TRC/ABS Master Cylinder Bleed

update April 2006.  I find bleeding the TRC/ABS master cylinder simple with it's built in electric motor and improves brake pedal feel.

July 2003

by Peter Scott

translations by Dominik Bloemhard, info from Jeff Harper  Japanese Workshop Manual

"Pump Autostart
(1) After switching ignition on, pump will start automatically
Note:
* Pump will stop after 30~40 seconds
* If pump does not stop by itself, there might be air in the system. Release this air by opening the pump bleeder plug"

I like to set up with 2 metres of 5mm plastic hose into an old drink bottle - that way I can easily see the colour of the fluid coming out. The hose is essential - without it brake fluid would spurt everywhere damaging paint work.

The first nipple is a bit tricky to get the hose on - I had to remove a small relay to get to it. I used an 8mm spanner to loosen the nipple. Once the nipple was cracked open 1/8 turn, I turned the ignition to "on", pressed the brake pedal and away the electric motor whirred pumping out fluid from the master cylinder into the plastic bottle. It's a big master cylinder and takes a minute for the old brake fluid to pump out. Before it emptied itself I turned the car off and re-filled with clean fluid.

The black cylinder next to the master cylinder with the yellow sticker is a nitrogen accumulator. An electric motor pumps fluid into the accumulator storing pressure for fast operation of the traction control and ABS systems. In the case of an engine stall the brakes still have maximum power available for a few applications because of this stored pressure. By opening the first nipple, fluid is pumped out of the system instead of stored against the nitrogen gas.

"Power System Air Release
(1) While brake pedal down, open bleeder plug until no more bubbles come out.
T=85kg.cm "

I found this second nipple quite hard to get to - it was fiddly to get the hose on and a squeeze to then loosen the nipple with the spanner. Once it was on I pressed the brake pedal with the ignition to "on", the pump motor started up and out come more old fluid. Like the first nipple I watched the fluid level drop in the master cylinder before re-filling. Once the electric motor starts up it keeps going by itself, until the car is turned off or the nipple is closed and the pressure builds in the accumulator. By now I had about 1 litre of old brake fluid in the bottle. Getting the second nipple is worth the effort.

"(5) Normally air is released from bleeder valve on edge (tip) of master cylinder "

The last bleed nipple is the one on the front - I removed the couple of brackets in the way to get a clean shot at it. The electric motor doesn't effect this nipple - so I pump the pedal up and down and pushed the old fluid out manually. The 2m of plastic hose means I can do it by myself. The fluid was nice and clean by now so it didn't take long for this final master cylinder bleed.

Now that the master cylinder had no air bubbles and no old fluid I bled each wheel.   If I'm not in a rush sometimes I gravity bleed the system - open the nipple and the fluid slowly makes it's way up through the hose all by itself and into the bottle. Other times I'll give the brake pedal quite a few long smooth pumps to speed up the process.

I'll use about 5 bottles of fluid (500 ml each so a total of 2.5 litres) which costs about $50. After a bleed the brake pedal is firmer - TRC master cylinders are especially prone to spongy brake pedal. I reckon it's well worth while. I would bleed my brake system once a year on average. I prefer Castrol Response superdot 4 - it looks to have the best specs for the price point.

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