Definitive list of AHC maintenance items (6 Viewers)

[Urtwob]

I think you're confused.

Keep the AHC, of course!

In addition to AHC, use air bags. They are used together as a complimentary system.

I am not suggesting you remove AHC. I rarely speak those words, haha.

Hi Suprarx7nut

I have just been chatting to a local company who are going to look into this for me.
They call it an air support kit.
There is aldo company who do make a specialist kit that fits inside the existing springs on my truck. However this local company are able to do a simple “off the shelf” makeup for this application.

We can keep it very simple ie airbags that we set to whatever pressure at a garage conpressor or go more sophisticated and instal a compressor and have controls at your fingertip.
I really like the idea in theory because we do know when driving our trucks, when we are stressing the AHC just that little bit too much. You can just feel it in your bones.
Loaded trailer, bad roads etc. Just set air pressure in air assist bag, up a little and then return to normal when standard highway driving.

 

[GTV]

30mm coil spacers on top of the original springs is a foolproof and inexpensive place to start.

 

[Urtwob]

30mm coil spacers on top of the original springs is a foolproof and inexpensive place to start.

30mm coil spacers on top of the original springs is a foolproof and inexpensive place to start.

Hi GTV

Thank you for replying.

I have to admit to zero knowledge on springs.
Does spring strength deteriorate over the years?
My truck is 1998 LC100. I can only assume that these are still the original.
If the springs don’t lose strength then I would certainly consider your suggestion.

Does anyone know If I were to put the Purple springs on to my truck, (they are 30mm higher than the Pink) does doing so upset the trucks natural AHC height reading sensors?? Or does the system compensate naturally?

But I would really like to hear views on the question, do the springs lose strength over the years, in my case may be 23-24 years old.

Thank you GTV and everyone.

 

[suprarx7nut]

30mm coil spacers on top of the original springs is a foolproof and inexpensive place to start.

Truth

 

[GTV]

Hi GTV

Thank you for replying.

I have to admit to zero knowledge on springs.
Does spring strength deteriorate over the years?
My truck is 1998 LC100. I can only assume that these are still the original.
If the springs don’t lose strength then I would certainly consider your suggestion.

Does anyone know If I were to put the Purple springs on to my truck, (they are 30mm higher than the Pink) does doing so upset the trucks natural AHC height reading sensors?? Or does the system compensate naturally?

But I would really like to hear views on the question, do the springs lose strength over the years, in my case may be 23-24 years old.

Thank you GTV and everyone.

Springs absolutely loose their strength over the years, the fact that AHC pressures increase over time to maintain ride height is proof positive of this.

 

[Urtwob]

Springs absolutely loose their strength over the years, the fact that AHC pressures increase over time to maintain ride height is proof positive of this.

Thank you GTV

I think from feedback via internet the Pink and Purple springs must only be used as per the originals fitted. Ie if I take out pink I can’t fit the Purple springs.

Am I correct to assume the only way to assist my AHC system when using trailers etc, is to upgrade my AHC system, new spheres new AHC Struts and replace my old springs with identical new spring.

if this is the case then the “spring assist” airbags are possibly my only option.
Whereby I inflate the airbags a little when using trailers or heavily loaded.

Any opinions on the above ??

 

[GTV]

The goal is to lower AHC pressures due to spring fatigue and/or added weight. The easiest and most inexpensive way to do this in the rear is to replace the springs with new or heavier ones and/or add spacers. It's in the springs, not in the spheres or anything else (replacing those is just maintenance, not an upgrade). The height of the spring alone does not tell you how strong it is, wire diameter and "wraps" must also be considered. For your use do not use springs that are not designed to be used with AHC, they will be far too heavy. I don't know about pink vs purple or any other colour. What I do know is that spacers work and they are cheap and easy to fit. Airbags also work but may be overkill for your application. I'd start with spacers and if you need more then consider stronger springs (possibly in combination with the spacers) and then lastly airbags. Every user and combination is different so there is no way to know precisely what you will need.

 

[2001LC]

30MM spacer will help by lower Mpa in rear. They'll not give much in way of extra load capacity.

I use AHC Toyota springs on Land Cruiser or LX470 (which are a bit taller than the Lexus), w/30mm spacers all the time. Not to add load cap, but to give better ride and extend life of globes. Tried old coil springs don't support as much as new. So new OEM springs, will increase load cap back to factory.

Air bag or King AHC coil spring, will give greater load capacity, at stock height. They also do not reduce the damping effect from AHC much (you'll not likely notice).

