How To; Replace Brake Servo & Master Cylinder - M20 E28

[Guest DazH]

Removing Under-bonnet braking system - E28 5 Series models with M20 Engines

[Right Hand Drive]

Reasons for doing such a job:

- Fluid leaking from brake master cylinder

- Servo/cylinder failure (Pedal to the carpet or Solid)

- Engine conversions

+ Remove vacuum hose from servo. Gentle pulling should do the trick. Leaver off with a screw driver if need be. Plastic plug can snap easily so, gentle.

+ Removal of master cylinder is as you would expect. Drain old fluid and careful of your eyes! brake fluid is nasty nasty stuff. There are two hydraulic pipes going to the master cylinder. Carefully remove both these pipes.Because the method i used to drain the system is pretty rubbish (Pulling hydraulic pipe and getting a chum to push on pedal), I still had a reservoir full of fluid. I used two bolts to stem the flow of excess fluid. M10 bolts if I remember correctly...

+ Now the master cylinder is gone (easy, right?) you can proceed to remove the brake booster/servo if need be. If you just need to change the master cylinder, pop a new one on and slam ya hands in reverse to put all back together. Will be loads of air in there now so new fluid and bleed your brakes.

+ Remove 4 bolts holding servo to the bulkhead bracket. These are behind the servo. It's wise to move the black bar going across the bulkhead for better access. Undo the bolt holding it on and swing it out the way.

+ [RHD Only] The servo's rod goes through the bulk head and into the cabin. You will need to remove the glove box from inside the cab to free the rod. This is very straight forward. The E28's glove box is held up with two black fabric straps. Undo the plastic clips on these straps. The glove box will now flop open all the way to the floor. Close it again and undo the 3 bolts on the hinge. The hinge is accessible when the box is closed. I don't need pictures for this bit as if you have reached this stage, you're a clever sausage anyways.

+ Now you should be staring at the car's ECU. Ignore that, what you are interested in is just below it. You can see the rod from the servo now. It connects to another rod leading back into the engine. Ignore that one. The one you want to disconnect is on the right. Unclip it using a flat head screwdriver. Simple stuff.

+ Pull servo out from engine bay. Do what you need to do. Fix it, Replace it, Change it to a smaller one like I am (Porsche 944 servo). Put back together is literally, reverse.

Hope this helps,

Daz

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[Guest Mister Dabsy]

Great guide Daz... ;)