S4Gunn's Tbird Front Suspension Options DIY
Here are your options if you want stiffer front shocks to match the Bilstein rears you purchased based on this thread:
Cobra Bilstein Rear Shock Info
This is based on my research and experimenting in Nov-Dec 2016 for a car I use for track racing (road course - not drag). NOTE: I use the terms struts/shocks interchangably. Some nerds will state that our car uses shocks for both the front and rear but often you will see the fronts advertised as Struts and the rears advertised as shocks. Whatever.
S4Gunn's track suspension rebuild log
Bilstein racing shocks - Front Shock Custom Design
So I wanted coil overs in the front...
1) Decide which insert you want from the list below
2) Cut down two front shocks.
3) Assemble the shock assembly with the insert. You may need to modify the shock body OR (easier) the insert.
4) Fabricate/Modify the shock top mount as needed
4) Assemble the whole front shock as if it was an OEM replacement
Easiest Option - Buy Tokico Illumina 2s #EU3869 and set to firm: $150/ea as of 11/2016 or Tokico Blues #TOHU3689
* Simple installation
* Likely have a similar amount of hydraulic fluid inside compared to a stock shock so if you are doing endurance racing, you'll have more fluid to heat up before seals start breaking down.
* Stiffest direct fit but not that stiff. See these comments: "Softer than my stock SC shocks after 60K mi"
tokico illumina's for sc
"a little stiffer than stock on FIRM setting"
* I also found comments that they blew fairly quickly (<60K mi) but this could have been a bad batch
* If you don't have ARC on your car (the electronically controlled suspension system), you will need to set them to FIRM and then add RTV/Hotglue/whatever to the top to prevent them from switching modes while you drive.
DAMPENER OPTION 1: Bilstein Inserts for Mitsubishi 3000GT - Bilstein #34-050224: ~$132 price matched
DIY Here: Proven by Saturn5/MaddMartigan: So I wanted coil overs in the front...
- 36mm diameter: 1.41" (should drop in)
- Top Nut: (holds spring retainer plate): M14x1.5 nut
- Bottom Nut (to Shock Assembly): M10x1.0 lock nut
- Amount of 5/8" diameter shaft above flange to retain dust guard: 40mm (2cm threaded, 2cm unthreaded)
- Weight of tbird front very similar to 3000GT.
- Good feedback from a guy with an S14 that autocrosses and has already blown several KONI inserts up multiple times already: Nissan Road Racing Forums - View Single Post - Jason Merritt's 2014 Street Mod Build...
- Much beefier shaft and larger volume than the circle track shocks below. This was designed as an insert.
- Stiffer than the circle track shocks. I'm not a super heavy guy @ +/- 150LBs but i really have to lean into it to get it to compress.
- Monotube design. More fluid capacity and better for racecar https://www.tein.co.jp/e/special/ni_toryu/
- Simpler installation into cut down strut assembly (bolts through hole you will drill in the bottom vs needing a horizontal bolt to be placed/drilled).
- Price is $50 more than the circle track Bilsteins but you get a significantly beefier shock and in my unscientific method (my weight on the shock vs. a shock dyno), the Bilstein inserts are a TON stiffer.
- Will likely require that you enlarge the ID of the cut down strut assembly OR press fit the insert in). The bottom-most section is only 1.717" in diameter (43.6118mm) but it flares out about 2.5" from the base. The challenge is that the ID of my cut down shock (a Monroe Sensatrac) is 1.787" or 45.39mm. This is a delta of 0.482mm or .019" you need to make up by shoving the bilstein down into the shock, putting the bilstein insert into a lathe, or reaming the shock out. All of this is discussed below.
- REQUIRES an modified spring retainer plate with an enlarged opening (5/8" hole vs 0.5" hole in stock spring retainer plate). See below for suggestions.
DAMPENER OPTION 2: Bilstein "circle track" shocks as inserts - #S7G-5555 aka F4-BE3-C239-H0: ~$80/ea or $158/pair
DIY Here: Bilstein racing shocks - Front Shock Custom Design
- 36mm diameter, 17.25" extended (assuming with the eyebolt you will remove), 11.75" collapsed
- Does NOT need a modified shock top mount (shaft is narrow enough to fit in stock shock top mount
- Challenge: Need to bolt through body of strut assembly. While the spring is holding most of the weight, the bolt going through the cut strut assembly is taking all the force of the dampener) so use a Grade 8. I went with a 1/2"-13 x 2.5" long.
- Slides in (doesn't need press fitting as interior of stock strut assembly is 1.79"
- Proven by tbirdtess: Bilstein racing shocks - Front Shock Custom Design
- POST TEST UPDATE: Unlike what Paul/tbirdtess suggested, the Bilstein S6G-5555 (#F4-BE3-A213-M6) are IMO too short to use even with a lowered car. I purchased these shocks and found that in order to make them work, I would have to place the bolt ABOVE the bottom most bracket (that mounts the strut to the LCA) instead of 1/2" below the top of the bracket. This would mean that the horizontal 1/2" bolt would only be supported by the thickness of the cut-down strut body vs the thickness of the cut-down strut body AND the brackets.
