The ABCs of AHC - How to Measure, Flush, and Adjust all in one place (7 Viewers)

[LndXrsr]

Awesome, thank you both for your input. I don't see any leaks from the shocks for now and I am happy with ride quality. I am at 211k miles, 2006 LX.

I wanted to further fine tune today. I measured with ahc off, engine off and there was a slight discrepancy between left and right heights which I corrected with respective turns of torsion bars. I remeasured at N and was spot on. Then I did 2 tiny turns on the heim(sp?) and got both front heights to 19.625 so calling that good. With these tweaks I remeasured pressures and got 6.7 front, 6.2 rear and 10.3 for the accumulator. The FR height is -2.4mm and the FL height is -4.6mm which if I understand it is in oem spec.

AHC fluid should arrive tomorrow so after flush ill recheck it all. Thank you for your help!!! The AHC(and TEMS/damper) is the wife and mine favorite part of the truck thus far.

You've got it dialed in! Nice work. AHC is still one of my favorite parts of the truck too, it's one of those things that makes the LC/LX truly unique. Even the Land Rover air suspensions that they've been refining for multiple decades doesn't compare. And this community helps keep those AHCs alive and well!

 

[PabloCruise]

This is a great re-do!

Putting a link to my aggregation of @PADDO quotes: AHC knowledge: Definitive list of AHC maintenance items

 

[kwon-offroad]

To the OP or others, section B, 7-8...

After bleeding globes on one side, the car is started and set to N. Then instructed to bleed globes on the other side.
Question: The other side is done when the car is still running and in N, as it wasn't specified to shut off the car at this point? Does bleeding this side also result in the vehicle dropping as AHC loses pressure?

 

[LndXrsr]

To the OP or others, section B, 7-8...

After bleeding globes on one side, the car is started and set to N. Then instructed to bleed globes on the other side.
Question: The other side is done when the car is still running and in N, as it wasn't specified to shut off the car at this point? Does bleeding this side also result in the vehicle dropping as AHC loses pressure?

Good question. The opposite side can be done running or after restarting, setting to N, and then shutting back off. Probably best to turn it back off. You are bleeding a very tiny bit of fluid out, so the vehicle height drops minimally if at all. The point of restarting is to get all your new AHC fluid pumped into the lines from the overfilled reservoir. The only parts that don't have new fluid at that point are the very last branches of the AHC plumbing going to the globes on the side you did not initially drain. So the quick bleed on opposite side gets just a few mL out complete your flush.

Edited that step for a little more clarity.

 

[kwon-offroad]

Thanks for the detailed procedure in one place. Was able to get the new-to-me 100's system tuned nicely. With 140k the rears are right at the upper but sure this is being contributed to the stock springs, so those will be on order shortly. Fronts now at 6.7, accume at 10.1. 12 graduations on the tank. A bleed is next but given the specs that's on the backburner although the process appear really easy.

 

[bajaguy949]

Thanks to all the provide information in this thread. I just needed some guidance with the three ride height sensor readings and pressure readings.

My pressures are within the threshold but should I adjust to get them closer or leave them as is? My LX rides pretty good now. As for the height of my sensors I would just need to adjust the heim joints in order to get them to 0mm?

My readings below.

Ride height is OEM spec.
front pressure sensor - 7.2
rear pressure sensor - 6.4
accumulator pressure - 10.2

front left height - -5mm
front right height - 1.6mm
rear height - 2mm

 

[LndXrsr]

Most here seem to feel pressures near the lower-middle of the range are best for ride, longevity, and give you wiggle room to load the vehicle up a bit and stay within spec. Yours are pretty good but if it's not too hard for you to make some adjustments, you can probably get them even better.

Height sensors within 10mm of 0 are very much acceptable. Adjusting what you have is as likely to get worse as it would be to improve.

 

[ramangain]

With proper ride heights, my front pressure sensors won't drop below 7.4. The ride height sensors are an average near zero, and the front delta is 0.3in. Rears sensor reads 6.3, and I don't run the 3rd row seats.

Any suggestions? I'm all about the comfy ride. Fluid was flushed 2k miles ago, and I have 10+ graduations.

I would think slightly higher pressures in the front AHC shocks would be better for ride, as the torsion bars are stiffer. My rig has always had a pretty supple ride from the start.

 

[uHu]

Looks like you are OK then, Raman, but it's easy to lower the front pressure a bit by turning both TBs a bit.
BTW, there are no front and rear pressure sensors - - there's only one pressure sensor in the ahc system.

 

[ramangain]

Thank you uHu

 

[IndroCruise]

With proper ride heights, my front pressure sensors won't drop below 7.4. The ride height sensors are an average near zero, and the front delta is 0.3in. Rears sensor reads 6.3, and I don't run the 3rd row seats.

Any suggestions? I'm all about the comfy ride. Fluid was flushed 2k miles ago, and I have 10+ graduations.

I would think slightly higher pressures in the front AHC shocks would be better for ride, as the torsion bars are stiffer. My rig has always had a pretty supple ride from the start.

Have you tried turning both front torsion bar adjusters clockwise 3 or 4 turns? That would transfer more load from the front AHC system to the torsion bars and bring your front AHC pressure lower in FSM-specified range of 6.4 to 7.4 MPa (6.9 Mpa plus or minus 0.5 MPa). Better damping performance and therefore better ride comfort is expected in the lower part of this range, say 6.7 MPa. Lower pressure also may be better for longevity of 'globes', 'shock absorber' seals, etc, in the AHC system.

