AHC Accumulator Bleed Valve -- broke off.

[bram]

Just a quick note regarding the amount of pressure in the AHC system. I recently changed out all four globes on my LC. I failed to adequately bleed off the pressure on the RR globe before unscrewing it. ( I bled through the bleed nipple prior to unscrewing the globe and thought I was good).

When I was down to just a couple threads left on the globe, it shot loose with a bang and sprayed fluid 20 feet across the garage, ripping the globe from my grasp in the process - good thing my hand was on the side of the globe, as it would have easily broken / crushed my hand when it popped off.

Other than using the bleeder screw on the actuator, how else could you relieve the pressure prior to unscrewing the globes?

 

[sonk76]

Any updates on best practice for how to address broken Accumulator Bleed Valve.?

(replacing all Globes with new OEM ones and figured this might be a good time to take care of this as well... that said, if trying to fix this will only cause more headaches, I'm happy to let sleeping dogs be...)

 

[YvesNL]

I recently did some work on my accumulator (and rusted hydraulic lines).

If you unplug the solenoid connector from the main accumulator you can apply 12v dc to the coil/solenoid.
This will relieve the pressure that is in the accumulator, this is what worked for me but YMMV.

 

[NoTempoLimit]

I just joined this unfortunate club. I have a couple of questions:

If you lower the system to the L position and then raise the truck on a lift (by the frame) causing the shocks to extend all the way, would that get the hydraulic system pressure down to a minimum?

Is there a procedure somewhere for removing the height accumulator?

Has anyone figured out part numbers for the bleeder screws?

 

[GTS550]

Another thread somewhere here on MUD quoted new bleeder plugs as Toyota part no. 49189-60010 and bleeder caps as part no. 49177-60010.

 

[IndroCruise]

I just joined this unfortunate club. I have a couple of questions:

If you lower the system to the L position and then raise the truck on a lift (by the frame) causing the shocks to extend all the way, would that get the hydraulic system pressure down to a minimum?

Is there a procedure somewhere for removing the height accumulator?

Has anyone figured out part numbers for the bleeder screws?

 

[IndroCruise]

I just joined this unfortunate club. I have a couple of questions:

If you lower the system to the L position and then raise the truck on a lift (by the frame) causing the shocks to extend all the way, would that get the hydraulic system pressure down to a minimum?

Is there a procedure somewhere for removing the height accumulator?

Has anyone figured out part numbers for the bleeder screws?

The Height Control Accumulator is recharged by the AHC pump as soon as it has finished a raise from “LO” to “N” or from “N” to “HI”. When the AHC dashboard light has stopped blinking indicating that the raise has finished, the AHC Pump then continues operate for a period (around 15 seconds in my case but it can be longer) while the pump recharges the Accumulator. When done, the solenoid valve at the Accumulator can be heard (and felt with the hand) to close and the AHC pump is heard to stop. The levelling valves in the Control Valve Assembly also are closed and this can be heard/felt if all are operating correctly. The process also can be observed in real time on Techstream during a raise.

The solenoid valve at the Accumulator remains closed and the Accumulator remains fully pressurised until called upon to raise the vehicle as directed by the Electronic Control Unit (ECU) and the switch on console operated by the driver. The Accumulator plays no part in damping or other suspension movements.

If not already seen, the relevant sections of the attachment which describe the operation of AHC/TEMS components may be helpful.

In the movement contemplated ….

“If you lower the system to the L position and then raise the truck on a lift (by the frame) causing the shocks to extend all the way, would that get the hydraulic system pressure down to a minimum?”

…. the solenoid valve on the accumulator will not be caused to open. Therefore the accumulator will remain fully pressurised (unless the valve is weak and some leakage occurs). Other parts of the system may be at a lower pressure but this does not help with the Height Control Accumulator.

This is why @YvesNL has described in post #23 above his experience of powering the Accumulator solenoid valve to cause the valve to open and allow discharge of the Accumulator pressure and fluid into the AHC system. (This may cause the vehicle to raise, or the AHC Fluid may simply go through the Return Valve in the AHC Pump Assembly on its way back to the AHC Tank).

Obviously, the idea is to leave the Accumulator depressurised without recharge, just as would happen if Accumulator bleeding was possible and not prevented by the broken bleeder screw. I have not personally done the process mentioned by @YvesNL so I cannot speak for the method. The method would cause all manner of DTC’s to show up because when the pressure sensor at the AHC Pump assembly detects low pressure in the Accumulator, the ECU would try to cause the AHC Pump to operate and recharge the Accumulator. @YvesNL does not say so but it may be that he proceeded with the engine and AHC system switched OFF, or maybe disconnected power to the AHC Pump by pulling its power connector to stop recharge of the Accumulator from happening.

