2-2.5" AHC Lift Using King Coils & Shock Spacers

[jtb517]

Me neither. They look good and the price was right (a bit under $600 shipped). I'm going to cut my AHC sensor brackets off the old arms and tack them onto the Nitro arms when I do the install so the AHC stuff should work roughly the same, I hope.

Pretty sure the latest version of the nitro arms has a attachment point welded on to accept the factory AHC and brake line mounts. Would be great if you can confirm if it can be swapped over to the nitro arms.

That was one of the reasons I was leaning towards nitros over SPC. SPC has a provision for the AHC sensor arm, but heard it wasn’t a very robust mount. I do like the SPC for its adjustability at the ball joint.

 

[krispykritter]

I've read a few horror stories about SPC arms failing and frankly pathetic customer service. I decided to avoid them long ago.

I'll definitely return to this thread with details on the nitro arms. It would be great if they had AHC brackets on them already!

 

[suprarx7nut]

@suprarx7nut do you run aftermarket UCAs? I've ordered a set of the new nitro arms so I'll probably throw those on first and see if the extra caster helps with the pitchiness at all. If not, then I'll be putting in the non-AHC torsion bars and seeing what effect that has. I'm hoping I can get a bit more lift with good driving manners but I think the softness of the AHC suspension is what is causing my bad behavior.

I do not. No need to run aftermarket with AHC, IMO. OEM Toyota is king when it comes to 100 front control arms quality. Unless you need extra adjustment, I like OEM. Since I run factory heights I have no need for any additional adjustment.

I had SPC arms on my 99 without AHC and with a small lift and they were fine. If you need to go aftermarket to get adjustment, I'd try to support one of the vendors on here (@TRAIL TAILOR comes to mind). A sale to a small vendor means a lot more than a sale to Nitro (now owned by a huge holding company, I think) or SPC. I thought SPC was much smaller than they are when I bought mine, otherwise I would have gone with a mud vendor.

 

[krispykritter]

Thanks @suprarx7nut. I've been running the Toyota ones for ages but finally have some free cash lying around to buy new UCAs. I've bought quite a number of things from TrailTailor actually - he makes top notch stuff. But I'd also feel really bad paying a mint for his control arms then grinding off the paint to tack weld on AHC brackets!

@jtb517 this thread shows the arms definitely lacking the AHC mount points but that could be a pre-production model or something. I'll let you know what I think when the arms get here. Invoice says they shipped 11/18 but I'll be out of town for thanksgiving.

Edit: oh cool, looks like they're getting delivered today!

 

[krispykritter]

Arms here. No AHC bracket. Beefy as hell. Probably going to drop my MPG from 15.5 to 15 (sarcasm).

 

[jtb517]

Arms here. No AHC bracket. Beefy as hell. Probably going to drop my MPG from 15.5 to 15 (sarcasm).

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Try mounting the stock brake line and AHC bracket to that threaded tab on the nitro arms when you get around to installing. It looks like in the very first photo of the thread you shared the rig has the stock bracket mounted to that tab, but is very hard to see given the photo is taken from the wrong direction.

 

[brauski]

Yup, my thoughts were similar. Check brake lines, sway bars. If you bleed any AHC pressure, take extreme caution. You can shift weight quickly and that can turn deadly if you're using precariously placed jackstands.

If you're having issues getting them on, you can relieve some pressure from the shocks by opening the bleeders and letting some fluid out. You'll need ot have more on hand to replenish when you're done. Also, keep in mind, the stock brake line isn't long enough to accommodate full droop of the axle with both wheels off the ground without bending the mount points or buying new longer lines. Also, your sway bar will hit your shocks at full droop as well. Longer end links take care of that problem.

Whenever I've messed with the whole rear axle, I was lucky enough to have a lift to put the lexus on. I haven't tried doing this job in the driveway on jack stands.

Thanks! Figured it out. No bleeding or anything crazy required. For anyone struggling with this in the future the key was allowing the whole axle to drop essentially level, sway bars off. My original issue was lateral fitment caused by lowering only one side at a time.

