[MtnClimber]

Attached below are some close-up photos of the SR5/Ltd coil-spring seats. Photos are of the passenger side. (Parts on the drivers side are identical except that the rear lower control arm is, of course, rotated 180 degrees.)

Looking at an online parts manual, it looks like the upper spring seat (part of the Rear #1 cross member of the frame) is identical with and without air suspension. (In the fourth photo below you can see that the passageway for the line going to the top of the air cylinder is present on an SR5.)

The rear lower control arms have different part numbers for SR5/Ltd (48730-09040) and Platinum (48730-09010). A key question is what is the difference and is it significant enough to preclude the Platinum rear lower control arm from accepting a coil spring?

Take a look at your platinum parts and see if there is any visible difference. One important feature that can be seen in the photos below is the "budge" protruding down from the far side of the lower control arm. This budge is where the bottom end of the coil spring terminates. (The end of the coil spring is keyed into this budge so that it is effectively restrained from rotating.) If the platinum rear lower control arm doesn't have this bulge I would guess that it wouldn't accept the springs from an SR5/Ltd. You would have to also swap out the rear lower control arm.

 

[MtnClimber]

Below I have attached another passenger-side SR5/Ltd photo from a thread by RinconVTR http://www.tundrasolutions.com/forums/sequoia/143820-sequoia-gen2-rear-spring-spacer-diy/#post1611515. This shows how the lower end of the OEM coil spring tapers down in diameter and terminates by wrapping around the center post in the lower control arm.

In minutes 0:46 to 1:05 of this YouTube video

you can see a side view of the Platinum rear lower control arms, but not their underside. The lower bulge that retains the end of the coil spring on an SR5/Ltd is not seen. Thus it appears that the Platinum rear lower control arms would not accept a coil spring from an SR5/Ltd. I'm guessing that the answer will be that to convert a Platinum to coil springs you would need to consider options such as:

1) Replace both the coil springs and rear lower control arms by OEM parts for an SR5/Ltd.

or,

2) Procure custom coil springs with lower ends that properly interface with the contours of the rear lower control arms on a Platinum.

or,

3) Fabricate custom coil spring spacers with bottom surfaces that conform to the shape to the rear lower control arms on a Platinum and upper surfaces that conform to the shape of the rear lower control arms on an SR5/Ltd. That would allow use of OEM SR5/Ltd coil springs and provide some level of rear lift.

Has anyone crawled under the back of their Platinum to see whether they agree with this preliminary conclusion? A comparison picture showing the features on the underside of the Platinum rear lower control arm would be helpful.