How To/Step-By-Step - Cosmo Coilovers with P30 Bilsteins

[mr_han_solo]

October 2021 Edit: I was notified that the image links are broken. Unfortunately, I am not familiar with how to replace the images so I redid the writeup as a PDF complete with the images. That PDF can be downloaded HERE.

 

 

Here is a how to/step-by-step guide on changing your S30 struts to P30-0032 (34-184530) Bilstein Sport Struts with Cosmo Racing Coilovers.

 

*DISCLAMER*

 

There are tons of better, tried and true, and working coil-over setups out there. I recommend anyone considering this to look into those setups as well and make your own decision. I got a REALLY good deal on the Cosmos so I wanted to do everything I could to make them work. They are "Cheap" (price point wise) and some will argue that they are the quality that the other brands are. That is a good point, as cheap and quality usually don't go hand in hand. I did read some other message board posts about Cosmos (BMW, VW's) and the people that tried them seemed to like them. There have been some people that put them on their Datsun's and they seemed happy as well. One thing that I can comment on is Cosmos technical support. I consulted them a lot over the past few days and they were very helpful all along the way. When I asked about cutting a piece out or removing the top hats they forwarded my messages to their technical department and I received an answer to every one of my questions.  No matter what method setup you choose, make sure you read reviews and ask plenty of questions. The Datsun community is great and always helpful.

 

Background: Earlier this Summer (2014) I wanted to upgrade the stock suspension (Springs/Struts) on my 1973 240z. I first looked into coil-over kits. there are tried an true kits made for racing and these have excellent reviews. I actually got a really, really good deal on the Cosmo Racing Single Spring Heavy Duty coil-over kit. This kit is $220 from Cosmo's online store, or eBay. Cosmo Actually sells several different kits, including a dual spring heavy duty, a dual spring racing, a single spring racing and the single spring heavy duty, which is what I have. This how to is specifically for the single spring setups, although the double springs work the exact same way. Later in this guide I will make a note of the difference between the single and double spring setup.

 

After I received the Cosmos, I needed to find a suitable strut I made the list below (was originally a chart), to try to figure out the different options and their prices:

 

Tokico Illumia $647

Tokico HP $400

Illumia Front/HP Rear $535

Koni Classics $680
Bilstein  $556
KYB $228

 

At the same time I also made a post on here inquiring about finding the correct strut. Some very helpful members helped steer me in the right direction. johnc, Leon, logr, and jhm. It was at this point that I found out that the Cosmo Coilovers were too stiff for anything but the Bilstein Struts. The Tokico's, KYB's and every other option would eventually blow out. I was leaning toward the Bilsteins as well because of their price point (midrange) and some people recommend them as much as the Koni's for autocross/performance means. The Bilsteins have a larger diameter rod than the Koni's or Tokico's. The shiny rod in the Bilsteins is actually the shock body, the Bilsteins are inverted shocks. You will not need a bump stop with the Bilstiens as they have an internal bump-stop. *ALSO* The 240z uses a smaller strut tube than the 260z and 280z. The correct gland nut for the 240z strut tube is Bilstein Part # B4-B30-U232B1. If you have a 260z or 280z (or the larger tubes on your 240z then the correct Bilstein gland but is Part # B4-B30-U232A1

 

*IMPORTANT* If you plan to lower 1" more than stock the Bilsteins will need to be re-valved. Someone in a thread somewhere, (sorry, can't find the source) stated they they should be re-valved anyways. I did not re-valve mine, and I know some other people that have done the swap did not go the re-valve route either. I couldn't find the price, but If I remember correctly re-valving was somewhere around $70 a strut. One poster stated that his re-valve was 300/100.

 

At this point I did a search to see if anyone else had done the swap and provided a write up. I found this thread, printed if off and used it as a guide and now as a template for this how to. Full credit goes to thehelix112 for his original guide.

 

What's Needed:

 

-Cosmo Coilovers

-4x P30-0032 (34-184530) Bilstein Sport Struts

-12x 3/4" washers. (These will be used as spacers)

- 4x Gland Nut B4-B30-U232B1 for 240z, OR 4x Gland Nut B4-B30-U232A1 for 260/280z or larger strut tubes.

-  1ft. of 1.5 x .095 tube or a one ton truck lug nut, or nut of equivalent size (will also be used for a spacer)

 

Tools:

 

- General toolkit with appropriate spanners, sockets, drives and ratchets.
- Angle grinder with cutting and grinding discs
- 9/16" drill bit
- M14x1.5 tap (optional, I didn't use it but the previous guide did and I will include the info in this guide in-case anyone wants to.)
- At least a 1-3/8" step bit. A 1-1/2" step bit, hole saw, mill, or die grinder with patience.

