Oem shocks and springs

[Drogon]

Hello,
I am trying to decide if it is worth while freshening my suspension with new shocks and coils. I have 123k on odometer, and shocks are not leaking. No major weight being added. However ARB drawers are in place of the third row. Is there any other parts i should replace while i am in the process?

 

[Nothinghead]

Are you having any problems with the suspension, handling or steering? any noises, vibrations, uneven tire wear? With those miles, you might have some worn suspension bushings that would warrant a closer look if you're going to be tearing into stuff. You're only 6 years old and unmodified mostly so you might be just fine. Have you wheeled it heavily? Lots of things could be worn with that mileage but miles is just one factor.

 

[daneo]

Do you feel like the truck carries on oscillating after hitting a bump? If yes, the shocks could be replaced.

Does the front or back end sag? You can see if it's changed over time from time by measuring the center of the wheel to the fender lip. Front should be 20", rear 21". If the front is low, probably easier to replace the whole pre-built strut. and if the back is low, might as well replace the rear shocks while you're in there. And heck, if you're doing one end, you might consider doing both front and rear.

While you're at it, there are some rubber pieces that you might consider replacing as well. The top bushings on the rear shocks, the sway bar bushings, and potentially the upper control arms if you want to be extra thorough.

Just gave a response like this for a truck with AHC, and completely missed the mark. Hoping I'm more zeroed in on this response for a standard suspension haha.

 

[CharlieS]

I swapped in takeoff springs and struts with front factory spacers into a 2013 with ~110k miles and after that it rode like a new vehicle.

 

[Drogon]

It does oscillate a bit after some bumps. I also seem to have some noticeable nose dive if i dont brake with care.

I messured from the center hubs and the passenger side is in spec at 20 front and 21 rear. However, the driver side is 19.5 front and 20.5 rear. I may need to find a more level service though.

Good thinking with the bushings. I will have to get a part list put together. How many hours does Toyota quote for this operation?

 

[skmaynard1]

I have a 2013 with 160K miles on it, and I just purchased 4 new factory shocks and springs to refresh mine. I haven't had it since new, but I felt it had a slight sag and didn't ride as well as a 2021 I test drove. I put them in (forgetting to measure height) and there was a major noticeable difference in both height and comfort.

 

[daneo]

It does oscillate a bit after some bumps. I also seem to have some noticeable nose dive if i dont brake with care.

I messured from the center hubs and the passenger side is in spec at 20 front and 21 rear. However, the driver side is 19.5 front and 20.5 rear. I may need to find a more level service though.

Good thinking with the bushings. I will have to get a part list put together. How many hours does Toyota quote for this operation?

Brake dive with the stock coils is totally normal.

The 20” & 21” measurements are for the passenger side. Usually the drivers side is higher due to the pressure in the KDSS system. I can double check the height of my front drivers side later today. Toyota says up to 1/2” difference between the two sides is within spec.

If you like a ride “like a Cadillac” then sticking with the OEM shocks will serve you well. If the brake dive bothers you, and you want a firmer, sportier ride, or you want to add significant accessory weight (steel bumpers etc) or get some lift, then the Pandora’s box of aftermarket coils+shocks opens up.

Not sure what mechanics book for this job, so I won’t quote anything, but I could see it easily getting into four figures. How handy are you on the tools? Know anyone who has done a suspension swap before? It’s a great way to familiarize yourself with all of the underpinnings of the vehicle. But it can also be a full-day activity and I wouldn’t recommend it as a first-time wrenching job.

 

[TeCKis300]

Usually the drivers side is higher due to the pressure in the KDSS system.

Agree with everything else but this is not a thing.

 

[daneo]

Agree with everything else but this is not a thing.

Pressure in the closed KDSS system exerts a force to extend the ram because there is greater surface area on the “top” of the piston for the pressure to act upon, because the bottom of the piston has the ram shaft displacing that surface area where it attaches to the piston. Same concept as the shaft of a shock absorber being forced out of a pressurized shock.

