The Jalopy Journal
Discussion in 'The Hokey Ass Message Board' started by 34Joe, Oct 21, 2021.
So it's not a situation where the master cylinder isn't getting full stroke then?
I am using Valvoline Synthetic Dot 3 & 4 brake fluid. This is the same type I have always used.
It appears to be getting a full stroke which I confirmed when I pedal bled the system originally .The system has never bled well using the brake pedal. It likes to be power bled , probably because of the booster.
Not mixed, I hope.
Not mixed, I am just reading what it says on the container.
I want to be sure that I understand the issue you have when the brakes are applied is with the brake pedal in relation to the floor and has nothing to do with how the brakes function, correct?
Personally I would not be 100% positive about a “new” part working correctly, lately. I’ve had better luck with parts that were cleaned up and reused or repaired
Amen to that.
The brake pedal at rest is 7 inches off the floor. When the brakes are applied the pedal stops at approximately 2 and a half inches off the floor. The brakes do not lock up, no matter how much pressure is applied.
I agree, as this is the second booster and master cylinder that I have installed, each time having to have the system power bled ,costly, and ending up with the same results.
Two simple test I use when I test the booster and master cylinder. This may be old news, but I am old, so I can repeat myself without feeling bad.
Pump the pedal a couple of times and hold pressure on the pedal while starting the engine. The pedal should drop a small amount and you should clearly feel it drop. If it does drop, then the booster is working.
To test the master cylinder, I pump it several times, then hold a lot of pressure on the pedal. If the pedal slowly moves down over a minuet or so, and you have no external fluid leaks in the system, it is a good indication your fluid is bypassing the internal seals in the master cylinder and the master cylinder is bad.
One of the problems with diagnosing the brake system is that a very small amount of fluid moves in the system when it operates. Even a very small amount of air or a small leak can cause big problems. I have found that most fittings made today, such as line size adapters or pipe to double flare adapters are a one time use fitting. The metal is so soft that the seating area is deformed the first time it is used. I bought special conical seals to use in these fittings. These seals are available on Amazon but none of my local parts sources sell them.
Good info is good info. Checked everything underneath again today, nothing unusual. Took it out for a test ride, no difference. The brake pedal is solid, but low and the brakes still will not lock up.
Have you checked the line pressures all round? [at the bleed screws]
And are you running a proportioning valve?
As stated above, I had the same issues with a project in the past. I bought an inverted flare plug and works from the Mc to the wheels, insuring a hard pedal at step. It eventually boiled down to the fact the the Mc was below the floor, and almost even with the calipers. It was just air.
Have you put a fresh master cylinder in yet?
Line pressure is good at the bleeders. I do not run a proportioning valve .
My Mc is below the floor also. The system has been pedal bled several times and has been power bled at least three times .The outcome is always the same, low brake pedal, and unable to lock up the brakes.
I have put two new master cylinders in , purchased from two different places, and two power boosters, and the outcome is always the same.
"Line pressure is good at the bleeders. I do not run a proportioning valve.
What is "good line" pressure to you, what pound number in each corner?
Moot point now as I removed the master cylinder and power booster. They are already on their way back to the company for a refund.
So have you been able to fix the problem
No, just returning the items that were the possible problem. This is the second time I am sending back the booster and master cylinder. This problem started only after I replaced the original booster and master cylinder which was leaking. Now I have to get booster and master cylinder #3 and hope it does not lead to the same outcome.
Do you still have the original old parts?
Wish I did. This has been going on since late June. Once the first new booster and master cylinder were installed I discarded the original parts. The booster looked identical but the original master cylinder looked like a GM unit but the brake line outlets were on the other side of normal tword the frame rail, as the brake system is under the floor. Was not able to trace it down, but it was a 1 inch bore unit.
You've learned the hard way, like most of us. Never throw old parts away. Drain and cover them up. Mark the box, year, engine and model...
The single master cyl. can work, you need to have a good working emergency brake..
Conical seals. Can you explain or post picture?
Thats too bad. It might have been helpful to compare the details. Or possibly to just repair the m/c that was working for you.
When the new ones show up, try breaking this system down and posting some pictures and measurements. Assuming you already bench bled the m/c and got the pedal, booster, and m/c installed…
With just the m/c, plug both outlet ports. You should have essentially no pedal travel. There will be a little bit, as the slack in the linkages and pushrods is taken up. How much pedal movement do you get?
I think you said you have pressure gauges. Put them on the m/c outlet ports. What are you reading there? Clearance may be tricky here.
Plug the rear port, connect only the fronts. What’s the line pressure at the fronts? Solid pedal or not? How much pedal travel?
If the fronts seem ok, now connect the rears. What’s the line pressure at the rears?
Everyone has their own preference for bleeding brakes. I like the one-man check valve bleeders, augmented by sticking my phone in the wheel well and using its camera to view the fluid coming out until I’m good and sure that there are no more bubbles.
From here on out nothing gets thrown away ,until the job is proven done.
Appreciate the info. I do not have any pressure gauges.
Summit racing sells the brake pressure gauge sets (about $60.00). This may help quantify your troubleshooting efforts and explain the inability to lock up tires.
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