brake question.

[campfire]

So before i tried the reverse thing and the brakes totally stopped working i drove it and i could get it to stop, but it felt like the pressure was bleeding off of it. So i could stop effeciently but if i were to need to stop in an emergency it wouldnt do it. Pedal was to soft. But like i said that was before i did the reverse thing because now i have no brakes, it wont even pump up now.

If you can stop, and the pressure gradually bleeds off, with the pedal sinking to the floor, it does sound like an MC problem. You should be able to continue getting brake pressure by rapidly pumping the pedal if this is the case.

If you can't get any fluid or air movement, it's time to replace the MC. Can't bleed the lines if neither air nor fluid is coming out. I had originally though you were just getting lots of air out the bleeders now. Sorry if I confused you.

 

[dyeager535]

When my master failed (after bleeding brakes, theory is that you push the seals into the built up crud inside the master cylinder bore due to more travel when bleeding) I got a squishy pedal for months, but it worked fine. Then one day sitting at a light, brakes disappeared, brake light came on. Was able to pump it up, brake light went off, kept driving, happened again in short order, so I replaced the MC. Problem solved.

If the pedal drops, the only place fluid can go is around the seals in the MC, unless there is an external leak. The system is closed.

 

[Fordum]

OK if you have no brakes at all now, that is actually a good thing. Intermittent and partial problems are a bear to find.
But a complete failure should be fairly obvious.
Do the first things first. Check to see if you have fluid. If the master is empty, pour some in, push the pedal down slowly and watch for where it shoots out.

If its full, push the pedal down slowly while watching the fluid in the master. If you don't see any movement, check the pedal linkage to make sure the pedal is still moving the master cylinder plunger.

If lots of fluid is shooting out of the reservoir when you push slowly, I suspect you have blown a seal inside the MC.

By the way, if you ever push down hard on a brake pedal, and then see a geyser when you let off, that is almost always an indication of air in the side of the brake system that gets its fluid from that side of the MC.

And don't forget, if it failed now, it almost certainly would have failed later. Great that it did it now while you are testing, and not when you were approaching a bus load of nuns......

 

[K5Titan83]

Yes, im glad it didnt fail on me while driving that would have been very bad. Anyway just called oreallys and they have 1 MC in stock. so im gonna have to go get it sometime today and put it on, then il rebleed the system and wel see what happens.

 

[diesel4me]

I would check all the rubber brake hoses--when you say the original problem was it pulling to one side,to me,that indicates a blocked brake hose ,or maybe a caliper or wheel cylinder that is seizing up and not applying at the same time as the other..as I explained in my first post,a bad hose gave me a lot of grief and I've had a lot of experience with brakes..I never thought a clogged hose could cause it not to be bled,and mimic a bad master cylinder..

You may have popped a weak metal line during your reverse "panic" stop..

I've seen master cylinders that were working fine get damaged during the bleeding process--the piston gets shoved much farther down in its bore during bleeding,than it usually does in normal use,and that part of the bore often has rust or crud in it that damages the rubber piston seals..but it doesn't happen every time either..

As I suggested,if you removed both brake lines from the master and plug the ports off ,(I used two old brake lines I had replaced with the right fittings to fit,with the tubing crimped and brazed shut as "plugs)--with those in place,if the master is bled,the pedal wont go down hardly at all and feel rock solid--if applying LIGHT pressure to the pedal lets it sink lower,then the seals in the master are leaking..no sense in buying one for nothing,if it isn't the cause of the trouble..

It's not a bad idea to replace all the rubber hoses if it has high miles and they look at all damaged--all weather checked,rusted crimp fittings,etc..my "bad: hose looked rather decent from the outside,so that isn't always a indication they are "good" either...

 

[K5Titan83]

I have replaced all the rubber brake lines. Except for the back one that goes from the metal line to a T block on the axel. I may try that next. But anyway, i took the master cylinder off, and it was pretty gunked up around the seal. But of course the previous owner had cross threaded one of the brake lines going into it, so im stuck replacing it anyway, i havent had a chance to go pick up the one oriellys had in stock yet i may do it tomorrow, along with the brake line closest to the firewall. Boy its just one thing after the next with this thing. So after i get the MC and brake line replaced wel see if that does it

 

[diesel4me]

That rear hose with the "T" fitting was the one on my van that decided to seal itself shut...even with both bleeders removed from the wheel cylinders I couldn't pump one drop of fluid thru it ,and 125 PSI from my air compressor wouldn't go thru it either..like someone super glued it shut--but it did it all by itself....

