"OBK" coil springs for AHC 100 Series Cruisers?

[oklastmod]

My stock (no armor, 1" sensor lift) 05 LX470 w/ AHC is on its original rear coil springs. The AHC works flawlessly -- 4 new globes, new AHC fluid -- both front and rear pressures in spec. To get the rear pressure in spec I had to install 30mm spacers. After riding around with those spacers for about 6 months, I felt like it was time to replace the tired original springs with new ones. After reading through a bunch of posts on AHC coil springs, I learned that we have options:

Post in thread 'Coil springs for AHC'

Dec 11, 2019

While researching replacement oem AHC springs for a friend of mine with a UAE spec 100 series with 1HD-FTE with a rear sub tank (I'm so jealous!) I came across this interesting observation. LHD 100 as a 15mm taller springs on the LH while RHD 100 has same springs on both sides.

48231-6A710 H=449.5, RED PAINTED ( GEN LX470 RH )
48231-6A720 H=???, ( GEN LX470 LH )
48231-6A730 H=???, YELLOW PAINTED ( USA LX470 RH )
48231-6A740 H=???, GREEN PAINTED ( USA LX470 LH )
48231-6A750 H=455, PINK PAINTED
48231-6A760 H=470, ORANGE PAINTED
48231-6A770 H=485...

• CivicFerio

• 

There's about a dozen part numbers for OEM coil springs w/ AHC, each spring varying in height (and possibly coil thickness?) . I was flirting with the idea of King Springs (KTRS-79), but opted out in fear of overkill for my stock weight. I didn't just want the same OEM springs that came with the LX, because I'm an idiot and wanted just a little more support, just in case. Normally I order my parts from Amayama, but found a great deal on new coil springs for a LC100 w/ AHC, but for the HDJ100, which was the Turbo Diesel European spec "Amazon" LC 100. The HDJ100 was ~500lbs heavier. The part number for the coil springs on the Ebay listing were T4014 and 48231-6A770 (Toyota OEM part number). Coil springs were advertised as 460mm tall, but I measured both at ~453mm. (See pics)

I thought I was getting Toyota OEM springs, but as soon as I saw them I could tell they were aftermarket. They're imprinted with a logo that reads "OBK Made in Japan". After doing some research, the manufacturer OBK looks legit. PRODUCTS | OBK | Manufacturing from JAPAN - https://en.osakabane.com/products/

Since both springs are the same height, I'm going to install a 15mm spacer on the driver, cuz that's what we do to cross-level our US spec Toyotas. I'll probably do this job tomorrow and will compare the old springs side-by-side with the new ones -- probably weigh them both and observe any differences in coil thickness. I'll try provide Techstream AHC data of before/after pressures as well as document any changes to drivability (for better or worse).

 

[David310]

The more AHC data points the better!

 

[GTV]

I would assume the additional weight from a diesel would only affect the torsion bars but perhaps the added weight from an aux tank/relocated spare would require different coils as well. Looking forward to your findings.

 

[hoser]

The 48231-6A770 coil springs are used in both the HDJ100 and UZJ100 with rear aux tanks.

 

[GTV]

The 48231-6A770 coil springs are used in both the HDJ100 and UZJ100 with rear aux tanks.

And those are AHC springs?

 

[hoser]

Yes

 

[Jack90210]

The 48231-6A770 coil springs are used in both the HDJ100 and UZJ100 with rear aux tanks.

I thought that the "brown dot" 48231-6A780 was the spec for the driver's side. Relevant post quote below:

Post in thread 'Coil springs for AHC'

Feb 28, 2021

Alas, sleeping easy is not always easy.

Thanks for confirmation of what I had read elsewhere. After sending the photos and misc other info to the service advisor, he and the service manager continued to offer alternate explanations like, 'manufactures quality control marks', 'Lexus has no documentation of colors' and 'the warehouse said it was not meaningful'. The service manager pulled off the remaining bit of part label on which the RR was visible, and that was his definitive lead off: 'Right Rear'. Leading credence to your possible explanation of why they were installed reversed...

• IndroCruise

 

[oklastmod]

Just finished the job and am very pleased with the results.

I failed to mention that I have a Uhaul trailer hitch (previous owner) so that adds some extra weight to the rear (~40lbs). Also worth mentioning, I always ride w/ 3rd row seats installed and carry a large duffle bag w/ tools & gear in the back weighing ~25lbs.

With a full tank of gas, here are the Before/After Techstream AHC pressures

Before w/ old OEM coil springs & pair of 30mm spacers)
Front Pressure: 7.0 Mpa-g
Rear Pressure: 6.5 Mpa-g

After w/ new OBK coil springs & 15mm spacer on Driver side
Front Pressure: 6.8 Mpa-g
Rear Pressure: 5.8 Mpa-g

Before AHC data:

After AHC data:

My "After" results were repeatable -- a consistent 0.7 Mpa-g reduction in rear pressure. In terms of any significant changes to drivability, I can't really say that I can tell, maybe the rear feels a little more put together? A tad softer? No bounciness or pogo effect that others have mentioned when going to a heavier spring like the KTRS-79.

Here's a pic of the new OBK coil next to a 21 year old OEM coil from my 2005 LX470:

The OBK coil is taller compared to the old OEM one by ~10mm. I measured the old driver's side OEM coil at 445mm. In terms of weight, the OBK coil weighed in at 2.6kg vs the OEM coil at 2.3kg. The coils themselves on the OBK were also slightly thicker at 1.37mm vs 1.27mm on the OEM. These are my own amateur measurements w/o calipers.

Closeup of the OBK coil:

Installation pic of driver's side w/ 15mm spacer

All in all, I don't think these are that much of a departure from OEM. They are mildly heavier duty than OEM AHC springs.

I think that tomorrow I'll start adding some heavy gym weights into the back and check the Techstream pressures. Might be a good analog for simulating the addition of a steel bumper. I'll add the weights in intervals until the rear pressure goes out of spec. Let's see how much they can handle.

 

[hoser]

I thought that the "brown dot" 48231-6A780 was the spec for the driver's side. Relevant post quote below:

Post in thread 'Coil springs for AHC'

Feb 28, 2021

Alas, sleeping easy is not always easy.

Thanks for confirmation of what I had read elsewhere. After sending the photos and misc other info to the service advisor, he and the service manager continued to offer alternate explanations like, 'manufactures quality control marks', 'Lexus has no documentation of colors' and 'the warehouse said it was not meaningful'. The service manager pulled off the remaining bit of part label on which the RR was visible, and that was his definitive lead off: 'Right Rear'. Leading credence to your possible explanation of why they were installed reversed...

• IndroCruise

Yes, 48231-6A780 is the complimentary LH side spring. 6A770 is the RHS.

 

[Jack90210]

Yes, 48231-6A780 is the complimentary LH side spring. 6A770 is the RHS.

Thanks, I appreciate you verifying!