Definitive list of AHC maintenance items (9 Viewers)

[Drogon]

So I was checking my ach fluid tonight and it is right below the max line. On Monday it was right above the max line. At what point should I worry about the difference in the measurements?

 

[trizzo]

Bled the AHC system tonight and dove into the Techstream data for a before/after look. Ride quality improved roughly 30% based on an uncalibrated butt-in-seat test before and after the bleed.

Measurements taken with half tank of gas, 3rd row installed, no spare tire.

Hub to fender measurements :
Front Left - 19.5
Front Right - 19.5
Rear Left - 20.5
Rear Right - 21

Front Pressure 7.8Mpa-g (before AHC bleed - 7.9)
Rear Pressure 6.6Mpa-g (before AHC bleed - 6.8)
Accumulator 10.6Mpa-g (before AHC bleed 10.6)

FR Height Control Sensor -0.2inch (before AHC bleed -0.1)
FL Height Control Sensor -0.2inch (before AHC bleed -0.2)
RR Height Control Sensor -0.1inch (before AHC bleed -0.1)

FR Height Adjust -0.1inch
FL Height Adjust -0.1inch
RR Height Adjust -0.0inch

FR After Height Adjust -0.0inch
FL After Height Adjust -0.1inch
RR After Height Adjust -0.0inch

If my target for the front is 6.8-6.9Mpa-g = 5 clockwise turns on both sides (7.8-6.8 = 1 = 5 * 0.2Mpa-g) - Is this correct @PADDO ?

Any other items of concern with the above height control sensor data? Im a bit concerned about the .5 inch cross level delta in the rear which can't be solved without a packer or new springs.

 

[PADDO]

Front pressure will lower 0.2MPa per CW turn on both adjuster bolts. I recommend experimenting to find the optimum pressure for your vehicle and 6.8-6.9MPa is a good place to start. 6.9 (+- 0.5) front is factory new - new fully charged globes, new P tires, new bushings and cushions, new fluid, new height feedback sensors assemblies.

 

[trizzo]

Front pressure will lower 0.2MPa per CW turn on both adjuster bolts. I recommend experimenting to find the optimum pressure for your vehicle and 6.8-6.9MPa is a good place to start. 6.9 (+- 0.5) front is factory new - new fully charged globes, new P tires, new bushings and cushions, new fluid, new height feedback sensors assemblies.

These clockwise turns will also raise the front and reduce the rake? Or just transfer weight from hydraulic suspension to the torsion bar itself?

 

[PADDO]

Height sensor feedback sets height, torsion bars set side-to-side level and front neutral pressure. In this case CW turns shifts the balance point from the hydraulics to the mechanical springs (torsion bars). You're looking for the optimum point of spring torsion v hydraulic damping as determined primarily by the charges in your 4 damper globes and pressures front and back.

 

[ChuckB]

For my 1000th post I thought it fitting to post my successful tech stream data! Thanks to this thread and all who provided input and the referenced tundra forum I was able to install the program and see my current status.

I'm still in the process of analyzing the data. I know for one I need to add some fluid as I'm slightly below the min line. Thank to @beno for shipping me the fluid all the way to Spain.

It looks like I'm going to need a few turns on the torsion bars at a minimum. I'm hoping that will get me back into spec. I'm planning on running the check again on a flatter surface to double check the numbers and take the fender to wheel center measurements before I touch anything.

Am I missing anything?

 

[ChuckB]

Looks pretty ok Chuck.
Those height feedback numbers are fine to start with particularly if the ground wasn't level.
To start with you want to check and adjust the front for cross level, it's pretty easy to get the front cross level within 5mm or so. Start your truck up and let the ahc settle then take some measurements. Front should be 500mm/19.75 and rear 520/20.5in. Initially just get the cross level sorted out then do the front/rear heights later. If you tighten (CW turn) on a lower side tb bolt 1 turn you'll raise that side by about 2mm, and if you have a larger lean, say 10mm +, then you want to adjust that out on both sides. By this I mean you'd tighten the low side 2 turns and lower the higher side 2 turns. It might take an iteration or two but you'll get there. Don't chase the numbers from Techstream as that can be inaccurate and confusing, just use a good old tape measure. I pop the center caps off and put a marker pen dot in the middle of the grease cap on both sides just for consistency. Once satisfied with your cross level then you can set front and rear heights as necessary. Never fiddle with the sensors with the engine running as you risk injuring yourself. If you need to raise the front height a little then you adjust up the sensor link of the sensor reporting the lowest number and if you need to lower the front you slide down the link on the higher reporting sensor. Just a small adjustment at a sensor is usually enough. On level ground you want the sensors reporting +\- 0.3 in or less difference. For the rear it's just slide the adjuster up or down a bit to raise or lower.
With your heights where you want them you then adjust your torsion bars equally (so as to not throw off the side level). If you don't need to adjust your heights and the front remains at your 7.9 then put on 5 full CW turns both bolts and recheck after a day or two. One turn on each side will lower the pressure about 0.2MPa. You'll find that by lowering the front about 1MPa your rear will come down a little bit too, but not enough so in all likelihood you'll need spacers or new coils. Target 6.9 front and then experiment by lowering or raising 0.1 or so might reveal a better ride. I usually have my front at 6.7-6.8. For the rear getting it down around 6.0 is pretty good.
If you haven't changed the fluid in a while then running a fresh can through is always good. Start at the height accumulator then work around the four damper globes.
The other numbers on your screen shot are all normal.
Good luck, it's all pretty easy, just take your time. Let me know if I can help anymore.

