Brake master cylinder issue?

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sceh

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I need to properly bleed my brakes tomorrow. I started using a Mityvac evacuator but I am not keen so I will do it the old way.
However, I am doing this because the brakes were soft and there is a funny vibration in the pedal when I brake at slow speed. I tested them in my garage (fortunately) and there was a point where the brakes were really hard but didn't stop the car and then they were soft and could be pumped up (due to air I guess) and DID stop the car.
This all seems a bit odd. The pads are new. Do these symptoms indicate either a master cylinder issue or a brake assist issue (or indeed the vacuum pump)?
The car is 2012 and has 25K miles only
 

ryanjl

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Pads are new, but what about the rotors? Rotors could explain the vibration, at least.
 

catman

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I had an issue in my LR3 where the brake booster got water in it from the main engine seal being slightly dislogged at the driver side top corner and allowing rain to drip on top of it. When it was below freezing I would have hard brakes and I could not stop the LR3 (quite dangerous). As soon as the engine warmed up the booster and the water in it unfroze, everything was normal.

All of that to say that there could be an issue with the booster (or the lines to/from it) causing the issue you described. Part LR014571 if you want to look at it and see if anyone else has had similar issues.
 

ktm525

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OK The pedal was hard and then soft. Please explain how you were using the mityvac to bleed them. I just did this with the mityvac and it was simple, impossible to get air in system if done the right way.

Did you first replace the pads and then had funny symptoms which you attempted to solve with a brake bleed? or did you do the pads and bleed at the same time?
 

sceh

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Progress.
The pedal was feeling a bit soft so I changed the front pads (rear are almost new). They still felt too soft and the pedal travel was still a bit long.
I used the Mityvac which is the one for extracting sump oil but is the same principle. Just attached it to the bleed ****** and pumped it up. It is a bit hard to do if you want to see the liquid coming out but have to get out from under the car to pump so I gave up and did it today with an assistant. There were a few bubbles in one of the front calipers but now the brakes are a bit better. It was only after trying the Mityvac method that I had this hard brake and no braking effect issue. Gone now.
The brakes are better but still a teeny bit soft but this could be the pads bedding in. I admit I am comparing this with my Mercedes saloon where I just changed all pads and it is much snappier braking and with less pedal travel.
So, I don't think it is the master cylinder or the booster but probably me expecting something better and sharper, though on a 2.7 tonne car it is not bad. I think I will give it a week or so and bleed again. There are no leaks anywhere but I don't feel that if I had an emergency the car would stop sharply.
Sorry for the panic post but if anyone has any advice, gratefully received - when I felt hard brakes but no braking effect I was sure I had a major issue since changing the booster or the vacuum pump is a nightmare on this car
 

ktm525

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What pads are you running? Did you resurface or prep the rotors with a non directional finish when you put on new pads? Were you using the mityvac with the wheels on?
 

sceh

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MV7201 fluid evacuator plus, Ferodo and just changed the pads and did nothing to the discs..
 

ktm525

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I used aquarium vinyl tubing to connect to the bleed *******. I got lots of air coming around the threads and between the tubing and ****** but I got a good bleed in about 5 min a wheel. That or a pressure bleed is the only way 1 man can pull off that job. How is the feel now?
 

sceh

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Feels much better though there is more travel on the pedal than I like. When I press the pedal at very slow manoeuvring speeds like when I leave the garage, there is an odd sensation in the pedal as though it is sticking slightly so I need to dig into this because it could just be rubbing on something
 

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