One thing I didn't like about my 1998 Plymouth Grand Voyager was the soft rear suspension. With a full load of passengers it didn't sag, but would bottom easily on a bump. So I installed some Hellwig helper springs, model EZ-550, $60 plus shipping. A couple of problems- the shackles they give you are too long, so I used some large nuts to add
3/4 " of additional spacing so I could properly clamp the front of the helper springs to the original springs.. Also, the kit comes with a warning which they don't mention anywhere else, that it can throw off your proportioning valve. So I didn't clamp the rear of the helper springs down all the way, just as far as the too-long shackles would go.This raised the rear about 3/4" with no load. It definitely helps with the bottoming out, but didn't make a huge difference.
Here's their application catalog:
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Here's a dealer to buy 'em from:
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