Pinning MC as culprit -- complete loss of brake pressure

[Ryker]

Howdy, happy, helpful USMB folk! As you may have already guessed, what follows is the plea for help that comes from a dejected backyard hack mechanic at wits' end...

 

A rather long time ago, I dropped my rear diff. on a bunch of large rocks and ledges and logs, etc. and, despite my best intentions, killed it. Naturally, I continued to drive around on it like that -- it would seize intermittently, making grating spats of noise that'd scare the bejesus out of pedestrians, and resulted in a warped brake drum. So I yanked the half-shafts, replaced the warped drum, hub and the wheel cylinder, then bled the break lines, but have not been able to return pressure to the brake system. I was sure to loosen the cap to the MC reservoir before disconnecting/reconnecting the brake line. I've tried bleeding in three different orders: RR-LF-LR-RF; LF-RR-RF-LR; and LR-RF-RR-LF. Of note: when the engine is off, the fluid expelled from the bleeder valves merely trickles out (I'm having a second person pump the brakes slowly, and not all-the-way-down, twice in a row, opening the valve during the second brake pedal depression for a couple seconds and closing it again before they begin to let the pedal out). Doing the same thing with the engine on, the fluid barely spurts out -- approximately an inch from the valve. I've checked the MC seals and along the lines for any leaks and have found none. The only way I can get resitance in the brake pedal is to pump it several times, but the pressure will have gone by the next depression -- thus, I don't think I can effectively implement the 'brake booster' test: checking to see whether an already depressed brake pedal sinks further when the car is started.

 

I hope I'm not , but is there any surefire way to determine whether the master cyclinder is to blame for this situation, without replacing it? In my searches, the thread that comes closest to an answer is this one, but it's really rather roundabout when it comes to the actual business of an answer.

 

Thanks in advance for any help,

Ryan

[GeneralDisorder]

You just have a stubborn air bubble in the master cylinder. You need to bleed the MC first before bleeding at the wheels. And with air at the MC, you may need to bleed quite a bit before you get good pressure at the wheels.

 

There are two bleeder screws on the bottom of the MC - one for each circuit. Bleed both of those, and then proceed to each wheel - making OFTEN checks of the MC to make sure it's full. Top it off after each wheel, and perhaps even halfway through bleeding each wheel. If it gets too low, you will have to start all over again.

 

GD

[Ryker]

 

Alright, there are 3 lines leading out of my MC (see points 1 thru 3 in the photo). I presume 1 and 2 are the brake circuits that split to the 4 lines; however, I tried bleeding each of them. The trouble is, in order to loosen line number 1 (having stripped the top of the nut), I had to disconnect line 2, which didn't allow me to pump the pedal more than once without introducing more air into the MC (at open point 2). There is nothing connected at number 4 -- there is a steel cap here. Will the only effective way to bleed the MC be to improvise two speed bleeders attached via tubing?

 

Thanks,

Ryan

[Ryker]

Alright, so I'm figuring that line 3 is being brought in from the brake booster, so I should leave it the hell alone. Since I've busted #1 loose, I am now able to loosen and bleed it with #2 still locked down. I've bled the MC and the lines at each wheel twice and now get pressure, but in order to properly engage the brakes, I have to pump the pedal three times. So now I have just one final question: Is RR-LF-LR-RF the correct order for an '88 GL Wagon?

 

Thanks again.

[Syonyk]

Line 3 shouldn't be coming from the brake booster - it's a high pressure brake line. It probably goes to the rear of the car (there's a splitter back there).

 

As near as I can tell, you have drum brakes in the rear. Have you adjusted the slack of the brake shoes? I don't know what kind of slack adjuster you have, but if there's a lot of travel needed before the shoes contact the drum, you'll have problems like this that no amount of bleeding will fix.

 

To my knowledge, there are two types of slack adjusters on the rear: Star wheel types (that are manually adjusted), and a ratcheting type (that should be automatically adjusting). If the slack adjuster is missing, seized, or fully retracted, the wheel cylinder will have to travel quite a bit to make contact with the drum, and this can take multiple pedal presses.

 

Once it firms up, is it a hard pedal? Air in the brake lines will come across as softness, even once things make contact. If it takes a few presses and then is a hard pedal, it's most likely caused by excessive play somewhere in the system.

