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Classic Saab 900: Curing convertible hydraulic piston groans

This article kindly written and supplied by Mel Smith

Remove the back seat and side panels

Start by removing the seat base, five or six bolts along the front and it pulls out. The seat back has four fixings. If you lean over the back of the seat there are two slots in the top of the bag that the top folds into near the headrests. There's a bolt behind each of these. You'll need a socket slacken but don't remove these. Remove the bolts at the bottom of the seat back near the seat belt clips, then the seat back should push up and come out. Remove all the screws that secure the side panels (some behind the speaker covers) and remove the side panels or place them to one side (no need to remove the speakers and the lights just push out)

Remove the Hydraulics, Pistons, Pump and Motor

Undo the clips and remove the clevis pins from the top of each piston. There's some washers and an oilite bush at the top note their orientation (I can't remember) press the down switch to fully retract the pistons. You should be able to see the bolts that hold the pistons in place, two on each side, take these out they hold the bracket for the pistons which will come out. You can now release the pistons (the one on the drivers' side, RHD, has to pass under the fuel lines/hand brake cable and the bypass valve pulls out) Remove the convertible top fuse from under the bonnet (hood) then cut the wires to the motor about half way between it and the relays. I know it sounds drastic but it really makes things simpler. Crimp or solder some connectors on. The motor/pump just pulls out and can now be removed from the car with the pistons.

The Pistons

Label at the motor/pump where the hydraulic lines go e.g.; lines to piston tops lines to piston bottoms. Get a container and wear some gloves Disconnect the lines at the pistons be prepared for some fluid loss Plug/cover the lines to stop any ingress of dirt The tops screw off the cylinders just push up the tab and rotate. Empty the fluid out You've now got to pull the piston out from the cylinder body. Mine were very tight I used a bolt passed through the eye of the piston rod, fastened it in a bench vice and pulled like hell on the cylinder body. Careful !!! I got fluid all over doing the first one. Leave the cylinder body to one side and concentrate on the bottom seals. Wipe off the old fluid being careful with the seal edges. Check the bottom seal isn't damaged, the seal should look the same on the top and bottom edges.

If the seals are badly damaged/worn you'll need new seals or pistons. Mine both showed some wear at the bottom edge, slight scoring and a rough edge, which was probably due to a lack of lubrication. Because of this I took the seal off and put it back the other way up. The top seal again holding the piston rod through the eye pour some of the new fluid, 10w oil, on to the piston rod while working the cylinder top back and forth until it becomes a nice smooth action. The bottom seal wipe out the cylinder body and rinse it out with some new fluid. Dip the bottom seal in new fluid and reassemble the piston, carefully inserting the seal again holding the piston rod through the eye cover the line connections with something, maybe newspaper, and work the rod in and out occasionally splitting the piston, re-oiling and stopping for a rest. The seals should eventually ease up to give a smooth action but this may take some time and effort. Note I got blisters doing the bottom seals they were initially very stiff and took some time to free off properly. Finally when a smooth action is achieved unscrew the top of the cylinder and with the piston rod pushed in fill the cylinder with new fluid and screw the top back on properly.

Flushing the Reservoir, Pump and Lines

Undo the bolt at the top of the motor/pump reservoir and empty out all the old fluid the lines may still have old fluid in them you should be able to drain this out without disconnecting them from the pump. Now flush out and refill the reservoir with new fluid letting it drain down through the lines Reconnect the cylinders to the lines and top the fluid up to the mark on the reservoir.


I made up some cable extensions and plugged them into the new connectors in the motor. Took the battery out of the car and bled the system in the kitchen with the motor pump on the side and the pistons on the floor. I just touched the wires to the terminals on the battery and swapped the wires back and forth to reverse the pump. In hindsight I should have swapped the wires over at the connectors well away from the battery (sparks and hydrogen from the battery don't mix very well but I didn't have any mishaps) Tip here is to concentrate on one piston at a time try to work all the bubbles up the pipes to the motor. Try not to pump them back in to the piston Also keep the connectors uppermost You'll know by now if the groaning's gone.

Refit everything

One of my pistons was still very slightly groaning so when I re-fitted everything in the car I left the clevis pins out from the tops of the pistons for a few days. Every time I stopped at traffic lights or wherever I'd operate the pistons in and out a few times.

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