I have wondered about whether very carefully cracking open the pipe connections into and out of the Accumulator might release its stored pressure (and make a huge mess!) but I suspect that this would not work if flow in and out of the Accumulator is controlled by the solenoid valve as I expect. Others with more experience working on the Height Control Accumulator may be able to offer clearer guidance.

Once depressurised, removal of the Height Control Accumulator is fiddly but do-able and is described in the FSM and in various IH8MUD posts. The hard part is removing two bolts which clamp the Accumulator bracket to the top of the chassis rail where working room is tight. Otherwise it is straightforward unless corrosion is an issue.

 

[NoTempoLimit]

Once depressurised, removal of the Height Control Accumulator is fiddly but do-able and is described in the FSM and in various IH8MUD posts. The hard part is removing two bolts which clamp the Accumulator bracket to the top of the chassis rail where working room is tight. Otherwise it is straightforward unless corrosion is an issue.

Thanks for posting that PDF I will study it. It's the first time I've seen a document that covers how the entire AHC system operates.

Unfortunately I KNOW corrosion will be a problem, or that bleeder would not have got stuck. I'll periodically squirt Kroil into it and I'm going to make a little cover that will block it off from any road spray this winter so it does not get worse.

If I had to guess I'd say that the system had been bled at least one time before, but they didn't bleed the height accumulator. That might explain why the bleeders on the corner units all opened up (not super easy but they opened), but the height control bleeder was galled/siezed.

I get the feeling that proper repair of my AHC system would involve de-pressurizing the entire system. At that point it would make sense to replace as many wear components as possible (globes, shocks, etc). Regrettably I won't be able to do a job like that any time soon.

 

[CanadianRockyCruiser]

I broke my cylindrical accumulator pump assembly bleeder years ago... The four corners bleed fine. I've just kept up with regular system flushes, using the four globes. Are there any downfalls to just cycling the system from H to L frequently and assuming that I'm getting enough fluid circulating, when bleeding every 20,000 km or so?

 

[cruiserpatch]

The Height Control Accumulator is recharged by the AHC pump as soon as it has finished a raise from “LO” to “N” or from “N” to “HI”. When the AHC dashboard light has stopped blinking indicating that the raise has finished, the AHC Pump then continues operate for a period (around 15 seconds in my case but it can be longer) while the pump recharges the Accumulator. When done, the solenoid valve at the Accumulator can be heard (and felt with the hand) to close and the AHC pump is heard to stop. The levelling valves in the Control Valve Assembly also are closed and this can be heard/felt if all are operating correctly. The process also can be observed in real time on Techstream during a raise.

The solenoid valve at the Accumulator remains closed and the Accumulator remains fully pressurised until called upon to raise the vehicle as directed by the Electronic Control Unit (ECU) and the switch on console operated by the driver. The Accumulator plays no part in damping or other suspension movements.

If not already seen, the relevant sections of the attachment which describe the operation of AHC/TEMS components may be helpful.

In the movement contemplated ….

“If you lower the system to the L position and then raise the truck on a lift (by the frame) causing the shocks to extend all the way, would that get the hydraulic system pressure down to a minimum?”

…. the solenoid valve on the accumulator will not be caused to open. Therefore the accumulator will remain fully pressurised (unless the valve is weak and some leakage occurs). Other parts of the system may be at a lower pressure but this does not help with the Height Control Accumulator.

This is why @YvesNL has described in post #23 above his experience of powering the Accumulator solenoid valve to cause the valve to open and allow discharge of the Accumulator pressure and fluid into the AHC system. (This may cause the vehicle to raise, or the AHC Fluid may simply go through the Return Valve in the AHC Pump Assembly on its way back to the AHC Tank).

Obviously, the idea is to leave the Accumulator depressurised without recharge, just as would happen if Accumulator bleeding was possible and not prevented by the broken bleeder screw. I have not personally done the process mentioned by @YvesNL so I cannot speak for the method. The method would cause all manner of DTC’s to show up because when the pressure sensor at the AHC Pump assembly detects low pressure in the Accumulator, the ECU would try to cause the AHC Pump to operate and recharge the Accumulator. @YvesNL does not say so but it may be that he proceeded with the engine and AHC system switched OFF, or maybe disconnected power to the AHC Pump by pulling its power connector to stop recharge of the Accumulator from happening.

