AHC works, High light Doesn't

[wildsmith]

Sorry for the hijack (ok I'm not that sorry ) but how do you find the AHC copes with corrugations compared to conventional shockers in terms of the heat I read can be a problem with a lot of shockers? I'm still on the fence with keep vs replace.

 

[1loudLX]

uHu took his apart I think

 

[RoderickGI]

From memory, every report I have read (and I have read a few, being interested) said that the internal parts of the sensors were in perfect condition. That's why I decided not to check mine. I suspect that there is more chance of getting dirt in or damaging them by pulling them apart, than there is that they are worn or have got dirt into them through use. No one has reported they were worn, from memory.

I have never had trouble with heat when running the AHC hard. I have used the LX in temperatures over 50°C on fast corrugations, deep sand (with woop-de-do's*), and slow rough tracks. No problem. The actual damping valves where the majority of heat is generated in any suspension system are in great chunks of metal bolted firmly to the chassis rails, and they have cooling fins on them. I suspect the AHC handles the heat much better than normal shocks.

I found the ability to adjust the shock absorbers while driving quite useful on long distance outback tracks where the road is quite good except for corrugations. I just softened the suspension and the LX rode over the corrugations much better. That way I could travel at higher speed on those roads. Of course it was necessary to be quick on the switch, because if there was a sudden change in the road condition you needed harder suspension than the "Comfort" setting to keep control.

*Woop-de-do: Large rounded bumps in the road, often found on sandy roads, where the distance between the peaks and troughs of each set match exactly the wheel base of a vehicle, so that at certain speeds, both the front and rear of the vehicle bounce high into the air as they cross the peak, and at least the front ploughs into the ground at the bottom of each trough. That is, the woop-de-do's exactly match the resonate frequency of your truck, and you get thrown around a lot if you don't see then and low down in time.

BTW Gebo, another trick I learned is to pull the battery cables for an hour or more, to reset the various ECUs in the truck. They seem to get out of whack sometimes, and need a reboot. It could be that the AHC ECU needs to reset its internal value for the zero position of the height control sensors, or something like that. It couldn't hurt to try this anyway. Be sure to pull any codes before you do this though, or they will be lost.

 

[wildsmith]

Thanks RoderickGI, interesting. Only see the problem cases reported in the uk, not much talk about capability in the rough.

 

[Gebo]

Well, I have a a confession to make. I recently loosened my T-Bars. And loosened them by several turns. Love the nice cooshy ride... You guys may have just identified my problem. I'm gonna tighten them by one turn at a time and see where that gets me.

Oh, I do have the FSM's so I'll try and figure out how to pull the codes.

 

[RoderickGI]

Well, I have a a confession to make. I recently loosened my T-Bars. And loosened them by several turns.

Well there you go. I think my post #15 above covers your problem.

The weight of your truck is supported by the combination of the springs/TBs and the oil pressure in the AHC. If you reduce the tension in the TBs, you are just increasing the required oil pressure in the AHC to lift the front to the correct height, as defined by the height control sensors. At the same time, increasing the oil pressure means that the gas in the Damping Force Control Actuator spheres is going to be more compressed, and therefore you will have less travel left to absorb bumps.

On any big bumps you will get a nice soft suspension response, right up until the spheres are full of oil, which will happen much sooner than normal. Then you will get a hard thump in the arse, and it is likely that the over-pressure valve will be activated in the AHC, bleeding oil pressure back into the reservoir.

Reducing the TB tension doesn't actually change the damping of course. It just changes the force required to twist the TB for it rest position when a bump is encountered.

Tightening up the TBs so as to just fix the problem of the high position light going out will not fix the above issue with the AHC. You will be running a higher oil pressure than the pump was designed to work with, and you will wear it out sooner. It is an expensive part. You will get the harsh response on larger bumps, and you will be activating the over pressure valve each time. The transient peak oil pressure caused by completely filling the actuator spheres will not be doing any good to your AHC.

If you plan to keep the truck for the long term, you should adjust the TBs so that the AHC is within the specified range in the FSM, or you will be doing damage to components. Set the damping force control switch to "Comfort" for a cushy ride. If that isn't good enough for you, find some thinner oil to use, or get someone to modify the valving in the Damping Force Control Actuators. Note that the make up of the oil used in the AHC is very specific, so you will need expert advice to find a replacement oil. Try asking Keith at B&B Suspensions.

