AHC pressure reading

[CapnSpaulding]

It looks like my pressures are a little high. I am getting about 6-7 ticks in fluid change between low and high, and my ride is a bit bouncy so I am thinking I need front globes. The fluid looks brand new as well.
Would that help the pressures at all? I am thinking if not, maybe cranking the TBs up front and maybe King springs in the back would solve the high pressure issue?

 

[craaaazzy]

Search for AHC thread for adjusting it before replacing the globes.

 

[Moridinbg]

Adjust your torsion bars to bring your front pressure to spec. This will probably bring back 2-3 ticks.
Graduation test is only done after the pressure is brought to spec.

 

[suprarx7nut]

I would replace the rear springs unless you know they're less than 10 years old. If the springs are new-ish, another option would be spring spacers to lower that rear pressure a little. King springs will move you 3 MPa or so. That's ok if you plan on adding a rear bumper and a platform or something, but probably overkill if not.

Crank the torsion bars up front and recheck. I'm guessing you'll need 5+ turns.

 

[CapnSpaulding]

Thanks for all the feedback! I will crank the TBs this weekend and peek at the rear springs. I have a feeling they are probably original so I will source a new set if so. I did a little more research the last few days and agree that for my setup, I will be better off going OEM on the springs instead of King springs. It looks like my globes are original, so I think I will still be in for a new set, but I will do this first and retest in techstream as well as check fluid levels. I may also do the 16 step test just for kicks, but will still likely replace all 4 globes if I am having to replace any of them.

 

[Cetus]

Thanks for all the feedback! I will crank the TBs this weekend and peek at the rear springs. I have a feeling they are probably original so I will source a new set if so. I did a little more research the last few days and agree that for my setup, I will be better off going OEM on the springs instead of King springs. It looks like my globes are original, so I think I will still be in for a new set, but I will do this first and retest in techstream as well as check fluid levels. I may also do the 16 step test just for kicks, but will still likely replace all 4 globes if I am having to replace any of them.

I had the same issue and cranked my torsion bars until in spec. That barely increased the ticks in my reservoir but my circumstance may be little different from yours. I ended up replacing all 4 globes and the ride is amazing again. My rear pressure is still little high and my front pressure is low. I'll have to crank the torsion bars to increase front pressure and install new OEM rear springs. Also getting around 14 ticks now if I remember correctly.

 

[Red Beard]

Thanks for all the feedback! I will crank the TBs this weekend and peek at the rear springs. I have a feeling they are probably original so I will source a new set if so. I did a little more research the last few days and agree that for my setup, I will be better off going OEM on the springs instead of King springs. It looks like my globes are original, so I think I will still be in for a new set, but I will do this first and retest in techstream as well as check fluid levels. I may also do the 16 step test just for kicks, but will still likely replace all 4 globes if I am having to replace any of them.

@CapnSpaulding, how did it turn out for you? Did you end up replacing your springs?

I seem to be in the same boat. Pressures are 8.8 and 7.0 for the Front and Rear respectively. I'm planning on doing torsion bars this weekend and seeing how that affects it. Seems like my front globes are "new", or at least, they look newer than the ones in the rear. I'm assuming I'm going to need new springs because they don't look replaced.

 

[ramangain]

When you crank the TBs and front pressures go down, the rear pressure almost always goes down as well. Maybe not linearly, but in the same direction.

 

[blinder52]

This link is helpful.

AHC Info

Note: AHC services are now offered at the Air Down Gear Up shop in Frederick, CO. The owner of YotaMD, Andy, is also a co-owner of ADGU and happy to provide some of the common AHC-related tasks you may be interested in. See the link here for details...

www.yotamd.com

I cranked the TB and added 30mm Ironman spacers to the rear (actually today) and my pressures are down to 5.9 in front and 6 in the rear. Easy and inexpensive.

 

[Red Beard]

This link is helpful.

