Stock rear shock mods

January 4, 2009

After being steered into a better direction by flatbed, I decided the least I could do short of buying new fox shocks was to modify mine. It's a money issue and being retired, time is not an issue. This project takes a while but I loved every bit of it especially when my riding friends said; "Your going to do what, your nuts?".

Looking at my shocks, http://good-times.webshots.com/photo/2916279060104282158irnRUN you can see that there is room for extra rod length. Also the shocks needed to be rebuildable and have better seals. The stock shock uses only an o-ring for the main rod seal. In order to add extra length, I decided to add a reservior to hold the extra oil being displaced when the shock is at full compression. The reservior also will hold the gas charge.

To lengthen the rod, I used a peice of 1" OD alloy steel bar which I machined down, ground and polished. Don't do this, you got to be a glutten for punishment and I already have that reputation sewed up. Here is the results; http://good-times.webshots.com/photo/2206975690104282158NBWBFi

From here, I needed to make the shock rebuildable. I machined a new gland to hold a good quality high pressure rod seal, a better wiper seal and doubloe o-ring seals to seal the gland itself to the shock body. You can see these parts in this picture; http://good-times.webshots.com/photo/2082941910104282158usQvba You will notice that I cut a groove into the end of the main tube to receive a snap ring which holds the gland in place (flatbeds susjestion). I originally was going to put a threaded cap on the end but I liked the snap ring better. To reinforce the end of the tube because of the cut groove, I wrapped a peice of stainless around the end and welded it in place. You can see the snap ring groove in the picture along with a shoulder a little farther in that prevents the gland from pushing further into the tube. This picture shows how it looked when assembled; http://good-times.webshots.com/photo/2125147240104282158sqZThZ.

From here I built a reservior from some aluminum tubing I had around. I wanted the reservior to have some oil in it when the shock was fully extended. While at it I thought I might as well make a polyurethane piston to seperate the gas from the oil. This was nothing more than a 1" long round peice of poly with a small lip projecting outward on an angle a both ends. The lip acts as a wiper seal. You can see the picture of the completed assembly with the reservior here; http://good-times.webshots.com/photo/2554252400104282158hkgUcl

As you can see, I am quite a bit longer then stock. I have about 9 1/2" of travel. I'm using a 500# x 12" main spring with a 350# x 8" tender. Fortunately a shop building rock crawlers near me went out of business so I found some cheap springs. I made a polyethylene seperator to go in between the springs. Yha, I know the hose is huge. There are a few reasons for this. First, I wanted at least a 1/4" line connecting the shock with reservior to minimize any dampening effect a small line might introduce. Second, I used a 4750# hose, not really knowing just how much pressure I needed to hold. And, third and most important of all, I had the hose and fittings.

The shock is pretty much being mounted to the same geometry as flatbed is using except my lower mount is about 1" farther back. However my bracket has multiple holes in it so I can move it forward or back a little. Again per flatbeds sujestion, I moved one of the valving disk from the compression side to the extension side to increase rebound dampening. I'll keep you posted.

I want to thank flatbed for sharing his vast experiance with suspension. He did not particapate in my change decisions but I gleened a lot of things from his post. I strongly sujest that you follow flatbeds lead with any suspension changes you may make. As I said before, I thrive on always going against the wind but I have fun doing it and I learn a lot.

Sorry for being so wordy. Hope everyone has a great New Year.

Lenny

flatbed · January 4, 2009

Very nice. Don't let any more oil go into you resovore than you need to, I did not notice if you have anything to protect your seal for when the shaft bottoms out with the rubber bump stop around the shock shaft. If the guy you are getting springs from has a set of 400 tenders grab them. Also you might have it, i just did not look for the collar that threads on the shock to take the tender out compresion and start working the 500s. Again great job

I've done my part, Enjoy,Jeff

flatbed · January 4, 2009

Lenny, i just went back and looked, you need the treaded collar, I will go take a picture and see if i can get jeff to post it. The collar that you made to seprate the springs needs to be about 3' taller on the top side, it needs to go up inside the tender spring. as the shock compreses it will go up and hit the treaded collar inside of the spring taking the tender out of use and making the 500 work. The way it is now you will not use the 500 untill the 350 is completley compressed.

I've done my part, Enjoy, Jeff

Kinarfi · January 4, 2009

Lenny, Flatbed, Great stuff from both of you. Lenny, your not too wordy, good info.

January 4, 2009

Lenny, i just went back and looked, you need the treaded collar, I will go take a picture and see if i can get jeff to post it. The collar that you made to seprate the springs needs to be about 3' taller on the top side, it needs to go up inside the tender spring. as the shock compreses it will go up and hit the treaded collar inside of the spring taking the tender out of use and making the 500 work. The way it is now you will not use the 500 untill the 350 is completley compressed.

