Master Cylinder Bleed: anyone tried this method??
- Thread starter swampy_swimmer
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rightyouareken
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I have not tried that method, but if the system was dry and/or replaced, the issue is more about the ABS solenoids than the master cylinder itself. There are passages in there that no fluid pressure gets to unless the ABS/traction control is activating. That's why the FSM has procedures for activating these solenoids so that you can bleed the air out of them.
That being said, I recently replaced my brake booster assembly with a new one from Toyota (ouch $$$$) and it came with some fluid in it already, and was very easy to bleed. I essentially did this, using speed bleeders and a silicon tube/catch bottle on each wheel:
1) With key off, and front right bleeder open, pump pedal until pressure started to build up (maybe ~15-20 pumps IIRC). The pedal essentially goes from feeling like there is almost no resistance to actually being able to feel fluid being pushed out to the wheel. This step essentially bleeds the master cylinder itself from what I understand. Close right front bleeder. Top up reservoir.
2) With key off, open left front bleeder and pump the pedal ~15-20 times. Close bleeder. Top up reservoir.
3) With key on (note, you have to have the key on to bleed the rear wheels because with the key off, no fluid pressure goes to the rear for some reason), open right rear bleeder and pump the pedal ~15-20 times. Close bleeder. Top up reservoir.
4) With key on, open left rear bleeder and pump the pedal ~15-20 times. Close bleeder. Top up reservoir.
5) With key off, open right front bleeder, and pump the pedal ~10 times. Close bleeder. Top up reservoir.
6) With key off, open left front bleeder, and pump the pedal ~10 times. Close bleeder. Top up reservoir.
Done.
I went through about a liter and a half of brake fluid through this process, and have a nice firm pedal. I've driven about 2k miles since, and the brakes feel great.
HOWEVER, back to the ABS solenoids part...I have not done the follow up step that people recommend where you take the truck to a gravel road or parking lot and get the ABS to activate several times. This would push fluid through the ABS passages and solenoids, and essentially bleed the ABS section. I do plan to do this when I can find time to bleed the brakes again. It essentially could push any air bubbles that are in the ABS section into the main lines to the wheels, and cause spongy brakes. Or, the manufacturer of the part could have essentially pre-bled the system, like I sort of expect they did based on the presence of brake fluid in the system when I received it.
Good luck!
That being said, I recently replaced my brake booster assembly with a new one from Toyota (ouch $$$$) and it came with some fluid in it already, and was very easy to bleed. I essentially did this, using speed bleeders and a silicon tube/catch bottle on each wheel:
1) With key off, and front right bleeder open, pump pedal until pressure started to build up (maybe ~15-20 pumps IIRC). The pedal essentially goes from feeling like there is almost no resistance to actually being able to feel fluid being pushed out to the wheel. This step essentially bleeds the master cylinder itself from what I understand. Close right front bleeder. Top up reservoir.
2) With key off, open left front bleeder and pump the pedal ~15-20 times. Close bleeder. Top up reservoir.
3) With key on (note, you have to have the key on to bleed the rear wheels because with the key off, no fluid pressure goes to the rear for some reason), open right rear bleeder and pump the pedal ~15-20 times. Close bleeder. Top up reservoir.
4) With key on, open left rear bleeder and pump the pedal ~15-20 times. Close bleeder. Top up reservoir.
5) With key off, open right front bleeder, and pump the pedal ~10 times. Close bleeder. Top up reservoir.
6) With key off, open left front bleeder, and pump the pedal ~10 times. Close bleeder. Top up reservoir.
Done.
I went through about a liter and a half of brake fluid through this process, and have a nice firm pedal. I've driven about 2k miles since, and the brakes feel great.
HOWEVER, back to the ABS solenoids part...I have not done the follow up step that people recommend where you take the truck to a gravel road or parking lot and get the ABS to activate several times. This would push fluid through the ABS passages and solenoids, and essentially bleed the ABS section. I do plan to do this when I can find time to bleed the brakes again. It essentially could push any air bubbles that are in the ABS section into the main lines to the wheels, and cause spongy brakes. Or, the manufacturer of the part could have essentially pre-bled the system, like I sort of expect they did based on the presence of brake fluid in the system when I received it.
Good luck!
Last edited:
swampy_swimmer
New member
Thanks.
The system was not dry, nor replaced. Just thought I'd do it next time and see if the pedal gets firmer.
I think the reason that you need the key on when bleeding rear is because it activates the booster pump and helps to build the pressure to push the fluid to the back.
But for the front, I'm not sure, I'd have the key on as well.
The system was not dry, nor replaced. Just thought I'd do it next time and see if the pedal gets firmer.
I think the reason that you need the key on when bleeding rear is because it activates the booster pump and helps to build the pressure to push the fluid to the back.
But for the front, I'm not sure, I'd have the key on as well.
