m1ghtymaxXx Posted September 19, 2012 Share Posted September 19, 2012 I finally got my Wilwood MC, and went to install it last night before realizing I didn't have the barbed fittings to bench bleed it. I've never bench bled a master cylinder before, and found conflicting reports on the procedure. Most tutorials I encountered simply said to run a length tube from the outlets to into the reservoir, fill the reservoir and pump the piston until no more bubbles are seen. I assume the open end of hose should not be submerged in the fluid in the reservoir? Some tutorials said not to run the tubes back into the reservoir, but into a container to expel any debris, and some reports said to to pinch off the lines when releasing the cylinder. I also picked up a cheap vacuum bleeder, is this any use for bleeding master cylinders, or does the piston need to be pumping for this to work? Lastly, I was thinking I would vacuum bleed the lines before installing the master cylinder. Am I correct in thinking this is a useful step, or is this just a waste of time and brake fluid? Could anyone clarify what the proper procedure to bench bleed a master cylinder is, and answers to the other 2 questions would be greatly appreciated! Quote Link to comment Share on other sites More sharing options...
GreenState Posted September 19, 2012 Share Posted September 19, 2012 To bleed a Wilwood MC (the easy, fast way): 1) Use two fittings and make two very short (~2") 1/8" hard lines and connect them to the outlets on the MC. 2) Using 1/8" ID tubing from the hardware store, connect the hard lines to two syringes full of brake fluid. 3) Clamp the MC level in a bench vise. If you have a vise that rotates, even better. 4) Using the syringes, push the fluid through the MC, filling the reservoirs from the bottom but leaving some fluid in the tubing/syringes. 5) While holding the syringes pointed down, use a screwdriver or other such pointy object to cycle the push rod. You may see some air bubbles come out in the tubing, if you do, let those float to the top of of the syringe before continuing. 6) After you've cycled about 2/3rds of the fluid out of the reservoirs, repeat step 4. 7) Rotate the MC in a few different positions and repeat steps 5 & 6 until you're bubble free. The piston has to be moved to dislodge any air bubble that may be hiding in the MC. Bleeding the lines before you hook up the MC will be a waste of you time and brake fluid. Before you attach the lines, make sure to take the Wilwood MC outlet fittings apart and verify that the springs for drum brakes are removed and the compression fittings are oriented in the correct direction, mine were not from the factory. For bleeding the rest of the system, I'm a huge fan of the Motive Products Pressure Bleeder. The Subaru fitting works on our cars if you use clamps to hold it on or you can buy the $30 240z adapter. Good luck! Quote Link to comment Share on other sites More sharing options...
Miles Posted September 19, 2012 Share Posted September 19, 2012 (edited) See picture for bench bleeding set up. I open up both bleed nipples and then push the piston in slowly until all of the bubbles are gone. When you remove the fittings in the outlets fluid will leak out so I plug the outlets with small rubber stoppers. Remove the rubber stoppers just as you are hooking up the hard lines to the MC to minimize fluid loss. Also, I hook up the hard lines before I bolt the MC to the booster. Makes it easier to line up the hard line with the MC outlets. The fittings in the outlets are old brake lines. Be sure when you attach the fittings to the MC that they are tight or air will be sucked in as you push and release the piston. Do not clamp the barrel (cylinder) of the MC in the vise as you could deform the cylinder causing it to leak. Edited March 9, 2015 by Miles Quote Link to comment Share on other sites More sharing options...
RebekahsZ Posted September 19, 2012 Share Posted September 19, 2012 What product do you use to seal the threads on the bleeder nuts? I'm having lots of trouble with air coming around the bleeder nuts!!! Quote Link to comment Share on other sites More sharing options...
Miles Posted September 19, 2012 Share Posted September 19, 2012 (edited) I use speed bleeders with teflon thread tape. For the flare nuts that attach to the outlets I just wrap the flare nuts with the teflon tape. Also, make sure that the flares on the old brake pipes you use for the outlets are in good shape or they will suck air. I learned all of this while bench bleeding a new master cylinder that kept producing bubbles. At first I blamed the speed bleeders until I checked the old flare fittings at the outlets. To fix the problem I went to Pep Boys and bought a new 12 inch brake lines with the correct flare and threads and then cut out two four inch pieces using a tubing cutter. I then formed a 90 deg. bend ( to clear the vise/bench) in each tube using a tube bending tool. No more air leaks through the outlets while bench bleeding. Edited March 9, 2015 by Miles Quote Link to comment Share on other sites More sharing options...
