Rear Air Shock Installation to Improve Flex

[Mr.510]

Yesterday I installed Gabriel HiJackers part number 49218 air shocks intended for the rear of a Chevy pickup in the rear of my '88 Pathfinder. While I was at it I did a whole lot of measuring and taking pictures so I thought I'd share the process and results. This might be a little long? No, this is going to be very long!

 

Background: My Pathy is an '88 SE-V6 with the Offroad package. 4.62 gears, LSD, rear disks, etc. One of my front torsion bars completely collapsed so I installed the slightly stiffer bars from a four door. I'm running it with about 1/2" between the droop stop and upper A-arm so it's not lifted, but at the upper end of factory spec. It's had mystery stock-replacement aftermarket shocks since I got it and the rears were about used up. I've been running 33-10.5-15 BFG All Terrain TA KOs on Lego wheels for a few years. When my Pathy is completely empty it sits level when measured at the top of the wheel arches. But it's never empty! I carry a lot of gear off road and the rear sags about an inch when we're 'trail ready'. I also put several hundred pounds of stuff in the back on a regular basis and that makes it sag a bunch.

 

Air bags: I considered running air bags in place of the rear bump stops in addition to my stock coils. They would be ideal except they are quite prone to damage offroad, especially in the forests of the NW where I wheel. Sticks, branches, and tree roots tend to skewer air bags rather easily. If I lived in Moab I might have gone with air bags. The air bags that fit inside the spring are better protected but don't actually increase ride height much, if at all. They function by keeping the existing coils from being able to compress. This increases spring rate massively thereby upping the load-carrying capacity. Unfortunately everything I've read says they make the truck ride like a buckboard wagon when pumped up enough to do their job. Since they only increase spring rate they could not be used to force articulation and cross linking would have little or no effect.

 

Air shocks: I decided that rather than installing cut-down JGC or aftermarket rear springs I would try air shocks. Remember that I'm not really after lift here, I like to keep my trucks as low as possible with big tires stuffed in the fender wells. After reading this article about cross linked air shocks to improve articulation in the front of an IFS Toyota I decided the same principles would help to keep the weight evenly distributed between the rear tires of my Pathfinder while it flexes. I thought it might be useful if I could manually force articulation and/or reduce the body roll angle in severe side hill situations as well. I also like the way my Pathy handles on tarmac and really didn't want to screw that up too much, if at all.

 

Cross linking: Cross linked is how air shock manufacturers assume you will install their product. This is where the air lines from both shocks are hooked together with a 'T'. In all the air shock kits I've seen this 'T' also contains the Schrader valve used for inflation. There is an upside and a downside to cross linked air shocks. Both air chambers are sharing one volume of air so as you compress one shock the other tries to extend. The upside is that offroad the further you compress the suspension on one side the more downward force is applied to the other. Another way to think of it is that whatever percentage of vehicle weight is carried by the shocks will be equally distributed between the rear tires. Now the downside. The more weight the cross linked air shocks are carrying the more body roll you will have while cornering, on or off the tarmac. Raise the rear of a truck 2" with cross linked air shocks and it will have a noticeable increase in body roll. The same goes for putting a whole bunch of weight in the back of your Pathy and pumping up the shocks. The shocks will correct the ride height but also make body roll even worse. In short, cross linked air shocks or air bags have exactly the opposite effect that anti-swaybars do!

 

Independent control: What I want is the best of both worlds. I think 90% of the time offroad I want my air shocks cross linked. Maybe 5% of the time I want them isolated but still at 'normal' operating pressure. Mild side hilling and going relatively fast on logging roads between trails are situations that come to mind. The remaining 5% of the time is when I'm in really ugly spots that are either serious side hills or really gnarly obstacles where some degree of forced articulation might be helpful. 100% of the time on tarmac I want the shocks isolated from each other so I don't have much, if any more body roll than stock.

 

Comparisons & measurements: Going into this project I wanted to know what, if anything I would really gain from my new shocks. They are much longer travel shocks than stock so I've got some flex numbers and pics that apply to any Pathy, at least if it's on stock springs. I have a slidebed tow truck and I've used it previously at events as an adjustable-angle RTI ramp. I set the bed at the standard 20 degree angle used on most RTI ramps and slid it back until the back of the bed was solidly into the ground. All of my 'standard' wheeling gear was in the Pathy except my Powertank as I forgot about it. I also aired my tires down to 15psi as this is what I run 99% of the time in the woods.

 

RTI: RTI or Ramp Travel Index is a calculated number that allows relatively fair comparison of the axle articulation or 'flex' of very different vehicles. For me it's also an easy way to accurately gauge what I've gained or lost in flex after any given mod.

