Props to PADDO's AHC fluid replacement method! (5 Viewers)
- Thread starter Clunky
- Start date
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@PADDO
Bravo. Your instructions were spot-on. I followed your instructions exactly and swapped out my AHC fluid. Thankfully like most things on this car I've found that the previous fluids weren't in bad shape. I did slap all five nipples with some PB blaster twice in the days before doing it even though there is no rust, just in case.
THE RIDE IS SO MUCH BETTER. The ride was ok before but the difference from old suspension fluid to new is just jaw-dropping. This procedure is now going on my 30k maintenance check off list. It is really no more difficult than an oil change so there is no excuse.
Bravo. Your instructions were spot-on. I followed your instructions exactly and swapped out my AHC fluid. Thankfully like most things on this car I've found that the previous fluids weren't in bad shape. I did slap all five nipples with some PB blaster twice in the days before doing it even though there is no rust, just in case.
THE RIDE IS SO MUCH BETTER. The ride was ok before but the difference from old suspension fluid to new is just jaw-dropping. This procedure is now going on my 30k maintenance check off list. It is really no more difficult than an oil change so there is no excuse.
flare wrench makes bleeding a bit easier.
I like that right angle adapter, I just use a hose straight into the bleeder valve.
I like that right angle adapter, I just use a hose straight into the bleeder valve.
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@95Fantasma80
His video is fine, it’s added that second round of bleeding which doesn’t really achieve much and fiddles around with the final fluid height. Any method that gets the maximum amount of old fluid out and replaces it with fresh and leaves you with a final reservoir level above Min (a bit over Max doesn’t matter either) at N height with engine running will get the job done.
Ignore the caption about front wheels being hydraulically connected only when front wheels are straight - the isolating gate valves only function when the vehicle is moving so it’s not an issue when exchanging AHC fluid.
Also, when you do the Low to High graduation check you need to ensure the system has finished charging the height accumulator to ensure an accurate reading. High neutral pressures will skew this test too.
His video is fine, it’s added that second round of bleeding which doesn’t really achieve much and fiddles around with the final fluid height. Any method that gets the maximum amount of old fluid out and replaces it with fresh and leaves you with a final reservoir level above Min (a bit over Max doesn’t matter either) at N height with engine running will get the job done.
Ignore the caption about front wheels being hydraulically connected only when front wheels are straight - the isolating gate valves only function when the vehicle is moving so it’s not an issue when exchanging AHC fluid.
Also, when you do the Low to High graduation check you need to ensure the system has finished charging the height accumulator to ensure an accurate reading. High neutral pressures will skew this test too.
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Glad it worked out for you and thanks for taking the time so say “thanks”. It really is a straight forward process if you’re not dealing with excessive rust; and even then you can get almost as good a result by driving the vehicle down to the bump stops in test mode and sucking everything out of the reservoir without dealing with corroded bleeders.
Finally got off my lazy ass and got Techstream set up (cheap Mini VCi cable works great!). The pressures are high both front and rear, so it's time to crank the front torsion bars. The driver's side is also sitting about an inch lower than the passenger side, so I should level that out too.
For rears, I think I will need to buy some spacers, I am sure that is all documented somewhere here.
For rears, I think I will need to buy some spacers, I am sure that is all documented somewhere here.
So I spent some more time with my again AHC to see if I can get rid of the crashy ride.
Take a gander:
Ok, may be the torsion bars need to be backed out some, but what is causing the rear pressure to drop so low?
Any help is appreciated
- Flushed the ACH fluid again - the old fluid came out looking brand spanking new (its only 1 month old, but I did this just to make sure there aren't any more contaminants left in the system
- Cranked the Torsion bars 3 turns on each side
- Drove a mile or so and check the AHC pressures.
Take a gander:
Ok, may be the torsion bars need to be backed out some, but what is causing the rear pressure to drop so low?
Any help is appreciated
Did you cycle up and down a few times? Did the test drive feel lofty?
I don't think three full turns would even get you into the right range, let alone beyond it.
I don't think three full turns would even get you into the right range, let alone beyond it.
I cycled it a couple of times because I was surprised too. Here's what the numbers looked like:
Spurious reading, assuming you haven’t (edit fixed) fitted aftermarket heavy coils and TBs. Try again later with the temp sensor disconnected for the rear reading. These seemingly weird readings are why I also like using a pressure gauge.
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Let the car sit for a few hours and then read AHC pressures again, everything seems to be in spec now:
The ride is still as crashy as ever. Truck is just too happy to lean and heave in every turn and every time brakes are used. Drive over minor imperfections in the road and you are suitably punished, keep up with the traffic on ever deteriorating Wisconsin streets and the very fillings in your teeth will be knocked loose
Since my shocks aren't leaking, I am assuming I either need new globes or it is time to strip all this dead weight
off and go to a more conventional set up.
The ride is still as crashy as ever. Truck is just too happy to lean and heave in every turn and every time brakes are used. Drive over minor imperfections in the road and you are suitably punished, keep up with the traffic on ever deteriorating Wisconsin streets and the very fillings in your teeth will be knocked loose
Since my shocks aren't leaking, I am assuming I either need new globes or it is time to strip all this dead weight
off and go to a more conventional set up.
I’ve got to admit I haven’t been following your particular story but have you done the basic tests like graduation counting and the damper step test?Let the car sit for a few hours and then read AHC pressures again, everything seems to be in spec now:
View attachment 1826246
The ride is still as crashy as ever. Truck is just too happy to lean and heave in every turn and every time brakes are used. Drive over minor imperfections in the road and you are suitably punished, keep up with the traffic on ever deteriorating Wisconsin streets and the very fillings in your teeth will be knocked loose
Since my shocks aren't leaking, I am assuming I either need new globes or it is time to strip all this dead weight
I will search for the damper step test, but here's what I have done so far.
