AHC vs non AHC torsion bars (1 Viewer)

[TheDuc]

Hello fellow mudders. I have a 2006 LX470 with AHC thats been removed prior to me buying it. I decided to lift the front end a little by turning torsion bars about 4 times resulting in about 1.25" lift and lots of torque steer. I installed new wheels and tires 295/70/18 (compliments of mckunz) that resulted in ever more torque steer although it only happens when I put the foot down hard. It drives fine under normal driving.
I was told that AHC and non AHC torsion bars are different and by switching to non AHC torsion bars will eliminate torque steer and stiffen up a ride a little. I wouldn't want an aftermarket torsion bars since Im not adding any weight to it but if thats the only alternative, perhaps a suggestion on what kind that closely resembles factory non AHC. Thanks in advance for the input

 

[LndXrsr]

AHC torsion bars cannot support the weight of the front end on its own. Typically they split the weight with the AHC "shock" which are really a hydraulic ram and the true AHC shocks are the damper modules attached to the frame rail.

Since your suspension now has true shocks where the AHC rams were, they are not supporting any weight, just dampening. You need full strength OEM non-AHC torsion bars to support the front end and not be vastly undersprung. There's no way to tighten or re-index the AHC bars enough.

 

[TheDuc]

AHC torsion bars cannot support the weight of the front end on its own. Typically they split the weight with the AHC "shock" which are really a hydraulic ram and the true AHC shocks are the damper modules attached to the frame rail.

Since your suspension now has true shocks where the AHC rams were, they are not supporting any weight, just dampening. You need full strength OEM non-AHC torsion bars to support the front end and not be vastly undersprung. There's no way to tighten or re-index the AHC bars enough.

Thanks for the help. I’ll start looking for these right away. 98-07 year range?

 

[GTV]

Did you get an alignment?

 

[TheDuc]

Did you get an alignment?

Not yet

 

[WarWagon]

Happened to me. You need a regular 100 series torsion bar or aftermarket.

 

[TheDuc]

What aftermarket brand resembles oem the most? I don’t want it too stiff

 

[geanes]

Hello fellow mudders. I have a 2006 LX470 with AHC thats been removed prior to me buying it. I decided to lift the front end a little by turning torsion bars about 4 times resulting in about 1.25" lift and lots of torque steer. I installed new wheels and tires 295/70/18 (compliments of mckunz) that resulted in ever more torque steer although it only happens when I put the foot down hard. It drives fine under normal driving.
I was told that AHC and non AHC torsion bars are different and by switching to non AHC torsion bars will eliminate torque steer and stiffen up a ride a little. I wouldn't want an aftermarket torsion bars since Im not adding any weight to it but if thats the only alternative, perhaps a suggestion on what kind that closely resembles factory non AHC. Thanks in advance for the input
View attachment 2422890

AHC/LX torsion bars are definitely different/smaller than other torsion bars. The AHC system is a hydraulic "assist" suspension. That is unlike conventional suspensions. In conventional suspensions, the springs (torsion bars and coils) are engineered to handle the full GVW of the vehicle. The shocks then function as dampeners to "control" rebound and compression. In an AHC system, the springs (torsion bars and coils) are designed to handle roughly 60% of the GVW of the vehicle with the hydraulics then managing the 40% delta along with controlling compression and rebound dampening.

Here are the relative sizes of various torsion bars available for our rigs. Bigger diameter equals more load capacity:

LX/AHC = 26mm
LC/OEM = 28mm
OME = 30mm
IronMan/ToughDog/SwayAway = 32mm

You need to first understand you pressures in the system. If you don't have TechStream or the iCarSoft TYT reader, get one. Don't "mess" with AHC until you can properly diagnose the system via one of those devices. If you do, you'll wind up chasing your tail and never properly getting the system in spec.

Lastly, you can NOT "lift" an AHC equipped vehicle by simply cranking the torsion bars. The height sensors will communicate to the AHC computer that the front is higher than the sensors see as "normal" and the AHC system will overpressure to force the height back to the level preset by the sensors. You can ONLY "lift" an AHC vehicle by adjusting the height sensors. Blindly cranking torsion bars will take the system out of spec and result in a myriad of poor driving dynamics.

 

[LndXrsr]

His truck no longer has AHC but still has the AHC torsion bars if I'm understanding correctly. No pressures to measure and it can be lifted in front by cranking torsion bars. But the wrong spring rate from the smaller AHC bars is creating the problem here.

 

[97 AZ LC]

Hello fellow mudders. I have a 2006 LX470 with AHC thats been removed prior to me buying it. I decided to lift the front end a little by turning torsion bars about 4 times resulting in about 1.25" lift and lots of torque steer. I installed new wheels and tires 295/70/18 (compliments of mckunz) that resulted in ever more torque steer although it only happens when I put the foot down hard. It drives fine under normal driving.

What is it that happens when you put your foot down hard?

