LX470 - yet another AHC suspension question!

[jeduir3]

Hi everyone

So I have a 99 LX wirh around 210k on the clock. It hasn't been off-road much and is in pretty great condition overall.

Of course the suspension on these things is meant to drop out (no pun) around this time, and a lot of people seem to preemptively replace with aftermarket shocks... but I actually love the AHC - I don't off-road a tonne but I like dialling it to 'sport' for the highway and then soft for dirt and gravel. So I want to keep it if possible.

So back when I bought the truck, about a year back, I checked the AHC reservoir before buying - the high-low test gave me 9 notches, so not perfect but not dire either. But since then I've noticed the height will occasionally abruptively give out, for example at traffic lights one side will suddenly give way. Then it would correct itself. Later I got under the truck and have noticed a couple of the shocks have sentiment built up around the seals, which would indicate leaking fluid.

I guess this means doom for the AHC, however I went down to the Lexus shop and - they don't really know much about the AHC, I should say - but they said they can replace the shock itself for a few hundred bucks.

Of course the system is comprised of accumulators and the shocks... I wonder if anyone has replaced just the shocks and had any luck with increasing the longevity of the entire system?

Or at which point do I consider replacing the whole thing?

Thanks

 

[PADDO]

Mate, save your money and just get your neutral pressures sorted out first off. For the Lexus shop to say they can replace a shock actuator for a few hundred is really, really suspect. Bottom line is shock actuators tend to leak due to high internal hydraulic pressures and they will often, but not always, stop weeping with the correct pressures. Have a search limited to key words like “actuator” posted by me an you’ll get the idea that replacing AHC shock actuators is the last thing on the list. And the system isn’t meant to drop out, it’ll provide years of service with a bit of regular maintenance. It’s not just comprised of the shock actuators and accumulators. The bit in between these two parts, your damper valve assembly, actually provides your damping by variably throttling fluid that’s moving back/forth between the actuators and the accumulators.

Here’s something I wrote previously for someone who thought they needed new “shocks” to improve their ride - the topic of “leaking AHC shocks” has been really well covered over the years.

.....as has been pointed out the AHC shock actuators aren't “shocks” repeat..repeat. The last thing you’d change in an AHC system are the shock actuators - and only then if they are riddled with corrosion or peeing fluid. The only obvious benefits from new shock actuators are fresh bushings and rubber cushions and a system bleeding.
Take you NIB shock actuator and slide the piston in/out and notice there is no compression force necessary. This is because there isn’t any gas charge like a conventional shock, accordingly AHC shock actuators do not go soft like conventionals do with time. They are just a ported piston that strokes in a cylinder. When fitted to the vehicle hydraulic lines connect them directly to the remote gas spring/damper valve assemblies for each wheel. Fluid from the damper assemblies is ported through the hollow piston rod to the lower working chamber at the bottom of the actuator and pressures are equalized in the top chamber via the drilled ports in the piston. That’s it, no gas or compression/rebounding forces provided by a stand-alone shock actuator.
You need to know what your neutral pressures are and they should be corrected which will very likely entail new coils. You need fresh gas free fluid in the system (or know exactly when it was last replaced) and you need to know the health of your damper globes aka gas springs/accumulators/spheres because they, in conjunction with the electronically controlled damper assemblies provide your damping.

 

[white_lx]

for example at traffic lights one side will suddenly give way. Then it would correct itself.

Highly unlikely that your shocks are leaking so much that one side would suddenly give way. That would be a burst of fluid, not a trickle.
How often are you topping up the fluid level?

Very sudden changes seem more like an electric issue (wiring, sensors) or a valve problem.

 

[jeduir3]

Mate, save your money and just get your neutral pressures sorted out first off. For the Lexus shop to say they can replace a shock actuator for a few hundred is really, really suspect.

Thanks for this mate and the rest of your post! Very insightful.

I have done a bit of reading on the other threads so broadly familiar. I haven't checked the pressures yet though because I haven't been able to find a connector for my old rig. The 98 and 99 models don't have the tech stream 2 connector. I asked the dealer to connect theirs but they said they couldn't find anything on pressure levels. I'll need to have another go at this because youre probably right this is the first step.

Regarding replacing the shock - or piston - the front driver one is the worst of the bunch and seems to have significant buildup. Do you think it's worth replacing, if only for the benefit of a better seal? I have other work being done on that side so could get it done at the same time. Will it help at all? Or would it be detrimental?

Highly unlikely that your shocks are leaking so much that one side would suddenly give way. That would be a burst of fluid, not a trickle.
How often are you topping up the fluid level?

This is really good point mate. A drop of that level would be a catastrophic failure of the seals! Therefore it's the computer trying to do something. So resetting the negative pressure per the other poster would be a good bet, to start at least.

Regarding topping up levels I think it's still within min-max so I haven't bothered, I've done around 3000 miles so far. I'll give it a check when I'm home tonight and see what it's running at now. At the very least I should give it a flush, haven't done that yet.