Given what you have said, I doubt that the codes will help you at all. In fact I doubt that there will be any codes to read, unless the system detected that it couldn't lock in the AHC at the high position, and you already know that.

 

[1loudLX]

well he shouldnt have messed with the TBs. The codes would say "abnormal pressure at pump"

 

[RoderickGI]

well he shouldnt have messed with the TBs.

True, but I thought I would explain why.









Mind you, I have messed with mine, tightening up the TBs to match the heavier springs on the back, and reduce the working oil pressure in the AHC. So I guess I shouldn't criticise.

 

[1loudLX]

As have I.

 

[Gebo]

The reason I backed them off was because when I went in to get it aligned, the mechanic tightened the TB's big time to align the front end. My ride became so harsh. He tightened one side about 1 inch on the threads and 1/2 inch on the other. I just couldn't take the harsh ride. So...I just reversed what he did. After doing so, the ride became what I would expect from a Lexus.

 

[uHu]

There is no problem opening up the sensors - if you know which end of a screwdriver to use, and enough about cleanliness to keep yourself clean.
OTOH, there is no need to open up the sensors if they measure OK, although that measurement can be difficult to do reliably. There are many reports of failing sensors. Worst thing for them seems to be wet and salted roads.

The springs of the AHC-cruiser, the coils and TBs, will wear just like on any other vehicle. After a few years they need tightening-up, otherwise the AHC will take more than it's share of the job, resulting in shorter life of the spheres and the pump.

Before I changed the rear sensor the first time, I had just the symptoms described in the first post here, only that the behavior changed over the weeks and days. The dealer did not get any codes, and didn't understand how the system worked. After a bit of studying, I found out it was the rear sensor, and confronted the dealer with this. They had a TSB on this and gave me a new sensor for free even tho' the warranty was out. This new sensor failed after a year or so. Opened it up, cleaned it out, sealed it better, and it was ok for another year. Then same procedure over again, and sealed it even better, and it has been ok since.

 

[RoderickGI]

It is understandable why you did that Gebo. It sounds like the mechanic didn't understand how the AHC works. I think you should get the TBs adjusted so that AHC oil pressure is within the specified range in the FSM. You may have backed them off too far.

Like I said, I had the problem occasionally, and it hasn't recurred since tightening up the TBs.

I was quite surprised that ARB, who fitted all my extra gear up front, didn't tighten the TBs when they added the extra weight. But I didn't know enough about the AHC back then, and I needed to get away on a six month trip, so I left them. I now realise that I should have tightened the TBs to compensate for the weight. It may have stopped the truck ploughing the bullbar into sand dunes occasionally. My TBs are now adjusted right up near their maximum (although I am thinking about backing them off a little) and I expect to need to replace them at some stage with stronger OEM Landcruiser versions.

So yes, I agree that TBs need to be tightened up over time, and if weight is added up front. I don't think they should have been adjusted for a wheel alignment though, since the height of the vehicle is controlled by the height sensors and oil pressure in the AHC, not the TBs.

I would also open and clean the sensors, if there was a strong case for them being the problem. My sensors look dreadful from the outside, and have spent quite a bit of time in fresh and salt water, mud, dust and being pelted by stones. They seem to still be working without problem, but the cases are so beaten up (at least the rear), I'm not sure they would go back together well if opened.

 

[wildsmith]

I opened up my rear sensor as PM and it was spotless and I'm expecting it fail now *because* I opened it up!

I have some none AHC TB's waiting to go on if I don't jump ship first. Hoping they'll eliminate some of the front end dive.

 

[Gebo]

Problem Solved!!!! I cranked up the TB's 3 turns and it works like a charm. Thanks for your help. AND...my ride is still soft

 

[nball]

Totally stock dood here…

The manual says speeds over 19 mph will set AHC to normal. I've tested this extensively at fast food places, my driveway, and several local malls. In fact, other than sitting in the lot at the dealer, I haven't seen any benefit to AHC.

Nonetheless, I want to crank my TB's to level the truck. Here's hoping my new AT's solve the sloppy handling/body roll problem (not) and I can back my way into the next level.

