AHC/AVS Question

[Wres157]

My 01 LX470 has gotten pretty bouncy. It really likes to seesaw front to back when driving over bumps, but if just the right or left side hit a bump the car reacts fine. AHC still works well, and there is still a big difference in dampening between comfort and sport. It almost feels like there's just no rebound to the shocks. Is this the beginning symptoms of accumulator fail?

This weekend I'll measure how much fluid the system is moving then do a full flush. I'm hoping it's just a little low and there's some air in the system. I guess if that doesn't work I'll move on to new accumulators.

Also, I've been searching every to see if the shocks themselves fail or need a rebuild, but I haven't found anything. Thanks!

 

[PADDO]

A fluid exchange and system bleeding is always desirable, particularly if you don't know when it was last done. But the first step with any AHC/AVS diagnosis is knowing what your neutral pressures are and getting those optimized.
The "shocks" are damped by their respective damper globe accumulators/valves and aren't rebuildable. If you are still on the original damper globes then those are nearing the end of their effective life, but don't start changing parts until you have the basics - neutral pressures - sorted out.

 

[Wres157]

Thanks PADDO. I was having problems getting the TIS working, but the suspension fluid was delevered today so I went ahead with the bleeding.

The fluid in the resirvor was dark and the accumulators drained milky looking, like the pictures I've seen. There was also a lot of air bubbles, some pill size in the tube while the fluid drained. I think a lot of the bouncieness was to due with air. Could all this air be from the accumulators leaking?

After the bleed the ride has improved dramatically, and I'm getting a move of at least 7 ticks now (from 3 ticks). The move between heights has also gotten much smoother. Now I'm not familiar with the way the system routes the fluid, but is it safe to assume that the shocks will still contain the old fluid after bleeding? My plan is to repeat the process in about a week, see how much more air I can get out.

 

[PADDO]

Sounds like you had a lot of nitrogen from the accumulators and potentially air from other sources fouling the system. With the design of this system fluid doesn't circulate as such and is prone to stagnate at the four ends of the system - the shock actuators. There will always be residual after a fluid exchange/bleed and a redo in a week or so would be beneficial, you can then be confident that you've minimized and diluted the old, contaminated and degraded fluid. When I bleed I let them drop down to the bumps to remove as much fluid as practical. I also cycle between low and high regularly too, to help redistribution, and change the fluid at 30k intervals. Additionally, by initially setting your fluid level higher (an inch) above the max line you can regularly crack each bleed point and draw off an ounce just to confirm all is ok and no gas is present. I do this at engine oil change intervals.
Going from 3 to 8 graduations by bleeding the system is a very good result - much better, and cheaper, than changing out 4x damper globes as the AHC illiterate would recommend as the first course of action! I expect you will pick up another one or two grads and even better damping with your neutral pressures optimized. It's a safe bet that if your fluid was as old as described and full of gas then your torsion bars haven't been adjusted nor coils changed or spacers added.

 

[Wres157]

Suspension became bouncy again, so I went ahead and did a small bleed to see how it looked. Sure enough there was air in the system, albeit much less than previously. White foam at first, then red with little bubbles. If the membrane in the accumulators has ruptured there would still have been residual air in the globe which I'm assuming still provided some of the cushioning effect. Air is leaking out of the accumulators into the system as a whole. While it might be subjective, the drive is much harder after rebleeding the second time, which make sense with the decrease of air in the system (both accumulators and system wide) to create a cushion. Speculation, but it seems air in the system outside of the accumulators seems to create a springing effect.

Anyway, new accumulators arrived today. I think I'd prefer to get the TIS Techstream working and check my pressure levels before putting fresh accumulators on. If my torsion bars/springs aren't pulling their weight I'd hate to stress the new accumulators. IDK, need to put a plan together.

 

[PADDO]

It can take several bleeding sessions to purge most of the entrained gases within the system - btw it's nitrogen in the accumulators, not air. It is so very likely your neutral pressures are high (i.e. the only people who report low neutrals are those who attempt the basic TB set up procedure at the expense of following the correct AHC torsion bar neutral pressures adjustment procedure) that I'd recommend getting those dialed in before installing the new globes.

