AHC Time LO to N, N to HI, LO to HI (1 Viewer)

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GTV

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I've seen this post by @IndroCruise but I'd like to know what other members experience is on this particular aspect of AHC.

Some backstory... I decided that at 207k miles it was time to replace the original globes on my '07 LC. My AHC pressures are well within spec. I got a good deal on globes from Impex and did the job along with a fluid flush on New Year's Day. I accidentally overshot the bleed so the fluid level was just under minimum at N height. Not enough to be alarmed about, but I did drive gently and didn't put it in HI for the last couple weeks out of caution.

Right away I noticed that it was taking an exceptionally long time to go from LO to N. What was normally done by the time I got to the end of my street, now was the end of the block. And the difference in ride quality I was expecting with the new globes just wasn't there. I figured air was still in the system so I immediately ordered up a fresh 2.5L can of AHC fluid to bleed it out again.

Got on it today. Did a drive earlier so I started with a warm truck. First thing, I couldn't find the 10mm wrench I use for bleeding. Classic car guy problems. Anyway, as per usual I followed the ABCs of AHC thread and got to bleeding. I did not suck the old fluid out of the reservoir as it had only been in there for less than two weeks. I just added to the reservoir and got to bleeding. A good amount of air was coming out of the system so that was a good sign. I got to the right front bleeder and found my 10mm bleeding wrench hanging out.
3E56E368-118C-45CA-B2AF-A215B644D4AC.jpeg

After the bleed the fluid level was spot on in N so I ran some tests. Here's the time from LO to HI. Without me in the seat, from the time I shut the door until the light stopped flashing.
B27AF843-AC47-4022-8F04-24BB1151AF76.png

That seemed like way too long to me. I still had extra fluid so I decided to bleed it again. More air came out, especially from the accumulator. Ran the test again.
F7A12210-A63F-46F1-BDB7-BEB74BB0BF0D.png

What the hell. I still have more fluid left in the can so might as well give it a third bleed. After the third bleed I was out of fresh fluid but the level was right on the MAX mark at N height on the reservoir. I ran the test again, forgot to screenshot it but it was around 56 seconds. So I tried it from LO to N.
DD7487C6-C74D-46E8-BA17-BB0BBBB8E7EA.png

That seems reasonable, I think? I tried it from N to HI and once again forgot the screenshot but it was at 24 seconds. That seems odd, 19+24= 43 but it takes a lot longer to go straight from LO to HI. So I ran the LO to HI test again for giggles.
2496E969-2937-4D98-B2EC-C101C77CCAD1.png

In any case, my ride quality does feel very much improved. If I had a 55 gallon drum of AHC fluid I'd keep pumping it through there but at roughly $70 a can delivered this could expensive really fast. Maybe I'll plan on replacing the pump the next time I need to do a fluid flush(?) I'm curious to know what others have experienced, what are your times?
 
Crickets in here! I had a chance to check mine as I waited for a train taking the kiddos to daycare. I had the truck in Park, foot off brake, and started timer from when I pushed the button. So these times include myself and two kiddos 4 and under in the back.

Truck history:
244k miles
4 globes replaced in the last 100k miles
Fluid flush done in 2021 at 225k


L to N: 13.03
N to H: 13.10
L to H: 24.03

*Edit: I'm posting just to add some timing data. My AHC seems to be in great shape with what I believe were about 12 graduations when I checked in 2021.
 
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A standard check on AHC is to count the fluid gradation between low and high on the container under the hood. What are those showing?
 
Crickets in here! I had a chance to check mine as I waited for a train taking the kiddos to daycare. I had the truck in Park, foot off brake, and started timer from when I pushed the button. So these times include myself and two kiddos 4 and under in the back.

Truck history:
244k miles
4 globes replaced in the last 100k miles
Fluid flush done in 2021 at 225k


L to N: 13.03
N to H: 13.10
L to H: 24.03

*Edit: I'm posting just to add some timing data. My AHC seems to be in great shape with what I believe were about 12 graduations when I checked in 2021.

