"The shock thread" lets talk shocks...

[THUREN]

I thought I'd start a shock thread and see how it goes...



With countless questions, opinions, and feedback coming in almost every thread I thought it would be nice to try and answer some questions.



I just figured something out on some of your guy's trucks, so here goes the first issue I think I have finally solved, but maybe not, just an educated opinion I guess... .



Soooooo, I have seen COUNTLESS threads where a "thump" is fealt in the front of the truck. I am very sure I came up with the solution, assuming all your bolts are tight. .



It's the shocks, not that the shocks are bad or worn out, but that they are not up to the task, by design, handling a very heavy truck. Here's the reason and a small list of shocks that would NOT have this issue...



Bilstein, KYB monotubes, and pretty much every monotube shock is excluded as long as they have enough gas pressure, at least 150psi or so... ANY twin tube shock does not have enough, if any, pressure behind the oil to keep cavitation from happening. On a light vehicle, with lighter valving, it would not be as much of an issue as the shock piston will not create enough resistance to pull a vacuum under the oil chamber. What I think is happening with some of these shock is that with a fast enough, hard enough hit, the oil is pulling up with the piston, creating a vacuum under the shock piston causing the "thump", when the super strong vacuum is slammed shut. If you have a good shock with high gas pressure the vacuum can not be created...



See if this makes sence as it may come off as rambling... I'll make a picture if need be...



Don

 

[JKinney]

Hi Don, Shocks would be a good thread, I have yet to put the level kit on my truck, but I did get it into the garage today, and will try to stop hunting long enough to get it done.



I am afraid that the oem shocks are probably toast and will have to order some new ones. and this would be the perfect time to install

Jon

 

[Nate]

I do know the Napa premium shocks I put under my truck this summer have a bunch of movement in the lower mount. Not sure why, but I'm not too happy. Pulling the driver's side shock out is a PITA!

 

[Extreme1]

ISoooooo, I have seen COUNTLESS threads where a "thump" is fealt in the front of the truck. Bilstein, KYB monotubes, and pretty much every monotube shock is excluded as long as they have enough gas pressure, at least 150psi or so... ANY twin tube shock does not have enough, if any, pressure behind the oil to keep cavitation from happening. On a light vehicle, with lighter valving, it would not be as much of an issue as the shock piston will not create enough resistance to pull a vacuum under the oil chamber. What I think is happening with some of these shock is that with a fast enough, hard enough hit, the oil is pulling up with the piston, creating a vacuum under the shock piston causing the "thump", when the super strong vacuum is slammed shut.

Don

You're talking about cavatation. While the cause is not really a function of the mass of the vehicle, gas pressure does help prevent it. It is caused by length of stroke and velocity. Current sleds and bikes (think motocross and snowcross) use gas charged monotube shocks to eliminate the problem. Some have reservoirs and some don't, the addition of the reservior (other than adding a handy compression damping adjustment) is to increase the oil capacity with the expectation that it will either dissapate heat more effectively or have enough oil to keep within the oil's operating range during the event.

 

[THUREN]

Hi Don, Shocks would be a good thread, I have yet to put the level kit on my truck, but I did get it into the garage today, and will try to stop hunting long enough to get it done.



I am afraid that the oem shocks are probably toast and will have to order some new ones. and this would be the perfect time to install

Jon

Hey Jon...



Yep, you will want some better, slightly longer shocks once you get the leveling in there...



Don

 

[THUREN]

I do know the Napa premium shocks I put under my truck this summer have a bunch of movement in the lower mount. Not sure why, but I'm not too happy. Pulling the driver's side shock out is a PITA!

See if you can slide a 9/16" washer in there to take up the slop. . Might fit...



I also suggest loosing the stupid "extra coarse thread" bolts dodge uses, and putting in FINE THREAD grade 8 bolts... Much more clamp force... .



Don

 

[THUREN]

You're talking about cavatation.

EEEEHHH... . Close...



