Drum brake issues

[red71cheyenne]

Hi all, I'm posting this in this board as I think it sees more traffic. This is a drum/drum 69 Blazer.

On my Blazer, I'm trying to get the drum brakes to work, but I'm not having any luck with the Master Cylinder. Its new, but I'm not sure if its good or not. Had to adjust the length of the push rod and it doesn't seem like I'm getting fluid out to the front brakes. When I try to bleed them, no matter how much I pump, I never get pressure and only a little fluid comes out at the bleeders.

What am I doing wrong? The backs work fine, pump up, bleed no problems. Is my push rod length off? How can I check to see if its long enough to be activating the front brakes?

Thanks for any help, Jeff.

[silverstreak]

I'm wondering why you had to adjust the length of the pushrod. If the bore in the back of one master cylinder was deeper than the other, one may be for power brakes and one for manual, just a thought.
Did you "bench bleed" the master cylinder prior to bolting it on? They make a special kit for doing this or you can make one yourself. Using some section of short brake line with the correct nuts, screw them inplace where the original lines would go, then bend the lines (or attach some hose to the lines) so they bend over into the master cylinder resivoir, then using a blunt instrument, slowly pump the master cylinder until bubbles no longer appear in the fluid. This gets most of the air out of the master cylinder and makes things go easier when you bleed the rest of the system.

[cparman]

Is the pedal very low or do you have no pedal at all?What happens when you gravity bleed the front brakes? Do you get a steady drip of fluid? Do you have power brakes? If you do I would recheck the clearance between the booster and master cylinder. The redneck way ( my way ) is to unbolt the master from the booster. Do not remove the brake lines, and get a small ball of clay and put it on the rod coming from the booster. Bolt the master back up, tighten both nuts tight. Remove the master again and see how much of the clay was crushed if at all. If it crushed a good bit guestimate how thick the remaining clay is. You need less than 1/16 clearence.

[red71cheyenne]

The pedal is very low, and this is on manual brakes, no power.

I did bench bleed the master before I installed it, it came with the little disposable plastic bleeders.

I had to reset the push rod because I had it entirely pulled out of the truck during the rebuild and I had disassembled it to clean and paint.

With the rod installed, I have set it to just contact the plunger inside the master cylinder when the pedal is in the up position.

Should I be able to bleed fluid from the master thru the wheel cylinder bleeders with my vacuum pump? I have tried that too and can't get any fluid to come out of the bleeders using the mighty vac. Makes me think there's something wrong with the master. Like I say, it is new. Thanks, Jeff.

[cdowns]

does the distribution valve have a pin that needs to b to centered like the disc/drum proportioning valve???

[ksbeatty]

I had the same problem and went around and around with it. I ended up taking it to a brake shop I knew and they "power bled" them to remove all of the air. I was told they readjusted the pedal and everything works fine. As for power bleeding there are different kits out there to presurize the system and push the fluid through.

[red71cheyenne]

Originally Posted by cdowns

does the distribution valve have a pin that needs to b to centered like the disc/drum proportioning valve???

Hmm, I'm not sure on that one. If it does, how does one do it? I guess that might explain why only one end of the brakes are working.

[red71cheyenne]

Originally Posted by ksbeatty

I had the same problem and went around and around with it. I ended up taking it to a brake shop I knew and they "power bled" them to remove all of the air. I was told they readjusted the pedal and everything works fine. As for power bleeding there are different kits out there to presurize the system and push the fluid through.

Ya, I have thought about doing the same and just taking it somewhere, but its too dangerous as it is! And if I don't figure it out with some help from you guys, I'll never know how to do it in the future.

[vectorit]

Did you check the rubber hoses to each wheel cylinder? If they are the original, they could be swollen so much to constrict the needed flow. When I replaced mine, I cut the old ones in half and the hole was half the size it should be.

Did you check each wheel cylinders? When I did my drums just recently, all of my wheel cylinders were so bad that the pistons barely moved.

Also, did you flush the entire line system with new fluid? If you haven't the lines could have muck in them along with water. When I did mine, the fluid came out black and had water in it. (Very little, but enough to be an issue).

Just some food for thought.

[red71cheyenne]

Originally Posted by vectorit

Did you check the rubber hoses to each wheel cylinder? If they are the original, they could be swollen so much to constrict the needed flow. When I replaced mine, I cut the old ones in half and the hole was half the size it should be.

Did you check each wheel cylinders? When I did my drums just recently, all of my wheel cylinders were so bad that the pistons barely moved.

Also, did you flush the entire line system with new fluid? If you haven't the lines could have muck in them along with water. When I did mine, the fluid came out black and had water in it. (Very little, but enough to be an issue).

Just some food for thought.

I did flush, but haven't checked the brake hoses to see if they were blocked. When I ran new fluid through, I got some thru after the old crap ran out, so I figured they were ok. They might be swollen inside though like you say. I replaced the rear wheel cylinders, they were leaking. The fronts weren't, but guess that might be because they are stuck/not getting any flow.

I'll look again at it tomorrow and see what I get out of it with my vacuum pump. Thanks for the help so far guys! Jeff.

[red71cheyenne]

Well, pulled the passenger side wheel off and guess what I found, leaking wheel cylinder, one side of which was frozen up. Guess thats part of the reason its not working. The fluid was running out of the hose just fine, so I don't think its blocked at all. Gonna pick up a set of shoes, cylinders and a spring set on my way home from work today.

[DPowers]

Just my .02, but I would replace the flex hoses as well.

[red71cheyenne]

Originally Posted by DPowers

Just my .02, but I would replace the flex hoses as well.

At some point I'm going to swap to a disc front axle, so I'm just trying to get it working long enough to last me til that happens. Its not like it'll be going very far anyway. Between the new Camaro, the 71 and the rest of the cars in my parking lot, I don't have time to drive them all!

[red71cheyenne]

Yep, looks like that was the problem. Swapped in new shoes and wheel cylinders, now I have good pedal and no leaks!

Thanks for all the help, Jeff.

[silverstreak]

Sweet! Glad you got it fixed.