LX470 AHC Stiff Ride Correction (1 Viewer)

[99RichieLx470]

I replaced my rear springs with factory Oem Lexus AHC springs and I also installed 30mm slee spacers. My trusty dusty MacBook has failed me for the first time so I am unable to get into XP and and check my new pressures.
I should have that fixed in a about a week.

My ride quality has improved noticeably, even my wife asked me "if I did something to the truck". It hits and handles the bumps better.
I used to run the truck close to the sport mode to match the harshness. Comfort used to bother me because the up and down compression of the shocks combined with bitterness over the bumps made the truck feel kinda outta control. At least sport mode I felt bumps but felt the truck more planted to the road.

I have a 99 with original accumulators and I'm in the lower end of spec of fluid gradient movement. (10ish).

I think on an older truck this is great way to get a "very good" adjustable ride that's "wife approved".

 

[99RichieLx470]

I'm about to start this whole thing again myself. I have an 05 with 127k on it, fully stock. I changed out the globes last year because of a horrific ride with 113k on it. Ride was back to stock, lovely. I never checked the pressures, everything worked fine. All of a sudden over the last few months the ride has been getting progressively worse. No changes at all, so I'm not sure the issue. I just borrowed the tech stream software and a cable (thanks @bozncsurf). I'm going to check my graduations, and the pressures and see whats' up. I will report back. Great info in this thread, thanks everyone.

I would think loosening ball joints ,sway bar links or worn tired would be a more likely suspect with potentially sagging rear springs a secondary issue. I'm curious to see your pressure ratings as well.

 

[maxse01]

Which way do I crank my tb's?

 

[ihadmail]

Clockwise to lower pressure counterclockwise to raise pressure.

 

[Kabanstva]

harsh ride / rough ride on expansin joints

Check out this thread also guys. It seems like it's referring to the same issue.

My LX is also not the smoothest over expansion joints and similar rough sections of road. It's nowhere near as bad as some people describe it here, but I think I will look at my body mounts in the next few days to see what condition they are in.

 

[99RichieLx470]

Before AHC springs and spacers with TB twist (third row removed)
3 lifts

front
8.0 7.1 6.9
rear
6.9 7.8 8.1

After Ahc Springs spacers and twist (third row installed - needed them for beach)

front pressure
7.0 6.6 and 6.5 (respectively)

Rear Pressure
6.7 6.5 and 6.5

would love to see rear pressures @ 6.0 but very satisfied with results as is.

 

[Kabanstva]

Guys, for those who experienced the harsh ride due to the torsion bars being twisted too much, did you mess with them at some point? Why would they be turned too much?

I asked my brother if his master tech at their Lexus dealership can look at my car next time its in for an oil change, and he said he doesn't understand why the torsion bars would need adjustment if they were never messed with or touched? The truck is an 07 with 118k miles. All stock. It's a one owner vehicle that has been solely serviced at their dealership since the day it was bought there. It's seen some alignment work but never any suspension work or anything like that.

Can someone clue me in. Kind of confused because he said they've never messed with the torsion bars on the LX470's in the 5+ years he's worked there.

I explained all the symptoms that everyone described in this thread, how it's butter smooth over bigger stuff and at higher speeds, but at slower speeds (less than 10-15mph) when going over expansion joints, and similar sharp imperfections in the road, it vibrates the whole truck (dashboard and surrounding panels) as if the suspension is rock hard and doesn't absorb anything. The different settings work perfect, comfort setting is very soft and max sport setting is extremely firm (night and day difference). Tire's are brand new Michelin road tires (can't remember the model off the top of my head), on the stock 18's. 31psi front and 33psi rear tire pressure.

 

[99RichieLx470]

ill let Paddo and Co. get real technical but in layman terms one would adjust the torsion bars to augment out of spec hydraulic pressures. Adjusting the Tbars is only one part of several variables one adjusts to get back in spec.

one shouldn't adjust torsion bars "just because" they should look at the neutral pressures from the TECHSTREAM dealership software and see how close to spec the vehicle is.

there are adjustments that can be made that cost far less than throwing a ton of money at OE parts which is what most dealerships would recommend.

I would guess your hydraulic pressure is too high and its dampening ability is now being compromised. On a smooth road its a great ride but when its time to absorb several imperfections in the road it can't dampen properly.

we are all here to get the best we can out of our vehicles, there are some awesome suggestions here. Ive spent 400$ on adjustments, fluid changes, springs and spacers and I have transformed my hydraulic ride for less than the cost of a set of bilstien shocks.

