Definitive list of AHC maintenance items (7 Viewers)

[Dannyboy lx470]

I sprayed them with PB blaster about 30 minutes before I began working on them. Pretty sure this is the first time these have been adjusted given the amount that was needed to get the system back in line.

When I went to start turning them, it wouldn't budge at all at first. So I jacked up the front, put some stands up just in case, and found it to be much easier. I didn't use a breaker bar or anything. Just a medium sized 1/2" ratchet. I did about 6 rounds or so of measuring and checking pressures in between. I found that after I started moving them, I didn't need to jack it up anymore and could adjust it just fine when the AHC was set to the High mode. I've heard of others needing to use breaker bars,but if you can lift the tires off the ground it should be pretty easy.

Thankyou will try that.

 

[PabloCruise]

My turn now...

I got Tech Stream working on a laptop and plugged into my LX.

I did a couple of cycles from L to H and came up with 7 graduations.

Next I went and tanked up with fuel and parked on a level surface. I plugged in, fired up the engine and went from L to N a couple of times and got the following:

 

[PabloCruise]

Front @ 7.2 Mpa-g - I have seen spec reported @ 6.9 +/- 0.5, yes?

Rear @ 7.8 Mpa-g - spec is 5.6 to 6.7, yes? So this is my problem area...

Accumulator @ 10.4 - is this normal?

FL @ -17.2mm and FR @ +13.8 for a delta of 31mm. I will go and measure heights from the bottom of the rim through center cap to fender lip.

Truck is a '99 LX 470 w/ 159k miles. BIOR rear bumper (no swing-outs) and BIOR sliders and 285/75R16 BFG ATs.

I thought I would start w/ @PADDO 1 can AHC fluid change and re-check pressures before playing with torsion bars:

Nothing to worry about. One can is sufficient for a good exchange and bleed, particularly if you're comfortable with working on hydraulic systems and can do it efficiently. For a lot of guys here though this is all new to them and in that case it's better to have more fluid (2 cans) on hand than being left short in the middle of the process; or if it's a first time ever fluid change then you'll benefit from a follow up bleeding to establish a good baseline. The trick is to not drain more than you can replace An opened second can be resealed pretty well and stored for later use.
Edited to include:
Here's my version of a quick and easy 1 can AHC fluid exchange/bleed. Following this process is less likely to get you into trouble by reducing the risk of accidentally bleeding too much fluid thereby allowing air to be drawn into your system.

Materials required. One can of fluid (Toyota suspension fluid, AHC 08886-01805), clear pvc pipe that's a snug fit on the bleeders, 10mm spanner/box wrench/crows foot and a suitable waste fluid container.

This process assumes the fluid level in the reservoir is between max and min at N height before starting. Clean around the reservoir cap and the spout of the AHC fluid can before opening.

1. Lower the vehicle to L and wait 30 seconds for the AHC system to settle and then turn the vehicle off, do not restart until step 8. The fluid level in the reservoir will now be at its highest. Using a turkey baster or similar remove as much fluid as practical from the reservoir. This amount should equal, or be slightly over, 1 liter.
2. Pour the entire 2.5 liters of new fluid into the reservoir, filling it.
3. Now we know that the reservoir's "normal" contents is ~ 1 liter (vehicle in L when fluid level is correct at N) and we have filled it with 2.5 liters so we don't want to drain more than 1.5 liters or else we may come up short.
4. Starting at the height accumulator (12 in long cylinder on DS outer frame rail, between front and rear damper assemblies) drain fluid, closing the bleeder as fluid flow stops which should be ~0.3 liters.
5. Move to the front LH damper and drain until the front is on the bump stops. Both sides will lower and you should drain ~0.4 liters. Again close the bleeder as fluid flow stops.
6. Move to the rear LH damper and drain until the rear is close to/on the bump stops. Both sides will lower and you should drain ~0.3 liters. Again close the bleeder as fluid flow stops.
7. Now we should have drained very close to 1 liter (0.3+0.4+0.3) leaving us about 0.5 liters additional in the reservoir.
8. Start the vehicle and raise to N. The system will refill and recharge with new fluid from the reservoir. The fluid level in the reservoir will lower to slightly over the max line if everything has gone as expected.
9. Turn the vehicle off and do a small, quick bleed on the PS front and rear dampers just to check that there isn't any gas trapped. You don't need to remove very much at all from the PS as essentially all available fluid (there will always be a small residual in each shock actuator that we can't access) gets pushed out when you do the DS and take it to the bump stops as both sides are hydraulically connected.
10. You're done, confirm that the reservoir fluid level is correct - between max and min at N height with the engine running. There is nothing wrong with leaving the level slightly over the max line.

As long as you don't drain more than 1.5 liters you can't mess up and accidentally draw air into the pump/system.