A front pressure change of approximately 0.2 MPa is expected per full turn in the same direction on both torsion bar adjusters.

Before and after adjustments, best to check that both front hub-to-fender distances are the same with engine "OFF", physically measured with a tape -- use torsion bar adjusters for cross levelling front Left and front Right if necessary.

Turning the torsion bar adjusters does not change heights. Torsion bar adjusters are used only to transfer load to or from the front AHC system and for cross levelling.

By the way, the AHC system uses the same pressure sensor at the AHC pump to measure front pressure and rear pressure and accumulator pressure only -- it cannot measure pressure at each wheel.

 

[IndroCruise]

Have you tried turning both front torsion bar adjusters clockwise 3 or 4 turns? That would transfer more load from the front AHC system to the torsion bars and bring your front AHC pressure lower in FSM-specified range of 6.4 to 7.4 MPa (6.9 Mpa plus or minus 0.5 MPa). Better damping performance and therefore better ride comfort is expected in the lower part of this range, say 6.7 MPa. Lower pressure also may be better for longevity of 'globes', 'shock absorber' seals, etc, in the AHC system.

A front pressure change of approximately 0.2 MPa is expected per full turn in the same direction on both torsion bar adjusters.

Before and after adjustments, best to check that both front hub-to-fender distances are the same with engine "OFF", physically measured with a tape -- use torsion bar adjusters for cross levelling front Left and front Right if necessary.

Turning the torsion bar adjusters does not change heights. Torsion bar adjusters are used only to transfer load to or from the front AHC system and for cross levelling.

By the way, the AHC system uses the same pressure sensor at the AHC pump to measure front pressure and rear pressure and accumulator pressure only -- it cannot measure pressure at each wheel.

Looks like a sending delay has duplicated the more succinct post from uHu -- anyway, you now have two opinions!

 

[bajaguy949]

Most here seem to feel pressures near the lower-middle of the range are best for ride, longevity, and give you wiggle room to load the vehicle up a bit and stay within spec. Yours are pretty good but if it's not too hard for you to make some adjustments, you can probably get them even better.

Height sensors within 10mm of 0 are very much acceptable. Adjusting what you have is as likely to get worse as it would be to improve.

So with my rear pressure at 6.4 I should raise the rear sensor which is at -2mm to bring the rear pressure down correct?

 

[ramangain]

OK, I'm a realist from experience with an undertone of optimism and a pessemistic cherry on top.

I cranked the TB adjusters to reduce the pressures to 6.7 and 6.2 and went for that placedo-induced test drive.

There is a difference. The ride was more compliant (some would say softer) while still being well-controlled.

I'm a believer.

 

[boobird]

Turning the torsion bar adjusters does not change heights.

So the torsion bar changes the cross-leveling (moves one corner up and down to match the other side) but it does not change the vehicle height?

If I crank both sides4x clockwise then the overall height won’t move up?

The actual height is set by the height sensor?

 

[bajaguy949]

Turning the torsion bar adjusters does not change heights.

So the torsion bar changes the cross-leveling (moves one corner up and down to match the other side) but it does not change the vehicle height?

If I crank both sides4x clockwise then the overall height won’t move up?

The actual height is set by the height sensor?

I was confused about this also. The TB’s are used for cross leveling to change height but actual height is done by the sensors IE AHC lift.

 

[uHu]

.... I crank both sides4x clockwise then the overall height won’t move up?
The actual height is set by the height sensor?

Yes, right. The other thing that happens when cranking both TBs is that more of the weight is carried by the TBs, and less by the ahc/globes. I.e. the pressure goes down.

 

[uHu]

So with my rear pressure at 6.4 I should raise the rear sensor which is at -2mm to bring the rear pressure down correct?

Height sensor reading of - 2mm is as good as zero. AHC height adjustments will attempt getting the sensor to zero, and will stop within + - 5mm, normally.

If your rear height is at spec, and the pressure too high, you actually have to change the coil springs to get the pressure within specs. (Assuming you don't carry extra weight.) It is possible to lower the rear up to 1" under spec as a temporary solution for lowering the pressure. If you lower it, it will affect the steering geometry, but up to 1" is not noticeable if geometry is well adjusted and front end parts not worn.

 

[bajaguy949]

Height sensor reading of - 2mm is as good as zero. AHC height adjustments will attempt getting the sensor to zero, and will stop within + - 5mm, normally.

If your rear height is at spec, and the pressure too high, you actually have to change the coil springs to get the pressure within specs. (Assuming you don't carry extra weight.) It is possible to lower the rear up to 1" under spec as a temporary solution for lowering the pressure. If you lower it, it will affect the steering geometry, but up to 1" is not noticeable if geometry is well adjusted and front end parts not worn.

So at 6.4 for rear pressure which is on the higher end of the threshold is it worth it to swap springs down the line to lower the rear pressures?

 

[uHu]

So at 6.4 for rear pressure which is on the higher end of the threshold is it worth it to swap springs down the line to lower the rear pressures?

Yes. I'm in the same situation and have lowered the rear by 1/2" in order to have a bit higher load carrying capacity. It takes about one minute to adjust the sensor by sliding the link a few mm down the slot.