Coil springs for AHC

Joined
Jun 25, 2006
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589
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Ridgefield, WA
 
 
Im going to install new coils in the rear in a couple weeks. Does anyone have a sense of how new OEM AHC coils compare to used and tired (180k) non-AHC coils? I can get a set of tired used springs for cheap, but I don't want a stiff ride. I may put a 150lb drawer system in the rear sometime this winter, but that's not really much heavier than the 3rd row.

Im running mostly stock weight now, with the exception of a heavy front bumper. Eventually I plan on running a little on the heavy side: extended range fuel tank, rear bumper with spare and swing outs, roof rack, and sliders. I'll probably do these in reverse order over a span of 3-4 years. (Or i go broke, which ever comes first.) With all this extra weight I expect I'll eventually be in the market for new non-AHC or 80 series springs. For now, for the next year or so, I'll be running more or less stock weight over the rear axles.

With whatever coils i put in, im also installing airbags for towing and other heavy conditions. Which should keep me in spec pressure wise between springs.

Thoughts?
 
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Jul 20, 2015
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Tallahassee, Florida
 
I'm looking to do the same exact thing. I just picked up a '99 LX470 with 103k and can feel that the springs are a bit worn. Toyed with the idea of airbags, but will need to replace springs regardless.
 
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Colorado
 
I replaced my worn AHC springs about a year ago. I normally carry 100lbs over stock in the rear and tow a light RV occasionally with no airbags. If I were to carry a constant heavy load with the AHC system, I'd use LC100 springs or something bigger as needed. I'd consider using airbags if I constantly was increasing and decreasing weight in the vehicle.
 
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PA
 
 
Assumption .. But wouldnt the new springs ride the same if not better ? The springs will decrease the pressure put on the system allowing it to respond more appropriately - sounds like a winner. Your springs are there to support / alleviate stress put on the AHC but not ultimately provide the "ride"

Ask PADDO - AHC guru

And congrats for having 180k miles on your AHC !
 
Joined
Sep 27, 2007
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Charlotte NC or ACT area Australia
 
 
Assumption .. But wouldnt the new springs ride the same if not better ? The springs will decrease the pressure put on the system allowing it to respond more appropriately - sounds like a winner. Your springs are there to support / alleviate stress put on the AHC but not ultimately provide the "ride"

Ask PADDO - AHC guru !
LOL, quash that slanderous comment quick smart. uHu rhymes with guru!

Anyways, bozncsurf is spot on. Replacing old, compressed springs helps support and maintain the rear's height so the AHC system doesn't have to make up for the springs' deficiency through higher pressures for more lift and support force. Higher pressures negatively affect the damping and ride quality provided by the damper assemblies and their accumulator globes, particularly as your accumulator globes' nitrogen charge diminishes naturally over the years.
 
Joined
Jun 25, 2006
Messages
589
Location
Ridgefield, WA
 
 
Thanks. I'm going to stick with AHC springs for now. If/when I get heavier, I will revisit the non-AHC springs.

Follow-up question. I've been working on sourcing some rear springs. Beno can hook me up with LC AHC springs but not LX springs. They have different part numbers. What is the difference between LX coil springs and Land Cruiser AHC coil springs?

LX PNs:
RH: 48231-6A730
LH: 48231-6A740

LC PNs:
RH: 48231-6A770
LH: 48231-6A780

As near as I can tell, the LX springs have the same PN from 98 to 2007. Of course the LC100 didn't offer AHC until later model years. Can anyone confirm/deny that the LC parts will fit the LX? Are there differences in the spring rate?
 

hankinid

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Jul 27, 2009
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SW Idaho
 
 
Thanks. I'm going to stick with AHC springs for now. If/when I get heavier, I will revisit the non-AHC springs.

Follow-up question. I've been working on sourcing some rear springs. Beno can hook me up with LC AHC springs but not LX springs. They have different part numbers. What is the difference between LX coil springs and Land Cruiser AHC coil springs?

LX PNs:
RH: 48231-6A730
LH: 48231-6A740

LC PNs:
RH: 48231-6A770
LH: 48231-6A780

As near as I can tell, the LX springs have the same PN from 98 to 2007. Of course the LC100 didn't offer AHC until later model years. Can anyone confirm/deny that the LC parts will fit the LX? Are there differences in the spring rate?
The LC springs will definitely fit...