 

[Urtwob]

The goal is to lower AHC pressures due to spring fatigue and/or added weight. The easiest and most inexpensive way to do this in the rear is to replace the springs with new or heavier ones and/or add spacers. It's in the springs, not in the spheres or anything else (replacing those is just maintenance, not an upgrade). The height of the spring alone does not tell you how strong it is, wire diameter and "wraps" must also be considered. For your use do not use springs that are not designed to be used with AHC, they will be far too heavy. I don't know about pink vs purple or any other colour. What I do know is that spacers work and they are cheap and easy to fit. Airbags also work but may be overkill for your application. I'd start with spacers and if you need more then consider stronger springs (possibly in combination with the spacers) and then lastly airbags. Every user and combination is different so there is no way to know precisely what you will need.

The goal is to lower AHC pressures due to spring fatigue and/or added weight. The easiest and most inexpensive way to do this in the rear is to replace the springs with new or heavier ones and/or add spacers. It's in the springs, not in the spheres or anything else (replacing those is just maintenance, not an upgrade). The height of the spring alone does not tell you how strong it is, wire diameter and "wraps" must also be considered. For your use do not use springs that are not designed to be used with AHC, they will be far too heavy. I don't know about pink vs purple or any other colour. What I do know is that spacers work and they are cheap and easy to fit. Airbags also work but may be overkill for your application. I'd start with spacers and if you need more then consider stronger springs (possibly in combination with the spacers) and then lastly airbags. Every user and combination is different so there is no way to know precisely what you will need.

Thank you GTV.

There is a company called RoughTrax on the internet. I copied the following from their website.

“Models with AHC cannot fit uprated rear coils if maintaining the original AHC setup due to the dampers etc, increasing springs rates will affect the ride and bring on the suspension warning lights so only standard coils can be fitted if maintaining the rest of the AHC system.”

Being a very respectable and recognised company I would be inclined to accept their online instructions and guidance.

So it’s like for like on the springs if I want to avoid upsetting the AHC Managment system.

So my question now is simply,
Can I add a spacer without affecting the AHC system or as they say, putting the AHC warning lights on,

What I meant in my previous post was that as I have new spheres and as of tomorrow will have new rear AHC struts, that side of things will be optimum.

Then as regards springs, my research so far suggests that it is best to replace only with direct identical springs.

I really like your suggestion of putting the spacers in.
I am just concerned if I do, will that additional 20-30mm not reduce the pressures within the AHC system and upset its operating system.

Is it the case that when I renew my rear springs, this is all I can do to help my rear suspension ??

Have you experience of adding the spacers with new springs?
Adding the spacers with old springs might work because the old spring has lost some of its strength thus adding spacers may be pushing the weakened springs carrying capacity back to its original non weakened carrying capacity.

Please bear with me, I know I’m verging on being irritating.

My last question is,
Could adding spacers with new springs upset the AHC in any way?

 

[GTV]

The only way you can upset the system is to have pressures far above (with worn out old springs) or far below (too much spring) what is recommended. Spacers will not do this. I currently have 35mm (30+5) spacers stacked on my 15 year old original rear coils with 300k+ kms, I don't have any problems, pressures are within spec, etc. As my weight increases I may replace those with 50mm spacers, I don't anticipate any issues with that either.

 

[Urtwob]

30MM spacer will help by lower Mpa in rear. They'll not give much in way of extra load capacity.

I use AHC Toyota springs (on Land Cruiser or LX470), which are a bit taller than the Lexus w/30mm spacers, all the time. Not to add load cap, but to give better ride and extend life of globes. Tried old coil springs don't support as much as new. So new OEM springs, will increase load cap back to factory.

Air bag or King AHC coil spring, will give greater load capacity, at stock height. They also do not reduce the damping effect from AHC much (you'll not likely notice).

Thank you 2001LC
You have just touched on the final issues I was discussing. I have come to the same understanding as you have described.

You mentioned King AHC
Are King the brand name of a spring manufacturer?

On my LC I have Purple 485mm original toyota stock springs. Compatible AHC.

I wonder if the King AHC springs would give me increased load capacity with no other AHC operating system problems.

I am disabled and I really do get big benefits from my AHC System. But I

The only way you can upset the system is to have pressures far above (with worn out old springs) or far below (too much spring) what is recommended. Spacers will not do this. I currently have 35mm (30+5) spacers stacked on my 15 year old original rear coils with 300k+ kms, I don't have any problems, pressures are within spec, etc. As my weight increases I may replace those with 50mm spacers, I don't anticipate any issues with that either.

Thanks GTV

Excellent. Giving me a lot more confidence in my plans.

