The ABCs of AHC - How to Measure, Flush, and Adjust all in one place (5 Viewers)

[Coin]

I just followed the steps above on my 2003 LX. Heights were good, so no adjustment needed. Checked pressure in TechStream:
Front pressure @ 8.2,
Rear pressure @ 7.3.

Cranked the torsion bars 7 turns and ended up with:
Front pressure @ 6.5
Rear pressure @ 6.9
so pretty close to spec in the front, still high in the rear. The ride is drastically improved. I thought it was good (a bit mushy, but comfy) before.

I did order some new springs, the LC w/ AHC springs. They are slightly stiffer than the LX springs (or so I've read). I do plan to tow a boat occasionally, and like to load up the family for road trips. I want to make sure the rear is supported well. I will post after install in case others are curious about the difference.
I currently get about 7/8 graduations of AHC fluid. This is on a truck with 260,000 miles and original spheres!

Update:
So after installing the LC AHC springs my pressures are at 6.8 front and 6.5 rear. I backed off the torsion bar one rotation from my previous reading to get the front closer to spec of 6.9.
The pressure with the new springs are not a huge difference, but driving the car, especially over speed bumps, is much improved. The rear doesn't sink as low after going over a speed bump as before, and the rear generally feels more planted on the road. One note, when adding replacing rear springs, remember to disconnect the height sensor bracket, or you may be in for some of this.

With a little reading, $90 in AHC fluid, and $250 for new rear springs, I have a comfortable suspension that rides almost like new. One day I will need new globes, but now that I know what AHC is supposed to feel like, I am certainly going to keep it.

 

[kcdobe]

***edit: first question is answered, I just had to get the paid version of the app***

Two questions as I get ready to do this. I have OBD Fusion and can't figure out how to add the pressure monitors to the screen. Do you know how to do that or what the PIDs are?

Second, i'm about 18.75" and about 18.875" on the front. I'd need to adjust that with the sensors only right? And then set the TBs to make the pressures correct? And I should be able to see on the height sensor that it's about an inch low right?
Thanks!

 

[LndXrsr]

Second, i'm about 18.75" and about 18.875" on the front. I'd need to adjust that with the sensors only right? And then set the TBs to make the pressures correct? And I should be able to see on the height sensor that it's about an inch low right?
Thanks!

Yup, assuming no error codes and those are your heights at the N setting, the FR and FL sensor are probably reading 1-2" low. Adjust them to get back within ¼" or so of spec then tweak the TBs first to get the left-right leveled and then the pressures correct.

 

[kcdobe]

Yup, it did. Actually as soon as I started the car it hoped up to 19.25 and 19.375. It's showing -0.6mm on the driver side a +3.1mm on the passenger side. So it's within spec side to side.

My pressures are 8.3 front and 7.3 rear before making adjustments. Hopefully a few turns will make it not sag over night.

 

[LndXrsr]

Sagging overnight would be more concerning for a leak somewhere in the system. That can happen from excess pressure causing the shocks to leak, so see if reducing pressure helps. But your pressures aren’t so high that I would think that to be the case. Do you have signs of significant seepage at any of the shocks?

 

[kcdobe]

Sagging overnight would be more concerning for a leak somewhere in the system. That can happen from excess pressure causing the shocks to leak, so see if reducing pressure helps. But your pressures aren’t so high that I would think that to be the case. Do you have signs of significant seepage at any of the shocks?

That's a good point honestly. I just checked and I don't see any signs of leakage near the rams, accumulator, or globes. But, the car has been parked for about an hour and it's already dropped about a 1/4". I'll adjust the TBs tomorrow and start a new post if it's still acting weird. Just realized I probably half-way hijacked this chain!

 

[LndXrsr]

Any luck with a leak source or otherwise?

 

[boobird]

@kcdobe
I also suspect my front is sagging overnight, even after adjusting TBs.

When you pull the car up by the fender wheel well, does the height also go up then eventually sag back down? (Mine does..not sure if that's normal or not)

 

[kcdobe]

So on tuesday I got distracted helping a buddy with an old motorcycle so this is now on the agenda for this weekend along with an oil change and some other minor updates.