Since the LC doesn't use AHC, LC springs are a higher rate (pounds per inch of deflection) than the LX.

Whichever you pick, you need to take the truck to a dealer or indy shop with access to TechStream and verify your AHC pressures are within specifications on all 4 corners. Local Lexus dealer here in BOI says that will take less than an hour to check and adjust as necessary, and costs ~$125.

hth

Steve
 

ranma21

Supporting Vendor
Joined
Apr 18, 2005
Messages
3,197
Location
Houston, TX
 
 
 
Thanks. I'm going to stick with AHC springs for now. If/when I get heavier, I will revisit the non-AHC springs.

Follow-up question. I've been working on sourcing some rear springs. Beno can hook me up with LC AHC springs but not LX springs. They have different part numbers. What is the difference between LX coil springs and Land Cruiser AHC coil springs?

LX PNs:
RH: 48231-6A730
LH: 48231-6A740

LC PNs:
RH: 48231-6A770
LH: 48231-6A780

As near as I can tell, the LX springs have the same PN from 98 to 2007. Of course the LC100 didn't offer AHC until later model years. Can anyone confirm/deny that the LC parts will fit the LX? Are there differences in the spring rate?
I can get the Lexus springs for you if you prefer to go with Lexus springs ;)
 

uHu

Bridgeburner
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Nov 27, 2005
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Location
Oslo, Norway
 
 
48231-6A750 W(ACTIVE HEIGHT CONTROL); H=455, PINK PAINTED
48231-6A770 W(ACTIVE HEIGHT CONTROL); H=485, PURPLE PAINTED
These are the ones used for both UZJ and HDJ in the EU market, right and left, and on both rhd and lhd. The pink is the standard, and the purple 30 mm longer, for a few pounds extra fat. It would have made sense to have a longer/stronger one on the left tho' as that's the heavier side.

So, in the N.A. market, the numbers are different:

48231-6A770 W(ACTIVE HEIGHT CONTROL); H=485, PURPLE PAINTED, RH
48231-6A780 W(ACTIVE HEIGHT CONTROL); H=500, BROWN PAINTED, LH
Also for the non-AHC, there's a longer spring on the LH side, which there isn't on the EU version.

Go figure.
Edit: Well - one difference is that in EU, the trailer tounge weight is never over 75 kg (150 lb), while in the US, I understand that 10 % is common, giving nearly 300 kg ekstra on a heavy one.

And I just ordered new springs, purple. Should have ordered one brown...

Edit: I'm sure you could get two Brown ones as well, and compensate with the torsion bars. That's how it is on my side of the puddle anyhow. That would be the highest spring rate we could get with oem ahc springs.
 
Last edited:
Joined
Oct 3, 2014
Messages
109
Location
San Diego, CA
 
I've had a lot of success and enjoyment with my king springs. KTRS-79. I will admit I have a friend in Australia who shipped them to me at a very good discount which helped substantially with cost. I have about 200-500 lbs in the back at most times with the least being about 200 because of my bumper and carriers. The springs are a bit shorter than stock but significantly beefier. My pressures are within normal range after the upgrade.

Just another spring to consider.
ImageUploadedByIH8MUD Forum1440450045.774604.jpg

And they're yellow so they're "obviously" more sporty. ;)
 

uHu

Bridgeburner
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Nov 27, 2005
Messages
2,011
Location
Oslo, Norway
 
 
More ingredients in the soup:
Australian market:
48231A SPRING, COIL, REAR RH
48231-6A770 H=485, PURPLE PAINTED - $130.46
48231-6B010 H=515.5 - $317.30
48231B SPRING, COIL, REAR LH
48231-6A770 H=485, PURPLE PAINTED - $130.46
48231-6B010 H=515.5 - $317.30

Are the 515 mm long ones for those with the sub fuel tank?

Edit:
The yellow ones look good. Nice color too.
 
Last edited:
Joined
Sep 27, 2007
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Charlotte NC or ACT area Australia
 
 
FWIW I've got a set of relatively new, very lightly used (less than 1 month fitted) LX coils on my shelf and they measure: 460mm/12.2mm dia green spot and 445mm/12.1mm dia yellow spot. Others have installed LC AHC coils in their LXs with no complaints.
 

