Aftermarket Rear Springs with Original AHC System? (1 Viewer)

[doober]

I've been pondering the idea of replacing stock, original springs on my 2002 LX (177K miles) with Dobinsons 220 lbs load springs (or something near-equivalent). Mainly for the benefit of extra load, as I don't tow but have significant tongue weight from hauling bikes around. I've tried to do my due-dilligence on the forums, and have gotten sucked into the rabbit hole of AHC testing, torsion bar adjustments, when rear springs should be replaced, etc. I'm happily more informed and also more confused than where I started..

In summary, the main question is: Will a heavier load spring (not significantly, only a 220 lb load spring) impact the current AHC system in a negative or positive way? Will I be doing the entire suspension/hydraulic system a service by replacing the springs and keeping stock shocks..? there is still at least 10K life in them IMO.

From my research, it appears as though the intelligent thing to do would be to check AHC pressures in the rear globes, and if to high over FSM spec, replace springs as they're likely worn out. Since I'm simply looking for extra load capacity with a stock AHC system, theoretically it seems like doing this install would only aid the AHC system over time. Having a heavier set spring rate would take more pressure off of the hydraulic system; not necessarily extending the AHC system's life, but also not causing any negatives.

This post is more of a logic check, as of course I'd like to get this right the first time...

On top of all else, I'm in the works of a AHC function check, as the previous owner was not great about system PM. beyond springs, I will be flushing the hydraulic fluid, and was also planning on adjusting torsion bars up front to ensure the AHC system is not supporting more load than it's suppose to, and concurrently cross-levelling and cranking torsion bars to proper vehicle height (and get an alignment...)

thanks all for the help in advance.

 

[suprarx7nut]

I think you get the jist, but a few corrections:

Dobinsons or ARB or any other normal land cruiser aftermarket spring are generally WAY too much spring for AHC, even if fully armored. Remember, with AHC the mechanical spring only provides a portion of the load support. You have to leave some for AHC. The progression is roughly like; AHC, spacer, King, king with spacer, lx450, non-AHC 100 spring. Notice how there's no dobinsons or ARB on that list?

Check pressures first and follow along with my YouTube guide and cheat sheet. Google YotaMD AHC.

Globes have their own pressure, but that's actually not something you can measure because they are permanently sealed chambers. When we talk about pressures, what that means is the pressure required in the shock to raise the vehicle to the correct height. The globe is completely irrelevant.

To estimate globe health, you check how much fluid is displaced from h to l. Aka gradation test.

 

[jLB]

Somebody else’s recent experience using a similar thought process…

Ironman 4x4 coil springs

I bought Ironman4x4 coil springs for my 2004 Lexus LX470. they seemed like a decent company to try for replacement suspension parts. I put in my information for year/make/model, and they sent me 0-440 load springs. I couldn’t get them on the car, so I had to take to my mechanic. They had to...

forum.ih8mud.com

 

[doober]

I think you get the jist, but a few corrections:

Dobinsons or ARB or any other normal land cruiser aftermarket spring are generally WAY too much spring for AHC, even if fully armored. Remember, with AHC the mechanical spring only provides a portion of the load support. You have to leave some for AHC. The progression is roughly like; AHC, spacer, King, king with spacer, lx450, non-AHC 100 spring. Notice how there's no dobinsons or ARB on that list?

Check pressures first and follow along with my YouTube guide and cheat sheet. Google YotaMD AHC.

Globes have their own pressure, but that's actually not something you can measure because they are permanently sealed chambers. When we talk about pressures, what that means is the pressure required in the shock to raise the vehicle to the correct height. The globe is completely irrelevant.

To estimate globe health, you check how much fluid is displaced from h to l. Aka gradation test.

Thanks for the input, your video is on my watchlist actually In general that makes sense, if you don't leave enough for the AHC to support then your complete hydraulic system simply won't function as it should.

Are globes nitrogen charged then?

Sounds like you'd recommend new, OEM AHC springs with a spacer to accomplish what i'd like to? Thanks! Also - King and King with spacer? Does King suspension make OEM replacement springs for AHC? Do they provide any benefit over OEM coils if so?

