Changing from DOT 5 To DOT3 brake fluid FED UP WITH AIR BUBBLES on my 67

[Al R.]

Re: Changing from DOT 5 To DOT3 brake fluid FED UP WITH AIR BUBBLES on my 67

Originally, the MC was bled on the car, but was removed and bench bled on the vise (and no, it was not clamped down too tight-just the opposite). It has been taken off the car as recently as yesterday and bled again on the vise again. Then did the gravity flow to the calipers and as Ed Johnson suggested, I started with the drivers side, followed by the passenger side, then the right rear inner bleeder, followed by the RR outer bleeder and on to the driver's side inner bleeder and finished up on the driver's outer bleeder. The MC was completed disconnected from the booster and allowed to hang by the fluid lines during this process to eliminate any possibility of the engagement rod holding the MC piston slightly forward inside the MC body and not allowing the piston to completely return to the rear of the body. The fluid level in the MC never got lower than 1/2 full. It's not a problem with runout as the car is not being moved, other than up & down on the jack stands. I talked with CSSB tech department this morning and he told me the MC had to be pointed downward toward the front when bleeding to insure all air was removed from inside the assy. at the rear, otherwise air could be trapped here. Anyone ever heard of this?? Anyway, he told me to do this & if it didn't work, call back, and they would send me a new MC. I'm not sure if some of the air I saw in the lines when my wife was PUSHING the pedal SLOWLY, was from within the lines, or being pulled into the hose at the bleeder threads. I tried to keep the bleeders turned only approx. 1/4 turn when manually bleeding, so I don't feel that the air was siphoned past the bleeder threads. Anyone have thoughts on this as a possibility. I also tried to re-tighten the bleeders before she had the pedal fully depress each time (not sure how successful this was). Again, all fittings have been checked for tightness and seepage by visual, fingertip, and using a shop towel. I don't see any leakage around the calipers, but cannot fully rule that out. I don't have hose clamp-off devices, but was wondering if grip pliers would severely damage the hose if the hose was wrapped with something prior to clamping down on it. I also wondered on 2 other possibilities, 1) the MC itself and 2) the new safety distribution switch. The switch is tightly screwed into the block. What else? Open to opinions on the above questions and wonderings.

[Al R.]

Re: Changing from DOT 5 To DOT3 brake fluid FED UP WITH AIR BUBBLES on my 67

I most like will not change to DOT 3 after hearing what's involved. I'll continue to try to solve this, as was previously stated in this thread, I believe it's not in the fluid, but something else.

[John P.]

Re: Changing from DOT 5 To DOT3 brake fluid FED UP WITH AIR BUBBLES on my 67

Hello Al, You can block off the brake hoses with vise grips and a small piece of rubber to protect the hoses. Just apply enough clamping force to block off flow. The leaks at the calipers that I had issues with were around the piston seals. In the case of my sons car, the calipers were only one year old and replacement of the right rear caliper solved his issue. Another possibility is you may have a crack in one of the brake tubing flares or if using stainless lines, a flare that's not seated. Usually these issues will cause a fluid leak. Did you get a full pedal when you last bled the system? If so, block off the hoses and if the pedal remains, you have issues with one or more calipers. Have the calipers and hoses been replaced? Keep in mind also that pressure applied to a hose may seal a poor crimp that possibly could draw air when the pedal is released. John

[Frank E.]

Re: Changing from DOT 5 To DOT3 brake fluid FED UP WITH AIR BUBBLES on my 67

I ran dot 5 in my 72 for over 20 years. When my master failed, SSB (at the time) sleeved it and I changed the dot 5 with new. No problems..... Now, this may be a silly question but in your bleeding set up, do you have a clear hose connected to the bleeder and the other end of the hose submerged in a container of brake fluid? The first time I bled the brakes on my 66 I overlooked this and could never get a good pedal. Submerging the bleed line into a container with brake fluid solved the problem.

[Jim T.]

