Definitive list of AHC maintenance items (4 Viewers)

[yuji]

My nagging "issue" with AHC is wondering if the suspension doesn't feel quite right. I feel bumps pretty well and I subjectively recall an older 100 series land cruiser standard suspension feeling like being on a cloud vs the small cracks in the road. The question is driving me insane when I'm on the road..

I've read what seems like every AHC topic on here over the past few months before and after my LX470 purchase. Knowledge is there but spread around.

I'd like to replace the major AHC wear items short of the globes and it would be very useful to confirm these steps in one post, for myself and others as well wondering about their suspension.

Here's what I've come up with for the most bang for the buck: please let me know if you'd add or remove anything / change ordering, etc. For the record, my LX is at 117k miles.


First you would want to diagnose if you have a problem with your AHC.
Unfortunately, the only test I know of is to check if your globes are bad via the "Height Test".
I have no way of knowing whether the other components are bad or if my ride is standard / okay. I just have a gut feeling that it can be improved. At worse, you'll be extending the life of your AHC by reducing wear on it.



AHC height test.
Put vehicle in LOW. Mark fluid level in AHC reservoir.
Put vehicle in HIGH.
Number of graduations (ticks) on the reservoir from LO to HI should be at least 7. If less, your globes are shot and it's very expensive to replace.

I personally get 14 or so so it appears they are in great condition.



Assuming those globes are fine, it's time to start working:



Flush AHC fluid.
https://forum.ih8mud.com/100-series-cruisers/438560-ahc-fluid-change-how-need-input.html#post6127557

Cost: $40 / can. Need 2.
Dealer charge around $200-250.
Difficulty: Easy.

Result: Many report increased ride quality. I didn't notice so much when the dealer did it. I am going to buy 2 cans and flush it till it's clean.




Test neutral pressure / crank torsion bars accordingly
Neutral pressure is the pressure of the AHC system at each wheel in the N position. The AHC system is designed to carry a certain load while the torsion bars in the front / coils in the rear pick up the rest.

My dealer refuses to check the neutral pressure for me saying it's only what crazy enthusiasts do so I've found a product called the Tactrix Open Port 2.0 which can read the pressures.

Once you have the pressures up front, you'll be able to crank the torsion bars until the AHC system is carrying the correct load. Others blindly do 3-6 cranks every 5 years.

Here's a post from somebody who cranked Tbars based on neutral pressure data: https://forum.ih8mud.com/100-series-cruisers/529309-measure-ahc-neutral-pressure.html

Cost: $100-200 used/new for Tactrix Open Port 2.0 Cable There's a $35 alternative discussed below; waiting for reports.
Cost at dealer: they cowardly refuse.
Result: Haven't done it yet. Hopefully noticeable.




Replace Rear Coil Springs
The neutral pressure test will probably show the rear AHC pressures too high due to age of the rear coils.

Posts on mud suggest 5 years max before rear AHC starts going over spec on load.

Anything else in this rear suspension setup I should replace?

Part numbers:
48231-6A730
48231-6A740

Cost: ~$200 for parts.
Cost at dealer / mechanic: ?
Result: haven't done it yet.




My hope is that after these changes I'll have done as much as I can (without spending too much) for my ride.

Any comments, additions, etc. appreciated.

 

[arbetrader]

I appreciate you posting this. It's nice to find this useful info in one thread. Cheers

 

[matticus]

Subscribed. Great list!

 

[SaadUK]

Thanks for the useful thread. If possible please mention do-it-yourself type of tutorials for maintaining and trouble shooting AHC. I found a scanner that shows the pressure values on each sensor. If my vehicles values are out, the way to adjust them is by adjusting torsion bars clock/anti clockwise ?

One more thing I am looking for is, almost everybody has his own way for bleeding and flushing AHC fluid. Any standard and easiest way to do that? Some say clear the fluid from accumulator completely , other say it will draw air into the system and things like that. Thanks.

 

[SerasLibre]

I just stumbled across a Tundra forum where they link to Techstream software and cable for $35! I have ordered mine and will post when I receive it.

TechStream software and cable for $35 - TundraTalk.net - Toyota Tundra Discussion Forum

 

[Jaws619]

very informative thanks!

 

[00N8]

I just stumbled across a Tundra forum where they link to Techstream software and cable for $35! I have ordered mine and will post when I receive it.

TechStream software and cable for $35 - TundraTalk.net - Toyota Tundra Discussion Forum

Thanks for the link, I'm going go order one and see how it works.

 

[agaisin]

I'm really curious to see whether it works better than the Tactrix solution. Here are two areas where Tactrix solution has not worked but I don't know if it's a Tactrix only issue, also a Mongoose cable issue or a Techstream issue (yes there are known bugs in Techstream):
1) In the AHC ECU, I can run active tests to verify individually that the Main Relay, Motor Relay, Accumulator Solenoid, Front Gate Solenoid, Front Leveling Solenoid, Rear Gate Solenoid, and Rear Leveling Solenoid all work (on/off). However, when I run the "all signal" or "one signal" test I get an error code 0x91010009 that says it lost communication with the vehicle.