I have wondered about whether very carefully cracking open the pipe connections into and out of the Accumulator might release its stored pressure (and make a huge mess!) but I suspect that this would not work if flow in and out of the Accumulator is controlled by the solenoid valve as I expect. Others with more experience working on the Height Control Accumulator may be able to offer clearer guidance.

Once depressurised, removal of the Height Control Accumulator is fiddly but do-able and is described in the FSM and in various IH8MUD posts. The hard part is removing two bolts which clamp the Accumulator bracket to the top of the chassis rail where working room is tight. Otherwise it is straightforward unless corrosion is an issue.

I have recently encountered the same "bleeder screw broken off" issue and purchased a second-hand HCA. It arrived with the bleeder screw in place and the smaller of the tubes still in tact and connected. The larger tube was cut by the person removing the HCA.

I believe this might answer your question about whether cracking these lines would relieve pressure on the HCA or if the solenoid must be activated to expel fluid in accordance with the @YvesNL method.

I will attempt to secure the new HCA and use the bleeder screw to relieve pressure on it. I will update you with results.

I contacted the seller of the new HCA and he did not attempt to depressuirze before shipping from Florida to Atlanta. I'm glad it did not explode.


As a reminder to all readers, safety should be considered above all when working on this system. High pressure fluids can potentially be dangerous and should be treated with caution.

 

[IndroCruise]

I have recently encountered the same "bleeder screw broken off" issue and purchased a second-hand HCA. It arrived with the bleeder screw in place and the smaller of the tubes still in tact and connected. The larger tube was cut by the person removing the HCA.

I believe this might answer your question about whether cracking these lines would relieve pressure on the HCA or if the solenoid must be activated to expel fluid in accordance with the @YvesNL method.

I will attempt to secure the new HCA and use the bleeder screw to relieve pressure on it. I will update you with results.

I contacted the seller of the new HCA and he did not attempt to depressuirze before shipping from Florida to Atlanta. I'm glad it did not explode.


As a reminder to all readers, safety should be considered above all when working on this system. High pressure fluids can potentially be dangerous and should be treated with caution.

If not already seen, the discussion and background information on Height Control Accumulator issues and bleeder valve problems at Post #183 through to Post #188 also may be of assistance at the link below:

The ABCs of AHC - How to Measure, Flush, and Adjust all in one place - https://forum.ih8mud.com/threads/the-abcs-of-ahc-how-to-measure-flush-and-adjust-all-in-one-place.1211999/page-10#post-13777003

And yes, the Safety Reminders are worth repeating again and again -- it is important to avoid risks of eye penetration and skin penetration by escaping hydraulic fluids, as well as taking the usual safety precautions when working on the AHC suspension components:

Wear Industrial strength eye protection and skin protection whenever dealing with hydraulic fluids under pressure. In the absence of relevant personal knowledge and competencies, always obtain qualified workshop help.

Use locked vehicle stands under chassis rails whenever a person works under a vehicle on the AHC system to ensure that the vehicle body cannot descend onto a human body.

It would be good to read an update on your progress in due course and also to read about similar experiences from other IH8MUD Members.

 

[cruiserpatch]

To answer previous questions about loosening the inlet and outlet tubes (No. 2 and No. 6) from the HCA, I have confirmed that doing so will NOT release pressure from the accumulator.

I was recently shipped a replacement HCA because the bleeder screw broke off in mine. Upon receipt of the replacement HCA, I bled it with the bleeder screw and about 16 ounces of fluid came out under pressure. I'm glad the HCA did not explode during shipping from Florida to Atlanta.

I bled it with both the inlet (larger tube) and outlet (smaller) tubes removed completely from the HCA.

 

[blips]

Bled my AHC and damned if this didn't happen to me too. I did the same as others here and bled the four corners and moved on. At first on testing the system I thought I was screwed. It took forever to raise from L to N. Then just kept blinking at me from N to H. I inspected things. No leakage at the accumulator screw, but did find some leakage on the PS bleeders, which were also both missing the covers and seem quite corroded. Re-bled a bit and tightened them up good and tight. System works better than ever now, raising from L to N in just under 10 seconds and N to H in a little over 10 seconds. Awesome.

Question: has anybody successfully relieved the accumulator pressure and put in a new bleeder? Proven methods? Thinking about replacing all the bleeder screws next time I do the AHC flush. Or, should I let sleeping dogs lie?

 

[NoTempoLimit]

Question: has anybody successfully relieved the accumulator pressure and put in a new bleeder? Proven methods? Thinking about replacing all the bleeder screws next time I do the AHC flush. Or, should I let sleeping dogs lie?