 

[Drogon]

Brake dive with the stock coils is totally normal.

The 20” & 21” measurements are for the passenger side. Usually the drivers side is higher due to the pressure in the KDSS system. I can double check the height of my front drivers side later today. Toyota says up to 1/2” difference between the two sides is within spec.

If you like a ride “like a Cadillac” then sticking with the OEM shocks will serve you well. If the brake dive bothers you, and you want a firmer, sportier ride, or you want to add significant accessory weight (steel bumpers etc) or get some lift, then the Pandora’s box of aftermarket coils+shocks opens up.

Not sure what mechanics book for this job, so I won’t quote anything, but I could see it easily getting into four figures. How handy are you on the tools? Know anyone who has done a suspension swap before? It’s a great way to familiarize yourself with all of the underpinnings of the vehicle. But it can also be a full-day activity and I wouldn’t recommend it as a first-time wrenching job.

I do enjoy the ride of the stock shocks. I had the ahc taken out of my 100 series, and replaced it with an ome lift. I ended up regretting it because the ride was harsh. I dont want to repeat that senario unless i add weight.

I am handy with tools as i replaced the starter in my 100 series when it died. The write ups for the job on this forum are priceless. However i dont think i will have the time to wrench this job.

Going to order the parts through Camelback Toyota. They seem to have desent discounts. Thank you all for the feedback.

 

[bloc]

Pressure in the closed KDSS system exerts a force to extend the ram because there is greater surface area on the “top” of the piston for the pressure to act upon, because the bottom of the piston has the ram shaft displacing that surface area where it attaches to the piston. Same concept as the shaft of a shock absorber being forced out of a pressurized shock.

Between length of the KDSS arm & LCA which are basically levers acting against the KDSS ram and the small amount of surface area of the KDSS ram shaft to work in concert with system pressure to exert force, we aren't talking about much force by the time it can actually impact ride height.

 

[jhgnag]

I just had my springs/shock/struts replaced with OEM on my 2008 with 236K miles. The ride is definitely better, although I had at least one shock and one strut that was leaking. Ride height increased by 1/4" - 1/2". In hindsight, not sure I needed the springs, but if I hadn't done it I would have wondered about it every time I drove it and I didn't want to pay for the labor a second time if I replaced the springs later. My non-dealership Toyota repair shop would not do it because of the KDSS. I ended up having a dealership do the work. It was expensive. I spoke with the mechanic and he didn't have to do anything special with the KDSS. He said he can work around it. I spoke with 3 dealerships and had to ask/beg each for a detailed estimate. They all were charging 30%-50% above MSRP for the parts. I pointed it out and one was at least willing to charge "only" MSRP. Funny...feels like I got a deal paying MSRP. I hated taking it to a dealership, but I didn't want to mess around with it and couldn't find anyone else who would to the work. With my daughter about to start driving I decided I didn't want to mess around with it and have confidence everything was done correctly.

 

[daneo]

We can calculate the force, albeit with lots of eyeballing.

Say the KDSS ram cylinder is 2.5" in diameter, with a piston area of pi*1.25^2 = 4.9in^2
Say the KDSS ram shaft is 1.5" in diameter, with a shaft area of pi*.75^2 = 1.7in^2

This doc for the 150 says that the KDSS fluid should be at ~400PSI at room temp.

http://zatonevkredit.ru/repair_manuals/raw_content/rm100000000vqfk.xml

So on the bottom face there is 4.9*400 = 1960lbs of force pushing up
And on the top face where the shaft is displacing fluid from the piston face (4.9-1.7)*400 = 1280 lbs of force pushing down.

1960-1280 = 680lbs of force pushing down from each ram.
The motion ratio for the front ram on the arm connecting it to the LCA looks to be ~2:1, then the arm to the LCA has a motion ratio of ~2:1 so 680/4 = 170lbs of force acting on the front suspension

The motion ratio for the rear ram on the arm connecting it to the axle looks to be ~5:1 so 680/5 = 136lbs on the rear suspension.

