Front suspension drops overnight (AHC Question)

[Humpzilla]

Hey all,

I've been noticing that my 2000 LX470's front suspension drops quite a bit overnight (or after a few days sitting). Probably to the equivalent of the 'low' setting. The rear seems to hold its height.

When I start it up, the AHC levels itself within just a few seconds and seems to have no issues when driving. I also am not seeing any drop in fluid levels and have observed no leaks.

I'm at about 7 to 8 grads when I test the system.

I'm curious if this is normal behavior for AHC, or if this is a symptom of something failing? Tried searching the forum but couldn't really find another thread with this particular question being answered.

Any thoughts, feedback or knowledge would be greatly appreciated!

Cheers,
Jeff

 

[ramangain]

Techstream + 30mm socket are good investments at this point

 

[suprarx7nut]

Check the front shocks for oil weeping, but root cause is probably simply that you're over spec on front pressure. Fix for that is nearly free and very fast. Techstream and a 30mm socket.

 

[dchilds]

Check the front shocks for oil weeping, but root cause is probably simply that you're over spec on front pressure. Fix for that is nearly free and very fast. Techstream and a 30mm socket.

I’m a rookie. What does the 30mm socket do?

 

[suprarx7nut]

I’m a rookie. What does the 30mm socket do?

There are 30mm adjustment bolts on the front torsion bars. Adjusting these varies how much force torsion bars apply and reduces how much the hydraulic system has to work.

It's extremely common for owners to neglect the system and fail to check and adjust front torsion bars.

You may want to give this a watch.

 

[IndroCruise]

Hey all,

I've been noticing that my 2000 LX470's front suspension drops quite a bit overnight (or after a few days sitting). Probably to the equivalent of the 'low' setting. The rear seems to hold its height.

When I start it up, the AHC levels itself within just a few seconds and seems to have no issues when driving. I also am not seeing any drop in fluid levels and have observed no leaks.

I'm at about 7 to 8 grads when I test the system.

I'm curious if this is normal behavior for AHC, or if this is a symptom of something failing? Tried searching the forum but couldn't really find another thread with this particular question being answered.

Any thoughts, feedback or knowledge would be greatly appreciated!

Cheers,
Jeff

Suggest note the fluid level in the AHC Tank level after start-up and after the AHC has levelled itself. Then note the fluid level at the AHC Tank when the vehicle has settled overnight or after a few days of sitting. The fluid has to go somewhere. Noting that there are no leaks, if the fluid level has risen when the vehicle settles, then most likely it has come from the 'shock absorbers' which are pushed down when the vehicle drops, thereby displacing fluid back to the AHC Tank. The Levelling Valves (one for Front, one for Rear) in the Control Valve should prevent this from happening but may be experiencing much higher than specified pressure perhaps causing some bypass allowing the front of the vehicle to sink. Springs and torsion bars eventually become tired and this is a 21 year old vehicle. Inevitably over time, more and more weight is tranferred from the tiring torsion bars and springs, to the AHC system which means its pressure rises way above its specified pressure range.

As mentioned by @ramangain and @suprarx7nut, the starting point is to transfer some load from the front AHC system to the front torsion bars by tightening the torsion bar adjusters, following the video and "cheat sheet" provided by @suprarx7nut.

In answer to your question, this is not a symptom of the AHC system failing but it is symptom of the ageing of the conventional torsion bars and springs which are part of this suspension. It is easily fixed.

By the way, if you are at 7 to 8 graduations of difference between "LO" and "HI" when you test the system, then you probably are due for new 'globes'. However, the test is only comparable with the Factory Service Manual numbers (14 graduations when new, 7 graduations at replacement) when the AHC pressures are in the correct range. If you get some weight off the AHC system you may see some improvement in the number of graduations -- and also experience a better ride, so there is some incentive! For longevity of the system, it really is a good idea to measure and adjust the AHC pressures periodically and also replace the AHC fluid at least every few years.

 

[dchilds]

There are 30mm adjustment bolts on the front torsion bars. Adjusting these varies how much force torsion bars apply and reduces how much the hydraulic system has to work.

It's extremely common for owners to neglect the system and fail to check and adjust front torsion bars.

You may want to give this a watch.

Ahh, of course, for some reason that didn't click with me. I just dialed mine in a few months back to within spec. It's a great system when maintained.

 

[suprarx7nut]

Ahh, of course, for some reason that didn't click with me. I just dialed mine in a few months back to within spec. It's a great system when maintained.

If pressures are ok, I would expect some leakage somewhere. It won't take much to cause the height to drop overnight. Time to start hunting!

 

[kunu]

@Humpzilla Were you able to figure out the cause of this?