AHC: what are the pros/cons?

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Is this a Lexus only feature of the AHC? I find that very strange. I haven't needed to put my LC in park the change heights.

Edit: in fact my routine when I'm parking is to press "Low" as I'm approaching the parking spot and by the time I'm finished the truck is already in Low long before I've put it into park.
Lexus AHC works the same. Manual adjustment is possible if you're moving slowly or if you're stopped and the brake pedal hasn't been pressed too long.
 
Maybe it can go into low when I am driving but will not go into high unless parked. And you are probably right I may not have needed as much as I did but like I said I am more cautious than most. And I agree it is nice that when you put it into high you get that lift no matter your load. With a traditional you are stuck with whatever height it sits at when fully loaded.
 
Maybe it can go into low when I am driving but will not go into high unless parked. And you are probably right I may not have needed as much as I did but like I said I am more cautious than most. And I agree it is nice that when you put it into high you get that lift no matter your load. With a traditional you are stuck with whatever height it sits at when fully loaded.
If you truly believe you need to stay in "H" above 19MPH, you can install the Slee override switch and keep it in "H" as long as you want.
 
If you truly believe you need to stay in "H" above 19MPH, you can install the Slee override switch and keep it in "H" as long as you want.

Does he still sell that. I couldn't find it on his site. It would have been nice to have on the trip but I am fine with have it in N most of the time.
 
Last year I went on a trip where we traveled from New Mexico to Colorado on primarily Forest service roads. I did this with AHC as mine was in great condition. My pressures and graduations were where they needed to be. We loaded up for the 10 day trip and the AHC leveled itself and handled the weight of the load very well. We even went on some very rough roads that had completely washed out. My problem with the AHC is that in order to put it in High you have to put it in park and wait until it has risen into high. This became very tedious because any time you reached that 20 MPH it would lower. I then would have to rinse and repeat. On roads where you are having to do this every few minutes became very annoying. I could have stayed under 20 but that would have put us into camp very late and I was traveling with some else so I did not want to slow them down.

I currently have 195,000 on my rig. Just recently the bushings on the top of the rear shocks have gone bad. I am opting to switch out for a traditional suspension. If it wasn't for that I would use the AHC until it went out. Just keep in mind you have it in park to raise or lower the Lexus. You cannot do this as you drive.

That's not normal behavior. My LX definitely changes height in drive. According to the manual, it should be reverting back to high as soon as your speed slows.

If yours really does not return to high while moving, I think something is off.

Were you in 4Lo?

Is this a Lexus only feature of the AHC? I find that very strange. I haven't needed to put my LC in park the change heights.

Edit: in fact my routine when I'm parking is to press "Low" as I'm approaching the parking spot and by the time I'm finished the truck is already in Low long before I've put it into park.

Agreed. Similar approach for me when I pull into my garage.
 
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That's not normal behavior. My LX definitely changes height in drive. According to the manual, it should be reverting back to high as soon as your speed slows.

If yours really does not return to high while moving, I think something is off.

Were you in 4Lo?



Agreed. Similar approach for me when I pull into my garage.
Interesting I will have to go do some testing tonight.
 
I wasn't in low range. And it doesn't seem to make any noise besides the pump doing its thing. But I have only had experience with one ahc. So it has never sounded different from the day I got it.
 
uHu has summarised AHC features in posts #4 and #7 in this thread. This Toyota attachment also may help:
 

Attachments

I wasn't in low range. And it doesn't seem to make any noise besides the pump doing its thing. But I have only had experience with one ahc. So it has never sounded different from the day I got it.

If you're in a situation where you really need high mode, you should probably also be in 4Lo, but I can understand the desire to stay in H and play it safe.

The Slee over-ride switch sounds like exactly what you want, if you can find it.
 
I have ran almost all aftermarket suspension brands from the last 14 years on different pickup trucks and suv, even the ones from Thailand and China. The AHC is by far the best in terms of ride comfort and convenience of adjusting damping/rebound resistance settings on the fly (IMO better than Rover’s air suspension in terms of ride comfort and reliability).

CONS - if you are not fond of going under the vehicle to drain the AHC fluid for its routine PMS drain & flush, it can be a little hassle.
 
uHu has summarised AHC features in posts #4 and #7 in this thread. This Toyota attachment also may help:
That's a great read thanks.
@suprarx7nut you where right. My LX can switch to H or L while driving. I am just an idiot. It cracks me up all the times I stopped to switch my height while on my trip this past summer.
 
