Quick AHC Flush (1 Viewer)

[Hokie99]

New member, long time Land Cruiser and Toyota 4x4 owner.

Having said that I am new to the AHC system, and am helping a friend flush his new to him 1998 LX 470. I have read the helpful how to guides on IH8Mud. Since his Lx470 has a lot of miles on it I would rather not mess with the fittings on the AHC system due to corrosion and just plain old age.

Here is my thought and I would like to get your opinions. What if we sucked out the AHC fluid out of the reservoir in the engine bay and measured it, the put back that same amount of new AHC fluid. Drove the vehicle for a week and each day cycled the AHC from low to neutral to high to circulate the new fluid, and then a week later sucked out the fluid in the reservoir once again and replaced with new fluid. Would this in essence change out the majority of the fluid in the entire AHC system?

Thank you.

 

[planomateo]

Follow this process, much easier. Have you even tried the bleeder valves?

Props to PADDO's AHC fluid replacement method!

I just had my AHC fluid replaced. My local indy shop quoted me over 3 hours labor. After reading many posts here that people were getting it done in an hour or less, I reached out to PADDO for advice. He provided me a step by step process that I gave to the local shop. They ended up following...

forum.ih8mud.com

 

[Hokie99]

Follow this process, much easier. Have you even tried the bleeder valves?

Props to PADDO's AHC fluid replacement method!

I just had my AHC fluid replaced. My local indy shop quoted me over 3 hours labor. After reading many posts here that people were getting it done in an hour or less, I reached out to PADDO for advice. He provided me a step by step process that I gave to the local shop. They ended up following...

forum.ih8mud.com

Many thanks! Yes, I have thought about the bleeder valves but I’m thinking with the miles on it and the age I’d rather not touch the bleeder valves as I’m worried about breaking them, introducing air into the system, etc....just stick to the drain and fill on the main reservoir....thoughts?

 

[planomateo]

Many thanks! Yes, I have thought about the bleeder valves but I’m thinking with the miles on it and the age I’d rather not touch the bleeder valves as I’m worried about breaking them, introducing air into the system, etc....just stick to the drain and fill on the main reservoir....thoughts?

You can buy new ones. No reason to make this a science project

Tried and true process.

 

[brauski]

I just did PADDO's method today. I was super worried about the bleeders too since I've got 175k and never wash the underside of the rig. Hit them with PB Blaster two days ago, and again this morning 2 hours before starting work. They moved incredibly easily. I was shocked. I'd atleast give it a try. Oh, and I was using the open end of a Tekton 10mm wrench.

 

[Hokie99]

Ok, I totally undertand that there is a Gold Standard and that I should leve well enough alone....but I geek out on fluids, I know, what a pitiful existence I must lead...

Anyway, if you all would induldge my quirks I would appreciate it, lol.

In the process that I am describing I am thinking it would kind of like 2-3 drop and drains in a transmission. Just suck the fluid out with a mityvac in 2 minutes fill it up, run the AHC up and down 2-3 times, suck the fluid out, run the AHC up and down again 2-3 times, fill it up and done in 10 minutes.

Does the fluid circulate through out the AHC system like in an automatic transmission to allow the above to work?

Thank you.

 

[planomateo]

Then do it.

 

[Hokie99]

Then do it.

Done.

 

[uHu]

Ok, I totally undertand that there is a Gold Standard and that I should leve well enough alone....but I geek out on fluids, I know, what a pitiful existence I must lead...
...
In the process that I am describing I am thinking it would kind of like 2-3 drop and drains in a transmission. Just suck the fluid out with a mityvac in 2 minutes fill it up, run the AHC up and down 2-3 times, suck the fluid out, run the AHC up and down again 2-3 times, fill it up and done in 10 minutes.

Does the fluid circulate through out the AHC system like in an automatic transmission to allow the above to work?

There is no circulation of fluid in the AHC system. Changing out the fluid in the reservoir will do nothing to the fluid down there between the shocks and the spheres. Nothing at all. Waste of time, waste of fluid. It's not like the ATF at all, where the whole purpose of the fluid is to circulate.

When you do attack the bleeders, if afraid of braking or rounding them, do not use an open ended. Use a hexagonal socket to break it loose, then use a spanner to open and close while bleeding.

This is not about a gold standard and an alternative method -- If you want to change out any bad ahc fluid, you have to drain at the business end (bottom end) of the system.
It's a bit like with brake fluid, in fact. Whatever you do with the brake fluid up at the master, there will still be water or humid fluid in the calipers.