 

 

How to:

 

The Cosmo box. 4 Springs (one is missing because I had it out for this guide) and all the parts you will need. You also get a 5mm allen wrench which will be put to good use.

 

The spring cover with its "Top Hat" installed.

 

 

Here you can see that the "Top Hat" is held on by two 5mm Allen head screws. These need to be removed and the top hats need to go back in the box. The reason is because the Bilsteins rod is larger than the hole through the spring cover and the top hat.

 

"Top Hat" removed.

 

Bilstein Strut and Gland Nut

 

 

Remove the Strut Make sure you loosen, but do not remove(!) the top damper nut while the assembly is in the car as its much easier to hold.

Remove the top damper nut. The stock assembly is preloaded so it explodes as the nut comes loose. So don't be sitting there looking directly down at it. Better yet go to your local auto parts store and rent/borrow a spring compressor and take it off that way. Coil springs are DANGEROUS!
 

Using Channellocks, or in my case a punch and a hammer undo the damper gland nut and remove the existing insert/original body. Don't worry about damaging the original gland nut unless you plan to put stock style struts back in it in the future.

 

At this point you should go ahead and cut your spacer tube. (Unless you are using the lug nut or equivalent. If you are doing that, then skip this section). You have to do this because the Bilstein strut is shorter than the stock strut.

\\

 

In Helix112's original guide he added a top and drilled a couple of holes in the spacer the same diameter/spacing as the holes in the bottom of the strut; and put some small dowels between the two to keep the strut from wobbling or side loading during cornering. I didn't really see this as a problem as the 240z is a pretty good fit (pretty much like stock), but It may be something to consider with the 260/280z tubes. (Photo credit to thehelix112)

 

The best way I found to make a spacer is to put your gland nut onto your strut and stop the strut into the tube and tighten the nut. The gland nut has a rubber seal that will keep the strut from sliding down into the tube. Once the nut is tightened take a sharpie or equivalent and make a bark where the but meets the strut. Then push the strut into the body. When the strut bottoms out make a second mark. Remove the nut and take the strut out of the tube. The difference between the two marks is the size of the tube. My marks can be seen in the picture below:

 

 

After you get the spacer cut go ahead and drop it into the tube, followed by your strut and gland nut. Go ahead and tighten your gland nut down.

*NOTE* From everything I read you should have one or two threads showing on your gland nut once it's tight. Not sure why this matters, but I remembered reading it and I wanted to make sure that was one point I followed.

 

I then modified my spring tower (metal threaded piece that the spring sits on) and top plate to fit over the Bilstein rod.

I originally did this with a 1-3/8" step bit as you can see below:

 

Someone then pointed out that 1-3/8" was indeed too narrow for the Bilstein. The threaded piece does not need contact the chrome rod of the Bisltein. A typical coil over spring setup has twist and bending loads in the spring which cause the spring (and seat) to move. You can see on the above photo where I made a mark to mill it out to 1-1/2. After talking to someone at Cosmo they stated that the entire top piece could me milled out making just a hollow tube, so if you wanted to cut it larger, you could.

 

I milled the top plate out to 1-1/2" as well. I wouldn't go any larger than that because the top plate will contact the bearing when compressed. If you mill it out larger than 1-1/2" you will have minimal contact area with the bearing.

 

Slide the spring tower over the strut until it sits on the bottom perch.

*NOTE* You can cut this lower perch down significantly. I have seen the lower perch removed and new stops welded on for the tower to rest on. You can see in the photo below I kept my lower perches intact. Cosmo does include Allen headed screws to secure your spring tower to the strut itself. Since I left my perch intact I was unable to install these set screws.

 

Slide your spring on and this is what it should look like:

 

 

Slide the top plate on and it starts looking complete.

 

At this point I had to modify the top isolator due to the fact that the threaded tops of the Bilsteins are larger then stock as well. In the original guide thehelix112 recommended drilling it out with a 13mm or 1/2" drill bit and tapping the hole with a M14x1.5 tap. He stated, "This, while perhaps not absolutely necessary, prevents the threads on the damper from being damaged by pressing against the metal in the strut-top during side loading. This helps hold the damper piston stable whilst doing up the top nut later." (Photo credit to thehelix112)

 

I didn't tap it, so just used a 9/16 bit and drilled it out.

 

At this point, there are two different ways to finish. I consulted with Cosmo on both of these methods and either one will work. Method one involved the stock top spring perch combined with the Cosmo top piece, and the second method involves the washers and spacers and the Cosmo top piece. I used the second method, but as I stated before both will work. If you are wanting to run larger than stock wheels/tires then the second method is the one you want. To go straight to the second method scroll down until you see the three bold !!!

 

Method 1:

 

Go ahead and put the stock top spring perch on-top of the Cosmo top hat. Then the stock bearing. It should look like this:

 

Now put the isolator on and tighten the nut down. Volia, finished!

