The Bilstein B6 4600 (part 24-011327) is a rear replacement shock built on Bilstein's monotube gas-pressure design, with a 46mm body meant for stock-height light trucks and SUVs. The manufacturer describes the B6 4600 as a direct-fit upgrade that keeps the oil under high gas pressure, uses digressive valving that responds to changing road surfaces, and is fine-tuned on Bilstein's road test. Compared with a worn factory unit or a budget replacement, the case for this shock is consistent damping under sustained use: the manufacturer says the design resists fade when towing, on gravel, or on longer off-road runs, and it works with the original springs, so a spring change is not required. Searches for a 1985 Land Cruiser rear monotube shock, Bilstein 4600 rear stock height upgrade, and gas-pressure rear shock for FJ-series trucks are a good match for this part.
Listings for this part tie it to the 1985 Toyota Land Cruiser Base, but application years and engine coverage differ from one source to another, so confirm fitment against your VIN with Bilstein before ordering. The shock uses the vehicle's original mounting points, and the manufacturer's general install procedure calls for removing the old unit, fitting the boot and stem hardware in order, and lowering the vehicle to full weight before final torque. Owners on user forums who have replaced rear shocks on Land Cruisers and similar trucks report that the upper nut is hard to reach and that old top studs can seize, so plan for penetrating oil, a ratchet with a short extension, and extra time on the passenger side.
The manufacturer states the B6 4600 does not require a spring change and can be used with the original OE spring.
The manufacturer's mounting instructions for its shock modules state that installation requires special tools and expert knowledge, and recommend a qualified suspension specialist and a chassis hoist for the work.
The manufacturer's installation instructions call for checking and adjusting suspension caster and camber to the vehicle manufacturer's specifications, checking the brake compensator and ABS, and aiming the headlights after installation.
This is a bolt-in rear shock, but it is not a quick job. Per the manufacturer's installation sheet, you remove the original shock following the vehicle service manual, slide the boot and boot adapter onto the stem, install the lower washer, sleeve, and bushing, seat the shock in its original location, then add the upper bushing, washer, and nut. Support the vehicle on a hoist or jack stands, and lower it so the full weight is on the suspension before torquing the fasteners to the service manual specification. Owners on user forums suggest removing the inner fender liners for more working room, and to expect the upper nut to be the most time-consuming fastener. A socket set, torque wrench, penetrating oil, and a wire brush for the stud threads cover most needs. Given the special-tool and alignment requirements, many owners choose a shop for the install.