AHC Info

Note: AHC services are now offered at the Air Down Gear Up shop in Frederick, CO. The owner of YotaMD, Andy, is also a co-owner of ADGU and happy to provide some of the common AHC-related tasks you may be interested in. See the link here for details...

www.yotamd.com

I cranked the TB and added 30mm Ironman spacers to the rear (actually today) and my pressures are down to 5.9 in front and 6 in the rear. Easy and inexpensive.

Yup I have that cheatsheet printed out and watched that video a couple times. The cheatsheet was super helpful for recording the values. Easy to see my pressures are uniformly higher than spec when I see it on the chart that @suprarx7nut put together.

I was just wondering to see if new springs helped the poster here. I guess spacers can't hurt and they're way cheaper than 4 new springs. I think also the torsion bar crank will help with the leveling too, my leftside is lower than my right on the wheel-to-fender heights.

I'm going to flush and crank this weekend. I'll get those spacers ordered as well. How was installing them?

 

[craaaazzy]

Adjusting the bars will only help with pressures, not height as that is dependent on the sensors. I went with spacers myself in the rear instead of springs also. Installing them was cake...jacking up one side of the rear, dropping the rear end (had to unbolt one item as well as keeping an eye on the brake lines as well as the emergency brakes which may require loosening), and putting the spacer in.

 

[blinder52]

Yup I have that cheatsheet printed out and watched that video a couple times. The cheatsheet was super helpful for recording the values. Easy to see my pressures are uniformly higher than spec when I see it on the chart that @suprarx7nut put together.

I was just wondering to see if new springs helped the poster here. I guess spacers can't hurt and they're way cheaper than 4 new springs. I think also the torsion bar crank will help with the leveling too, my leftside is lower than my right on the wheel-to-fender heights.

I'm going to flush and crank this weekend. I'll get those spacers ordered as well. How was installing them?

Installing coil spacers or replacing the springs on LC/LX is about as easy as it gets for suspension work. There are a couple of YouTube videos to give hints. If found the spacers did the trick for me. That said, I think I see a Dobinson replacement for AHC (hopefully not too soon) in my truck’s future, otherwise the real thing would probably be a better long term choice.

 

[Red Beard]

Adjusting the bars will only help with pressures, not height as that is dependent on the sensors. I went with spacers myself in the rear instead of springs also. Installing them was cake...jacking up one side of the rear, dropping the rear end (had to unbolt one item as well as keeping an eye on the brake lines as well as the emergency brakes which may require loosening), and putting the spacer in.

Installing coil spacers or replacing the springs on LC/LX is about as easy as it gets for suspension work. There are a couple of YouTube videos to give hints. If found the spacers did the trick for me. That said, I think I see a Dobinson replacement for AHC (hopefully not too soon) in my truck’s future, otherwise the real thing would probably be a better long term choice.

Did you guys only replace the rear? Would I want to replace the front as well to keep it even?

 

[suprarx7nut]

Did you guys only replace the rear? Would I want to replace the front as well to keep it even?

I'm not sure what you mean by "even". Maybe this will help:

Front: Torsion bars. Torsion bars have a constant (for the sake of conversation, at least) spring rate. The nifty thing is that you can change the pre-load. This means you can keep the overall ride behavior, but you can increase the spring support at neutral height.

Rear: Coil springs. Normal springs like you see on most vehicles. The springs wear over time (as with any spring), but unlike the torsion bars the coil springs cannot be adjusted. If the spring wears out, you must install new springs, or add spacers to maintain the spring support.

Therefore, you don't need to replace the front torsion bar, even if you add weight. You just need to adjust the adjustment bolts.

If you add a lot of weight, a new bar makes sense. Exactly where that threshold is, I'm unsure. I like the LX bars with my front bumper and winch. Some folks prefer to increase that spring rate. Either way, new front torsion bars are by no means required.

 

[Red Beard]

I'm not sure what you mean by "even". Maybe this will help:

Front: Torsion bars. Torsion bars have a constant (for the sake of conversation, at least) spring rate. The nifty thing is that you can change the pre-load. This means you can keep the overall ride behavior, but you can increase the spring support at neutral height.