 

[ihadmail]

Guys, for those who experienced the harsh ride due to the torsion bars being twisted too much, did you mess with them at some point? Why would they be turned too much?

I asked my brother if his master tech at their Lexus dealership can look at my car next time its in for an oil change, and he said he doesn't understand why the torsion bars would need adjustment if they were never messed with or touched? The truck is an 07 with 118k miles. All stock. It's a one owner vehicle that has been solely serviced at their dealership since the day it was bought there. It's seen some alignment work but never any suspension work or anything like that.

Can someone clue me in. Kind of confused because he said they've never messed with the torsion bars on the LX470's in the 5+ years he's worked there.

I explained all the symptoms that everyone described in this thread, how it's butter smooth over bigger stuff and at higher speeds, but at slower speeds (less than 10-15mph) when going over expansion joints, and similar sharp imperfections in the road, it vibrates the whole truck (dashboard and surrounding panels) as if the suspension is rock hard and doesn't absorb anything. The different settings work perfect, comfort setting is very soft and max sport setting is extremely firm (night and day difference). Tire's are brand new Michelin road tires (can't remember the model off the top of my head), on the stock 18's. 31psi front and 33psi rear tire pressure.

I believe you're misunderstand the adjustment we are all needing to make to our torsion bars.

Torsion bars are, in essence, springs. They provide their springiness because they are under a load due to being twisted. As any spring is under a load for a length of time, it looses some of its spring rate. It becomes accustomed to the new position and no longer attempts to return to its former position.

With a coil spring this relates to a shorter free height. With a torsion bar this relates to a couple of degrees less twist when unloaded.

This twist is what controls the amount of weight the torsion bars support in an AHC vehicle. In a standard LC without AHC this relates to a loss in height in the front suspension.

We are simply measuring the hydraulic pressure in the front, because we have a standard (set of values it should be at). When this pressure is high it means the hydraulic portion of the AHC system is carrying too much of the weight. This directly relates to a harsh ride, and if far rough out of specification the inability to change heights. So we tighten the adjuster on the torsion bar, which puts more twist on it. This increase in force that's twisting the bar causes it to carry more of the weight. This adjustment is comparable to adding spring spacers to old coil springs to achieve the same height as they were when they were new.


Hope this helps and isn't too confusing, I'm not the best at describing things.

 

[PADDO]

Guys, for those who experienced the harsh ride due to the torsion bars being twisted too much, did you mess with them at some point? Why would they be turned too much?

I asked my brother if his master tech at their Lexus dealership can look at my car next time its in for an oil change, and he said he doesn't understand why the torsion bars would need adjustment if they were never messed with or touched? The truck is an 07 with 118k miles. All stock. It's a one owner vehicle that has been solely serviced at their dealership since the day it was bought there. It's seen some alignment work but never any suspension work or anything like that.

Can someone clue me in. Kind of confused because he said they've never messed with the torsion bars on the LX470's in the 5+ years he's worked there.

I explained all the symptoms that everyone described in this thread, how it's butter smooth over bigger stuff and at higher speeds, but at slower speeds (less than 10-15mph) when going over expansion joints, and similar sharp imperfections in the road, it vibrates the whole truck (dashboard and surrounding panels) as if the suspension is rock hard and doesn't absorb anything. The different settings work perfect, comfort setting is very soft and max sport setting is extremely firm (night and day difference). Tire's are brand new Michelin road tires (can't remember the model off the top of my head), on the stock 18's. 31psi front and 33psi rear tire pressure.

The issue is quite the opposite of the torsion bars being turned too much, but that's been covered by others.
Now, I'd have your brother invite the master tech to read up on Toyota's own published literature on how their AHC/TEMS system works and then invite him to open up his FSMs and read the dozens of DIs on the system including the ones dedicated to adjusting torsion bars for correct neutral pressures. Sad indeed that a "master tech" at a Lexus dealership isn't aware of basic, fully documented, maintenance procedures for a system that has been in service since 1998 across the world. I wonder just how many systems they have neglected and how many dollars they have fleeced from unsuspecting owners over the years? Maybe invite the master tech to join Mud so he can learn something about the system his boss is charging $130? an hour on. I've previously posted relevant FSM docs on how pressures are measured and adjusted, that was in response to a mud member being in a dealership trying to convince unbelieving techs there was such a thing as neutral pressure adjustment procedures. One step at a time I suppose.....

