The Stovebolt Site Forums The Shop Area Driveline Brake system bleeding?

Hi guys, I have a problem. I have a new master cylinder and two rear wheel cylinders (using original lines though) for my 1951 Chevrolet 3604 (3/4 ton) truck and want to know if I would be better off simply draining the entire system or bleeding each wheel cylinder area as I replace the wheel cylinders. I am really tempted to bleed the whole thing and replace all of the fluid. Thanks in advance for your suggestions! Wada

Hy Wada, my advice would be to replace all the steel and rubber lines on the truck and the front two wheel cylinders as well, then you would have a whole new system. Personally I would use silicone [DOT5] fluid when I bled the system, but that's a personal prefference, if you do decide to do that make sure you ask the wheel cylinder provider if their cups are compatable with that fluid, hope that helps.

I actually do have the rubber lines as well, but I had my old mechanic check out the system several years ago and he only needed to replace the line section than ran over the rear differential which had a pinhole leak in it. The others look very sound. Thanks for the advice. Jeff

Wada -

In my opinion, you'll be draining a good portion of the line as you change the cylinders, so why not flush it all anyway. I don't see the need to drain it completely before changing out the cylinders, just bleed it as you would AFTER you've changed BOTH cylinders.

Is it the original small master?

Can't go wrong bleeding it all after all the work is done.

Mark

Wada I also did as 3B did, replaced the entire brake system using DOT5 fluid... It serves as good peace of mind when you are on the road knowing there is a fresh brake system installed...

Brake fluid needs to be changed periodically.

If you have a new MC, I presume that will be filled with new fluid, as well as rear lines when you bleed them -not much more fluid needed to completely flush system and have all new ?

Healingbear: Why did you go with DOT 5 instead of DOT 3 ?
Thanks

I will go ahead and replace the fluid, all wheel cylinders and the master cylinder. I actually just finished removing and adding on the new master cylinder. That was easier than I thought it would be. Thanks for all the advice guys! Wada

Jimmi_V I removed 50 + years of rust/dirt from the frame/axles and painted... Did no want DOT 3 eating paint when I bled the brakes ... The main reason after doing research I felt DOT 5 was a better choice over all seeing that the entire brake system was new...

Dot 5 is silicone fluid No moisture when parked for long periods of time.Donot mix with Dot3.everthing must be flushed if going to Dot5.pays in the long run.I've used it for 11 years now,no problem.The millitary only uses dot 5.No moisture.water is a killer when things set for long times

I don't know if it was neccesary but when we converted our stuff to silicone we used all new rubber components and and flushed everything with alcohol as we had issues with the rubber that had been in contact with the dot 3 it seemed to swell up and not want to move much. It pretty much eliminated rust in the cylinders and lines.This is very important when you are in Chignik Alaska. Metal just dissolves in the air up there. Weirdest thing I've ever seen.

Brake lines rust from the inside out,60 year old lines need to be changed.

healingbear, I'm in Northern California too, Sonoma County. Where are you?

Dot 5 is very controversial. Most people hate it, claiming it makes the pedal "soft". I learned in physics that liquids are not compressible. Presumably that includes Dot 5.

I have Dot 5 in my '36 Chevy pickup. When you first pour it into a system it forms what I call "microbubbles". At that stage, no matter how much you bleed it the pedal is soft.

If you wait a day or two, the microbubbles coalesce into normal bubbles and bleed out easily.

I also have Dot 5 in my '32 Ford roadster street rod. Both vehicles have a firm pedal and my chassis paint is safe.

That's not exactly correct. Older vehicles with vented master cylinders, like the '59 and earlier GM trucks, can still get moisture in the system. It tends to condense in the lowest piont in the system, making a water "slug" in the lines. When the brakes get hot, the water will vaporize, causing a low pedal and poor brake performance. There is also an issue with the water freeezing in the lines, causing total brake failure. See Bob Adlers article in the current issue of Vintage Truck, which covers that particular problem.