Fiero Projects

Purpose and Reason for the 88 cradle


To improve the rear suspension. Thier are many improvements in the rear 88 cradle over the 84-87 cradle.

Why is the 88 rear suspension on the left better than the 84-87 suspension on the right? Read on for the answers.
88 cradle 86 cradle

Proper bump steer in the 88.

Both cradles have bump steer. This is as designed. The problem with the early cradle is that the bump steer is for front wheels, that is the further the suspension moves up the more the tire toes out. This cause the trailing throttle over steer. As the car slows down in a corner weight shifts from the rear to the front, the rear suspension moves down in relation to the rest of the car. This causes the tire to toe in, and increase the slip angle requirement with less weight on the wheel. This leads to the tire slipping and the car spinning around.

Also in the early cradle as the car increases speed in a corner the weight of the car shifts to the rear. This cause the rear suspension to move up in relation to the car ( the suspension compresses ). This causes the wheel to toe out. This causes rear steering in the car.

In the 88 cradle the bump steer is designed for a rear wheel. As the suspension moves up the tire toes in slightly. This cause the proper response to driving input. As the car slows down in a corner the weight shifts from the rear to the front, the rear suspension moves down in relation to the rest of the car. This causes the tire to toe out. This decreases the slip angle requirement, in proper relation to the lessened weight on the tire. This causes the car to maintain the same line through the corner.

Also in the 88 cradle as the car increases speed in a corner the weight shifts to the rear. This cause suspension to move up, this causes the tire to toe in slightly. This increase the slip angle requirement in relation to the increased weight on the tire. This causes the car the maintain the same line through the corner.

Anti squat in 88

The early cradle with a lower a-arm and level inner pivot points has no forward/rearward movement.

The 88 cradle has a trailing arm that is mounted higher at the front than at the nuckle. This causes slight rearward movement as the suspension travels up and the trailing arm levels out. The inverse is also true. As the suspension travels down the trailing arm angles more causes the tire to move forward slightly. As the car accelerates in a straight line the tire pushes backward on the ground and forward on the car. The inertia of the car pushes backward on the tire. This tries to move the tire forward in the wheel well. The only way for the tire to move forward in the wheel well is also move down. This is anti squat.

Solid mounts in 88

The early cradle used rubber mounts in both front and rear of the cradle. This allowed the cradle to move in relation to the rest of the car. This caused poor handling by introducing slop in the movement of the suspension.

The 88 cradle uses no rubber to attach to the frame. This holds the cradle ridgid in relation to the rest of the car. This prevents the slop the early cradle has.

Relocated upper strut mounts

The relocated upper strut mounts when using the 88 cradle cause more camber per unit of upward suspension movement. This allows the tire to maintain better contact patch with the road as the cars body rolls in a corner.

The Plan

To replace the rear cradle in my car with a the rear cradle from an 88. I plan to start with just replacing the cradle and keeping the stock 86 struts. I will use the coilover kit from to relocate the strut mounting points.

How to

Thier are parts needed from both cars to properly complete this conversion.
From the early (84-87) fiero you need:
Car (of course).

From the late (88) fiero you need:
cradle (of course)
drive side engine mount bracket
drive side engine mount
rear calipers
two rotors (from front or rear)
all parking brake cables
exhaust from cat back

Cross over pipe from exhaust, cross over pipe for coolant, and exhaust down pipe must all come from same year car.

Parts that can come from either car:
passenger side engine mounts

Problems you will have

There are several things about this swap do not quite fit right.

Strut relocation

strut tower new mount
This is the most well know and easiest to solve problem. The struts must be moved in board and forward. If using held motorsports coil over kit it comes with the proper bracket to relocate the strut. You need just cut one hole per side.

Driver side coolant

Before with interference
If using the early exhaust crossover pipe and coolant crossover tube, the drive side trailing arm will interfer with the lower driverside rubber coolant tube. To fix this I cut the metal coolant crossover tube just after the first bend. I then went to the parts store and got some rubber hose the same size and with a simple 90 bend in it. To get one I had to look thur there stock and find one I could cut to fit. It ended up looking like this.
After with new rubber

Passenger side coolant

contact on passenger side
The passenger side coolant tube will rub the front mounting washer on the 88 cradle. This is not a problem and does not need to be changed. I simply made sure that the washer was rubbing on the metal pipe clamp and not the rubber. I have been driving the car about 1500 miles so far with no trouble.

Fender well

area needing cutting
On both sides the parking brake cable and trailing arm will interfere with the fender well. This is easy to fix with a knife, just cut the fender well in the interfering area. As seen in the picture, I cut the green outlined area.

Driver side parking cable

needed wire holder
On the driver side the parking brake cable will rub the tire if not held in place by a little wire. On the 88 this attaches to the mounting slot the 86 brake line is mounted in. A small hole must be drilled in the frame. As seen in the picture the hole is circled in green and the wire is highlighted in green.

Other pics of interest

just before install
just before install
Passenger side installed notice I had to buy longer braided steel lines. The frame mount for the brake lines on the 86 is in front of the wheel well. On the 88 the frame mount for the brake line is in the rear of the wheel well. To reach from the frame mount on the 86 and the caliper from the 88 a longer than stock line must be used.
passenger side installed
88 passenger side engine mount on top. 86 passenger side engine mount on bottom. They are not interchangable and the 88 mount must be used. As evident by the picture I had to buy a new 88 mount.
passenger engine mounts
88 rear sway bar mounts. These attach to the lower strut mounting bolts.
88 rear sway bar mounts
88 engine mount bracket. This is only on the 88 and must be used. In the second picture you can see the new mount I had to buy.

86 engine passenger side engine mount bracket ( can't be used ).

Final thoughts

This swap was a lot of work and time. Was it worth it? YES YES YES. The car drives way better ! It is WAY better. All the talk of the differences can't explain the feeling of driving the transfigured car. Cornering is a whole new game. No longer must I stay on the throttle to get around the corner without endoing. I can accelerate in a corner without the rear end steering itself out of the corner. The 88 really is a much better rear suspension design than the 84-87 for all those reasons I listed above. Particular corners I had trouble driving hard though before because of an uneven road surface are no longer a problem. The difficulty as high speeds (80-100 mph) over uneven roads is gone. We will see, come race season, if I can do any better ( read as less spinning out ).

My Costs

$800.00 for running 88 GT.
$324.00 for coilover kit from
$10.00 rubber coolant hose
$50.00 new passenger side engine mount