The ABCs of AHC - How to Measure, Flush, and Adjust all in one place (11 Viewers)

[kevgentile]

The early shocks has a smaller top, to fit a smaller hydraulic connector. So you would need that part as well from a newer car.

When you say rusted shafts, do you actually mean the inner shaft, or only the dust shield? The shaft hardly rusts at all, even in my very salty environment, put the outer shield (the biggest diameter of the shocks) rusts away easily. The shield is not required for the functioning of the shock, but should be replaced. It is an easy job to put on a plastic shield instead. It can even be done with the shocks in place, by taking off the bottom mount only. There are pics in here somewhere.

The actual upper double-D threaded shaft under the cushion/retainer stack is severely corroded and lost quite a bit of material. Would probably hold out for quite a while, but could also snap and fail under the right load or hit while off road.

Thanks for the info on the hydraulic line fitting sizes. I figured it was there that made the difference since the part numbers did not carry over.

 

[Pulgasari]

About to do a partial AHC refresh - already have new fluid, globes, and front ram bushings. Would like to do all of them at the same time, does this order make sense?

1. Truck in Low on flat ground
2. Empty old fluid from reservoir with vacuum pump
3. Add most of the new fluid to the reservoir
4. Bleed globes and accumulator piston
5. Use some of the new fluid to lubricate new globes, install new globes
6. Add remainder of fluid to reservoir
7. Place front of vehicle on jack stands
8. Front ram bushings (each side):
   1. Remove tire
   2. Lock ram in position with duct tape
   3. Remove/disconnect ram
   4. Replace bushings and consumables
   5. Reinstall/reconnect ram
   6. Remove duct tape from ram
   7. Install tire
9. Remove front jack stands
10. Follow AHC/TechStream steps to check pressures, adjust torsion bars if necessary, etc...

Still have a few unanswered questions:

• I will be installing my Coastal Offroad rear swingout bumper around the same time (don't know if before or after AHC refresh, depending on when my welder can assemble it), which should add around 160 lbs when fully loaded with full jerry cans. I have sliders, aluminum skids, and a wood sleeper platform, and plan on getting an aux fuel tank at some point in the next few years. Should I go ahead and install some King rear springs?
• Are all 10 items doable in a day if I don't have too much mechanic experience? I don't have room for a hydraulic press and don't have a flat driveway so I'll most likely be doing this at someone else's place... and I'd feel bad leaving my inoperable vehicle overnight.

Thanks for the help so far, can't wait to see how good AHC actually is. It's pretty bumpy with the original 25 year old globes and 15-25 year old fluid.

 

[suprarx7nut]

About to do a partial AHC refresh - already have new fluid, globes, and front ram bushings. Would like to do all of them at the same time, does this order make sense?

1. Truck in Low on flat ground
2. Empty old fluid from reservoir with vacuum pump
3. Add most of the new fluid to the reservoir
4. Bleed globes and accumulator piston
5. Use some of the new fluid to lubricate new globes, install new globes
6. Add remainder of fluid to reservoir
7. Place front of vehicle on jack stands
8. Front ram bushings (each side):
   1. Remove tire
   2. Lock ram in position with duct tape
   3. Remove/disconnect ram
   4. Replace bushings and consumables
   5. Reinstall/reconnect ram
   6. Remove duct tape from ram
   7. Install tire
9. Remove front jack stands
10. Follow AHC/TechStream steps to check pressures, adjust torsion bars if necessary, etc...

Still have a few unanswered questions:

• I will be installing my Coastal Offroad rear swingout bumper around the same time (don't know if before or after AHC refresh, depending on when my welder can assemble it), which should add around 160 lbs when fully loaded with full jerry cans. I have sliders, aluminum skids, and a wood sleeper platform, and plan on getting an aux fuel tank at some point in the next few years. Should I go ahead and install some King rear springs?
• Are all 10 items doable in a day if I don't have too much mechanic experience? I don't have room for a hydraulic press and don't have a flat driveway so I'll most likely be doing this at someone else's place... and I'd feel bad leaving my inoperable vehicle overnight.

