Is there a way to measure neutral pressure on AHC suing the ODBII port? I hear the torsion bars get weak with the years and it would be good to adjust but I need to measure NP first.
Measure AHC neutral pressure? (1 Viewer)
- Thread starter Loyota
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OBDII does not have this information. But it is accessible through the special Toyota handheld tester (using the OBDII connector). I'm wondering if there is an aftermarket (copycat) solution.
Alternatively, it should be possible to measure the output of the "Fluid Pressure Sensor" transducer. One would need a conversion table (voltage v.s. psi). I have not seen that. But it may exist. If someone has a transducer, I can hook it up to a pressure tester @ work, and make the graph.
hoser
SILVER Star
Search "techstream" but do your research before buying.
uHu
Bridgeburner
Alternatively:
Just change the coils and turn the TBs 2-3 turns every 5-6 years. Not the right way, but that seems to be the outcome of measuring for me.
Just change the coils and turn the TBs 2-3 turns every 5-6 years. Not the right way, but that seems to be the outcome of measuring for me.
This should be regular maintenance. Coil springs and Torsion bars lose their spring rate over time. Torsion bars can be adjusted to compensate, coil springs can be replaced with new coils, augmented with helper air bags or replaced completely with an airbag system. Of course, my local Lexus dealer had no interest in hooking up their test equipment and telling me my neutral pressures and said that this was not something they do, that it was not necessary and so on.
When the steel springs are worn, the AHC fluid globes carry more weight than normal to level the truck. You don't see this, because working AHC gives a level truck all the time. 6 people inside? level. Fill the back with tools and hook a trailer on? level. However, the AHC will drop into low mode if the vehicle is filled beyond the AHC weight capacity. With old springs, this capacity is greatly reduced.
However, I think the neutral pressure method of setting the torsion bars is maybe a bit more complex than it needs to be.
If someone has recently checked their neutral pressure and adjusted their torsion bars, could they give us the measurement in low mode between the center of the hub cap and the fender lip? -low mode, truck moved slightly since suspension dropped, level surface, etc.
When the steel springs are worn, the AHC fluid globes carry more weight than normal to level the truck. You don't see this, because working AHC gives a level truck all the time. 6 people inside? level. Fill the back with tools and hook a trailer on? level. However, the AHC will drop into low mode if the vehicle is filled beyond the AHC weight capacity. With old springs, this capacity is greatly reduced.
However, I think the neutral pressure method of setting the torsion bars is maybe a bit more complex than it needs to be.
If someone has recently checked their neutral pressure and adjusted their torsion bars, could they give us the measurement in low mode between the center of the hub cap and the fender lip? -low mode, truck moved slightly since suspension dropped, level surface, etc.
uHu
Bridgeburner
Typical for many dealers. This IS the one most important PM info for the AHC.
Don't know the measurement, but it's sitting om the bump-stops. Can give you a number tonight.
I did. Got a lot of help from "agaisin" by email as well. Thanks all. Purchased a Tactrix OpenPort 2.0 last week. Hooked it up to my '00 LX470 (this one) with ~62kmiles. Note that this is probably not a typical vehicle with only 62kmiles in 11 years.
Here are my numbers before AHC adjust. Level surface. No rear seat. 1/2 tank of gas.
Front: 7.5 MPa, Rear 6.6 MPa, Accumulator: 10.6 MPa
Sensors: Right: 1.0mm, Left: -4.6mm, Rear: -1.8mm
Height floor to fender (through the wheel hub, perpendicular to the floor) was 880 mm with 285/75/R16's.
The spec pressure for the front when measured electronically is 6.9+/-0.5 MPa and rear is 5.6-6.7 MPa. The aging of the vehicle seemed to have softened the torsion bars a bit, resulting in higher AHC fluid pressure to compensate.Sensors: Right: 1.0mm, Left: -4.6mm, Rear: -1.8mm
Height floor to fender (through the wheel hub, perpendicular to the floor) was 880 mm with 285/75/R16's.
Time to crank the torsion bars (TBs). 30mm socket and 3ft ratchet. I did not even have to lift the vehicle. I could turn them by hand. Maybe thanks to Krown oil undercoating?
