Weak rear suspension?

JAYALLAN3391

MEMBER
1994 JEEP GRAND CHEROKEE LAREDO
4.0L
6 CYL
4WD
AUTOMATIC
140,000 MILES

I just got the vehicle and noticed that even over small bumps it slams and bottoms out mainly on the rear passenger but some on the rear drier as well. I did notice that my trailing arm bushings could be replaced but that shouldn't cause a slam like it is, that should only cause an uneven horizontal movement in the rear.

1 Reply

CARADIODOC

MECHANIC
33,757 POSTS

This is a coil spring issue. Normally I'd have you start by measuring the front and rear chassis ride height, but in this case, I can't find the specs in any of my usual places. The next best approach is to visit any tire and alignment shop for the needed information. They all have very small books that show every model, where to take the measurements, and what they should be. Most manufacturers specify to simply measure from the ground up to a certain point, such as the bottom of the bumper or to the top of a side marker light, and compare the readings on both side to specs. Chrysler often had you measure in two places on each corner of the vehicle, subtract one from the other, to get the reading. They did that so they didn't need a huge, complicated chart to cover all the optional tire sizes that could be used.

If you don't measure chassis ride height, it is going to very close to specs if new springs are installed. The procedure is shown below. The only step I don't remember is needing to unbolt the track bar. If you do unbolt anything with a rubber bushing on something that rotates, like this one does, it should only be retightened with the vehicle sitting at normal ride height. If you tighten it with the vehicle jacked up and the suspension hanging down, that's where the bushing will be clamped. Once lowered onto the tires and the linkage pivots to its at-rest position, that bushing will be clamped in a permanent twist. That will greatly shorten its life.

If the front wheel alignment is okay now, nothing needs to be checked or changed if only the rear springs are replaced. The same is not true for the front. Even when a solid tube axle is used for strength on the front, changing the ride height changes the relationship of the steering components between the body / frame and the axle. With this design it will not change "total toe" which is a tire wear angle, but it can put the steering wheel off-center. The good news is that can be tweaked without having an alignment performed. I can address that if necessary.

Let me know how this turns out.

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