AHC mini lift (1 Viewer)

[CrusrDug]

I recently lifted my truck with the AHC sensors and thought I would document it for others. My goal was to increase ride height about an inch and attempt to keep ride quality with the minimal lift.

First was moving the front sensors to the top of the slider. I have not messed with the heim joint yet.



Second was to move the rear sensor to the top of slider.



Next, you need to trick the AHC into thinking it is stock and remove some of the pressure from the system. Since the sensor slider adjustment basically raises it an inch, I added 30mm spacers to the rear coils (not in the above picture) and cranked the TB's 3 turns for the front. There is no mechanical or scientific reason for the 3 turns, just test drove it several times and got it to where I thought it was comfortable.

Eventually I will measure the pressure when I change my AHC fluid here soon and adjust the TB's so the system is back in spec. Who knows, it may already be close.

Measurements are as follows from bottom of wheel lip to fender lip:
DS F 30"
PS F 30.25"
DS R 31"
PS R 31"

Here is how it looks in AHC normal mode

 

[CrusrDug]

Before I adjusted the TB's, I noticed they were adjusted different and the PS (afer referring to the FSM) was actually out of spec. The bolt heads are supposed to be above the bottom bracket, not sticking below it. I'm not sure what to think about this since I have AHC, but I also noticed the heim joint on the sensors were different as well. The PS side heim joint is shorter which would make the vehicle ride higher on that side. That could account for my 1/4 in difference.

DS Torsion bolt


PS Torsion bolt


Compare this picture to the DS heim joint in the first post. 5-6 threads here compared to 8-9 threads there.

 

[Zazoo62]

Hey - thanks very much for taking the time to do this post - this is great help for me, as it is one version of exactly what I was asking about in my LIFT post a day or so ago (wanting 1" lift and level stance while retainign AHC functionality). Couple of questions (and forgive my ignorance in advance): why are spacer(s) needed in the rear - cant you adjust the AHC sensor for this amount of rear lift as well? I sort of thought spacers were not the first choice of lift methods since don't they just add body lift, higher center of gravity and no additonal clearance (thereby making rear lift via AHC an arguably "better" alternative wiht no additional cost, etc? Also, it's hard to see in the photo, but did you try to obtain a level stance? It appears that you ended up with about 1" higher rear and not sure if this was what you wanted or just ended up with.

 

[Zazoo62]

Oh yeah - you mentioned wanting to retain stock AHC ride quality(ies). So how is it?

 

[1loudLX]

you can adjust the sensors, and have to adjust the sensors. the 30mm packer is to make the rear spring back to the way it would normally sit at unadjusted height.

You're confusing spring spacers with body lift.

 

[cmfhsu]

Spacers aren't needed to run an AHC lift is it? Sure, the pressure's a lil higher, but nothing out of spec, right?

 

[wildsmith]

The higher the AHC system pressure is, the lower your trucks load carrying ability is and it's not great to begin with.

 

[RoderickGI]

Before I adjusted the TB's, I noticed they were adjusted different and the PS (afer referring to the FSM) was actually out of spec. The bolt heads are supposed to be above the bottom bracket, not sticking below it. I'm not sure what to think about this since I have AHC, but I also noticed the heim joint on the sensors were different as well. The PS side heim joint is shorter which would make the vehicle ride higher on that side. That could account for my 1/4 in difference.

The Left and Right side (for me, the DS is the right side, so I'll use left and right so that I don't confuse myself) Torsion Bolts are supposed to be adjusted differently, according to the FSM for my 1998 LX, but yes the bolt head on both sides should be above the bracket.
Left: 8 - 25 mm above bracket
Right: 2 - 18 mm above bracket

Having worked on mine recently, I suspect that because the AHC levels the vehicle regardless of TB adjustment, as long as the pump can produce the oil pressure, the TBs don't get adjusted properly. The method of adjusting them to get the correct oil pressure based on the voltage at the pump sensor seems a little indirect to me, and possibly inaccurate, which may explain the TB adjustments.

I wanted to measure the AHC oil pressure directly to do my adjustments, so I bought an "ABS and Brake Pressure Testing Master Kit". I don't know if you have such a unit, but if you don't they make it easy to measure and adjust, though a little time consuming to set up.

