I wish I could go Mike, I have my son's 1st birthday party going on that day. Drop me a line next time your going and I will be sure to try and make it. The schedule is getting full though, its graduation season and we have a lot of family members/friends with kids that age. Who knows what kind of time Im going to have.
Glad to hear that your car is ready to go. Did you get your 700R4 all squared away?
Be sure to post your times or at least let me know how she ran.
Good luck to you and Ray. Are you guys just runing time only or is something going on?

Congratulations Joe! I didn't join this post to win a prize and besides, I understand that Vikki probably helped you a lot more than I did. Even if I hadn't been the one to guess the problem, my reward is seeing you triumph. Let me know if you're coming this way for the Firebird and TA Nationals and we'll hook up for a beer. It must feel good to finally get this behind you.

John

Jim,
Unfortunately we did not have time to conduct a post mortem on the distribution block. We got a late start and quit about 11 last night as I had a 4 AM morning today. I would like to conduct a post mortem just to satisfy my curiosity and keep anyone else listening from experiencing similar grief.

All,
My theory…
Remember the beginning of this trauma. We had bled the brake system after finding an air leak and gained a hard pedal. (no fluid; just air being drawn into the system from a loose rear hard line) We then decided to re-bleed the front system as a precaution. That’s when the trouble started. I suspect as soon as we opened the front bleeder screw the pressure differential between the front and rear systems caused the spool in the distribution block to shift. Why the spool never returned to the center position through all of the subsequent bleeding/MC changing/tail chasing is a mystery. Likely stuck in 38 years of crud. Why we were unsuccessful at bleeding the system with the spool off center (assuming this theory is correct) is also a mystery to me. We continued to push a good amount of fluid out of all four wheel cylinders so it didn’t appear that the shifted spool restricted the system flow.

Given all of the above information my dilemma is:
• We appeared to have good fluid flow from all four wheel cylinders;
• If the system was indeed closed I think we still should have been able to gain a hard pedal even if the spool was shifted off center but not off center far enough to restrict system flow.

I still feel we had an air leak somewhere. Obviously, the original distribution block sealed as the system was functional prior to the differential being removed for rebuilding. The problem didn’t appear to be any of the hard line connections at the original distribution block as we had a hard pedal after finding the loose rear hard line. So…what happened when we went to re-bleed the front system? I wonder if it is possible that after the spool shifted we gained an air leak around the switch. I don’t know; just a thought. I’m not sure why, how or even if this could happen as I’m not familiar with the exact construction of these switches nor the distribution blocks. And I’ve never heard of a switch failing – either electrically or sealing to atmosphere. Certainly an air leak at the switch on the distribution block, assuming the system could be properly bled with a shifted spool, would explain the issue.

Unfortunately, hypothesis above is conjecture on my part. What we do know is replacement of the original distribution block resolved the problem. We don’t know why.

And I dont care at this point, I have brakes. Beer is on me John. When are the TA Nat's?

Dennis,
Could be that changing the block simply let a trapped pocket of air move on out. I've seen it happen.

Joe,
If we all took the 'got mine' tough sh** 'I don't care' attitude there wouldn't be much advice floating around now would there? Wouldn't you want to know if it happens again? Lessons are funny, they come back if you don't learn them.

Jim,
Certainly could have been trapped air. I think it unlikely however I wouldn’t discount anything at this point.

I experienced air trapped in my car several years ago after a MC failed. I had a devil of a time chasing all of the air out of the system. But that situation was different. I could get a spongy pedal, just not real solid one. Careful vacuum bleeding cured the problem.

This was different. We had no pedal; none to speak of. She went clear to the floor with no resistance. The kind of pedal that makes one think there is a growing puddle of brake fluid on the ground somewhere every time the pedal is pumped. And nothing we did until changing the distribution block had any effect whatsoever.

Maybe if I get a chance this weekend I can inspect the block we removed as I would like to determine a cause. I've personally never had an issue with either a distribution block or a switch thus I've never had cause or opportunity to fool with one.

Thanks

Great! Chevies, Pontiacs, Mopars, Fords, never seen this. For me it's the unusual problem where I learn. You answer a million questions and then you finally get an unusual problem and it's interesting. Like an interesting story you want to know the ending... Yes, it's great Joe's car has brakes now, but lets get to the bottom of this. Right now it's just as likely that the bleeder screw wasn't getting closed before the pedal rose as anything else. Honestly, this would be the first dis block problem causing no brakes in the history of the American automobile. You would think that it would be known by now! These blocks and other brake components are designed so that you can't get a total brake failure unless two things go wrong at once.

