TECH: Dial in the Rear Suspension
GOAL:
Check clearances for stuffing 34s in the rear, size the bumpstops, and take measurements for spring/shock applications.
PURPOSE:
I have had the Bilstein 5100s, PN: 33-187174, for a few years now. Considering they were for lifted FJ Cruisers, I've often questioned they're actual performance considering it was a popular mod and everyone says that "it's all good."
Overall, I've never been happy with the Bilsteins and I've pondered on what to get, but with no measurements, it's hard to find a shock that could possibly work.
Add in the fact that I've never checked clearances with the 34s in the rear, it was time to get off my laurels (finally) and stamp this out.
DURATION: 2 hours
TEST SUMMARY:
The idea is to cycle the rear suspension from full stuff to the bumpstops to max droop and measure the required spring and shock lengths.
I, basically,...
- Remove the rear coils
- Unbolted the shock from the lower pin
- Cycle the suspension using jack
Stuffed on bumpstops:
At max droop:
RESULTS:
With the Califab arms installed, I found that the downtravel limiting component was the panhard bar. To a lesser extent, the parking brake cable. Not much extra slack there.
For springs, all measurements are from the bottom of the rubber isolator to the perch on the axle.
For shocks, all measurements are from the metal mount surface to the pin centerline on the axle.
At bump:
Compressed Spring length: 7-3/8"
Compressed Shock length: 17-5/8"
Max droop:
Extended Spring length: 20-3/8"
Extended Shock length: 29-3/4"
OEM/Dobinson rear coils:
Extended Shock length: 26-1/2"
As a result of this test, it confrmed my suspicion that the 5100s are completely inadequate as a shock replacement. Even when using OEM/Dobinson rear springs, the 33-187174 5100 shock is too short and is constantly using up the entirety of its length long before the OEM springs fully extend.
Thankfully, the bumpstops do not need to be modified for the 34s (295/70r18). There is plenty of clearance to stuff 35s in the wheel well with margin using OEM bumpstops.
That's one less thing to worry about.
In short, to maximize articulation, in theory, you need a spring 20-3/8" tall that can collapse to 7-3/8" mated with a shock that has a compressed length of 17-5/8" and extended length of 29-3/4". A linear spring probably could achieve that. A progressive spring might not, especially one that tall.
Probably will need the Califab links to achieve these numbers since the OEM rubber bushings tend to bind and limit articulation, much like what the OEM panhard is doing at the moment. You could probably achieve another couple of inches with a heim'ed and polyurethane panhard bar...