Snap-on make such a unit, but it would have cost me AU$1,589 plus shipping! I found a Waekon alternative and bought it from USA Tools who price matched The Tool Warehouse, so I got it for US$268.82 plus US$50 shipping, or AU$352 total. It was worth it to understand what the AHC was doing, and get new acctuator spheres spec'd correctly for my heavy LX. I see they have gone up to US$302.50 now, but they are reasonable quality, and look identical to the far more expensive Snap-On version. (Really. Same colour, same bits, same manual except for the cover.) I did have to run a die over the thread of one of the fittings I needed to use though, as it wasn't cut deep enough and wouldn't screw into the bleed nipple hole. I suspect the Snap-On would have had the same issue.

If you use the above tool, you could adjust the TBs based on oil pressure, leave them in place then adjust the height control sensors to level the vehicle, then check the oil pressures again, since they may change with height adjustment. I even took a short test drive with the gauges attached, to get the AHC normalised, and check the maximum pressures reached. Neat.

 

[RoderickGI]

Spacers aren't needed to run an AHC lift is it? Sure, the pressure's a lil higher, but nothing out of spec, right?

The higher the AHC system pressure is, the lower your trucks load carrying ability is and it's not great to begin with.

Plus the higher the pressure is, the more oil is forced into the accumulator spheres, meaning the less travel you have in the suspension before the spheres are full and you lose the dampening effect. You get a kick in the pants when that happens (hard ride).

Not to mention the higher the pressure, the more wear on the AHC components, particularly the pump. I now run my AHC below the specified pressures, because I have heavier springs on the back and have adjusted the TBs up tight, to lift all the extra weight I've put on the LX. This means I get the full travel of the shock absorbers (hydraulic rams) and was able to lower pressure in the spheres to get a better ride. It also means that when I run in the high position, the oil pressure doesn't get so high that I lose travel in the shock absorbers.

 

[wildsmith]

I balanced my TB's by dropping the AHC down to L so there should be no or very little pressure in the system, parked on a level / flat surface and measure the gap between the bump stop and the suspension arm. Mine are cranked up a little though to level it out more and compensate for the bumper and winch. On a stock truck there might not be any gap at all where on mine there is a small gap.

 

[Zazoo62]

you can adjust the sensors, and have to adjust the sensors. the 30mm packer is to make the rear spring back to the way it would normally sit at unadjusted height.

You're confusing spring spacers with body lift.

Yep - I sure did. That's it, I'm ripping this system out, installing OME and running over curbs and small animals.

 

[LandCruiserPhil]

Yep - I sure did. That's it, I'm ripping this system out, installing OME and running over curbs and small animals.

 

[1loudLX]

Let's make March 7th international rip your AHC out day.

 

[LandCruiserPhil]

Let's make March 7th international rip your AHC out day.

Nope, mine is staying as long as its working. So far no down side only up

 

[1loudLX]

Youre selling it, you have no say on the matter

 

[CrusrDug]

Zazoo62- I saw your thread and thought I would do this just for you!

The first time I did this a couple years ago I only adjusted the sensors. You will notice a ride that becomes stiffer and as RoderickGI said a bit hard. I did not try to get a level stance because I have read you want about an inch of difference to retain droop.

The truck will settle wherever you tell it to based on the sensor adjustment regardless of the springs spacer or TB adjustment. By adding the spacers and adjusting the TB's you are essentially trying to trick the AHC into thinking the sensors are not adjusted by relieving some of the pressure in the system. I know this because LandCruiserPhil told me so

Basically, you will have to play with it to get it comfortable or do the pressure adjustments noted above. I think mine is a little springy so I am going to play with it some more by either reducing the TB or increasing the height with the sensor adjustment heim joint. The ride has definitely changed, not necessarily too much in the comfort, but (for me) the performance. Today was wet around here and I like to play hard on wet pavement days. I noticed the front end was a bit out of control under heavy acceleration, which I noticed the other day on dry going over bumps, but really noticed it today. I have not got the alignment yet.

I also need to change my fluid or at least get some new stuff in there and bleed the system as I'm at 60k. Could be affecting the dampening. My tires are worn too and I'm sure they aren't soaking up the road like they used to.