 

[Hokie99]

BridgeBurner, many many thanks....exactly the full explanation/comparison I was looking for. The comparison to the braking system makes total sense. I will now go and work on the bleeder valves with some PB blaster. Thanks again.

 

[Rad26rio]

Hey Hokie, I am here in Richmond and have done this before. I too was surprised at how well the bleeders acted after so many years of crud etc on them. They worked fine after a couple of PB Blaster baths. The old fluid I removed was disgusting... system was far better with clean juice within.

 

[shiretowndown]

The @PADDO documented process is so very helpful. I flushed the AHC on my previous LX using it.

The area I am still fuzzy on is:

When bleeding into small plastic hose can I let the fluid bleed all the way until fluid stops or am I at risk of allowing air back up plastic pipe? When I bled my ‘06 I got nervous when dirty fluid slowed in clear pipe and I could see air pocket in plastic hose begin to make it’s way up toward bleeder screw...

If someone could please clarify that all 5 bleed points can be allowed to bleed until fluid stops or does the person bleeding need to be ready to re-tighten bleeder screw when old fluid slows so much that air pockets begin back-travelling the clear tubing?

Thank You

 

[suprarx7nut]

The @PADDO documented process is so very helpful. I flushed the AHC on my previous LX using it.

The area I am still fuzzy on is:

When bleeding into small plastic hose can I let the fluid bleed all the way until fluid stops or am I at risk of allowing air back up plastic pipe? When I bled my ‘06 I got nervous when dirty fluid slowed in clear pipe and I could see air pocket in plastic hose begin to make it’s way up toward bleeder screw...

If someone could please clarify that all 5 bleed points can be allowed to bleed until fluid stops or does the person bleeding need to be ready to re-tighten bleeder screw when old fluid slows so much that air pockets begin back-travelling the clear tubing?

Thank You

You want to avoid air getting back into the bleeder if you can. Air in the lines or height accumulator can take a long while to bleed back out as one member recently experienced. That said, plenty of people swap bleeders during that task so sucking air back into the system isn't a disastrous scenario. It happens and the bleed procedure should correct it.

You don't need to act fast because the fluid (and air bubbles) moves very slowly. What helps is that your tube fits well on the bleeder and that your tube sits in fluid in your container.

Also keep in mind, this isn't like brake or clutch bleeding where there's a pedal sucking back in on the bleeder if a step gets out of order. That reduces your chance of sucking in air.

 

[IndroCruise]

Ok, I totally undertand that there is a Gold Standard and that I should leve well enough alone....but I geek out on fluids, I know, what a pitiful existence I must lead...

Anyway, if you all would induldge my quirks I would appreciate it, lol.

In the process that I am describing I am thinking it would kind of like 2-3 drop and drains in a transmission. Just suck the fluid out with a mityvac in 2 minutes fill it up, run the AHC up and down 2-3 times, suck the fluid out, run the AHC up and down again 2-3 times, fill it up and done in 10 minutes.

Does the fluid circulate through out the AHC system like in an automatic transmission to allow the above to work?

Thank you.

Ok, I totally undertand that there is a Gold Standard and that I should leve well enough alone....but I geek out on fluids, I know, what a pitiful existence I must lead...

Anyway, if you all would induldge my quirks I would appreciate it, lol.

In the process that I am describing I am thinking it would kind of like 2-3 drop and drains in a transmission. Just suck the fluid out with a mityvac in 2 minutes fill it up, run the AHC up and down 2-3 times, suck the fluid out, run the AHC up and down again 2-3 times, fill it up and done in 10 minutes.

Does the fluid circulate through out the AHC system like in an automatic transmission to allow the above to work?

Thank you.

Strongly agree with @uHu. Also suggest please note the experience around the world as recorded on IH8MUD and on other forums elsewhere. Without wishing to be unkind, if your suggested process was worthwhile, we all would have been doing AHC fluid change this way since AHC first appeared on LX470’s 20+ years ago. Also note that engineers who wrote the Factory Service Manual also would have advised this method if it was satisfactory.

It is hard enough to achieve fluid replacement by the recommended IH8MUD and FSM methods. It often requires several iterations.