2) Customize Settings - many of them do not work. Some have reported that they haven't been able to control any of them with Tactrix and Techstream. Personally with versions 6.01.021 and 7.10.030 of Techstream I have been able to at least access the Wireless Door Lock and the Door Lock customize functions (they take very long to load up - like a few minutes). Here's a list of them:
Wireless Door Lock, Security, Wiper, Warning, Tilt & Telescoping Steering wheel, Smar Key/Access, Seat, Door Lock, Power Window, Illuminated Entry, Light Control, Slide Roof, TVSS, Others.

I don't think I've tried them all but the other ones I did try, I don't think worked for me. For interest's sake, I tried using the Tactrix cable with the TIS VIM, with the Mongoose MFC VIM and neither of those work with the tactrix cable (I guess to be expected since Tactrix uses it's own drivers). I also "upgraded" to the beta version of the tactrix (have to install the full ECUFlash package) and I still got the same error in #1 above, and I don't think anything new worked in the customize settings either - certainly most of what I tried there still didn't work.

Btw, to get an idea of the kinds of bugs that exist even with the official TechStream Lite here's the known bugs list for v7.12 of Techstream: https://techinfo.toyota.com/techInf...chinfo/html/prelogin/tsrss/ts_known_bugs.html
(I currently have 7.10.030 but don't have the list of known bugs for my version)

I'd be very interested to hear what works and doesn't work with the other solutions out there.

 

[chadiln]

Thanks for the link, I'm going go order one and see how it works.

X2

Just ordered one... and don't' forget to use Coupon Code 960908 for an additional 2% discount.

 

[agaisin]

Thanks for the useful thread. If possible please mention do-it-yourself type of tutorials for maintaining and trouble shooting AHC. I found a scanner that shows the pressure values on each sensor. If my vehicles values are out, the way to adjust them is by adjusting torsion bars clock/anti clockwise ?

One more thing I am looking for is, almost everybody has his own way for bleeding and flushing AHC fluid. Any standard and easiest way to do that? Some say clear the fluid from accumulator completely , other say it will draw air into the system and things like that. Thanks.

Regarding your question on how to adjust the torsion bars, on an AHC equipped vehicle you should only adjust torsion bars for 2 reasons:
1) To level front left and front right. For example if the front left is too high, you could either crank (clockwise) TBar on front right to get it up or crank down (counter clockwise) TBar on front left to bring it down. Seems most typical for the driver's side to sag over the years so in the US at least most of us find that we need to crank (clockwise) the drivers side TBs up a bit to get it level with the front right.
2) To adjust neutral pressure on the front shocks. In this case you would crank (clockwise) both TBars up (equal amounts on each side) to bring neutral pressure down, and you would crank down (counter clockwise) on both TBars (equal amounts on each side) to bring neutral pressure up.

To appreciate this better, just picture that the TBars are supporting roughly 60% of the vehicle's weight and the hydraulic pressure of the AHC system is supporting the remaining 40% under normal conditions. Actually the AHC will pump or release pressure as needed to maintain the vehicle's set height (based on readings from the AHC height sensors).

By cranking the TBars clockwise, you are increasing the amount of weight the TBars support, therefore less pressure is required by the hydraulic system to maintain the set height so you are in effect decreasing the neutral pressure by cranking TBars clockwise. By turning tbars counterclockwise you decrease the amount of weight the TBars carry, and increase the amount of weight the AHC system carries and in effect the neutral pressure is increased. Now - you might think that you'd measure pressure and adjust pressure on front left separately from front right but that's not correct. There's a Valve that opens and closes the oil passage between the front right and left shock absorbers. Normally it stays open (typically closes when your steering wheel is turned >30 degrees). Since that valve is open when you take your readings, the pressure is the same for both front left and right - there's only one value for the front and one pressure reading for the rear. Therefore, when you're making adjustments to the front neutral pressure you really need to adjust both tbars equally or else you will create a lean. The only time you adjust front left alone or front right alone is to correct a lean in the front.

Regarding your question about bleeding, see the thread that the yuji the OP linked to: https://forum.ih8mud.com/100-series-cruisers/438560-ahc-fluid-change-how-need-input.html

You asked "Some say clear the fluid from accumulator completely, other say it will draw air into the system and things like that."

I believe the only way you could draw air into the system would be to drain so much fluid at one time that the reservoir runs empty. Even in that case, there is a procedure to fix the issue. Also, if you were afraid of that happening (like you just replaced all globes and shocks?), you could have someone standing at the reservoir refilling as the fluid level goes down...

If you are conservative in your bleeding approach and you only bleed (and refill as you go) one accumulator at a time while in Low, you should be fine. There were three important points there:
1) one accumulator at a time (to be conservative don't shortcut and do more than one accumulator at once)
2) refill as you go - in other words make sure when you start you're at full reservoir capacity (actually fill up to the top of the reservoir if you want to be safe), then you go into Low and bleed as much as will come out from a single accumulator, then raise to N height and the fluid level will come down, then refill back up etc... Also - if your goal is to COMPLETELY replace fluid (and not just to bleed air), you may want to empty the reservoir - that's fine, but refill it with fresh fluid prior to raising the system or you will have an empty reservoir and draw air into the pump...
3) while in Low - in other words, if you are in Normal or High height and bleed, you may bleed more than the reservoir can hold which means unless your standing there filling as the level goes down you may draw in air. So be sure to go into Low first.

