Brake bleeding trouble... still

[Stocker]

Originally Posted by 68shortfleet

I have ran into this air problem before on a truck when the piston pins did not get installed into the brake shoes correctly.

Sucks pulling 3/4 drums back off, but maybe a picture of each side would show something that got missed?

Wish I could post pics, but have never figured it out (I am technologically challenged! ). I was thinking of that possibility a couple hours ago and pulled the drums off just to check. Everything looked good to me and both sides looked the same. (I did one side at a time, also had a manual for reference).

Now I'm wondering if a bad wheel cylinder could somehow cause the problem....

I also just tried opening the rear hose so I could block off the wheel cylinders and then test. Could not break the connection and it's soaking in penetrating fluid right now.

[chipflyer]

I went through all of this 3 or 4 years ago after I bought a BRAND NEW master cylinder from Advance Auto. Replaced everything, bled the brakes numerous times and still no luck. Gave up and had the local Midas power bleed the brakes and a block from their shop the brake light came on again and only had front brakes. The easy fix was to go to NAPA and get a re manufactured master cylinder, install and bleed, which was pud (as it should be) with a good master cylinder.
The moral of my story is new Chinese or Mexican master cylinders are JUNK.
Good luck to you.

Jeff

[PHAT TONY]

This may be silly, but; did the brakes work before all this?

[Stocker]

Originally Posted by PHAT TONY

This may be silly, but; did the brakes work before all this?

Excellent question! Brakes worked very well for several years -- truck was my DD until I retired 3 years ago. Short commute so typically driven just a couple thousand miles a year. Lately it has been mostly sitting until I need to haul something like lumber or firewood.

A couple months ago I did my spring woodcutting and noticed there was a problem. The pedal was soft & sunk near the floor (but not every time). Pumping the pedal 2 or 3 times would usually firm it up (but not always).

I figured it was probably a bad MC and a few others agreed that was probably it. When I pulled off the old MC, fluid poured out of the back of it, so it had been leaking past the seals.

That would have been the end of the project but I wanted to purge all the old fluid and start with all new, so I blew out the lines. And I had been wanting to replace the OEM front hoses so I did that.... then figured it would be a good time to check the rear shoes. They weren't too bad but had been installed wrong, with the long shoe in front, so I got new shoes and cleaned up the adjusters.

It all seemed good until I tried bleeding the system.....


More info than you asked for, sorry. Short answer is yes, they worked well until about 2 or 3 months ago.

[PHAT TONY]

I have nothing more to offer I guess, you're on the money with the m/c swap and I've been through the rest of these symptoms to the letter-including the frustration and google searches. Get the air out of the rear lines and your good to go.

[Stocker]

Thanks to everyone who has replied! The problem persists but this thread has been very gratifying for me. The interest shown and suggestions offered by fellow board members has been terrific. If my front brakes will work with such a soft pedal, it's going to the shop soon -- and I will update this thread when the problem is found & fixed.

[jaros44sr]

have you tried those speed bleeders, the ones with a ball and spring in them. Seems like if your still getting air out, and not pulling air in, your on the right path...hate to see it go to the shop, post #6

good luck

[Stocker]

^^ Yes, purchased for this project.... lots of air still coming out so it must be getting sucked in somewhere. Nobody hates to see it go to the shop more than I do, but I am no longer making progress -- so it went to the shop this morning. Can't wait to see what they find.

[jaros44sr]

weird...curious to see the answer, thanks for sharing. Valuable info. on here

[dragonwrecker]

Originally Posted by jaros44sr

weird...curious to see the answer, thanks for sharing. Valuable info. on here

same here would like to know.

[litew8]

so.... where was the air coming from?

[BMERDOC]

Bump for curiosity's sake.

[Stocker]

The shop called this afternoon but we were gone, and got home just after they closed. Drove by the shop and the rear brakes are apart and both wheel cylinders are removed. That may be a clue....

I'll call them as soon as they open tomorrow.

