Questions for people with LC torsion bars and springs in an LX (1 Viewer)

[thebeedeegee]

1. I'm confident in saying you would never wear the bars out. Spring degradation like that occurs over a very long time and to a small degree.

2. Yes. That's a good point. The LC bars could be setup to provide improved trail reliability (assuming you carry a 30mm wrench on the trail with you) at the expense of having a non-ideal spring rate.

number 2 may be a good enough reason for me to swap them, I dunno.

Maybe if I swap them all and do a sensor lift (to the top of all the adjusters) it would balance the system a little better with LC bars and springs? I just don't want to hose my boots since other stuff seems to be catching up with me on this truck all at once. I've seen reports both ways on the sensor lift without diff drop. Some say it will definitely destroy your CV boots, others say it's perfect fine.

 

[suprarx7nut]

number 2 may be a good enough reason for me to swap them, I dunno.

Maybe if I swap them all and do a sensor lift (to the top of all the adjusters) it would balance the system a little better with LC bars and springs? I just don't want to hose my boots since other stuff seems to be catching up with me on this truck all at once. I've seen reports both ways on the sensor lift without diff drop. Some say it will definitely destroy your CV boots, others say it's perfect fine.

There are plenty of opinions on the sensor lift, but my take is to do the minimum required for your use. It does nothing good for any mechanical component and it downgrades on road performance. If you aren't hitting obstacles, you don't need more lift.

If you're concerned about reliability, keep the heights as close to OEM as possible. You already have a 2" lift with AHC. That's the standard lift for the 100. Almost nobody has a 4" lift - largely because it involves a large cost and complexity increase to maintain any sort of reasonable reliability. If you max out the sensors that's about where you'll be. That's not necessary, IMO.

Embrace the non-lifted, big-tire look and enjoy the reliability and on-road handling that affords.

 

[Shortpencils]

Lx, LC and aftermarket bars can all be used with AHC, and your pressures brought into spec with any of them- while you're sitting in the driveway. Static. Depending upon your vehicle's configuration, loading, your driving style, driving location and a hundred other variables, AHC can be overwhelmed as could any suspension system that is not matched to conditions. AHC is a master of flexibility, another way of saying it specializes at nothing. I'm more interested in the capabilities and safety of the vehicle when driving. The Lx, with its AHC, IFS and vestigial transfer case to lend it mall cred was designed for soccer moms carting their Patagonia-clad brats to REI. At a certain point, modifications to weight and weight distribution fall outside of the design parameters of AHC and must be addressed.

There is nothing we can do to change the design parameters of AHC other than tweaking the knob between comfort and sport (ooooo, fancy), or cranking TBs until our static "pressures" are within "spec" for the design parameters we no longer conform to, while we geek away on Techstream; again, in the driveway. Our only modification then is to the springs.

Will your Lx bars carry the weight of bumpers in the driveway? Yes. Driving you will experience additional nose dive when braking, a measurable but unnoticeable amount of additional body roll, and may experience rubbing with wheels turned and coming down an obstacle. AHC does not respond to dynamic loading in the same way springs do, regardless of setting. Springs of different specs will respond differently too. This will be an iterative process and you may be perfectly happy and safe with the Lx bars. Swapping bars is simple and reversible, and I think reason enough to at least try LC bars. But don't rely only on pressures being within spec. Road test and do some hard braking, cornering and obstacles.

And of course torsion bars experience a compromised constant over time, it is a normal result of the load/unload cycle. If they didn't, they wouldn't need to be adjustable... Springs wear out, even fancy Lexus torsion bars.

In @Moridinbg 's case, adding a tent places a lot of mass up high. This, more than anything else in my opinion makes the stock AHC setup unsuitable. There will be additional nose dive and a potentially dangerous amount of body roll depending upon conditions. LC bars with a greater constant will help with this.

FWIW I run Slinky TB's. They are as big as you can go, and way bigger than the LC bars. My pressures are in spec and the ride is much improved over the stock Lx bars I had. It is unnecessary to go with this size of bar unless you have specific needs.

I agree with not doing a sensor lift.

 

[thebeedeegee]

This is with lx torsion bars and LC springs after 3 turns on each adjustor once cross leveling. There is some extra weight in the back right now my sleeping platform (about 50 lbs, and some hunting gear. Total maybe 80 lb)

 

[suprarx7nut]

Springs wear out, even fancy Lexus torsion bars.

They wear, but do they ever fall outside the range of adjustment of a reindex or two?

In @Moridinbg 's case, adding a tent places a lot of mass up high. This, more than anything else in my opinion makes the stock AHC setup unsuitable. There will be additional nose dive and a potentially dangerous amount of body roll depending upon conditions. LC bars with a greater constant will help with this.