1998 LX470 with 242K miles. Always dealer maintained. pages upon pages of service logs, never any mention of AHC maintenance.
1998 LX470 with 242K miles. Always dealer maintained. pages upon pages of service logs, never any mention of AHC maintenance.
- Bought the vehicle with left side ride height sensor broken - Installed the new AISIN sensor which restored the rider height and AHC function
- Flushed the AHC fluid - it came out black and full of suspended particles. Improved the height adjustment funcion (goes up and down quickly and smoothly now!)
- Flushed AHC fluid again - it came out looking pristine
- AHC pressures are front: 8.2 and rear: 7.2
- Adjust TB on both side 5 full turns: Pressure improved to front: 6.6 and rear 7.1
- Graduations count about 10 when going H to L
Ok, good info, thanks. Do you have any AHC DTCs? Obviously your rear pressure is high, optimum is in the range 5.6-6.0 MPa. If you’re truly getting ~10 graduations for the L to H check on a 20yr old 242k vehicle then you’ve done exceedingly well, assuming original fit globes as you’ve said there’s no AHC system maintenance history. I changed my own out at about 150k in an 03 that I’ve owned since essentially new. They collectively returned about 9 grads which roughly equates to 70% worn, 30% life left until they needed to be junked. For me the next step would be to verify your front and rear damping values change as a function of speed, road conditions and comfort setting. You can hook Techstream up and drive while monitoring the front and rear Step values. You should see them adjust constantly if you’re accelerating, braking, hitting speed bumps and pot holes. In your driveway you can put the system into test mode (Techstream not required but handy to watch Step values change) by shorting Ts and E1 in DLC1 and pushing the brake pedal to step through softest to firmest damping. Walk around the vehicle and push down each corner and ideally you’ll feel the suspension stiffen as you progress through the test. You can then lock the system in say the softest setting (1) and drive. This should tell you if you’re looking at a hydraulic/mechanical issue or a control issue. I’ve posted the FSM excerpts in a number of places and definitely in the “definitive AHC maintenance items” epic.
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Ok, I just realized that I was counting the graduations wrong.
The real difference between L and H is just under 5 graduations! Which clearly means the globes are shot.
I will raise the truck on the jack stands as hogh as I can tomorrow and will see how the rest of the system looks like. If everything else is not too rusty I will order new globes and rear springs
The real difference between L and H is just under 5 graduations! Which clearly means the globes are shot.
I will raise the truck on the jack stands as hogh as I can tomorrow and will see how the rest of the system looks like. If everything else is not too rusty I will order new globes and rear springs
Geez, at <5 graduations what you’re seeing is essentially just the fluid displaced by the 4x shock actuators stroking between heights and nothing from the 4 damper accumulators. Those accumulators will be either very, very full due to gas permeation or completely full of fluid due to ruptured diaphragms. With nowhere for displaced fluid to go (expelled/make up fluid is supposed to pass through the variable damping orifices going to/from the accumulators) on shock actuator compression all that energy is transferred up into the vehicle and your butt and not damped due to shock actuator hydraulic locking. On shock actuator extension if you’re hitting a pot hole the accumulators don’t expel any make-up fluid as you’ve got a vacuum lock, nothing passes through the damper orifices and therefore no damping. No effective damping in both compression and rebound with blown damper accumulators.
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This is consistent with what my but is feeling 
I raised the truck on jack stand and crawled underneath with a good flashlight. Almost all the lines I can see have significant rust (blessings of living in snow belt!) and all shocks, accumulators and the pump (on driver side rail) has at least surface rust. Some bubbling is also apparent in places.
I think it may be advisable to switch to more conventional setup at this point.
I really don't need a lift so I am planning to throw on used stock LC TBs, OME 2865 springs and new stock shocks
. Feel free to talk me off this ledge if you see anything inadvisable in this plan.
I raised the truck on jack stand and crawled underneath with a good flashlight. Almost all the lines I can see have significant rust (blessings of living in snow belt!) and all shocks, accumulators and the pump (on driver side rail) has at least surface rust. Some bubbling is also apparent in places.
I think it may be advisable to switch to more conventional setup at this point.
I really don't need a lift so I am planning to throw on used stock LC TBs, OME 2865 springs and new stock shocks
. Feel free to talk me off this ledge if you see anything inadvisable in this plan.
Just knocked out mine. Fluid from front was black, fluid from rear was milky. Did a quick bleed afterwards of all 4 and got nice pink fluid coming out immediately. Drove it around and big difference. Seems less squirelly on the road. Thanks Paddo!!
Hey Guys is it even worth doing my AHC fluid flush if I'm not getting substantial graduations?
AHC still works for low and high and I can see a height difference but this reservoir looks pretty much the same for all 3 modes.
Maybe someone had added windshield wiper fluid as its not anywhere close to max/min when in normal.
The ride is very harsh so I wanted to start with Flush but I heard if you aren't getting correct graduations that its not worth doing a flush.
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AHC still works for low and high and I can see a height difference but this reservoir looks pretty much the same for all 3 modes.
Maybe someone had added windshield wiper fluid as its not anywhere close to max/min when in normal.
The ride is very harsh so I wanted to start with Flush but I heard if you aren't getting correct graduations that its not worth doing a flush.
View media item 77566View media item 77567View media item 77568
