AHC pressures (1 Viewer)

[thetoyotaman]

Hi,

I have a question about AHC pressures. The FSM shows how every turn of the torsion bars nets a pressure change on the AHC. Curious if height sensors are raised if it has much effect. I’m just trying to understand the net effect once I install all the armor and gear. I installed the front bullbar and adjusted the torsion bars 6 turns and my current pressures are 7.0. If I raise the height sensors an inch will that make a big pressure change? I have more armor to add. Thanks!

 

[nukegoat]

yes, the computer cannot tighten your torsion bars for you

 

[thetoyotaman]

More specifically, if the rear axle is a little under pressure and I haven't adjusted the height sensor yet would it dial it in better by adding AHC lift? I'm assuming the more height adjustment on the AHC the more pressure would be present but I'm trying to find out if it's significant enough to be in the overall equation. Thanks!

 

[nukegoat]

More specifically, if the rear axle is a little under pressure and I haven't adjusted the height sensor yet would it dial it in better by adding AHC lift? I'm assuming the more height adjustment on the AHC the more pressure would be present but I'm trying to find out if it's significant enough to be in the overall equation. Thanks!

its literally the only coefficient in the equation

 

[PADDO]

Hi,

I have a question about AHC pressures. The FSM shows how every turn of the torsion bars nets a pressure change on the AHC. Curious if height sensors are raised if it has much effect. I’m just trying to understand the net effect once I install all the armor and gear. I installed the front bullbar and adjusted the torsion bars 6 turns and my current pressures are 7.0. If I raise the height sensors an inch will that make a big pressure change? I have more armor to add. Thanks!

Raising the front’s N height 1 inch via sensor lift adds ~+2.2MPa (per inch) to the front pressure for a stock vehicle; raise the rear’s height 1inch ~+0.6MPa (per inch) So yes, sensor lifting increases pressures which will usually negatively affect damping. The other factor that affects pressures is weight.

 

[thetoyotaman]

Thank you! That’s exactly what I was looking for.

 

[FxFormat]

Raising the front’s N height 1 inch via sensor lift adds ~+2.2MPa (per inch) to the front pressure for a stock vehicle; raise the rear’s height 1inch ~+0.6MPa (per inch) So yes, sensor lifting increases pressures which will usually negatively affect damping. The other factor that affects pressures is weight.

On a completely stock vehicle, no added bumpers or anything, how many turns of the TBs would drop the pressure 1MPa, approximately.

 

[PADDO]

On a completely stock vehicle, no added bumpers or anything, how many turns of the TBs would drop the pressure 1MPa, approximately.

5

 

[katit]

So I don't open another topic. And before I replace fluid. 194k, L-N-H seem to work OK. Truck visually leaning to the driver side a little. Here is readings at N, what should be done?

 

[95Fantasma80]

some rear springs will definitelt put you in spec

 

[uHu]

Depends on heights as well, I.e. physical height (the sensors only tell you the height relative to the zero point you adjust them to).
If height is OK, you need to adjust torsion bars (more on left) and change rear coils. If the steering wheel was straight when doing the reading above, you need to get it zeroed.

 

[katit]

Depends on heights as well, I.e. physical height (the sensors only tell you the height relative to the zero point you adjust them to).
If height is OK, you need to adjust torsion bars (more on left) and change rear coils. If the steering wheel was straight when doing the reading above, you need to get it zeroed.

Steering wheel wasn’t straight, I attached wrong image. But with straight wheel (which showed +-6 degrees it was the same

So, do I understand correctly?

1. Pressure upfront is too high. Also, according to sensors there is difference of about 1/2 in height between L/R. I can adjust torsion bars to get front readings to proper specs. I will be adjusting more on left. Of course I will measure physical height to make sure it agrees with sensors

2. Pressure on back is high. However, there is no way to adjust it. It’s basically springs compressed over time. Yes spacers will work but they will change damping ratio. New spring preferred

Did I get it right?

And should I change fluid before adjustments?

 

[uHu]

Yes, all ok. Except that the pressure depends on the height you're running, so if the rear is an inch too high, that's partly the reason for the pressure being too high. So always check actual heights before reading ahc values.
Change fluid whenever.

 

[katit]

I did crank left 1 full turn clockwise, R 1/2 turn. Contrary to what I read here - I didn't get any noticeable resistance, went smooth. But bolts clean, wheels were in air and I did squirt some liquid wrench on threads.

Should I measure going from L to N or from H to N?
Also, should I set it to specific comfort mode?
FSM confusing. To me it makes sense to crank L torsion bar more to get it level, but it says by same amount?
Attached 4 pics I measured twice both ways. Higher pressures when going H to N and lower pressures going L to N

Truck sits at
F: 19 1/4 L and 19 3/4 R
R: 20 1/2 L and 21 R

I understand I need to keep cranking, but how many turns?