 

[suprarx7nut]

Thanks for the input, your video is on my watchlist actually In general that makes sense, if you don't leave enough for the AHC to support then your complete hydraulic system simply won't function as it should.

Are globes nitrogen charged then?

Sounds like you'd recommend new, OEM AHC springs with a spacer to accomplish what i'd like to? Thanks! Also - King and King with spacer? What is this?

Globes are nitrogen, yes.

I'd check pressures first before doing anything with springs.

Once you check your pressures, then you can buy the right spring combo. King is the only manufacturer that makes aftermarket springs for AHC which increase load carrying. It's a good first step for anyone that has added armor/cargo systems to their AHC 100. Spacers increase the preload for any given spring. It's like a half step of load capacity increase.

Once again - check your pressures.

 

[doober]

Globes are nitrogen, yes.

I'd check pressures first before doing anything with springs.

Once you check your pressures, then you can buy the right spring combo. King is the only manufacturer that makes aftermarket springs for AHC which increase load carrying. It's a good first step for anyone that has added armor/cargo systems to their AHC 100. Spacers increase the preload for any given spring. It's like a half step of load capacity increase.

Once again - check your pressures.

Understood! I'll definitely look into the King springs, they sound interesting, but maybe just a spacer will be sufficient for me. If anything different from OEM AHC springs are installed, do pressures actually need to be adjusted in Techstream? Or just measured to confirm proper system operation...

 

[suprarx7nut]

Understood! I'll definitely look into the King springs, they sound interesting, but maybe just a spacer will be sufficient for me. If anything different from OEM AHC springs are installed, do pressures actually need to be adjusted in Techstream? Or just measured to confirm proper system operation...

Pressures need to be adjusted no matter what. Once per 5 years is normally good, or anytime you alter vehicle weight more than a couple hundred pounds. The pressures rise over time as the mechanical springs wear. Increased pressure means the hydraulics are supporting more load. That's ok within a certain range, but outside that range, you will lose comfort and/or function.

Often, simply adjusting the torsion bars improves the pressures front and rear. It's a free adjustment you can do in 30 minutes or less... once you check pressures. You can't adjust it without pulling pressure data.

 

[doober]

Pressures need to be adjusted no matter what. Once per 5 years is normally good, or anytime you alter vehicle weight more than a couple hundred pounds. The pressures rise over time as the mechanical springs wear. Increased pressure means the hydraulics are supporting more load. That's ok within a certain range, but outside that range, you will lose comfort and/or function.

Often, simply adjusting the torsion bars improves the pressures front and rear. It's a free adjustment you can do in 30 minutes or less... once you check pressures. You can't adjust it without pulling pressure data.

Appreciate the info. Following up to this, is there ever a reason to replace torsion bars either with OEM or aftermarket? Can people typically run aftermarket torsion bars with the AHC system? Or are they specifically designed for lifts/AHC deletes...

 

[suprarx7nut]

Appreciate the info. Following up to this, is there ever a reason to replace torsion bars either with OEM or aftermarket? Can people typically run aftermarket torsion bars with the AHC system? Or are they specifically designed for lifts/AHC deletes...

Generally, you can keep the original torsion bars forever. Since the torsion bars are fully adjustable you can simple increase the preload over time. The reduction in spring rate isn't enough to warrant replacement, IMO.

If you're adding a 200# steel bumper with a 100# winch and a 50# second battery in the engine bay, then a non-AHC Toyota torsion bar makes sense.

If you're not adding huge weight, consider those torsion bars lifetime parts.