CavItation is air bubbles in the shock oil... very common, and some shocks actually plan for it. Not really what I'm talking about but still of concern. Any shock with under 150psi nitrogen pressure will PROBABLY cavitate, but, you won't notice it under normal conditions. .

While the cause is not really a function of the mass of the vehicle, gas pressure does help prevent it. It is caused by length of stroke and velocity. Current sleds and bikes (think motocross and snowcross) use gas charged monotube shocks to eliminate the problem.

Yep, know all about Moto --->video



Cavitation CAN have to do with the mass of the vehicle, as a larger rig, will usually have more firm valving. With stiffer valving you are forcing the oil though the valves at a much higher pressure which is causing the cavitation in the first place. So actually, stroke length and velocity don't matter much with very light valving. The oil won't see much resistance so the bubbles won't be forced out...

Some have reservoirs and some don't, the addition of the reservior (other than adding a handy compression damping adjustment) is to increase the oil capacity with the expectation that it will either dissapate heat more effectively or have enough oil to keep within the oil's operating range during the event.

That would be one of the reasons... . Just as important, if not more important, are these things. .



#1 The reservoir adds a larger chamber to displace shaft volume... When the shock compresses, the shaft area/volume has to go somewhere. If there is no reservoir it all gets shoved in the small(1. 5"??) nitrogen chamber which makes the nitrogen pressure rise a TON. This will make it harder to compress the shock...



#2 With no reservoir, but not an emulsion shock, the shock has to be longer to use a nitrogen chamber. The same stroke(travel) shock will be about 2" shorter with a reservoir...





NOW, back to what I was originally talking about as the "thump" coming from the front end... and it's not technically cavitation...



The best way I can explain is this... You have a shock piston surrounded by oil, under it, and above it... When the piston rises very fast, with very much resistance, the piston is lifting the oil on the top AND lifting the oil underneath it. It should be only pushing the piston through the oil but with the low gas pressure the piston can actually pull one-big-airbubble under it for a split second. This is the "thump"... . A high pressure gas shock has the gas pressure to hold the oil down instead of being able to lift it...



This, is what I think is the problem... Heavy truck+heavy valving+ cheap shock= problem...



Don

 

[Nate]

I think I'm going to put new shocks. The rear are shot I found out this afternoon. I guess 2700lbs in the truck down the ALCAN did it for the cheapos.

See if you can slide a 9/16" washer in there to take up the slop. . Might fit...



I also suggest loosing the stupid "extra coarse thread" bolts dodge uses, and putting in FINE THREAD grade 8 bolts... Much more clamp force... .



Don

 

[Extreme1]

#1 The reservoir adds a larger chamber to displace shaft volume... When the shock compresses, the shaft area/volume has to go somewhere. If there is no reservoir it all gets shoved in the small(1. 5"??) nitrogen chamber which makes the nitrogen pressure rise a TON. This will make it harder to compress the shock...

Don

Yes, the pressure rise is more abrupt when the nitrogen volume is smaller but, unless the shock/spring set up is really wrong, the force to compress the gas charge is still WAY less spring force.

#2 With no reservoir, but not an emulsion shock, the shock has to be longer to use a nitrogen chamber. The same stroke(travel) shock will be about 2" shorter with a reservoir...

Don

On snowmobile shocks (and our trucks), the shock length is determined by the suspension mounting limitations. The reservoir and non-reservoir shocks have the same bodies and rods, the reservoirs and hoses are simply added on to the existing shocks. Of course, the floating piston that separates the gas and oil needs to be removed from the shock body. Gotta run, more later.

 

[jabird]

Hey Eric, have you tried a 1/2" spacer yet... ... worked on the x-country set-up

 

[THUREN]

Yes, the pressure rise is more abrupt when the nitrogen volume is smaller but, unless the shock/spring set up is really wrong, the force to compress the gas charge is still WAY less spring force.

I admit that it makes a small difference in spring/shaft force but if the nitrogen chamber is small, the pressure can quickly get close to maxing out the shock body PSI rating,even more important factor with a larger diameter shaft shocks... It will make a much bigger difference in a light vehicle...