I have noticed that it's not sagging by a measurable amount this week. I thought I had recently driven it when I took the measurements earlier this week but I'm wondering if I was mistaken. The last several times I've measured I've come up with 19.25 dead. I couldn't find any evidence of a leak (apart from on my steering rack, which is super).

I'm going to have to pull off the wheels to check the brakes this weekend so I'm hoping I can get a better look at everything then.

Thank you!

 

[slus]

This is great. It took me a week of research before I tackled it, should be added to the FAQ

 

[silver02accord]

When testing the AHC pressures does the car need to be on a level surface? I just realized my driveway is built tilted for drainage. Will an uneven surface also affect the FR,FL and RR height control sensor number results? My AHC is operating great, I just want to get pressures in spec. I tested ~7.9 front and 6.8 rear. I am going to try to the torsion bars, but will that raise the rear pressure? I don't think the coils have been replaced- are most people adding spacers when they replace coils?

 

[LndXrsr]

The car should be on a relatively level surface, doesn't have to be perfect perfect. Significant tilts/inclines will mess with things.

See my response to your PM for some other details you asked about.

 

[silver02accord]

The car should be on a relatively level surface, doesn't have to be perfect perfect. Significant tilts/inclines will mess with things.

See my response to your PM for some other details you asked about.

Thanks so much,very helpful.

 

[IndroCruise]

When testing the AHC pressures does the car need to be on a level surface? I just realized my driveway is built tilted for drainage. Will an uneven surface also affect the FR,FL and RR height control sensor number results? My AHC is operating great, I just want to get pressures in spec. I tested ~7.9 front and 6.8 rear. I am going to try to the torsion bars, but will that raise the rear pressure? I don't think the coils have been replaced- are most people adding spacers when they replace coils?

You want avoid the weight being skewed left-to-right (or vice versa) or front-to-rear (or vice versa) so a practically level floor in the manner of a garage floor is desirable because

1. The aim of the vital, must-be-done-first, static ‘cross-levelling’ step (equal heights hub-to-fender, engine “OFF”, AHC “OFF”, full fuel, no freight, no passengers) is to get RH and LH torsion bars carrying equal loads. Does not matter what the actual hub-to-fender heights are in this step but vital that they are equalised using Torsion Bar Adjusters (never Height Control Sensor adjusters). This cannot be achieved correctly on a non-level floor – if it is done on a significant slope, a ‘lean’ will be built-in due to the difference in weight on either side of the vehicle,
2. Checking the functional height setting comes later using Height Control Sensor Adjusters (never Torsion Bar Adjusters) with engine “ON”, AHC “ON”, full fuel, no freight, no passengers, steering straight ahead – although turn engine and AHC “OFF” for safety when tools and hands are on the adjusters and head may be in the wheel arch or under the vehicle.
3. With steering straight ahead, AHC Electronic Control Unit (ECU) opens valves connecting RH and LH sides of AHC system and so they are at equal pressure -- BUT if torsion bars are carrying different loads due to slope left-to-right (or vice versa), then it will be hard to get AHC functional heights correct and consistent on both sides and front and rear using Height Control Sensor Adjusters. It is important when the vehicle is being driven that heights do not have built-in bias due to adjustments in a significant slope because as well as having an effect on damping characteristcs, the inputs from the Height Control Sensor Adjusters to the AHC ECU also have a bearing on the level control and roll control of the vehicle when driving, and pitch control of the vehicle under acceleration and braking. All of these things add up to ‘ride quality’.
4. If there is a significant slope front-to-rear (or rear-to-front), then it will be difficult to get AHC pressures correct to FSM specification because front and rear are carrying different different load shares compared to the on-the-level workshop floor situation on which the FSM is specification is based.

What is too much slope? A man-made slope rarely is perfectly level because usually some slope is provided to allow surface water or spillage to run off to a drain. Maybe a practical idea is to choose a slope on which the vehicle would not roll when pointed down dip with all brakes “OFF” and transmission and CDL in neutral. Others may be able to suggest better ideas.

It definitely is a good idea to get the front pressures down using the torsion bar adjusters so that the seals in the front 'shock absorbers' (struts) are not challenged and start to leak. Best to get the front sorted out and then decide what choices to make at the rear.