Can you elaborate? I thought the opposite. I had an RTT on my LX when I bought it. Brake dive was far better than my 99 without AHC and without an RTT. Brake dive is one of the highlighted improvements with AHC in the Toyota/Lexus literature and if the damper actuators work as described, by quickly increasing damping force during braking, that seems logical.

 

[thebeedeegee]

I decided to try the LC bars with the LC springs. These are my pressures at stock ride height (no sensor lift) with a rear swing out and front TJM bumpers. I'll swap back if it screws up the ride

 

[suprarx7nut]

I decided to try the LC bars with the LC springs. These are my pressures at stock ride height (no sensor lift) with a rear swing out and front TJM bumpers. I'll swap back if it screws up the ride

View attachment 2520423

Looks like you got neutral pressures dialed. Nice work. Anxious to hear how she rides!

 

[LXKevin]

I decided to try the LC bars with the LC springs. These are my pressures at stock ride height (no sensor lift) with a rear swing out and front TJM bumpers. I'll swap back if it screws up the ride

View attachment 2520423

This data looks excellent now.

Are you using new or used LC parts?

I ask this question because it seems the main problem with people who declare X TB will or will not work with AHC and X amount of additional weight is that each of our systems is in some state other than 100% of original AHC performance. To guess at how much weight some other guy can safely add with stock TB's is silly. Really that's why it's a trial and error process accomplished using techstream data and how it drives. I agree that TB's loose some of their spring rate over time just as coil springs do. Maybe not as much or as fast but how to quantify that loss in a number or even ballpark the number is beyond my pay grade. The answer to the question "Are you using new or used LC parts?" should also shed some light on why we are seeing the pressures you have been able to achieve- especially for the rear LC springs. Now go drive her and see how it feels. Good Luck

 

[thebeedeegee]

This data looks excellent now.

Are you using new or used LC parts?

I ask this question because it seems the main problem with people who declare X TB will or will not work with AHC and X amount of additional weight is that each of our systems is in some state other than 100% of original AHC performance. To guess at how much weight some other guy can safely add with stock TB's is silly. Really that's why it's a trial and error process accomplished using techstream data and how it drives. I agree that TB's loose some of their spring rate over time just as coil springs do. Maybe not as much or as fast but how to quantify that loss in a number or even ballpark the number is beyond my pay grade. The answer to the question "Are you using new or used LC parts?" should also shed some light on why we are seeing the pressures you have been able to achieve- especially for the rear LC springs. Now go drive her and see how it feels. Good Luck

These are used LC springs and torsion bars I got off of rigs that had 150k+ miles if I remember right.

 

[LXKevin]

These are used LC springs and torsion bars I got off of rigs that had 150k+ miles if I remember right.

Thanks thats evidence that TB's do in fact lose some of their spring rate over time. Nice work on your part in deeply understanding the AHC system & using trial and error and techstream to get in spec while blocking out the noise from the peanut gallery.

 

[Shortpencils]

They wear, but do they ever fall outside the range of adjustment of a reindex or two?

Probably not, but are we talking about a stock vehicle in normal driving conditions, or...? And therein lies the problem. We have a lot of variables to consider. If we consider only the springs, ultimately what we are talking about is: what is their spring constant currently, and what preload is now required to hold a static vehicle with the help of AHC? Increasing the preload (rotation) on an old spring will hold the static vehicle, but ultimately moves us into a different area of the spring curve. Does this matter? Maybe, maybe not. It depends upon the spring. But at the point that we've re-indexed and added 5 cranks per mod to the bars, I'd say it's time to upgrade or refresh. They ain't that expensive. When we go dynamic, that's where we really find out how everything is coming together. My anecdotal experience has been that the ride, steering, and braking all improved dramatically.

Can you elaborate? I thought the opposite. I had an RTT on my LX when I bought it. Brake dive was far better than my 99 without AHC and without an RTT. Brake dive is one of the highlighted improvements with AHC in the Toyota/Lexus literature and if the damper actuators work as described, by quickly increasing damping force during braking, that seems logical.

In this scenario we need to restrict our variables to the Lx, and consider the differences between the Lx and LC, loaded or unloaded as a separate question. In the scenario of a built and heavy AHC 100 with a high and heavy load, I think the benefits of heavier bars become apparent quickly.

 

[suprarx7nut]

Thanks thats evidence that TB's do in fact lose some of their spring rate over time. Nice work on your part in deeply understanding the AHC system & using trial and error and techstream to get in spec while blocking out the noise from the peanut gallery.

We don't know spring rate, do we? Techstream data shows the result of spring rate and preload, but unless we get fancy with some dynamic testing of some sorts, we can't separate the two very easily.

 

[LXKevin]

We don't know the spring rate because they are used LC TB's. If they were new we could look it up.
What do you think the front pressure number would do if he swapped the used LC TB's for new LC TB's indexed & cranked identically ?
Why do we need to index and crank preload on stock weight trucks over time to get front pressure back in spec? Do they lose preload or spring rate over time?