Great numbers, that gives me a target.

A standard check on AHC is to count the fluid gradation between low and high on the container under the hood. What are those showing?

I haven't checked recently. When I bought my 100 two and a half years and 43k miles ago I remember that it was on the lower end of the range. I'll check again this weekend.

Since last weekend I feel like the ride quality has improved since the first flush but it's still not where it should be and the high times are testament to that. I think I'll order up another 2.5L tin of fluid and try not to contaminate what I bleed out this time so I can flush it back through if needed.
 
Curious, are you timing it when the light hold solid or when you hear the pump stop working? There seems to be a variance between those two, at least in my rig (11 graduations).
 
Curious, are you timing it when the light hold solid or when you hear the pump stop working? There seems to be a variance between those two, at least in my rig (11 graduations).
I just did it based on the light since I was in the truck with kids.

I can do more tests more in line with the OP:
-Lean in to push button with door open
-Hop out, close door, start timer
-Stop timer when pump stops
 
I noticed when I replaced the front two height sensors, This shortened the time drastically. Not sure what happened but im back to having slightly long times again. I did notice that its not as long as it was before I replaced the front sensors. Im going to replace the rear sensor to see if that can resolve it once and for all. I read a thread somewhere saying if one of the three sensors are slower in response times, the entire system will go at that slower sensors pace. Cant find that thread
 
Curious, are you timing it when the light hold solid or when you hear the pump stop working? There seems to be a variance between those two, at least in my rig (11 graduations).

When the light goes solid the height is set. The pump will keep going for a bit.
 
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So I decided to bleed just the accumulator to save the (nearly new) fluid and dump it back in the res. I got some more air out at first then it went to a solid stream. Naturally some ended up on my floor so between that and the air volume that I bled out my reservoir is now at the MIN line in N height.

Did a graduations test and I'm easily at 14+ from LO to HI.

Did a time test again. 18 seconds from LO to N, 24 seconds from N to HI and 51 seconds from LO to HI. Better. I'd like to bleed out each corner at least one more time to be confident that I've got all the air out but I'll need some more fluid first. In HI the fluid is really low in the reservoir so I'd prefer some more insurance anyway.
 
So I decided to bleed just the accumulator to save the (nearly new) fluid and dump it back in the res. I got some more air out at first then it went to a solid stream. Naturally some ended up on my floor so between that and the air volume that I bled out my reservoir is now at the MIN line in N height.

Did a graduations test and I'm easily at 14+ from LO to HI.

Did a time test again. 18 seconds from LO to N, 24 seconds from N to HI and 51 seconds from LO to HI. Better. I'd like to bleed out each corner at least one more time to be confident that I've got all the air out but I'll need some more fluid first. In HI the fluid is really low in the reservoir so I'd prefer some more insurance anyway.

This all looks very healthy -- reflecting usual @GTV care and attention to detail.

FSM suggests the following numbers for raise times and height differences.

100 series - AHC vehicle height  variation.jpg

Your raise times look reasonable.

AHC Raise times will vary with
  1. air in the system – your repetitive bleeding appears to be eliminating air, persistence pays, AHC Pump spends less time compressing air (or nitrogen),
  2. nitrogen in the system, leaking through slowly failing membranes in old ‘globes’ -- your fluid displacement “HI” to “LO” with 14+ graduations mentioned suggests overall healthy ‘globes’ IF the test is done with AHC pressures within the FSM-specified ranges,
  3. high vehicle mass compared to ex-factory stock condition with no persons, no build or accessories, no load, fuel full,
  4. adverse condition of the AHC Pump -- age and wear and also more particularly the condition of the internal strainers inside the Pump and also the Strainer inside the Return Valve. (The Intake Strainer rather than the Bypass Strainer or the Return Valve Strainer are the more usual problem),
  5. faulty Height Control Accumulator -- the ONLY purpose and function of this Accumulator is to speed up “LO” to “N” and “N” to “HI” raise, otherwise it does nothing during vehicle operation,
  6. increasingly common AHC harness problems – especially the BI1 connector high up toward the back inside the LHS Rear quarter panel (same for LHD and RHD vehicles) -- see alerts published on this forum by @suprarx7nut and @2001LC -- also see my Post #9 with pics in this thread which also leads to other Posts with pics: https://forum.ih8mud.com/threads/ahc-done.1299423/#post-14719487
Suggest stay with Toyota/Lexus AHC Fluid in 2.5 litre cans -- Part Number 08886-01805 -- unless all doubts have been overcome with quality (gel issues) in US supply of AHC Fluid in 1 litre plastic bottles -- Part Number 08886-81221.