 

[maxse01]

Problems with my laptop, so I didn't get to plug in the techstream yet. I did the graduation test, only 5 marks from low to high....not good. I got all new globes from B&B a year ago, so I can't imagine they're shot already...but the evidence is showing that to be the case.

 

[ihadmail]

@maxse01 its my understanding that the graduation test is only accurate if all other variables are correct: height, pressure and vehicle on level ground unloaded with a full fuel tank

Also I e read a lot of issues with the B&B remanufactured globes.

 

[PADDO]

@ihadmail is correct but don't panic, yet. For the L to H test to be truly accurate the system pressures need to be correct along with known volumes and charges of the front and rear damper spheres. Your spheres aren't OE so the charge and volume may not be identical to OE hence the test may not be valid. This test indicates the fluid displaced from the OE damper accumulators when they are subject to lower pressure (vehicle at L height) and higher pressure (H height). The OE accumulator gas charges "push back" against the two system pressures (both being higher than the gas charges) and the degree of push back determines how much fluid is displaced (at L) and subsequently forced into the spheres (at H) along with the fluid displaced due to the shock actuators stroke. The question is how many grads did you have when the new non OE spheres were installed and at what system neutral pressures? I have 20+ grads with 4 x rear accumulators fitted as an example of how changing system components changes test results.
Hopefully the seller of your globes can help with volume/pressure data and how/if it changes the OE test parmeters.

 

[maxse01]

@ihadmail is correct but don't panic, yet. For the L to H test to be truly accurate the system pressures need to be correct along with known volumes and charges of the front and rear damper spheres. Your spheres aren't OE so the charge and volume may not be identical to OE hence the test may not be valid. This test indicates the fluid displaced from the OE damper accumulators when they are subject to lower pressure (vehicle at L height) and higher pressure (H height). The OE accumulator gas charges "push back" against the two system pressures (both being higher than the gas charges) and the degree of push back determines how much fluid is displaced (at L) and subsequently forced into the spheres (at H) along with the fluid displaced due to the shock actuators stroke. The question is how many grads did you have when the new non OE spheres were installed and at what system neutral pressures? I have 20+ grads with 4 x rear accumulators fitted as an example of how changing system components changes test results.
Hopefully the seller of your globes can help with volume/pressure data and how/if it changes the OE test parmeters.

I had 7 on the OEM ones before I changed them, but the ride was atrocious, much worse than it is now. When I swapped in the new ones I didn't do anything other than install, bleed and add new fluid. Ride was perfect, no other adjustments were made. I never checked the graduation differences with the new ones since it was working correctly. It's been fine up until about a month ago when it started getting bad. This vehicle is my wife's, extremely light duty. 99.9% of the time it's just her and the 2 kids in it. No towing, no offroading, all pavement.

 

[Kabanstva]

The issue is quite the opposite of the torsion bars being turned too much, but that's been covered by others.
Now, I'd have your brother invite the master tech to read up on Toyota's own published literature on how their AHC/TEMS system works and then invite him to open up his FSMs and read the dozens of DIs on the system including the ones dedicated to adjusting torsion bars for correct neutral pressures. Sad indeed that a "master tech" at a Lexus dealership isn't aware of basic, fully documented, maintenance procedures for a system that has been in service since 1998 across the world. I wonder just how many systems they have neglected and how many dollars they have fleeced from unsuspecting owners over the years? Maybe invite the master tech to join Mud so he can learn something about the system his boss is charging $130? an hour on. I've previously posted relevant FSM docs on how pressures are measured and adjusted, that was in response to a mud member being in a dealership trying to convince unbelieving techs there was such a thing as neutral pressure adjustment procedures. One step at a time I suppose.....

In what part of my post did I state that their master tech didn't know anything about these vehicles? I meant to say my brother didn't understand the issue I was telling him about.

The fact is, they probably get one LX for every hundred ES and RX models so maybe my brother just doesn't remember doing this to them. He said he will talk to him for me. I will definitely direct him to this thread. Thanks guys for the info.

 

[PADDO]

....master tech followed by "he said", twice, implied to me you were referencing comments back to the technician. Notwithstanding, I hope you can resolve your problem.

 

[Julian Stead]

The reason the master tech doesn't know anything about the AHC System is that he has only worked there for 5+ years. I trained as a Master Tech and the car manufacturers only train you on current or future technology, it is the reason why I wouldn't take an old car to a dealership as the technicians will not be trained on any obsolete systems. It's all about keeping new car buyers happy and not keeping older ones running forever as it costs money to train people up. Unless you have a technician that has an interest in 100's or has worked there for along time then you are better off using this site for getting info. Good info = Good diagnosis = Good repair. The training coarses for AHC probably ended 10 years ago.