Thank you!! Getting the tape measure and the 30mm socket out ASAP.

 

[ihadmail]

@PADDO @uHu I have slider steps installed and my ~110lb spare in the trunk. My rear AHC pressures were 8.9 at the ride height it was at when I bought it.

I installed LX450 rear springs and adjusted the sensor so my rear fender to center hub is 21.5". The springs were swapped in prep for the full sensor lift and the addition of a steel rear bumper and swing out. My front was adjusted to 20.5" and torsion bars adjusted to 6.7mPa read from techstream.

The rear pressure came down to 6.4, but resulted in an extremely bouncy ride. I would have expected the bouncy ride if my pressures were lower than they are. Is it common to still be overcompensating with the springs with my rear pressure still so high? Could I have kinked a rear line when installing my step sliders enough to give a falsely high reading?

I understand when I add the extra weight my springy ride will go away, but my pressures will also go up again. I'm really confused by the bouncy ride at the same time as (relatively) high pressure readings.

 

[PADDO]

At 6.7/6.4 you should be good to go, something isn't right. I guess it's possible a line was pinched or possibly one of the damper assembly cables has been crushed/cut - they loop over the rail top and it wouldn't be hard to damage them. I'd grab a good flashlight and run the lines and cables to check for damage. How many graduations do you get on the L to H test? Could be one or more of the globes are past their serviceable life or just done. You can hook up Techstream and go for a drive and monitor what the ecu is telling the dampers to do, they are the front and rear STEP fields, 8 is mid damping and they range from 1 to 15. You can also lock the damping into its softest setting (1) and go for a drive, this can tell you if it's responding to the ecu or if it's more than likely a hydraulic/mechanical issue. I'll have a think...

 

[ihadmail]

Thank you so much for that extra info. I will have a look over it all soon and report back.

I can't check graduations without removing some fluid, it was overfilled when I had new globes put in about 7k miles ago. Fluid change is approximately 1.75" from high to low.

 

[PADDO]

I'd bleed off some of the excess fluid from all 5 points - could have air/gas in the system causing shenanigans.
Edit.
I suspect it's going to take some trial and error to find that critical point where your damping system is best matched to the new coils. And when you do find that point it's going to change with the addition of any significant sprung weight and height. I'd look at eliminating all simple, yet potentially confounding variables like air in the system and then experiment with different damper settings and neutral pressures if your globes are new and returning the 14 grads during the L to H test. I guess I'm surprised that 6.7/6.4 didn't return reasonable performance results, but those pressures are functions of a system operating within design parameters with design hardware. I'm not sure how far the 450 coils are from OE AHC; are they linear or progressives? Rate, load range, free length etc. In general for a bouncy ride you'd look to stiffen the damping, how's it perform on sport 2? It will be more harsh but could reduce the oscillations.

 

[ihadmail]

I double and triple checked that the sliders hadn't affected any of the wiring. My slight tweak that was needed to the pressure lines created no kinks that I could see or feel.

When driving in comfort the front and rear steps cycle from 1-5 as I drive. When in sport they cycle from 8-12. When stopped in any mode they go to and stay at 8.

I did a full fluid flush with no change. The old fluid looked like grape Gatorade.

I have 12 graduation change from H to L.

When going from L to N the rear no longer cycles back and forth with the front like it used to. The rear instantly "jumps" to the N height and then the front cycles a few times. When going from N to H the front and rear both cycle a few times as it did before.

There are no DTC in the AHC ECU.

Here is a screenshot of techstream after the fluid change, after going L to H. My front pressures are elevated due to the street in front of my house is a slight incline. It's the levelest place without driving a good bit.

I am completely perplexed as to why it's so bouncy with the pressures in spec and new fresh fluid. The system cycles properly through all modes. I feel and see on techstream a change when changing from comfort to sport.