Thanks for the help so far, can't wait to see how good AHC actually is. It's pretty bumpy with the original 25 year old globes and 15-25 year old fluid.

Your order of operations sounds fine, but I would strongly recommend you do a few extra steps:

After step 6, bleed the system. completely. Get all the gas out.

After each side on step 8, bleed the first side before doing the other.

Springs: Yes, install them now.

All 10 items doable in a day? Not a chance. Not even for somebody that's done this before. If you're not experienced please give yourself tons of extra time. The last thing you want is to rush this and make a silly mistake on a very user-error punishing system. Give yourself a day to do the globes. Another day to do the springs. Another day to do one ram. Another day to do the other ram. Honestly, if you're not a seasoned mechanic I might skip the ram bushing replacement for now, lol.

AHC work is not necessarily hard, but the chances of getting yourself stuck with too much gas in the system are significant. If you end up with too much gas in the system, it can be very tedious and difficult to get it out. Take your time and bleed often, ensuring the reservoir is full. I wouldn't worry about vacuuming out old fluid. Use the old fluid to bleed out air as you go. Plan on needing to bleed a LOOOOOOT.

Good luck!

 

[Coin]

The ram bushing aren’t difficult with a press, but will take you most of a day to do both.

I managed it with little mechanic experience. You can too. Keep the air out and you’ll be fine. Good luck!

Btw, what’s with the duct tape?

 

[john100]

@john100
Definitely get new rear springs. Get 48231-6A780 (Brown paint spot), if you are not carrying a lot of permanent extra weight. They are slightly stronger than the standard purple spot. Toyota 48231-6A780 (482316A780) SPRING, COIL, REAR - https://www.amayama.com/en/part/toyota/482316a780

If the globes are original, I would say they are probably worn out. The pencil test will only tell if the membrane is completely ruptured or not. You need more force than a pencil can take to test the remaining nitrogen pressure.

Edit: Good job getting the globes off. Looks like you don't give up easily. Make sure to bleed well, and more than once.

@uHu Thank you for your help. I got my new rear springs from Amayama delivered the other week and installed them

I have adjusted the torsion bars and I'm only seeing 0.2 drop in pressure (6.3 and 7.5 rear now)...... However more worryingly I noticed 2 things on my readings.....

1- My steering angle sensor was way out. I have done a reset on that and thats now fine. (obviously over 30 degrees is no good). Great.
2- My Accumulator pressure Sensor reads ZERO!? (same everytime i took a reading, see previous post)

I have to admit I forgot to bleed that last time and I only bled once. I will bleed a couple more times now. However im worried that the accumulator is the issue now?

What do you guys think?

 

[IndroCruise]

@uHu Thank you for your help. I got my new rear springs from Amayama delivered the other week and installed them

I have adjusted the torsion bars and I'm only seeing 0.2 drop in pressure (6.3 and 7.5 rear now)...... However more worryingly I noticed 2 things on my readings.....

1- My steering angle sensor was way out. I have done a reset on that and thats now fine. (obviously over 30 degrees is no good). Great.
2- My Accumulator pressure Sensor reads ZERO!? (same everytime i took a reading, see previous post)

I have to admit I forgot to bleed that last time and I only bled once. I will bleed a couple more times now. However im worried that the accumulator is the issue now?

What do you guys think?

View attachment 3657092

Yes -- best to bleed the Height Control Accumulator.

Probably preaching to the converted but suggest when doing a raise LO > N (or N > HI), listen for the AHC Pump which should continue after the raise is finished and the green AHC light has stopped flashing. Allow say 30 seconds after the AHC light shows constant green with engine and AHC running before reading AHC pressures.

Re-charging the Height Control Accumulator is the last step in the sequence of a raise before the Pump turns itself off.

