The Stovebolt Site Forums The Shop Area Driveline Brake pedal went to the floor on my 52 Chevy truck half ton

Went out to cruise this afternoon and noticed my brake pedal sinking towards the floor. This happened three times in a span of about 10 minutes. I was able to pump up the brakes and they held just fine. No further problems during my 40 minute cruise. I looked at the inner sidewalls under the truck all dry and no puddles. I had the front wheel bearings repacked and the drums turned, wheel cylinders and shoes all 4 wheel complete inspection about 3 months ago. I topped off my master cylinder about 9 months ago. What should I do next, could this have been a simple problem of air in the line or symptoms of something else, thanks HUGH

I would bench bleed the MC, install Speed Bleeders on all four corners to make a more uniform method for bleeding, and make sure each wheel is adjusted so that there is just a small amount of drag. On my website, there is a diagram showing which way to turn the star adjusters. I needed to document that for me! Hope this helps!

I'd suspect the master cylinder needing a kit put in or replacing the master cylinder with a new one.
Speed bleeders can make the process of bleeding the brakes easier, as to doing a better job than regular bleeder screws I disagree.

Wheel cylinders go bad they leak. Fluid gets past the cups and...at least that is not the issue. MC goes bad and fluid leaks past the cups and no pressure to move the wheel cylinders. I would pull the MC and take a good look at the inside. You might save it with a hone and some new parts. Cheap. You can bench test it with out too much hassle and save the cost of a new one. If it needs to be sleeved or replaced you are half way there. Do the bleeding first to make sure there are no air bubbles. But if the MC is bad you won't make much pressure and it will be frustrating to get all the air out of the system. Take your time and see what you have. Your life and some others may depend on your work. Take your time.

I would check the level in the master cylinder. If it is down, you have to find out where it went. If it is not down, you likely have a problem with it. The problem will reoccur and probably at the worst possible moment.

In the mean time, practice your parking brake emergency stopping technique. Left foot on the parking brake, left hand on the release lever.

I pulled the floor mat today to check the brake fluid level and it was still full from when I topped it off about 9 months ago. Problem has yet to come back. Will order a new master cylinder this week as I don't want to wait for it to go out completely, it looks to be an original piece, not going to try to rebuild it, as replacement cost is only 95.00 plus shipping. Already have bleeder valves on the wheel cylinders. Truck was converted to 5 lug, thanks for all of your replies.

Reviewed the process for bleeding drum brakes, and looked up speed bleeders at Summit. Will try the 2 person method seems easy enough.

This kit makes one-person bleeding clean, fast, and easy.

Tim, have you used this? I've heard the HF plastics don't get a good seal, so let's air back in system when release brake pedal.
Not so?

Yes, I have successfully used that cheap bleeding apparatus on my small trucks. I made sure the hose made a good seal at the bleeder and at the jar.

Yes, I have successfully used that cheap bleeding apparatus on my small trucks. I made sure the hose made a good seal at the bleeder and at the jar.

Speed Bleeders for the whole truck (4 of them) will set you back $20. Many people don't feel they need them. If you have someone to help then there is no need. I hope that person is on the side of the road with you when your brakes need a shot to get you home. It IS one of those keeper products that really does make life easier. Thanks to Cosmo for the idea!