Bouncy AHC. Can I check health of system before trying replacing globes? (1 Viewer)

[IndroCruise]

I followed this video:


Here are the numbers:


Neutral height - Fender to center of wheel
FL: 19.5
FR: 19
RR: 19.9
RL: 20.2


Pressure test in Neutral
Attempt 1
Front: 8.6
Rear: 7.7

Attempt 2
Front: 8.8
Rear: 7.4

Attempt 3:
Front: 8.4
Rear: 7.7

Height control sensors at N: 0.0 (for all)

Gradation check between H and L: 8 (I didn't add the fluid back)


I didn't adjust the torsion bars but the high front pressure indicates I need to do that. The heights in the front are pretty even though. What should it ideally be, after adjusting the torsion bars?

The rear pressure is also high, and the gradation check seems things are within spec. So that leads me to believe the globes are fine but I need new springs in the back? That's what creating the crazy bounce? One more thing, both the swaybar end links in the rear are broken Dunno if that's contributing to the bounce.

Your post #17 and later posts shows that you are on top of things -- great work!!

Suggest cross-level a little more to equalise Left front and Right front using torsion bar adjusters, then make large adjustments clockwise (looking up from below) to both torsion bars to bring front pressures back into FSM range. They are way high -- expect a lot of turns on both sides at about 0.2Mpa per turn.

Rear AHC pressures also are way high -- probably will need replacement springs -- it is unlikely that pre-loading with spacers will cut it.

Torsion bar adjusters do not change heights on an AHC-equipped vehicles but only affect pressures - only the Height Control Sensor adjusters cause heights to vary -- because the self-levelling design of AHC system means that the ECU will cause the system to seek the position at which Height Sensor readings are near zero (inches or millimetres) at "N" height setting (provided the Sensors are healthy). [Actually, the signal from the Sensors to the ECU at "N" height should be about 2.25 volts but you don't need to worry about these details unless chasing down Sensor problems].

With AHC pressures corrected, an improvement in the HI/LO test could be expected -- there may be some life left in the existing 'globes'!!

The high AHC pressures Front and Rear mean that damping is heavily compromised -- damping usually is best with Front and Rear AHC pressures below mid-point of the prescribed range -- and the ride will be rough and abrupt until these are corrected and decent damping is achieved.

DEFINITELY sort the broken sway bar links and other bushes -- this situation cannot be helping. Also have a close look at the bushes in Rear upper and lower control arms and Rear shock absorbers. While thinking about bushes, also scrutinise all Front bushes -- control arms, sway bar, shock absorbers, everything.

There are few challenges as mentioned above but nothing out of the ordinary for a 17 year old vehicle -- seems like you have a great truck in the making!

 

[chilllx470]

Thanks for the info, really helps.
I think the next step is to flush the fluid and adjust the torsion bars, and find some good springs. I'll have to test the globes again.

 

[chilllx470]

I flushed the fluid today. It only slightly improved the bounce. I got some good OEM replacement springs too which I’ll add next week. Next would be replacing the rear globe assemblies. One of them is very rusty as PO missed it when spraying rust preventative.

This is what came out of the system:

 

[FJC]

Give the flush a little time. The fluid in my 06 had never been changed until i did it this year. The ride I thought was good when i bought it. After flush, the ride was basically the same. After an additional 2 to 3 weeks, the ride that i thought was good, turned into a great ride, much more damping over rough roads. Noticed more adjustments to height in varying circumstances. Noticeable difference when using the settings. I still need to get around to tech stream and check the condition, but after the flush, it dId take some time for the system to readjust and start working better with the new fluid.

 

[IndroCruise]

I flushed the fluid today. It only slightly improved the bounce. I got some good OEM replacement springs too which I’ll add next week. Next would be replacing the rear globe assemblies. One of them is very rusty as PO missed it when spraying rust preventative.

This is what came out of the system:
View attachment 2682272

Seems like good progress with AHC Fluid change! Many people see some improvement in pressures, damping and ride quality after a fluid change, especially if the removed fluid is very old. This is unsurprising. It is the result of getting rid of as much detritus, sludge and dissolved air from the system as possible.