 

[krispykritter]

Alright, got the new arms and non-AHC T-bars installed. Man, what a difference. The control arms frankly weren't that huge of a difference in feeling but there's no longer any interference between the arms and the shock body even with my slightly extended shocks. Definitely a little more steering effort and it no longer kinda turns itself at high steering angles, which is really nice.

No AHC sensor bracket, so I cut them off the OEM arms and tack welded them onto the nitro arms. With the brackets tacked on, my AHC set my ride height about 2 inches higher than before the new arms, so I had to extend my sensor adjuster a lot to get it back to my standard ride height (longer distance between arm and sensor = lower ride height). If you've chopped your sensor adjusters down too far, this might be an issue for you.

Even with extended front shocks, I no longer get any contact between the various suspension parts or body. Even the AHC sensor bracket clears the body now (the bottom picture isn't quite full extension but it's close).

Now, the OEM t-bars made a huge difference! No more carolina squat. I can floor the truck again and it just hauls off perfectly controllably. It's so frickin nice.

I put the t-bars in with the adjusting bolts backed nearly all the way back out (aka top ends flush with adjuster piece). When I put it down, it needed 1.5 turns to get my front pressures back in spec. I might re-index them a little to get the adjusters a bit higher up in the end mounts to avoid smacking them on a rock offroad one day since they stick out pretty far right now.

Edit to add: After a few days of settling, I did a level and pressure adjust again. I added around 1.5-2 more turns on each t-bar to bring my pressure back to spec. I've been thinking about this, and while you can generally adjust the AHC t-bars for most things, I think it makes a lot of sense to upgrade even at relatively light weights. When you're increasing the preload on the torsion bars, it's the equivalent of keeping the same coil spring rate but adding a longer spring. Generally this is okay, but the possible negative side effect is the torsion bar pushes LONGER (a great amount of travel) as the suspension unloads. This longer unload distance is what was causing me to get into my bump steer range at high throttle inputs - if you have a 100 lbs/in spring and put 1000 lbs on it, you compress it 10 inches. When you unload it, after six inches of travel, it's still pushing up with 400 lbs of force. Take the same weight on a 200 lbs/in spring, and it's done pushing at only 5 inches of unload travel.

 

[xplore]

It's still a work in progress, but I installed some takeoff 80 series coils on the back of my LX along with the rear shock spacers (the front spacers will be going in soon).

Previously, the rear pressure was 8.4 in N. It was slightly bouncy in comfort mode, but it wasn't an awful ride. It also had 9 gradations of change from high to low, and I'm guessing it would have been higher if the rear pressures weren't so excessive. With the new rear coils, the rear pressures are now 6.2 in H, but the suspension is extremely firm driving around in H whether in comfort or sport mode. Also, the gradations are now measuring higher in the reservoir (maybe because of the shock spacers), but the gradations are about 19 now which seems implausible.

Right now, I'm driving around in H mode, but I plan to do the sensor lift to drive around in N. Does the suspension dampening and the comfort/sport adjustment go out the window when in H mode? I expected the ride to be better than before with my rear pressures coming down. Also, I'm puzzled by the massive increase in gradations. Has anyone else experienced this?

 

[krispykritter]

Thinking about this - lower pressures basically equate to less fluid in the globes and more in the reservoir, so that makes some sense.

High mode adds fluid to the globes, which in turn raises system pressure and lifts the truck until you get the 'high' suspension height. In your case, it doesn't need much fluid (6.2 is just barely above the rear spec of 5.9 for neutral), so I would expect the rear stiffness to be a result of the 80 series springs as opposed to high AHC pressures.

With normal AHC springs, high mode is stiff because you raise the AHC pressure a bunch to lift the truck. That's not your case, though, so that leaves the springs as the cause of your stiff ride. Did you look at what your front pressures were at when you had it in high mode? Might be a combo of high front pressures in High coupled with much stiffer rear springs.

Did you end up getting LX450 coils? Wouldn't think they'd be too terribly much stiffer over my kings. I find the ride with the kings perfectly fine with 100-150 lbs of tools plus a small fridge in the back of the LX.