 

This is my Pathy 'stock' ramping 562:

 

 

 

Edited to change 'F150' shocks to 'Chevy pickup' shocks!

Edited June 12, 2010 by Mister510

[Mr.510]

Next up I disconnected the driver's side swaybar endlink. I left it disconnected for the remainder of the pics and measurements as I will be making quick disconnects and won't be using it offroad.

 

With the rear swaybar disconnected the Pathy ramped 606:

 

 

 

 

Now that I had a 'baseline' for comparison I pulled the existing rear shocks off the Pathy and unpacked the new ones. This is what was in the box:

 

 

Notice how huge in diameter these things are!

 

 

The contents of the plastic bag:

 

 

You can see the 'T' that cross links the shocks and contains the Schrader valve I mentioned above and the hardware for installing it through a panel. There are also some line clips, a couple extra O-rings in case you loose some, and the two flexible plastic air lines with fittings on both ends. In my installation I used only the lines and the fittings on one end of them.

 

Since the shocks are intended for a Chevy pickup they don't quite drop into a Pathfinder as supplied. The upper end has a pinched tube through the eye that has to be removed. First, I cut off one end with the bandsaw but a hacksaw would do it quickly enough:

 

 

 

 

Next I pounded the tube out of the bushing with a drift and hammer:

 

 

 

The hole in the rubber bushing in the upper eyelet is too small to fit on the Pathfinder's mount and the one in the lower bushing has a sleeve through it. Once the sleeve is removed the hole in the bushing is too big for a snug fit. I pushed all the bushings out with my hydraulic press, a socket, and a drift:

 

 

A vise could be used for this if you don't have a press. Alternatively you could pound the sleeves out and carve the rubber out with a steak knife but it wouldn't be any fun! The rubber isn't just pressed into the eyelets, it's bonded to them.

 

I didn't plan ahead well enough and didn't have new shock bushings on hand. I pressed the ones out of my old shocks as they were in good shape. They come out much easier than the Chevy pickup ones as they are simply pushed into the eyes and are retained by a lip on each end. I forgot to take a pic of this step as I was busy beating myself up for not having all the right parts on hand.

 

Next I pushed the old rubber bushings into the new shocks by hand. Spraying them with WD40 makes them slip right in and then stick like they're glued. They fit like they were made for these shocks:

 

 

Edit: 'F150' to 'Chevy pickup' again.

Edited June 12, 2010 by Mister510

[Mr.510]

Next up I bolted the new shocks into the Pathy:

 

 

There wasn't much to see here and it's exceedingly difficult to take pics while installing a shock! The passenger's side shock slips right in with no issues whatsoever. The driver's side is really a tight fit as the shock slips between the spring & mount, exhaust, and Panhard rod. I found that I had to slip the upper eye on about half way and then do the same with the lower. Next slide the upper all the way on and then repeat for the lower. My exhaust clears the shock with plenty of room but this needs to be checked on each individual truck:

 

 

 

Note that the air chamber portion of the shock can be rotated relative to the upper shaft. I rotated mine so the air fittings point straight out toward the outside of the truck. This kept them the most protected from damage from both debris and the hot exhaust on the driver's side. Next up I slipped the O-rings, sleeves, and nuts off one end of the supplied air lines and connected the other ends to the shocks. I made sure to put a nice strain relief loop in the lines where they leave the shocks so there is plenty of room for them to flex as the shock angle changes with suspension travel:

 

 

 

I zip-tied the driver's side air line to a wiring harness that's just above the front of the fuel tank. I then ran it across to the passenger's side tying it every six inches or so. I routed the lines forward along the frame rail where the fuel and brake lines are:

 

 

There is a large body plug underneath the passengers seat and it was the perfect protected spot to get the lines into the interior so I cut an 'X' in it and pushed the lines through:

 

 

After they were routed I used some of Nissan's own amazing silicone gasket maker to seal around them so the floor remains waterproof:

 

 

I unsnapped the ECU cover and cut a slit in the carpet about 2" long to access the spot where the lines come through and zip tied them to the rear ECU bracket:

 

 

With the cover in place they will be well protected from damage:

 

 

Note that when I finish the control system the way I want it the lines will be routed under the carpet and up under the console further forward. For now I have to be careful not to damage them. They are tied to the seat mount base so the slider mechanism can't hit them.