This approach is simpler than others, but slightly more elaborate than the FSM. It is intended to remove as much old fluid as practical in a quick and efficient manner. Hopefully it fills an information gap by associating approximate quantities to the height accumulator and front/rear hydraulic circuits. Hopefully this guidance falls between the very brief FSM directions and other available AHC bleeding procedures that may appear complex and daunting to some.

 

[PabloCruise]

Front @ 7.2 Mpa-g - I have seen spec reported @ 6.9 +/- 0.5, yes?

Rear @ 7.8 Mpa-g - spec is 5.6 to 6.7, yes? So this is my problem area...

Accumulator @ 10.4 - is this normal?

FL @ -17.2mm and FR @ +13.8 for a delta of 31mm. I will go and measure heights from the bottom of the rim through center cap to fender lip.

Truck is a '99 LX 470 w/ 159k miles. BIOR rear bumper (no swing-outs) and BIOR sliders and 285/75R16 BFG ATs.

I thought I would start w/ @PADDO 1 can AHC fluid change and re-check pressures before playing with torsion bars:

AHC was last flushed in Jan '15, and then torsion bars adjusted in Feb '15.

Fronts look pretty good, but the rear pressures worry me.

I am contemplating switching rear coils to some 100 coils that I can get my hands on cheap as I don't think inserts will get me down an entire 1.2 to hit the high end of spec...

 

[sorich]

I'm interested to see where you end up. I want to add that same rear bumper later this year. When I got my truck at the beginning of the year stock, my rear pressures were around 6.7 or so. After AHC fluid swap, torsion bar adjustment, and new Lexus rear springs is down to 6.0.

When I install that BIOR rear
Bumper, I also plan on adding 30mm spacers to those new coils in hopes that my rear pressures will be in range.

 

[PADDO]

Front @ 7.2 Mpa-g - I have seen spec reported @ 6.9 +/- 0.5, yes?

Rear @ 7.8 Mpa-g - spec is 5.6 to 6.7, yes? So this is my problem area...

Accumulator @ 10.4 - is this normal?

FL @ -17.2mm and FR @ +13.8 for a delta of 31mm. I will go and measure heights from the bottom of the rim through center cap to fender lip.

Truck is a '99 LX 470 w/ 159k miles. BIOR rear bumper (no swing-outs) and BIOR sliders and 285/75R16 BFG ATs.

I thought I would start w/ @PADDO 1 can AHC fluid change and re-check pressures before playing with torsion bars:

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.

 

[PabloCruise]

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.

Thank you @PADDO - unfortunately I know very little about adjusting the sensors. Do you have a favorite post you can link me to on these?

Do you think the Kings will net me 3 Mpa with the extra weight I have put on the vehicle?

Do you think 100 springs are too much? We are going on a trip and I will be pulling a pop-up camper. I guess I would rather have low pressure in the rear vs. 1.2 Mpa over spec. Is there any peril in trying the 100 springs for the trip?

I got the fluid changed out thanks to your 1 can method. I did not get to check pressures b/c the wife was standing there waiting to take the LX...

 

[PabloCruise]

Thank you @PADDO - unfortunately I know very little about adjusting the sensors. Do you have a favorite post you can link me to on these?

Do you think the Kings will net me 3 Mpa with the extra weight I have put on the vehicle?

Do you think 100 springs are too much? We are going on a trip and I will be pulling a pop-up camper. I guess I would rather have low pressure in the rear vs. 1.2 Mpa over spec. Is there any peril in trying the 100 springs for the trip?

I got the fluid changed out thanks to your 1 can method. I did not get to check pressures b/c the wife was standing there waiting to take the LX...

Have not checked pressures this morning, but the wife said the truck "felt better" after driving yesterday.

 

[PabloCruise]

Have not checked pressures this morning, but the wife said the truck "felt better" after driving yesterday.

I wanted to check on the truck before we head out for the morning - not enough time to plug in Tech Stream, but checking graduations, I now see 10 lines when going from L to H and then back down to L.

I was getting 7 on the old fluid. And when I say "old", it was changed a little over 2 years ago...

 

[PADDO]

Thank you @PADDO - unfortunately I know very little about adjusting the sensors. Do you have a favorite post you can link me to on these?

Do you think the Kings will net me 3 Mpa with the extra weight I have put on the vehicle?

Do you think 100 springs are too much? We are going on a trip and I will be pulling a pop-up camper. I guess I would rather have low pressure in the rear vs. 1.2 Mpa over spec. Is there any peril in trying the 100 springs for the trip?

I got the fluid changed out thanks to your 1 can method. I did not get to check pressures b/c the wife was standing there waiting to take the LX...

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

 

[PabloCruise]

I wanted to check on the truck before we head out for the morning - not enough time to plug in Tech Stream, but checking graduations, I now see 10 lines when going from L to H and then back down to L.

I was getting 7 on the old fluid. And when I say "old", it was changed a little over 2 years ago...

So this is troubling - I plug in the Tech Stream cable today and now the pressures are all 0.

I drove the truck today and it certainly did feel better.

