Bleeding Brake System after replacing Master Cylinder & 4 Calipers

[slshearer]

Hello,

I just changed the complete braking system on my 1990 Q45 except the ant-brake controller, I now have a soft pedal although I have bled the system 3 times, I suspect there is still some air in the system probably in the anti-lock brake system, Does anyone know how to properly bleed the system, I have an automatic bleeding system and lots of dot4

Thanks!!!!

[elwesso]

I have one of those little plastic bottles with a hose. If your master cylinder isnt bled then youll never get all the air out, theres a bleeder. Start with the MC, then RL, RR, FR, FL..

[carmo]

On newer Nissans the FSM says to disconnect the ABS actuator (electrical connector). The newer cars have the control unit built into the actuator. If yours is the same I would suggest that. If not you may try disconnecting the ABS control unit, then bleed.

[slshearer]

Appreciate the input, actualy I had a mechanic I know do the work at the dealership, he prebled the Master Cylinder before he installed it, I was hoping someone knew how to belled the system including the anti-brake cylinder, I think that maybe the real issue.

Thanks

[Q451990]

I have never had a problem doing it the way it's outlined in the FSM. I would re-inspect all of your connections for leaks. Did you bleed the ABS actuator as outlined in the FSM?

Heath

[Unnatural1]

I suspect there is still air in the system at the M/C and you will never bleed it out by bleeding at the calipers. Even if the M/C is bench bled it will still have air in the lines. Try pumping the brake pedal a few times (slowly) to build pressure in the system. Hold the pedal down and crack open the line at the M/C. Do this a few times for each line at the M/C.

Then as mentioned before, use a bottle and a piece of hose (filled with enough brake fluid to cover the end of the hose) and bleed each caliper. I ALWAYS use the bottle method even if I've got another person helping me bleed the system. It allows you to see the air coming from the system. Bleed each caliper one at a time, starting with the right rear (passenger rear), left rear (driver rear), right front, and left front, until you can't see any large air bubbles coming from the line. I guarantee you there is more air in the brake lines.

Bleeding brakes without using the bottle method usually allows air to enter the brake system in my experience. It becomes almost impossible to bleed the system without it. Also, I don't find that ABS interferes with bleeding the system. Usually the only time I've had to perform ABS bleeding is when the unit is replaced. But, if there is a procedure outlined in the FSM that you can follow for bleeding the ABS hydraulic unit then it couldn't hurt.

[slshearer]

hello

I do not have the FSM so I am not sure what it calls for when bleeding the anti-lock system. We did bleed the unit but I am not sure of the FSM sequence.

Do you know the procedure? or where I might find how to do the correct bleeding, I do not have any leaks that are evedient.

Thanks!Stewart


Modified by slshearer at 5:56 PM 10/8/2008

[Unnatural1]

Don't worry about the ABS unit to start with...just bleed the conventional brake system using the bottle method as described above until you can SEE no more air escaping from the system (air bubbles). Then recheck the pedal and see how it feels...I'm betting that's as far as you will need to go.

But for future reference do a search on here for Q45 FSM and you will find a link to download it.

[Q451990]

Do you know the procedure? or where I might find how to do the correct bleeding, I do not have any leaks that are evedient.

The FSM that you download will be different as the 94+ had a different ABS actuator, apparently without bleeder valves. So the correct sequence for the 90 is:

Left RearRight RearLeft FrontRight FrontFront Air Bleeder on ABS Actuator (marked "F")Rear Air Bleeder on ABS Actuator (marked "R")

Seems a little counter-intuitive since the master cylinder is on the left side, but you have to rememer that the ABS actuator is on the right side and essentially becomes an extension of the master cylinder since everything feeds through it.

Don't forget that the master cylinder has two chambers, so you can suck the front or rear dry while still having fluid in the other chamber... so you have to be careful to keep both chambers topped off. If you suck air in then it's time to start the whole process over again.

Good luck!

Heath