You can get a brake line that has the proper size & thread fitting for the master cylinder ,or get a brass adapter to let the lines screw in--GM masters use a 9/16" x 18 thread for the front brakes and the usual steel line that's 3/16" has a fitting with a 3/8" x 24 thread,so GM used a special line nut fitting there..
The rear brake port has 1/2" x 20 threads ,and the 1/4" steel line fitting on a ready made line might be that size,or might be different ..
It's best to make sure you have lines with the right fittings or adapters before you leave the parts store..or if you can flare your own tubing,you could re-use the existing line fittings..

I usually save the old original fittings off the master cylinder lines by snipping the tube off close the fitting and using a 6 point socket to get them off,to prevent rounding them off...the tubing left in the fitting can be coaxed out with a punch or a 3/16" drill bit..

I used to buy ready made brake lines they sell,but lately I've started buying 25 foot rolls instead,its better stuff,flares easier,and cheaper in the end,rather than buying sections of ready made lines and unions to join them all together....and rarely do I get away with doing just one "failed" brake line,usually more pop during the bleeding process,or are so crusty it would be stupid to leave them on there,risk failure ,and have to fix it again later--if you dont get in an accident from having no brakes that is--..

 

[K5Titan83]

Well then once i get this MC thing figured out and that doesnt work, that rear rubber hose will be next. Yeah im with you, im okay with it all goin bad as long as its sitting in my shop and not doing 35 or 40 miles through town. And i totally forgot about my flaring tool i bought, i got it a long time ago when i was helping a friend of mine work on his old ford truck. So if i get the proper threaded fitting i should be able to cut my existing brake line put the new fitting on it and flare it and it should be fine right?

 

[diesel4me]

You might be able to find the line right fitting at a parts store,or re-use the old factory one--or buy a brass adapter fitting that'll screw into the master cylinder's port --usually just the front brake port with the 9/16 threads is the one that needs to be "reduced" to fit a 3/16" line ,but sometimes the rear 1/4" hard line fittings were 7/16" threads and the master has a 1/2" threads,so you may need two adapters...

One other place that has a weird fitting is the on the proportioning valve,there too,it will have a 9/16" thread port and the brake line fitting is "special" and must be re-used,or an adapter obtained to reduce it to the "normal" sized fitting they put on those ready made lines...I don't know why GM did this--other than to make it a pain in the butt when its time to replace the lines..

This is what the brake lines with the "factory" sized fittings looks like--and then the brass adapter that can also be used to let "standard" sized line fittings screw into the master cylinder..

 

[K5Titan83]

Okay. Well, finally got the MC put on and i could get anything to fit in the hole, so i had to get an adapter that sized it down, and then i couldnt get the old brake line to flare right because it kept leaking brake fluid. So i finally went and got a small piece of brake line from oiellys and fitted it into the MC with the adapter, and.cut the new brake line and used a compression fitting to fit the old brake line to it. Its been a huge ordeal. haha. But anyway bled the system again and it went well and the brakes so far are working plus no more lurching to the left so all is finally good haha. Thank god.

 

[diesel4me]

Well,glad its working now--but be aware a typical brass compression union is not "legal" nor is it rated for brake system pressures or useage..
There are some special steel compression fittings that are "brake system compatible" but they are expensive and hard to get in some places..
Even if you used one of those-
You will be denied a sticker if you have vehicle inspections where you live....they don't care what its rated for,the rules say "no compression fittings"...

That said,I have found some compression unions on more than one of my "used" trucks--in fact,one had 3 of them joining sections of line going to the rear end -I had driven it 5+ years with no troubles,till one day the line popped during a panic stop,it was so rusted...

I have to admit I have also used them in a pinch,when a line blew on the road and it had to be fixed (and no flaring tool to be had),and or during extreme weather conditions when I was plowing,and could not tie the truck up for a whole day to fix it "right"..

 

[campfire]

Well,glad its working now--but be aware a typical brass compression union is not "legal" nor is it rated for brake system pressures or useage..
...
You will be denied a sticker if you have vehicle inspections where you live....they don't care what its rated for,the rules say "no compression fittings"...

What are these "vehicle inspections" that you speak of?

Aside from that, I was gonna mention that compression couplings are mediocre at best. It will probably hold without incident, but it is a weak point, and the cost of it failing can be severe (as you already found out while testing).

 

[diesel4me]

I have complete faith in compression unions..
Well--more faith than I have in old brake lines that look like barnacles are growing on them anyway..

In every instance where I found a compression union,it was because I had to replace the line after it blew out due to rust...I never had one fail or leak..the line always failed first..

I'd even drive a truck with copper for brake lines,it might not have quite the PSI rating of steel,but its better than rusted steel !..however,its not legal here either,nor is aluminum...only the nickel-copper terne coated line is legal,and I know of a few people who spent hundreds replacing all their brake lines with that stuff--then get shot down by an inspector because he doesn't know the difference between "plumbing" copper tubing and the nickel-copper terne brake line !..