There is only one Pressure Sensor in the AHC system (next to the Pump). It displays the AHC final pressures in sequence with the Height Control Accumulator reading being the last reading to populate in the ECU memory and then show in Techstream (or other reader).

If still concerned about the Height Control Accumulator, suggest test the raise time LO > N -- should be ~15 seconds on a new stock vehicle, gets longer as the vehicle gets older (and heavier as more things are added to the vehicle).

The Height Control Accumulator has only one function in the AHCsystem -- to speed up the raise. It has no other role at any other time.

Suggest place the vehicle at LO, then listen and feel for the operation of the solenoid on the front end of the Height Control Accumulator when another person presses the button on the centre console to initiate a raise (or, press the button with the LHS Front door open, then close the door when ready for the AHC system to initiate the raise).

If the Height Control Accumulator really seems not to be operating, check the solenoid per FSM. If that checks out, then check the connector for damage and check the harness/wiring for continuity.

 

[Pulgasari]

Your order of operations sounds fine, but I would strongly recommend you do a few extra steps:

After step 6, bleed the system. completely. Get all the gas out.

After each side on step 8, bleed the first side before doing the other.

Springs: Yes, install them now.

All 10 items doable in a day? Not a chance. Not even for somebody that's done this before. If you're not experienced please give yourself tons of extra time. The last thing you want is to rush this and make a silly mistake on a very user-error punishing system. Give yourself a day to do the globes. Another day to do the springs. Another day to do one ram. Another day to do the other ram. Honestly, if you're not a seasoned mechanic I might skip the ram bushing replacement for now, lol.

AHC work is not necessarily hard, but the chances of getting yourself stuck with too much gas in the system are significant. If you end up with too much gas in the system, it can be very tedious and difficult to get it out. Take your time and bleed often, ensuring the reservoir is full. I wouldn't worry about vacuuming out old fluid. Use the old fluid to bleed out air as you go. Plan on needing to bleed a LOOOOOOT.

Good luck!

Thanks so much for the reality check, definitely want to take it slow and not mess anything up since I'm gonna be driving around the country in about a month. Since I'm going to have to bleed it a lot I'll go ahead and order another 2.5L can.

Bushings are going to need to be replaced, whether I do them with some help or take the truck to a shop...

 

[Boondoggle]

Can't thank LndXrsr and the other folks here for the incredible amount of help and knowledge. I did an AHC flush today and other than the catch bottle nipple falling off and making a mesh when I bled the right rear globe everything went great.

I do have one question on torsion bar adjustment for side to side height on the front. I seen folks say raise the AHC to high and leave the wheels on the ground to adjust the torsion bar nuts (30mm) and I've seen folks say it's easier/better to have the wheels off the ground for the adjustment.

I thought at first it was the difference between having and not having AHC but now I'm not sure. I wanted to get find out from the definitive source so I came back here.

So with AHC to adjust the torsion bar for side to side height, is it best to do it wheels on the ground or in the air?

Thanks again for all your time and sage advice!!!

 

[IndroCruise]

I do have one question on torsion bar adjustment for side to side height on the front. I seen folks say raise the AHC to high and leave the wheels on the ground to adjust the torsion bar nuts (30mm) and I've seen folks say it's easier/better to have the wheels off the ground for the adjustment.

The point of raising the vehicle to use the Torsion Bar adjusters on an AHC-equipped vehicle is only because in that condition less weight is carried by the Torsion Bars (and more weight is carried by the AHC 'Shock Absorbers' which really are just hydraulic struts) -- and in that way some folks then find it easier to turn the Torsion Bar adjuster bolt.

However, once the adjustment is done, the measurement to check Front cross-level, meaning the Front Left and Front Right heights, is done typically by measuring with a tape-measure (not Techstream nor any scanner) from hub-centre to wheel arch. This measurement should be done with the vehicle returned to "N" height using the console switch, with wheels straight ahead, on the ground on a level surface, and with the engine OFF after "N" height is achieved. See attached FSM extract. The FSM mentions a tolerance of +/- 10mm or +/- 0.39 inches but it usually is possible to do better than that.

