Changing out the AHC suspension fluid?

[PADDO]

Four graduations on the reservoir going from L to H isn't good, suggests they have failed well and truly.
Reading through your posts it seems you've been able to lower your front pressure from 10.4 (which is abnormally high for a stock vehicle (no bull bar + winch) at an N height of 19.75in/500mm) to 7.5 and have maxed out your adjustment range. Dropping close to 3MPa will take about 15 turns so you'd need to query the torsion bar indexing or the accuracy of the pressure reading, and maybe contaminated gassy fluid compressing. That screen shot of your pressures - is that from a Snap On scan tool? Also, when you're doing your pressure reading you go from L to N and wait 30 seconds or so for the system to settle and for the height accumulator to finish charging. Do this a couple of times to ensure you get a consistent reading. The alternate - most accurate method - of measuring neutral pressures is with a gauge fitted directly to a damper bleeder. But reading pressure data from the ECU should be sufficiently accurate for most, but I've only used Techstream and have seen results from an iCarsoft 905.
Describing the fluid as milky coffee colored isn't healthy either. Old AHC fluid tends to goes dark, cola colored. If there's micro bubbles entrained it will be definitely lighter but not really a milky coffee. Any chance that brake fluid or washer fluid was added to the reservoir? Regardless, that old stuff has to be purged before you contemplate replacing the four damper accumulator globes because if you've got glycol ethers, detergents and/or water in the system it's very harmful and will ultimately cause components to failure, sludge build up, rust, varnishes to form. If it were mine I'd run a gallon of the lowest viscosity R&O mineral based hydraulic fluid you can locate (the general purpose stuff is much cheaper than AHC fluid) through as an intermediary fluid - do two full drain and refills over a few days/miles and when the stuff you bleed out is clear and similar in color to the stuff that goes in then you'll want to then dump it and replace it with proper AHC fluid. With the system internally cleaned you'd now consider new, or serviceable take off, globes if you're still only returning four grads L to H.

 

[uHu]

@hagani - You are jumping around the threads, not very nice, but I managaged to follow...
With 4 grads' and a bouncy ride -- sounds like your spheres/accumulators are shot.
"Coffee with milk" sounds like my ahc when it had been topped up with brake fluid. It killed the membranes in the spheres -- and ahc-fluid with nitrogen looks like foamy double cappucino.
For the front pressure you might have to re-index the torsion bars. You'll find the recipe in here somewhere. FOr the rear -- change the coils.

Edit: Paddo typed faster than me And he wrote all the right words too.
Just wanted to add that reading the pressure with any OBD device works only when the ahc level is changed from Lo to N. Any ahc pressure readings at any other instances, transitions or levels will not give any indication of real ahc pressure. (there are no pressure sensors around the system, only one at the pump).
And then I would like to add on to Paddo's words, that it is important to clean out the system before changing the globes/spheres/accumulators (3 words - same thing).

 

[hagani]

Four graduations on the reservoir going from L to H isn't good, suggests they have failed well and truly.
Reading through your posts it seems you've been able to lower your front pressure from 10.4 (which is abnormally high for a stock vehicle (no bull bar + winch) at an N height of 19.75in/500mm) to 7.5 and have maxed out your adjustment range. Dropping close to 3MPa will take about 15 turns so you'd need to query the torsion bar indexing or the accuracy of the pressure reading, and maybe contaminated gassy fluid compressing. That screen shot of your pressures - is that from a Snap On scan tool? Also, when you're doing your pressure reading you go from L to N and wait 30 seconds or so for the system to settle and for the height accumulator to finish charging. Do this a couple of times to ensure you get a consistent reading. The alternate - most accurate method - of measuring neutral pressures is with a gauge fitted directly to a damper bleeder. But reading pressure data from the ECU should be sufficiently accurate for most, but I've only used Techstream and have seen results from an iCarsoft 905.
Describing the fluid as milky coffee colored isn't healthy either. Old AHC fluid tends to goes dark, cola colored. If there's micro bubbles entrained it will be definitely lighter but not really a milky coffee. Any chance that brake fluid or washer fluid was added to the reservoir? Regardless, that old stuff has to be purged before you contemplate replacing the four damper accumulator globes because if you've got glycol ethers, detergents and/or water in the system it's very harmful and will ultimately cause components to failure, sludge build up, rust, varnishes to form. If it were mine I'd run a gallon of the lowest viscosity R&O mineral based hydraulic fluid you can locate (the general purpose stuff is much cheaper than AHC fluid) through as an intermediary fluid - do two full drain and refills over a few days/miles and when the stuff you bleed out is clear and similar in color to the stuff that goes in then you'll want to then dump it and replace it with proper AHC fluid. With the system internally cleaned you'd now consider new, or serviceable take off, globes if you're still only returning four grads L to H.

