How to replace the pressure reservoir for the hydraulic brake booster on a BMW E23, also known as a pressure accumulator. This particular car is a 1984 733i, this system was found on many BMW models in this generation. When the pressure reservoir fails, this will cause a hard brake pedal and is noticeable when you hit the brakes in an emergency so its certainly a safety risk.
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Tools/Supplies Needed:
-13mm wrench and socket
-3/8" drive ratchet
-12mm, 17mm, and 19mm line wrenches
-new pressure accumulator reservoir
-degreaser
-oil pan
-new power steering fluid
Procedure:
Remove the vacuum pump, this pulls straight off. Disconnect the electrical plug. Remove the two bolts hold on the power steering reservoir. The one on the top bracket is a 13mm. There is a retaining bracket holding on the power steering hose, this used a 10mm socket and wrench. Finally one more inside the fender well, this uses a 13mm socket.
Reinstall the top 13mm on the top where the reservoir was bolted up to, this will hold the pressure regulator assembly in place so you can apply leverage when disconnecting the lines.
Disconnect the two sensors, one at the top of the pressure regulator assembly. Removing the 3 lines, the first closed to the front of the car on the engine side is a 12mm. Fluid will come out of the lines, so have a pan handy below. Next will be a 17mm. Moving over to the firewall side, there will be twice lines here which needs to be removed as well, both a 17mm and 19mm.
Remove the two 13mm bolts at the top to pull out the assembly. Using large interlocking pliers to loosen the reservoir. The new reservoir should come with a new o-ring, make sure this is installed, otherwise you’ll have a leak. Clean the assembly if needed and install the newly supplied o-ring.
Install the assembly, make sure there isn’t any dirt inside the line mating surfaces. Tighten down those two 13mm bolts.
Tighten the new reservoir, the torque specification for this is 31-36 ft lbs or 42 to 48 nm. For this I used a strap wrench, with the assembly in place, this gave me a secure spot to sufficiently tighten the reservoir.
Next is installing the power steering lines. Make sure all the fittings are clean. If you are having issues getting the lines started, you may consider loosening or completely unbolting the assembly allowing for more movement.
The 17mm on the firewall side, the torque specs are 18 to 25 ft lbs or 24 to 34 nm. The 19mm is 22 to 29 ft lbs or 30 to 39 nm. The 17mm on the engine side is 33 to 36 ft lbs or 45 to 49 nm. And the last 12mm is 11 to 13 ft lbs or 15 to 18 nm.
Remove the one 13mm for the fluid reservoir, bolt on the tab and tighten. Install the 10mm for the line retaining clip. Install the 13mm bolt inside the fender well.
Reconnect the sensors on the pressure regulator assembly. Install the vacuum pump back into place.
And after that is bleeding the power steering system. Add fluid until the it’s even with the bottom of the screen. The system should be that low, however with the engine off, you can turn the steering or any possible change of air in the system.
Then start the engine, turn the steering from left to right multiple times, full lock each way. Add more fluid as needed, make sure it’s even with the bottom of the screen.
Turn the engine off and pump the brake pedal. The air is shown by bubbling in the fluid, this is cavitation. The fluid level will rise which is normal, just don’t let it overflow over the top. Stop when it gets close to the top, then start the engine, allow the fluid level to drop, then pump the pedal again. Continue to do this while the engine is running until the bubbling has disappeared.
When done with the engine off, pump the brake pedal at least 10 times until the fluid stops rising. If the fluid gets too close to the top, remove the access fluid. The final fluid level once it’s stopped rising should be 10mm or 3/8” below the top of the reservoir. When done, install the reservoir cap and tighten the retaining nut.
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