I've done my part, Enjoy, Jeff

Thanks to everybody. I see that the threaded collar limits the tender to a fairly small protion of its total available compression.I don't fully understand the threaded collar. Without it, when the tender is compressed say 2", its pushing with 700#. This would then also compress the main spring to nearly 1 1/2" less it's preload. It would seem to me that as the tender compresses past 500# that the main spring would then be taking on some compression thus providing some transition from tender to main. Would it be that you are concerned with the tender being in play for too long and thus not allowing the spring rate to move into the higher 500# rate soon enough?

By the way I have added limit straps as my shocks can extend a little past the CV limit. I also am using a 1 1/2" bumper. The pic shows the short one. I'll also remove some oil from the reservior. Currently, there is about 2" of oil in the reservior when at full extension.

Lenny

flatbed · January 4, 2009

Lenny, that is a 8 1/2 " shock, I am getting over 14" of travel, so if i have 2" of compresion after ride height i an getting 4 to 5" of travel on the 350, That is quite a bit, you will do alot of driving on your susp moving 4 or 5"> when you get into a bump you want that 500 to start working right now, The 350 is taking the sharpness out of the ride. That shock is a front shock in the picture. I have probably compresed that spring combo 5" before puting the shock in the car. On the collar you will also need to have a set screw in it to keep the collar from moving, the treads on the shock have a slot from top to bottom so the set screw does not mess the treads up. On another note if you have a 350 and a 500 the 350 is going to compress untill it is almost colapsed before the 500 goes to work. That 350 is a crusing spring. a sharp bump you will be hitting the bottom of the car on the ground, that is wy you need the collar, like you say to get the 500 to get the work done.

January 4, 2009

Lenny, that is a 8 1/2 " shock, I am getting over 14" of travel, so if i have 2" of compresion after ride height i an getting 4 to 5" of travel on the 350, That is quite a bit, you will do alot of driving on your susp moving 4 or 5"> when you get into a bump you want that 500 to start working right now, The 350 is taking the sharpness out of the ride. That shock is a front shock in the picture. I have probably compresed that spring combo 5" before puting the shock in the car. On the collar you will also need to have a set screw in it to keep the collar from moving, the treads on the shock have a slot from top to bottom so the set screw does not mess the treads up. On another note if you have a 350 and a 500 the 350 is going to compress untill it is almost colapsed before the 500 goes to work. That 350 is a crusing spring. a sharp bump you will be hitting the bottom of the car on the ground, that is wy you need the collar, like you say to get the 500 to get the work done.

Thanks, I see what you want to do now. Makes sense. I am staying in the tender for too long and have bottomed a couple of times already. I'm also getting 14 1/2" of suspension now. My shock doesn't have a key slot down the threads but I'll machine one in. The slot will also serve to help scrape off any dirt that may get into the threads. I do however make sure I blow off the threads well before any adjustments are made. I have an onboard Viair 200 psi compressor with 3 gal tank so I can blow off and adjust in the field. This is fun stuff.

Lenny

flatbed · January 4, 2009

I am running 200 psi in all 4 shocks, if you can use nitrogren. It will be alot cleaner and more consistent when it gets hot. With your shock being 3" longer over all than i am you might have to change your upper rear shock mount to keep the hiems from working to much, you might be ok, just a thought. Not sure how big your res is. You want oil in it when the shock is fully extended, but you need to make sure when it is compressed all the way you have room for you nitrogen. Take your measurements while the shock is together so you can figure out how to make the slider betweeen the springs.You are getting it.

January 5, 2009

flatbed' i'm running air at about 100psi. I really haven't played with gas pressure yet but I will. Once I zero in, I'll switch to argon. Correct me if I'm wrong but I understand that argon will preform like nitrogen but it is just more expensive. I have it for my TIG. I'm not sure about raising my upper mount to allow for the aditional length. I ran all the numbers for leveraging and angle ratios and picked a suspension frequency before selecting my springs. My frequency runs from about 1.2 htz at full droop, about 1.35 at ride heigth and 1.57 at full compression. I picked these values because it is a little faster than a racing sports car and somewhat slower than an indy car, I think. Hey, I had to start somewhere. I then allowed for about a 35% of droop for ride heigth and adjusted my springs accordingly. Right now it seems that if I raise my upper mount, I will just have to adjust my springs down farther. I hope this all makes sence and i'm not just whsitleing dixie. I'm pretty good at getting myself off where I don't belong. How much off full droop do you set as your ride heigth? The slider looks pretty easy. Seeing as I only have 2" thick UHMW, I think I'll just make an additional sleeve to set on top of the existing slider then add a stop ring. This is a little like my hillclimbing. Going up the hill was always pretty basic, It was when I was flying through the air at the top that made me wonder what I got myself into.

By the way, my reserviors are 1 5/8" ID by 11" long. I delibertly made them big to help keep the gas pressure more consistant. The differance between the oil level from full droop to full bump is only about 3".