I'm going to have to check the TB's because I really don't like how far out of spec the PS is. That alone could be causing my performance concerns putting different characteristics on that wheel. It makes me wonder if something else was out of whack from the factory and they adjusted it out with the TB?

 

[LandCruiserPhil]

Youre selling it, you have no say on the matter

 

[RoderickGI]

I balanced my TB's by dropping the AHC down to L so there should be no or very little pressure in the system, parked on a level / flat surface and measure the gap between the bump stop and the suspension arm.

You may be surprised to know that on my LX, with an ARB Bullbar, winch, dual batteries, ARB compressor, and some other bits on the front, the oil pressure in my AHC, when set at the Low position and before adjusting the TBs was 600 to 610 psi.

In fact the pressures were:
Front Left:
LOW 600 psi
NORMAL 1030 psi
HIGH 1430 psi

Front right:
LOW 610 psi
NORMAL 1030 psi
HIGH 1440 psi

As the specification for the front AHC oil pressure is 825 +/- 43 psi at the Normal position, I would estimate that the oil pressure at the Low setting should be 400 psi when the AHC is correctly set to specification. That estimate is supported by the (copious) measurements I did as I progressively tightened up the TBs, although I never adjusted the AHC to exactly 825 psi at the Normal setting. But for example, I got the values below as I tightened the TBs:

Normal : Low
980 : 530
530 : 140

Assuming a linear pressure change and doing the math, at 825 psi in Normal position, Low position should be 396 psi. Close enough to my estimate. So when you dropped your AHC down to Low to adjust the TBs, if the adjustment was close to the specification, the pressure in the AHC would be about 400 psi. If you had extra weight on the front, the pressure would be greater than 400 psi.

That is not exacty a small amount of pressure.

Mine are cranked up a little though to level it out more and compensate for the bumper and winch. On a stock truck there might not be any gap at all where on mine there is a small gap.

As CrusrDug, I and others have said, adjusting your torsion bars on an AHC equiped vehicle does not adjust the height of the vehicle. It just adjusts the AHC oil pressure required to lift the vehicle to the correct height setting, as per the control switch.

You will only see a height change when you adjust the TBs if the AHC had previously been unable to cope with the weight on it, or, more likely, the AHC hasn't kicked in to readjust the height by dropping the oil pressure after you tightened the TBs. I noticed a lot of stiction and lag in the AHC system when the vehicle was stationary. It was necessary to follow the FSM procedure of dropping the AHC to Low and then raising to Normal in order to get valid oil pressure readings.

In fact, if you are still using the original AHC specific Torsion Bars, and you adjust them right up to near the maximum setting, which is about 14 full turns from the minimum setting, then go for a short drive, park on a flat surface, lower the vehicle to Low, then raise to Normal, then drop to Low, you will find that the gap from the bump stop to suspension arm is back to where it started from. The AHC will have adjusted the height according to the height setting. The oil pressure in the AHC at the Low setting will be about 100 psi.

BTW, from memory the gap between the bump stop and the suspension arm at the Low position on my LX, which hasn't had the AHC height sensors adjusted, is about 30 mm at the front, and 70 mm at the back. ( Or the other way around. I forget.) This the same gap it has always been, even though I have lots more weight on the LX than when it was new.

Sorry, but your method of leveling the vehicle and adjusting the TBs doesn't work with an AHC fitted vehicle. Adjust the height sensors to adjust the height and level the vehicle. Adjust the TBs to reduce the oil pressure in the AHC and regain some shocker absorber travel and hence gain damped wheel travel, and load capacity.

Of course, if someone thinks I am wrong, go ahead and tell me. I can take it. At worst the information above might help someone understand what is going on in the AHC.

 

[wildsmith]

I understand the spring / sensor / pressure relationship but I had assumed the low position depressurised the system. Scrap that method then! I'll have to either get a gauge set like you so I can set them up properly or throw it out and fit the Bilstien shocks and RidePro springs I have on the way from Darren

 

[CrusrDug]

So I have noticed a difference in ride height on the rear after I drive around and then park. It's seems to adjust 1/2 in higher, but if I put it in low and then back to normal, it goes back to my measurements in post 1. Now that i think about it, I'm pretty sure it did this before I messed with it too.

What do you guys think is causing that?