I cranked the torsion bars to get the front into spec. Since Left was a bit low, I ended up with 2-1/2 turns clockwise on the Left side and 1-1/2 turns on the Right side.
Techstream results after TB adjust:
Front: 6.7 MPa, Rear 7.1 MPa, Accumulator: 10.7 MPa
Height floor to fender did not change (as expected) but L&R were equal now.
Height floor to fender did not change (as expected) but L&R were equal now.
TBs needed adjustment after 11 years to get AHC fluid pressure in spec. Problem now is that the Rear increased from 6.6 to 7.1 MPa and is out of spec due to spring sag. I'll have to research my options. Don't want to over-stress the AHC system.
New springs? Air bags? Spacers? Or even Model 80 coils? - Their spring rate seems to be in between those of AHC 100's and non-AHC 100's.
Since I do tow now and then, the airbags make most sense. It would be nice if I could get an instant pressure readout on the dash. Just adjust the rear airbags depending on the load and trailer. Hmm, maybe it is time for a pressure transducer in the rear AHC lines with dash readout. [edit: I did find numerous posts about this topic. Great info. Trying to catch up from being away from this forum for a few years. Babies, toddlers and moving does not help to focus.
]
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- Thread starter
- #9
Excellent info - thanks white_lx. Looks like its time for me to crank my bars a couple of turns. What else can you use the Tactrix for? Trying to decide if I should but one now or just crank the bars blindly.
As far as airbags, I put those on a couple of weeks ago and they seem to work great - have not towed yet but looks like you can turn of AHC, level truck with air bags and then turn AHC back on - basically eliminating any tongue weight load on the hydraulics. I tow a 5000lb camper so this should be very helpful.
As far as airbags, I put those on a couple of weeks ago and they seem to work great - have not towed yet but looks like you can turn of AHC, level truck with air bags and then turn AHC back on - basically eliminating any tongue weight load on the hydraulics. I tow a 5000lb camper so this should be very helpful.
In theory the Tactrix cable should allow you to fully use Techstream, which can be used for diagnostics as well as customization of settings. I'm still new to this and trying to learn. So far I have only been able to read the sensor data. I'm having troubles customizing settings or running active tests.
Personally I would not blindly turn the torsion bars.
Good to hear. I ordered a set too. Seems to be the best solution to get variable springs required to keep AHC happy and neutral under all conditions.
PabloCruise
SILVER Star
I did. Got a lot of help from "agaisin" by email as well. Thanks all. Purchased a Tactrix OpenPort 2.0 last week. Hooked it up to my '00 LX470 (this one) with ~62kmiles. Note that this is probably not a typical vehicle with only 62kmiles in 11 years.
Here are my numbers before AHC adjust. Level surface. No rear seat. 1/2 tank of gas.
Front: 7.5 MPa, Rear 6.6 MPa, Accumulator: 10.6 MPaThe spec pressure for the front when measured electronically is 6.9+/-0.5 MPa and rear is 5.6-6.7 MPa. The aging of the vehicle seemed to have softened the torsion bars a bit, resulting in higher AHC fluid pressure to compensate.
Sensors: Right: 1.0mm, Left: -4.6mm, Rear: -1.8mm
Height floor to fender (through the wheel hub, perpendicular to the floor) was 880 mm with 285/75/R16's.
Time to crank the torsion bars (TBs). 30mm socket and 3ft ratchet. I did not even have to lift the vehicle. I could turn them by hand. Maybe thanks to Krown oil undercoating?
I cranked the torsion bars to get the front into spec. Since Left was a bit low, I ended up with 2-1/2 turns clockwise on the Left side and 1-1/2 turns on the Right side.
Techstream results after TB adjust:
Front: 6.7 MPa, Rear 7.1 MPa, Accumulator: 10.7 MPa
Height floor to fender did not change (as expected) but L&R were equal now.
TBs needed adjustment after 11 years to get AHC fluid pressure in spec. Problem now is that the Rear increased from 6.6 to 7.1 MPa and is out of spec due to spring sag. I'll have to research my options. Don't want to over-stress the AHC system.
New springs? Air bags? Spacers? Or even Model 80 coils? - Their spring rate seems to be in between those of AHC 100's and non-AHC 100's.