 

[Shortpencils]

New for old, with the same installation parameters, the AHC pressures would go down. No idea by how much as we wouldn’t necessarily know what the life of the used TB was like.

If we are defining preload as the amount of force exerted by the TB to bring AHC into spec, then as the “spring rate” decreases over time (really use), the amount of force, or preload, also decreases requiring us to restore the preload by cranking the bars.

I think it’s quite possible that there is a drastic change in the spring rate early in the life of the TB, followed by a slower decline with use over time. This is speculation though.

 

[suprarx7nut]

We don't know the spring rate because they are used LC TB's. If they were new we could look it up.
What do you think the front pressure number would do if he swapped the used LC TB's for new LC TB's indexed & cranked identically ?
Why do we need to index and crank preload on stock weight trucks over time to get front pressure back in spec? Do they lose preload or spring rate over time?

If we had a set of data where the bars were indexed identically and the same angular preload applied with no sensor height changes, we could figure out relative spring rate differences (I think). My assumption of the data here is that @thebeedeegee isn't showing us exact like for like.

We all agree springs wear over time, don't we? That's why t-bars need adjustment and coil springs need replacement eventually. They definitely do wear over time. I made a comment that I don't think they wear so much so that you can't reindex and crank an LX T-bar to handle the weight of a bumper and winch. Did that comment send us down this trail? Sorry if so. I think we all agree here.

New for old, with the same installation parameters, the AHC pressures would go down. No idea by how much as we wouldn’t necessarily know what the life of the used TB was like.

If we are defining preload as the amount of force exerted by the TB to bring AHC into spec, then as the “spring rate” decreases over time (really use), the amount of force, or preload, also decreases requiring us to restore the preload by cranking the bars.

I think it’s quite possible that there is a drastic change in the spring rate early in the life of the TB, followed by a slower decline with use over time. This is speculation though.

Yup, agreed.

 

[LXKevin]

 

[remac226]

I have done 2 LX470s now (2000 and 2005). After adding bumpers, winches, and drawer systems to both I got tired of trying to adjust pressures and worrying about it so I just pulled all the AHC stuff out and went with front and rear Dobinson in both of them. Rides great and no worries about the AHC anymore.

 

[suprarx7nut]

I have done 2 LX470s now (2000 and 2005). After adding bumpers, winches, and drawer systems to both I got tired of trying to adjust pressures and worrying about it so I just pulled all the AHC stuff out and went with front and rear Dobinson in both of them. Rides great and no worries about the AHC anymore.

For my own edification, which specific part of the AHC adjustment was problematic for your rigs? Or was it more the worry about potential surprise failure in the future?

AHC adjustment for goodies should be very quick, inexpensive and simpler than a conversion. I've added full armor, drawers, solar, batteries, compressor, etc... Measured pressures once after installing the goodies and adjusted the T-bars and will install spacers shortly (already had King springs, but need a touch more support). I think I'm into it for 3 hours and $300 hundred bucks for the rear spacers and King coils. Converting would be way more time and money in my case so these comments confuse me. I appreciate your insight.

 

[remac226]

On both trucks the AHC was in good shape (cycling and giving the measurement mark movement on the res etc.) even though the specs were in (I have the software) it never felt right to me compared to how it rode prior to the extra weight. I just got tired of messing with it on the 2000 and then even tried again on the 2005 based on all the good luck people had been have figuring I had not followed the "instructions". In the end I pulled that off as well and went with Dobinson again. Yes it cost a little more money but it wasn't any more work (with the exception of the PIA rear shocks) than changing rear springs and T-bars for King or standard LC. And yes to some extent, even though it was working properly, I feel better knowing that I no longer need to worry about the sensors going bad and it settling when I am on a trip etc. Plus I got the added bonus of pulling the AHC switch out of the console and replacing it with the pocket.

 

[suprarx7nut]

On both trucks the AHC was in good shape (cycling and giving the measurement mark movement on the res etc.) even though the specs were in (I have the software) it never felt right to me compared to how it rode prior to the extra weight. I just got tired of messing with it on the 2000 and then even tried again on the 2005 based on all the good luck people had been have figuring I had not followed the "instructions". In the end I pulled that off as well and went with Dobinson again. Yes it cost a little more money but it wasn't any more work (with the exception of the PIA rear shocks) than changing rear springs and T-bars for King or standard LC. And yes to some extent, even though it was working properly, I feel better knowing that I no longer need to worry about the sensors going bad and it settling when I am on a trip etc. Plus I got the added bonus of pulling the AHC switch out of the console and replacing it with the pocket.

Ok, thanks. Fair enough. I did love that pocket on my 99!