Does anyone have a rear shock top mount lying around? Need some measurements.
 

Evening,

I'm almost done converting a set of Koni Yellows to coilovers and need to fab up some 2.5'' spring adapters for the rear upper perch. Car is covered in snow/salt/ice right now so it's a little cumbersome to get to the rear shock mount. I was wondering if anyone had an extra perch lying around around and could take some measurements. The part I'm making is going to be similar to the one in the image linked below but made from steel and with a longer tube on the spring side for an isolater and thrust bearing:

http://www.good-win-racing.com/miata...elrinMiata.jpg

I need to know:
A) Height of the spring locator from top tangent to the flat face
B) Diameter of the spring locator at the base where it meets the spring perch
C) Diameter of the spring locator at the top tangent

No need to be super-accurate - tape measurements would be fine...

Thanks so much!

-Chris

Update:
Had a chance to make the measurements this weekend.
A) ~0.75''
B) 3.45'' OD
C) No taper on 2005 RX-8, 0.090'' wall thickness on 3.45'' OD tube

I've elected to keep the top perch and adapt some 2.75''/3.75'' ID Lower/Upper springs. Clearance to 2.5'' springs is too tight given the damper motion inside the perch. QA1 makes tapered 2.5''/3.5'' ID springs if anyone is looking for an OTS option to use stock upper perches and 2.5'' lower perches.

Anyway,

Thanks for looking

Even though you've already changed your mind on this, I have a little bit of experience to offer. I made perches like the ones in the good-win racing link except that they captured the spring on the OD at the top to give more clearance (obviously this can be trouble if you change spring rate drastically). The perches never rubbed but the springs themselves would just rub the shock body when driving over speed bumps and the like. I ended up with patches of paint missing on my rear shocks but it was pretty minor. With your plan to have a longer tube to capture the spring, I don't think you'd have clearance though. You can see the perches a little bit in this picture as well as where I shot the shocks with some black paint to cover the bare metal after a while.

https://lh6.googleusercontent.com/-B...4/DSC_0663.JPG

Kenneth, thanks for the insight. I went ahead and adapted the existing springs I had because they were the right length, rate (tested), and had generous clearance to the damper. 2.5'' springs in the front were fine because the perch is mounted coaxial with the damper rod rather than flat with the chassis. I also went with welded perches instead of snap rings because I wasn't comfortable with the groove depth and unknown shock body material strength. The 0.032'' grooves should be okay with about 1500lbf yield in shear if the shock bodies are mild steel (40ksi). I also went up to 10wt fluid in hopes to get a little more compression damping. Anyway, I'm pretty happy with how everything came together and nothing has broken in the first two days of testing on Michigan roads.

For anyone wondering about setup or cost:

Koni Yellows: $520
Ebay coilover sleeves: $47
Eibach front springs (400 lb/in, used): $60
Road magnet rear springs (330 lb/in): ~$110
QA1 2.5'' thrust bearings: $60
Perch material: ~$20
Paint: ~$10
Maxima 10wt shock fluid 1500ml: $20

Total: ~$850

You can use QA1 3.5-2.5'' tapered springs on the rear and avoid having to make the lower rear perch adapters.

1st and 2nd Generation Pro Coil Springs | Pro Coil Springs | QA1

Rates higher than ~400F/325R will need helpers for <~13.5'' ride heights.

It's a little too late for this to help you, but instead of welding on perches or using snap rings, I just parted the existing perches off on a lathe and then turned them down until they were round and fit inside a recess bored into the coilover sleeves (I have the same cheapie eBay ones). I set the height of the coilover sleeve by the depth of the bore. Obviously not everyone has a lathe with which to do that, but it was a good option for me because I didn't want to drain and refill the damper in order to weld to it.

https://lh5.googleusercontent.com/-k...0/IMG_1336.JPGhttps://lh4.googleusercontent.com/-3...0/IMG_1338.JPG

I hope you had the shocks re-dyno'd after taking them apart.

Yeah, I too used a lathe to cut off the old perches and clean up the OD. The sleeves we have must be slightly different because mine don't have nearly enough wall thickness to safely cut a ledge. How much shear area do you estimate is supporting the aluminum sleeve?

I did not. Do you have reason to believe that taking the shocks apart would have any effect on the damping (other than the fluid change)?

-Chris

It's the only way to confirm they are operating properly after being re-assembled. You can pinch an O-ring, maybe leaking seal, or any other type of etc. issue that you might not be aware of.

The valves and seals that control the damping (besides the reservoir/piston top seal/bushing) are all "self-contained" in the inner assembly of the twin tube design. The shock body just acts as a reservoir. So I essentially removed the working bits of the shock from a fluid reservoir and only touched the top reservoir seal (a leak would be very evident). You're right that it would be ideal to re-dyno them to characterize the fluid change and check for any mistakes in re-assembly and I would have done so if I had easy/discounted access to a dyno.

Bump. Why do you guys think some coilover setups use all of the factory bolting points (some reuse the factory hats some have their own tops on them) and some only bolt up on the bottom section on the trunk floor and not to the gold brackets up on the body? Do you think it is purely cost savings and that some just want them to fit and that is it? It seems to me that Mazda did it that way from the factory for a reason but I just wonder what you guys think.

For example these Teins (not the greatest I know) have the rear brackets to mount to the factory bolt points.
https://www.rx8club.com/attachments/...87632451_n.jpg


And as another example (also cheapies), these BC's do not use all of the mounting points in the rear.

http://image.modified.com/f/29960278...ilover_kit.jpg


Where as higher end setups like Ohlins and Motons still retain the use of the factory hats.

http://www.good-win-racing.com/miata...s_Mazda_NC.jpg

http://i7.photobucket.com/albums/y25...ps5b28c479.jpg

Yes, they have no travel compared to using the OE length top. Losing 2” - 3” has to be made up somewhere else whether in extension, compression, or both. Essentially what they are doing is taking a much shorter shock and adding an extension on the body end to make it work.

Yes. Suspension travel is not something you want to lose if you can avoid it. I argued with a few suspension shops about this when looking for a race suspension; it seems they all wanted a short rear shock. I was lucky to get a used set of properly sized Koni 2812LB shocks.