 

[2001LC]

Thank you 2001LC
You have just touched on the final issues I was discussing. I have come to the same understanding as you have described.

You mentioned King AHC
Are King the brand name of a spring manufacturer? The below link will help you.

Coil springs for AHC

Im going to install new coils in the rear in a couple weeks. Does anyone have a sense of how new OEM AHC coils compare to used and tired (180k) non-AHC coils? I can get a set of tired used springs for cheap, but I don't want a stiff ride. I may put a 150lb drawer system in the rear sometime...

forum.ih8mud.com

On my LC I have Purple 485mm original Toyota stock springs. Compatible AHC. IDR recall color codes or MM,. Above thread I linked in, may help you with that also. But understand: When one states LC coils, those a very thick diameter heavy coils on all stock non AHC LC. LC or LX AHC coils, are a very thin diameter coil. AHC coils LC or LX are interchangeable.

I wonder if the King AHC springs would give me increased load capacity with no other AHC operating system problems. YES. We put them on heavy built off-road LC/LX that wish to keep AHC system. They will stiffen damping of AHC just a little, on stock weight LC/LX. Loaded they're just right! If a fully load rig i.e bumpers, winch, rack, underarm, box, fig, etc.. We swap on LC (non AHC) torsion bars, also.

I am disabled and I really do get big benefits from my AHC System. But I


Thanks GTV

Excellent. Giving me a lot more confidence in my plans.

The Air bags are nice, for stock 100 series (weight). That only occasionally add rear weight beyond factory recommended limits. They do require airing up or down PSI, for desired ride and weight.

 

[ChaoticSquare]

Kings will give you more load capacity and not cause issues. Just make sure you get the ktr-79 springs NOT the ones meant for a non AHC vehicle… been there done that. Kings are a brand of spring, search on eBay for “ktr-79” and there will be 2-3 vendors in Australia.

If anyone is looking for a new OEM set for front globes let me know. Still in box, ordered four fronts by accident (common theme…).

 

[Urtwob]

Hi Guys.
I’m having problems
We can’t get our AHC system to bleed through.
We have just installed 2 new rear AHC struts and 2 new springs.

We have run the small AHC pump manually, opened the oil-out pipe and applied 12v to the motor.

Motor running well, spat out a little air and then new AHC fluid.

However
When I turn Jeep on the AHC goes immediately to off.

All door shut.

We also filled the new struts with new oil when installing.
Idea was to help with bleeding system.
Car was up on lift when work done.

Then when all plumbing finished on new struts etc we lowered the car to the ground.

This should of pushed the new oil out of the newly filled struts, back up the lines towards the spheres.

VERY IMPORTANT.
My rear lhs strut burst over a month ago.
And I have been driving the truck every day on the rubber bump stops.

I have also pulled a 4 wheel builders trailer a few times.

I am Declaring all of the above in hope someone might know what may be wrong now.

We can’t get the system to pump and oil to any of the spheres or the main cylinder on chassis between the spheres.

It’s as if some valve is closed not allowing the pump to push the oil through.

When we start truck and hold hand on AHC pump we can feel a small clunk and on goes the AHC off light inside the truck.

Any guidance or help would be most appreciated.

We are 98% certain the AHC pump is healthy.

 

[IndroCruise]

Hi Guys.
I’m having problems
We can’t get our AHC system to bleed through.
We have just installed 2 new rear AHC struts and 2 new springs.

We have run the small AHC pump manually, opened the oil-out pipe and applied 12v to the motor.

Motor running well, spat out a little air and then new AHC fluid.

However
When I turn Jeep on the AHC goes immediately to off.

All door shut.

We also filled the new struts with new oil when installing.
Idea was to help with bleeding system.
Car was up on lift when work done.

Then when all plumbing finished on new struts etc we lowered the car to the ground.

This should of pushed the new oil out of the newly filled struts, back up the lines towards the spheres.

VERY IMPORTANT.
My rear lhs strut burst over a month ago.
And I have been driving the truck every day on the rubber bump stops.

I have also pulled a 4 wheel builders trailer a few times.

I am Declaring all of the above in hope someone might know what may be wrong now.

We can’t get the system to pump and oil to any of the spheres or the main cylinder on chassis between the spheres.

It’s as if some valve is closed not allowing the pump to push the oil through.

When we start truck and hold hand on AHC pump we can feel a small clunk and on goes the AHC off light inside the truck.

Any guidance or help would be most appreciated.

We are 98% certain the AHC pump is healthy.

Just wondering whether you have Techstream running and if so, what Diagnostic Trouble Codes (DTC's) are appearing? Also wondering what the AHC pressures may have been before this situation developed?