The point of so-called Front "cross-levelling" is simply to equalise the Left and Right heights with the vehicle in a static condition at "N" height to ensure that

• the vehicle does not have a built-in lean to one side, which if significant, can confound the AHC system (meaning the Height Control Sensors, the Levelling Valves, ECU and the AHC Pump) in attempts to automatically self-level the vehicle in real time -- which is what is meant by Active Height Control (AHC), and to ensure that,
• the torsion bars are equally loaded -- which if significantly different will affect the way the vehicle behaves when turning Left versus turning Right,

It does not matter what the actual height measurements are when "cross-levelling", the aim is simply to equalise them at "N" height with engine OFF.

On an AHC-equipped vehicle, Torsion Bar adjustment and cross-levelling etc has nothing to do with setting the 'ride height' of the vehicle.

Adjusting the 'ride height' is done at "N" height using the Height Control Sensor adjusters, and not the Torsion Bar adjusters.

The other use of the Torsion Bar adjusters in an AHC-equipped vehicle is to increase (or reduce) the weight carried by the Torsion Bars and in that way vary the weight carried by the AHC system (via the 'Shock Absorbers' acting as hydraulic struts). In this way, the Front AHC pressure can be adjusted. The aim is for the AHC pressure to be within the FSM-specified range (preferably towards the lower end) for optimal damping performance and best 'ride comfort'.

 

[bobNoobie]

Guys I am in a pickle. My AHC fluid barfed itself out from the rear driver side shock top mount

I really want to save the AHC but I don't think I have the will to do it myself with getting really hurt.

Looking at this condition and not being able to do DIY? Should I take the bitter pill and conver to regular land cruiser suspension?

New video · Thursday, Aug 15, 2024 ð¬

Tap to view!

photos.app.goo.gl

 

[suprarx7nut]

Guys I am in a pickle. My AHC fluid barfed itself out from the rear driver side shock top mount

I really want to save the AHC but I don't think I have the will to do it myself with getting really hurt.

Looking at this condition and not being able to do DIY? Should I take the bitter pill and conver to regular land cruiser suspension?

New video · Thursday, Aug 15, 2024 ð¬

Tap to view!

photos.app.goo.gl

That is a rusty vehicle. I would covert that over.

I'd also have your brake lines inspected closely. If the AHC lines are going, the brake lines must be shortly behind...

 

[baltistyle]

That is a rusty vehicle. I would covert that over.

I'd also have your brake lines inspected closely. If the AHC lines are going, the brake lines must be shortly behind...

As a lover of a rust free ahc vehicle, I’d have to agree here. With all the rust, I don’t know that I’d invest in that truck. I had a rusty hundred, then upgraded to rust free to make the money spent a better value. IMHO

 

[Nori470]

Ahc noob here, so apologies if the answer can be found in here. I’ve read though a large portion but have not seen the answer…

I am currently looking at an ahc truck with some rust, but does not look critical. I was told the ahc tank is dry and the rear is sagging. Is this a huge mechanic bill in the waiting, or can it be revived reasonably easy with new globes/fluid?

Thank you in advance!

 

[suprarx7nut]

Ahc noob here, so apologies if the answer can be found in here. I’ve read though a large portion but have not seen the answer…

I am currently looking at an ahc truck with some rust, but does not look critical. I was told the ahc tank is dry and the rear is sagging. Is this a huge mechanic bill in the waiting, or can it be revived reasonably easy with new globes/fluid?

Thank you in advance!

"Some" rust and a bone dry reservoir are not great signs. Why wouldn't they simply top off the reservoir?

Sounds suspicious to me.

 

[Nori470]

He said he was on a road trip with extra weight in the back when he thinks it leaked out the rear shock or globe. He agreed to take it to Lexus for an inspection before I make any decision.