 

[xplore]

Thinking about this - lower pressures basically equate to less fluid in the globes and more in the reservoir, so that makes some sense.

High mode adds fluid to the globes, which in turn raises system pressure and lifts the truck until you get the 'high' suspension height. In your case, it doesn't need much fluid (6.2 is just barely above the rear spec of 5.9 for neutral), so I would expect the rear stiffness to be a result of the 80 series springs as opposed to high AHC pressures.

With normal AHC springs, high mode is stiff because you raise the AHC pressure a bunch to lift the truck. That's not your case, though, so that leaves the springs as the cause of your stiff ride. Did you look at what your front pressures were at when you had it in high mode? Might be a combo of high front pressures in High coupled with much stiffer rear springs.

Did you end up getting LX450 coils? Wouldn't think they'd be too terribly much stiffer over my kings. I find the ride with the kings perfectly fine with 100-150 lbs of tools plus a small fridge in the back of the LX.

The front pressure was 6.7 in H, and the firmness in the ride is present in both axles. As soon as the front wheels hit a bump, you can feel the harshness. That's why I wasn't sure it was the rear coils and why I suspected the H mode could be to blame. I thought it had to be something with the hydraulic system.

Yes on the LX450 coils. I heard many examples of people using them with success on heavier trucks, and I wasn't sure the King coils would cut it based on other people's input. I have 4 kids and I usually weigh it down pretty good.

What you say about the lower pressure in the globes makes sense when talking about the raised fluid level in the reservoir, but what could make the gradations go so high? I thought 14 was as high as you could ever see.

 

[krispykritter]

The front pressure was 6.7 in H, and the firmness in the ride is present in both axles. As soon as the front wheels hit a bump, you can feel the harshness. That's why I wasn't sure it was the rear coils and why I suspected the H mode could be to blame. I thought it had to be something with the hydraulic system.

Yes on the LX450 coils. I heard many examples of people using them with success on heavier trucks, and I wasn't sure the King coils would cut it based on other people's input. I have 4 kids and I usually weigh it down pretty good.

What you say about the lower pressure in the globes makes sense when talking about the raised fluid level in the reservoir, but what could make the gradations go so high? I thought 14 was as high as you could ever see.

TBH I've never really paid attention to my graduations. I do intentionally overfill my reservoir by a bit and haven't paid attention to my low-to-high graduation count as I've never encountered the jarring pogo-stick ride that's an indicator of a blown globe.

When you say 18 graduations, I assume you mean doing the low-to-high graduation test you count 18 graduations? My guess on that would be that in order to drop to low (or as low as your truck can go with those springs) you're having to basically drop your AHC pressure to zero, which means nearly ALL the fluid in the globes and lines would be pushed back into the reservoir. Then, when going to high, the level has to drop significantly in order to take the system from essentially zero pressure to 6.5ish mpa.

I believe, on a normal AHC system going to low mode, it just relieves pressure on the system until it sees the vehicle at the low ride height. The system doesn't pay attention to pressures beyond avoiding an overpressure situation in the case of an overweight vehicle. It just adds or remove fluid to get the height sensors to read the appropriate value.

I'm really not sure what could be causing your harshness problem since your pressures aren't very high. Maybe high mode sets the damper modules to max stiff regardless of comfort switch setting?

I think @PADDO is our real AHC expert but not sure how often he's around these days. Maybe he can chip in if he's got time.

 

[xplore]

TBH I've never really paid attention to my graduations. I do intentionally overfill my reservoir by a bit and haven't paid attention to my low-to-high graduation count as I've never encountered the jarring pogo-stick ride that's an indicator of a blown globe.

When you say 18 graduations, I assume you mean doing the low-to-high graduation test you count 18 graduations? My guess on that would be that in order to drop to low (or as low as your truck can go with those springs) you're having to basically drop your AHC pressure to zero, which means nearly ALL the fluid in the globes and lines would be pushed back into the reservoir. Then, when going to high, the level has to drop significantly in order to take the system from essentially zero pressure to 6.5ish mpa.