Rear AHC springs are said to be past their best in 5 years. I left mine in place for 13 years. By then, they were DEFINITELY were long past their best! The suspension defaulted to "LO" even with light loads, rear pressures were high, all indicating that the rear AHC needed help. Spacers may have bought time and pressure improvement, especially if new OEM rear springs were added. I needed more load capacity so I installed King KTRS-79 springs instead -- the ride is great when loaded for cruising but unsurprisingly is a little more harsh when the vehicle is empty because Rear AHC pressure is too low without a load and damping is less effective. Your solution will depend on intended use, accessories, freight and passengers to be carried and the resulting Gross Vehicle Mass. For some, a middle course is new OEM springs, spacers and airbags inside springs to deal with variable weight.

 

[silver02accord]

You want avoid the weight being skewed left-to-right (or vice versa) or front-to-rear (or vice versa) so a practically level floor in the manner of a garage floor is desirable because

1. The aim of the vital, must-be-done-first, static ‘cross-levelling’ step (equal heights hub-to-fender, engine “OFF”, AHC “OFF”, full fuel, no freight, no passengers) is to get RH and LH torsion bars carrying equal loads. Does not matter what the actual hub-to-fender heights are in this step but vital that they are equalised using Torsion Bar Adjusters (never Height Control Sensor adjusters). This cannot be achieved correctly on a non-level floor – if it is done on a significant slope, a ‘lean’ will be built-in due to the difference in weight on either side of the vehicle,
2. Checking the functional height setting comes later using Height Control Sensor Adjusters (never Torsion Bar Adjusters) with engine “ON”, AHC “ON”, full fuel, no freight, no passengers, steering straight ahead – although turn engine and AHC “OFF” for safety when tools and hands are on the adjusters and head may be in the wheel arch or under the vehicle.
3. With steering straight ahead, AHC Electronic Control Unit (ECU) opens valves connecting RH and LH sides of AHC system and so they are at equal pressure -- BUT if torsion bars are carrying different loads due to slope left-to-right (or vice versa), then it will be hard to get AHC functional heights correct and consistent on both sides and front and rear using Height Control Sensor Adjusters. It is important when the vehicle is being driven that heights do not have built-in bias due to adjustments in a significant slope because as well as having an effect on damping characteristcs, the inputs from the Height Control Sensor Adjusters to the AHC ECU also have a bearing on the level control and roll control of the vehicle when driving, and pitch control of the vehicle under acceleration and braking. All of these things add up to ‘ride quality’.
4. If there is a significant slope front-to-rear (or rear-to-front), then it will be difficult to get AHC pressures correct to FSM specification because front and rear are carrying different different load shares compared to the on-the-level workshop floor situation on which the FSM is specification is based.

What is too much slope? A man-made slope rarely is perfectly level because usually some slope is provided to allow surface water or spillage to run off to a drain. Maybe a practical idea is to choose a slope on which the vehicle would not roll when pointed down dip with all brakes “OFF” and transmission and CDL in neutral. Others may be able to suggest better ideas.

It definitely is a good idea to get the front pressures down using the torsion bar adjusters so that the seals in the front 'shock absorbers' (struts) are not challenged and start to leak. Best to get the front sorted out and then decide what choices to make at the rear.

Rear AHC springs are said to be past their best in 5 years. I left mine in place for 13 years. By then, they were DEFINITELY were long past their best! The suspension defaulted to "LO" even with light loads, rear pressures were high, all indicating that the rear AHC needed help. Spacers may have bought time and pressure improvement, especially if new OEM rear springs were added. I needed more load capacity so I installed King KTRS-79 springs instead -- the ride is great when loaded for cruising but unsurprisingly is a little more harsh when the vehicle is empty because Rear AHC pressure is too low without a load and damping is less effective. Your solution will depend on intended use, accessories, freight and passengers to be carried and the resulting Gross Vehicle Mass. For some, a middle course is new OEM springs, spacers and airbags inside springs to deal with variable weight.

I measured wheels with engine on, ahc on (switch was not "off). I'll retry per your instructions.