 

[LBridges]

It can take several bleeding sessions to purge most of the entrained gases within the system - btw it's nitrogen in the accumulators, not air. It is so very likely your neutral pressures are high (i.e. the only people who report low neutrals are those who attempt the basic TB set up procedure at the expense of following the correct AHC torsion bar neutral pressures adjustment procedure) that I'd recommend getting those dialed in before installing the new globes.

^what he said.

I'm still pretty new to this game, but both the front and rear numbers were too high (8.3 up front) and there was no record of anything ever being done to the AHC system. Did a flush, then found that adjusting the TBs to get 6.9 not only made the ride better, but also had the positive side effect of lowering the rear pressures to back in the normal range as well. I've checked it several times now just to make sure it worked (didn't trust myself really). Amazing what advice from Mud members, some Toyota branded hydraulic fluid, and a 30mm socket can do.

 

[Drogon]

Uh

^what he said.

I'm still pretty new to this game, but both the front and rear numbers were too high (8.3 up front) and there was no record of anything ever being done to the AHC system. Did a flush, then found that adjusting the TBs to get 6.9 not only made the ride better, but also had the positive side effect of lowering the rear pressures to back in the normal range as well. I've checked it several times now just to make sure it worked (didn't trust myself really). Amazing what advice from Mud members, some Toyota branded hydraulic fluid, and a 30mm socket can do.[/QUOTE
How many turns did your t-bars take to bring the n pressure in spec?

 

[Drogon]

^what he said.

I'm still pretty new to this game, but both the front and rear numbers were too high (8.3 up front) and there was no record of anything ever being done to the AHC system. Did a flush, then found that adjusting the TBs to get 6.9 not only made the ride better, but also had the positive side effect of lowering the rear pressures to back in the normal range as well. I've checked it several times now just to make sure it worked (didn't trust myself really). Amazing what advice from Mud members, some Toyota branded hydraulic fluid, and a 30mm socket can do.

How many turns did your t-bars take to bring the n pressure to spec?

 

[LBridges]

How many turns did your t-bars take to bring the n pressure to spec?

Seven. Each turn roughly corresponds to 0.2. Since my truck was 1.4 high (should be 6.9 was 8.3), I did 7 turns. I later had to make another adjustment to equalize the height between the sides. That is Techstream was reporting a +0.1 on one side and a -0.1 on the other (vehicle unloaded, including me outside looking in the window). Ultimately I backed off a half turn on the passenger side. I believe the numbers were within spec before, but I wanted to see if I could get it spot on (that and I enjoy playing with the truck).

 

[PADDO]

Adjusting cross level to the height sensor feedback doesn't actually achieve cross level unless your sensors are identically aligned, and that's pretty rare noting how long ago these things left the factory. Much better and less error prone to adjust cross level as per the fsm - physically measuring heights - and then set the sensors to null when the vehicle is physically cross level and at the desired N height. Don't forget the sensors just follow the height deltas between the upper arm and chassis; you can be way off cross level and adjust both sensors to read 0, or be cross level and have one sensor reporting -1 inch with the other at +1.
If your sensors are reporting +\- 0.1 and you are level then you are in pretty good shape

 

[LBridges]

Adjusting cross level to the height sensor feedback doesn't actually achieve cross level unless your sensors are identically aligned, and that's pretty rare noting how long ago these things left the factory. ...

Thanks, I kinda already knew and appreciated that but appreciate you pointing it out so someone didn't chase down a wrong path. I measured the heights physically a couple of times before I got techstream and got about a 0.2 to 0.3 difference (still within spec I think). I didn't want to mess with it until I knew some numbers. As near as I can measure they are in agreement. But again I do appreciate you pointing this out 'cause my normal state is go off half-cocked then have to un-do the work (like I did recently with the brakes).

 

[Wres157]

I haven't gotten techstream to work so I haven't touched the tbars, but I couldn't take the bounce any longer and replaced the accumulators yesterday. The ride is so smooth, it's so nice. But now I'm worried I'm putting to much stress on the accumulators and they'll blow out. With proper flushing hopefully they last the 100k/14 years the others had.

While the system may be a pain in the ass when not working and expensive to fix; when you get such longevity out of it I don't see where the traditional spring/shock setup saves any money over the long haul.