The level sensors are reporting - but no pressure values? Did I do something wrong?

 

[PabloCruise]

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.

HTH

Thank you Paddo, that does help. I do have some follow up questions if anyone on here can help me out...

Regarding height adjustments, I am not looking to get any lift out of the AHC system.

When I measure from the bottom lip of the wheels through the center cap to the bottom of the wheel opening, I get the following:
DF: 28"
PF: 28.5"
DR: 28.75"
PR: 29.75"

If I am to do height adjustments first, do I start by cross leveling the front via torsion bar adjustments? Meaning I would torque the DS torsion bar until the front distances to the wheel opening are equal - so tighten DS TB, drive it around the block, pull back onto level surface, measure - repeat as necessary?

Perhaps a silly question, but you tighten the DS TB by torquing counter-clockwise, yes? And PS TB gets tightened by torquing clockwise?

And then play with the front sensors until I can get them both as close to 0 as possible? Then adjust rear sensor to 0?

Thank you all.

Not sure why my pressure readings do not show up today. I hope I did not do anything when I did the fluid exchange in the AHC system yesterday.

 

[PabloCruise]

So this is troubling - I plug in the Tech Stream cable today and now the pressures are all 0.

I drove the truck today and it certainly did feel better.

The level sensors are reporting - but no pressure values? Did I do something wrong?

View attachment 1423890

I forgot the basic instruction that you read pressures after raising from L to N - ouch!

Today's readings are better than yesterday for sure! Yesterday the pressures were 7.2/7.8 F/R.

Today:

 

[PabloCruise]

I still need to learn about adjusting the height sensors, but also running out of time before our trip.

I gave the DS torsion bar a total of 6 turns, in 2 turn increments.

Then I met up with a friend who had both a set of 30 mm spacers left over from a lift kit, and a set of 100 rear coils that he took off. I can't believe how quick it was to pull the sensor, sway bar links and bottom shock bolts. We tried the spacers, put everything back on, took it for a quick drive, and then cycled the AHC a few times.

L to N pressures look like this - I am very pleased, and the truck feels very good. I think it is happy:

 

[PabloCruise]

When I got home, both front wheel openings measured @ 28.25" - nice!

Not sure what to make of the front being under spec.

And need to learn about the height sensor adjustment - wondering if my wheel openings are now equal, as in cross-balanced, do I now adjust the sensors to read 0?

 

[PADDO]

Thank you Paddo, that does help. I do have some follow up questions if anyone on here can help me out...

Regarding height adjustments, I am not looking to get any lift out of the AHC system.

When I measure from the bottom lip of the wheels through the center cap to the bottom of the wheel opening, I get the following:
DF: 28"
PF: 28.5"
DR: 28.75"
PR: 29.75"

If I am to do height adjustments first, do I start by cross leveling the front via torsion bar adjustments? Meaning I would torque the DS torsion bar until the front distances to the wheel opening are equal - so tighten DS TB, drive it around the block, pull back onto level surface, measure - repeat as necessary?

Perhaps a silly question, but you tighten the DS TB by torquing counter-clockwise, yes? And PS TB gets tightened by torquing clockwise?

And then play with the front sensors until I can get them both as close to 0 as possible? Then adjust rear sensor to 0?

Thank you all.

Not sure why my pressure readings do not show up today. I hope I did not do anything when I did the fluid exchange in the AHC system yesterday.

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

 

[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

Thank you @PADDO, I will back off on the front torsion bars first in equal turns since my front fender heights seem uniform. I will double check measurements from center of wheel to opening lip. I had been measuring from the bottom of the rim, through the center cap to the fender lip. Then I will check pressures to verify the front pressure goes up, and see where the rear pressures land.

 

[PabloCruise]

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.

HTH

I guess I have been playing with height and pressure at the same time...
Taken in context with your above comments related to cross-level and loosening the TBs, once I have even cross level and pressures optimized, then I play with sensors to get as close to "0" as possible, eh?

The sensors had been adjusted in Jan of 2015. Are they off simply due to changes in the rear coils and TB tension? In those cases does the AHC simply apply pressure as best as it can between F & R and the sensors fall where they may if the pressures cannot generate 0s on the height sensors?

 

[PabloCruise]

The sensors had been adjusted in Jan of 2015. Are they off simply due to changes in the rear coils and TB tension? In those cases does the AHC simply apply pressure as best as it can between F & R and the sensors fall where they may if the pressures cannot generate 0s on the height sensors?

Still wondering about this - why/how do the height sensors get off 0? Is it aging of the springs? Drift in the sensor? Both? Neither?

 

[PabloCruise]

I got a chance to play with this a little more. Loosened the PS TB a total 5 turns, and backed of the DS TB 2 turns.

Before I did that I took a look at system pressures - that is the first screen capture.
2nd screen capture is after loosening the TBs as per above and measuring height to wheel openings as uniform - yippee!
3rd screen capture is after pulling the rear third row seats in preparation for our trip!