I got 19.25 Driver front, 20.25 Driver rear, 19.75 Passenger front, 20.75 passenger rear.

I would be down for new springs for the rears as preventive and to keep load off but I'm gonna flush at torsion bar first.

Thank you so much for the help

 

[SlowBuild]

I’m putting this here from @PADDO in the fluid replacement thread because it was useful to me:

7. Now you should have drained very close to 1 liter (0.3+0.4+0.3 for healthy damper accumulator spheres; if you have degraded or blown spheres then you'll likely drain less fluid as there's limited/no nitrogen charge to expel the spheres fluid contents) leaving you about 0.5 liters "excess" in the reservoir.

I started out with 9 ticks L-H in the reservoir, which was acceptable for the time being, 65k miles ago. Along the way I added King spring and adjusted sensors up to bring pressures back to spec (they became low with the Kings). This worked except that my reservoir change went to 19 or 20 ticks. I checked again before a fluid change last week coming up on 200k and was at about 16 ticks. I’m pretty sure by raising the sensors the system pulls more fluid from the reservoir, but that L height remains about the same as what it was before. I didn’t confirm this theory by measuring but it makes sense to me as an explanation why the reservoir level changes so much.

Anyway, replacing fluid according to @PADDO directions, I did pull only about .5 liter from my globes and accumulator. This seems like a useful indicator to use in this case instead of relying on reservoir ticks to determine globe health. I’m searching now for new globes.

* Someone more knowledgeable should confirm or dispel this reasoning before I lead others astray.

 

[IndroCruise]

I measured wheels with engine on, ahc on (switch was not "off). I'll retry per your instructions.

I got 19.25 Driver front, 20.25 Driver rear, 19.75 Passenger front, 20.75 passenger rear.

I would be down for new springs for the rears as preventive and to keep load off but I'm gonna flush at torsion bar first.

Thank you so much for the help

Compare to IH8MUD recommendations when engine and AHC are operating:
19.75 Driver front, 20.50 Driver rear, 19.75 Passenger front, 20.50 Passenger rear.

Your measurements tell you that you have a slight ‘lean’ at the front when the engine is “ON” and the AHC is operating. The Driver front is a little bit low. As a result, the diagonally opposite Passenger rear is a little bit high, just as you would expect.

First things first.

Always do the ‘cross levelling’ step first to get the torsion bars carrying equal loads before doing anything else. This is done by using the torsion bar adjusters to equalise the front hub-to-fender distances when the engine and AHC are “OFF”. It is best to drop the high side and raise the low side by equal amounts to avoid running out of thread on the torsion bar adjusters. This is best done on a level surface. In this step, it does not matter what the front hub-to-fender measurements are so long as they are equal. The AHC system must not be operating because it will self-level the vehicle and interfere with this step.

After ‘cross-levelling’ is done, turn “ON” the engine and AHC and let the vehicle self-level. Sometimes it helps to rock the vehicle or drive it around the block to let the suspension settle after the ‘cross levelling’ step. Then measure the hub-to-fender distances again with the engine and AHC “ON” -- level surface, steering straight, full fuel, no freight and no persons on board. If necessary, use the front Height Control Sensor adjusters (not the torsion bar adjusters) to bring both of the Front hub-to-fender distances as close as possible to 19.75 inches. After the front is done, and with the engine and AHC still “ON”, check that the Rear is as close as possible to 20.50 inches. Adjust the Rear Height Control Sensor adjuster if necessary.

Consistent with the "The ABC of AHC" post #1, the sequence is always the same for basic checks on the AHC suspension:

