AHC 1998 237,0000 - Where and When to Start? (1 Viewer)

[Todd Atchison]

Good morning group from an icy Kentucky. I'm currently working from home and have a great deal of extra time. So, having recently purchased a 1998 Lexus LX 470 with 237K on it I'm still deep in the throughs of frenzied research and the honeymoon period.

The truck is in remarkably great shape for its age and had a great service record and at the time was the only one within 500 miles of me in my price range. So I made the plunge and she's ours. We are the fourth owner and she was maintained flawlessly according to Lexus records up until about 10k ago.

I don't know about you guys but I've wanted a Land Cruiser since I was a young man (I'm 53 now) and ironically could only afford one many years later... I digress. I give a whole diatribe on how I chose this truck and why in another thread. That being said, I'm going through her pretty thoroughly (When I say I that's my very trusted mechanic and I). I'll do the body, suspension, power steering flush, heater t's etc.. I'll have him do the timing belt, pump, serpentine etc.

It's at his shop now being checked out for a random "fire and no start" issues early this week (it started as soon as AAA got here of course but hey its free so I had them drop it there). I was taking it there anyway to be checked out (check engine on PO says it's an O2 sensor). I've ordered an OBD2 reader that should be in any day.

All that being said here is my question:

The AHC currently goes into the N and L position. It will not go into H. It seems to be working. You can hear the pumps and it leveling. The level in the reservoir changes from L to N. But, will not go any higher. It even changes height when in L once moving. Just no H. So, that would tell me the system is "working" somewhat.

Question 1. If I can't do a graduation test where do I begin? Is it just low? Could I add fluid see if it raises then do a flush later? Just kind of don't know where to start? All the information I've seen starts with assuming everything is working - i.e. the graduation test. The fluid is expensive as you all know and I don't just want to go throwing it away.

Question 2: It seems to ride just fine now - actually very nice. Telling me the globes and system is again, "somewhat functional." What is the harm in not addressing the AHC? I have timing belt and other "essential maintenance" to get though in the next couple of months. Can this wait for warmer weather assuming simple adding fluid doesn't fix it? Can it wait on my list? Looks like I may be dealing with the known "fuse box" issue also...we'll see what the mechanic says today. Just trying to pick my battles as I rides just fine today. There is a lot of rust around the components and I'd like to soak them down for the next month with some WD40 and penetrating lubricant before I attempt to turn the first wrench. Thoughts?

 

[nbailz]

I'd suggest reading through the dedicated AHC thread below and asking there; you'll get the attention of the AHC gurus:

The ABCs of AHC - How to Measure, Flush, and Adjust all in one place

I initially put this in the Definitive list of AHC maintenance items thread, but at almost 800 posts long and growing, it's going to get buried and the thread itself is very unwieldy. In an attempt to make as focused a summary as possible, I present "The ABCs of AHC." It's intended as a...

forum.ih8mud.com

 

[suprarx7nut]

Welcome! Start with pressure checks. I'd wager a share of GME that your neutral pressures are too high. The fix in the front is fast and completely free. Got a windows laptop? It'll come in handy.

Check out the thread linked above. All the info you need is in the first page of that thread. My cheat sheet and video may be helpful (again, see the first page of that thread).

Worth prioritizing? Absolutely. If you are over pressure (again, I'm sure you are), you are putting undue pressure on the hydraulic system - pump and globes, most notably. If you can't get techstream running, it would be reasonable to blindly crank the t-bars up 5 turns on each side.

I'm not as old as you (insert light hearted old fart joke ), but I can relate to wanting "that" car for quite a while. The Land Cruiser isn't my dream car, but I did have my eyes on one for years before I could actually have one. The car I've wanted since childhood is a clean and modified/resto-modded mk3 Supra. I've owned a few of them, but none were really "nice". I'm rebuilding one now and it likely won't be "nice" for another ~5+ years. I'll be lucky to consider it "almost done" by the time I'm 40 - about 25 years and something like 3000 hours in the garage after the lust for it began.

Cheers!

 

[Todd Atchison]

Thanks so much - TechStream is on its way! BTW its not a daily so I'm keeping the miles down until all the baseline stuff is done (and even then keep it as our weekend adventure wagon). I'll do the belt and H2O pump and Heater T's next month. Thanks again for the encouragement. BTW - Nice Choice on the Supra - I had a friend in high school who had an early on (the old wedge mid 80's) he use to blow the doors off everything... Good Luck!

 

[Todd Atchison]

I wanted to add that I've been researching the AHC system extensively and I understand the almost fanatical commitment to keeping it and why it's garnered so many fans over the years. Though somewhat complicated - it's logical and remarkably robust. My 1998 has 237k on the clock and after doing my homework - I have no reason to disagree with the diagnosis offered here - crank up the torsion or get some new springs / spacers - to much pressure in the Neutral position. Makes complete sense and when the weather breaks I'll give it a try.