Re: Changing from DOT 5 To DOT3 brake fluid FED UP WITH AIR BUBBLES on my 67

Originally, the MC was bled on the car, but was removed and bench bled on the vise (and no, it was not clamped down too tight-just the opposite). It has been taken off the car as recently as yesterday and bled again on the vise again. Then did the gravity flow to the calipers and as Ed Johnson suggested, I started with the drivers side, followed by the passenger side, then the right rear inner bleeder, followed by the RR outer bleeder and on to the driver's side inner bleeder and finished up on the driver's outer bleeder. The MC was completed disconnected from the booster and allowed to hang by the fluid lines during this process to eliminate any possibility of the engagement rod holding the MC piston slightly forward inside the MC body and not allowing the piston to completely return to the rear of the body. The fluid level in the MC never got lower than 1/2 full. It's not a problem with runout as the car is not being moved, other than up & down on the jack stands. I talked with CSSB tech department this morning and he told me the MC had to be pointed downward toward the front when bleeding to insure all air was removed from inside the assy. at the rear, otherwise air could be trapped here. Anyone ever heard of this?? Anyway, he told me to do this & if it didn't work, call back, and they would send me a new MC. I'm not sure if some of the air I saw in the lines when my wife was PUSHING the pedal SLOWLY, was from within the lines, or being pulled into the hose at the bleeder threads. I tried to keep the bleeders turned only approx. 1/4 turn when manually bleeding, so I don't feel that the air was siphoned past the bleeder threads. Anyone have thoughts on this as a possibility. I also tried to re-tighten the bleeders before she had the pedal fully depress each time (not sure how successful this was). Again, all fittings have been checked for tightness and seepage by visual, fingertip, and using a shop towel. I don't see any leakage around the calipers, but cannot fully rule that out. I don't have hose clamp-off devices, but was wondering if grip pliers would severely damage the hose if the hose was wrapped with something prior to clamping down on it. I also wondered on 2 other possibilities, 1) the MC itself and 2) the new safety distribution switch. The switch is tightly screwed into the block. What else? Open to opinions on the above questions and wonderings.

Al my GM Corvette Service Manual on bench bleeding the master cylinder says to first bench bleed the master cylinder with the front end pointed down. After this is completed change the position with the rear of the master cylinder pointed down to again bleed the master cylinder to complete the bench bleeding. I use a kit purchased from auto parts stores that has plastic fittings that fit the master cylinder with tubes to put in the master cylinder fluid. Tubes are submerged in the fluid. With this set up you can see the air being removed from the bleeding operation and subsequently see only fluid being bled into the master cylinders fluid.

[Al R.]

Re: Changing from DOT 5 To DOT3 brake fluid FED UP WITH AIR BUBBLES on my 67

Frank, yes, I am using a clear tube with 1 end submerged in a bottle of fluid to keep from sucking air back into the system. Jim, I used fittings such as you describe with a clear hose going back into the resevoirs at each fitting. However, I did not tilt the MC forward and back as you describe. After all the bubbles had stopped and you could see a stream of fluid going into the resevoirs I stopped and re-installed it on the car and started the gravity flow. I will pull the MC back off and try tilting it front & back and see how that works. Thanks for the tip.

[Paul S.]

Re: Changing from DOT 5 To DOT3 brake fluid FED UP WITH AIR BUBBLES on my 67

Al my GM Corvette Service Manual on bench bleeding the master cylinder says to first bench bleed the master cylinder with the front end pointed down. After this is completed change the position with the rear of the master cylinder pointed down to again bleed the master cylinder to complete the bench bleeding. I use a kit purchased from auto parts stores that has plastic fittings that fit the master cylinder with tubes to put in the master cylinder fluid. Tubes are submerged in the fluid. With this set up you can see the air being removed from the bleeding operation and subsequently see only fluid being bled into the master cylinders fluid.

Interesting. May be I'm the lone ranger here, but I have not found positioning of the MC (front up/down, whichever) critical when bench bleeding in a vice. I have bench bled both a generic (bendix, I think) master cylinder (using DOT 4) and one of the new Delco Moraine DC stamped master cylinders (using DOT 5) with the master cylinder basically level, clamped by one of the mounting flange bolt holes. And once it's bled (provided you don't run it dry on the car), I've not had a problem thereafter as far as air goes.

I've used the NAPA bench bleeding fittings and both are connected (to clear hoses purchased at the hardware store) during the process with the tubes submerged in their respective halves of the master cylinder. I continue to use short strokes (pausing more between strokes with DOT 5) for a couple of hours until no air bubbles and it's either firm enough the piston cannot be moved (DOT 4) or only moves roughly 1/4" (DOT 5--I could never get the DOT 5 so firm that the piston would not move at all, which I attributed to the DOT being more compressible than DOT 3/4).

[Paul J.]

Re: Changing from DOT 5 To DOT3 brake fluid FED UP WITH AIR BUBBLES on my 67

I hate to get into a thread this late.

Al, about 40 posts earlier you said that the pedal went to the floor when you pressed it after bleeding and the engine was running. After bleeding you have no leaks, but you have air in the lines at the calipers, which continues.

What is happening is that the either the fluid in the MC is slipping past the seals, or a fitting somehwere at the MC is sucking air (maybe the back seal). It is unusual that this would happen with an MC as new as yours, but the symptoms are there. I think you've already realized that it's not the type of fluid.

I live 20 minutes from you and I'll be glad to look at it (free, of course). Send me a PM.

Paul