 

[uHu]

Totally stock dood here…

The manual says speeds over 19 mph will set AHC to normal. I've tested this extensively at fast food places, my driveway, and several local malls. In fact, other than sitting in the lot at the dealer, I haven't seen any benefit to AHC.

Nonetheless, I want to crank my TB's to level the truck. Here's hoping my new AT's solve the sloppy handling/body roll problem (not) and I can back my way into the next level.

Are you saying that you can't get the height to "N"? Or it just doesn't go automatically from H to N? Or from L to N?
In low range it will not move out of H at any speed.

AT's will not improve the handling. The AHC equipped 100 is rather soft, but I find it acceptable by turning the TEMS control to the Sport setting (for my sedate style). Changing the AHC fluid and airing the system well is crucial for good performance. Throwing out the AHC and fitting upgraded springs and shocks will make the handling better, but you loose the possibility to "switch off washboards" and the possibility to lift-on-demand without wearing out the CVs when you don't require the lift.

And, you can not level an AHC truck by cranking the Tbars. You have to adjust the AHC height sensors first, and then adjust the Tbars in order to get the AHC Neutral Pressure back to spec.

 

[Gebo]

And, you can not level an AHC truck by cranking the Tbars. You have to adjust the AHC height sensors first, and then adjust the Tbars in order to get the AHC Neutral Pressure back to spec.

Adjusting my AHC sensors either up on down (in the slider) didn't seem to make any difference. I went from top to bottom (one extreme to the other) and then drove around the block and it didn't affect the height. I have noticed the every now and then, if I stop and am idling for an extended time, the pump will come on and some kind of adjustment takes place.

Any ideas?

 

[pman]

Adjusting my AHC sensors either up on down (in the slider) didn't seem to make any difference. I went from top to bottom (one extreme to the other) and then drove around the block and it didn't affect the height. I have noticed the every now and then, if I stop and am idling for an extended time, the pump will come on and some kind of adjustment takes place.

Any ideas?

Have you adjusted the t-bars after adjusting the sensors?

If you move the sensors to increase the ride height, you also have to crank up the t-bars so that it will not require a higher pressure than stock.

 

[nball]

Are you saying that you can't get the height to "N"? Or it just doesn't go automatically from H to N? Or from L to N? In low range it will not move out of H at any speed.

I thought the AHC operated per the user regardless of speed. This was a misreading by me. After a closer read of this forum and the manual, and then doing it in real life, I find this not to be the case, no problem. I question the value of AHC, both in concept and design. Also don't care much.

AT's will not improve the handling. The AHC equipped 100 is rather soft, but I find it acceptable by turning the TEMS control to the Sport setting (for my sedate style). Changing the AHC fluid and airing the system well is crucial for good performance. Throwing out the AHC and fitting upgraded springs and shocks will make the handling better, but you loose the possibility to "switch off washboards" and the possibility to lift-on-demand without wearing out the CVs when you don't require the lift.

You're right about the AT's, yet with the enormous body roll of the LC, the new LT rated AT's are an improvement. I know it's not a sports car, I drive like an old woman (now that I have an LC… happily at that).

I am gauging the replacement of the AHC against the warranty now. The AHC will go once I know more about the warranty.

And, you can not level an AHC truck by cranking the Tbars. You have to adjust the AHC height sensors first, and then adjust the Tbars in order to get the AHC Neutral Pressure back to spec.

Thank you for making this clear.

Thanks man!

 

[uHu]

The design of the AHC is mainly to level the truck during different loads. An added bonus is the ability to lift 2" for even better clearance, or to lower 2" for easier access/entry/exit for the short or frail.

The design of the TEMS is to give you variable damping and to give a soft ride while maintaining control of roll, pitch and squat. The OM has a warning against driving with the TEMS at the softest setting at high speed.
The "shock absorbers" have 4 valves, which give 16 steps of damping, and react to input from the comfort/sport-switch, the steering angle, the brakes, the accelerator, and the ahc-height. I do notice a marked difference between the 4 switch positions. If you want less roll, try 18 or 20" wheels. I even notice a marked difference between 16 and 17". (Just don't expect off-road-ability with less rubber)

Can't someone find a solution for keeping the AHC, increasing the travel, improving handling, AND improve the load range.
OK. Just a fantasy. Let's swap to stndrd suspension.