 

[geanes]

His truck no longer has AHC but still has the AHC torsion bars if I'm understanding correctly. No pressures to measure and it can be lifted in front by cranking torsion bars. But the wrong spring rate from the smaller AHC bars is creating the problem here.

Ah, so he's been converted. I wonder if it's the damnable Strutmasters kit that doesn't replace the TBs. If he's on AHC TBs, then he needs to swap them out ASAP. Go with OEM Toyota if he wants the stock ride, OME if he wants a little bit more "stiffness". The rear swaybar for the AHC system is also smaller diameter. Ideally, he'd replace that rear anti-sway bar as well.

 

[TheDuc]

AHC/LX torsion bars are definitely different/smaller than other torsion bars. The AHC system is a hydraulic "assist" suspension. That is unlike conventional suspensions. In conventional suspensions, the springs (torsion bars and coils) are engineered to handle the full GVW of the vehicle. The shocks then function as dampeners to "control" rebound and compression. In an AHC system, the springs (torsion bars and coils) are designed to handle roughly 60% of the GVW of the vehicle with the hydraulics then managing the 40% delta along with controlling compression and rebound dampening.

Here are the relative sizes of various torsion bars available for our rigs. Bigger diameter equals more load capacity:

LX/AHC = 26mm
LC/OEM = 28mm
OME = 30mm
IronMan/ToughDog/SwayAway = 32mm

You need to first understand you pressures in the system. If you don't have TechStream or the iCarSoft TYT reader, get one. Don't "mess" with AHC until you can properly diagnose the system via one of those devices. If you do, you'll wind up chasing your tail and never properly getting the system in spec.

Lastly, you can NOT "lift" an AHC equipped vehicle by simply cranking the torsion bars. The height sensors will communicate to the AHC computer that the front is higher than the sensors see as "normal" and the AHC system will overpressure to force the height back to the level preset by the sensors. You can ONLY "lift" an AHC vehicle by adjusting the height sensors. Blindly cranking torsion bars will take the system out of spec and result in a myriad of poor driving dynamics.

I appreciate all the info; however, my AHC was removed already so I have conventional coils and shocks now.

 

[TheDuc]

Damn it. I do have the strutmasters. I’m having trouble finding oem TBs. may just go OME just to get this corrected sooner.

 

[geanes]

Damn it. I do have the strutmasters. I’m having trouble finding oem TBs. may just go OME just to get this corrected sooner.

Yeah, Strutmasters should be ashamed of themselves for selling a kit like that. The idea that a torsion bar designed for 60% of the GVW could simply be cranked to compensate for the delta is negligent on their part and shows they lack a complete understanding of suspensions. If it were me, I'd look at sourcing OEM TBs from someone who recently upgraded to an aftermarket kit or even look at a complete swap using something like the IronMan NitroGas kit which is around $799 shipped. That would net you new TBs, coils and shocks.

Sorry you got stuck with the Strutmasters kit. Now that I know that's what it is, that explains a LOT of the negative handling characteristics you're experiencing.

 

[TheDuc]

Yeah, Strutmasters should be ashamed of themselves for selling a kit like that. The idea that a torsion bar designed for 60% of the GVW could simply be cranked to compensate for the delta is negligent on their part and shows they lack a complete understanding of suspensions. If it were me, I'd look at sourcing OEM TBs from someone who recently upgraded to an aftermarket kit or even look at a complete swap using something like the IronMan NitroGas kit which is around $799 shipped. That would net you new TBs, coils and shocks.

Sorry you got stuck with the Strutmasters kit. Now that I know that's what it is, that explains a LOT of the negative handling characteristics you're experiencing.

where did you find it for $799?

 

[geanes]

where did you find it for $799?

Looks like they just went back up to $999. They were $799 for like the past 6 months. Bet they go on sale again real soon.

 

[suprarx7nut]

Damn it. I do have the strutmasters. I’m having trouble finding oem TBs. may just go OME just to get this corrected sooner.

I'd hold out for finding used OEM. OME is going to be terrible without a bumper's worth weight out front to mellow that spring rate out.

 

[GTV]

Not yet

It won’t drive right after a lift until you do.

 

[TheDuc]

Just bought a set of ome from cruiser outfitters. $275 plus shipping cost. Figured I’ll deal with stiff ride. Beside I’ll have an excuse to get bumper later.

 

[LndXrsr]

Yeah, Strutmasters should be ashamed of themselves for selling a kit like that. The idea that a torsion bar designed for 60% of the GVW could simply be cranked to compensate for the delta is negligent on their part and shows they lack a complete understanding of suspensions. If it were me, I'd look at sourcing OEM TBs from someone who recently upgraded to an aftermarket kit or even look at a complete swap using something like the IronMan NitroGas kit which is around $799 shipped. That would net you new TBs, coils and shocks.

Sorry you got stuck with the Strutmasters kit. Now that I know that's what it is, that explains a LOT of the negative handling characteristics you're experiencing.

No kidding. And even if you could/do crank the AHC bars tight enough at rest, the lower “spring rate“ (really torsional stiffness) will always result in a horrible ride.