 

[LndXrsr]

Approximate change in pressures by type of spring/spacer:

The ABCs of AHC - How to Measure, Flush, and Adjust all in one place

I initially put this in the Definitive list of AHC maintenance items thread, but at almost 800 posts long and growing, it's going to get buried and the thread itself is very unwieldy. In an attempt to make as focused a summary as possible, I present "The ABCs of AHC." It's intended as a...

forum.ih8mud.com

 

[SARguy]

I've been pondering the idea of replacing stock, original springs on my 2002 LX (177K miles) with Dobinsons 220 lbs load springs (or something near-equivalent). Mainly for the benefit of extra load, as I don't tow but have significant tongue weight from hauling bikes around. I've tried to do my due-dilligence on the forums, and have gotten sucked into the rabbit hole of AHC testing, torsion bar adjustments, when rear springs should be replaced, etc. I'm happily more informed and also more confused than where I started..

In summary, the main question is: Will a heavier load spring (not significantly, only a 220 lb load spring) impact the current AHC system in a negative or positive way? Will I be doing the entire suspension/hydraulic system a service by replacing the springs and keeping stock shocks..? there is still at least 10K life in them IMO.

From my research, it appears as though the intelligent thing to do would be to check AHC pressures in the rear globes, and if to high over FSM spec, replace springs as they're likely worn out. Since I'm simply looking for extra load capacity with a stock AHC system, theoretically it seems like doing this install would only aid the AHC system over time. Having a heavier set spring rate would take more pressure off of the hydraulic system; not necessarily extending the AHC system's life, but also not causing any negatives.

This post is more of a logic check, as of course I'd like to get this right the first time...

On top of all else, I'm in the works of a AHC function check, as the previous owner was not great about system PM. beyond springs, I will be flushing the hydraulic fluid, and was also planning on adjusting torsion bars up front to ensure the AHC system is not supporting more load than it's suppose to, and concurrently cross-levelling and cranking torsion bars to proper vehicle height (and get an alignment...)

thanks all for the help in advance.

When I bought my 04 LX in 2017 it was seriousely sagging and AHC pressures were way off. The ride was horrible. I knew I would be doing a lot of off road, and a lot of towing. I replaced the back springs with the 06 land cruiser AHC version of springs which are visibly more stout than the LX version ( and much less cost than the LX springs) . I added in airbags and adjusted the torsion bars. All pressures are in spec and the ride is amazing, both on road and off. 70k miles later, and a lot of serious fast/rough off road use, I couldnt be more pleased with the ride and performance.

 

[doober]

When I bought my 04 LX in 2017 it was seriousely sagging and AHC pressures were way off. The ride was horrible. I knew I would be doing a lot of off road, and a lot of towing. I replaced the back springs with the 06 land cruiser AHC version of springs which are visibly more stout than the LX version ( and much less cost than the LX springs) . I added in airbags and adjusted the torsion bars. All pressures are in spec and the ride is amazing, both on road and off. 70k miles later, and a lot of serious fast/rough off road use, I couldnt be more pleased with the ride and performance.

That's another great option, thanks so much for the tip. Do you think going with non-AHC springs was a better route compared to a 30mm spacer? Like the one Ironman offers, for example. I don't think I need all the support King Springs offer, maybe non-AHC springs would be a good middle ground for me to. I'll be ripping it off-road loaded up with stuff, but no towing. Nice to know pressures can adjust back to FSM spec with them easily. Torsion bar adjustments took care of getting the rear pressures in spec on their own?

 

[newbielx470]

Generally, you can keep the original torsion bars forever. Since the torsion bars are fully adjustable you can simple increase the preload over time. The reduction in spring rate isn't enough to warrant replacement, IMO.

If you're adding a 200# steel bumper with a 100# winch and a 50# second battery in the engine bay, then a non-AHC Toyota torsion bar makes sense.

If you're not adding huge weight, consider those torsion bars lifetime parts.

Thank you for the great insight! The only after-market item I have on my 250k miles LC with stock AHC is an ARB front bumper and aluminum skid plates, would it be sufficient if I just check the front/back pressures and gradation regularly (currently all good) and adjust the stock torsion bars per needed?

 

[suprarx7nut]

Thank you for the great insight! The only after-market item I have on my 250k miles LC with stock AHC is an ARB front bumper and aluminum skid plates, would it be sufficient if I just check the front/back pressures and gradation regularly (currently all good) and adjust the stock torsion bars per needed?