TeCKis300

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Apr 27, 2011
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San Diego
 
Another option is to add a 30mm spacer to the rear. This will add additional pre-load to the stock rear springs to enable more constant weight handling of the AHC system. I did this recently in prep to tow a travel trailer. Worked great. I can't quantify how much more weight handling it added, but I was at the lower end of calibrated AHC pressures at normal right height.
 

txtortoise

SILVER Star
Joined
May 7, 2004
Messages
405
Location
San Antonio, Tx
 
 
 
Lexus Parts Discounts

I'm going to post this separately, but in case it helps here:

I know Beno and one other vendor offer great prices on LC parts, but sometimes you must have LX specific stuff. My local Lexus Parts guy is able offer 15% off to the group, at a minimum, and depending on the item maybe a bit more.

If you're in a bind and every little bit helps, give him a call:

Brian Sargent
Lexus at Dominion (San Antonio)
Phone: 210-816-4000
email: bsargent@northparklexus.com (same parent company)
 
Joined
Jun 25, 2006
Messages
589
Location
Ridgefield, WA
 
 
PMed you back ranma21.

Thanks y'all... very much appreciated!

I'm convinced my rear springs are tired enough I don't want to use a spacer. I don't want too much spring.

@uHu, and others, a little spring theory: the springs appear to be differentiated by uncompressed height, right? So going back to freshman physics, the force provided by a spring is F = kx where 'x' is the compressed (or stretched) height and 'k' is the spring constant.

If I understand correctly, the intent is the springs are compressed to the same ride height with the same AHC equipped vehicle? That being the case, then assuming the OEM AHC coils, have roughly the same spring constant (k), then with the longer springs will be compressed (x) more to reach the same ride height and thereby can support more weight for the same hydraulic pressures. It is a similar theory to adding a spacer. In fact, based on all of the above PNs and Heights, there's about 30mm difference between the several springs. 40mm for the LC to LX springs.

I just can't quite nail down how much extra weight capacity those 40mm add. Or, how much added weight would approximate the similar spring force as a stock unlaoded LX. I've driven a stock AHC equipped LC and it felt good, not noticeably more or less harsh than my LX before things started showing their age. I don't imagine LC had much, if any, extra weight over my LX. It seems like the LC springs should do fine, especially as I plan to add a little extra weight in the form of sliders, drawers, roof rack, etc, over the next several months.

@PADDO, why did you take off the near new LX OEM springs? Are you looking to get rid of them?
 
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Charlotte NC or ACT area Australia
 
 
I picked up new coils, new and used globes and shocks from a local guy who did an AHC delete. Not looking to sell, sorry. Last time I looked LC AHC coils were $70ish ea, if there is any difference between LC and LX coils I suspect you'd never know due to other variables like damper accumulator charge variations, tires etc etc.
 
Joined
Jun 25, 2006
Messages
589
Location
Ridgefield, WA
 
 
I've got a set of new 770/780 springs with insulators and lower shock bushings on order from Beno. Thanks for the discussion so far.

I put a tired set of LC100 non-AHC torsion bars up front to counter the added weight of the winch/bumper a couple weeks ago. (Well, my friendly neighborhood mechanic installed them.) That worked great. I had to turn down the tbars a bit, but the pressures up front are good.

I hope to do the rears myself. I can't wait to get the rear squared away too. :bounce:
 
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Jun 25, 2006
Messages
589
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Ridgefield, WA
 
 
Update. I got my springs and installed them over the weekend along with the airbags.

With no pressure in the airbags, I was surprised that my Neutral pressure wasn't lower in the rear. I went from 7.7MPa with old springs to 6.9MPa with the new springs. (Front pressure is 6.6MPa) I think that is exactly in spec, but I had expected to have slightly lower rear pressure with the longer springs and no additional weight in the rear.
 
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Sep 27, 2007
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Charlotte NC or ACT area Australia
 
 
How's your rear height? if too high that'll cause higher than expected pressures. At correct height, and with the front set at 6.9, you should see rear pressures around 6.2 to 6.3MPa. Of course that's without any additional weight due to a front bar and winch and the moment that creates. Installing 30mm spacers with new coils gets the rear pressure below 6.0MPa which I think is pretty satisfactory, particularly if you don't have new damper accumulators.
Did you happen to measure the dia and free standing coil lengths of the LC AHC coils? Just to confirm they are same-same with LX coils.
 
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