Definitive list of AHC maintenance items (11 Viewers)

[PabloCruise]

So I am happy that my heights are adjusted, and pressures are now w/in spec for F & R, but still want to know about adjusting the height sensors. For the rear, it looks like only one adjustment at the slider. For the front, it looks there are 3 different opportunities to adjust - the big slider, the threaded portion (is that a locknut that is loose?) and the little slider by the actual sensor. I would love to 0 these puppies out, but would like to know what I am doing...

 

[PabloCruise]

So I am happy that my heights are adjusted, and pressures are now w/in spec for F & R, but still want to know about adjusting the height sensors. For the rear, it looks like only one adjustment at the slider. For the front, it looks there are 3 different opportunities to adjust - the big slider, the threaded portion (is that a locknut that is loose?) and the little slider by the actual sensor. I would love to 0 these puppies out, but would like to know what I am doing...

Forgot pictures...

 

[PabloCruise]

Ah, probably not a loose lock nut, but how you adjust the threaded rod portion...

 

[Jaybob]

Need to do another flush on my AHC system. This seems like the best place to post the question rather than starting another thread.

Anybody have an idea about what the fluid actually IS? I was just in Baja, and got a little nervous when the system dropped to low with our full load in it. Had all of the people exit the vehicle and it went back to normal height. The fluid was within the normal volume, and I had checked pressures before we left, but it had me worried about what I would do if I needed to repair it in MX.

Thanks Jay

 

[DirtDawg]

So I am happy that my heights are adjusted, and pressures are now w/in spec for F & R, but still want to know about adjusting the height sensors. For the rear, it looks like only one adjustment at the slider. For the front, it looks there are 3 different opportunities to adjust - the big slider, the threaded portion (is that a locknut that is loose?) and the little slider by the actual sensor. I would love to 0 these puppies out, but would like to know what I am doing...

Its pretty straight forward my man: you can adjust the fronts using the adjustment slot or the threaded link. The threaded portion is opposing threads on either side, so you can loosen both lock nuts and adjust on the vehicle. I use the slot to make my large adjustments, and the threaded portion for fine tuning. The rear is only adjusted using the slot.

Shorten the linkage in the front to raise it, lengthen to lower.

 

[uHu]

So I am happy that my heights are adjusted, and pressures are now w/in spec for F & R, but still want to know about adjusting the height sensors. For the rear, it looks like only one adjustment at the slider. For the front, it looks there are 3 different opportunities to adjust - the big slider, the threaded portion (is that a locknut that is loose?) and the little slider by the actual sensor. I would love to 0 these puppies out, but would like to know what I am doing...

You got most of your answers. What you call "the little slider by the sensor" i guess is the shipping support for the sensor arm. Supposed to be removed when installed, or just broken like here.

 

[PabloCruise]

Need to do another flush on my AHC system. This seems like the best place to post the question rather than starting another thread.

Anybody have an idea about what the fluid actually IS? I was just in Baja, and got a little nervous when the system dropped to low with our full load in it. Had all of the people exit the vehicle and it went back to normal height. The fluid was within the normal volume, and I had checked pressures before we left, but it had me worried about what I would do if I needed to repair it in MX.

Thanks Jay

Hey Jay, I think I saw a post by @PADDO that said it is a variation of mineral oil. I would try to get the Toyota fluid if at all possible.

 

[PabloCruise]

Its pretty straight forward my man: you can adjust the fronts using the adjustment slot or the threaded link. The threaded portion is opposing threads on either side, so you can loosen both lock nuts and adjust on the vehicle. I use the slot to make my large adjustments, and the threaded portion for fine tuning. The rear is only adjusted using the slot.

Shorten the linkage in the front to raise it, lengthen to lower.

Gratitude!

 

[PADDO]

Ah, probably not a loose lock nut, but how you adjust the threaded rod portion...

Here is a repost of the fsm process to adjust height sensors and TBs for the correct pressure.

 

[flintknapper]

Need to do another flush on my AHC system. This seems like the best place to post the question rather than starting another thread.

Anybody have an idea about what the fluid actually IS?

Use only:
GENUINE TOYOTA 08886-01805 SUSPENSION FLUID

 

[PabloCruise]

We just got back from our trip which was about 1000 miles, a good deal of it with the pop-up camper hooked up, fridge/freezer in the back and some mild off-road, a couple of stretches using Low range.

On the way back the truck did not feel like it was handling ideally, so I grabbed a quick set of pressure readings with the camper still attached and the fridge still in the back - no wonder it did not feel ideal, front is too light, rear too heavy. I grabbed as level of a spot as I could, but with the camper hooked up parking in the garage is no longer an option:

 

[PabloCruise]

Now that the trip is over, and I have some time to play with this more, I will unpack everything and take a look at the truck...