 

Also, when you were replacing the wheel unit, did the master cylinder run dry? If there was always fluid in the reservoir, the gentle flow towards the rear from gravity will keep the lines mostly air-free (and just make a big mess on the driveway - I do miss working in a gravel parking lot), so you just have to bleed the wheel cylinder. If the master cylinder did run dry, then... you've got air in a lot of places it shouldn't be, and good luck getting it all out. I've heard a few hours of gravity bleed can help in that situation (open all the bleeders & let them flow, add fluid as needed to keep the master cylinder level up).

 

-=Russ=-

[Ryker]

Line 3 shouldn't be coming from the brake booster - it's a high pressure brake line. It probably goes to the rear of the car (there's a splitter back there).

Ah-hah!

 

As near as I can tell, you have drum brakes in the rear. Have you adjusted the slack of the brake shoes? I don't know what kind of slack adjuster you have, but if there's a lot of travel needed before the shoes contact the drum, you'll have problems like this that no amount of bleeding will fix.

 

To my knowledge, there are two types of slack adjusters on the rear: Star wheel types (that are manually adjusted), and a ratcheting type (that should be automatically adjusting). If the slack adjuster is missing, seized, or fully retracted, the wheel cylinder will have to travel quite a bit to make contact with the drum, and this can take multiple pedal presses.

 

Once it firms up, is it a hard pedal? Air in the brake lines will come across as softness, even once things make contact. If it takes a few presses and then is a hard pedal, it's most likely caused by excessive play somewhere in the system.

Yes, the rear brakes are drums -- the adjusters are ratcheting. I added some slack to the shoes in order to get the drums back on. (The brake pedal achieves normal resistance after three pumps. Bingo!) ...Reckon I'll go back in and make the drums' fit more flush.

 

Also, when you were replacing the wheel unit, did the master cylinder run dry? If there was always fluid in the reservoir, the gentle flow towards the rear from gravity will keep the lines mostly air-free (and just make a big mess on the driveway - I do miss working in a gravel parking lot), so you just have to bleed the wheel cylinder. If the master cylinder did run dry, then... you've got air in a lot of places it shouldn't be, and good luck getting it all out. I've heard a few hours of gravity bleed can help in that situation (open all the bleeders & let them flow, add fluid as needed to keep the master cylinder level up).

Fortunately, the MC reservoir never ran dry.

 

As for missing the gravel lot, do you also miss the gravel in your hair, clothes, and sheets? Can you tell I work in a gravel lot?

 

 

Thanks, GD and Syonyk, for your responses!

[daeron]

ive always pumped the pedal at least three times, fairly quickly, held pressure, and only THEN released my bleeder valves.. the more you pump, the more pressure you build up and the more you force the air to the bleeder valve. When you are done, you should get good pedal pressure on a single pump.

 

and he said bleeder valves, not bleed them at the brakeline fittings... or am i wrong? i seem to recall not being able to find any bleeder valves on the MC on my 87 gl10 NA....

 

i mean, if youre kosher then great.. but those two comments seemed like they might help you in the long run. If not, then they'll probly help me, cuz it means im wrong about something.

[Syonyk]

As for missing the gravel lot, do you also miss the gravel in your hair, clothes, and sheets? Can you tell I work in a gravel lot?

 

It beats "You're going to have that stain cleaned off the cement when you move out, right?"

 

My old GL... leaked. Everything. Mostly oil, but there was some power steering fluid, and then the nice stains of brake fluid from when I was working on the brakes.

 

Three hours with a powerwasher later... it was mostly clean.

 

-=Russ=-

[GeneralDisorder]

Yeah - the EA82's don't have bleeders on the MC (weird, since the EA81's do...), but they still sometimes need to be bled. Basically crack each line in turn and pump till you get a good flow from them. That's how I've always done it.

 

GD

[daeron]

Yeah - the EA82's don't have bleeders on the MC (weird, since the EA81's do...), but they still sometimes need to be bled. Basically crack each line in turn and pump till you get a good flow from them. That's how I've always done it.

 

GD

 

 

good god i dont believe no one in my family was kind enough to suggest that.

 

thank you, i thought i was friggin nuts. WTF, why cant they put bleeders where they need em!?!????

[Ryker]

Victory! It may have been a combination of air in the lines/MC and the shoes not fitting snugly enough into the drums, but after 'expanding' the shoes as far as I could and still get the drums back on, I've got normal brakes again!

 

Thanks again for the help!

[Syonyk]

Great! Glad we could help to get you rolling (and stopping) again!

 

-=Russ=-