1. Equalise front torsion bar loads – by ‘cross-levelling’ using torsion bar adjusters with engine and AHC “OFF” to make static front hub-to-fender distances equal,
2. With engine and AHC “ON”, check operating hub-to-fender distances: Front 19.75 inches, Rear 20.5 inches
3. If necessary, adjust the operating hub-to-fender distances using Height Control Sensor adjusters (not the torsion bar adjusters),
4. When the operating hub-to-fender distances are correct, check front and rear AHC pressures,
5. If operating hub-to-fender distances are not correct, then AHC pressures cannot be measured correctly and compared to FSM specifications,
6. If operating FRONT hub-to-fender distances are correct but FRONT AHC pressure is not within FSM specifications, correct front pressures using torsion bar adjusters – turn both adjusters clockwise by equal amounts to increase load carried by the torsion bars and reduce front AHC pressure, or, turn both adjusters anti-clockwise by equal amounts to decrease load carried by the torsion bars and increase front AHC pressure,
7. After setting correct front AHC pressure, re-check torsion bar loads by repeating ‘cross-level’ check (Step 1 – engine and AHC “OFF”) and readjust again if necessary,
8. Re-check front operating hub-to-fender distances (Step 2 -- engine and AHC “ON”),
9. After completing FRONT adjustments, check REAR AHC pressures (FSM says disconnect temperature sensor at AHC pump),
10. If operating REAR hub-to-fender distances are correct but REAR AHC pressures are not within FSM specifications (rear AHC pressures usually become too high because rear springs weaken with age and miles), consider spacers or replacement rear springs or both.

 

[silver02accord]

Compare to IH8MUD recommendations when engine and AHC are operating:
19.75 Driver front, 20.50 Driver rear, 19.75 Passenger front, 20.50 Passenger rear.

Your measurements tell you that you have a slight ‘lean’ at the front when the engine is “ON” and the AHC is operating. The Driver front is a little bit low. As a result, the diagonally opposite Passenger rear is a little bit high, just as you would expect.

First things first.

Always do the ‘cross levelling’ step first to get the torsion bars carrying equal loads before doing anything else. This is done by using the torsion bar adjusters to equalise the front hub-to-fender distances when the engine and AHC are “OFF”. It is best to drop the high side and raise the low side by equal amounts to avoid running out of thread on the torsion bar adjusters. This is best done on a level surface. In this step, it does not matter what the front hub-to-fender measurements are so long as they are equal. The AHC system must not be operating because it will self-level the vehicle and interfere with this step.

After ‘cross-levelling’ is done, turn “ON” the engine and AHC and let the vehicle self-level. Sometimes it helps to rock the vehicle or drive it around the block to let the suspension settle after the ‘cross levelling’ step. Then measure the hub-to-fender distances again with the engine and AHC “ON” -- level surface, steering straight, full fuel, no freight and no persons on board. If necessary, use the front Height Control Sensor adjusters (not the torsion bar adjusters) to bring both of the Front hub-to-fender distances as close as possible to 19.75 inches. After the front is done, and with the engine and AHC still “ON”, check that the Rear is as close as possible to 20.50 inches. Adjust the Rear Height Control Sensor adjuster if necessary.

Consistent with the "The ABC of AHC" post #1, the sequence is always the same for basic checks on the AHC suspension:

1. Equalise front torsion bar loads – by ‘cross-levelling’ using torsion bar adjusters with engine and AHC “OFF” to make static front hub-to-fender distances equal,
2. With engine and AHC “ON”, check operating hub-to-fender distances: Front 19.75 inches, Rear 20.5 inches
3. If necessary, adjust the operating hub-to-fender distances using Height Control Sensor adjusters (not the torsion bar adjusters),
4. When the operating hub-to-fender distances are correct, check front and rear AHC pressures,
5. If operating hub-to-fender distances are not correct, then AHC pressures cannot be measured correctly and compared to FSM specifications,
6. If operating FRONT hub-to-fender distances are correct but FRONT AHC pressure is not within FSM specifications, correct front pressures using torsion bar adjusters – turn both adjusters clockwise by equal amounts to increase load carried by the torsion bars and reduce front AHC pressure, or, turn both adjusters anti-clockwise by equal amounts to decrease load carried by the torsion bars and increase front AHC pressure,
7. After setting correct front AHC pressure, re-check torsion bar loads by repeating ‘cross-level’ check (Step 1 – engine and AHC “OFF”) and readjust again if necessary,
8. Re-check front operating hub-to-fender distances (Step 2 -- engine and AHC “ON”),
9. After completing FRONT adjustments, check REAR AHC pressures (FSM says disconnect temperature sensor at AHC pump),
10. If operating REAR hub-to-fender distances are correct but REAR AHC pressures are not within FSM specifications (rear AHC pressures usually become too high because rear springs weaken with age and miles), consider spacers or replacement rear springs or both.