AHC Fluid which has passed through the system inevitably will have picked up some aeration and debris. New fluid is best if possible -- but becomes expensive when doing multiple bleeds. If re-using AHC Fluid, suggest let it stand as long as possible (overnight?) to allow air, nitrogen to dissipate to atmosphere and visual cleanliness can be inspected.

In my own case of longstanding very slow and incomplete raise “LO” to “N” during testing (improves after driving), all other causes have been addressed, so I am suspecting harness issues. The only problem is that I live in Brisbane in Eastern Australia but the vehicle lives with my son-in-law in Perth Western Australia -- the test write-up I did for him is attached. We will get back to it one day!!

Meanwhile, all and any advice or suggestions are welcome.

Australia-USA Map.jpg


Brisbane-to-Perth distance map.jpg
 

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This all looks very healthy -- reflecting usual @GTV care and attention to detail.

FSM suggests the following numbers for raise times and height differences.

View attachment 3225941
Your raise times look reasonable.

AHC Raise times will vary with
  1. air in the system – your repetitive bleeding appears to be eliminating air, persistence pays, AHC Pump spends less time compressing air (or nitrogen),
  2. nitrogen in the system, leaking through slowly failing membranes in old ‘globes’ -- your fluid displacement “HI” to “LO” with 14+ graduations mentioned suggests overall healthy ‘globes’ IF the test is done with AHC pressures within the FSM-specified ranges,
  3. high vehicle mass compared to ex-factory stock condition with no persons, no build or accessories, no load, fuel full,
  4. adverse condition of the AHC Pump -- age and wear and also more particularly the condition of the internal strainers inside the Pump and also the Strainer inside the Return Valve. (The Intake Strainer rather than the Bypass Strainer or the Return Valve Strainer are the more usual problem),
  5. faulty Height Control Accumulator -- the ONLY purpose and function of this Accumulator is to speed up “LO” to “N” and “N” to “HI” raise, otherwise it does nothing during vehicle operation,
  6. increasingly common AHC harness problems – especially the BI1 connector high up toward the back inside the LHS Rear quarter panel (same for LHD and RHD vehicles) -- see alerts published on this forum by @suprarx7nut and @2001LC -- also see my Post #9 with pics in this thread which also leads to other Posts with pics: https://forum.ih8mud.com/threads/ahc-done.1299423/#post-14719487
Suggest stay with Toyota/Lexus AHC Fluid in 2.5 litre cans -- Part Number 08886-01805 -- unless all doubts have been overcome with quality (gel issues) in US supply of AHC Fluid in 1 litre plastic bottles -- Part Number 08886-81221.

AHC Fluid which has passed through the system inevitably will have picked up some aeration and debris. New fluid is best if possible -- but becomes expensive when doing multiple bleeds. If re-using AHC Fluid, suggest let it stand as long as possible (overnight?) to allow air, nitrogen to dissipate to atmosphere and visual cleanliness can be inspected.

In my own case of longstanding very slow and incomplete raise “LO” to “N” during testing (improves after driving), all other causes have been addressed, so I am suspecting harness issues. The only problem is that I live in Brisbane in Eastern Australia but the vehicle lives with my son-in-law in Perth Western Australia -- the test write-up I did for him is attached. We will get back to it one day!!

Meanwhile, all and any advice or suggestions are welcome.

View attachment 3225949

View attachment 3225953

I really appreciate the detailed responses you always give!