Lenny

flatbed · January 5, 2009

See you do understand what is going on. I run about 2" of droop, don't forget i lowered my diff, run those springs down, you want to use as much as that shock as you can. More oil you have to push or pull. Adding the shim on the rebound, did that help, its not letting the car buck. The springs i ran, a 8 and a 10 just fit on the shock to start the threads, i used a spring compresser and wound the nuts down. You are going to want to run 200 psi. exclent choice on the hose and fittings. With the 350s your going to have to wind them down a bit. another thing is do the math and make sure your coil is not binding before you get into the collar. You want your 500s to come in before you get spring bind on your 350's. Argon is ok

January 5, 2009

Moving the disk from compression to rebound did help a lot. It's a little hard to tell with the front not being modified yet. It almost acts as if it has just a little too much rebound yet. Possibly going to heavier oil will be enough. The rebound is good within the tender. I don't have the experience to know exactly what feel I want. So far I'm lookng for the suspension to suck up the heavy bumps but then sort of float back up. Sort of like running along at one level and then say hitting a a fairly short rise (2' or 3') to a higher plane maybe 10" higher. I probably want the suspended weight to get back to ride heigth in about 4' to 6' of travel at maybe 35mph. If it's just a bump that high, I want the unsuspended weight to get the tires back on the ground within a foot or two. Beyond that, I'm not sure what i'm looking for. I'm trying to learn as I go.

Starting to look at the front. Did you lower your front dif? It doesn't look too complicated, probably easier then the back.

Lenny

flatbed · January 5, 2009

no, i did not lower the front. You will know when you have the 500s working in the back if the shock is working. When you push the back of the car down then let go it should not spring back like before but come up smooth. You are just trying to control the spring on rebound.

January 5, 2009

Well, I cranked the springs down. I didn't extend the sleeve yet because the tender is fully collapsed not much after where the collar would stop it. I will be adding them soon. My ride droop is currently at about 2 3/4" and this I will drop down to 2" like yours. I did feel that with the tenders being this close to where they will end up anyway that I could give it a test run. Everyting now is pretty close to where it will be when tuned in.

The ride was great. You were so right. I was plush on the top side but without the wishy washy feel I had when I had the bottom shock mounts a lot closer to the arms pivot point. The ride felt stable with just a little lean in the turns but not at all excessive. When I push down on the rear and release it, it rebounded softly without bounce. 'When I jumped it, and I'm not a jumper, maybe about 12" to 15" off the ground, it landed soft without excessive compression. In other words I felt it could land the same from somewhat higher. On landing, their was no bounce, just a fairly quick but soft return to ride heigth.

At this point I feel that I need to rework the front before I can really tune the back further. I do plan on lowering my front diff. It will stick down a little but I'll protect it with a stout guard plate. I like the idea of it being lower because It will allow my center clearance to be better for clearing when I go over sharp humps plus it will help with fender clearance. I will not be able to modify the front shocks for extra travel. There just not long enough to begin with. I'll be looking for a pair of Fox 2.0 x 8.5 and more springs. Unfortunately, my wife is starting to call it a money pit. So, i guess for now I'll have to be patient, not my best quality.

In. the mean time I again want to thank flatbed for being patient with me. I'm sort of stubbern and don't get swayed easily, but when flatbed shared his concerns with what I was doing, he really made sence. I can't thank him enough. He is a good teacher, he made me think.

Lenny

Kinarfi · January 5, 2009

Lenny, love your photos, fun, neat, interesting, do you have any photos of the installation and mounting?

One question, the seal or seals where the shaft come out of the body, I thought the 'wiper' was the pressure seal and the other 'thing' was just a guide for the shaft, but is the 'guide' the pressure seal?, what are the four small holes in the guide for?

Thanks

Jeff

January 5, 2009

Lenny, love your photos, fun, neat, interesting, do you have any photos of the installation and mounting?
One question, the seal or seals where the shaft come out of the body, I thought the 'wiper' was the pressure seal and the other 'thing' was just a guide for the shaft, but is the 'guide' the pressure seal?, what are the four small holes in the guide for?

Thanks

Jeff

The part your showing is the gland, the part your calling the guide. Your correct in assuming that the gland guides and supports the shaft. However it also containes the main rod seal within it. There is a groove in the hole going through the center which encompasses the main seal. In the stock shock this main seal is nothing more than an o-ring. Having a second wiper seal turned around would be better than the o-ring. In my case I went to a much higher quality wiper and main seal. The four holes are to provide oil pressure to the front side of the gland where the wiper seal is. If you were to look at the back side of the stock wiper seal you will see rings of rupper protruding out towards the direction to the top side of the shock. The front side of the stock gland has grooves also. When these grooves mesh into the rubber rings it developes a seal between the ID of the main tube and the gland body itself. Thus oil cannot go around the outside of the gland and escape. The holes provide the back side pressure the rubber rings need to press them firmly against the tube OD and the gland. If you take the wiper and the gland and mesh them together you will see how it all works.

Lenny

Kinarfi · January 6, 2009

Thanks, I had some seals for motorcycle shocks that used the internal pressure to enhance the sealing action of the seal, I did look at my shock after asking and saw where holes came out. I appreciate your explanation.