Need your advice guys! Can't bleed brakes Help

[jmillsUT28]

I know this should be in the Blazer forum but thought you guys would be able to help me. Having a heck of a time with this my 72 blazer that I bought. The guy I bought it from had it as a project since 1995. So did not drive it much at all.

Please tell me what I am doing wrong.

Problem: can not bleed front or rear brakes.

What I have done. Replaced master cylinder, front calipers and combination valve. I've bleed the mast. Pushed the needle in on the combination valve while trying to bleed the front brakes but can not get any fluid at all at the bleed valve on the caliper.

What am I doing wrong? I have not tried the rears as I have found they are missing a few spring that hook up to the brake shoes.

Can't believe I am having this much problems out of brakes!

[davepl]

Your "problem" description is a little misleading because you say you can't bleed the front or back but you "have not tried the rears".

Is it possible the center slug of the combination valve has slide to one end? Then you could only send fluid to the back but you didn't try.

If it's gone all the way your "brake" light will be on, or if nothing else ground will be present at the sender on the combination valve. If that's the case we'll go from there, or there are a number of threads about it already.

[coppertone]

I had the same problem with my truck, changed the mc,front calipers,rear pistons and still could't bleed the front brakes. Turns out it was both my front brake hoses that were clogged,I guess over time the fluid dried up in the lines.Replaced them and had no more problems,just a thought.

[jmillsUT28]

Just went back out there to check the lines coming out of the combination valve. I am not getting fluid out of either the front or the rear. So does this mean the master cylinder is not bleed correctly?

[LS short box]

I bought one of those small pressure bleeders. Works like champ. Best way to bleed brakes.

[Smith & Sons]

Bench bleeding the master cylinder properly is the first step.I have had problems with the bleeder kits because the threads will leak air.With a gloved hand,cover the outlet on the master cylinder while you work the stroke of the piston with your other hand(MC mounted in a vice)Do front ,then rear.Your rubber flex lines at the front wheels & rear axil may have collapsed inside,like copper tone said.

[LockDoc]

Originally Posted by jmillsUT28

Just went back out there to check the lines coming out of the combination valve. I am not getting fluid out of either the front or the rear. So does this mean the master cylinder is not bleed correctly?

Or the proportioning valve is plugged....

LockDoc

[jmillsUT28]

Ok I bled the master again. Now I am getting a little fluid at the left front caliper but still has a lot of air in it. Pumped the brakes 20 times and can not get a solid flow. I can not get any fluid at the front right or the rears.

I do have a pressure bleeder and it has not been any help at all. It will hold pressure if I put my finger on the end of the hose but when I have the needle on the combination valve pressed in it will not hold pressure. I can hear air coming from that needle. Should I be hearing air from that needle when pressed in? Also I do need to have it pressed in when I am bleeding the front brakes correct?

[88Ironduke]

I situations like this I like to start with low hanging fruit. My thoughts on a pressure bleeder is it can cause more problems than it solves if not used effectively. If you're getting air under pressure it at the combo valve your master cylinder is full of air and out of fluid, time to start over. Also I am going to assume power brakes? Make sure the push rod from the booster is not slightly depressing the master cylinder piston when bolted up tight. Not all boosters and master cylinders play well together. A booster rod that is slightly too long will depress the piston covering the ports that allow fluid to move around out of the master cylinder with your foot off the pedal. This happened to me...

Remove the master cylinder and do a good bench bleed. You can use the run-around hoses or plugs. They all get the job done. Does fluid freely flow out of the ports if left open? If not the master cylinder may have a clogged port internally. Mount the master cylinder again, start pulling output lines from the combo valve one at a time and check for free flowing fluid. The master cylinder and combo valve porting is such that fluid should run thru both via gravity. If the combo valve has some air in it a few light taps with a screw driver handle will usually dislodge it. If I get good clean fluid under the hood I move to connections where the hard line meets the rubber hose. This is good for front and back brakes. Disconnect a hose one side at a time and check for free flowing fluid, it may take a minute to get there. Once you get good fluid, reconnect the hose and make you way to the caliper. Pull the bleed port completely out, heck even hang the caliper as low as you can with damaging the hose. If you get no fluid, R2 the respective hose assembly. Pumping the brake pedal too often too fast will cause the bubbles to foam up and you're never get it bled out correctly. Drink a beer, watch some Netflix and hit again later. Sometimes leaving it sit for a bit and regrouping is the best option. Remember to have a helper pump the brake pedal and hold it, open the bleed port at the caliper and then snug it up again. Repeat till fixed or cursing begins.

Paul

[cdowns]

It is really best if you have the factory service manual and read the detailed instructions how to properly bleed the brakes and set up the master cyclinder and the job will go smoothly

[franken]

After the MC, bleeding at the wheels starts w/ the right rear since its furthest from the MC.

[GASoline71]

Originally Posted by franken

After the MC, bleeding at the wheels starts w/ the right rear since its furthest from the MC.

Actually the left rear (drivers side) is further away as the fluid travels. The right side rear (passenger side) is physically farthest away.

For the OP... Gravity is your friend.

Make sure your MC is full and crack the left rear bleeder screw and give it some time. Eventually fluid will start dripping from the bleeder screw. Close it and then do the same for the right rear, right front, then the left front. Now you have fluid at all 4 corners. Just make sure the MC stays full. Leave the top off of it too.

If the pedal is still a bit soft you can then bleed them by the old pump the pedal method. But at least you will know you have fluid at all 4 corners.