It sounds like everything is happening as should under the hood, pumps are pumping, goes into L back to N when she starts rolling....Reservoir goes up and down when in L and N. I'll bet the recommended torsion lift will fix the problem. I say fix, though it's clear a decision on globe health, springs, shocks etc... will need to be made once it's functioning again.

I'm looking forward to getting the system back online and using it. We will rarely if ever go off-road - as discussed earlier in the thread. That being said, we do tow a 22ft sailboat and would benefit from a reduced wind profile when hauling on a level interstate. Has anyone ever used the height adjustment to ad efficiencies when towing? Just curios - I've seen threads on "overriding" the system. Any first hand experience lowering while towing? Also, I'm realizing I may need to "stiffen up" the rear end to accommodate the tongue weight - can the rear be raised via torsion or does torsion only apply to the front? Is there another way to reduce pressure while also stiffening up the rear other than adding new springs / shocks?

 

[ramangain]

I wanted to add that I've been researching the AHC system extensively and I understand the almost fanatical commitment to keeping it and why it's garnered so many fans over the years.

My oh my have time changed. Look in the archives and you'll discover quite a bit of AHC bashing until semi-recently.

Let's call it Foxbody fanaticism at this current time in history ... but the AHC love will stick, unlike the current obscene values of Foxbodies.

 

[suprarx7nut]

I wanted to add that I've been researching the AHC system extensively and I understand the almost fanatical commitment to keeping it and why it's garnered so many fans over the years. Though somewhat complicated - it's logical and remarkably robust. My 1998 has 237k on the clock and after doing my homework - I have no reason to disagree with the diagnosis offered here - crank up the torsion or get some new springs / spacers - to much pressure in the Neutral position. Makes complete sense and when the weather breaks I'll give it a try.

It sounds like everything is happening as should under the hood, pumps are pumping, goes into L back to N when she starts rolling....Reservoir goes up and down when in L and N. I'll bet the recommended torsion lift will fix the problem. I say fix, though it's clear a decision on globe health, springs, shocks etc... will need to be made once it's functioning again.

I'm looking forward to getting the system back online and using it. We will rarely if ever go off-road - as discussed earlier in the thread. That being said, we do tow a 22ft sailboat and would benefit from a reduced wind profile when hauling on a level interstate. Has anyone ever used the height adjustment to ad efficiencies when towing? Just curios - I've seen threads on "overriding" the system. Any first hand experience lowering while towing? Also, I'm realizing I may need to "stiffen up" the rear end to accommodate the tongue weight - can the rear be raised via torsion or does torsion only apply to the front? Is there another way to reduce pressure while also stiffening up the rear other than adding new springs / shocks?

Air bags are great for occasional load changes like towing. You install them within the coil springs and then inflate as needed. It's a nice way to significantly vary the mechanical assist.

My oh my have time changed. Look in the archives and you'll discover quite a bit of AHC bashing until semi-recently.

Let's call it Foxbody fanaticism at this current time in history ... but the AHC love will stick, unlike the current obscene values of Foxbodies.

I think a few of us have been a bit forceful with mythbusting lately and it's paying off. Paddo gets my vote as the "originator" a few years back. Even with the progress recently, I would say more than half new owners with an LX still have the initial impression that AHC is hot garbage and must be removed immediately. There's still a long ways to go...

 

[ramangain]

Air bags are great for occasional load changes like towing. You install them within the coil springs and then inflate as needed. It's a nice way to significantly vary the mechanical assist.


I think a few of us have been a bit forceful with mythbusting lately and it's paying off. Paddo gets my vote as the "originator" a few years back. Even with the progress recently, I would say more than half new owners with an LX still have the initial impression that AHC is hot garbage and must be removed immediately. There's still a long ways to go...

I'm just waiting for @JunkCrzr89 to post a meme of you in a YotaMD cape holding up an AHC globe like the Statue of Liberty ......

 

[Todd Atchison]

I'm just waiting for @JunkCrzr89 to post a meme of you in a YotaMD cape holding up an AHC globe like the Statue of Liberty ......

I realize I’m wading into uncharted territory and will be the first to admit I have a different need and build in mind - so that being said it’s been my experience that it’s hard to beat or improve original designs. Whether they be Japanese or German, generally speaking of course. But again - I’m not crawling over rocks. As I understand it - this system was many years in development. Its funny how a mind set takes over and drives a market. It’s like when everyone ripped off factory air boxes on their Honda and through on pods - they never run correct again. It’s hard to beat (and I say this with ALL DUE RESPECT it’s hard to beat a Team of Japanese’s engineers - even if they did start designing it with slide rulers in the 60’s... relatively speaking.

 

[ramangain]

For towing, AHC is convenient to help in hitching on and off. However, like mentioned before, you'll want airbags in the OEM rear springs for any significant towing weight. I can vouch that AHC and rear spring airbags are plenty to tow the max GVWR, although a proper WD/AS hitch system aids tremendously if one can be used.