AHC 81k miles - squatting (1 Viewer)

[Piney1]

Question on the AHC: My 2005 LX just turned 81k miles, it had 71k on it in November of 24 when I became the second owner. It is stock other than the LC200 wheels and better rubber. The AHC has been working as designed until two weeks ago. Lowered it to let my mother-in-law get in (she is feeble and 86). When I drove after that, it was bouncy. Once I stopped and restarted, it seemed to get better. I’ve loved smooth ride on this thing. Then, I noticed that the rear was squatting about an inch lower than normal.

Techstream showed no codes or errors. The screenshot below on the right is after I raised it so it is communicating just fine. Changing from firm to sport makes it get rough and that is not normal. Pic on left is before the squat, on right is now.

Is it worth fixing this? I’d love to get it done and keep it stock.
Is there an aftermarket solution that retains the ability to control ride and height from inside the vehicle?
I’m not far from Johnson City, TN - would love to know if anyone knows a good tech for this. The local dealer is OK but I’d prefer a specialist that ain’t a dealer.

 

[excessive]

its probably the age, not the miles

 

[jaewastooshort]

just from memory (can't remember operating specs), the front and rear pressures look really high. torsion bars are an easy adjustment, but you may need new springs in the rear to get in spec if it's way out. do your height sensors all look ok?

 

[Piney1]

just from memory (can't remember operating specs), the front and rear pressures look really high. torsion bars are an easy adjustment, but you may need new springs in the rear to get in spec if it's way out. do your height sensors all look ok?

Visually, yes - they look good to my untrained eye.

Should have added, fluid level is good in the reservoir.

When I put it in high, it seems to take longer than normal for the light to stop flashing but it does raise fully. No signs of any leakage.

 

[jaewastooshort]

If you haven't yet, go through this comprehensive guide: The ABCs of AHC - How to Measure, Flush, and Adjust all in one place - https://forum.ih8mud.com/threads/the-abcs-of-ahc-how-to-measure-flush-and-adjust-all-in-one-place.1211999/

I looked up the specs there, and yeah, your front and rear pressures are both high.

Measure your front/rear pressures, accumulator pressure, and sensor heights using Techstreamand a Mini-VCI cable, a manual inline gauge, or an advanced OBDII reader (iCarsoft, TYT II, OBDLink, VGate, etc.)

• Front spec: 6.9MPa +/- 0.5
• Rear spec: 5.6-6.7MPa
• Accumulator spec: 10-10.6MPa

 

[dchilds]

Have you looked at the height sensors themselves?

 

[Jack90210]

The AHC system is having to compensate for the loss of spring capacity that happens over time, and the harshness that you feel in "Sport" is likely related (though there may be other causes, like fatigued globes, as well).

It's likely that you can mitigate these symptoms with a few turns of the torsion bar adjuster and by removing the 3rd-row seats in the rear (if they are still there, looks like it in the first pic).

 

[Piney1]

The AHC system is having to compensate for the loss of spring capacity that happens over time, and the harshness that you feel in "Sport" is likely related (though there may be other causes, like fatigued globes, as well).

It's likely that you can mitigate these symptoms with a few turns of the torsion bar adjuster and by removing the 3rd-row seats in the rear (if they are still there, looks like it in the first pic).

I have the third row seats in the garage now. We take the GX if there is a need to haul more than 5.

I’ll try that adjustment of the torsion bar. I’ll search the threads for how to do this if it ain’t readily apparent.

Thanks.

 

[jaewastooshort]

I have the third row seats in the garage now. We take the GX if there is a need to haul more than 5.

I’ll try that adjustment of the torsion bar. I’ll search the threads for how to do this if it ain’t readily apparent.

Thanks.

It's pretty simple. Follow the torsion bar from the front control arm to the rear bracket, and in the bracket there is a large bolt that runs through, "B" in this pic:

(source: For those with torsion bar questions - https://forum.ih8mud.com/threads/for-those-with-torsion-bar-questions.491948/ )

The thread has a good guide to adjustment. Between this thread on adjusting the torsion bar, and the previous one I linked on AHC setup, you should easily be able to get the front pressure back in-spec, and I'd be willing to bet that it will solve your harsh ride issue and allow the system to put more effort into keeping the rear height set appropriately. If you don't want to bother with replacing the rear springs, a 30mm spacer might be enough to get you back to the correct height and bring your rear pressure back to where it should be.

 

[Piney1]

It's pretty simple. Follow the torsion bar from the front control arm to the rear bracket, and in the bracket there is a large bolt that runs through, "B" in this pic:
View attachment 3953976
(source: For those with torsion bar questions - https://forum.ih8mud.com/threads/for-those-with-torsion-bar-questions.491948/ )

The thread has a good guide to adjustment. Between this thread on adjusting the torsion bar, and the previous one I linked on AHC setup, you should easily be able to get the front pressure back in-spec, and I'd be willing to bet that it will solve your harsh ride issue and allow the system to put more effort into keeping the rear height set appropriately. If you don't want to bother with replacing the rear springs, a 30mm spacer might be enough to get you back to the correct height and bring your rear pressure back to where it should be.

Thanks for the links and information. I’ll have to get this done this weekend. I use an iPad almost exclusively and the font is yellow on the headings of those pages - nearly invisible to my 57 year old eyes.

To summarize though - do it a level surface, do not jack it up, keep suspension in middle setting and then adjust each of the torsion bars the same amount? The droopy drawers look is killing me.

 

[jaewastooshort]

Generally, if you're just doing a tune-up, yes.

In a properly functioning system, the height is measured by the height sensors at each wheel, and the AHC system adjusts pressure in the hydraulic struts in order to keep the ride height set.

Since your pressures are way higher than the specified range for normal height/operation, that indicates that your springs are not doing enough work and the AHC system is increasing pressure to compensate.

Adding additional preload to the torsion bars will force them to take more of the weight, which will bring the front pressures down. If you have any difference in height measurement from side to side on the front, you would adjust the torsion bar preload on the lower side to bring it back to level left-to-right, then adjust both torsion bars equally to decrease the pressure.

Once you have your front pressure in-spec (needs to come down about 3.5 MPa based on the screenshot you posted), the system may have enough capacity to compensate in the rear. However, it also seems possible that your rear height sensor needs to be adjusted or repaired, since it's sagging so much in the rear. If we assume that the sensor is ok and it's just a pressure issue, you may need to replace your rear springs (or add a 30mm spacer) to reduce the load the hydraulic system is being forced to carry. If the height sensor is off in the back for some reason, you could put a much stronger spring in the back and the system would just reduce pressure in the rear shocks to try and keep the height at what it sees as "normal", which could keep it where it is currently.

A lot of small things to check.