Gary

[jmillsUT28]

Thanks for the replies.

Before I start when I bleed the front power brakes do I need to push in the pin on the valve and keep it pushed in the entire time I am bleeding the front brakes? This is what I thought but wanted to make sure.

[engineer_gregh]

Just went through this with my 71 pickup. Turns out the new MC was bad. Here is the thread;

http://67-72chevytrucks.com/vboard/s...d.php?t=691627

[jmillsUT28]

How did you know your new MC was bad? When you bench bled it were you not getting fluid out of the outlets?

Originally Posted by engineer_gregh

Just went through this with my 71 pickup. Turns out the new MC was bad. Here is the thread;

http://67-72chevytrucks.com/vboard/s...d.php?t=691627

[engineer_gregh]

The MC bench bleed as it should but I could never get a firm pedal and the brake light stayed on. I had fluid at all four corners when bleeding but very little at the rear wheels.

[jmillsUT28]

Ok gotcha.

[jmillsUT28]

Looks like I am going to replace the complete brake system. When to the rear to let it gravity bleed but had nothing after 2 hours. Figured I would unscrew the brake line going into the rear wheel cylinder and it snapped off.

So going to buy a complete brake line kit. What's my options? I see GMCPauls Truck Parts has a kit for $155 or a stainless kit for $185. Anyone else have a good one? Should I get stainless or does it not even matter?

[CC69Rat]

jmills -- Hey, just an idea and a few questions.. if I missed it, please forgive me but I read through your post and it seemed all too familiar.

I'm not really a Blazer guy, so I am kind-of asking here .. did the Blazer come originally with power disk? Being 72, I'm guessing this is the case.

Do you know if the PO maybe replaced any of the brake components, or may have converted it to Power Disk?

The reason I'm asking, is as I read through the post I am thinking "The push rod is too short"

I upgraded a truck once upon a time that was an original Power drum setup. When I changed over to an aftermarket MC, the push rod was not the correct length so I was not getting full pressure from the pedal, out to the MC. That little rod and boot connection could be wrong. The aftermarket companies sometimes will include a 'bullet' that adds additional length to the rod to make it correct, drum vs. power drum vs. disk setup.

Could it be your Blazer has an earlier year gas pedal / push rod setup? Maybe from an earlier drum brake truck etc. ? Maybe the MC has a deeper center bore than the push rod length? If you use the traditional screwdriver technique on the bench bleed and you're getting full pedal / fluid push I would think it's the MC. I'm betting that push rod is just too short.

Check out this video around 1:35
https://www.youtube.com/watch?v=lNtMx_4PBtk

It will all make sense This fixed the setup I was working on at the time, and could be an easy / cheap fix for you.

[jmillsUT28]

hmmmm that could be a good point. How can I tell if the push rod is not long enough? Unscrew the line that is coming out of the MC. Have someone push the brake and hold it. Then put my thumb over the hole and have them release it to not add air in the MC. If it shoots out fluid when they press it down will mean it's the right length but if it does not then it might be to short or needs to be adjusted?

As for the PO who knows that he did. He has had it since 95 as a project. ha I do know that when I took the rear drum off it was missing about 5 parts for the brakes. ha

[CC69Rat]

Maybe post on the parts board and see if someone has one off a 72, and may be able to measure it for you? I'll dig around and see if I can find one online and get the correct length. So you're just using an OE type master cyl or is it aftermarket?

Maybe even the local parts store,.. take yours with you and see if it's different than the one they carry(?)

It would be well worth the effort, it won't cost you anything but your time just to make sure before you drop the coin on the new brake lines / kit.

[snipescastle2]

yeah, the push rod is different for manual brakes, sounds like you're onto something there.

[midniteblues]

be sure your bleeders are not clogged up with crud that you cant see.takem out run a drill bit into them and blow them out if ya can.

also a single line in the rear could cost as much as $10 and alot less work than replaceing EVERYTHING.but only you can evaluate the system.

when workin with old rusty brake lines a penetrant i like to use is the acetone/atf mix.
3 applications over a 24 hr. period and anything should break free. workin the fitting back an forth a very little at a time helps.

also some heat but ya gotta be carefull when an where.

with dang near everything disconnected i like to blow air through the lines you'll be surprized at the crud that comes out. and it'll show ya if your rubber lines are collapesd

to check the push rod what i have done is, drain the reseviour almost completly and slowly and evenly loosen the master and watch the piston movement it may show ya something.

i recently had push rod problems on a 95 i was working on for someone an that was the way i figured it out. a few twists of the rod an it worked great got them bleeded and down the road it went after all that. but that system is slightly differnt than these trucks/blazers

[engineer_gregh]

I bought my kit from InLine Tube. I didn't go with stainless as many posts here had advised not doing so as the stainless is a lot less forgiving and harder to work with. The kit from InLine Tube was dead on as far as the bends.

http://www.inlinetube.com

They will need to know year, short or long bed, coil or leaf spring rear, power or manual brakes.

[jmillsUT28]

Update, I tried to gravity bleed the left rear brake and after a full weekend had no fluid coming out. I actually broke off the brake line going into the wheel cylinder as I was replacing the cylinder. Even with it not connected I did not get any brake fluid that came out. From what I hear I should have. So does this mean I have a blocked brake line somewhere? Are we sure power brakes should be able to gravity bleed?

Greg, I will check out inlinetube today. Thanks.