My weight is currently very close to stock and I have approximately 19mm of sensor lift. I have Kings springs with 40mm (L) and 30mm (R) of spacers which is a bit overkill for daily driving but when the awning, RTT and bike rack is fitted the pressures are very good- I spent a lot of time this past August dialing it in. Soon I will install my sliders and skid plates which will add another 100kg or so. Then I have a pair of LX570 coils that I want to try out, they are much longer than the Kings and are different lengths as you would expect from Toyota.

I assumed the accumulator was there to speed up raising the vehicle, thanks for the confirmation. I'm curious to know why I'm still getting air through there after so many bleeds though.
 
Just finished bleeding an additional 2.5L through just the accumulator (I salvaged what came out this time).

I'm still getting air through it.

Bad accumulator?
 
Just finished bleeding an additional 2.5L through just the accumulator (I salvaged what came out this time).

I'm still getting air through it.

Bad accumulator?
Sounds like it. Tiny bubbles emulsified in the liquid? Or like glugs?
 
Sounds like a failing bladder. I can't recall if there's a unique test procedure for that beyond the raise times.

The bladder is part of the accumulator I'm assuming?

A "burst" of air/fluid to start is more accurate. I find it interesting that something failed right after installing new globes.
 
The bladder is part of the accumulator I'm assuming?

A "burst" of air/fluid to start is more accurate. I find it interesting that something failed right after installing new globes.
Diaphragm is probably a better term than bladder. Yes, the diaphragm contains the nitrogen gas in each globe and the height accumulator. If it fails it can burst or just leak.

Never ending fine bubbles are a sign of a leak.

If you just changed globes then perhaps you're just experiencing a little stubborn air and you just need to keep bleeding. It can be tedious.
 
Diaphragm is probably a better term than bladder. Yes, the diaphragm contains the nitrogen gas in each globe and the height accumulator. If it fails it can burst or just leak.

Never ending fine bubbles are a sign of a leak.

If you just changed globes then perhaps you're just experiencing a little stubborn air and you just need to keep bleeding. It can be tedious.

I've bled eight liters through the system since changing globes but the accumulator bleed doesn't seem to be improving. And the time to raise is getting worse. That doesn't seem normal to me?

49130-60010 is currently $352 shipped via Impex. Not bad, I just don't want to be blindly throwing parts at this thing. I also have a low(er) mileage pump assembly on the shelf just in case.

I'm not finding a lot of info when it comes to changing the HCA out. I would think that I would just need to bleed it first to take the pressure off, remove the lines (hopefully there are valves to keep the hydraulic fluid from just running out?), unbolt it and bolt the new one back in place. This post by @IndroCruise makes it sound like a dangerous proposition though.
 
I've bled eight liters through the system since changing globes but the accumulator bleed doesn't seem to be improving. And the time to raise is getting worse. That doesn't seem normal to me?

49130-60010 is currently $352 shipped via Impex. Not bad, I just don't want to be blindly throwing parts at this thing. I also have a low(er) mileage pump assembly on the shelf just in case.

I'm not finding a lot of info when it comes to changing the HCA out. I would think that I would just need to bleed it first to take the pressure off, remove the lines (hopefully there are valves to keep the hydraulic fluid from just running out?), unbolt it and bolt the new one back in place. This post by @IndroCruise makes it sound like a dangerous proposition though.
When you say raise time is worse are we talking 25 seconds instead of 15? Or are we talking 60-90 seconds?

I think the change out procedure is pretty straightforward if the bleeder is functional. The post from Indro Cruise was for a broken bleeder where the system pressure remains within the unit during disassembly. I think if you found yourself in that situation you could just very slowly crack the fluid connection loose. It will leak fluid and relieve pressure before it comes loose. That's essentially your bleeder. Messy and perhaps dangerous, but minimally so if done with care. He's right to urge caution with high pressure hydraulic fluid though. Thick gloves and of course eye pro are a must if you can't discharge pressure properly.

I think the system will inevitably drool out plenty of fluid and require some extensive bleeding for the HCA changeout.
 

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