Thank you for the further explanation and detail. So as I understand it the torsion bars are used to set the correct height (19. 75 front and 20.5 rear) as well as reduce/increase pressure in the globes. Since my driver side front is low would I be going counter clockwise on the torsion bolt? Get it to spec/level with the passenger side then I can begin to reduce pressure(I have high 7s low 8 at front) by equal amount of clockwise turns on both torsion bars? Of course following the above protocol and steps.

 

[IndroCruise]

Thank you for the further explanation and detail. So as I understand it the torsion bars are used to set the correct height (19. 75 front and 20.5 rear) as well as reduce/increase pressure in the globes. Since my driver side front is low would I be going counter clockwise on the torsion bolt? Get it to spec/level with the passenger side then I can begin to reduce pressure(I have high 7s low 8 at front) by equal amount of clockwise turns on both torsion bars? Of course following the above protocol and steps.

Apologies – I can see that my wording has caused some confusion so I will try again to be more clear.

No – the torsion bar adjusters are not “used to set the correct height (19. 75 front and 20.50)”.

The torsion adjusters are used to do only two very separate things in a vehicle with AHC suspension:

1. Cross-levelling
2. Adjusting front AHC pressure

The aim of so-called ‘Cross-levelling’ in Step 1 using the torsion bar adjusters is only to get the same load carried by RHS torsion bar and LHS torsion bar. It is not to set the height of the vehicle. The principle here is that torsion bars behave like springs. To get the same load, we want the same deflection or movement on both the RHS side of the vehicle and the LHS of the vehicle, without any involvement of the AHC system. This is why this is done with engine and AHC turned “OFF” in this Step. We assume that the RHS torsion bar and LHS torsion bar are the same product, same specification and not defective. Then if the front hub-to-fender distance on the RHS and LHS are the same, we can conclude that the RHS torsion bar and the LHS torsion bar are carrying the same load. It is only important in Step 1 that the RHS front hub-to-fender distance and the LHS front hub-to-fender distance are equal. The actual distances do not matter in this Step. Do not worry about 19. 75 front and 20.50 rear in this Step – it is not relevant in Step 1. Those numbers are the specifications which are only relevant when the engine and AHC are switched “ON” and running. That comes later, not in Step 1. Achieving “19. 75 front and 20.50 rear” is never done with the torsion bar adjusters.

It is important to have the torsion bars carrying the same loads because

• the Right and Left sides of the vehicle must be in balance so that the vehicle does not behave differently when turning left and right, and,
• so that the operating heights can be set correctly in the later Steps.

When ‘cross-levelling’ complete, then we think about correct heights. We switch “ON” the engine and also make sure that the AHC is switched “ON” and operating. The AHC Electronic Control Unit (ECU) will now receive information from the Height Control Sensors at Front Left, Front Right and Rear. These Sensors will determine the actual heights. Probably the heights will not be correct. We now wish “to set the correct height (19. 75 front and 20.50 rear)” on the RHS and LHS of the vehicle. We definitely do not do this with the torsion bar adjusters because that would change the loads carried by the torsion bars and make them unequal. That would destroy the effort already made in Step 1. So we “set the correct heights (19. 75 front and 20.50 rear)” using the adjusters at the Height Control Sensors, starting at the Front LHS and RHS and then at the Rear.

After “setting the correct heights (19. 75 front and 20.50 rear)” using only the adjusters at the Height Control Sensors (not torsion bar adjusters), then it is time to consider Front and Rear AHC pressures.

The front AHC pressure is adjusted using the torsion bar adjusters. Note that this will not change the operating heights because the heights are set by the Height Control Sensors when the engine and AHC are running and these already have been adjusted.

In your case, you mention that you have “high 7s low 8 (Mpa) at front”. This may be different when you have set the correct heights as previously discussed – so the AHC pressures should be measured again before going further. If the pressures really are so high even at the corrects heights (maybe due to other loads, 'armour', or equipment on the vehicle?), then you need to get down to the lower part of the FSM-specified range for front pressure of 6.4Mpa to 7.4Mpa. Usually, one full turn on both torsion bar adjusters in the same direction makes a change of about 0.2Mpa, so you will need to do at least 5 turns, probably more like 8 turns.