 

Next up is the temporary 'control system'. I'm using a ball valve to select between cross linked and isolated. I've got a Schrader valve on each line so I can add air independently though this is only practical for testing so I don't have forced articulation in the real world yet. Here are the fittings used:

 

 

These parts are all 1/8" NPT. At the top of the pic are the Schrader valves and at the bottom are 1/8" push-to-connect fittings. These are really cool as you just push the line into them until it stops. When you want to remove it you push in on the little ring that sticks out and pull the line out.

Edited June 12, 2010 by Mister510

[Mr.510]

A little teflon tape and some wrenches and I've got a $15 setup to get me by until I can afford to do a high pressure onboard compressor, tank, and valve system to replace it:

 

 

Here it is hooked up and resting on the console. It seems to be happy on the passenger's seat while driving for now:

 

 

I guess it makes the most sense to talk about the permanent control system now. These shocks have to be pressurized with at least 25psi at all times to prevent internal damage. Their maximum operating pressure is 200psi. It takes very little volume to go from zero to 175psi with these shocks. Plugging a tire inflater onto one of the Schrader valves with the cross link valve open will do it in less than 3 seconds. What I intend to do is get a small 12 volt compressor that's capable of at least 200psi and mount it and a small tank somewhere, probably in the storage compartment that will replace my folded back seat. Then I'm going to put one of these in the dash space to the right of the steering column that's made for an emergency brake handle:

 

 

 

It's an Air Lift part number 26157 dual air pressure gauge with two paddle valves built into the panel. It has two needles in one gauge, one red and one black. It's about $70 on eBay or from various online vendors. I will make a couple of changes, one being the addition of a valve to select cross linked vs. isolated and the other being an adjustable relief valve on the 'dump' line from the valves. By adding a relief valve here it will not be possible to drop the pressure in either shock below whatever that valve is set to. In the world of CNC machine shops we call this an 'Operator Resistant' feature. It'll keep me from being stupid, letting all the air out of my shocks, and ruining them.

 

 

With the shocks inflated to their minimum of 25psi I drove up the ramp with the cross link valve closed and ramped 714:

 

 

The distance from the ground to the top of the rear fender arch in this pic is 48". Sitting on level ground it measures 34-13/16". So I now have about a foot of rear wheel droop, the rest being due to tire flex.

 

 

After measuring this I opened the valve and nothing happened. I scratched my head for a second and decided that the air shocks will not effect full flex since one shock is already fully extended and the other tire is crammed hard into the rear of it's fender opening:

 

 

I need more tire clearance! The only place they rubbed before was the tread hitting the very top of the inner fender at full flex. Now, due to longer travel and 'flex steer' I have to do some fender well massaging with my handy BFH. As the driver's side of the axle droops it moves forward. This in turn moves the passenger's side rearward. Not having the tire buried in the sheet metal may help full flex a tiny bit but it's pretty much maxed out here:

 

 

So the air shocks don't help with full flex. That makes sense to me now since I'm out of travel without needing air pressure. They might limit full flex if they were at a higher pressure but I didn't think to test this while I was set up. I'm sure they will improve flex until the point that one runs out of travel. Remember that it's not just keeping the tires touching the ground, it's keeping weight on the tires to gain traction that counts. The tricky thing is that I can't think of a simple, scientific way to test this though digital race car scales and a floor jack or forklift do come to mind. When I think of something I'll try it and post an update.

Edited June 12, 2010 by Mister510

[Mr.510]

On flat ground the back of my Pathy was about 3/4" lower than the front prior to the air shocks. At 25psi the rear gains 13/16" and looks level:

 

 

This is at 25psi and is where I'm running it on tarmac for now:

 

 

This is with 175psi as that's the maximum pressure of my shop air compressor:

 

 

Here are the results of air pressure vs. ride height. I'm going to list these by decimal rather than fraction as it's easier (at least for me) to visualize. This is in inches:

 

25psi 0.812 lift

50psi 1.250 lift

75psi 1.875 lift

100psi 2.500 lift

125psi 3.000 lift

150psi 3.500 lift

175psi 4.000 lift

200psi ????? lift

 

So 175psi will get you 4" of suspension lift and with cross linking I'll bet one tippy-flexy ride as the springs won't be carrying much weight. I have not driven with that much pressure cross linked and I don't know if I will! I do not know how quickly the air can pass from one shock to the other through the tiny supplied lines. The fact that mine run all the way to the console can't help. I'm going to test my current setup and see how it works. The hole through the existing fitting into the air chamber is about 3/16" diameter. If I feel that removing the air restriction may help I'll go up to 1/4" lines. This will require either making some custom fittings to screw onto the shock ports or TIG welding fittings onto them while the shock is under water so I don't burn the seals.

