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The Caddy has a rather unique (to VWs anyway) suspension. MacPherson struts up front and a leaf spring over axle rear suspension. The main leaf is approx. 52"? long, with a long second leaf and a shorter overload type leaf on the bottom of the pack. A conventional spring shackle is in back to accomodate the flexing of the spring. Two shock absorbers mount between tabs on the tube axle and brackets on the bed sub frame.
After getting tired of the rear end bottoming out over bumps, I picked up a +1000lb. rated helper spring to attach to the rear leaf spring. This helper attaches to half the spring, clamping to it near the spring perch and then it lifts under the stock leaves.
With the bed unloaded, the ride is rather stiff in back. However, with my Caddy Shack installed and its aerodymamic down force, the ride is very nice on the highway. An advantage of the stiffer rear springs is that the lack of a rear sway bar is minimized. Until I stiffened the springs, I was looking for a sway bar that could be adapted to the Caddy, but I don't think it is necessary now.
However, I'm not totally happy with the helper springs. I suspect they cause the leaves to bind and probably unduly stress the leaves since they only strengthen 1/2 the leaf. My plans for a better fix include:
Which of the above options I choose will depend on whether I have any extra leaves from my Toyota 4Runner after I finish its suspension mods. If one of those leaves is available and fits, I'll go that route (i.e. no-cost), otherwise, I'll investigate the other options.
I had the stock (I think) rear shocks replaced with KYB Gas-A-Just shocks in 1992 (model KG5449). They have held up very well and seem to be as firm as when new. The shocks have 10mm (3/8") diameter mounting bolts top and bottom and measure 10-7/8" collapsed and 17" fully extended from center to center at the mounting holes. I find that the 17" length is slightly short and the spring wants to drop a fraction of an inch at full droop. With my helper spring, I find the shock is compressed 2" (of its 6" travel) at rest and there is about 4" of axle travel to the bump stop. So, it appears this is a decent length shock for this application.
There are some interesting Rancho shock applications that might be adapted to fit the Caddy. From the shock selection table on Off-Road.Com, I see:
Several other RS9000 models are of similar length. The RS9000 shock is adjustable and can be fitted with an in-cab remote adjuster too. The RS5000 models come in similar lengths but are fixed rate and typically are very stiff, equivalent to the 9000 at a 4 or 5 setting.