How to Rebuild IFP Coilovers w/ Pictures! (Demonstrated on Fox/Fabtech FTS2100)

About a month ago I purchased a pair of used Fox/Fabtech FTS2100 coil-overs. Not the best coil-overs in the world, but for the price I couldn't pass them up. Anything has to be better then my original stock suspension with blocks, right? The seller claimed that his "friend who is pretty good at this stuff" rebuilt them, but when I picked them up I realized his friend really wasn't "pretty good" at this stuff. They leaked, didn't hold air, and weren't even screwed together properly. I called Fox to see what their rates would be to get a rebuild and they claimed that they sold all their stock for my particular shock to some guy in Oceanside CA. I went ahead and gave that guy a call and he wanted $300 minimum to rebuild them. That was twice what I paid for these, it didn't seem worth it. I spent about a month researching coil-over rebuilds but I couldn't find any guides that went into the detail I was looking for. So I now present to you:

How to Rebuild Coil-overs, a Guide by an Internet Stranger in his Garage!​

Disclaimer: I am not a professional! I am not responsible for shock failure. This is purely an informational tutorial. I cannot guarantee results. Wear the proper protective gear when working on things and be safe. If you think this is beyond your skill level, then do not attempt! A butchered shock rebuild can be deadly.​

Definitions​

IFP: Internal Floating Piston

CO: Coil-Over

BC: Bearing Cap

Tools/Parts​

From left to right, top to bottom: Paper Towels (this will get messy); Paint (optional); Rags; Bike Shock Pump (delicately removing IFP, can use air compressor or standard bike pump), Torque Wrench (we want those nuts properly tightened); Pliers; Small Triangular Files (fixing threads); Wrench Set (for me, 7/16, 5/8, 7/8, 18mm); Seal Pick; Socket Set (for torque wrench); Rubber Mallet; Wire Wheel (optional); Flash Light; Scrubber (optional); Tubing; Marker; Tapered Shaft Bullet (very important!); Tweezers (grabbing metal flakes); Flat Head Screwdrivers (good for picking); Hammer; Wire Brush (optional); Large Wrench (for removing bearing cap); Tape Measure; Tooth Brush (optional); Allen Key Set; Spanner Wrenches (for removing coil spring); Mas Airflow Cleaner (great for cleaning up oil/parts); Vice.


Tools I wish I had bought: IFP Tool (really makes setting the depth and removal easier); A real Tapered Shaft Bullet (I made my own, should have just bought one)

Parts Required: 2x Standard CO Rebuild (new seals, 1 kit per CO); 2qt Shock Oil; Worn or broken parts needing replacement found after tear down.

Procedure​

Prep:
P.1. Begin by determining your CO model number. This is usually stamped in the BC or written on a sticker on the shock body. For me it was stamped into the BC: FTS2100

P.2. Once you have determined the CO model go ahead and find any information you can about it. MOST IMPORTANTLY ensure it is a rebuild-able unit! Most likely after market CO's are, but just be sure to double check. I found this guide from Fox on how to rebuild my particular unit. I found this useful for things like IFP depth, Nitrogen PSI, and torque specs, all very important info.

P.3. Once you are positive you can proceed, purchase 2 basic rebuild kits with seals, one for each CO. No matter what, once you break the seals they should be replaced. They may look and feel okay to you but is possible for micro scratch/dents/cracks to form in them that will ultimately cause problems further down the road. We will purchase more parts once we open the shock, but for now, be sure to have the seals.

P.4. Once you have your parts, go ahead and remove the CO's from your truck (if required). I won't go into detail here but if you have trouble doing this I would not attempt the rebuild.

Disassembly

1. First things first, put the CO in a vice. Use a rag to create "soft jaws" to keep from scratching/damaging components.


2. Depressurize the CO. Hold down the schrader valve until it stops making noise. This is important! Not doing so could be catastrophic.

3. Remove the bushing at the bottom of the CO. This will ensure all parts can slide off the shock body. I used a hammer and pounded it out, using the vice to hold the CO. BE SURE NOT TO HIT THE SCHRADER VALVE. REMOVE IF NECESSARY. Replace this bushing if needed.




4. Remove the CO spring. Loosen the pre-load nuts(?) using the spanner wrenches. Do Not use a screwdriver and pound it. This is soft Aluminum and can damage easily. Remove the spring, pulling it from the bottom. You'll notice my spring is already off, courtesy of "the friend who is really good at this stuff".


5. Focus your attention to the top of the CO. Loosen the nut holding the mount and rubber bushings. Remove these Items. I used a wrench for the nut and a pair of pliers to hold the shaft.


Once you have this step done you should have a pile of parts similar to this:

PRO TIP: Lay out your parts in orientation and order in which they were removed (like I have done above). It will make reassembly much quicker and easier.

Your CO should look similar to this:


Now we can start getting into the innards!

6. Loosen and remove the fill screw. An Allen key made quick work of this.


Now the fun stuff!