On snowmobile shocks (and our trucks), the shock length is determined by the suspension mounting limitations. The reservoir and non-reservoir shocks have the same bodies and rods, the reservoirs and hoses are simply added on to the existing shocks. Of course, the floating piston that separates the gas and oil needs to be removed from the shock body. Gotta run, more later.

The shocks DO NOT have the same bodies..... Example...



If a 10" travel "floating piston shock" is "x" length long, you could make a 12" travel same length(compressed) shock using the same body... . When you remove the floating piston you now have 2" more shaft depth to work with...





Before adding anymore info please give me a little background as to where your knowledge is coming from... You are stating things a FACT but they are not...



Don

 

[Extreme1]

Sorry I didn't reply sooner, too much time crouching motionless in front of a PC at work.



I finally had time to check out the vid, nice recovery.

I admit that it makes a small difference in spring/shaft force but if the nitrogen chamber is small, the pressure can quickly get close to maxing out the shock body PSI rating,even more important factor with a larger diameter shaft shocks... It will make a much bigger difference in a light vehicle... Don

If the nitrogen chamber is that small, the shock is assembled WRONG. The floating piston on a rear bike shock or sled shock (reservoir or not) is set up so that when the shock is bottomed (limited by either the shock parts or the suspension), the reservoir volume reduction (delta V) is small enough that the pressure rise won't affect suspension motion and isn't beyond the capabilities of the shock parts.



When I build sled shocks, they are charged to 200 PSI (250 psi for cross-link assemblies). The pressure rise could be calculated using the good old Ideal Gas Law: PV=nRT and the shock body max pressure rating could be calculated using some static loading calculations but this has already been done and we aren't getting close enough to the limits. (What exactly is a shock body rated at?)



As for the vehicle weight, if it is light enough to notice a gas pressure rise, the shock isn't right for the application. Note as I stated above: "unless the shock/spring set up is really wrong, the force to compress the gas charge is still WAY less spring force. " The exception to this is the Fox Float Shock It relies on pressure rise to act as the spring which is why they work well when long travel and rising spring rates are favored (snowcross and probably motocross) and not so well when long travel and straight spring rates are favored (cross-country).

The shocks DO NOT have the same bodies..... Example...



If a 10" travel "floating piston shock" is "x" length long, you could make a 12" travel same length(compressed) shock using the same body... . When you remove the floating piston you now have 2" more shaft depth to work with...

Cut it out! We actually agree but are arguing from different starting points.



Typically, they do have the same bodies, but the rod length changes (my bad) to increase travel. You do end up with more "shaft depth", usually around an inch, but in order to utilize it, you need to increase static ride height and rod length. Take a look at a clicker reservoir shock and an internal floating piston shock. Note that the part numbers for the bodies are the same and also note that the rods are different, the reservoir shock rod is 15/16" longer to utilize the added body depth. This increases the ride height by whatever effect 15/16" of increased shock length has on the suspension position. As this is on a "Cross Country" edition sled the slight increase in travel is welcomed but it wasn't even noted in the travel specs for that year.



Like I stated above: "On snowmobile shocks (and our trucks), the shock length is determined by the suspension mounting limitations. " You are talking about increasing shock stroke which won't affect anything unless other changes are made. On 2nd gen Rams however, a slight increase in travel in the 4X4 front suspension makes a significant ride improvement. If you stick a longer shock in, you don't gain travel because the spring length, rate and bump stops are the limiting factors. Add longer front springs (or spacers) and you will need longer shocks to fully utilize them.



I added 2" spring spacers to my front end 3 years ago and it made the truck ride a lot better. Since I didn't do anything to the shocks (I couldn't find my 2" shock extenders), it wasn't as good as it could be. The addition of the KORE system helped but the shock valving isn't as good as it could be (Bilstein HD) for my application (steet only). These shocks could use a little more low speed damping and less high speed damping but it is a lot better than it was.