The ‘pumping effects’ assumed in your method hopes to achieve progressive mixing and dilution of old fluid with new fluid over a period of time by (i) raising and lowering the vehicle to operate the shock absorbers (which actually are just hydraulic struts on AHC vehicles), and (ii) driving the vehicle so that fluid moves to and from the ‘globes’ as wheels run over bumps and holes. This assumed mixing and dilution of old fluid will take a very long time -- even longer if the ‘globes’ are in poor condition and not pushing much fluid back to the AHC tank (as measured by the ‘graduation test’). Even then, the fluid in the system will be seriously compromised by considerable amounts of degraded fluid which remain in the system. In this condition, the overall properties of contaminated AHC fluid will be much closer to the old, dirty, heat-affected fluid than the new fluid, rendering the exercise pointless.

It is worth bearing in mind that if the AHC/TEMS system is to survive on any vehicle to which it is fitted, then the ‘globes’ will have to be replaced at some point. If this has not already been done and visible on the record of a vehicle which is 15 to 20 years old, then it WILL be required in the foreseeable future. This will be indicated by the “HI”/“LO” graduation test – at the AHC Tank: 14 = as new; 8 = order new ‘globes’ quickly; 7 = replace ‘globes’ now. The ‘globes’ are a ‘wear’ item in the same way as a conventional shock absorber is a ‘wear’ item. To enable safe removal and replacement of ‘globes’, AHC pressure must be released at the bleeder nipples on the Damping Force Actuators and proper bleeding of the system must be done. This is inevitable and unavoidable.

So bleeder nipple condition and proper bleeding procedure is inevitable and will have to be confronted. Avoidance does not help.

AHC Fluid change is not a hard job – much easier procedure than bleeding brakes. It does take care. There is plenty of advice on IH8MUD.

Some suggestions ….

• Prepare properly,

• Buy five new bleeder nipples and caps so as to replace all originals as part of the process – one at each Damping Force Actuator (to which the ‘globe’ is attached) and one at the Height Control Accumulator -- cost is a few dollars only – part numbers are shown in the pic below,

• Use a wire brush or similar to remove mud, rust, etc from around the existing bleeder nipples,

• Use multiple applications of your favourite thread penetrating oil – PB Blaster or whatever – over several days before doing the job,

• Place a groundsheet of some kind below the job – spillage of escaping fluid can happen,

• Wear eye protection as a precaution,

• Place body next to but not under the vehicle – when pressure is released the vehicle can drop quickly,

• Use a 10 millimetre hexagonal (six-sided) box wrench to obtain the best non-slip grip on the nipple and avoid rounding its corners – not a multi-point ring spanner nor an open ended spanner – with a tube placed tightly on the nipple and leading to a container,

• Use gentle pressure to start, tap the wrench lightly with a hammer if necessary, not heavily – it is the vibrations from light repeated blows which may help to release the thread,

• Follow the procedures recommended in IH8MUD at the four actuators and the Height Control Accumulator,

• Gently open the bleeder slowly to control pressure release and volume flow,

• Go slowly – if things happen too quickly, tube blows off or whatever, gently close the bleeder, does not have to be very tight, and regain control,

• Maintain fluid level in the tank at the AHC Pump at all times,

• When pressure has gone, immediately replace old bleeder nipple with new and bleed again. (Note: Air will not suddenly rush into the system -- there is no negative pressure, no 'suction' -- but replace bleeder nipple without any delays),

• Before bleeding the Height Control Accumulator, best to make sure that it has recharged with all other bleeders closed. (It has finished recharging when AHC pump has stopped),

• Repeat bleeding at all points until bubbles are eliminated and fresh pink fluid is flowing -- if this takes more new fluid, then it takes more new fluid,

• If vehicle is slow to rise after this process -- has happened but not often -- then suspect that some residual air is still in the system and bleed again. [Air in the system may cause the AHC system to spend time compressing the air before it gets around to raising the vehicle, causing a slow rise to be observed. Note: A slow rise can be caused by other problems unrelated to the bleeding process such as AHC pump wear or partial blockage of pump internals filters -- but always start with simple things first].

• Be confident -- after you have done this process once, you will wonder why you ever thought it was difficult!

 

[s2kmr]

Strongly agree with @uHu. Also suggest please note the experience around the world as recorded on IH8MUD and on other forums elsewhere. Without wishing to be unkind, if your suggested process was worthwhile, we all would have been doing AHC fluid change this way since AHC first appeared on LX470’s 20+ years ago. Also note that engineers who wrote the Factory Service Manual also would have advised this method if it was satisfactory.

