Bleeding brakes?
- Thread starter elstx65
- Start date
greg92jeepxj
Official Supporter
The only time I've ever had to reset the proportioning valve is when someone continued to drive the vehicle with bad brakes and brake pressure was lost transferring most pressure to the opposite end of the vehicle to compensate to pressure loss. In that case it was bad rear wheel cylinders and the front calipers were strong so the valve's internal piston moved from its centered position to divert all pressure to front brakes . I had to open the front bleeders just to get the valve back into centered position in order to bleed all four wheels .
Yes , I agree , you'll want to avoid this . What your manual is telling you is to loosen a mounting bolt and insert a flat piece of steel with a forked 45 degree end tightened under the mounting screw to hold the internal valve in the correct position while bleeding to avoid having to reset the valve and bleed all four brakes to correct this condition and not make more work for yourself than should have been . Assuming you know the master cylinder MUST be bench bled BEFORE. Installing it . As long as no fluid is lost in the line(s) when removing the master cylinder , the bleeding process will be minimal . Since you are changing a master cylinder , it is a concern that the valve can move feel it's centered position while bleeding a front or back brake first and the bleeding method used is to pump the pedal . But as I've stated , as long as there is minimal fluid loss and the lines are still full of fluid and little air gets in to the system , the lines should bleed quickly and pressure should remain strong equally front and back . The only time a problem could occur is if the valve jams in the opposite position and freezes due to internal corrosion due to a now stuck valve. This is one reason why it would be good practice to follow the manual . From my experience , the last master cylinder swap worked out fine without any concern of the proportioning valve moving out of position since I made certain the lines were kept full of fluid when I disassembled the master . I know you'll want to bleed the system , but start with full lines to make the process faster and no problems.
Yes , I agree , you'll want to avoid this . What your manual is telling you is to loosen a mounting bolt and insert a flat piece of steel with a forked 45 degree end tightened under the mounting screw to hold the internal valve in the correct position while bleeding to avoid having to reset the valve and bleed all four brakes to correct this condition and not make more work for yourself than should have been . Assuming you know the master cylinder MUST be bench bled BEFORE. Installing it . As long as no fluid is lost in the line(s) when removing the master cylinder , the bleeding process will be minimal . Since you are changing a master cylinder , it is a concern that the valve can move feel it's centered position while bleeding a front or back brake first and the bleeding method used is to pump the pedal . But as I've stated , as long as there is minimal fluid loss and the lines are still full of fluid and little air gets in to the system , the lines should bleed quickly and pressure should remain strong equally front and back . The only time a problem could occur is if the valve jams in the opposite position and freezes due to internal corrosion due to a now stuck valve. This is one reason why it would be good practice to follow the manual . From my experience , the last master cylinder swap worked out fine without any concern of the proportioning valve moving out of position since I made certain the lines were kept full of fluid when I disassembled the master . I know you'll want to bleed the system , but start with full lines to make the process faster and no problems.
greg92jeepxj
Official Supporter
The master cylinder you have has bleeder screws tapped into the body above the front and rear ports for the purpose of bleeding the master on the vehicle . They are used the same way as bench bleeding except the brake lines will be attached to the master and you will just put tubing on each bleeder and insert them into the resivour and pump the brake pedal . Afterwards , you can now bleed each wheel cylinder or caliper to complete the job. A master cylinder not equipped with these bleeders will have to be bench bled only and you'll need the kits that come with a new or rebuilt master cylinder or purchased separate . They have different size plastic adapters to thread into the front and rear ports and barbed ends to attach tubing onto and insert into the resivour . Then , you must pump the piston on the rear of the master with something appropriate to make full strokes SLOWLY to cycle the brake fluid from the resivour into the piston chamber and out the ports back into the resivour via the tubing until no air bubbles are present. Then , the master cylinder can be mounted on the vehicle and each wheel can be bled in the recommended order the manufacturer advises . Usually , it will be starting from the wheel furthest from master cylinder and finishing up at the wheel closest. So that will be r/r , l/r , r/f and finally l/f. Hope this helps.
greg92jeepxj
Official Supporter
Not certain of tubing size , they are usually included in the kits but you'll want a size that will fit tight and not pop off during the process . A good auto parts store should have these available .
greg92jeepxj
Official Supporter
A lot of times these fittings are massed produced and whom ever is doing the rebuilding will just grab fittings that will thread into the tapped holes just as long as they fit regardless of head size . I have found that 3/8" will fit sometimes and then you must hunt for a socket or wrench that fits best others. It may be sizes such as 9/32" or 11/32" for example or even 8,9 or 10 millimeter possibly . They have a habit of making it fun for you as if your not having enough fun already but it's trivial to be too concerned with sizes if you can use a small adjustable wrench if you can swing it at the angle needed and range needed to open and close bleeder . If this proves too tedious , just forget the bleeders and bench bleed as though your master didn't have bleeder screws and attach the plastic fittings and vinyl tubes included in the bleeder kit and bench bleed the master on a bench vise.
