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MG MGA - BRAKES STUCK
|My MGA has a stuck brake pedal which will not allow my my brakes to work correctly. The brakes feel like they are under pressure and NOT releasing. I have a brake booster which I just replaced. Before the replacement, I had a rough idle and the engine would diesel when turned off.The engine now does not diesel and idles smoothly. I am looking for ideas when I go to fix it this Saturday. I am running dot 5 brake fluid. All four brakes are locked up.|
1. Open bleeder to see if brake releases
2. check for any bent brake lines
3. check master cylinder for blocked release hole by making cardboard piece for front of master
Any ideas would be appreciated.
|I wonder whether your engine rough running could have been due to a split vacuum pipe feeding the booster. That would allow air to be drawn into the manifold causing very weak mixture, overheating as a result and running-on.|
|If I understand it correctly, you only have the brake problem since replacing the booster?|
Try bypassing the booster.
|Dave O'Neill 2|
|Master cylinder pushrod is not returning fully to the rest position. This will not allow relief of pressure, so the brakes drag. If you open one bleed nipple to relieve the pressure, and all brakes release, then it is a master cylinder problem.|
The vacuum is taken directly from the intake manifold with a Judson Supercharger on top of the manifold. The car had been running hot on cool days and in normal traffic. I am not sure what you mean by "split vacuum"
This problem is only since replacing the booster. I had done the work about 6 weeks ago, but had not tested the car or fired it up since then.By passing the booster is hard because it is a hard line from the four way to the booster.
Yours is the first test I plan to do as it is the easiest. If I bleed the brake system and fluid comes out, that would indicate to me that my problem is the master cylinder. The first thing I did before putting in the booster was to rebuild the master. The problem was still there as the pedal went too low to the floor which made me believe the problem was the master. When using Dot 5 the seals sometimes swelled up to block the bypass bleeder in the master and prevent the pedal from releasing. To fix this problem, I would need to make a cardboard gasket to fit in the front of the master to allow the pistons to clear the bypass relief hole. Would you suggest I try this first after the bleeding and if it does not work, put in new rubbers? Any other suggestions would help as I love to learn from other people who have this problem and fixed it and will save me time. Barney, would the booster have anything to do with causing this problem as it has worked beautifully before this problem so I can eliminate this component as a possible problem.
|Systematically, one step at at time. Crack a bleed nipple first to see if that relieves the pressure and frees up all of the brakes. If so then the problem is at the master cylinder end.|
Too bad you're in California, as I am currently in Georgia, headed for Illinois on my way to Pennsylvania. Scratch and sniff first hand would be easier.
I have a feeling the problem is interference in the pushrod from pedal to booster, or the pushrod from booster to master cylinder. Check to be sure you have minimal free play at the pedal. You should be able to push the pedal a small but with one finger before you feel it take up the slack and begin to push the booster.
If that's okay, then loosen the bolts between booster and master cylinder to let the MC move a bit away from the booster. That may relieve interference fit on the MC pushrod to allow full return. If that relieves the pressure then you would need to investigate why there may be interference at that point.
|Jeff: my thoughts were a flexible connection from the inlet manifold to the brake servo (booster?) and giving thoughts to the effect of that flexible hose splitting allowing air to be sucked into the manifold. |
It maybe what you refer to as a "booster" is not how I understand it (I'm thinking brake servo vacuum operated device, typically Lockheed)
The booster is remote under the passenger fender. The only push-rod is from the pedals to the master cylinder. I will do the bleed test first.As the engine is smooth at idle and no dieseling it would make me believe the booster has no leaks now. I see no external fluid.
The hose is a short flex hose to a solid steel pipe which runs at the firewall. I then used bulkhead fitting to get it to the inside of the fender. Look on Barney's site and you will find pictures of my installation under remote booster.
Hope this helps
|Went out to the car this morning to bleed the brakes to see if I could free them up. Before turning on the engine, I check the brakes by hand turning the drums and to my surprise, they were free and spun freely. The brake pedal when pushed on, the pedal went down and was not locked up or tight. I turned on the engine, and tried the brakes and the pedal was hard and tight and I was back again to no play. I check the rear drum and tried to spin it, it was locked up.|
Does it sound like the master cylinder relief by pass is blocked?
|It sounds to me like the booster, as it happens once you start the engine.|
|Dave O'Neill 2|
|I went out today to try to figure out the problem again. I checked the brakes and the drums turned freely and so did the front disc brakes.I then started up the engine without touching the brake pedal. Went out to check the free movement of the drums and they were locked up without the brake pedal not being touched. This would make me believe the problem is the booster. I have not tried to bleed the brakes yet, but that is next. What would happen if I took off the vacuum hose to the booster. Would this deactivate the booster? Looking for any idea's and help. As the brakes were not touched, it seem to me that the master is ok.|
HELP HELP HELP
|Disconnect the large vacuum hose from the booster, and plug it (so you don't have a large vacuum leak into the intake manifold). It should then work normally as manual brake (no power assist). If so then the booster is whacky. I don't recall hearing of one that was self-energizing. That must be a fault in the regulating control valve.|
For a remote booster, is may be too much residual pressure between the master cylinder and the booster. If it locks up again (with vacuum connected), try loosening a pipe and fitting between master cylinder and booster to eliminate any residual pressure there and try it again. If it can then run without locking up the brakes, the problem is residual pressure at the master cylinder.
|I bought the booster from VB and the booster has an second diaphragm on the booster with a plastic cap and a seal. I have put on the washer which looks like the type you would use on a hose on the second diaphragm and I now have brakes but the power boost is not there yet. I will go back to that second unit and remove the spring which the original unit had which was Lockheed. Tomorrow I will remove the spring to see what happens. I hope this fixes the problem. The instructions are not clear at all or has an exploded view of how the washer and springs are placed.|
This thread was discussed between 18/03/2016 and 21/04/2016
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