Sudden AHC failure and leak

[Ramathorn15]

The AHC H mode is a 1-2" lift compared to the stock LC suspension. If you need the extra ground clearance, I would suggest the OME lift.

 

[PADDO]

So, if I end up going the route of replacing the AHC with stock LC shocks and springs, would that give me the same ride height as the AHC in N? I've always found the H mode sufficient for the kind of wheeling I do, plus, much higher than that and my 265 75 16 Duratracs may start to look a little bit small. If I wanted to match that height, what sort of lift would be required? I assume it's not much, since we're abel to go to high mode, and not need a diff drop.

If you replace your AHC with stock LC shocks, coils and torsion bars you will achieve approx. the same height as present, if your AHC N height is stock (roughly 19.75in front axle center to fender bottom and 20.5in axle center to fender at the rear). AHC in H is approx. +1.6in front and +2in rear over Normal AHC height, wherever that happens to be set.

 

[Tbay LX]

Hey guys, I'm finally back in town and able to take a look at the truck. I was able to get fluid to seep out by raising and lowering the truck on a jack. It looks like the leak is somewhere around the lower cushion bolt, but it's hard to see exactly where its coming from, as it appears to be running from the back side. Is it more likely that the housing is cracked, or that it's an issue with the bolt. How does the control valve assembely work? Is the whole unit filled with hydrolic fluid? What would you suggest trying to service first? Here's a link to a video of the drip, Dropbox - Tots truck.3gp and I've attached a couple photos. Thanks again.

 

[uHu]

Looks like your problem is rust. Rust is not as good at keeping pressurized fluid in as steel pipes are.

 

[Tbay LX]

Hahah thanks... The question is, what rusty part needs replacing. Is it likely to be that cushion screw? I'm not sure what the cushion screw does, I wouldn't have thought there'd be any fluid in that unit, I assumed it was all contained in pipes at that point. Maybe someone can explain the workings of the housing in question?

 

[Ramathorn15]

I wouldn't have suspected that the cushion bolts have any access to the AHC fluid. It sure does look that way from your photos though. I would have guessed the seal o-ring was the culprit but it looks relatively clean around the cover. I would probably replace the entire assembly unless I was able to determine more specifically where the leak was coming from.

Paging AHC Dr. @PADDO

 

[PADDO]

^cs looking top down.
That valve block houses the two leveling valves and two gate valves and all pressure is contained with the aluminum block and the galleries connecting the solenoid valves. The cushion bolts just seat into blind threaded holes and there is no pressure behind them. It's possible that one of the four valves is leaking into the plastic rectangular solenoid cover, which is there just for physical protection of the solenoids and to house the connectors, but based on the rust and dissimilar metals corrosion going on I'd expect to find one of the four upper fittings/lines has failed.
If you can take the plastic cover off (4x 4mm cap screws) and check there's no fluid leaking past one of the valves then that pretty much seals it that one of the upper four unions/lines has let go I reckon. If you're short of AHC fluid I wouldn't be concerned if it were mine to substitute in a low viscosity hydraulic fluid that may be more available, like John Deere low vis HyGard, to get things up and running. Dump it out after the repair and replace with AHC fluid.

 

[Tbay LX]

Thanks Paddo, so if I open up the cover, and everything seems clean inside, you're saying you'd suspect one of the fittings/lines marked 15 (155, 11) in this screenshot?

 

[PADDO]

Yes, it wouldn't take much corrosion to eat through one of those 4 lines at the top allowing fluid to dribble (or spray under pressure) down the side of the valve block. An inspection camera would be handy here.

 

[Tbay LX]

Yup, an inspection camera would definitely help. I tried taking a look today, and after cleaning the lines well, I still can't see where the leak is. I tried opening the cover, but the cap screws are so corroded the hexagon is now a circle. I'm a little worried about taking vice grips to 'em.

 

[PabloCruise]

I had the same problem on my 2006 LX470 at around 105K miles, the leak was under front passenger side door. I went through the same exercise of trying to figure out why it just happen without any warning or tale-tale signs of trouble. Things I consider at the time was rust, temperature swings, recent work, AHC service and driving conditions from the previous owners, my driving history...etc. Long story short, after a month of screwing around, there was 2 facts that stand out: 1> High moisture in the fluid, positively determined by multiple test with moisture strips at multiple locations, and the accumulator joints has rust around it when I took it off. 2> There is NO record of AHC fluid change from the previous owners. This was a stock very clean accident free southern rig with about 86K miles when I got it, the guy that had it live and work in the suburbs that has light traffic and he never wheeled the rig. So, I never expect the AHC system to blowup after 20K miles, it completely surprised me. I also remember checking all the fluids before I buy the rig, and the AHC fluid was very clean and translucent, and the system worked quickly and properly. So it gave me so much confidence that all is well. Moral of the story, if I ever get another 100 rig again, I'd not just go by clean fluids and "it works good" as a sign of confidence, it must have AHC service records at proper intervals and free of rust. Otherwise I just can't pay top $ for it, because there will be an increase chance of failure that would cost me big $ down the road, especially if I plan to keep the rig awhile. I didn't know as much back then so it was definitely lesson learned. I'm sure there're people that lucked out, but there's a good reason why Toyota / Lexus put it in their books as one of their many periodic service requirements.

What was your solution? Replacing joints and fluid?

 

[Tbay LX]

What was your solution? Replacing joints and fluid?

No solution yet. I had to go out of town for a couple weeks, and just got back. Going to try to take it to the mechanic this week, as I seem to have reached the limits of my abilities in tracking this down. Hopefully he'll have an answer for me soon.

 

[stady isetta]

My input to the discussion.

A lot of debris accumulates on top of the height control accumulator/pump, right where the hydraulic lines connect, and causes rust. It is very hard to see these lines. My '98 has been leaking from this area for a week. Fluid in reservoir is going down very slowly, but vehicle height remains the same. I have turned off the AHC system and monitor, investigate, and diagnose. I do short drives and do not notice any ride quality issues. I am assuming the AHC system is closed now, hence ride height and quality constant. I am going to replace the lines into the height accumulator....and MAYBE the unit. This will be the last fix to the system before I convert to a lift..pretty good for 20 years! I do love the ride though. I do a lot of medium speed travel to access across fields to access construction sites and am always impressed by the air ride.