Rear: Coil springs. Normal springs like you see on most vehicles. The springs wear over time (as with any spring), but unlike the torsion bars the coil springs cannot be adjusted. If the spring wears out, you must install new springs, or add spacers to maintain the spring support.

Therefore, you don't need to replace the front torsion bar, even if you add weight. You just need to adjust the adjustment bolts.

If you add a lot of weight, a new bar makes sense. Exactly where that threshold is, I'm unsure. I like the LX bars with my front bumper and winch. Some folks prefer to increase that spring rate. Either way, new front torsion bars are by no means required.

I think I didn't word my last post correctly. I was talking about replacing coils or adding spacers.

So put another way: why would I only put in spacers in the rear but not the front? Or, why would I only replace the rear coils and not the front? Wouldn't that create more pressure on the front by propping up the back?

 

[suprarx7nut]

I think I didn't word my last post correctly. I was talking about replacing coils or adding spacers.

So put another way: why would I only put in spacers in the rear but not the front? Or, why would I only replace the rear coils and not the front? Wouldn't that create more pressure on the front by propping up the back?

I think we're still missing each other, haha.

The following are equal in effect: Spacer in the rear and adjusting torsion bar in the front.

There's no spacer needed in the torsion bar. Adjusting the torsion bar *IS* the "spacer".

The effect of each action is to increase preload on the spring. Same thing, different means.

Does that help? Or am I still missing the point?

 

[blinder52]

Did you guys only replace the rear? Would I want to replace the front as well to keep it even?

Well at least in my case I wasn’t looking for a change in height. I wanted to reduce the pressure AHC was using to make up for my springs weaking from age. The front torsion bars will adjust to take more of the weight of the truck. Also the fact that my AHC lines are rusty and I always worried they were over pressured to take up the slack of my springs. I wanted to bring my AHC front and rear pressure readings down to spec at least.

 

[ramangain]

Educational for coil springs vs torsion bars

 

[Red Beard]

So... this whole time I thought there were coils in front and back. I was always confused why everyone only referenced replacing the rear coils and not the front. I had to go outside and look behind my front wheel

@ramangain that's a super helpful breakdown on how the torsion bars and rear coils system works.

 

[Red Beard]

Here's my update:
I followed the PADDO method and changed my AHC fluid. Pretty simple to get the old fluid out and new fluid in.
Then I followed the cheat sheet directions and cranked the torsion bar on the "low side", until the heights were even.
Then cranked both torsion bars three full turns. Pressures are now in spec and heights look good.
Got 11 gradations as well! Very happy to have done this job finally. The cruiser drives noticeably better. Nicer on turns, less bouncy.

When I was under there, it looks like the PO replaced the left torsion bar and both front globes somewhat recently.. And I think when they installed the torsion bar (looks pretty recent - still has stickers on it), they never evened things out.

Just to add to the collective intelligence on the AHC topic and for my own post mortem, here are my thoughts on the task:

• Definitely put a lot of new fluid in the reservoir when bleeding and restarting the car the first time. I got super lucky that I didn't run out, but I was close. The second set of globes poured out clear fluid pretty quickly.\
• If you're feeling up for it, you can totally syphon out the fluid from reservoir with a longer, clean hose. This was much faster than the turkey baster method. Plus, my turkey baster couldn't fit all the way in to get all the fluid at first.
• If you're working in the cold like I was, keep a disposable coffee cup of boiled water around to warm up your bleeder hose with. The tiny hose I had could fit snug on the bleeder only after I got the hose hot. It would get cold pretty quick and stiffen up.
• Cranking the torsion bars can be really tough. I used a 1/2" drive craftsman breaker bar. I wish I had some extra pipe laying around. I sprayed the threads with PB Nut Blaster and cleaned them the best I could with a wire brush. I wish I sprayed the PB when I sprayed the bleeders the night before.
• The best position to crank them was lying under the car right in the center. I would put my left arm on the back axle housing and my right on the breaker bar.