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Joe,
If we all took the 'got mine' tough sh** 'I don't care' attitude there wouldn't be much advice floating around now would there? Wouldn't you want to know if it happens again? Lessons are funny, they come back if you don't learn them.</font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">I dont think you understand here Jim. What I am saying quite clearly is that I dont know what the exact problem was with the block, but the problem was the block.
Oh, and in addition to this, when have you ever known me to do that on this board?
I dont know what happened to the block to cause this failure? I posted that so others can check the block in the future. I think that's pretty clear.

OK Picture this. A question comes up with the same problem you have/had. Right now the answer would be, switch the block. I don't know why, just do it. You would have said,"I'm not switching it until I know why". You are asking us to do what you would not have done. Throw parts at the problem.

I understand that you are an electrical engineer. After 4 years of engineering school you have the tools to inspect the part and tell us what happened to it. I have been through engineering school and trade school not to mention being a mechanic for 25 years and nothing that has been written makes any mechanical sense. Just tell us what happened. 'I don't know' doesn't fly well after three pages of heartfelt help and time donated to your problem. Also, you owe the future board answers now that you have reaped the help provided. Wouldn't you like to be able to provide a logical answer to a problem that you have hands on experience with? You have been down the path of the rear end diff R&R and brake R&R and many other paths. It would be great if you could help your fledgeling brothers in Birds with the their questions. Look back at these postings and concider how much time and thinking went into the answers. We actually cared that your brakes were not working. It's like a puzzle and you are running off with the last pieces.

Perhaps I am missing something here but I don’t exactly have the means to dissect the block. Dennis may, but as an ELECTRICAL engineer I surly do not.
Also, we have systematically eliminated all other possibilities which have been painfully detailed out in this thread which LEAD Dennis and I to the block.
If you would recall, the block was on of the first identified culprits. Only after systematic elimination of all other culprits did we replace that block.
So if you have eliminated all other possibilities except 1, wouldn’t you be compelled to eliminate that very last "puzzle" piece? That’s what we did, we replaced the last puzzle piece and our problem went away. I am not an expert on the working of that block or how it could produce the problem that it did so I cant give you a exact reason. But I can tell you or anyone else that is reading this now or in the future that it was the cause. We didn’t haphazardly throw parts at this problem nor would I ever ask anyone to do that on their car or in their professional life. As an engineer for a major global corporation I can assure you that just doesn’t fly. Other industries however make a lot of money at the customer’s expense this way but we don’t.

So here is the lesson for our "fledgling brother in birds":
If you eliminate all other possibilities detailed in this thread or others and still cannot yield a high, hard pedal, replace the block. It will cost you about 20 bucks from FirebirdBill and may solve your problem.
This should about do it for this one Jim, I whole heartily apologize if this explanation isn’t good enough for you. But it’s all I have.

It normally would be good enough, BUT, if what you are saying is true, if any of us had a failure at a front wheel cylinder our brakes would be totally gone. While we are driving or not. I say 'failure at a front wheel cylinder' because that is what you described by having the problem arise while bleeding at the front wheel cylinder. Can you see why it's so important to be sure of the problem? Spring a leak in one corner and die. Is the block you bought used? Is it going to do the same thing your last one did but when you are driving? Is your car safe to drive if you have not pinned down the problem? It's not like a carb adjustment or timing or charging system..... What if the problem comes back????

I agree with you Jim I believe it was trapped air.
That's what I tried to explain in my post.
Anyway's it's over now.
Maybe he could send the block to Vikki and see if she would be willing to dissect it.

Well if it was trapped air, I shouldn’t have to worry about a catastrophic failure that Jim described. That, or the problem was resolved by changing the block out.
Either way, I think this thread has fully covered all the bases.

If anyone wants the block to post mortem it, be my guest. Dennis has first dibs though.

I really do appreciate everyone's help on this.

They are simple. I'm sure Dennis can handle it. With the link that John provided it should be a simple task to figure what's up.

Not likely to be trapped air. As Dennis and Joe stated, the pedal was not soft...it was not there.