It is hard enough to achieve fluid replacement by the recommended IH8MUD and FSM methods. It often requires several iterations.

The ‘pumping effects’ assumed in your method hopes to achieve progressive mixing and dilution of old fluid with new fluid over a period of time by (i) raising and lowering the vehicle to operate the shock absorbers (which actually are just hydraulic struts on AHC vehicles), and (ii) driving the vehicle so that fluid moves to and from the ‘globes’ as wheels run over bumps and holes. This assumed mixing and dilution of old fluid will take a very long time -- even longer if the ‘globes’ are in poor condition and not pushing much fluid back to the AHC tank (as measured by the ‘graduation test’). Even then, the fluid in the system will be seriously compromised by considerable amounts of degraded fluid which remain in the system. In this condition, the overall properties of contaminated AHC fluid will be much closer to the old, dirty, heat-affected fluid than the new fluid, rendering the exercise pointless.

It is worth bearing in mind that if the AHC/TEMS system is to survive on any vehicle to which it is fitted, then the ‘globes’ will have to be replaced at some point. If this has not already been done and visible on the record of a vehicle which is 15 to 20 years old, then it WILL be required in the foreseeable future. This will be indicated by the “HI”/“LO” graduation test – at the AHC Tank: 14 = as new; 8 = order new ‘globes’ quickly; 7 = replace ‘globes’ now. The ‘globes’ are a ‘wear’ item in the same way as a conventional shock absorber is a ‘wear’ item. To enable safe removal and replacement of ‘globes’, AHC pressure must be released at the bleeder nipples on the Damping Force Actuators and proper bleeding of the system must be done. This is inevitable and unavoidable.

So bleeder nipple condition and proper bleeding procedure is inevitable and will have to be confronted. Avoidance does not help.

AHC Fluid change is not a hard job – much easier procedure than bleeding brakes. It does take care. There is plenty of advice on IH8MUD.

Some suggestions ….

• Prepare properly,

• Buy five new bleeder nipples and caps so as to replace all originals as part of the process – one at each Damping Force Actuator (to which the ‘globe’ is attached) and one at the Height Control Accumulator -- cost is a few dollars only – part numbers are shown in the pic below,

• Use a wire brush or similar to remove mud, rust, etc from around the existing bleeder nipples,

• Use multiple applications of your favourite thread penetrating oil – PB Blaster or whatever – over several days before doing the job,

• Place a groundsheet of some kind below the job – spillage of escaping fluid can happen,

• Wear eye protection as a precaution,

• Place body next to but not under the vehicle – when pressure is released the vehicle can drop quickly,

• Use a 10 millimetre hexagonal (six-sided) box wrench to obtain the best non-slip grip on the nipple and avoid rounding its corners – not a multi-point ring spanner nor an open ended spanner – with a tube placed tightly on the nipple and leading to a container,

• Use gentle pressure to start, tap the wrench lightly with a hammer if necessary, not heavily – it is the vibrations from light repeated blows which may help to release the thread,

• Follow the procedures recommended in IH8MUD at the four actuators and the Height Control Accumulator,

• Gently open the bleeder slowly to control pressure release and volume flow,

• Go slowly – if things happen too quickly, tube blows off or whatever, gently close the bleeder, does not have to be very tight, and regain control,

• Maintain fluid level in the tank at the AHC Pump at all times,

• When pressure has gone, immediately replace old bleeder nipple with new and bleed again. (Note: Air will not suddenly rush into the system -- there is no negative pressure, no 'suction' -- but replace bleeder nipple without any delays),

• Before bleeding the Height Control Accumulator, best to make sure that it has recharged with all other bleeders closed. (It has finished recharging when AHC pump has stopped),

• Repeat bleeding at all points until bubbles are eliminated and fresh pink fluid is flowing -- if this takes more new fluid, then it takes more new fluid,

• If vehicle is slow to rise after this process -- has happened but not often -- then suspect that some residual air is still in the system and bleed again. [Air in the system may cause the AHC system to spend time compressing the air before it gets around to raising the vehicle, causing a slow rise to be observed. Note: A slow rise can be caused by other problems unrelated to the bleeding process such as AHC pump wear or partial blockage of pump internals filters -- but always start with simple things first].

• Be confident -- after you have done this process once, you will wonder why you ever thought it was difficult!

View attachment 2536920

Thank you, sir!