 

As far as forced articulation goes I only did one test. On flat ground if I keep 25psi in one shock and put 175psi in the other the low pressure side goes up 1-3/8" while the high pressure side goes up 3-1/8".

 

The ride of the Pathy is great with 25psi in the shocks. It is smoother under compression than before but a little harsher when rebounding. The added rebound harshness was expected as my old shocks were just about toast. Handling is the same with the shocks isolated and that makes me very happy.

 

[tmoore4512]

Heheh, good stuff. I just recently did the same thing. The link is in my profile.

 

Air shocks are awesome, aren't they!!

[GrimGreg]

So, you guys both used full size pickup shock kits, did you do that based on the overall extention length and those were the only air shock available in that size?

[tmoore4512]

I used the Chevy air shocks because I needed a longer shock to accommodate the lift in the rear...and to have extra shock for more articulation. Did some hunting in order to find the right length, and the Chevy was what I needed, and it worked like a charm.

 

Gabriel manufactures a set of air shocks designed specifically for the Pathfinder, but it was $20 more than the Chevrolet shocks, and they were factory length.

Edited June 12, 2010 by tmoore4512

[Mr.510]

So, you guys both used full size pickup shock kits, did you do that based on the overall extention length and those were the only air shock available in that size?

 

I knew I wanted to gain a whole bunch of droop travel so I searched the forum to see what shocks people use with JGC springs and 3-4" of lift and bought air shocks for that application... and I miss-posted above. (I'll fix it now!) They aren't for an F150, they are for a Fullsize Chevy pickup. D'oh! Here's the application chart from the eBay auction where I got my shocks:

 

*

CHEVROLET C1500 ALL 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 .

*

CHEVROLET C2500 ALL 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 .

*

CHEVROLET C3500 ALL 1988 1989 1990 EXCEPT WITH HEAVY DUTY STRAIGHT FRONT AXLE .

*

CHEVROLET C3500 ALL 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 .

*

CHEVROLET C3500 ALL 2001 2002 EXCEPT WITH SOLID FRONT AXLE .

*

CHEVROLET K1500 ALL 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 .

*

CHEVROLET K2500 & K3500 ALL 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 .

*

GMC C1500 ALL 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 .

*

GMC C2500 ALL 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 .

*

GMC C3500 ALL 1988 1989 1990 EXCEPT WITH HEAVY DUTY STRAIGHT AXLE .

*

GMC C3500 ALL 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 .

*

GMC C3500 ALL 2001 2002 WITH SOLID FRONT AXLE .

*

GMC K1500 ALL 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 .

*

GMC K2500 & K3500 ALL 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 .

 

I paid $49 including shipping for them. Add the $15 for a valve and fittings and I'm into this project $64. I figured it was cheap enough I'd just try it and see what happens.

[tmoore4512]

Yea, wasn't going to say anything...lol but we did the same thing...just routed em differently...SWEET

[Kittamaru]

You should totally do a write up on that!

[GrimGreg]

You should totally do a write up on that!

What do you call this post?

[ANDY]

i like it alot , thinking of doing this now but the valve stem outside and a on board air unit for when it runs out ,

[Mr.510]

You should totally do a write up on that!

 

I dunno, I'll think about it...

 

i like it alot , thinking of doing this now but the valve stem outside and a on board air unit for when it runs out ,

 

I carry a large CO2 tank (similar to the biggest Powertank) for inflating tires and such when I go wheeling but I really want a small dedicated compressor & tank installed for the air shocks when I put the permanent control system in. I may also end up with air shocks in the front. The article linked at the start of the thread is what got me started thinking about doing this. It's interesting that the guy who wrote that article kept slacking off his T-bars and increasing air pressure until he got the results he wanted with his IFS Toyota. Makes me wonder about chopping a coil off my rear springs and upping my 'standard' pressure so the shocks carry more weight all the time and force more flex offroad. If I put air shocks on the front, slack the T-bars off, and chop a coil or two out of the back I could run *really* low on the street and my Pathy would look like a stadium truck!

[tmoore4512]

I have tried the air shocks in the front...it worked, but was not for me. Got the concept from the Rancho 9000 setup...

 

It was done on a full size GMC truck, the problem was simply that the camber changed so much that the tires wore out quickly.

 

The way that I was able to achieve lift/lower with the shocks was to discard the factory lines that came with the shocks and run larger lines with a solenoid system. The truck was a field maintenance truck with a compressor mounted in the bed. The solenoid system was ran off of the compressor and controlled by a 2 way momentary switch on the dash...

 

Keeping the lines on the shocks was tough, the pressure required to lift that heavy thing up was immense, and continually popped lines.

 

Its a good idea I guess, just not sure that you will be able to fit a set in the small space our trucks have.