After I did a 4-corner bleed on mine (my HCA bleeder sheared right off). Afterward, I noticed that the damping felt much better. But it did not last, not even a couple of days. I'd really like to get that "new shocks" feeling back.

I'm going to have to deal with this HCA bleeder issue eventually. Prob. going to have to give the job to someone with a lift.

Getting frozen sheared off threaded fasteners out is not easy. Sometimes you succeed and sometimes it's just a fail. But the one thing that I have found is CRUCIAL is that your setup has to be RIGID. It can't be done hand-held.

I've had success in removing sheared fasteners by drilling them out on my milling machine at high speed (3000 rpm - I'd go higher if I could) using a carbide drill bit (which usually breaks in the process - use resharpened circuit board drills). I'm using an optical scope to align precisely on the center of the stub of the screw within <0.001".

Can't do any of that hand held under a LandCruiser that's up on jackstands....

 

[cruiserpatch]

After I did a 4-corner bleed on mine (my HCA bleeder sheared right off). Afterward, I noticed that the damping felt much better. But it did not last, not even a couple of days. I'd really like to get that "new shocks" feeling back.

I'm going to have to deal with this HCA bleeder issue eventually. Prob. going to have to give the job to someone with a lift.

Getting frozen sheared off threaded fasteners out is not easy. Sometimes you succeed and sometimes it's just a fail. But the one thing that I have found is CRUCIAL is that your setup has to be RIGID. It can't be done hand-held.

I've had success in removing sheared fasteners by drilling them out on my milling machine at high speed (3000 rpm - I'd go higher if I could) using a carbide drill bit (which usually breaks in the process - use resharpened circuit board drills). I'm using an optical scope to align precisely on the center of the stub of the screw within <0.001".

Can't do any of that hand held under a LandCruiser that's up on jackstands....

When I bled the 4 corners I sheered my HCA bleeder clean off as well (see previous posts).

I bought a used HCA and swapped it out for the old one. During that process the large line into the HCA rounded off so I replaced the line from the HCA to the pump motor.

I do not have a lift or a garage. I was able to do all of that on my driveway (not recommended. it was a PITA bigger than I think most professionals would have ever agreed to).

I'm driving a '99 and the ride comfort is impeccable. It feels like I'm gliding on air at 70 mph. I barely feel the road.

If you can fix it, do it, but it's not easy and I've never heard of anyone with a high mileage truck who was able to bleed the HCA successfully.

Replace the bleeder screws and torque them to spec. If you have to overtorque them to stop the leaks it is already too late. Your threads are probably whack.

That said, if you're cool tightening the sh!t out of it and calling it a day, i don't blame you. Its a pain sometimes and parts aren't cheap.

Patch

 

[suprarx7nut]

Bled my AHC and damned if this didn't happen to me too. I did the same as others here and bled the four corners and moved on. At first on testing the system I thought I was screwed. It took forever to raise from L to N. Then just kept blinking at me from N to H. I inspected things. No leakage at the accumulator screw, but did find some leakage on the PS bleeders, which were also both missing the covers and seem quite corroded. Re-bled a bit and tightened them up good and tight. System works better than ever now, raising from L to N in just under 10 seconds and N to H in a little over 10 seconds. Awesome.

Question: has anybody successfully relieved the accumulator pressure and put in a new bleeder? Proven methods? Thinking about replacing all the bleeder screws next time I do the AHC flush. Or, should I let sleeping dogs lie?

Personally, I'd start sourcing a used accumulator assembly and verify with the person that the bleeder isn't frozen. Then swap at your convenience. Or pony up for a brand new one if you're committed to the system long term. To relieve pressure, I wonder if you could very carefully dremel a slot in the remaining stud and then chisel it unscrewed. Not a fun task.

PSA to anyone with old bleeders: change them out. New bleeders are very cheap. A broken one is a PITA.

When I bled the 4 corners I sheered my HCA bleeder clean off as well (see previous posts).

I bought a used HCA and swapped it out for the old one. During that process the large line into the HCA rounded off so I replaced the line from the HCA to the pump motor.

I do not have a lift or a garage. I was able to do all of that on my driveway (not recommended. it was a PITA bigger than I think most professionals would have ever agreed to).

I'm driving a '99 and the ride comfort is impeccable. It feels like I'm gliding on air at 70 mph. I barely feel the road.

If you can fix it, do it, but it's not easy and I've never heard of anyone with a high mileage truck who was able to bleed the HCA successfully.

