AHC: Where is the air?

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RocketCityCrzrs

RocketCityCrzrs

Supporting Vendor
SILVER Star
10 Year
Joined
Nov 14, 2013
Threads
68
Messages
580
Location
Huntsville, AL
Website
www.rocketcitycruisers.com
SO, I can apparently rebuild engines and restore 40's but cant get air out of a damn hydraulic system. I wanted to query the braintrust to see if someone can spot what i am missing. Bought a 570 last week and had no record of an AHC flush being done on it. I have done a few of them before so no big issue i thought.....
Typical, cycle through each setting, lower the truck, open the bleeders until it crushes my face, drain and refill reservoir (i would like to meet the jackass that put it behind the tire). So all of that being basically simple one banana job. Started the truck in its lowest setting to let the AHC level out and refill the accumulators and thats where the issues start. The pump kicked in and got increasingly louder and louder until i could hear it whining across the shop but the truck never adjusted height. finally it timed out and threw a "CHECK 4wd AHC SYSTEM" code. hmm, weird, shut off truck gave it a few minutes for the pump to cool off, started the truck again and it sounded exactly the same, loud and high pitched whine. A buddy was over working on his mini truck and said, welp sounds like the pump is cavitating from an air pocket in it. Cool, i can address that. Cracked open the line coming out of the pump and ran the pump again so i could see fluid shooting out. Tightened the line while it was running and the pump started to calm down and behave a little better. Awesome, problem addressed. WRONG.

Now the rear of the truck is starting to level out but the front wont move. crack open the bleeders again and let a little fluid out to see if i get an air pocket, nothing. proceed to start the truck and turn it off for about an hour back and fourth dropping fluid and crap (including the 5th accumulator behind the resonator), until the front FINALLY started to level out slowly. after about 4 hours (of what should have been a 45 minute job) the truck seems to be cycling through the settings albeit VERY slow to bring the front up.

Driving yesterday normally, threw the check AHC code again. Got home and tried to raise it to H and the rear end pops to attention like a donkey on viagra but the front isnt moving again. SO all of that novel being written down, give me some thoughts. Air in the system still? Pump failing? Something else? I should close up shop and sell ice to eskimos?
 
When you are trying to get it to lift, from the initial bleed downs, are you leaving the cap off the reservoir fill tube? I think when doing this initial big lifts there is a check valve there creating vacuum when the pump is going.

this topic has been glossed over here before, but isn’t generally included in fluid swap posts. I’m not sure if there is a common failed part at the reservoir, so it only applies in some cases, or if it is universal.
 
@lx200inAR initially i had the cap off the filler tube, and then noticed the rubber O ring on the cap and had the same thought. Maybe it was trying to either build vacuum or pressure in the tank so i closed it all back up and tried again. That seemed to help initially but ultimately didn't make much difference. I combed through the AHC System Sticky on the main page but didnt really have a whole lot of luck finding similar problems
 
Here's one example...it's where i posted having disconnected the cover with a little backstory, but another user confirming that they needed to do it as well. My post he is replying to has the retelling of changing my globes, which is probably similar to what you did, so maybe some useful info in there. I definitely had similar issues as far as it taking a long time for the system to get settled again after doing a fluid exchange.

It's definitely not easy to wade through the 2-3 very long AHC threads now...

 
Last edited:
I meant to post this earlier too, here is the only data TS is providing on it.
TS-570.webp
 
Couple things.

1) Are you initiating bleeding from AHC low position? Not sure that's advised as generally you want the AHC system in a higher pressure state to begin bleeding, which is N or I prefer H. Bleed from low would be like bleeding brakes without someone applying pedal pressure. I don't think this is the issue but it could have brought in more air into the system.

2) What fluid are you using and when did you buy it? There was AHC fluid stock about 1-2 yrs ago sold in the 1L plastic bottles that had contaminantes. Enough to clog hte inlet filter on the AHC pump
3) General debris/dirt entering the resevoir causing the same issue as above.

forum.ih8mud.com

AHC fluid contaminated

Was trying to put on stiffer springs for my 570, (which didn't work with the AHC because they were too stiff), and I had to scavenge a quart of AHC fluid from a dealer 100 miles away. Refilling resevoir and had this at the bottom. WTF!?
forum.ih8mud.com forum.ih8mud.com

Here's a deeper dive into the pump and clog issue
forum.ih8mud.com

HELP! AHC Pump Issue After Reservoir Drain/Refill

forum.ih8mud.com forum.ih8mud.com
 
I also suspect that if you're filling with the in-neck filter still in- you can have vacuum issues as well- since the fluid is creating a bit of a seal on and around the neck filter.

Total speculation here, but given we are seeing a lot of vacuum I'd like to keep the reservoir completely open to eliminate that possibility.
 
A little more info, as I am out here with it again today. In N I bled a little fluid from the two front accumulators without issue or air. Started the truck and now I'm back a whining pump with no movement. Dropped it to L thinking it might be angry because of the height difference but no change. Mud won't let me include the video of the pump sound but it's quite loud

I tried popping the cap on the pump but it didn't seem to have any vacuum. Left it off (verified fluid level as well) and cycled truck again. No change, lound pump no pressure.
 
RocketCityCrzrs said:
Also, the ahc fluid is from 21 but don't see a date on the bottle for when it was filledI
Click to expand...

Is it the black plastic cans then? If you have any that you haven't used yet, you may want to open and pour into a clear vessel so you can see if it's the bad stuff. Hope that isn't your issue. (I"ll add, just because it's black cans doesn't for sure mean it's bad, but the bad fluid has only come from the black cans).
 
Zill said:
I thought the bad fluid was coming from the plastic bottles? Not the cans?
Click to expand...
I called it a “can”, but was referencing the black plastic bottles. Most dealers only stock the 2.5l metal can now.
 
OK all so, resolution was pulling the pump and cleaning the filters. Ultimately what is seems has happened was the fluid was in fact contaminated and as the pump tried to refill the accumulators after the drain, it pulled the contaminants into the filters and caused the pump not to build pressure. Having lots of aside conversations with @lx200inAR he was able to catch and point out my pressure from the pump was only 1.9 mPa when it is supposed to be in the high 7s. I pulled the pump from the truck and took the reservoir off to reveal the inside bits. Pulled the allen screws out and began to clean (pix attached of the problem). After assembly i did a bench test to prime it and it seemed to be functioning normal and was quiet again. I used the link below as a guide to get this done and a HUGE shout out to @lx200inAR for bouncing ideas with me all day.
I installed the pump and ran the new AHC fluid through the inlet filter into a clear bottle, then back through the inlet filter to fill the reservoir (just to be safe). System seems happy now. I am going to give it a week or so then probably do another flush and fill with fluid from the metal can and hopefully wrap this issue up.

Link:
AHC Pump Fun - Disassembly and Clean - Verbose Edition - https://forum.ih8mud.com/threads/ahc-pump-fun-disassembly-and-clean-verbose-edition.1254063/

Filter on both sides of this aluminum block held in by a brass ring. Very obvious when you know what to look for:

20230404_125842.webp
 
Good stuff.
 
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