So 170+130 would be like lifting 300lbs off the driver's side. Again, with plenty of fudge factors in there that could influence the actual result. But seems reasonable to consider it "a thing" versus "not a thing". In my measurements on a relatively new 200, Toyota has offset the imbalance with different rear coil lengths and different lengths or preloads on the front shocks. It can also be easily overcome by shimming rear coils or adjusting preload on front coil overs.

On 4Runners and GXs, the rams work directly on the sway bars, not on a motion-ratio-reducing arm, so the effect is more prevalent when installing equal-length rear coils and equally pre-loaded front coilovers.

I believe this is the same effect used on AHC to raise and lower the vehicle (still learning): apply a massive pressure to a single-acting piston and exploit the differences in area that the pressure can work upon to effect a force. In TeCKis300's teardown of the AHC shock, that shaft is massive! And does a great job of causing a surface area mis-match between bottom and top piston surface area for the pressure to work against.

Major hat tips to @bloc and @TeCKis300 for their major contributions to the collective understanding of KDSS and AHC among their other contributions here. I'm hoping this examination also helps add to that collective understanding.

 

[mahoolaha]

I do enjoy the ride of the stock shocks. I had the ahc taken out of my 100 series, and replaced it with an ome lift. I ended up regretting it because the ride was harsh. I dont want to repeat that senario unless i add weight.

I am handy with tools as i replaced the starter in my 100 series when it died. The write ups for the job on this forum are priceless. However i dont think i will have the time to wrench this job.

Going to order the parts through Camelback Toyota. They seem to have desent discounts. Thank you all for the feedback.

If you haven’t ordered already I just replaced my oem suspension with practically new heritage take offs from Ed Martin Toyota at a nice discount. Very happy customer.

 

[bloc]

We can calculate the force, albeit with lots of eyeballing.

Say the KDSS ram cylinder is 2.5" in diameter, with a piston area of pi*1.25^2 = 4.9in^2
Say the KDSS ram shaft is 1.5" in diameter, with a shaft area of pi*.75^2 = 1.7in^2

This doc for the 150 says that the KDSS fluid should be at ~400PSI at room temp.

http://zatonevkredit.ru/repair_manuals/raw_content/rm100000000vqfk.xml

So on the bottom face there is 4.9*400 = 1960lbs of force pushing up
And on the top face where the shaft is displacing fluid from the piston face (4.9-1.7)*400 = 1280 lbs of force pushing down.

1960-1280 = 680lbs of force pushing down from each ram.
The motion ratio for the front ram on the arm connecting it to the LCA looks to be ~2:1, then the arm to the LCA has a motion ratio of ~2:1 so 680/4 = 170lbs of force acting on the front suspension

The motion ratio for the rear ram on the arm connecting it to the axle looks to be ~5:1 so 680/5 = 136lbs on the rear suspension.

So 170+130 would be like lifting 300lbs off the driver's side. Again, with plenty of fudge factors in there that could influence the actual result. But seems reasonable to consider it "a thing" versus "not a thing". In my measurements on a relatively new 200, Toyota has offset the imbalance with different rear coil lengths and different lengths or preloads on the front shocks. It can also be easily overcome by shimming rear coils or adjusting preload on front coil overs.

On 4Runners and GXs, the rams work directly on the sway bars, not on a motion-ratio-reducing arm, so the effect is more prevalent when installing equal-length rear coils and equally pre-loaded front coilovers.

I believe this is the same effect used on AHC to raise and lower the vehicle (still learning): apply a massive pressure to a single-acting piston and exploit the differences in area that the pressure can work upon to effect a force. In TeCKis300's teardown of the AHC shock, that shaft is massive! And does a great job of causing a surface area mis-match between bottom and top piston surface area for the pressure to work against.

Major hat tips to @bloc and @TeCKis300 for their major contributions to the collective understanding of KDSS and AHC among their other contributions here. I'm hoping this examination also helps add to that collective understanding.

