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I'm bleeding the brakes on my 71 cutlass with manual drum brakes all around. When I bought the car, it hadn't been driven in 2 years. I'm going through the brakes now and the shoes and drums look brand new, seems the previous owner changed it all and the hardware as well. When bleeding the brakes, there seems to be constant bubbles. Not just the typical tiny ones, but enough of the occasional large bubbles to make me suspicious. I'm using a helper to pump the pedal, not a vacuum bleeder. I'm keeping an eye on the fluid level in the MC. Any ideas? No apparent leaks in the system but I havent gone through and tightened all the fittings.
You obviously know the order in which to bleed the brake lines, but sometimes we forget - longest to shortest (RR>LR>RF>LF). Ensure your helper doesn't push the pedal down to the floor before you close the bleeder valve & ensure you close the bleeder valve before the brake pedal gets to the floor.
Next thoughts: (1) Do large bubbles arise from each bleeder valve; (2) Just the rear bleeder valves; (3) Just the front bleeder valves? As you said, check fittings for tightness including the combination valve.
^^^ Agree ^^^ Get two brake lines about a foot long, thread one into each port on the master, loop each back into their reservoir then bleed the master until it is bubble free. Re-install and bleed the entire system until it is air free.
Just re-read the OP, manual brakes...don't see why the master bleeding couldn't be done with the master on the car vs removing it to a bench...anybody???
Good luck!!!
Last edited by Sugar Bear; June 9th, 2019 at 07:21 AM.
Thanks for the suggestions all. I did start the bleeding process in the right order but never made it to the front. Since I was seeing so many bubbles I thought I should stop and hunt down the problem before continuing on. In my ignorance, I'm wondering what bench bleeding the MC is going to do for me. If I'm seeing bubbles, then I'm effectively bleeding the air out anyway, correct? The issue is that the air keeps coming! I've ran through enough brake fluid to fill the reservoir three times with nonstop bubbles. The pedal is soft compared to what I'm used to, it's been a long time since I've driven a car with manual brakes. Lets put it this way, I can barely stop the car when in drive and idling forward. If I have to pull the master cylinder, I might as well install a power brake setup while I'm at it. I have most of what I need, i just wanted to tackle other items first but I guess this changes up my priorities. I appreciate the help, I'm learning as I go.
Location: Edmonton, AB. And "I am Can 'eh' jun - eh"
Posts: 24,525
Adding power brakes is a bit more than just changing the master cylinder. I'm sure you have researched that?
If you are sure your MC is bled properly and you're still seeing a huge amount of bubbles you obviously have a leak somewhere. Have you checked the rear center brake hose that feeds the 2 lines going the rear wheel cylinders? Have you replaced any of the brake lines on the car? I'd also look at the distribution block to see if anything is leaking there.
It's been years since I've bled all drum brakes, but I've done it many times on my older cars - they can be a PITA. Two items I'll mention: (1) As I recall, the bleeder screws are different than the more modern types - aren't they like slightly recessed & require an allen wrench or something? My point is this. Bleeder screws don't last forever, and the threads get mucked up, corroded & will allow air to seep past the threads. I believe I replaced some of them on some older cars w/ newer style bleeder screws. Make sure the bleeder screw threads are 'clean'; (2) When you're bleeding drums, I always found it handy to bang (moderately) on the drums while you're bleeding - to dislodge air bubbles which might be lodged. And, don't be surprised if it takes you 3-5 times to do a thorough bleed job - you will go through some brake fluid.
I'm doing my homework for the power brakes, that's for sure. I think I'm going to break down and start from the ground up. I should just run all new brake lines but I would like to box the frame first. I guess that settles it, boxing the frame will commence next. Wow, how did that happen? One minute I'm getting bubbles in my brake lines and the next I'm stripping the car down to the frame. Anyway, pumping the brakes has been working for me for years, habit I guess but it's always worked out well. I appreciate all the input.
I guess I'll be pulling the MC back off to check the pin is correct. I didn't give it much thought and assumed it was correct. Thanks to all for the suggestions. I read on another post about a bleeding pump that pushed fluid the other direction. From the wheel to the MC. Has anyone used that?
This may not solve your problem, but addresses your comment on why bother with bench bleeding the MC first. The very first time I installed a new MC, I thought the same thing. Boy, was I wrong; so I ended up taking it off, bleeding it correctly and then had no issues when I did the final bleeding on the lines.
If you did not bench bleed the MC first, you will play hell trying to get all the air out of the system. A spongy pedal that needs to be pumped up means there is still air in the system.
The proper way to bleed the lines with a helper is for the helper to pump the pedal until its firm and hold a gentle pressure on it. The person at the wheel loosens the bleed screw and the pedal moves to the floor. Once the pedal is at the floor the helper holds it there until the person at the wheel snugs the screw down. Then the helper pumps the pedal until the pedal is firm again and you repeat the process at each wheel until all the air is gone and the pedal remains firm. Periodically check fluid level in the master cylinder during the process.
I did bench bleed the MC totally and used the exact steps you stated. The CSM said to bleed the LF, LR, LR, RR, in that order which I did. Others have said to start RR, LR, RF, LF. I removed the rear bleeder valves to clean them up and noticed what appeared to be a sealer on the threads. I've read that air can possibly enter through the threads, seems unlikely. Anyone use teflon tape or a sealer on them? When I pumped the pedal once or twice I could get a clear stream of fluid, then doing it once more for good luck and I think pumping the pedal 5 or 6 times I would get a flood of bubbles. It was frustrating because at time it seemed like all was well.
Confused,
Steve
You are correct, the threads are not used for sealing, it is the face of the screw that contacts the port in the wheel cylinder or caliper that makes the seal. The threads are just there to pull the parts into contact with each other and create a seal at the mating surfaces.
And, to Kenneth's point I believe the majority of brake bleeder valves are designed in this fashion - when you examine the innards. The hydraulic brake fluid under pressure forces the check ball to close the orifice (hole) at the top of the bleeder valve.
I did bench bleed the MC totally and used the exact steps you stated. The CSM said to bleed the LF, LR, LR, RR, in that order which I did. Others have said to start RR, LR, RF, LF. I removed the rear bleeder valves to clean them up and noticed what appeared to be a sealer on the threads. I've read that air can possibly enter through the threads, seems unlikely. Anyone use teflon tape or a sealer on them? When I pumped the pedal once or twice I could get a clear stream of fluid, then doing it once more for good luck and I think pumping the pedal 5 or 6 times I would get a flood of bubbles. It was frustrating because at time it seemed like all was well.
Confused,
Steve
Silly question, but are you closing the bleeder as the fluid is flowing., ie as the pedal is being depressed ?
June 8th, 2019, 10:17 PM
