexi or Cusco are the contenders.

Does anyone have any experience with those, and may be able to help answer some questions (I sent a few emails to vendors plus contacted a couple sellers on eBay but no response yet):

- Generally speaking, these mounts seem to come with a large inner diameter pillowball, and are meant to have an insert to fit it to the shock diameter. Are those fitting available for the 10mm shock shaft I have? The Cuscos seem to have a wide selection of fittings but I am not sure which is the correct one

- There may need to be a spacer as well, with the correct ID, to space the top spring perch down a bit from the mounting plate

- The stock mounting plates on the RX-7 appear identical front to rear. So not sure why these are listed as specifically front or rear on the sites i found.

- If you ordered either of these brands, can you help with the part numbers for both fronts and rears?

- Any vendor you would recommend to buy these from?

I know this is a very specific ask but appreciate any help.

 

Another alternative is to buy these and weld them into the stock upper mounts:

https://steinjager.com/shop/10mm-bor...-Pack-J0024095

Would still likely need a spacer machined to make sure the top spring perch clears the upper mount, but i have a good local machine shop.

 

Much like you, I am also in search of a solution. I managed to come across "threaded tube inserts" on the web that could potentially be one way to make this work. It appears to just be a case of finding one with the correct length and outer diameter that is either already compatible or can be made to work with a spacer or reduced on a lathe.

 

maybe the ohlins floating top mounts work?
or have you checked VORSHLAG top mounts, idk if they have something for FD though.

 

Did more research. I think the Cusco pillow ball mounts will work best for this.
I am planning on procuring a section of 17mm hex bar stock and having it cut into sections, center drilled and tapped for the thread, and turned down on a lathe to fit within the inner diameter of the spherical bearing. I figured that the spacer that separates the upper spring perch from the pillow ball bearing can be bored out to accommodate the shaft diameter if necessary. I will need to get the part and measure it first. Can't find many dimensions on it.

 

I agree Simon, looks like Cuscos are the way forward. However, which specific part number is the question.

I emailed Nengun, and got this reply:

Your springs are 2.5" / 63.5mm ID. If you mount the top of that spring into the Cusco upper mount, maybe the 60mm version? You will have 3mm of play tho.

You would also need to get the pillow nut that works with your shock shaft ID (iirc that is 12mm? but measure it)

I am looking at 2.25" / 57.15mm ID springs but the Penske 8300s have a top spring perch so not sure how that works with a top mount that has a spring perch built into it. If that is a modular piece I am guessing I can simply leave the Cusco spring perch off, and it looks like that from the diagram I found on an eBay auction (image below). Hopefully just use the Cusco Pillpw Spacer/Collar and go. I emailed Nengun back to confirm that and will update here once I hear back.

 

The harbor freight digital calipers that I managed to pilfer from my father's garage tell me that the shock pin diameter is 12.7mm (0.500) or thereabout. I had initially been planning on using a generic 2.5" wide upper spring perch with a 14mm bore to accommodate that section of the shaft while also being kept above the approx. 16mm OD section of the rest of the shaft. I'm not sure if 1.3mm is too great a tolerance for such an application, so I will have to look further into that.

the RHDjapan website shows several available spherical bushings for use with the Cusco kit as replacements, all in different diameters. https://www.rhdjapan.com/search/?q=cusco+spherical
Identifying the thread pitch on the shaft pin has given me some trouble. I tried all of the available thread pitches offered with the upper mounts and none of them worked. Have a fractional thread gauge on the way so I can get to the bottom of it. I think I may end up having to get one of my buddies that has access to a lathe to manufacture the pillow ball nut once I am able to determine the outer diameter of the section that goes into the bearing if that makes any sense.

 

Given the load on the shock shaft threads, i wouldn't be surprised if it was 1.25mm. Or given Penske is a US brand and those shocks are a bit older now, maybe even SAE?

The folks at Lowes or Home Depot look at me funny when i bring various car parts in and attempt to screw them into the bolt finder gauge in the fastener aisle...

 

The closest metric equivalent I could find in stores was m12x1.5 and m12x1.25, which were too small for the major diameter of the thread. The next size up that was available was an m14, which was too large. 1/2-20 wouldn't thread, so I think I have the correct diameter, I measured 18 threads per inch, so I think it may be a 1/2-18. It's just that none of the hardware stores I went to seemed to have it. Once I confirm it, I should be able to find a tap for it. We will see!

Seeing the reactions of store employees and other patrons when I lug vehicle parts into hardware stores is one my many hobbies!