Thanks for the props!

Cylinder to shaft ratio is irrelevant, it’s the internal pressure forcing the shaft out of the system that matters.

Also the KDSS arm doesn’t attach at the outboard end of the LCA, it’s closer to the middle, halving any forces applied.

Yes even if it’s a small force lots of small forces add up to large ones, but mr T is pretty good at designing things as systems and to your point I believe they accounted for these forces in the overall suspension design.

For the record my rig was significantly lower on the drivers side when I got it at 105k, I blame the sagged coils. No other signs the PO was.. heavy.

 

[CharlieS]

Your experience may vary, but my factory springs were sagging after 100k miles. The new springs definitely increased height and returned bounce to the big girl's step.

 

[daneo]

Cylinder to shaft ratio is irrelevant, it’s the internal pressure forcing the shaft out of the system that matters.

I respectfully disagree with the piston and shaft sizes being irrelevant In stasis, the force on the ram in a single-acting piston of this type is due to the delta in surface area that the pressure in the system can act against.

Also the KDSS arm doesn’t attach at the outboard end of the LCA, it’s closer to the middle, halving any forces applied.

Agreed. Accounted for a halving of the force due to the motion ratio of the connection point of the sway bar to the LCA in the calculations.

Yes even if it’s a small force lots of small forces add up to large ones, but mr T is pretty good at designing things as systems and to your point I believe they accounted for these forces in the overall suspension design.

Agreed.

For the record my rig was significantly lower on the drivers side when I got it at 105k, I blame the sagged coils. No other signs the PO was.. heavy.

Gotcha. I wonder what effects are at play here. Perhaps the driver's side has shorter and/or lower rate coils that sag more quickly than the passenger side. Perhaps some slight leaking of pressure in the KDSS system over time. Perhaps bushings compressing at several locations over time. Perhaps all of the above and then some.

Maybe a poll is in order. "Which way does your high mileage stock truck lean" and the much trickier "Which way did/does your lifted truck lean with equal rear coils and equal front preload?"


@Drogon sorry for all this side discussion Get new shocks, coils and bushings and you should be set

 

[TeCKis300]

I respectfully disagree with the piston and shaft sizes being irrelevant In stasis, the force on the ram in a single-acting piston of this type is due to the delta in surface area that the pressure in the system can act against.
View attachment 3275670

Agreed. Accounted for a halving of the force due to the motion ratio of the connection point of the sway bar to the LCA in the calculations.



Agreed.


Gotcha. I wonder what effects are at play here. Perhaps the driver's side has shorter and/or lower rate coils that sag more quickly than the passenger side. Perhaps some slight leaking of pressure in the KDSS system over time. Perhaps bushings compressing at several locations over time. Perhaps all of the above and then some.

Maybe a poll is in order. "Which way does your high mileage stock truck lean" and the much trickier "Which way did/does your lifted truck lean with equal rear coils and equal front preload?"


@Drogon sorry for all this side discussion Get new shocks, coils and bushings and you should be set

I applaud you for working through this and I didn't mean to dismiss it. Just that there's so much anecdotal or wrong things in social media these days, suggested without basis.

I agree with your analysis. I don't believe the system is statically loaded in that manner however. The KDSS balancing screws are there to equalize the circuits when the system is setup for ride height.

Regarding the asymmetric springs, IMO they are more to account the driveshaft putting torsional load on the rear axle axle, and possibly for some minor panhard geometry. AHC similarly uses asymmetric rear springs, but the hydraulic part of the AHC suspension system is generally mirrored in design.

 

[daneo]

I applaud you for working through this and I didn't mean to dismiss it. Just that there's so much anecdotal or wrong things in social media these days, suggested without basis.

Totally. Especially about suspension. See: my response for the rough riding AHC thread

I agree with your analysis. I don't believe the system is statically loaded in that manner however. The KDSS balancing screws are there to equalize the circuits when the system is setup for ride height.