When the vehicle is in motion, ‘damping’ is all about how the Damping Force Control Actuators give the damping effect by controlling the rate of flow of fluid in and out as the attached Gas Chambers a.k.a. ‘globes’ respond to road conditions. The passageways, valves and miniature 'step motors' in the Actuators are tiny – see pics below -- but are meant to control damping in 16 steps under the control of the driver's console switch and the ECU, which uses inputs from the Height Control Sensors, Wheel Speed Sensor, Steering Angle Sensor, Pressure Sensor, ABS system, among others. Inevitably, dirty fluid will flow less well than clean fluid through these fine pathways and valves, and so damping will be poorer with dirty fluid. The AHC system might still function to some extent with old fluid but will perform much better and live longer with good maintenance, including regular AHC Fluid changes.

Going forward, also suggest keep in mind adjusting the Torsion Bar adjusters as well as doing the Rear Springs for better damping and longer life of components – including ‘globes’ and ‘shock absorbers’.

The median suggested by the numbers in your Post #17 above for your AHC Neutral Pressures (at “N” height) probably is around the following

Actual Front: 8.6 Mpa compared to FSM specification** of 6.4 Mpa to 7.4 Mpa

Actual Rear: 7.6 MPa compared to FSM specification** of 5.6 Mpa to 6.7 Mpa (without sub-tank)

** At FSM-specified standard conditions – no load, no driver, no pax, correct height, fuel full, on level ground, steering straight ahead.

At these pressures, it won’t need much weight in the vehicle – passengers or other load – to cause the vehicle to refuse to raise to “HI” and occasionally to drop from “N” to “LO” where the AHC pressures are lowest.

With these Front and Rear over-pressures, it is unsurprising that the vehicle feels ‘bouncy’ at the rear. Damping will be poor all round. The Rear is lighter and will ‘bounce’ more. Adjusting the Front pressures will help the Rear ‘bounce’ but it will not be solved until both the Front and Rear pressures are fixed. The broken rear sway bar links will be worsening the ‘bouncy’ effects.

For best damping and ride comfort, it is best to aim for both pressures slightly below the mid-point of the specified range, if possible -- but any improvement is good.

‘Overall ‘globe’ condition: 8+ graduations compared to FSM specification** of better than 7 graduations

(Heights only slightly low, correction would result in slightly higher pressures, and slightly less graduations; corrected pressures will result in slightly better graduations. As discussed previously, AHC pressures via Techstream indicate nothing about ‘globe’ condition.)

More details at https://lc100e.github.io/manual/, follow index tabs to
Repair Manual > SUSPENSION & AXLE > ACTIVE HEIGHT CONTROL SYSTEM (Independent Front Suspension) > ON-VEHICLE INSPECTION

Note that in addition to adverse effects on damping and ride quality, high AHC pressures such as the above pressures stresses the whole AHC system, eventually leads to various problems – such as leakage at ‘shock absorber’ seals and eventual need to replace ‘shock absorbers’. Happened to me – added ARB Deluxe Bar at Front (say +75 kg = 165 pounds net of removed parts), slow to learn about AHC workings and limitations, finally discovered IH8MUD, eventually measured pressures but too late, result was badly leaking front ‘shock absorbers’ requiring replacement a year later.

Best wishes for ongoing success with this vehicle – it is all do-able!!

 

[IndroCruise]

Give the flush a little time. The fluid in my 06 had never been changed until i did it this year. The ride I thought was good when i bought it. After flush, the ride was basically the same. After an additional 2 to 3 weeks, the ride that i thought was good, turned into a great ride, much more damping over rough roads. Noticed more adjustments to height in varying circumstances. Noticeable difference when using the settings. I still need to get around to tech stream and check the condition, but after the flush, it dId take some time for the system to readjust and start working better with the new fluid.

Good advice. Makes sense. No mystery.

After some time working in the system, new fluid will have diluted the remaining ‘gunk’ and helped clear the fine passageways and valves everywhere, including the tiny ‘step motors’ in the Damping Force Control Actuators which are responsible for the adaptive damping by the TEMS part of the system – see diagrams at Post #25 in this thread. This will result in better damping and better ride quality.