- Nut Removal: After removing the top eye-bolt, I also noticed that removing the nut below the top eye-bolt will require you to hit the nut while holding the shaft with a sheet of rubber or something else non-marring. I can confirm though that the shaft diameter will fit through a stock strut assembly (once this nut is removed).
* Cheapest "race" shock. These things are impressively stiff.
* Bilsteins have great support in the US. Can be revalved/rebuilt by third parties. Bilstein themselves will do it but the cost is greater than just buying a new replacement ($95/ea - Service
* Compared to the insert route, this will be MUCH easier to fabricate.
* The body of the shock is tiny so I'm personally concerned about overheating the fluid in my application (endurance racing). Paul races on dirt w/o any issues (bumpier so will generate much more heat) but IIRC, races are measured in minutes vs. hours.
DAMPENER OPTION 3: KONI inserts
- Double adjustable (Rebound on top, compression on bottom) 8611-1259RACE - $340/pair
- Single adjustable (rebound on top) KONI 8610-1437RACE - $240/pair
- 1.71" diameter (may need to press fit).
- UNKNOWN: not sure if insert will be needed to place insert at right height
- Rebuildable. Twin tube hydraulic (not necessarily as good as the monotube bilsteins)
- Adjustable (you will need a bigger hole on bottom vs. the Bilsteins to access the compression adjustment)
- CONCERN: The S14 autocrosser mentioned above blew out 8611-1257RACE (same as 1259RACE inserts but with a slightly shorter stroke) and this drove him to the Bilsteins.
DAMPENER OPTION 4: QA1 Coil Overs
- Buy and install
- Favorable review
- Crazy expensive.. esp considering that the shocks themselves are only $260/pair. FWIW, the premium you are paying covers the tbird specific brackets + this retailer's R&D.
- Springs NOT included with this setup but 650LB QA1 springs were ~$30 at Jegs when on sale
- This is PURE speculation but I suspect you might be able to piece this kit together yourself but you'll have to fabricate your own brackets. A stock strut might be the right donor for the bottom mount but you will need to fabricate your own top mount
Reference: Front Spring Options
Most people looking to fabricate their front dampeners probably already have aftermarket springs on their tbird. Just in case you haven't picked one out yet or are looking for something stiffer, here are the options I've found.
The classic lowering springs article on TCCOA: Thunderbird Lowering Springs
Besides the SC springs, Eibach, Suspension Techniques, Tokico, JAMEX, here are two more options to consider:
* Sprint Springs #2200: 1.5" drop but ???? spring rate. Maddmartigan uses them.
* QA1 Springs QA1-650 (10" long, 650LB-IN linear springs): stupid cheap at $28.85 on sale @ JEGS
Also available in 450LB and 550LB variants but at 2x more each
QA1 10-650: 10" Powdercoated Coil Spring Rate: 650 lbs | JEGS
MY CHOICE: Bilstein inserts
* I originally ordered the Bilstein circle track shocks but was surprised a bit at how small they were compared to the OE shock. My concern is that for endurance racing, we would cook the hydraulic oil (get it hotter than spec) which would cause the seals to fail.
* Since I also ordered the slightly shorter shock (S6G-5555) and realized that it wasn't going to be ideal for my needs and would need to be returned, I debated about what I should buy (S7G-5555, Bilstein inserts, or Tokicos).
* I ultimately decided on inserts for availability reasons and because quite a few people coming from SC shocks weren't happy with the Tokicos. At this point, no SC shock is available that ISN'T beat to hell (100K mi).
TIPS: How to cut down an existing strut assembly for insert installation
- The key here is to start with as blown a front shock as you can find. This will minimize the spewage under pressure.
- Drill a small hole (take your smallest bit) at the center of bottom of the shock assembly since you are going to need to drill an insert mount hole at that point anyway.
- Contents may be under pressure (esp if it's not completely blown). I found it was easiest to do this by using a hand drill and doing this within a dry cleaning bag (or any other large plastic bag) as this will catch any side spraying. Just in case though, keep you mouth closed and the hole aimed in a direction where it won't spray too much stuff in your garage. Do NOT do this in your living room even if you are a bachelor as the oil is kinda stinky (not gear oil stinky but still stinky).
- A rag in the plastic bag is also handy to mop up any spray.
- Once the drain hole is made, drain the shock completely. I found pumping the shaft helps as well as leaving it to dribble out into a rag in a cup overnight.
- Once completely drained, cut the top off and remove the guts. You don't need to be accurate here but I would aim for ~3/4" below the lip. Keep in mind that you will likely need to cut it down again as you don't want the shock body to be higher than the body of the bilstein insert as that could potentially limit travel).
