AHC Bouncy & Stiff Front End (1 Viewer)

[NorCalFJ100]

I have replaced all my globes. Rear shocks are 3 years old. Fluid has been flushed, replaced and bled. Overall down the highway at high speed it floats and feels great! If I am going slow and hit a pothole or speed bump it feels pretty jaring. I can also hear what sounds like maybe some sort of squishing noise which I assume to be from the front shocks. Besides the coils in the back, system is all pretty new-ish and refreshed. No trouble codes within Tech Stream.

Any specific tests for front AHC shocks? They do not appear to be leaking, etc. Do they also go bad? What could be causing the front end to feel so harsh over low speed bumps, etc?

 

[Zer0zg]

The shocks themselves are just hydraulic pistons, so unless they’re leaking visibly they’re probably fine. If I were you I’d be checking/refreshing your fluid, checking your graduations to see if your globes are ok, and making sure your neutral pressures are in spec.

 

[Christian]

Have you had the diagnose tester on it and tested sensors, pressure, height etc? And have you dialed in your torsion bars, and are your rear springs still good?

 

[NorCalFJ100]

@Zer0zg @Christian

Thank you both, that is great info. I replaced the fluid in the last 9 months maybe...also replaced the globes in the front at that time. The globes and assumably the fluid change made a world of difference. The rear globes were replaced about 3 years ago and the rear shocks replaced at that time, from PO.

Any test for the springs? My 2006 has about 150k miles, is this just a wear item at this mileage and year.

I will run the diagnostic check with Tech Stream and verify pressures, etc.

As mentioned, after I replaced my front globs and swapped fluid a while back the truck drove so much nicer. Was night and day really. My only struggle now is just low speed bumps and that squishing sound like I have blown shocks when I go over speedbumps and such.

 

[Zer0zg]

To me a squishing sound sounds like there might be some air in the line, at least that is the only thing I could think of. I suspect air in the line would also increase ride harshness.

 

[LndXrsr]

Squishing could also be something else entirely...rotted bushings come to mind.

 

[geanes]

What are your neutral pressures? Sure sounds to me like you might by over-pressured on the front. Should be 6.8-6.9 on the front. I'd bet you're in the mid to high 7s which would explain your ride characteristics. The squeaking is most likely "joint" related i.e. upper/lower ball joints or even UCA bushings. The AHC "shocks" don't squeak.

 

[suprarx7nut]

+1 on Pressures.

Any AHC problem needs to start with inspecting pressures. That's step 1.

 

[NorCalFJ100]

Thanks all! I will check pressures tonight and report back.

 

[NorCalFJ100]

Alright fellow luxury AHC mudders!

Here is the sequence of events:

1: This was on immediate startup

2: This was going from N Height to Low

3: This was going from Low back to Neutral

4: This was going from Neutral to High

5: Now this is interesting. I did a full cycle from N to H, back to N, then to L and back to N and my pressure readings were much lower. I did a test drive and went over some speed bumps in my neighborhood and it went much smoother. No noise either! BUT the only time I can get this lower pressure is after I go from N to H, back to N, then to L and back to N. Once I go back to H from that point the pressure increases.

Another thing I noticed is my height sensors are not even! I do not have a code, but do you think one of these may not be good? Does anyone know what the factory spec is for height sensors at L-N-H?

THANKS EVERYONE!!!!!!!!!!!!!!!!!!!!!!!!​

 

[LndXrsr]

Your height sensors in front are about 0.5 inch off which does need some adjusting but they are very unlikely faulty. Pressures should only be measured in N after going N-->L--N. Pressures in H or N are not used for reference (they are presumed to be good if N pressure is good). Your N pressures look quite good really.

I created this a while back to help understand and baseline your AHC, factory specs for pressures, sensor height, etc are in there:
ABCs of AHC

 

[NorCalFJ100]

Your height sensors in front are about 0.5 inch off which does need some adjusting but they are very unlikely faulty. Pressures should only be measured in N after going N-->L--N. Pressures in H or N are not used for reference (they are presumed to be good if N pressure is good). Your N pressures look quite good really.

I created this a while back to help understand and baseline your AHC, factory specs for pressures, sensor height, etc are in there:
ABCs of AHC

This is great! So it would seem my front pressure is slightly low actually and my FL sensor also shows a bit more low than the FR - Do you think if I adjust the torsion bars to get this in spec, that should help bring my pressure back into spec?

Side note, the whole motivation for this thread was my ride became super stiff. Once I cycled the height it seems to ride smoother. As a practice do you cycle your suspension from N-->L-->N occasionally? I never use mine, but my truck is always self adjusting when I am parked/stopped at different grades and sometimes it feels it will randomly self adjust.