I believe, on a normal AHC system going to low mode, it just relieves pressure on the system until it sees the vehicle at the low ride height. The system doesn't pay attention to pressures beyond avoiding an overpressure situation in the case of an overweight vehicle. It just adds or remove fluid to get the height sensors to read the appropriate value.

I'm really not sure what could be causing your harshness problem since your pressures aren't very high. Maybe high mode sets the damper modules to max stiff regardless of comfort switch setting?

I think @PADDO is our real AHC expert but not sure how often he's around these days. Maybe he can chip in if he's got time.

You may be right about the extra low-to-high graduations being affected by the springs, although, I would assume the globes would displace the same amount of fluid just based on the system pressure applied to the accumulators.

Yeah, I wondered about the possibility of the system going into sport mode (or beyond) based on being in high, but I've never heard anyone mention anything like that before. I may try adjusting the sensors to attain the same lift in normal height to see if that softens things up. If I'm not successful with that, it may just be the springs. I might end up trading down to the kings and possibly adding spacers or airbags if I need to drop pressures.

Regardless of the springs, I'm surprised it's riding so hard if the pressures are within a normal range, but I am by no means a suspension expert.

 

[krispykritter]

Yeah, I'd agree that getting it to normal at that height is step 1 then reevaluate.

 

[xplore]

You may be right about the extra low-to-high graduations being affected by the springs, although, I would assume the globes would displace the same amount of fluid just based on the system pressure applied to the accumulators.

Yeah, I wondered about the possibility of the system going into sport mode (or beyond) based on being in high, but I've never heard anyone mention anything like that before. I may try adjusting the sensors to attain the same lift in normal height to see if that softens things up. If I'm not successful with that, it may just be the springs. I might end up trading down to the kings and possibly adding spacers or airbags if I need to drop pressures.

Regardless of the springs, I'm surprised it's riding so hard if the pressures are within a normal range, but I am by no means a suspension expert.

An update...
I stopped driving around in high mode, and I just did a sensor lift. I did the lift so that it's slightly lower in normal mode than what it was in high previously, and it rides a little better. It's still a bit stiff all around even though the pressures are within a good range, so it seems like the diminished ride quality is tied to the height.

I have what I believe to be the Slee AHC override switch (installed by the previous owner). I hit some bumps with the override switch on and off, and it seems like the suspension is softer with it off. Maybe it was installed improperly, or maybe my mind is just playing tricks on me. Either way, the suspension still feels a bit on the stiff side, so I think I'm going to install the King springs. In the meantime, it feels great on the highway. It just feels bad hitting bumps at lower speeds.

 

[krispykritter]

An update...
I stopped driving around in high mode, and I just did a sensor lift. I did the lift so that it's slightly lower in normal mode than what it was in high previously, and it rides a little better. It's still a bit stiff all around even though the pressures are within a good range, so it seems like the diminished ride quality is tied to the height.

I have what I believe to be the Slee AHC override switch (installed by the previous owner). I hit some bumps with the override switch on and off, and it seems like the suspension is softer with it off. Maybe it was installed improperly, or maybe my mind is just playing tricks on me. Either way, the suspension still feels a bit on the stiff side, so I think I'm going to install the King springs. In the meantime, it feels great on the highway. It just feels bad hitting bumps at lower speeds.

Just seems very odd that both axles would feel excessively stiff when only one axle had stiffer springs added. I don't know much about the override switch but my assumption is that is just removes the speed input to the AHC computer so it doesn't sink back to low mode when the max speed threshold is exceeded.

As before, I'll be interested in what you do to try in fix this in the future. Wonder if you've got a bad globe or something. Gotta think running around in high mode all the time (with so much pressure in the globes) has gotta be bad for the system.

 

[suprarx7nut]

An update...
I stopped driving around in high mode, and I just did a sensor lift. I did the lift so that it's slightly lower in normal mode than what it was in high previously, and it rides a little better. It's still a bit stiff all around even though the pressures are within a good range, so it seems like the diminished ride quality is tied to the height.