@PADDO Thank you for so informative input as always. Screenshot from MATCO Maximus2 computer. I did take few readings on the pressure as you suggested. Right now I have 2 canisters of OEM AHC Fluid on hand (5liters total). Might as well do the flush with OEM fluid. And as I got from your post contaminated fluid possibly can be a reason for the higher pressure. Correct? I bought this truck used (initially we had a chat with you on clublexus.com, but that forum has almost no activity so I jumped here) and I have no history or any idea who worked on it and what possibly they may add to the fluid in the past.

 

[hagani]

@hagani - You are jumping around the threads, not very nice, but I managaged to follow...
With 4 grads' and a bouncy ride -- sounds like your spheres/accumulators are shot.
"Coffee with milk" sounds like my ahc when it had been topped up with brake fluid. It killed the membranes in the spheres -- and ahc-fluid with nitrogen looks like foamy double cappucino.
For the front pressure you might have to re-index the torsion bars. You'll find the recipe in here somewhere. FOr the rear -- change the coils.

Edit: Paddo typed faster than me And he wrote all the right words too.
Just wanted to add that reading the pressure with any OBD device works only when the ahc level is changed from Lo to N. Any ahc pressure readings at any other instances, transitions or levels will not give any indication of real ahc pressure. (there are no pressure sensors around the system, only one at the pump).
And then I would like to add on to Paddo's words, that it is important to clean out the system before changing the globes/spheres/accumulators (3 words - same thing).

@uHu Sorry for jumping from one thread to another. I started on the thread with common suspension problems and jumped here where we talking about changing fluid in particular. Didn't mean to cause any inconvenience.

I did re-adjusted TB. They are maxed out now.

 

[PADDO]

@PADDO Thank you for so informative input as always. Screenshot from MATCO Maximus2 computer. I did take few readings on the pressure as you suggested. Right now I have 2 canisters of OEM AHC Fluid on hand (5liters total). Might as well do the flush with OEM fluid. And as I got from your post contaminated fluid possibly can be a reason for the higher pressure. Correct? I bought this truck used (initially we had a chat with you on clublexus.com, but that forum has almost no activity so I jumped here) and I have no history or any idea who worked on it and what possibly they may add to the fluid in the past.

Hydraulic fluid that's been contaminated with water for example will negatively affect the systems load carrying ability because of compressibility, change the viscosity of the fluid and change it's thin film characteristics to name just a few problems it causes. It certainly may contribute to what would appear to be high front neutral pressures but I'd be very surprised it's 100% responsible. I'd cycle your new AHC fluid through to purge the old stuff out and see where you're at pressure wise then. 30mm trim spacers for the rear should lower your rear pressure about 0.5MPa and combined with new rear coils you should get the rear pressure down to the lower end of the design range. This will also positively affect the front pressure too, but not to the extent you appear to need so reindexing the torsion bars is probably required. With your fluid clean and serviceable and good front and rear pressures then make the call on replacement damper accumulators.