AHC is a fully active suspension only added to higher end vehicles because it is an expensive technology. It's most famous counter part is actually used in Tanks, the hydro-pneumatic suspension developed by Citroen which I'm sure Toyota bench marked due to its similarities

You have guys who get wet for the KDSS (looking at you GX470 guys) which is a semi-active suspension but provides many of the Active suspension capabilities, why not the same response to a more superior and technologically advanced suspension, maybe lack of understanding?

Toyota has managed to give us a fully active suspension that for the most part is a reliable beast with many examples reaching 20 years and 200k miles with no service ever done and still functional. Read resident expert @PADDO 's extensive posts on the AHC system and replace the fluid, replace the rear springs, adjust torsion bars and you are likely set for the next decade if you had functional system. You will then be rewarded with a system that is capable of the following:

1. Self-levelling and height adjustment
2. Pitch and roll mitigation
3. Pitch and roll control for improved aerodynamics/lean into curves
4. Handling enhancement
5. Comfort enhancement
6. Road friendliness

I just read parts of a PHD's extensive thesis on Active Variable Geometry Suspension for Cars by Carlos Arana Remirez Submitted in part fulfillment of the requirements for the degree of Doctor of Philosophy Imperial College London Electrical & Electronic and Mechanical Engineering Departments Control & Power Research Group London, United Kingdom September 2015

You guys have to check this out its a really good read talking about the technology dating back to beginning of automobiles.

https://spiral.imperial.ac.uk/bitstream/10044/1/41040/1/Arana-C-2016-PhD-Thesis.pdf

Some quotes:

The 1989 Toyota Celica (see Fig. 2.3) was the world’s first road car to be fitted with a (narrowbandwidth) fully active suspension [Aburaya et al., 1990], dubbed Toyota TACS (Toyota Active Control Suspension). Using hydraulic actuators it achieved pitch and roll reductions of 66% and 75% for acceleration levels of up to 7 m/s2 , and reduction in body vibrations at frequencies of up to 7 Hz (particularly at 1 and 2 Hz). In terms of control, PID (Proportional-Integral-Derivative) schemes were used, in some cases helped by feedforward factors. Soon after, Toyota integrated the control for the TACS, the four-wheel steering system and the anti-lock braking system (ABS), providing slightly better performance than when controlling each system independently [Yokoya et al., 1990].
Thus, although fully active systems remain rare, simpler, less capable but more economical solutions have proliferated. This is the case, for example, of active roll control systems, which have become very popular for Sport Utility Vehicles (SUV). They can make the SUVs feel more “car-like” when on the road [Parsons et al., 2000] and they are not as costly as fully active solutions. Some examples are Land Rover’s Active Cornering Enhancement [Parsons et al., 2000] introduced in 1998, BMW’s Active Stabilizer Bar System presented in 2001, Toyota’s Kinetic suspension (initially developed by Kinetic Pty Ltd and Tenneco Automotive) commercialised in 2003 on Lexus SUVs, Mercedes’ Active Curve System, or ZF’s Active Roll Stabilisation. In general these systems rely on having an anti-roll bar with controllable stiffness. This is achieved, for example, by splitting a conventional anti-roll bar into two and connecting both ends through a hydraulic actuator. The actuator can then be asked to remove all relative motion between both sides, to let them rotate freely, or to do anything in between. Thus, the system can provide tight roll control when driving on road (both axles are rolling in the same direction), and disengage the anti-roll bar in off-road situations when maximum articulation is needed (axles rolling in opposite directions). Moreover, this system can be easily combined with either air springs and/or semi-active dampers, as done in Mercedes’ SUVs.
 
AHC is a fully active suspension only added to higher end vehicles because it is an expensive technology. It's most famous counter part is actually used in Tanks, the hydro-pneumatic suspension developed by Citroen which I'm sure Toyota bench marked due to its similarities

You have guys who get wet for the KDSS (looking at you GX470 guys) which is a semi-active suspension but provides many of the Active suspension capabilities, why not the same response to a more superior and technologically advanced suspension, maybe lack of understanding?

My answer: Irrational fears of erroneous repair estimates from mechanics that don't understand the system and don't understand how to diagnose it.

The internet has helped exaggerate and proliferate these [IMO, falsely based] concerns and now there's a significant amount of content on the internet that basically says, "if your AHC has any minor problem throw it away immediately."