I had never seen a torsion bar fitted to the front suspension let alone know how to adjust them, but with the info from this site(@PADDO's posts) I managed to setup and improve the ride of my 18yr old truck at minimal costs.

 

[wkbogie]

Hey Guys, thought I would give you and update.

I drove it around for a few minutes and I do not think it is much better, but I will find out tomorrow when I have some more seat time.
Just for more data, I plugged my $25 Amazon Techstream into my 13 year old XP laptop to get some pressures.

AHC Pressure from the FSM-
Spec calls for
Front 6.9+/-0.5 MPa (6.4-7.4)
Rear 5.6-6.7 MPa

1. Before:
Front 8.1mpa-g
Rear 6.8mpa-g
Accumulator 10.2mpa-g

2. TB bolt turn Only (6 complete turns)- This did help some, but not enough
Front 6.7 mpa-g (pressure lowered 1.4) = 0.23mpa-g/1 full turn of TB bolt
Rear 7.1 mpa-g (pressure raised 0.3)
Accumulator 10.2 mpa-g

3. Rear Spacers AND previous TB twist
Front 6.9mpa
Rear 6.3mpa (30mm spacers = only 0.5mpa drop)
Accumulator 9.7mpa

So it rode much better at #3, so I thought maybe I could turn the TB 2 more times and see how that rode.
4. Rear Spacers AND previous TB twist plus 2 more TB turns
Front 6.2mpa
Rear 6.3mpa
Accumulator 10.4mpa
-This was worse, felt like a TB leveling lift on regular suspension truck like old Tahoes.

5. So I backed out the TB bolt 2 turns and drove it today. (5 turns in now)
Front 6.8mpa
Rear 5.9mpa
Accumulator 9.7
-The values are not exactly correlating to the turns of the TB bolt, they do not always go back to the same pressures when the bolt is at the same depth on the TB's. Also it seems the decrease in pressure is exponential to the turns. Meaning the more I turn them in, the higher the rate at which the pressure decreases. Showing that there is only so much that can be done by turning in the bolts, eventually the TB's will need to be replaced. This also means 1/2 turns are effective increments in adjusting the pressures as well.
However, this is an acceptable ride, but I feel it can be better. I will continue to play with the TB's (possibly back it out one more turn) and drive it around. I will prob flush the fluid one more time as well.

 

[ihadmail]

Hey Guys, thought I would give you and update.


So it rode much better at #3, so I thought maybe I could turn the TB 2 more times and see how that rode.
4. Rear Spacers AND previous TB twist plus 2 more TB turns
Front 6.2mpa
Rear 6.3mpa
Accumulator 10.4mpa
-This was worse, felt like a TB leveling lift on regular suspension truck like old Tahoes.

5. So I backed out the TB bolt 2 turns and drove it today. (5 turns in now)
Front 6.8mpa
Rear 5.9mpa
Accumulator 9.7
-The values are not exactly correlating to the turns of the TB bolt, they do not always go back to the same pressures when the bolt is at the same depth on the TB's. Also it seems the decrease in pressure is exponential to the turns. Meaning the more I turn them in, the higher the rate at which the pressure decreases. Showing that there is only so much that can be done by turning in the bolts, eventually the TB's will need to be replaced. This also means 1/2 turns are effective increments in adjusting the pressures as well.
However, this is an acceptable ride, but I feel it can be better. I will continue to play with the TB's (possibly back it out one more turn) and drive it around. I will prob flush the fluid one more time as well.

I get my pressures close in 1 turn increments. Then I go for a drive. Then I tweak them in 1/2 turn increments. Going for a drive between each adjustment.

As @PADDO has mentioned, the FSM values are valid for a completely new system. Aged accumulators, torsion bars, rear springs, hydraulic shocks, accumulator and pump will cause a slight shift in the optimal pressures.

To truly dial the system in it takes some patience and a bit of trial and error on each individual vehicle.

Good luck on your search for hat plush comfy ride.

 

[DirtDawg]

Well finally got all my parts in for my AHC lift. I will be installing this Friday and will post my results on here (I'll also be starting a build thread). Here's what I'll be installing: King AHC Springs, Japanese Shock Spacers, possibly rear spring spacer if needed, and new sway bar bushings. Goal is to sit at a lifted height (2-2.5"), with stock shock range and stock pressures.