Before adding anymore info please give me a little background as to where your knowledge is coming from... You are stating things a FACT but they are not... Don

Several years racing snowmobiles both cross country and snowcross (and building a few hundred (OK, it only seems like that many) shock set ups) and a bunch of Mechanical Engineering classes.

 

[jabird]

What?????????

 

[Lorenz]

My clunk us from the wrench that I dropped in the frame. :{



I have the perfect picture in mind but can't find it. I'll be back.

 

[RMarkey]

More going on here than I need to know right now. But anyway

I installed the Skyjacker kit with their nitro8000's (if my memory serves correctly, which doesn't mean much) and over real bumps, like medium speed speed-bumps and curbs(don't ask) they do great and I start to believe them about their "softride" springs, but through town over the cracks in the road it is louder that my 88 K-5 Blazer! Sounds like a cheap car with crappy struts, chips your teeth sort of ride. I had been wondering if it might be the shocks but didn't want to spend major money on new expensive shocks just to find out, since these are still basicly new.

 

[Lorenz]

Found it thanks to DezertRangers.com and friends

 

[Jeremiah]

Life expectancy of OEM shocks?

I realize it's often a matter of what kind of roads a truck is driven on, but is there a general rule of thumb that says how long shocks last? Truck springs are stiff enough that the old "bounce rule" (push down on one corner and see if the vehicle bounces more than once) doesn't apply. My '03 TD has 60K on it and seems to ride fiine. I load it to gross (10,000#) about once a week but don't run on rough roads, so it's hard to tell if the OEMs are shot. Thanks in advance for any replies.

 

[Lorenz]

If your happy with the OEM's run them. There is a huge difference when you strap on an adjustable shock, that's tuned to your liking. I've heard it expressed as a BMW type ride. Tight and predictable. Your correct with the one bounce test. 1 event is what I like to see after a bump. Speed bumps, curbs, and 2' drops included.



Race shocks will outlast the Cummins. The technology today allows each shock component to be replaced or rebuilt indipendent of each other. I've rebuilt my fair share of Race Quality Shocks and found the only thing that goes are the seals, and this is because of user error; running hard on a dirt road behind somebody that is throwing up rocks and dirt. This tends to happen if the shock shafts become pitted from rocks hitting them, thus, chewing up the seals. A simple shock boot would cure this. Seals rebuild kits are about $15, new shafts are about $35. Easy, relatively inexpensive fix.

 

[Diesel Power]

If your happy with the OEM's run them. There is a huge difference when you strap on an adjustable shock, that's tuned to your liking. I've heard it expressed as a BMW type ride. Tight and predictable. Your correct with the one bounce test. 1 event is what I like to see after a bump. Speed bumps, curbs, and 2' drops included.



Race shocks will outlast the Cummins. The technology today allows each shock component to be replaced or rebuilt indipendent of each other. I've rebuilt my fair share of Race Quality Shocks and found the only thing that goes are the seal, and this is because of user error. This tends to happen if the shock shafts become pitted from rocks hitting them, thus and chew up the seal. A simple shock boot would cure this. Seals rebuild kits are about $15, new shafts are about $35.

i want that BMW type ride do you have a street type of kit avalible for the dodge cummins equiped trucks? i'm not suspention savy so i dont know much about them, except that my passenger side tire is wearing way more than the rest and the alinement is spot on!! thanks :-laf

 

[Lorenz]

i want that BMW type ride do you have a street type of kit avalible for the dodge cummins equiped trucks? i'm not suspention savy so i dont know much about them, except that my passenger side tire is wearing way more than the rest and the alinement is spot on!! thanks :-laf

Ball joint issues maybe? Then again I'm not a mechanic.



I ship everything out one way when it comes to valving. I think 95% of pple will be very happy with it. If you would like a different feel you can always play with nitrogen pressure to start. It's just like filling a tire, except your using 175-280 psi. If you want change the ride even more than that you can open up the shock and change out washers that cost $2 a piece. Here's a detailed article (click here) on how to "revalve" and rebuild a Sway-a-Way shock.