 

[PADDO]

I have done a bit of reading on the other threads so broadly familiar. I haven't checked the pressures yet though because I haven't been able to find a connector for my old rig. The 98 and 99 models don't have the tech stream 2 connector. I asked the dealer to connect theirs but they said they couldn't find anything on pressure levels. I'll need to have another go at this because youre probably right this is the first step.

Regarding replacing the shock - or piston - the front driver one is the worst of the bunch and seems to have significant buildup. Do you think it's worth replacing, if only for the benefit of a better seal? I have other work being done on that side so could get it done at the same time. Will it help at all? Or would it be detrimental?

I wouldn’t have the shock actuators replaced just yet, as long as it’s not chronically leaking. Without seeing it I’m imagining just a shock body with say 1/2 the outer cylinder moist with oil? If it’s dripping fluid then that’s a different story.
Re not being able to hook up the vehicle interface/Techstream for pressure checks - you can use a load sensing proportioning valve (LSPV) test kit quite easily too. You’ll need a M7x1 adapter, which should be standard for a Toyota test kit, to replace the damper assemblie’s bleeder and go from there. I’ve made up a my own test gauge from a brake pressure tester, a couple of adapters and a section of braided flex brake line. Works great, actually prefer it to using Techstream because you’re reading actual pressure where it matters and not the pressure at the pump output when the solenoids are de energized. There’s a couple of tricks to ensure you loose very little fluid too so it’s not a messy or wasteful procedure.

 

[uHu]

First and foremost, either find another place to service the truck, or get TechStream yourself. That dealer sounds like they shouldn't be allowed to touch an AHC vehicle.
Have you checked with your local LC club for help?

 

[BEG]

...I haven't checked the pressures yet though because I haven't been able to find a connector for my old rig. The 98 and 99 models don't have the tech stream 2 connector. I asked the dealer to connect theirs but they said they couldn't find anything on pressure levels. I'll need to have another go at this because youre probably right this is the first step.

Any vehicle sold after '96 will have an OBDII connector. I futzed around with techstream for a while, but just ended up buying an iCarsoft TYT II scanner and it's literally plug-and-play. Very easy to read AHC information and a good investment, since you will continue to use it to monitor AHC and it works on other Toyota/Lexus/Scion vehicles.

Regarding replacing the shock - or piston - the front driver one is the worst of the bunch and seems to have significant buildup. Do you think it's worth replacing, if only for the benefit of a better seal? I have other work being done on that side so could get it done at the same time. Will it help at all? Or would it be detrimental?

Don't bother until you do all the other stuff first. Most weeping actuators stop seeping fluid once the pressures are back within spec.

This is really good point mate. A drop of that level would be a catastrophic failure of the seals! Therefore it's the computer trying to do something. So resetting the negative pressure per the other poster would be a good bet, to start at least.

The AHC will adjust itself under certain conditions (off-camber terrain, height delta between sensors, etc.). It doesn't necessarily mean there's something wrong with the system.

 

[PADDO]

Any vehicle sold after '96 will have an OBDII connector. I futzed around with techstream for a while, but just ended up buying an iCarsoft TYT II scanner and it's literally plug-and-play. Very easy to read AHC information and a good investment, since you will continue to use it to monitor AHC and it works on other Toyota/Lexus/Scion vehicles.



Don't bother until you do all the other stuff first. Most weeping actuators stop seeping fluid once the pressures are back within spec.




The AHC will adjust itself under certain conditions (off-camber terrain, height delta between sensors, etc.). It doesn't necessarily mean there's something wrong with the system.

Aus and RoW had many different vehicle interface requirements to the US so the post ‘96 statement isn’t accurate from a global perspective unfortunately. That’s why I suggested the pressure gauge because, from experience with working with older Aus vehicles, it’s easier, quicker, more better.

 

[BEG]

Aus and RoW had many different vehicle interface requirements to the US so the post ‘96 statement isn’t accurate from a global perspective unfortunately. That’s why I suggested the pressure gauge because, from experience with working with older Aus vehicles, it’s easier, quicker, more better.

Oops! I didn't bother to check where the OP was located. I defer to PADDO's superior knowledge!

 

[jeduir3]

Aus and RoW had many different vehicle interface requirements to the US so the post ‘96 statement isn’t accurate from a global perspective unfortunately. That’s why I suggested the pressure gauge because, from experience with working with older Aus vehicles, it’s easier, quicker, more better.

You've correctly spotted me as being in Aus!

With the pressure gauge approach, how you you adjust the computer to set the correct pressure without a techstream? Do you happen to know a connector or piece of kit which will allow interface with the older models?

Cheers mate, you've been a big help.

 

[jeduir3]

Without seeing it I’m imagining just a shock body with say 1/2 the outer cylinder moist with oil? If it’s dripping fluid then that’s a different story.