The KDSS rams come out with extreme force when you don't loosen the shutter valves (balancing screws). Ask me how I know

But let's keep working through the diagrams.

I need more time to revisit bloc's explainer on the valves, but I think I've got it right to this point.

When the shutter valves are open, everything is at the same pressure (say ~400PSI). There's no net force on the ram because the fluid can flow from the upper to lower chambers. This mode lets us swap suspension parts with less donations to the swear jar.

Once we open the shutter valves, the flow between upper and lower chambers is shutoff, so the forces upon the different areas of the piston (top and bottom) are allowed to act. The upper and lower accumulators expand/contract to compensate for the shaft of the ram leaving the cylinder in the short term, and in the long term, the lower valve (in bloc's diagrams) allow the pressures to be maintained fairly consistently throughout the system.

This is the heavy swear jar donation mode during suspension swaps.

Need to revisit the "zener diode" style representation of the valves at some point. This visual isn't accurately reflecting the valves.

And keep in mind this is all at long term stasis. KDSS goes into double-acting mode when there's articulation.

 

[bloc]

Totally. Especially about suspension. See: my response for the rough riding AHC thread


The KDSS rams come out with extreme force when you don't loosen the shutter valves (balancing screws). Ask me how I know

But let's keep working through the diagrams.

I need more time to revisit bloc's explainer on the valves, but I think I've got it right to this point.

When the shutter valves are open, everything is at the same pressure (say ~400PSI). There's no net force on the ram because the fluid can flow from the upper to lower chambers. This mode lets us swap suspension parts with less donations to the swear jar.

View attachment 3275770

Once we open the shutter valves, the flow between upper and lower chambers is shutoff, so the forces upon the different areas of the piston (top and bottom) are allowed to act. The upper and lower accumulators expand/contract to compensate for the shaft of the ram leaving the cylinder in the short term, and in the long term, the lower valve (in bloc's diagrams) allow the pressures to be maintained fairly consistently throughout the system.

This is the heavy swear jar donation mode during suspension swaps.

View attachment 3275771

Need to revisit the "zener diode" style representation of the valves at some point. This visual isn't accurately reflecting the valves.

And keep in mind this is all at long term stasis. KDSS goes into double-acting mode when there's articulation.

I’d advise checking the KDSS valve anatomy thread. Your analysis would be correct if the circuits were truly isolated with the screws shut, but they aren’t. One of the communication valves allows the circuits to adapt to different conditions, which explains why people that routinely park on a side hill or diagonal hump can get a lean, one of the few truly caused by KDSS, and it isn’t from fluid leaking past the ram pistons.

Here’s another way of thinking about it.. the accumulators in the valve, which are what effectively maintain ideal system pressure in spite of differing temperature, physical, load, handling, and importantly system volume conditions (both rams can be pushed in at the same time with enough force).. those accumulators are plumbed to the center circuit, not either of the top or bottom circuits that actually communicate with the rams.

With no accumulator on the top/bottom circuit to maintain pressure in a non-compressible fluid-filled system, that 400psi wouldn’t last very long as soon as the shaft were pushed out. And yet when we disconnect the sway bar link we get a nice fluid pushing motion forcing the arm down without much reduction in that force through its travel.

What is actually happening is the more complex of the internal valves is allowing communication between the center circuit with its accumulators, and the top and bottom circuit. In small doses, I should add. As soon as we go into a corner and put real load on the bars the intricate valve setup locks pressure in the appropriate part of the system.. until we hit flat road again then if it’s all working as designed things slowly equalize again.

That same feature is what means ultimately the force exerted on the shaft at rest is a function of the surface area of the cross section of the shaft, and system pressure. The ironic thing is in this scenario I suspect the force is actually greater than yours with it simply being a net difference between the top and bottom of the piston area. But still between the motion ratios (thanks for the proper term) we have, the weight of the rig, and the overall system design, I believe if this has any impact on vehicle attitude it is extremely minor.

I’m probably making this clear as mud. I really like your diagrams and wish I had that skill..