Since I do tow now and then, the airbags make most sense. It would be nice if I could get an instant pressure readout on the dash. Just adjust the rear airbags depending on the load and trailer. Hmm, maybe it is time for a pressure transducer in the rear AHC lines with dash readout. [edit: I did find numerous posts about this topic. Great info. Trying to catch up from being away from this forum for a few years. Babies, toddlers and moving does not help to focus.
I realize this is an old thread, and @white_lx was last seen in 2014, but wondering if other folks see the same happen - crank the TBs and the rear pressure goes up?
What to do?
Do 30mm inserts restore pressure w/in spec?
PabloCruise
SILVER Star
Hmm... If my rear is at 7.8 right now, that might not be enough.
I have a BIOR rear bumper and sliders on this rig. Wondering about trying a set of 100 rear springs in there, seeing if it is too stiff. I can get my hands on a set cheap.
Look Into king ktrs 79 springs. They are are little bit stiffer than the standard LX springs, 120 pounds per inch vs 90 on the standard lx Springs and the land cruiser Springs are 180 pounds per inch they will be far to stiff and you will hate way the truck rides if you install standard non ahc springs.
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PabloCruise
SILVER Star
Thank you! Are you speaking from experience? Did you try the 100 (non-AHC) rear coils and hate them?
Speaking from experience.
I was going to purchase 2 new rear lx470 springs my rear pressures was 7.4, but then I started reading about ahc sensor lifts. I saw people talking about using king springs and thought I'd give them a try.
I moved the 3 height sensors to the top of the slider and achieved a 3/4" lift and installed the king springs at the same time. Adjusted the front torsion bars 5 turns to lower the front pressure in the front, with the sensor adjustment and new king springs my rear pressure was now 5.4.
I then shortened the sensor link arms 1/2 each and made a little metal bracket to adjust the rear sensor arm higher. This resulted in a 1.5" lift. Turned the front bars another 4 turns
My front pressure is now 6.8 and rear went from 5.4 to 6.2. The truck now rides just as good as before while having lower rear pressure and a very modest 1.5" lift.
PabloCruise
SILVER Star
Thank you for detailing the steps for me.
Do you have any extra weight on your rig?
None at the moment, hope to have a Dissent front bumper and winch soon. I'll report with pressures after the install.
Just checked the pressures. 6 years after last adjustment and at 80k miles:
Front: 7.3 MPa, Rear 6.9 MPa, Accumulator: 10.6 MPa
So in 6 years and only 18k miles driven, the front pressure increased 0.6 MPa and rear pressure reduced slightly. Same configuration, half tank and no rear seats.
I might crank the TB's again and see what happens with the rear and go from there. Technically the front is still in spec (6.9+/-0.5). I have the airbags, but never got around to installing them.
Just adding another data point...
My 2006 LC has 134k miles. I just bought it. I assume the truck has never been adjusted.
Front Pressure was ~10.4
Rear Pressure was ~7.9
I put in King KTRS79 rear coils and adjust the front height roughly 3/4" to level the truck a bit. The rear coils have no adjustment but I did adjust the stock torsion bars. I ended up with:
Front Pressure of ~6.2
Rear Pressure of ~5.2
I realize these new values are under spec. I intend to add some weight shortly and I have a trailer with quite a bit of tongue weight. I couldn't come up with a reason to have an issue with being under pressure other than a slightly rough riding truck. The truck does ride a bit stiffer but on the lowest "comfort" setting its still pretty soft. Not a recommendation just where mine sits now.
My 2006 LC has 134k miles. I just bought it. I assume the truck has never been adjusted.
Front Pressure was ~10.4
Rear Pressure was ~7.9
I put in King KTRS79 rear coils and adjust the front height roughly 3/4" to level the truck a bit. The rear coils have no adjustment but I did adjust the stock torsion bars. I ended up with:
Front Pressure of ~6.2
Rear Pressure of ~5.2
I realize these new values are under spec. I intend to add some weight shortly and I have a trailer with quite a bit of tongue weight. I couldn't come up with a reason to have an issue with being under pressure other than a slightly rough riding truck. The truck does ride a bit stiffer but on the lowest "comfort" setting its still pretty soft. Not a recommendation just where mine sits now.