[ANDY]

yeah i was wondering about the fron too but might have to check out the rear first hopefully i can get shop price cause 75 is steep for my cheap arse lol but gotta figure out my timing belt tension first but i cant wait to start modding my pathy

[The_Magicians_Eye]

Great right up!

 

Ok I do want to add something though. For those reading this don't miss the fact that the air shock itself did nothing to help improve his RAMP TRAVEL INDEX (RTI). The length of the shock and the sway bar being disconnected is what did that. I know this for fact because I'm running SkyJacker 8000 Nitro shocks on my Pathy. The rear are out of a Dodge 1500 and are two inches longer than the stock Pathy rear shock. I figured out my RTI using both a ramp and a forklift. The ramp I used wasn't 20 degree so I just measures how high the tire was lifted and then did all the math. I got the same amount of lift on both the forklift and the ramp (28 inches). After doing the math my RTI came to 785 using the calculator at this link.

 

http://www.offroaders.com/info/tech-corner/rti.htm

 

And yes I know this post is old but I figured this is helpful information for those trying to maximize the amount of flex they have.

Edited May 14, 2011 by The_Magicians_Eye

[feyded]

So after reading this very informative thread, Im still having trouble on whether or not when I buy my 3" SL that comes with the RS9000XL shocks, will my rear flex be limited by the shocks that come with the lift(assuming I have a rear sway quick disconnect installed)?

 

Would love any input from someone.

[silverton]

I wheeled with Mr.510 when he had this set up, and I had a 3" suspension lift with rancho 5000's. we had very similar droop, but it just looked more drastic on his truck as it was still at stock ride height.

 

I also had my sway bar removed.

Edited May 30, 2011 by silverton

[feyded]

So the shocks that come with the 3" SL 'shouldnt' limit my flex in the rear any, or am I reading that wrong.

 

Thanks for the reply by the way.

[silverton]

So the shocks that come with the 3" SL 'shouldnt' limit my flex in the rear any, or am I reading that wrong.

 

Thanks for the reply by the way.

 

That is correct but, if your axle droops too much your springs will fall out. Mr.510 is using monstrous 1" zip ties to keep that from happening.

[Mr.510]

Great right up!

 

Ok I do want to add something though. For those reading this don't miss the fact that the air shock itself did nothing to help improve his RAMP TRAVEL INDEX (RTI). The length of the shock and the sway bar being disconnected is what did that.

 

Thank you. And you are correct, since the tire on the compressed side was already stuffed into the inner fenderwell and the droop side shock was at full extension with no pneumatics in play it did not improve the total amount of travel, which is basically what RTI measures. What it DOES do (and do very well) is put a lot more weight on the drooped side tire until the point that it leaves the ground. The weight carried by the two rear tires is much closer to even when the truck is flexing over stuff so I gain forward traction. Being able to droop a tire some massive amount looks cool in pics but does not actually improve traction unless there is weight on that tire.

 

Ask anyone that's wheeled with me how well my Pathy flexes and keeps it's tires planted to go over obstacles. There is a tremendous difference in the trucks's off road performance depending on whether the cross-linking valve is open or closed. It makes no difference at the point I'm hanging a tire in the air obviously, but until that point the improvement in grip is substantial. One neat side benefit to the way I set this up is that I can attempt an obstacle with the valve closed so there is no cross linking and my suspension works like everybody else's. Then I can back up, open the valve and see the actual difference the cross linked air shocks make on the same obstacle under the exact same conditions.

 

Since this write up I removed one of my front sway bar end links and this made a noticeable improvement in flex and traction as well. After seeing how well that worked I bought air shocks for the front and intend to do the same thing I did in the rear. The problem is the shocks are too big in diameter to fit through stock UCAs so I'm going to be making UCAs that will clear them.

 

I have gathered a bunch of pics to use for an update to this thread. My driving/wheeling impressions, load hauling capabilities, etc. As soon as I get these pics uploaded to Photobucket I'll post a substantial update. To give a quick synopsis of how I like it: This modification cost me $64 and an afternoon including all the RTI comparison measuring and pics. If it had cost $300 and a weekend I would do it again in a second, it really does work that well!

 

[silverton]

it is pretty impressive to watch Mr.510's truck wheel. it gets over stuff that I wouldn't expect it to.

[Kingman]

Yes, it's impressive. Riding with him I was amazed how the truck walked right over parts of terrain with ease that made others struggle quite a bit.

[Desert89]

Mr 510 I just wanted to say thanks for this thread post and all the pictures. You inspired me and I did this mod to my 89 Pathy last week.