More like a significant caked-on build-up all over the assembly. Which would indicate long term minor leaking is my guess. I haven't witnessed any drips and didn't seem fresh when I looked at it. The other shocks are minor but the drivers front is the worst (per above description).

 

[uHu]

You've correctly spotted me as being in Aus!

With the pressure gauge approach, how you you adjust the computer to set the correct pressure without a techstream? Do you happen to know a connector or piece of kit which will allow interface with the older models?

Cheers mate, you've been a big help.

It's all there in his post. Using the t0yota LSPV gauge kit is the easiest.
You set the pressures by adjusting the steel springs, i.e. adjusting the torsion bars up front, and changing the coils at the back. Also, the adjusted height (sensor adjustment) have a big impact on pressure, so the pressure has to be checked at the correct height (Either correct according to the handbook (FSM), or at the height you want it to have (in which case you have to compensate with different springs, or some variation thereof).

In other words, by using the pressure gauge method, it's a purely mechanical job, no need to connect to any ECU. (As long as the system works right). There is a bit of work connecting hoses and bleeding air twice for each tho', so the electronic approach is a bit faster.

 

[jeduir3]

It's all there in his post. Using the t0yota LSPV gauge kit is the easiest.
You set the pressures by adjusting the steel springs, i.e. adjusting the torsion bars up front, and changing the coils at the back. Also, the adjusted height (sensor adjustment) have a big impact on pressure, so the pressure has to be checked at the correct height (Either correct according to the handbook (FSM), or at the height you want it to have (in which case you have to compensate with different springs, or some variation thereof).

In other words, by using the pressure gauge method, it's a purely mechanical job, no need to connect to any ECU. (As long as the system works right). There is a bit of work connecting hoses and bleeding air twice for each tho', so the electronic approach is a bit faster.

Excellent, thanks to clarifying there mate. That all makes sense. I do think the rear coils need replacement as I'm occasionally bottoming out (at least, I feel like it) when going over speed humps. I've also got the drawers back there so a couple hundred pounds/kilos depending on what I'm carrying. I think I read a while back that king coils here in Aus aren't bad so I'll do a bit more reading and see if I can figure out this gauge method. Is there no other option for connecting to the electrics if the techstream II isn't an option?

 

[uHu]

Likely to need new coils, yes. They don't last that long before they get lazy anyhow, even without any extra weight.
Is there no DLC3 plug under your dashboard, somewhere over the drivers feet?

I wouldn't try any other way of connecting electronically, as you would run into problems with timing and several conditions that have to match. (Even as an electronic engineer). It would be too time consuming for me.

Theoretically, it should be possible to connect a meter to the pressure sensor, but the problem is that the pressure is read at one exact moment when one end reaches level and while the gate valve to that end is still open. That value is then stored i memory for presentation on the tester or TechStream. There is only one pressure sensor, located at the pump, so all readings in TechStream (or other device) are momentary readings timed by the height logic.
BTW, the reading is only somewhat accurate for level N, when coming up from Lo. If/When using pressure gauges directly on the actuators, you get a continuous real-time reading.

 

[uHu]

Btw: Can't the Diagnostics connector under the hood also be used for TechStream? @PADDO

 

[PADDO]

DLC1 (the one under the hood) is missing the SIL (software in loop) pin, #7, that’s on DLC3 and its the data line to the ECUs so that’s a bit of a show stopper for e access. I’m not familiar with any electronic interface that Toyota may have had in their SST inventory that connected to DLC1 - but it’s really good for shorting Tc,Ts and E1 as they are easily accessed parallel extensions to Tc, Ts and Cg at DLC3. IIRC it wasn’t until the Aus 2003 model year, petrol versions, that you could hook up the 16 Pin mini VCI and run Techstream for LCs/LXs. My North America 03 only has four terminals active at DLC1, the three mentioned and battery, B+. @uHu is spot on with his points regarding capturing momentary pump output pressure values to coincide with the leveling and height accumulator solenoids. If the timing is out for whatever reason you get an invalid reading whereas with a gauge fitted you’re reading actual, real-time pressure in the system. The pressure sensor’s output will be a linear pressure-voltage output that can be monitored, but the voltage you’d be reading has no value to it unless it’s precisely synced to the solenoids.

 

[spaber05]

This forum is a wealth of knowledge when it comes to AHC, probably much more so than a local dealer that doesn't have experience with it. I have an '06 with 175k miles and I have no intention of preemptively replacing it in the near future simply because I spent some (ok, probably too much) time perusing some of the AHC threads. I just cranked my torsion bars 3 times to get my front pressures back to spec and it was the easiest thing to take care of, I was left wondering why I hadn't done that years ago.

I would continue to do some reading up, definitely listen to @PADDO on this subject, and get your hands dirty before you resign the AHC to the trash! It's a great system that people seem to underestimate the longevity of when in reality adjusting neutral pressures and replacing fluid (amongst other things) can go a long way.

Also, ditto to what @uHu said about connecting with locals, there have to be a few LCs around there with AHC that could offer up some help.

Good luck!