 

[hagani]

Hydraulic fluid that's been contaminated with water for example will negatively affect the systems load carrying ability because of compressibility, change the viscosity of the fluid and change it's thin film characteristics to name just a few problems it causes. It certainly may contribute to what would appear to be high front neutral pressures but I'd be very surprised it's 100% responsible. I'd cycle your new AHC fluid through to purge the old stuff out and see where you're at pressure wise then. 30mm trim spacers for the rear should lower your rear pressure about 0.5MPa and combined with new rear coils you should get the rear pressure down to the lower end of the design range. This will also positively affect the front pressure too, but not to the extent you appear to need so reindexing the torsion bars is probably required. With your fluid clean and serviceable and good front and rear pressures then make the call on replacement damper accumulators.

@PADDO
Ok.. Here is the deal..

I did replace the fluid following your method.. First I bled height accumulator. Here is what I got from it:

Then I bled LH Front accumulator, but got almost nothing out of it (maybe 50ml - see photo) and truck never lowered completely on the bumps. Here is the picture:

After that I bled Rear DH accumulator and truck went down significately and more fluid coming out the bleeder (but different color):

Then I start the engine, went up and down a few times and checked the pressure. Pressure was pretty much the same:

So I decided to do it again since I had an extra fluid. Next round fluid from accumulator came out pinkish but with lots of bubles:

Same small amount came out of the fron driver side bleeder nd truck did not lower on the bumps and same amount and same color like first time came out of rear driver side accumulator.

I guess at this point I am running out of options and replacing globes looks like unavoidable process..

 

[Dannyboy lx470]

Here in the UAE the hydraulic fluid we buy from toyota genuinen is a gold yellow colour in the USA it's red now.

 

[PADDO]

@PADDO
Ok.. Here is the deal..

I did replace the fluid following your method.. First I bled height accumulator. Here is what I got from it:

Then I bled LH Front accumulator, but got almost nothing out of it (maybe 50ml - see photo) and truck never lowered completely on the bumps. Here is the picture:

After that I bled Rear DH accumulator and truck went down significately and more fluid coming out the bleeder (but different color):

Then I start the engine, went up and down a few times and checked the pressure. Pressure was pretty much the same:

So I decided to do it again since I had an extra fluid. Next round fluid from accumulator came out pinkish but with lots of bubles:

Same small amount came out of the fron driver side bleeder nd truck did not lower on the bumps and same amount and same color like first time came out of rear driver side accumulator.

I guess at this point I am running out of options and replacing globes looks like unavoidable process..

That fluid looks very rough! Who knows what's been added but it doesn't appear to be 100% mineral oil. I bet you'll find your front accumulators are blown at a minimum. That would explain the reduced fluid output (from a "normal" L height to the bumps should push out about 400ml) and as you've got the TBs cranked to max that may be holding the height up too and not letting it fall to the bumps. It's likely that a front accumulator blew giving a nasty ride and then someone saw the low fluid level and added something to "fix it" and you've had cascading problems. I note your height accumulator pressure is creeping up too. Could be just as a result of all that gas in the system+torsion bars+coils not lifting their share or it could also indicate internal leakage past the floating piston in the height accumulator.

 

[hagani]

@PADDO

Ok, ordered 4 globes yesterday, should get it sometime next week. How can I be sure that when I install new globes I still don't have contaminated fluid in the system that will ruin new globes?

Because just by looking at the fluid that came out of the rear on the second bleeding it doesn't look healthy to me. Should I just keep bleeding it?

 

[PADDO]

Yes keep running fluid through the system. Drive and cycle the height between bleeds. Consider running a gallon of cheaper R&O general purpose hydraulic fluid through once or twice before finishing with proper AHC fluid prior to fitting your new globes. Did you order OEM or the modded Citroen globes from the UK?

 

[hagani]

Yes keep running fluid through the system. Drive and cycle the height between bleeds. Consider running a gallon of cheaper R&O general purpose hydraulic fluid through once or twice before finishing with proper AHC fluid prior to fitting your new globes. Did you order OEM or the modded Citroen globes from the UK?

I ordered used globes (with relatively low usage) from one of the guys who pulled the AHC.