PRO TIP: This will get messy, have paper towels or rags ready!

7. Remove the BC. This usually just unscrews. Some CO's require a special tool to remove. If this is the case you will either need to get creative or purchase the tool. I had to use a huge a$$ adjustable wrench and a pipe extension to remove mine! Thanks "friend who is pretty good at this stuff!!"


8. Go ahead and remove the BC (simply slide it off the shaft and set it to the side) but DO NOT remove the shaft quite yet. We need to drain the oil first (unless you like oil everywhere) I dumped the oil into an oil collection bucket to take to the hazard waste disposal center at some point. Be careful, the oil will try to run down the side of the CO, so be prepared with a rag to stop it. As you can see I wasn't quick enough.


9. Now pull out the shaft. It will still have some residual oil on it, so set it on a rag. You will probably drop, as I call, the smooth brown slidy thingy. Don't worry about this, your rebuild kit should have new ones. I found a little wiggling helps if it gets caught. Some CO's may have a snap ring on the inside, be sure to remove this.


10. I then removed the CO plastic spring-body protector. It was just 2 snap rings and it slid right off.


11. Now we are going to remove the IFP. Get your bike pump ready. Set up a bucket with towels in it like I have done. This thing shoots out like a rocket and the first one I did went flying across the garage, so just stand clear. (If you have the IFP tool just screw it into the IFP and wiggle it out). Connect the bike pump to the schrader valve and begin pumping, pointing the CO at the towel bucket. DO NOT EXCEED 80 PSI while doing this. That much pressure can cause serious injury and chances are if it is that stuck it is beyond repair. The IFP has a brown slidy thingy too, again don't worry if you loose this.



12. Remove the schrader valve. I just used a wrench. Pretty easy.


13. Inspect the CO tube for deep scoring or scratching. Use the flash light to get a good look. Replace if necessary. Mine had some visible scratches but I couldn't feel any with my finger nail, so I figured it was probably okay.


Optional Cleaning/Painting

14. Cleaning/Thread repair is completely up to you and optional though I would at least recommend repairing the damaged threads. Here is what I did:

14a. Locate any dents (probably from rocks) where the threads may be damaged. We are going to repair these.


14b. Using the small triangle files go ahead and file new threads into the dent. Be careful not to go deeper then the original threads. This could weaken the shock. Putting this in a lathe or finding the correct tap would be ideal. When you are done it will be hard to tell that there was even a dent here. Test the thread is good by screwing the pre-load nuts onto it. If they screw right over you are done, if not, continue to file until it does. Repeat steps 14a and 14b for any dents/damage.


14c. Cleaning! I used a mix of wire brushes, wire wheels, tooth brushes, and MAF Sensor cleaner to get it how I wanted. The difference a little elbow grease makes is unreal and will make your rebuild more professional!


14d. Painting! I decided to paint these bad boys silver. Honestly they looked good clean, but since I had them apart, why not? I just did a few coats of silver spray paint. Make sure this is fully dry or you will scratch it. Also keep chemicals away from it. Shock oil didn't seem to do anything but my cleaning products remove the paint. Paint it however you want! Try not to get paint into the tube. I used tape and paper towels to prevent this.


Okay now we can continue disassembly.

Disassembly Cont.

15. Put the shaft assembly into a vice. Remove the top nuts. I used 2 wrenches and some muscle. The "friends who is pretty good at this stuff" stripped the nuts for me. So I ordered some new ones.


16. Remove the valving and bearing assembly making sure to keep things in the order and orientation they came off in! THIS IS VERY IMPORTANT. These should just slide off.


17. Now focus on the BC and IFP. Remove all seals with the seal picker. Make sure to be careful to not scratch the soft aluminum! With the BC it is important to remember the orientation of the seals. Each one can fit in upside down, so make sure you keep track! THIS IS VERY IMPORTANT. Notice how I stacked the BC seals so i could remember the order and orientation.


Cleaning/Inspection

18. Begin cleaning and inspecting parts. If you notice large scratches, bent washers (one pictured below), fatigued parts, pitting, missing chunks, irremovable dirt/seal gunk, REPLACE THE PARTS. They are relatively inexpensive compared to replacing the entire CO. It's good insurance. I used clean paper towels and MAF Sensor cleaner on all the parts. Ensure you have no paper towel particles on your parts. This takes time but the longer you spend here, the longer you can spend in the trails.

It's hard to see, but the bend is there, and this part was replaced. Attention to detail will ensure your CO's last for years, and not months.

Purchase any parts you believe are worn out. Waiting a few days for a new part will be well worth it in the end, trust me.

Now we can start assembly!

Assembly:

Assembly is virtually the reverse order of disassembly, except with new parts!

19. Begin by clamping the shaft into the vice. Install all components in the reverse order they came out. Ensure you put in any new parts you purchased. This should be relatively easy because we kept the parts in order.