Replace the bleeder screws and torque them to spec. If you have to overtorque them to stop the leaks it is already too late. Your threads are probably whack.

That said, if you're cool tightening the sh!t out of it and calling it a day, i don't blame you. Its a pain sometimes and parts aren't cheap.

Patch

My bleeder at 225k was still in great shape. I think it's really hit or miss. If nobody has touched it in 20 years and it's a rusty you'll be in tough shape compared to a well maintained system that's rust free.

 

[bobNoobie]

hellow I join the club here.. the broken bleeder club. wish me luck

 

[suprasvobodea]

When I bled the 4 corners I sheered my HCA bleeder clean off as well (see previous posts).

I bought a used HCA and swapped it out for the old one. During that process the large line into the HCA rounded off so I replaced the line from the HCA to the pump motor.

I do not have a lift or a garage. I was able to do all of that on my driveway (not recommended. it was a PITA bigger than I think most professionals would have ever agreed to).

I'm driving a '99 and the ride comfort is impeccable. It feels like I'm gliding on air at 70 mph. I barely feel the road.

If you can fix it, do it, but it's not easy and I've never heard of anyone with a high mileage truck who was able to bleed the HCA successfully.

Replace the bleeder screws and torque them to spec. If you have to overtorque them to stop the leaks it is already too late. Your threads are probably whack.

That said, if you're cool tightening the sh!t out of it and calling it a day, i don't blame you. Its a pain sometimes and parts aren't cheap.

Patch

Hello,





I unfortunately have a broken bleeder on my southern LX 470 (Texas-234K miles) too! I thought about trying to drill out the sheared bleeder stub in situ, but - No Tempo LImit posted above is probably correct... drilling out and using an extractor, while on jack stands, lying on your back, and drilling with a hand drill, completely parallel to the stud, is nearly impossible. So...............



I decided to REMOVE the Accumulator.. and what a PITA it is!! Ya'll are right about this procedure.



Ok, so as I'm removing the larger supply tube 14mm, and using a crowfoot, flare wrench, after 2 days soaking in PB Blaster,, than using a MAPP gas torch to heat it, and finally banging ( shock) on the accumulator,.with a BFH....... I managed to get the damn thing loosened & eventually removed. But not without rounding off the sides like (CRUISER PATCH did in a similar post ) The other connection to Accumulator- 10 mm flare nut I also heated with a torch and soaked in PB blaster, and it came out easily.



Hello,

I unfortunately have a broken bleeder on my southern LX 470 (Texas-234K miles) too! I thought about trying to drill out the sheared bleeder stub in situ, but - No Tempo LImit posted earlier is probably correct... drilling out and using an extractor, while on jack stands, lying on your back, and drilling with a hand drill, completely parallel to the stud, is nearly impossible. So...............

I decided to REMOVE the Accumulator.. and what a PITA it is!! Ya'll are right about this procedure.

Ok, so as I'm removing the larger supply tube 14mm, and using a crowfoot, flare wrench, after 2 days soaking in PB Blaster,, then using a MAPP gas torch to heat it, and finally banging ( shock) on the accumulator,.with a BFH....... I managed to get the damn thing loosened & eventually removed. But not without rounding off the sides like (CRUISER PATCH did in a similar post ) The other connection to the Accumulator- 10 mm flare nut I also heated with a torch and soaked in PB blaster, and it came out easily.

Ok, so there's the background ... now my question guys...


There are ( 2 )12 mm bolts ON TOP of the frame rail in addition to the 2 on the side ( which you can easily remove) The fwd one is accessible after removing the pressure globe and the bracket for the running board. HOWEVER... the rear bolt is not accessible on either side of the frame. On the inboard side are 4-5 fluid lines, and on the outboard side, is the accumulator. There is a small gap on the outboard side to move the end of a 12mm wrench, but I don't see how to put the box end over the head of the bolt! This part was installed at the factory BEFORE the body was fixed to the frame ( no thought was given to how to remove those 2 bolts in the future obviously by any mechanic or Ih8MUD groupie like us).
But somehow, several people have removed their accumulators and removed that "hidden " rear bolt.

My question is ..HOW DID YOU DO IT?? Is there a special service tool wrench with two 90-degree "S-" bends I need to make to reach the head of the 12mm aft bolt on top of the frame rail?

 

[cruiserpatch]

Removal of Height Control Accumulator?

So today we had a nice day and I decided to tackle the AHC fluid flush that needed to be done. Things went smoothly up until I tried to bleed the Height Control Accumulator. The bleed screw was completely rusted and ended up snapping right off. I tried drilling and tapping it out but had no...

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