After such a big change, you should again re-check the ‘cross-levelling’ (with engine and AHC “OFF”) and the correct operating heights (with the engine and AHC “ON”), in case something has been disturbed.

Hope this is more clear.

 

[silver02accord]

Apologies – I can see that my wording has caused some confusion so I will try again to be more clear.

No – the torsion bar adjusters are not “used to set the correct height (19. 75 front and 20.50)”.

The torsion adjusters are used to do only two very separate things in a vehicle with AHC suspension:

1. Cross-levelling
2. Adjusting front AHC pressure

The aim of so-called ‘Cross-levelling’ in Step 1 using the torsion bar adjusters is only to get the same load carried by RHS torsion bar and LHS torsion bar. It is not to set the height of the vehicle. The principle here is that torsion bars behave like springs. To get the same load, we want the same deflection or movement on both the RHS side of the vehicle and the LHS of the vehicle, without any involvement of the AHC system. This is why this is done with engine and AHC turned “OFF” in this Step. We assume that the RHS torsion bar and LHS torsion bar are the same product, same specification and not defective. Then if the front hub-to-fender distance on the RHS and LHS are the same, we can conclude that the RHS torsion bar and the LHS torsion bar are carrying the same load. It only important in Step 1 that the RHS front hub-to-fender distance and the LHS front hub-to-fender distance are equal. The actual distances do not matter in this Step. Do not worry about 19. 75 front and 20.50 rear in this Step – it is not relevant in Step 1. Those numbers are the specifications which are only relevant when the engine and AHC are switched “ON” and running. That comes later, not in Step 1. Achieving “19. 75 front and 20.50 rear” is never done with the torsion bar adjusters.

It is important to have the torsion bars carrying the same loads because

• the Right and Left sides of the vehicle must be in balance so that the vehicle does not behave differently when turning left and right, and,
• so that the operating heights can be set correctly in the later Steps.

When ‘cross-levelling’ complete, then we think about correct heights. We switch “ON” the engine and also make sure that the AHC is switched “ON” and operating. The AHC Electronic Control Unit (ECU) will now receive information from the Height Control Sensors at Front Left, Front Right and Rear. These Sensors will determine the actual heights. Probably the heights will not be correct. We now wish “to set the correct height (19. 75 front and 20.50 rear)” on the RHS and LHS of the vehicle. We definitely do not do this with the torsion bar adjusters because that would change the loads carried by the torsion bars and make them unequal. That would destroy the effort already made in Step 1. So we “set the correct heights (19. 75 front and 20.50 rear)” using the adjusters at the Height Control Sensors, starting at the Front LHS and RHS and then at the Rear.

After “setting the correct heights (19. 75 front and 20.50 rear)” using only the adjusters at the Height Control Sensors (not torsion bar adjusters), then it is time to consider Front and Rear AHC pressures.

The front AHC pressure is adjusted using the torsion bar adjusters. Note that this will not change the operating heights because the heights are set by the Height Control Sensors when the engine and AHC are running and these already have been adjusted.

In your case, you mention that you have “high 7s low 8 (Mpa) at front”. This may be different when you have set the correct heights as previously discussed – so the AHC pressures should be measured again before going further. If the pressures really are so high even at the corrects heights (maybe due to other loads, 'armour', or equipment on the vehicle?), then you need to get down to the lower part of the FSM-specified range for front pressure of 6.4Mpa to 7.4Mpa. Usually, one full turn on both torsion bar adjusters in the same direction makes a change of about 0.2Mpa, so you will need to do at least 5 turns, probably more like 8 turns.

After such a big change, you should again re-check the ‘cross-levelling’ (with engine and AHC “OFF”) and the correct operating heights (with the engine and AHC “ON”), in case something has been disturbed.

Hope this is more clear.

View attachment 2377887

Crystal clear! Thank you so much- really helps. Waiting for my 30mm socket to arrive then getting to work. I'll report back w/ progress.