 

!!!METHOD 2!!!:

Take your blue strut dust boot and cut everything off but the the top lip. Doesn't have to be pretty, because it won't be seen. Also, the boots wont fit inside the springs so they are useless otherwise.

 

Put the top lip of the boot over the strut followed by the bearing.

 

Now take three of the 3/4"washers and put them on top of the bearing. These are needed to space the isolator from the top plate. If you don't do that the isolator won't spin freely from the spring.

 

You may want to cut the top lip off of the isolator as well. This will give you even more space between the top plate and isolator itself. (Photo credit to thehelix112)

Put the isolator on and tighten the bolt. One strut down, three to go.

 

*ONE LAST NOTE*

 

As you can see from the above photo there is a 2"-2.5" space between the top of the spring and the bearing/bottom of the isolator. I contacted Cosmo and they said that this is normal. There reply was, "Yes the gap in between it is normal for the single spring coilover; once the car is on ground then you can start adjusting the height. To eliminate the gap in between the spring and top mount here we have the dual springs coilover kit. With an additional helper spring It works the same as progressive spring that the helper spring functioning only in filling the gap and once it is with weight the helper spring will be fully compressed." Someone also stated Tein and Swift both make springs in the 3.75 range. This will give you other options when it comes to rates and lengths.

 

Feel free to point out any mistakes, criticize, etc.

 

 

*DISCLAMER AGAIN*

 

There are tons of better, tried and true, and working coil-over setups out there. I recommend anyone considering this to look into those setups as well and make your own decision. I got a REALLY good deal on the Cosmos so I wanted to do everything I could to make them work. They are "Cheap" (price point wise) and some will argue that they are the quality that the other brands are. That is a good point, as cheap and quality usually don't go hand in hand. I did read some other message board posts about Cosmos (BMW, VW's) and the people that tried them seemed to like them. There have been some people that put them on their Datsun's and they seemed happy as well. One thing that I can comment on is Cosmos technical support. I consulted them a lot over the past few days and they were very helpful all along the way. When I asked about cutting a piece out or removing the top hats they forwarded my messages to their technical department and I received an answer to every one of my questions.  No matter what method setup you choose, make sure you read reviews and ask plenty of questions. The Datsun community is great and always helpful.

Edited October 16, 2021 by mr_han_solo

[seattlejester]

Good job on the write up.

 

Question, if you wouldn't mind, so the way you have it installed, are you getting any more travel? Or is the higher spring rate just allowing you to sit lower in the stock travel?

[jhm]

Ditto on the great write-up!  One advantage of leaving the stock lower spring perches intact is that if you, or a future owner, ever wants to go back to using a non-coilover setup, it's an easy swap back.

 

Now that you have coilovers, you may want to consider taking advantage of some adding some negative camber......these are the cheapest plates I've seen.  And they're actually of decent quality (I bought a set just out of curiosity).  http://www.ebay.com/itm/MK1-PillowBall-Bearing-Strut-Upper-Mount-For-Coilover-Kit-Mounts-Plates-240Z-/161203739866?pt=Motors_Car_Truck_Parts_Accessories&fits=Model%3A280Z&hash=item25887ddcda&vxp=mtr

 

Hope you enjoy your new setup.

[Z Guy KY]

So how is the ride with the Cosmo Coilovers and the Bilstein's??

 

Any further updates since you installed them in January on ride, noises, etc..

 

Thanks for the detailed write up!

 

Steve

[Z Guy KY]

Thanks again for the write up on this!

 

I installed mine several weeks ago and love it

 

Boy is it a different ride around the corners now.

 

 

- Steve

[mr_han_solo]

Thanks again for the write up on this!

 

I installed mine several weeks ago and love it

 

Boy is it a different ride around the corners now.

 

 

- Steve

 

Enjoyed doing the write up and giving back to the community.

 

I never really followed up on how the ride is, and honestly most of my driving this year has been on and off the trailer going to car shows. However, this past weekend I hit the road with it.

 

Here is my first impression, the ride is AWESOME! I was really worried that it was going to be way too stiff, like a lot of people have mentioned. However, my stock struts were busted and my car would shake like an earthquake once i got up to 65mph. With the Bilsteins and Cosmos it rides 1000x better. Honestly, I got up to 115 and the ride was perfect. I opted with the Heavy Duty springs over the full race, but hopefully someone in the future will go the race route and chime in.

 

We have a pretty good mountain road around here that was recently repaved, and I wanted to see how she would handle the turns both going up and coming down. It does handle the corners like a dream. The more confident I became, the more I wanted to push it. Still haven't figured out the limit, but these struts and springs have made a huge difference in this department as well.

 

Just wanted to give a follow up.

 

- Han