However, be wary of possible legacies of old AHC Fluid – see pics at Post #67 through to Post #70 at
AHC pump out? - https://forum.ih8mud.com/threads/ahc-pump-out.1226629/page-4#post-13401098

With enough bad luck, the tiny strainers inside the actual AHC Pump itself (not the strainer at the top pf the AHC Tank), and in the internal Return Valve immediately after the Pump, can and do block, causing build-up of ‘gunk’ inside the Pump and probably backing up elsewhere in the system.

Slowly deteriorating ‘raise’ times, “LO” to “N” and “N” to “HI” (both about 15 seconds when new with no added weight) and/or DTC’s C1718, C1751, C1762 and/or symptoms of associated ‘fail safe modes’ also can be a reason for suspicion about this. A replacement AHC Pump by itself (not including motor, sensors, tank, etc) is not too expensive – but careful disassembly of the Pump for inspection is cheap and easy (see post #69 in the above-referenced thread) and maybe cleaning is all that is required. The strainers can be removed with a pick – carefully – and backwashed. Source of replacement strainers is unknown.

 

[chilllx470]

The ride kept getting slightly better after the flush, but the bounce in the rear remained.

In the last few days I replaced the rear springs with better used ones to relieve pressure on the shocks. I also replaced the rear globes from a newer car and that fixed the bounce!
The car drives a lot better now. I have yet to adjust the torsion bars and I believe it will get even better after the adjustment.

One of the globes was really rusted on and I couldn't take it off. I took it to two shops and they didn't want to touch it because of the rust. SoCal mechanics are spoiled...
Anyways, I got myself a propane blowtorch and PB Blaster and was able to take off and replace the globes in less than 60 minutes. Pencil test was at about 6 inches for both the globes, so they were both shot.

This might be helpful: I was able to rent (you pay $0 if returned within 48 hours) a clutch wrench kit from my local Oreilly's for the 36mm wrench. Worked really well.

New vs old:

 

[IndroCruise]

The ride kept getting slightly better after the flush, but the bounce in the rear remained.

In the last few days I replaced the rear springs with better used ones to relieve pressure on the shocks. I also replaced the rear globes from a newer car and that fixed the bounce!
The car drives a lot better now. I have yet to adjust the torsion bars and I believe it will get even better after the adjustment.

One of the globes was really rusted on and I couldn't take it off. I took it to two shops and they didn't want to touch it because of the rust. SoCal mechanics are spoiled...
Anyways, I got myself a propane blowtorch and PB Blaster and was able to take off and replace the globes in less than 60 minutes. Pencil test was at about 6 inches for both the globes, so they were both shot.

This might be helpful: I was able to rent (you pay $0 if returned within 48 hours) a clutch wrench kit from my local Oreilly's for the 36mm wrench. Worked really well.

New vs old:
View attachment 2703734

Seems like good progress! As you mention, adjustments come next -- bounce elimination and best ride quality is highly unlikely if Front and Rear AHC pressures remain as discussed in Post #17 and Post #25 in this thread, even with new 'globes'. Hope all continues to go well.

 

[suprarx7nut]

The ride kept getting slightly better after the flush, but the bounce in the rear remained.

In the last few days I replaced the rear springs with better used ones to relieve pressure on the shocks. I also replaced the rear globes from a newer car and that fixed the bounce!
The car drives a lot better now. I have yet to adjust the torsion bars and I believe it will get even better after the adjustment.

One of the globes was really rusted on and I couldn't take it off. I took it to two shops and they didn't want to touch it because of the rust. SoCal mechanics are spoiled...
Anyways, I got myself a propane blowtorch and PB Blaster and was able to take off and replace the globes in less than 60 minutes. Pencil test was at about 6 inches for both the globes, so they were both shot.

This might be helpful: I was able to rent (you pay $0 if returned within 48 hours) a clutch wrench kit from my local Oreilly's for the 36mm wrench. Worked really well.

New vs old:
View attachment 2703734

Nice work! New fluid and globes makes for a happy AHC system.