m1ghtymaxXx Posted September 20, 2012 Author Share Posted September 20, 2012 So bled the Wilwood as shown in Miles' picture, and it seemed to work just fine, with a few additional details. Simply pumping the piston only pushed bubbles back and forth in the tube, so I closed the bleeder valve when releasing the piston, as you would bleeding a brake system. For a laugh I tried reversing the flow (closing the bleeder when pushing the piston in) to ensure no air came through the other way. Also I after all the air was out, I tilted, shook, and tapped the cylinder to try and free any air. I did this twice. Unfortunately bleeding the system didn't go quite so smooth. After the rears bled astonishingly easy (the old fashion way), I found there was a massive leak somewhere beneath the master cylinder, on the rear circuit. At this point it was late at night and I was working on my driveway with a flashlight and called it a night. My suspicion is that leak is coming from the "pressure differential sensor". I would guess most likely a worn fitting or flare, but it is there any harm in bypassing the sensor all together if it makes for an easier repair? No brake light was coming on on the dash. Just as a background, I bought the car recently and have yet to drive it. I was told by the previous owner that it had a leak at the right front wheel (which I noticed briefly on my lunch brake today), but to my suprise it has a much more serious leak on the left somewhere near the m/c. It seems that has been leaking for a while as all the paint has been eaten from the inside of the frame rail and t/c bucket. Thankfully the factory primer seems quite resistant to brake fluid, as the paint is gone, but the white primer beneath seems perfectly intact, and no rust! To finish on a question, there were shockingly few to no bubbles when bleeding the system after installing the master cylinder. Is this normal, or could one of the leaks actually be releasing all the air without drawing any in? Quote Link to comment Share on other sites More sharing options...
RebekahsZ Posted September 20, 2012 Share Posted September 20, 2012 In an unrelated situation (hydraulic clutch), I'm having trouble getting all the air out of my system. Does the cylinder need to go FULL stroke to purge all the air? I'm not getting bubbles anywhere but pedal still is good at times and soft at others. I can't understand why I could have such intermittent performance. It is totally unpredictable. Any ideas? Quote Link to comment Share on other sites More sharing options...
Miles Posted September 21, 2012 Share Posted September 21, 2012 So bled the Wilwood as shown in Miles' picture, and it seemed to work just fine, with a few additional details. Simply pumping the piston only pushed bubbles back and forth in the tube, so I closed the bleeder valve when releasing the piston, as you would bleeding a brake system. For a laugh I tried reversing the flow (closing the bleeder when pushing the piston in) to ensure no air came through the other way. Also I after all the air was out, I tilted, shook, and tapped the cylinder to try and free any air. I did this twice. Unfortunately bleeding the system didn't go quite so smooth. After the rears bled astonishingly easy (the old fashion way), I found there was a massive leak somewhere beneath the master cylinder, on the rear circuit. At this point it was late at night and I was working on my driveway with a flashlight and called it a night. My suspicion is that leak is coming from the "pressure differential sensor". I would guess most likely a worn fitting or flare, but it is there any harm in bypassing the sensor all together if it makes for an easier repair? No brake light was coming on on the dash. Just as a background, I bought the car recently and have yet to drive it. I was told by the previous owner that it had a leak at the right front wheel (which I noticed briefly on my lunch brake today), but to my suprise it has a much more serious leak on the left somewhere near the m/c. It seems that has been leaking for a while as all the paint has been eaten from the inside of the frame rail and t/c bucket. Thankfully the factory primer seems quite resistant to brake fluid, as the paint is gone, but the white primer beneath seems perfectly intact, and no rust! To finish on a question, there were shockingly few to no bubbles when bleeding the system after installing the master cylinder. Is this normal, or could one of the leaks actually be releasing all the air without drawing any in? Go to Pap Boys etc and get two 12 inch brake lines and replace the old ones on your pressure differential switch. Just bend them per your old lines. Don't bypass the brake switch. It is a safety device and also serves as distribution block for the front brakes. I have never had a problem with the brake switch. You might want to consider rebuilding your brake system given its age and condition. Quote Link to comment Share on other sites More sharing options...
m1ghtymaxXx Posted September 21, 2012 Author Share Posted September 21, 2012 Go to Pap Boys etc and get two 12 inch brake lines and replace the old ones on your pressure differential switch. Just bend them per your old lines. Don't bypass the brake switch. It is a safety device and also serves as distribution block for the front brakes. I have never had a problem with the brake switch. You might want to consider rebuilding your brake system given its age and condition. [/size] [/size] It was the rear line coming out of the master cylinder to the pressure switch. I pulled it out and the flares looked fine to me, so I put it back in hoping maybe it wasn't seated properly. Sure enough it went from a gushing leak to a very slight drip at full brake pressure with the engine(booster) running. At this point I think the car would be fine to move, but I'd be weary about driving it great distances. I measured the old line at 12-3/4", and went out and got a 12" length of line (next up was 20"). I think I can make up the extra 3/4" with less bends, but I was also thinking of adding an extra compression fitting to the master cylinder to make up a bit of length. Another issue I forgot to mention; The booster push rod seemed seized to it's shaft. There's no rust or anything, but for the life of me I could not turn it using vice grips on the splines (I can't remove the rod from the booster can I?). To the best of my ability I measure the rod to be about 1mm short of the master cylinder piston, which is pretty dame close to perfect isn't it? Despite the leak and only 3 corners bled, the pedal felt fairly firm, and I did not notice any dragging. Quote Link to comment Share on other sites More sharing options...
m1ghtymaxXx Posted September 21, 2012 Author Share Posted September 21, 2012 (edited) Delete Edited September 21, 2012 by m1ghtymaxXx Quote Link to comment Share on other sites More sharing options...
m1ghtymaxXx Posted September 21, 2012 Author Share Posted September 21, 2012 (edited) Delete Edited September 21, 2012 by m1ghtymaxXx Quote Link to comment Share on other sites More sharing options...
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