I have what I believe to be the Slee AHC override switch (installed by the previous owner). I hit some bumps with the override switch on and off, and it seems like the suspension is softer with it off. Maybe it was installed improperly, or maybe my mind is just playing tricks on me. Either way, the suspension still feels a bit on the stiff side, so I think I'm going to install the King springs. In the meantime, it feels great on the highway. It just feels bad hitting bumps at lower speeds.

It's all about pressures.

AHC is inherently and unavoidably stiffer in H compared to N. From what I recall, all the Slee switch does is make the AHC ECU blind to speed. That will result in a harsher ride quality.

The hydraulic fluid and globes are pre-loaded with more force in H. That reduces the suppleness of the system because the globes (your shocks, in effect) have a reduced dynamic range.

Wherever you are going to keep your "N" height, it is critical that you re-adjust torsion bars and configure rear springs to net the proper neutral pressures. If you're lifting the "N" height more than an inch or so, you may want to be using the spacer links so that you can retain most the factory flex.

 

[xplore]

It's all about pressures.

AHC is inherently and unavoidably stiffer in H compared to N. From what I recall, all the Slee switch does is make the AHC ECU blind to speed. That will result in a harsher ride quality.

The hydraulic fluid and globes are pre-loaded with more force in H. That reduces the suppleness of the system because the globes (your shocks, in effect) have a reduced dynamic range.

Wherever you are going to keep your "N" height, it is critical that you re-adjust torsion bars and configure rear springs to net the proper neutral pressures. If you're lifting the "N" height more than an inch or so, you may want to be using the spacer links so that you can retain most the factory flex.

Wow, this is really helpful information! I was almost wondering if the harshness in H and with the Slee switch on was all in my head! That explains so much about why the front was ridding harsher too.

Although the pressures are in a good range, it still isn't riding right, so I'm downsizing the rear springs to the Kings with plans to use airbags for even heavier loads. I haven't put on the extended sway bar links yet, but I'm going to order those as soon as Trail Tailor has them back in stock.

 

[LXstatic]

Posting to update.

I lowered the lift down to improve handling characteristics and to decrease the bump steer I had.

Before/After:
Front Height: 21.75" / 20.5"
Rear Height: 23" / 21.5"
Front Pressure: 6.5 / 6.4
Rear Pressure: 6.5 / 5.6

Wow, I was amazed at how much the ride improved from lowering the front ~1". Bumps are less harsh and my bump steer is completely eliminated. I found that my lower bushings on my front and rear "shocks" are pretty much blown.

As for the squeaky spacers, I found that both lower mounting boots were not fully torqued, so I disassembled, covered the mating surfaces in anti-seize, then reassembled. I'm glad to report that my Lexus no longer sounds like a '90s chevy coming down the road.

Hey dude, are you still "Creak-Free"?? I need to do this if so!! My LX sounds like hell!!

 

[krispykritter]

Wow, I completely forgot about this thread. Guess it's been almost two years since I posted here last.

Some more work has been done to keep the AHC relevant:

• I bought new cheapo rear shocks from Rock Auto, cut the bottom eyes off, and welded them onto the bottom of the AHC shocks on the rear. I didn't like how the spacers torqued the bushings on the rear shocks, so I just welded on extensions.
• I went from King Springs (130 lbs/in), to 80-series LX springs (150 lbs/in), to 80-Series LC springs (170 lbs/in) on the rear to give good lift and load handling capabilities and more closely match my front non-AHC t-bars. The rear is STILL noticeably softer than the front though, which leads to...
• Can't recall if I told this thread at any point, but I've gone to non-AHC front t-bars to fix my crazy bump steer when accelerating. While the ride isn't what I'd call harsh, it is noticeably stiffer and doesn't flex nearly as well. When I come across the exra non-committed funds, I'll likely be purchasing some custom-sized t-bars from sway away to split the difference between the AHC and non-AHC t-bars
• I also bought a new set of four globes that are sitting in the garage waiting for the day when one dies. The LX is at 187k miles now, but it appears to be a crap shoot on whether they'll last to 50k miles or 500k miles. Parts are ready when one dies.