 

[katit]

Now I'm really confused. I did more adjustments. Specifically tightened L 6 turns and R 2 turns. Pressures dropped, now I think it's little too low on front. However, truck still sits tilted to left.

I measure 19 on left and 19 1/2 on right FRONT
20 1/4 on left and 20 3/4 on right REAR

I feel like I need to loosen RIGHT 2 turns back to raise pressure a little and hopefully even it out? Do I understand correctly? It feels like left side was very loose for some reason. Does it sound correct?

Another though.. I sit in a car while running TechStream. Maybe that's why it's not leveling up? Obviously I measure height when noone in a car.

 

[uHu]

Read values only after going from Lo to N. All other readings are just nonsense. An do that without any weight in the car.

The FSM indicates to adjust the same number of turns, but in opposite direction! But that is for when you have the pressure within spec. Since your pressure is too high, you just tighten the left one until it's level, and then do both until pressure is right.

Sounds like you could do with some more reading. Have you read twice through the whole Definitive AHC thread?
If you have reading problems, just say so and we'll be more helpful.

 

[katit]

Sounds like you could do with some more reading. Have you read twice through the whole Definitive AHC thread?
If you have reading problems, just say so and we'll be more helpful.

Obviously I do have reading problems! Read through this topic (as time allowed) but 32 pages of stuff with only maybe 20 useful posts

Got truck leveled. Sits about 19F and 20R. Sounds like need to raise it a little bit. Just to summarize info found:
Suggested is 19.75F 20.5R

Sensors read 0.3 apart, will need to address that separately.
Going to replace AHC fluid now just so I have it done.

To summarize next steps as I understand them in order. I understand doing every step in this order will not require me going back.
1. New rear springs. What is the target rear pressure? Did not find it in 32 pages
2. Adjust sensors and height again to bring it to specs
3. Check how many graduations on AHC fluid tank and decide if new globes needed.
4. Replace globes if needed - this should not require readjustment as height regulated by pressure + springs + torsion bars.

Correct?

Also, is there any way to switch TechStream to metric?

 

[uHu]

To summarize next steps as I understand them in order. I understand doing every step in this order will not require me going back.

Also, is there any way to switch TechStream to metric?

1. New rear springs. What is the target rear pressure? Did not find it in 32 pages Pretty sure it's in there, but it is 5.6 to 6.7, so you're just at the top limit. Not too bad.

2. Adjust sensors and height again to bring it to specs. No need. Changing springs will only change the pressure.

3. Check how many graduations on AHC fluid tank and decide if new globes needed.
4. Replace globes if needed - this should not require readjustment as height regulated by pressure + springs + torsion bars.
Right.

I get the readings in metric, so maybe just selecting Europe at start up ?

 

[katit]

1. New rear springs. What is the target rear pressure? Did not find it in 32 pages Pretty sure it's in there, but it is 5.6 to 6.7, so you're just at the top limit. Not too bad.

2. Adjust sensors and height again to bring it to specs. No need. Changing springs will only change the pressure.

3. Check how many graduations on AHC fluid tank and decide if new globes needed.
4. Replace globes if needed - this should not require readjustment as height regulated by pressure + springs + torsion bars.
Right.

I get the readings in metric, so maybe just selecting Europe at start up ?

1. Thanks! Nice it's at the limit but I ordered springs anyway, I want to preserve AHC as much as possible.
2. I was thinking since I'm going to install different ratio springs L/R (780 on left, 770 on right) I may get leaning truck again. Also, I still have discrepancy in sensor readings which I want to get little more precise. Basically this is my "to do" item after springs/fluid change to do fine-tuning. Also, the way truck sits now looks little high so it's another reason to mess with sensors.
3-4. Cool! Once all leveled, checked I will be making decision on globes.


... with this mileage I'm thinking globes need to be changed. It is my understanding that measuring graduations is just a hint. Do globes wear evenly? Maybe one is shot and it's going to show 75% OK overall on fluid. Is there way to check individual globes for sure? And if one bad - when is the next one going to go? Sorry I didn't see "globe testing" procedure in 33 page topic

 

[uHu]

Yes, you'll likely have to re-adjust L/R lean after changing coils.

Testing individual globes cannot be done on the car, afaik. When standing still (and when driving straight) the left and right sides/globes/shocks are interconnected, so if there is "give" in one globe and the other is shot (stiff), you can't find out which one is which. If you take them off there must be a test setup which could be used, for someone with the right skills and tools.
I think we could close the Gate Valve (between L and R) manually, and then do a "push down by hand test" at each corner to see if one is much harder than the others. Maybe.

PS: WHen talking about sensors -- They are among the weak parts of the AHC, both because of possible ingress of water/salt and because they wear out, so it's good to have a spare one. The Dorman replacement is not expensive (it's mentioned in a thread in here).