Yes, check pressures and gradations every year or two (or if you add/remove lots of weight) and you're good.

 

[doober]

Yes, check pressures and gradations every year or two (or if you add/remove lots of weight) and you're good.

Quick update. Thanks for the great video, that helped a bunch with checking pressures. I was way high in the front at about 8.6 mPa, I put 8 turns on the torsion bars which brought me down to about 6.5 mPa, a little low but I felt it was fine. My rears only dropped 0.3 mPa with all those turns on the bars and it settled at 7.3, so I'm fairly certain it's time for new springs since my truck is bone stock atm. My ride is noticeably better all-around and a lot less harsh up front. With new springs, I think it'll feel great. I thought my globes were bad, but after doing this procedure I think they have life to 200K left in them (I have 9 graduations in the reservoir, before doing this I had 8).

Anyways, mostly wanted to say thanks for the great video and help, I can't imagine an easier way to basically determine everything wrong with your suspension system... I've decided to stick with AHC springs (found used ones with 40K miles on them) and I'm going to buy an ironman spacer kit for a bit extra load capacity. Thx again!

 

[Daniel11]

Bonsoir,
je suis en France et j'ai modifié mes suspensions à l'arrière,
j'ai remplacé les ressorts d'origine par des ressorts de Mercedes à charge progressive, j'ai gagné 150 kg de plus et je garde toute la plage de reglage de la suspension,
pour le poids j'ai fait des essais jusqu'à la surcharge
mon 100 est super confortable et je n'en changerai pas,
je fais aussi des modifications sur les sphères, je les modifies pour y insérer des clapets de recharge et recharge à l'azote avec 26 bars et 28 bars, bien entendu cette recharge se fait sur des sphères en état c'est à dire avec une plage de 9 graduations c'est à dire qu'il reste la moitie des pressions dans les sphères,
j'ai aussi bricolé un système pour contrôler la pression des sphères.
voici quelques photos

 

[Daniel11]

La sphère modifiée

 

[suprarx7nut]

Bonsoir,
je suis en France et j'ai modifié mes suspensions à l'arrière,
j'ai remplacé les ressorts d'origine par des ressorts de Mercedes à charge progressive, j'ai gagné 150 kg de plus et je garde toute la plage de reglage de la suspension,
pour le poids j'ai fait des essais jusqu'à la surcharge
mon 100 est super confortable et je n'en changerai pas,
je fais aussi des modifications sur les sphères, je les modifies pour y insérer des clapets de recharge et recharge à l'azote avec 26 bars et 28 bars, bien entendu cette recharge se fait sur des sphères en état c'est à dire avec une plage de 9 graduations c'est à dire qu'il reste la moitie des pressions dans les sphères,
j'ai aussi bricolé un système pour contrôler la pression des sphères.
voici quelques photos

View attachment 2825284

View attachment 2825285

View attachment 2825286

View attachment 2825287

View attachment 2825288

La sphère modifiée

View attachment 2825319

I think the factory pressure of the spheres is about 750 psi, or 52 bar. Is the 28-29 bar meant to be less or more than factory?

 

[Daniel11]

Sur un serie 100 diesel la pression des sphères est de 24 et 26 bars pas plus

 

[drspace5]

When I bought my 04 LX in 2017 it was seriousely sagging and AHC pressures were way off. The ride was horrible. I knew I would be doing a lot of off road, and a lot of towing. I replaced the back springs with the 06 land cruiser AHC version of springs which are visibly more stout than the LX version ( and much less cost than the LX springs) . I added in airbags and adjusted the torsion bars. All pressures are in spec and the ride is amazing, both on road and off. 70k miles later, and a lot of serious fast/rough off road use, I couldnt be more pleased with the ride and performance.

This sounds like what I may need to do. My 06 LX is my wife's daily driver. Only added weight so far is a roof rack, but when we go for an expedition, we pack several hundred pounds of gear in back and on the roof. We probably do 2-3 trips per year. For such intermittent heavy loads, the King springs seem like overkill. Do you ride with heavy loads with your set up? If so, how does the AHC function for you?