Does this sound like big money? The asking price is decent enough where I would be comfortable spending some to bring it back to spec.

Thanks for the reply!

 

[baltistyle]

He said he was on a road trip with extra weight in the back when he thinks it leaked out the rear shock or globe. He agreed to take it to Lexus for an inspection before I make any decision.

Does this sound like big money? The asking price is decent enough where I would be comfortable spending some to bring it back to spec.

Thanks for the reply!

If going to a Lexus dealer, they will either refuse to fix, or quote the whole system. 5-7k If anything, it’s a point of negotiation, but it CAN BE one of the most expensive repairs to these trucks. Once diagnosed, come back and we can help. A dry pump likely needs replaced, and at least the line that leaked. If not maintained, then globes or “shocks” or lines are needed as well.

Invest in a rust free truck that is working and that money will be best spent, even on ahc. I’ve just written in another thread to someone else with a rusty AHC line that I had a rusty 100 and learned that lesson and then bought a completely rust-free one so when repairing it, it was a better value for longevity of the repairs and truck. I don’t feel bad spending the money knowing the rust is not slowly taking the truck from me. Parts can be expensive but last forever (that 250k, 25 year claim)when maintained.

 

[suprarx7nut]

He said he was on a road trip with extra weight in the back when he thinks it leaked out the rear shock or globe. He agreed to take it to Lexus for an inspection before I make any decision.

Does this sound like big money? The asking price is decent enough where I would be comfortable spending some to bring it back to spec.

Thanks for the reply!

That will be a good negotiating point for you, but I wouldn't expect too much helpful info from Lexus.

I wouldn't buy a rusted LX. Living in Dallas, you have access to plenty of cars in the west that might basically have zero rust. Not worth the hassle.

 

[Pulgasari]

Alright, I just swapped in the Kings and tried to do an AHC flush and globe replacement, and the truck will now go into H but not L.

Will I damage anything by doing a flush in N? Should I swap back the old OEM springs on to try and get it to go into L?

 

[IndroCruise]

Alright, I just swapped in the Kings and tried to do an AHC flush and globe replacement, and the truck will now go into H but not L.

Will I damage anything by doing a flush in N? Should I swap back the old OEM springs on to try and get it to go into L?

Mmmm -- I have the recommended King KTRS-79 springs fitted on LH Rear and RH Rear and find that it sinks to LO when required, no problem.

Suspect other causes may need investigation, such as

-- anything binding in the mechanical suspension which may restrict movement,

-- condition and age of Height Control Sensors (poor sensors can send an erroneous voltage signal to the Suspension ECU causing strange effects WITHOUT indicating a DTC),

-- there may be other causes.

Meanwhile, no damage is done by bleeding after dropping from HI to N -- but it does mean that the 'shock absorbers' are not sweeping through their full stroke, not clearing out as much as possible of air-polluted fluid. This will make bleeding less effective -- but probably solved with multiple bleeding attempts.

 

[Pulgasari]

Mmmm -- I have the recommended King KTRS-79 springs fitted on LH Rear and RH Rear and find that it sinks to LO when required, no problem.

Suspect other causes may need investigation, such as

-- anything binding in the mechanical suspension which may restrict movement,

-- condition and age of Height Control Sensors (poor sensors can send an erroneous voltage signal to the Suspension ECU causing strange effects WITHOUT indicating a DTC),

-- there may be other causes.

Meanwhile, no damage is done by bleeding after dropping from HI to N -- but it does mean that the 'shock absorbers' are not sweeping through their full stroke, not clearing out as much as possible of air-polluted fluid. This will make bleeding less effective -- but probably solved with multiple bleeding attempts.

Thanks for that info. I do plan on swapping the sensors at some point soon.

I was able to get it to go into L by putting some more weight in the truck and driving it a bit, and it’s visibly in L now.