Do I still have cross-level?
How are heights front and rear?
Now that I have seen the FSM height sensor adjustment, I can adjust those.
Then adjust torsion bars for 6.9 Mpa up front and see what the rear pressures are. Maybe play with rear height sensor a little if it will help rear pressures. Rear sensor is pretty darn close to 0 as is.

I may start with air bags in the rear, just because I need one more thing that is adjustable to fuss over in my life...

 

[PabloCruise]

You need to get your front cross level within 10mm, so loosen up your FL TB a few turns and tighten your FR the same amount - split the difference. When you're satisfied that you're pretty close to cross level take height readings at all four corners so you can set your desired rake. Now is the time to adjust height sensors if necessary (the front sensors don't change cross level, just superimpose + or - height onto the mechanical system, so if the TBs are skewed you'll just end up higher or lower but still not level). Last thing to do is tighten or loosen both TBs (the same amount both sides to preserve your cross level you just established) to dial in your pressure for the front, rear is determined by your coils and their free length so no easy adjustment there unless you have air bags.

Chasing techstream heights and pressures while the vehicle isn't cross level and not at your desired height physically is just going to frustrate the hell out of you. I'm not sure if you've moved your sensors to up your neutral ride height, if so you'll have higher rear pressures (unless you've got bags or taller springs/spacers). I set my pressures whilst in the vehicle (190 lbs) and my weight adds about 0.2MPa. In your situation I'd work towards getting it cross level, then at the right height and lastly dial in pressures as best you can.

It'll all fall into place, just attack it sequentially.
Edit. Don't use techstream until you're ready to adjust pressures and fine tune your front height sensors to be pretty closely matched because I think it's giving you more info than you need. Just use a tape and 30mm socket to get cross level. Then use the tape to measure all four corner heights and tweak sensors to move the vehicle front/rear up or down and when you're satisfied then hook up techstream to tune pressures and balance the front height sensor readings. They work out the actual displacement and the ECU works out an average and commands an up/down signal to get the sum displacement to zero or if one sensor says +2 and the other says -2 then the sum displacement is 0. Ideally, after you have your physical height where you want it use the techstream FL and FR height numbers to incrementally get the displacement signals close, within 0.3 inch delta is fine.

The first task at hand is to take height reading at all four corners, these are your baseline references. Don't touch height sensors yet. Your front pressure of 10.8 is ridiculously high, it should be 6.9 MPa and your rear reading should be closer to 6.0 MPa. The rear height sensor reading of +1 inch is odd.
On level ground with no additional weight in the vehicle measure the height at all four corners. Front, stock, should be 19.75 and rear 20.5 hub centre to fenders, vehicle running and settled.
Adjust the torsion bars as necessary to get the front cross level. When cross level then apply equal turns to both adjuster bolts, clockwise to tighten the bars and lower pressure. No need to touch height sensors unless you need to raise or lower the front. 1 full turn on both torsion bar bolts will lower pressure 0.2MPa.
Rear height sensor reason should be close to 0.0 inch at N with 20.5 inches between fender bottom and hub centre. You' may need to adjust the sensor here. Always have vehicle engine OFF if fiddling with height sensors.
Getting that front pressure down will also lower the rear pressure a small amount and it's a bit of an iterative process. You will most likely not be able to get the rear pressure down into the mid to low 6.0 range without replacing the coils.

No tire size doesn't matter because you're measuring the height between the centre of the axles and body. This method is kinda rough, and not as per the FSM, but it's close enough.

Pretty standard approach to dialing this in, and yes your F and R pressures are a bit high.
First, on flat ground check and adjust front cross level, you should be able to easily get in within 1/4". One turn on one torsion bar bolt will lift/lower that corner approximately 1/8". Engine doesn't need to be on for cross level check/adjustment. Wheels on the ground, if the TB bolts are really tight you can raise to H to take some preload off. Use penetrating oil liberally if they haven't been adjusted in a while. Breaker bar doesn't hurt either.
Second, measure all four corner heights at N with engine running and AHC settled. If you have 19.75F and 20.5R hub center to fender bottom you are very close to stock spec height. Adjust height sensors if necessary, engine off, to avoid potential injury.
Lastly, hook up techstream and check pressures, same number of CW turns on both TB bolts to lower pressure, one turn (on both bolts) will lower pressure about 0.2MPa (CCW to raise pressures). Target front pressure is 6.8 - 6.9MPa. All you can do for the rear pressure is to ensure you aren't physically too high and then you may need to add 30mm spacers to get the pressure down a reasonable amount or ideally, new AHC coils AND spacers to get the pressure down to the lower end of its design range of 5.6 - 6.7 MPa. Expect a small variance in the front height sensor height values, if they fall within say 0.3" from 0 there isn't any need to tweak them. Best just to see how it all plays out. Additionally, lowering the front pressures also has a positive effect on the rear, and vice versa.
I know the FSM says to adjust pressures with full tank of gas etc etc well lately I've been adjusting pressures with the vehicle set up how I normally drive it and that's with 2nd and 3rd row seats out, 1/2 tank gas and my tool box, myself in the drivers seat. I just think it makes better sense that way. If I'm loading up for a trip I readjust TBs as necessary, it only takes a minute.
HTH