Following those tips I don't think you have to worry about drawing air into the system.

 

[yuji]

X2

Just ordered one... and don't' forget to use Coupon Code 960908 for an additional 2% discount.

Any word on this?

 

[uHu]

got one. works like a charm. fantastic. gives all the data i need. 1st thing i did was switching off the auto up-and-away steering wheel. Didn't get any stored/history fault codes tho. Shouln't there be some?

Also, I can see that the steering wheel position data in the ahc-ecu is wrong. When going straight, it shows 30-35 deg, which is when the gate-valves close, so that's not good. Couldn't find a way to reset it. Maybe I have to move the steering wheel and then adjust the tie-rods.

 

[agaisin]

got one. works like a charm. fantastic. gives all the data i need. 1st thing i did was switching off the auto up-and-away steering wheel. Didn't get any stored/history fault codes tho. Shouln't there be some?

Also, I can see that the steering wheel position data in the ahc-ecu is wrong. When going straight, it shows 30-35 deg, which is when the gate-valves close, so that's not good. Couldn't find a way to reset it. Maybe I have to move the steering wheel and then adjust the tie-rods.

With vgrs (variable gear ratio steering) you would normally use the steering angle adjust procedure - there's a utility function in techstream. Just read the fsm on it beforehand.

also - if/when you have a chance could you test out some of the features above i listed and let me know whether they work for you or not? like the all signal test for ahc, and which of the customize functions are you able to see/use? like i assume you changed your steering wheel settings in he the tilt & telescopic steerin wheel section of customize functions?

wow - good to know about this other option - for the price i moght just get this too if stuff works with it that doesn't work on the tactrix...
Sent from my iPhone using IH8MUD

 

[yuji]

Thanks for he heads up guys. At the price I've ordered one just now.

Agaisin I will definitely post about it when I get it. Thanks for your awesome input!

 

[RoderickGI]

Thanks for he heads up guys. At the price I've ordered one just now.

Agaisin I will definitely post about it when I get it. Thanks for your awesome input!

For those who have bought this device, or who are considering it, like me, just be aware of this comment from the manufacturer: XHorse • View topic - Mini VCI Drivers

It looks like there will be no future updates for this device. It is end of life. But I can live with that for $35.

 

[white_lx]

Replace Rear Coil Springs
The neutral pressure test will probably show the rear AHC pressures too high due to age of the rear coils. Posts on mud suggest 5 years max before rear AHC starts going over spec on load. Anything else in this rear suspension setup I should replace?

An alternative is to add air bags to the springs. This also allows to keep the AHC pressures nominal with heavy trailers. This is the route I'm going (still have to add the bags).

 

[RoderickGI]

An alternative is to add air bags to the springs. This also allows to keep the AHC pressures nominal with heavy trailers. This is the route I'm going (still have to add the bags).

Having gone the heavier springs route, I now tend to agree with this, as it allows you to adjust the bags according to the load you have in the truck. When I did the work on my truck there weren't any suitable solutions though. I believe that they are now.

However, my brother added air bags a couple of years ago, and they wore out and holed pretty quickly, so make sure you pick high quality bags.

 

[chadiln]

Any word on this?

Mine just came in this morning.

I have gone ahead and changed the rear coil springs and flushed AHC fluid during the wait... Now I gotta go find my Windows laptop somewhere in my junk pile.

Will report back with the AHC readings.

 

[yuji]

Having gone the heavier springs route, I now tend to agree with this, as it allows you to adjust the bags according to the load you have in the truck. When I did the work on my truck there weren't any suitable solutions though. I believe that they are now.

However, my brother added air bags a couple of years ago, and they wore out and holed pretty quickly, so make sure you pick high quality bags.

Air bags sound great! They just sound a bit pricey. If you carry highly variable loads though, it sounds like it's an amazing option.

What's the consensus cost on a reliable airbag setup including stuff like AHC pressure monitors to make sure you're at the right pressures?

Also, I heard the AHC springs are small and cause pinching / deflating of the airbag.. I suppose this is for the airbag threads, but it's actually pretty relevant here!

 

[RoderickGI]

AHC springs are very light weight compared to normal Landcruiser springs, but I don't know if that contributes more to pinching. My brother's airbags failed because the valve was torn out, probably due to a bad installation, or bad design, and he has a Landcruiser. I don't know which brand he used.

As for price, no idea these days. I looked at them nine years ago.

I haven't heard of anyone putting pressure monitors into the AHC system either. Sure, you can get pressure monitors for airbag systems, and control units to inflate the bags to the desired pressure with an on-board compressor. I guess if you had a laptop with you and the TechStream cable discussed above, you could check the AHC pressure while on the road, whenever you adjusted the airbags.

In line pressure sensors in the AHC system and some sort of monitoring panel would be nice if you were going to use airbags though.