The point is that if the AHC Pump runs open circuit (gushes fluid when the discharge line is disconnected) but not when the line is reconnected, then the AHC Electronic Control Unit (ECU) is detecting a problem and preventing the pump from running.

This may be because the AHC pressures are excessive and the pump cannot lift the vehicle. Or it might be as simple as air in the pump after disconnecting and reconnecting discharge line from the AHC Pump. In either case the pump will not run.

Suggest read the attachment and try the “Active Test” -- this is used to check AHC operation.

It also can be used when it is desired to start an AHC Pump which has stopped and will not start automatically.

The main reason for such a stoppage is when air gets into the AHC Pump – such as during bleeding of the system, or if there is a poor seal between the AHC Tank and the AHC Pump, or at the O-rings within the AHC Pump assembly.

Air causes low pressure to be detected by the Pressure Sensor. The AHC Pump then stops for its own protection – it is not good for a gear pump to run without fluid for a long period.

The “Active Test” also can be used to start a pump when in ‘fail-safe’ mode while resolving the ‘fail-safe’ problem.

The “Active Test” can be done from the ‘Utility’ feature in Techstream, or, it can be done manually using the procedure below and at Section 5 of Page 6 of the “Pre-check” attachment.

The procedure should only be done for a short period of time -- about 10 seconds -- long enough to be sure that the pump is drawing fluid from the tank. This is called “priming” the pump:

1. With Ignition OFF, connect terminals Ts and E1 at DLC1 (this is the socket in the engine bay, usually over the RHS wheel arch with the word DIAGNOSTIC on the top cover. The terminal "map" is shown inside this cover. Instead of Special Service Tool (SST) 09843-18020 which is just a piece of bridging wire, find something simple -- I use an unbent paperclip for this test. Voltages here are low, about 4.5 volts, and will not cause a problem -- but be careful to connect the correct terminals,

2. Turn ON the engine.

3. Select “COMFORT” on the variable damping switch on the centre console,

4. Push the DOWN button on the Height Select switch within 5 seconds of engine start and hold it down for 5 seconds. There will many flashing lights in the instrument cluster (because the ECU functions are being by-passed). Ignore these -- they will revert to normal later, after the test, when the bridge (paperclip) is removed and the AHC ON/OFF switch is pressed down for a couple of seconds,

5. Use the combined settings to move front or rear up or down (listen for the operation of the AHC Pump and its motor),

6. When finished, switch OFF engine and switch OFF ignition, then remove the bridge (paperclip),

7. Re-start, push down and hold down the AHC ON/OFF for a couple of seconds to clear the test.

 

[Urtwob]

Just wondering whether you have Techstream running and if so, what Diagnostic Trouble Codes (DTC's) are appearing?

Unfortunately I don’t have any techstream. Yet.
When I turn the truck on the low light is always on a solid green light on low.

Even when I push the up button, the “high” green light flashes but the “low” solid green stays on also.

Interestingly the system can remain light that for 10minutes before the “off” light is shown.

 

[Urtwob]

Just wondering whether you have Techstream running and if so, what Diagnostic Trouble Codes (DTC's) are appearing? Also wondering what the AHC pressures may have been before this situation developed?

The point is that if the AHC Pump runs open circuit (gushes fluid when the discharge line is disconnected) but not when the line is reconnected, then the AHC Electronic Control Unit (ECU) is detecting a problem and preventing the pump from running.

This may be because the AHC pressures are excessive and the pump cannot lift the vehicle. Or it might be as simple as air in the pump after disconnecting and reconnecting discharge line from the AHC Pump. In either case the pump will not run.

Suggest read the attachment and try the “Active Test” -- this is used to check AHC operation.

It also can be used when it is desired to start an AHC Pump which has stopped and will not start automatically.

The main reason for such a stoppage is when air gets into the AHC Pump – such as during bleeding of the system, or if there is a poor seal between the AHC Tank and the AHC Pump, or at the O-rings within the AHC Pump assembly.

Air causes low pressure to be detected by the Pressure Sensor. The AHC Pump then stops for its own protection – it is not good for a gear pump to run without fluid for a long period.

The “Active Test” also can be used to start a pump when in ‘fail-safe’ mode while resolving the ‘fail-safe’ problem.

The “Active Test” can be done from the ‘Utility’ feature in Techstream, or, it can be done manually using the procedure below and at Section 5 of Page 6 of the “Pre-check” attachment.