To level the front side to side you do not touch the height sensors, you add turns to the low side torsion bar bolt and subtract turns from the high side. One turn will lower/raise its respective side about 1/8 inch. Get it to within 1/4 in difference. It's an iterative process but easily achievable. Do it via one or two turn steps, remeasuring and bouncing the front between steps. Only after you've got the front level then you set your heights by adjusting the links in their sliders and the last thing you do is set the front neutral pressure by applying equal turns to both torsion bar bolts so as to not undo your cross level you just set.
Everything you need to know about setting cross level, setting heights and setting front/rear pressures is in this thread. There is lots of good, old, info posted by knowledgeable people in some of the older threads but be cautious as there is lots of speculative rubbish that has no AHC technical basis what so ever too and that will lead you down the wrong path.

Much better. If you're interested you might try experimenting with the front pressures, maybe try a little lower and see how that responds. It's all about finding the best combination of mechanical springs (torsion bar) and gas springs (remaining charges in your damper accumulators). Your rear pressure isn't going to lower unless you jettison weight or drop the vehicles height. Adding 30mm spacers while you've got the springs out will normally give you another 0.6MPa pressure reduction. I haven't encountered anyone yet who has had to deal with too low rear pressures by adding spacers on new AHC coils.
Regarding the factory pressure tolerance and range. The front's design pressure is 6.9 MPa and the design engineers concluded that the acceptable deviation from their design pressure is +\- 0.5. There is a marked difference between new globes and 6.9MPa and how it performs at the outer limits of the tolerance. For the rear we obviously don't have 30mm bolts to dial in/out tension so the designers gave us a range of 5.6-6-7MPa but the best I've heard off is for new coils to get the rear's pressure down around 6.3 or 6.4MPa. It doesn't take much weight (about 210lbs for +1MPa over the axle) to creep up into the high pressure/poor damping and drop to L when loaded up zone.

There's a marked difference in the performance you'll see/feel between "optimum" and "in spec" pressures. You can just accept "in spec" pressures if rough enough is good enough but I'd recommend taking a little extra time to find pressures that perform better than in spec and you'll be happier. Grad test suggests your damper spheres are approaching the end of their useful life and you definitely need to get the rear pressure down. Don't forget that general pressure readings also need to be taken in context of actual vehicle heights too, not only additional weight.
You've got a lot of variance in your front sensor readings. I'd adjust the low side to read closer to 0 and vice versa for the high side. You can do this with just the ignition on and a USB extension cable lets you sit beside the wheel and monitor as you adjust. When both sensors are close to 0, iirc fsm says +\- 5mm, then you're ready to check and adjust, if necessary, actual heights - creep both sensors up a fraction to raise/down to lower - of course this is done with engine off so as to not have the vehicle adjust itself on your head/fingers. Your height accumulator pressure is very normal. A set of 30mm spacers will drop your rear pressure about 0.5-0.6 MPa so you'll need more than spacers such as king ktrs 79s which will net you approx 3.0 MPa, maybe a little more or less. Beauty of the kings is if you drop your pressure a little to low so it's outside the optimal damping range then just tweak the height up a bit. Baby lift with optimum pressure with rear bar etc should be ok. HTH.

Re sensor adjustment, I'll track down something from the fsm with pictures but it's really as simple as slide them up/down to get similar feedback numbers then adjust them equally up or down to set your overall height. Rear is even simpler - slide up to raise, down to lower the rear. Always done with engine off for safety, but you can monitor the height feedback numbers with just IG on. Do your height adjustments first then set pressures, not the other way around.
3MPa is 3MPa regardless of weight. I've done several king spring installs back in Aus and one dropped pressure about 2.5 and the other 3.5, no idea why the difference - maybe just spurious Techstream readings (which happens from time to time) - people on here have seen similar results. You want to target a rear pressure close to 6.0MPa so if you're starting at 10MPa then the kings won't be enough; if you're starting at 6.5MPa then the kings will be too much (then you'd lift to raise pressure back up to a point where the damper spheres (gas springs) have some loading and can function, but even then you'd struggle.
100 springs may well be to much at your weight/height today for daily driving, could work fine with a load full of stuff and the camper hooked up. Do a mock up with all your gear, add camper tongue weight etc and do a pressure reading then that'll give you a good reference point to base decisions on. One reference point is 210lbs over the rear axle equates to +1MPa in rear neutral pressure. If you move that weight to the absolute rear/on the bumper then the multiplier is 1.25 (derived from a guy who took his LX on some race scales and played with the corner loading and slid some weight about the truck.) I haven't done that myself but I've tested the 210lbs per MPa over the axle. There's really no need to guess at this as neutral pressure is just a function of weights, its distribution and heights.
AHC coils run about 90-95lbs/inch, king KTRS 79 aftermarket AHC coils advertised as +25% capacity over standard at 130 lb/in and standard 100 coils at 170 lbs/in from various sources. 30mm trim packers are good for about -0.5MPa.
HTH