[ole dollor]

stocker: did you blow out the lines with air pressure before you put the shoes on the rear, or after, the wheel cylinders may have a piston or seal that is almost out or cocked a little, this may let air in if so, i would look real close at the rear wheel cyl. and make sure everything is ok back there, looks like you have tried everything else, would not hurt to look at this, may save more $$$ on fluid...hope you the best on this i hate when we get snake bit and can't figure things out.....

[litew8]

Both wheel cylinders removed, jives with -

Brake cylinder,


"As the piston retracts after the brake is released, it no longer has that outward force on the cups and there may be a
brief moment of negative pressure inside the slave cylinder. This is the time when air might sneak past the cup seals even
though no outward signs of fluid leakage is present. This applies to rear drum brakes only."

You had put teflon tape on the bleeder valve threads to ensure no air passed, but you couldn't have
done anything (short of replacing/rebuilding the cylinder) to have known the guts were on their way to Chevy heaven.

[Stocker]

Originally Posted by ole dollor

stocker: did you blow out the lines with air pressure before you put the shoes on the rear, or after, the wheel cylinders may have a piston or seal that is almost out or cocked a little, this may let air in if so, i would look real close at the rear wheel cyl. and make sure everything is ok back there, looks like you have tried everything else, would not hurt to look at this, may save more $$$ on fluid...hope you the best on this i hate when we get snake bit and can't figure things out.....

There were shoes on when I purged the lines (can't recall if they were the old or the new shoes) so the pistons should not have blown outward. Luckily I didn't buy all the fluid I've used, just one quart and three 12-ounce bottles. After it started coming out looking like new, I started re-using it. I'll be sure to look at the wheel cylinders in the morning after the shop opens up.

Originally Posted by litew8

Both wheel cylinders removed, jives with -

"As the piston retracts after the brake is released, it no longer has that outward force on the cups and there may be a brief moment of negative pressure inside the slave cylinder. This is the time when air might sneak past the cup seals even though no outward signs of fluid leakage are present. This applies to rear drum brakes only."

That may well be what's been happening.... where's the quote from?

[litew8]

"where's the quote from?"

Not taken from this thread.
Someone on the internet talking of a past experience.

[Stocker]

Originally Posted by ole dollor

you couldn't have done anything (short of replacing/rebuilding the cylinder) to have known the guts were on their way to Chevy heaven.

Thanks, that makes me feel just a little bit better....

[southern parts]

i had a similar problem several years ago. i kept getting air out of one side of the rear brakes. as it turned out one of the drums was turned out past max. diameter. this made the wheel cylinder push out beyond it`s limits ,allowing air to get in at the wheel cylinder.

[VWNate1]

I'm piqued to find out what the problem was .

I just ordered up a new Motive Brake Bleeder from JEGS ~ they're simple , easy to use and fairly cheap too .

Cheaper than paying a shop to pressure bleed .

Did you ever lift the edge of the rear brake cylinder's dust boots to check for weeps & seeps ? .

[Stocker]

Just returned from the shop and the mystery appears to be solved. Seems the wheel cylinders were indeed the problem. The seals were shot and allowed air to enter, and I failed to notice the very minor fluid leakage.

Good news: the drums are okay.

A little extra info: I was also told the brakes weren't adjusted tight enough. I stopped when the drums began to drag on the shoes. You're supposed to adjust them out until they are tight, then back the adjusters off several clicks. My backing plates have no holes for access to the adjusters, so there's no way to do that. I was told they drill a hole in the backing plate.....

On a positive note, I have learned from this experience, and maybe it will save someone else a bit of time & trouble in the future.

Thanks again to all who followed this thread and offered advice. This is a great forum with great members.

[BMERDOC]

Good to know your problem got solved! I hope it didnt hurt your wallet too much.

[Stocker]

Two hours labor + the parts I needed anyway. I haven't had truck payments for 35 years so I'm not gonna complain.

[ole dollor]

stocker: i am happy for you, i hate when it takes days to figure out problems, that is why two heads are better than one, past experince is a good thing, now you can enjoy your pickup....like you have done for so many years.....

[litew8]

Yes, and you should post a picture of your truck so we can all appreciate.