In reality, AHC in very simple terms is an on-demand lift of 2+ inches with a ride more comfortable than any other suspension system available at any price point. It offers a lift when you need it without the objective faults of traditional permanent lifts. Increased CV wear (or reduced ground clearance if you drop the diff to compensate), poor highway handling capabilities, restricted access to parking garages and low clearance driveways, etc...

  • The rams (shocks) very rarely fail and are reasonably priced at ~$230 each.
  • The accumulators need replacement a little less often than traditional shocks and cost a similar amount (compared to aftermarket performance shocks)
  • The pump very rarely fails.
  • The lines very rarely fail unless the undercarriage is severely rusted.
  • Torsion bar adjustments are free.
  • Rear springs are ~$325 per set and needed once every ~10 years
 
Okay so my bushings at the top of my rear shocks have gone I believe. I am going to lift it this weekend but I believed this is the source of some clunking when going over any type of bump.

If it is the bushings do I need to replace the whole shock or can you do just the bushings?

Secondly is it possible on a rust free vehicle to get the shock off?

Thirdly I can put in a dobinsom suspension for 997. New shocks and springs will cost me around 850. Should I do a full swap out? I will be adding front bumper with winch, bumper and a gamiviti roof rack. So if I don't replace what will I need to do to help the ahc out?
 
Okay so my bushings at the top of my rear shocks have gone I believe. I am going to lift it this weekend but I believed this is the source of some clunking when going over any type of bump.
The lower bushings wear out faster than the tops. Put the ahc in Lo first, then jack up -- in order to not have pressure on the shock (ram). Then check lower and upper bushings.
If it is the bushings do I need to replace the whole shock or can you do just the bushings?
No need to change the shock unless it's leaking severely.
Secondly is it possible on a rust free vehicle to get the shock off?
Should be OK, but it's damned tight. Remove spare wheel and get the best tools for the job (search this forum). Easiest is to cut a hole above.
Thirdly I can put in a dobinsom suspension for 997. New shocks and springs will cost me around 850. Should I do a full swap out? I will be adding front bumper with winch, bumper and a gamiviti roof rack. So if I don't replace what will I need to do to help the ahc out?
No need to change shocks. If only adding weight up front, you should be OK with tightening the torsion bars. Might need a re-indexing. You do need to use TechStream or similar to get the ahc pressure right.
 
The lower bushings wear out faster than the tops. Put the ahc in Lo first, then jack up -- in order to not have pressure on the shock (ram). Then check lower and upper bushings.
No need to change the shock unless it's leaking severely.
Should be OK, but it's damned tight. Remove spare wheel and get the best tools for the job (search this forum). Easiest is to cut a hole above.
No need to change shocks. If only adding weight up front, you should be OK with tightening the torsion bars. Might need a re-indexing. You do need to use TechStream or similar to get the ahc pressure right.
I have techstream so checking pressures won't be an issue. I didn't know about putting it in low so thanks for that!
 
My answer: Irrational fears of erroneous repair estimates from mechanics that don't understand the system and don't understand how to diagnose it.

The internet has helped exaggerate and proliferate these [IMO, falsely based] concerns and now there's a significant amount of content on the internet that basically says, "if your AHC has any minor problem throw it away immediately."

In reality, AHC in very simple terms is an on-demand lift of 2+ inches with a ride more comfortable than any other suspension system available at any price point. It offers a lift when you need it without the objective faults of traditional permanent lifts. Increased CV wear (or reduced ground clearance if you drop the diff to compensate), poor highway handling capabilities, restricted access to parking garages and low clearance driveways, etc...

  • The rams (shocks) very rarely fail and are reasonably priced at ~$230 each.
  • The accumulators need replacement a little less often than traditional shocks and cost a similar amount (compared to aftermarket performance shocks)
  • The pump very rarely fails.
  • The lines very rarely fail unless the undercarriage is severely rusted.
  • Torsion bar adjustments are free.
  • Rear springs are ~$325 per set and needed once every ~10 years

I have to agree with a lot of what you said. The system seems scary and expensive at first, but now that I've learned about it I plan to keep it as long as possible. Even full glob replacement can be done for about $1300 with OEM parts. I bought new rear springs a few months ago from McGeorge and only paid about $100 per side, maybe $220 total after shipping.
 

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