no brakes

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Well, I darn near got in a crash today. My brakes decided to quit working. Had to pump the heck out of em to get the truck to stop. I thought something was a bit fishy on my way home from work yesterday. The pedal travelled too far before engaging the brakes. I've had that problem before and it was the rear slack adjusters which needed to be cranked up some. So, my plan was to adjust the rear brakes today, which I did, after the close call. Went out for a drive and still had a squishy pedal and very little brakes. Decided to open up the master cylinder and check the level. The front resivor was totally EMPTY! Well, that explains why I had no brakes, but why did this happen? I checked all of the lines and hoses, no leaks. But it looks like the master cylinder is leaking toward the back where it attaches to the booster. I bled the air out of the master cylinder and the brakes are working just fine now. I'll keep an eye on the fluid level and see what happens. So, anyone else have a master cylinder go out in a similar fashion? Is it normal for just the front resivor to get drained? If it is shot, I'm going to replace it with a NEW one, any reccommendations on a particular brand?



Thanks,

Sean

 

[dusthomps]

Sean...



Sounds identical to a problem I had with my 91 about 6 months ago. Brakes went bad while I was on vacation, checked the MC and the front resivor was empty. Just like yours, I noticed brake fluid on the booster. Well, after replacing both wheel cylinders and replacing all the lines to the rear, I had the same problem a month later. I bought a new MC from a local parts store and haven't had any problem since. Hope this helps.



Dustin

 

[jbolt]

Sounds like you have a leaky seal in the master cylinder. When they get worn or damaged fluid can pass from the primary to secondary valve, visa versa or show up as an external leak between the MC and the booster. They are rebuildible if you can find the parts but usually it is just as easy to get a rebuild unit and excahnge it. If you fill it and it empties again you know you have a leak!



The other cause of low fluid level is worn brake linings/pads and or drums/ rotors. As these wear the fluid level lowers as the wheel cylinders/ calipers have to travel farther.



Check all the brake lines and around the combination valve.

 

[formula]

It's looking more and more like the master cylinder is fried. Just looked down at the frame from in front of the truck. Directly below the master cylinder the frame is all wet with brake fluid. I'll be ordering a new one tomorrow. I looked at paccool's "master cylinder took a dump" thread and found some good info on bench bleeding the master cylinder prior to installation.



Sean

 

[keimmmo]

I had my first experience with a dieing master cylinder back in the late 60s. I have replaced dozens of them since then! When a master cylinder dies, it will usually do one of two things:



One is that it will leak out the back and you will see the fluid running down the booster.



The other is that the pedal will fall away. In the beginning, this may happen only once in a while... but it WILL NOT get better! It is often most noticeable sitting stopped with constant pressure on the pedal. It will feel fine... and all at once the pedal begins to drop. This condition is caused by fluid leaking between the front and rear portions of the cylinder. I have seen many cylinders that didn't leak a drop that you could see on the outside, but they were bad internally!



In either case, you need to replace the master cylinder. New or rebuilt is up to you and will probably be determined by availability and/or price.



I agree that as brake pads wear, the fluid level lowers in the master cylinder to fill the now greater volume in the brake caliper bore because the piston is farther out. CHECK THE LINING THICKNESS!!!



Hope this helps.



Steve

 

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New master cylinder has been in for about 3 months now. I checked the fluid today. Hasn't leaked a drop



Sean

 

[paccool]

Sean,

The new MC I got was from NAPA and has worked well since I put it in. I had put in a rebuilt one about 2 years before that and that was the one that took the dump.



I don't recommend a rebuilt one, if it is new it probably won't make a lot of difference where you get it as long as it is made in the US and not China or some place like that!

 

[formula]

I got a NEW Raybestos master cylinder



Sean