20. Torque down the 2 nuts. The first one on was tightened to 30ft/lb and the lock nut was tightened to 40ft/lb. Check with your manual to confirm your own numbers. Set the shaft assembly to the side (on a clean surface).



21. Open your rebuild kit. Ensure all seals are there. If they are not, purchase what you need. Begin re-installing seals onto the IFP and BC. It is suggested to dip the seals in shock oil during assembly to help with install. Make sure all seals go into the correct positions and have the correct orientation. Placing the seals in the center of the BC was a PITA but with a little fines they fit right in.




Okay thread is getting long so I will split this into two posts. Stay Tuned!

 

Part II, continuing where we left off!

22. We will now be inserting the BC onto the shaft assembly. This step requires the Shaft Bullet. I made one but do your self a favor and just purchase one. I originally tried this step without it but I found it is pretty much a necessity if you do not want to damage your brand new seals. Basically just slide the Shaft Bullet on the shaft and the slide the BC over that until it is on the shaft. Be sure to oil this (I poured a slight bit of oil into the BC center). make sure to double check and ensure all seals are installed on the BC before doing this.




I honestly think that is the hardest part.

23. Okay, set the shaft and BC to the side for now. Grab the CO tube and the IFP. Place the CO tube in the vice. We want to set the IFP depth. This is a VERY IMPORTANT step. For my particular shock the depth was 8.375". You measure the depth from the top of the CO tube to the top of the IFP, like the image below. The knife represents the CO tube top and the line is my target depth. I measured the distance on a piece of tube for easy depth setting.


24. Lube the IFP with shock oil and install the brown slippy thingy. Insert the entire assembly into the CO body ensuring not to pinch the blown slippy thing between the body and IFP. Once you get it in I found applying pressure directly in the center helped it slide for it would bind if I pushed on the edge. An IFP tool would be useful here too. Using a rubber mallet can help it down too. I used the mallet for fine adjusting the depth.



25. Reinstall the schrader valve into the bottom.


26. Once you have the correct depth (tripple check you have the correct depth!), and the schrader valve installed you need to fill the CO body about 2" from the lip. Just dump the oil into the top of the body.


27. Once you have filled it 2" from the top with oil we are ready to install the shaft assembly. Again, don't forget the brown slippy thingy. Hold the shaft assembly so the BC is resting against the valving components (as if the CO was fully extended). Insert this entire assembly into the oil. You will need to stroke the shaft up and down a few times to remove any air bubbles. Tapping it with a mallet can help with this. DO NOT TAP OR STROKE TOO VIOLENTLY. We do not want to shift the IFP. Keep in mind liquid doesn't compress, so if you push too fast you essentially create a hydraulic piston.


28. Once you believe there are no air bubbles and that the IFP didn't shift go ahead and top off the oil about 3/4" from the top (see above picture)

29. Making sure the top of the valving assembly is making contact with the BC (I just pulled the shaft up while doing this step) we can begin to screw the BC into the body. Oil will come out of the fill screw hole, this is good! Screw it until you reach the O-ring seal. Once you reach the seal you may use a wrench and tighten it just until the seal is no longer visible. DO NOT TORQUE IT TO SPEC QUITE YET.



30. Insert the fill screw and O-Ring seal provided. Tighten this screw to spec.


31. Now you may tighten the BC to spec. For me it was 55 ft/lb. So I just tightened it pretty snug using the wrench (I don't have a torque wrench that would work on the BC).


32. Reinstall the top washers, bushings, etc. and torque them to the proper spec.


33. Install the spring and retaining pre-load nuts for the spring. Set the amount of pre-load you desire. Tighten everything using the spanner wrenches. You may want to adjust pre-load once the CO's are on the truck, so unless you know exactly where you want them, don't spend too much time doing this.


34. Install the bottom shock bushing.

35. Refill the CO with the proper nitrogen PSI (for me it was 200psi). Most likely you will need to take them to a shop to do this. I took mine to a local offroad shop and they were kind enough to fill them for free but most shops will charge a small fee.

36. Once they are filled go ahead and install them in your car.

38. Sit back, crack open a cold one, and bask in your glory!

Thanks for looking! Hopefully someone will find this guide useful.

 

wow, I am so thankful you created this thread. Found a pair for sale and the price was right so I went for it without doing any research and of course there was very little I could find about them. Been searching TW for about an hour now and never thought I would stumble upon a write up as comprehensive as this. This is awesome man, looking forward to rebuilding mine

 

No problem! I was in the same situation as you when I bought mine so I decided I would post SOMETHING helpful about them online. Glad it's helping someone!

 

Hey man what rebuild kit did you buy for these? Called around to a few shops and they said the rebuild kits for these are discontinued. I’m sure there’s something out there that works tho, what did you use?

 

Got them from Kartek. Part # 80300057A. Here is a link:
https://www.kartek.com/parts/fox-20...build-kits-for-58-shaft-remote-reservoir.html

 

awesome, thank you!