I am seeing three options here:
1) live with it until I get my rear bumper and see how the added weight changes it
2) perform the sensor lift now and drive it a few weeks like that before I have time to install my shock spacers
3) install my new OEM LX470 rear springs and trim packers/slee Spring spacers as needed to get pressures right. I have the springs, 30mm spacers, 10mm Packers and 5mm Packers on hand.

Thoughts? Advice? Opinions?

Thanks again for taking the time to help me look at this and get it documented for anyone else that chooses to go down the 80 series spring route.

 

[ihadmail]

The 450 springs are approximately 5/8" diameter where the 470 springs are approximately 1/2" diameter.

The 450 springs are approximately 1.5" taller than the 470 springs.

It seems the 450 spring rate is 170 lbf/in and they are linear by the looks of them. The coil wrap spacing is the same throughout the length of the spring.

 

[uHu]

...Here is a screenshot of techstream after the fluid change, after going L to H. ...

Is that screenshot after going up to Hi? Or to N?
And what is the physical height difference between Lo and N at the rear wheels, left and right?

 

[DirtDawg]

@ihadmail at this point I'd be blaming the 450 springs. I'd try swapping back in OEM coils with spacers and see if the ride changes.

 

[ihadmail]

Is that screenshot after going up to Hi? Or to N?
And what is the physical height difference between Lo and N at the rear wheels, left and right?

That is going L to N. Height difference is 1.5" driver 2" passenger.

@ihadmail at this point I'd be blaming the 450 springs. I'd try swapping back in OEM coils with spacers and see if the ride changes.

I 100% blame the springs also. I'm more on the task of figuring out why ride is so horrible with pressures in spec

Ultimately I will most likely put the new OEM springs and 30mm spacers in until I get the bumper and do the lift. Then I'll be right back in the swapping things around to hope I find a winning combination mode

 

[DirtDawg]

I 100% blame the springs also. I'm more on the task of figuring out why ride is so horrible with pressures in spec

I think it has to do with the higher spring rate and strength of the 450 coils. So even though your pressures are spec when your static (not moving), I believe the pressure curve is different as you are driving. The 450 coils are overpowering the system with no added weight. IMO I'm currently building up my AHC for a lift/load setup and when adding weight I am considering the king AHC springs, because ultimately the 450 coils were not designed for our system.

 

[PADDO]

^Agree. The additional 1/8 inch in wire diameter and 1.5in length of the 450 coils over the OEs isn't trivial and I summize they are providing too much support at your current weight/height whilst in motion. It was telling when you mentioned the rear sprang up on a raise cycle much quicker than the front, as you know the front and rear raise together until the height accumulator is exhausted then they do their final shuffle to the set level N point. I'm trying to think of a plausible reason the system's pressure sensor would report incorrectly and give you a false OK reading of 6.4 - maybe when the rear springs up the ecu data input reading gets thrown out of sync? More than once I've had spurious readings raising from L to N of something dumb like 2.7MPa front. Repeat once or twice and I'd get normal expected values. I submit the pressure reading process via Techstream may not be perfect 100% of the time. It would be interesting to hook up a pressure gauge to the rear and confirm the actual pressure is the 6.4-1.2 the book says to expect. I suspect in your current configuration there is barely enough weight to overcome the 450 springs force to drop to L. It would also seem that you've demonstrated that static neutral pressures "in spec" don't necessarily correlate to good dynamic damping performance if you modify one of the key system elements like the coils. Those damper step cycles as a function of comfort switch setting match what I get too.
@ihadmail thanks for taking the time to work and document this - it all adds to the AHC book of knowledge.

 

[PabloCruise]

I think it has to do with the higher spring rate and strength of the 450 coils. So even though your pressures are spec when your static (not moving), I believe the pressure curve is different as you are driving. The 450 coils are overpowering the system with no added weight. IMO I'm currently building up my AHC for a lift/load setup and when adding weight I am considering the king AHC springs, because ultimately the 450 coils were not designed for our system.

Can you tell me more about the King AHC coils?

 

[ihadmail]

@PADDO I have spent countless hours reading every thread I could come across regarding AHC and modifying the full time weight and height.

I came across a few post where @sleeoffroad had mentioned using 80 series could in the rear of an LX so for the low cost I had to give it a shot. Now I know that at close to stock weight and close to stock height they are WAY too stiff.

Since I already have them in, and the sensor lift is so easy to perform/reverse I am going to perform it and report back on my findings. If the lift isn't enough to make me happy I'll simply swap the new OEM springs and if needed spacers in.

It'll take me a few days to get the time to do any messing around but I'll report back my findings. Maybe I should start a thread dedicated to documenting all of my experiments?