The procedure should only be done for a short period of time -- about 10 seconds -- long enough to be sure that the pump is drawing fluid from the tank. This is called “priming” the pump:

1. With Ignition OFF, connect terminals Ts and E1 at DLC1 (this is the socket in the engine bay, usually over the RHS wheel arch with the word DIAGNOSTIC on the top cover. The terminal "map" is shown inside this cover. Instead of Special Service Tool (SST) 09843-18020 which is just a piece of bridging wire, find something simple -- I use an unbent paperclip for this test. Voltages here are low, about 4.5 volts, and will not cause a problem -- but be careful to connect the correct terminals,

2. Turn ON the engine.

3. Select “COMFORT” on the variable damping switch on the centre console,

4. Push the DOWN button on the Height Select switch within 5 seconds of engine start and hold it down for 5 seconds. There will many flashing lights in the instrument cluster (because the ECU functions are being by-passed). Ignore these -- they will revert to normal later, after the test, when the bridge (paperclip) is removed and the AHC ON/OFF switch is pressed down for a couple of seconds,

5. Use the combined settings to move front or rear up or down (listen for the operation of the AHC Pump and its motor),

6. When finished, switch OFF engine and switch OFF ignition, then remove the bridge (paperclip),

7. Re-start, push down and hold down the AHC ON/OFF for a couple of seconds to clear the test.

Hi, Indrocruise
No unfortunately I don’t have Techstream.

I’m quite confused, if I open the oil “out” port from the pump, and run the pump manually with 12v, it pumps out fresh oil.
However it is not pumping any oil to any of the 5 points down on the chassis.

Last time I started truck, the “Low” indicator was on solid and it stayed on solid even when I pressed the “high” button it up. The “Hi” light flashed and the Low light remained solid but no oil is being sent to even the first bleed point.
They are all bone dry or when we open each nipple there is neither air nor fluid coming out.

Any ideas or ticks to try get it pumping fluid??

Thank you.
Unfortunately I’m in a bit of a jam I. That I urgently need the truck tomorrow.

Many thanks.

 

[IndroCruise]

Unfortunately I don’t have any techstream. Yet.
When I turn the truck on the low light is always on a solid green light on low.

Even when I push the up button, the “high” green light flashes but the “low” solid green stays on also.

Interestingly the system can remain light that for 10minutes before the “off” light is shown.

First check that Rear Height Control Sensor and linkage was not damaged when working on Shock Absorbers and Springs. This can happen -- and if so, that can be enough to put the AHC system into 'fail safe mode' which prohibits AHC operation and so pump will not work. Rear Height Control Sensor is located on the cross-member in front of the rear differential with a linkage to the LHS Rear Upper Control Arm

If all good, then suggest try "Active Test" as mentioned in late edit to my previous post to see if that will get the AHC system operating again. Techstream is not necessary for this purpose.

 

[sunfic]

Thank you guys I leant a lot from this thread.

How I have a question, how do you think about the spring spacers vs new OEM springs? I don't want to do heavy load on my LX just want to have the OEM performance.

 

[IndroCruise]

First check that Rear Height Control Sensor and linkage was not damaged when working on Shock Absorbers and Springs. This can happen -- and if so, that can be enough to put the AHC system into 'fail safe mode' which prohibits AHC operation and so pump will not work. Rear Height Control Sensor is located on the cross-member in front of the rear differential with a linkage to the LHS Rear Upper Control Arm

If all good, then suggest try "Active Test" as mentioned in late edit to my previous post to see if that will get the AHC system operating again. Techstream is not necessary for this purpose.

Just to add ....

No fluid emerging from the bleeders means that the AHC system is not yet pressurised.

To pressurise the system, you will need to get the AHC Pump running to prime the system properly using the "ActiveTest" procedure as described previously. (I see that you have not yet opened the attachment sent previously??) When that is done, exit the "Active Test" procedure and allow the AHC system to run.

You have wondered about valves downstream from the Pump.

The Control Valve Assembly is located midway along the inner edge of the LHS chassis rail. This contains the Front Levelling Valve and the Rear Levelling Valve. When the vehicle is being raised (or lowered) these valves are opened by the Electronic Control Unit (ECU) but only when the system is not in 'fail safe' mode.

After the vehicle is raised, the AHC Pump re-pressurises the Height Control Accumulator.

While theae latter details are all very interesting, they are not relevant.

At the moment, the AHC system is in 'fail safe' mode and the ECU is not allowing anything to happen.

Manual operation using the "Active Test" procedure is your way to bypass this control and prime and re-pressurise the AHC system, then exit this procedure. The ECU will then allow the system to run again.

The problem and the resolution are not unusual.