 

[geanes]

This is great! So it would seem my front pressure is slightly low actually and my FL sensor also shows a bit more low than the FR - Do you think if I adjust the torsion bars to get this in spec, that should help bring my pressure back into spec?

Side note, the whole motivation for this thread was my ride became super stiff. Once I cycled the height it seems to ride smoother. As a practice do you cycle your suspension from N-->L-->N occasionally? I never use mine, but my truck is always self adjusting when I am parked/stopped at different grades and sometimes it feels it will randomly self adjust.

Yes, you need to most likely re-index your torsion bars. You are over 1mpa-g low. That's a LOT of cranking. Depending on how much thread you have on the TB adjustment bolt, you will most likely need to reindex. Should be 6.8-6.9 on the front. You can start by maybe cranking (counterclockwise to relieve tension on the TB) equally on both sides 4 full rotations, drive a few blocks to "settle" the system and remeasure. Your rear at 6.8 is on the high end of neutral pressure. Accumulator pressure at 10.3 is BARELY high (10.2 is the target), but no big deal or worry at all.

 

[LndXrsr]

Agree with the above. 4-5 turns loosening both TB nuts euqally, then recheck to start. One full turn of a TB nut changes pressures about 0.2mpa is the typical math. Whether you need to reindex will really depend on how tight the TBs are cranked on the adjustment bolt. 4-5 turns on the nut isn't out of the question without reindexing if things are really tight currently, which is quite possible given that your pressures are actually low. Many run out of room tightening due to high pressures that worn out TBs can no longer compensate for.

 

[geanes]

Agree with the above. 4-5 turns loosening both TB nuts euqally, then recheck to start. One full turn of a TB nut changes pressures about 0.2mpa is the typical math. Whether you need to reindex will really depend on how tight the TBs are cranked on the adjustment bolt. 4-5 turns on the nut isn't out of the question without reindexing if things are really tight currently, which is quite possible given that your pressures are actually low. Many run out of room tightening due to high pressures that worn out TBs can no longer compensate for.

Yup. The only time I've seen pressures that low is when people have put in LC torsion bars instead of LX/AHC torsion bars. More often you'll see front pressures in the 7.4-7.8 range which is worn out TBs that need to be tightened or re-indexed.

 

[NorCalFJ100]

@geanes @LndXrsr I will take a look at the torsion bars. Is there a quick and easy way to "reindex"? Or should I just make equal adjustments in increments and remeasure the pressure and see if I can get into spec?

@LndXrsr being that my height sensors upfront are uneven, do I need to adjust one torsion bar an extra turn or two to compensate? I read in your ABC post that the TB are the way to adjust this.

Thanks again!!!!

 

[geanes]

@geanes @LndXrsr I will take a look at the torsion bars. Is there a quick and easy way to "reindex"? Or should I just make equal adjustments in increments and remeasure the pressure and see if I can get into spec?

@LndXrsr being that my height sensors upfront are uneven, do I need to adjust one torsion bar an extra turn or two to compensate? I read in your ABC post that the TB are the way to adjust this.

Thanks again!!!!

Just make equal adjustments for now. 1 full crank counterclockwise (loosen) on each side at a time until you've done probably 3 total. Then drive a few blocks to settle the system and then remeasure pressures. Most likely will need one more counterclockwise crank on each side after that. You'll only need to reindex if there isn't enough thread on the bolt to make the adjustments. Most of the time it impacts the top end only as people tend to overcrank the TBs to compensate for lack of spring....you've got the opposite issue...too much spring. You'll probably be fine.

 

[LndXrsr]

@LndXrsr being that my height sensors upfront are uneven, do I need to adjust one torsion bar an extra turn or two to compensate? I read in your ABC post that the TB are the way to adjust this.

Thanks again!!!!

Equal torsion bar adjustments won’t change your sensor readings, only pressures. Unequal ones typically don’t either. You will have to tweak the sensors to read as close to zero as possible but only after you fix your current pressures by loosening the TBs. usually sensors should read +/- 0.1 in. Read my ABCs post about how to adjust the sensor brackets. after that you’ll need to check your ride height in N to see if you’re level from side to side. If not, one TB will need tightening and the other lessening until you are level from side to side in the front. Then you can adjust both height sensors again to get the final ride height you want.

 

[NorCalFJ100]

^^^Thanks guys! I will check this out tomorrow!

 

[fotomon]

The timing on this thread is awesome. My 07 has no shock absorption after a bump in the road or after going over a speed bump. I'm not mechanically inclined so I work with a local shop. For the most part I used a Toyota dealer but they have become more interested in getting their commissions than actually working with me on what needs to be done. With that said, would you all suggest shocks, etc or should I look into something else. Sorry to highjack this stream of info but you all really seem to have a handle on this issue. Thanks in advance.