Notes on brake bleeding

Bleeding the E Type brake system can be very difficult, especially if there is a lot of air in it.

The use of a urinary catheter syringe has revolutionised this process for me. I replaced a brake servo on my S1 4.2 yesterday, and went from scratch to hard pedal in about 10 mins. I used just under 500ml of fluid, 240ml for flushing, the rest for refilling the reservoir bottles, although it would be wise to have a litre available. 

These syringes are designed for flushing urinary catheters. They hold 60ml and differ from normal Luer-Lok syringes in that they have a much larger diameter conical tip. This is a perfect size to make a good push fit into the brake reservoir hose. I steal them from work but I'm sure you could buy them from any pharmacy. 

 

Catheter syringe1

 

Catheter syringe

A note about reservoirs. On 3.8 cars each master has its own reservoir. On most 4.2 cars the reservoir attached to the brake master cylinder supplies the front calipers. The servo reservoir supplies the rear calipers. This is apparently reversed on some early 4.2s but won't affect bleeding as long as you know which reservoir serves front and rear. You can tell by tracing the metal pipes coming from the booster. If you are unsure check the schematic diagram in the manual. If you are wrong you won't be able to inject fluid. 

To bleed the brakes: 

1. Select either the front or rear reservoir. It doesn't matter which as the systems bleed independently. Using the syringe, remove all the old fluid from the reservoir and discard this fluid. 

2. Disconnect the reservoir from the end of the hose.

3. Fill the syringe (or another clean one) with 60ml of brake fluid. The less air in the syringe the better as you will be able to generate more pressure. Push the syringe firmly into the hose. 

4. Attach a clear PVC tube about 1m long to the end of the brake caliper nipple. Run the hose so that it loops above the height of the nipple for a small distance before going into a waste container on the ground. The upward section of tube will allow you to see any air bubbles in the fluid. 

5. Open the brake nipple. As usual start with the nipple furthest from the reservoir. 

6. Forcing the syringe tip firmly into the hose, inject the majority of the 60ml of fluid. Hold the hose very firmly or brake fluid will go everywhere. 
I tend to inject the first half of the syringe slowly, then inject more in a jerky, pulsatile fashion to try to dislodge any small bubbles. 
If you have a helper they can tell you when no more bubbles are coming out of the PVC tube. You can do this by yourself however; just leave the syringe and inspect the clear tubing on the nipple for bubbles. If you have a few inches of fluid in the tube with no bubbles in it the bleeding has been successful. Keep going, with more syringes of fluid as necessary, until you have no air. Close the bleed nipple and move to the other side. and repeat 3 to 6. 

7. Once you have finished the other side, carefully remove the syringe. Carefully add small amounts of fluid into the end of the hose until you can see a meniscus of fluid about half an inch below the end of the hose. 

8. Reinstall the reservoir onto the hose. There will still be a small bubble of air within the hose. Put about 20ml of fluid into the reservoir. Tap and squeeze the hose until you see no more bubbles emerging into the fluid in the reservoir. Now put the reservoir back into the supporting clamp and refill it with fluid.

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