CHALLENGE: make the Bilstein insert fit
There seems to be a ton of variance on how the OE/OEM shocks were made so your particular experience may be slightly different. See this pic of how two shock bodies have substantially different body thicknesses. The one on the left is a Monroe Sensatrac and the one on the right is an Ford OE shock from a SuperCoupe. Go figure.
- MaddMartigan used a pipe cutter and found he had to press fit his inserts. This could be due to the pressure of the pipe cutter taking the body out of round OR it could be the ID of the shock housing (more likely).
- In the 4 shocks I cut down, I used both a bandsaw and an angle grinder. Both worked equally well and if you cut just the outer body, the guts can all come out with the shaft.
- My goal was to make the bilstein servicable without cutting off the shock and having to redo this work so I set about looking for the right combination of tools to allow the Bilstein insert to drop in.
- Drill any additional holes as needed (across the bottom bracket if using the Bilstein circle track shocks, on the bottom if using inserts).
- Your sacrificial shock assemblies may be different but I found that the Monroe Sensatracs were just a hair (0.019") too small for the Bilstein inserts to drop right in.
There seems to be a good deal of variance here in how the original shocks were built so depending on what issues you encounter, you may need one/all of these techniques to get your Bilsteins to drop in:
1) Reaming the inside of the shock assembly out 0.019". I found this method to be ineffective as while it caused some rubbing, it didn't really cut much metal.
2) Use a Lathe to reduce the oD of the bilstein insert: it was a ton easier to put the bilstein insert itself on a lathe and mill it down by 0.019". You are in effect making the upper half of the Bilstein insert a similar diameter as the lower 2.5" section. This took <15 min so even if you are paying a machine shop retail pricing, it shouldn't cost too much. Finally, it should be noted that the now thinner Bilstein body is still a good deal thicker than the stock shock assembly so you aren't sacrificing strength of the body here. Since the stock bilstein insert is narrower at the bottom than the top and they probably didn't machine the tube out of billet, it's very likely that the Bilstein body started out as one thicker tube and was cut down thinner at the bottom end.
3) Press it in (this is what MaddMartigan did).
CHALLENGE: Bolting the Bilstein inserts to the donor shock assembly
On both the SC OEM shock and the (3) Monroe shocks I cut down, I found that the bottom of the shock was formed by a cap that is stuck inside the shock body and then crimped down. The result is that the ID inside is more like 0.05" smaller than the OD of the shock and prevents the bottom mounting thread from sticking through the mount hole.
- MaddMartigan encountered a similar issue and his solution was to press the bottom of the donor shock to be flat using a hydraulic press.
- My ultimate solution for the second shock was a "nut sleeve" -- basically a bolt with the threads on the inside of the shaft vs outside. Since I couldn't find any in the US (even online) in M10x1.0, I decided to make my own and it took surprisingly less time on a lathe than expected. NOTE: I did find some "union couplers" for european brake lines but i'm not 100% sure that the M10x1.0 threading is the same for flare fittings as what I'm using. There are both brass and steel variants but my machinest friend suggested to avoid the brass fittings as the threading might not be strong enough). The length is also questionable so I skipped them. https://www.amazon.com/AGS-Steel-Bra.../dp/B00U1MWFI2
- A more detailed step-by-step instruction list on how to do this on a lathe can be found in this post: S4Gunn's track suspension rebuild log
- Unverified suggestion: for those of you without access to a lathe and are too cheap to pay someone to make one of these for you fairly quickly, you might be able to build one out of an existing M14 or M16 bolt and trying to drill through the center yourself before hand-tapping it. I would try to use one of the softer bolts (Class 8.8 or Stainless vs Class 10.9 or 12.9 - https://www.boltdepot.com/fastener-i...ade-chart.aspx
) as drilling through hardened steel doesn't seem like fun. Here's a DIY that suggests how to do so with a decent drill press (basically using it as a mini-lathe): http://vik-olliver.blogspot.com/2010...wn-middle.html
CHALLENGE: Dust Cover
- Dust Cover: The shiny silver dust cover seemed to act like a way to prevent gunk that might attach to the central shaft from entering the Bilstein body. The problem is that the dust cover's OD is slightly larger than the OD of the shock assembly by maybe 1/8". I went all over my local ACE HW store and couldn't find an appropriate rubber gasket. I ended up using some rubber from an semi truck inner tube (like the ones you float down the river in).
1) Cut up a 1" wide strip of rubber material the length of the circumference of the shock assembly and super glue it to the top of the cut shock.
2) After the glue dries, drop in the Bilstein insert and bolt it to the bottom of the shock assembly.
3) Drop the dust cover down and with a little force install the cover snuggly. It's not going to ride up the shaft under compression.
4) Finally, take a razor and cut off any excess rubber visible from beneath the dust cover.
5) Once you have the Spring retainer plate put together(see below), just assemble and install.