One thing - truck sits at my repair facility, I don't drive it. Nor before, nor between the bleeds.

 

[PADDO]

I think it's important to ensure the vehicle's height system is very well cycled to get as much old fluid and any solid contamination and sludges into solution so it can be drained. If static drain and refills are your only option then that will have to do but if it were mine I'd take it for a drive, compress and extend the shock actuators, cycle it up/down and get the fluid and system nice and hot then drain/refill.

 

[uHu]

If I suspected contamination, I would take the shocks off and empty them, and the lines between actuators and shocks. Impossible to get this part of the fluid out effectively in any other way. (Rear shocks can be a pain to remove)
Flush shocks once with new fluid, then fill them up while compressed (not extended) before re-installing.
You'll need a big syringe or similar and a couple of pieces of clear hose to do this.

Edit:
Could be easier to bleed the system if you filled the shocks while extended, and then attach the top first and push the excess fluid out through the pipe and bleed nipple when attaching the bottom end. I never tried this method, but next time....

 

[PADDO]

If I suspected contamination, I would take the shocks off and empty them, and the lines between actuators and shocks. Impossible to get this part of the fluid out effectively in any other way. (Rear shocks can be a pain to remove)
Flush shocks once with new fluid, then fill them up while compressed (not extended) before re-installing.
You'll need a big syringe or similar and a couple of pieces of clear hose to do this.

Edit:
Could be easier to bleed the system if you filled the shocks while extended, and then attach the top first and push the excess fluid out through the pipe and bleed nipple when attaching the bottom end. I never tried this method, but next time....

Agree the best approach is to dissemble the system down as far as achievable and manually expel any remaining fluid from the shock actuators off vehicle. The reason I advocate multi drain/refills here is that it's much more likely to be achieved {very doable by most} as you just need general purpose light weight hydraulic fluid, 10mm spanner, drain pipe and jug and anyone can do it in their own garage or driveway. A front shock's capacity is only 200ml, and rear is 175ml, and when compressed down to the bumps there might be 10% maybe 20% remaining. With several thorough drain/refills you'll get that pretty much diluted out - but likely not as perfect as off vehicle cleaning I'll acknowledge. I'll drop my vehicle down to the bumps and take some measurements on how compressed the shocks are just to get a real idea of the actual fluid remaining, same with the damper assemblies in that I'll fill a spare unit to see just how much fluid they retain.

 

[flintknapper]

If I suspected contamination, I would take the shocks off and empty them, and the lines between actuators and shocks. Impossible to get this part of the fluid out effectively in any other way. (Rear shocks can be a pain to remove)
Flush shocks once with new fluid, then fill them up while compressed (not extended) before re-installing.
You'll need a big syringe or similar and a couple of pieces of clear hose to do this.

Edit:
Could be easier to bleed the system if you filled the shocks while extended, and then attach the top first and push the excess fluid out through the pipe and bleed nipple when attaching the bottom end. I never tried this method, but next time....

Would the shocks have to be physically removed, or could low pressure compressed air be used to expel the fluid from the shocks (and lines)?

I would think once certain lines are removed, it would be a simple matter to apply compressed air to any openings (unless valved).

 

[uHu]

In case of contamination with some other fluid than ahc-fluid:
Remove shocks completely. Turn upside down and "pump" them empty. They are just simple hydralic rams. Fill them up again with fresh fluid, and pump/drain again. Then fill them up as much as you dare (for not spilling too much when fitting) and put them back into place.

 

[Dannyboy lx470]

Guys going to attempt to drain and replace my fluid with PADDOS easy step way.Just a question do have to remove that filter thing in the AHC box were you fill up does it come off.

 

[looking4lc]

it does come off but you can fill thru it.

 

[Dannyboy lx470]

it does come off but you can fill thru it.

Ok thankyou. I wanted to empty old fluid out from box and thought would be easier to take it off.

 

[Dannyboy lx470]

Guys just a question do I need to put stands under the car when i bleed the system.