In the spirit of truly getting to know the AHC system in my LX, I went back and read this entire thread from page 1. While reading I was impressed that @PADDO truly has the Zen approach to AHC.

These 8 quotes struck me as the most informative for tackling the AHC system diagnosis and service. My hope is that if someone new to the 470 (or 100 w/ AHC) were to come looking for AHC basics, these quotes would serve them well.

At the same time, at some point you have to stop reading and just slide under your rig. Someone in here quoted my statistics instructor, "Nothing to it but to do it!". Very applicable here...

 

[PabloCruise]

So 20/20.5 front and 20.75/21.75 rear?

Cross level first - splitting the difference - so tighten (cw) the low side 2 turns and loosen (ccw) the higher side 2 turns. Re measuring and final adjustment as necessary. Regardless of vehicle side CW turns tighten and lower pressure / CCW loosen and raise pressure.
Just saw in a subsequent post your front pressure has dropped after installing 30mm spacers. I've seen that before and you'll need to rebalance the front by loosening off the bars to get the front pressure consistently reporting 6.9 (or a fraction lower), your rear pressure will raise a bit too and you'll likely see a net drop of 0.5MPa with the front pressure reset correctly. It's all a balancing act and somewhat iterative. I guess that's why we have TB adjustment bolts

To be clear, I was measuring from the bottom of the rim lip, up through the center of the cap, to the bottom of the wheel opening in order to get the most reproducible result.
I have seen some lift kit instructions advise this method of measuring. I don't think I could get an accurate measure to the wheel center.
I think the factory 16" wheels measure 8.5" from lip to center.
I got some time to look at my height sensors today and adjusted, but now I believe I am too low when I measure heights and compare to your notes for factory heights.
As you have said, it is an iterative process, but I am getting closer.
More later...

 

[JTinAZ]

I went to a Toyota dealer to buy AHC fluid to flush out the system. According to the parts guy, the 2.5 L metal can ahc fluid (08886-01805) has been replaced with a one-liter plastic bottle version (08886-81221). The last thing I want to do is put in the wrong stuff. Any experience with the plastic bottle version?

 

[uHu]

Never saw the plastic bottle version, but after a beer or three, I would use that stuff as an ATF, according to the picture. Bad t0yota.
There is some indication on guugle that the part# corresponds to the right stuff tho'

 

[DirtDawg]

Hmm.. wonder what the difference is. The cans are still being sold: Amazon.com: GENUINE TOYOTA 08886-01805 SUSPENSION FLUID: Automotive

 

[PabloCruise]

View attachment 1435142 View attachment 1435143

I went to a Toyota dealer to buy AHC fluid to flush out the system. According to the parts guy, the 2.5 L metal can ahc fluid (08886-01805) has been replaced with a one-liter plastic bottle version (08886-81221). The last thing I want to do is put in the wrong stuff. Any experience with the plastic bottle version?

What was the 1L price?

 

[bouncylexus]

Any thoughts on what would cause a choppy height adjustment. If the truck is sitting on unlevel ground and it adjusts itself, the adjustment is very harsh and is sometimes accompanied with a popping noise.

I recently replaced the globes and this problem predates the swap out.

 

[bouncylexus]

To level the front side to side you do not touch the height sensors, you add turns to the low side torsion bar bolt and subtract turns from the high side. One turn will lower/raise its respective side about 1/8 inch. Get it to within 1/4 in difference. It's an iterative process but easily achievable. Do it via one or two turn steps, remeasuring and bouncing the front between steps. Only after you've got the front level then you set your heights by adjusting the links in their sliders and the last thing you do is set the front neutral pressure by applying equal turns to both torsion bar bolts so as to not undo your cross level you just set.
Everything you need to know about setting cross level, setting heights and setting front/rear pressures is in this thread. There is lots of good, old, info posted by knowledgable people in some of the older threads but be cautious as there is lots of speculative rubbish that has no AHC technical basis what so ever too and that will lead you down the wrong path.

So the steps in order are
Cross level
Adjust height sensors to get the correct height
Adjust TB to neutral pressure

Is that correct?