 

I always get nervous that they have me on camera pulling nuts and bolts out of my pocket to measure and then putting them back in pocket, and will tackle me when i attempt to leave the store and cavity search me

 

Wouldn't like your chances! Even here, hex comes in imperial, so you'd still have to do an extra operation and set-up....assuming no fancy lathe. I wouldn't be using unplated carbon steel either unless you like a near permanent assembly if it gets wet very often, 303 ss is a good material for shoulder bushes.

​​​​​​​With 18tpi, almost certainly 9/16 UNF.

 

I think you're spot on with respect to the diameter and pitch. Don't know how I missed that! I was able to find a thread data sheet on a machining resource website and the measurements displayed are very close to what I recorded. It also suggested that the metric equivalent was m14x1.5, which may mean that no machining will be required as there are already commercially available pillow ball nuts from Cusco. In any case, what little knowledge of metallurgy I have came from perusing this forum, so I was planning on avoiding the use of carbon steel and using 304 stainless in its place. In your experience, are there any other characteristics that 303 has that would make it better suited for an application like this?

 

303 is free machining, easier to drill, tap, turn generally although I suppose a quantity of 4-off won't kill too much tooling.

 

I was able to use the thread gauge on the damper shaft today. Turns out I should have paid a bit more attention when they were teaching me how to count as a young child. I'm actually working with 20 threads per inch which suggests that the closes metric callout is M14x1.25, which is consistent with my measurements of the shaft thread major diameter.

 

I would give Shaftworks USA a call. Jonathan Lugod is the owner and his company deals in high performance racing suspensions. Jonathan is an accoplished racer and he won the SCCA 2022 Solo Nationals in the ASP class RX-7.

I picked up my Penskes Racing Shocks 8300 from him. If you only need the upper shock mounting plate or "top hat" only for the 8300. He can definitely get one for you.

 

Thanks James, will give him a ring!

 

My apologies for the delayed response, sir. Unfortunately, my car does not offer a viable solution or insight since it uses NLA Tripoint (monoball) Upper Bearing Hats. A couple of decades ago, when I installed the Penske's, that was the lone if excellent solution.

 

No worries!

I think Guy contacted Pro Parts (bought part of Tri-Point's business) just in case they would do one-offs.

 

@MilesBFree Just curious, how has your search panned out? were you successful in having Pro Parts make you a set, or were you able to procure some from shaftworks? I'm still dragging my feet with my suspension refresh and was wondering if you had made any developments in that time.

 

Hi @SETaylor, I ended up getting the Cusco ones from Nengun in Japan. Guy turned some bushings and I am going to put a jam nut on, instead of using the combination bushing nuts Cusco provides. I think either way would work fine.

Shaftworks said they could make the hats but I would need to have the bushings made since they only had 12mm ones

ProParts told Guy they aren't making those any longer

 

I'm having a set of Penske 8300's built as we speak, and I am re-using the CUSCO uppers from my JRZ setup. I'd double check the thread, I believe it's a M12x1.25, but CUSCO makes a shim nut for it that spaces the gap to the 18mm ID bearing that's in them. Or you could look for some shoulder spacers that fit. Other option might be Ohlins top mounts, I believe @SakeBomb Garage sells them separately and they may have the same size shafts.

NOTE: When I originally bought the CUSCOs, the spacer nut was the right thread/spacer diameter, but the actual hex nut part on the top was so large it actually interfered with the hole in the sheet metal of the shock tower. I ordered a different one from CUSCO with same thread but smaller hex.

 

We have 10 and 12mm shaft bearing spacers, so we should be able to accommodate either shaft size.

We also have a 2 and 3 way Ohlins remote can solution coming very soon for those looking for an amazing race setup coming very soon

 

The 8300s are 10mm.

iirc the 8100s may have been 12mm? (but don't quote me on that.)

The bushing Guy made is on the shaft; the Cusco combo bushing and nut combo is above it. I think either would work fine but trust Guy's expertise so went with his recommendation.

 

If anyone wants the 4 Cusco bushing nuts let me know. Would be willing to give away for free but you cover the shipping. I wouldn't object if you threw $10 at me for the effort but not required :-)

 

Here is an interesting piece of info: the bolt pattern of the front and rear plates are different.

When I took the stock ones off the car they visually look identical.

When I ordered the Cusco plates from Nengun, they showed two different part numbers so I went with what that even though I thought they were the same. When they arrived, I was too excited unboxing everything that I didn't pay attention to which was which and lost track of the boxes / part numbers so went out to the car and test fit them and discovered the rear plates (ones with holes) won't fit on the front. You learn something new every day