I did have the same problem on my '70 'Cuda, a failed rear wheel cylinder caused the pedal to go to the floor while driving, and after replacing all four wheel cylinders and gravity bleeding gallons of fluid the pedal would not come back. I installed another known good master cylinder from my fleet and the pedal still would not come back. I took it to a repair shop that could not resolve it either, and they quoted me $1100 to replace the entire brake system which "should" solve the problem, but would not guarantee that they would fix it. So home it went. I never did resolve it, sidelined the car while I focused on caring for my son and growing my new business, and never did get it fixed.

When Joe had the same problem it stirred up some memories and a desire to help solve it by logic. Dennis and Joe together went through every other possibility besides a line with a pinhole leak (which would not show up in vacuum bleeding, but would show fluid with as much pumping as they did).

I just happened to obtain a spare '68 block the week before Joe's problem surfaced. I cleaned it up and examined it carefully and I now know what they do and how they do it. Yes, it's a "dumb" device, but things must be just so for it to do its job.

Hint #1: No pedal despite free flow of fluid.
Hint #2: Presumably 38 year old part, probably never been serviced or replaced. After all, they never fail, right?
Hint #3: No gravity bleed. Vacuum and pressure bleeding could move fluid through the circuit, but I am willing to venture that it was through a groove in the shuttle, not past the end.

I would be happy to do the post-mortem, and ask only for a detailed photo of the block as installed and the lines attached to it with a description of where they lead.

It's going to be very interesting to learn how the block could cause catistrophic failure in both front and rear systems. Even after bleeding with positive fluid movement.

I’m just curious about something Jim. If you say that it wasn’t the block,,,, then what was it?
Obviously you don’t believe that it was the block or that it could have even been a possibility.
I am interested in hearing your assessment of the situation?

I'm waiting to hear what the problem was. At this point it would be foolish to go any further with speculation when you can simply take the block apart. If there's no obvious problems with the block then the question would arise of what else could it be. For example, if the spool moves freely, the springs and o-rings are intact and there is no fluid present around the switch assembly I would be skeptical if there was any problem with the block. The only other thing would be a crack which you could check with a crack check spray.
Take a look at the picture of the block and tell me how the block could cause the symptoms?

Something tells me that even if an answer was given you wouldn’t accept it because it wasn’t your idea.
I’m out of this one my man. I just dont have anything else positive to add to this thread.
Hope someone satisfies your curiosity.
I do appreciate your help on this though.

Quote
"Something tells me that even if an answer was given you wouldn’t accept it because it wasn’t your idea".

Something tells you??? Give an f-in answer and find out! Any idiot can take the ends off the block and look!

Let's not get personal, Joe. I'm talking about car parts and a story that's really hard to believe.

The diagram posted above is NOT the design used by Pontiac on a Firebird. There are no "blocks" on the end. Take a good look at yours, Jim, if you don't believe me.

Just because you haven't seen it doesn't mean it can't be true. We've been down that road before.

I assumed that John had the correct picture. It's probably close enough to see what a long shot that it was that the block was the problem.

The philosophical rule that the simplest explanation is preferred over the more complicated one and that explanations should be first proposed in relation to concepts that are already known.

Another way of seeing it is to say that the fewer assumptions that need to be made to support an explanation of something, the better. The principle is attributed to William Occam of the fourteenth century.

From Occam's Razor. It admonishes us to choose from a set of otherwise equivalent models of a given phenomenon the simplest one. In any given model, Occam's razor helps us to "shave off" those concepts, variables or constructs that are not really needed to explain the phenomenon. By doing that, developing the model will become much easier, and there is less chance of introducing inconsistencies.

IE The master cylinder and then some less than successful bleeding. And, is it I that needs to be right or is it that I need to be wrong? I have only supported or disputed other peoples' theories so how could I be right? Or, at least, original and right????

Wow - I just got home from a trip to find this post is not dead. The only reason I even suggested the distribution block is because I had an experience like Joe's many years ago on a Chevelle (which I'm sure had a virtually identical design). I replaced the shoes, bled the brakes, then bled the other circuit and was without brakes. I couldn't get the brake light to go out either. Someone wiser than me suggested the distribution block and indeed that was the problem. In my case, getting the piston to recenter solved the problem, but only after a week of trying other things and a gallon of brake fluid.

I actually think Dennis has a plausible theory. The piston moved far enough to one end to lose the o-ring seal, thus allowing air to enter the line from around the switch threads. Surely you can agree that this theory is plausible Jim because you suggested that the same problem was occuring at the front wheel cylinders. Similarly, the o-ring could've gotten cut when it moved over some crud that could've easily built up over so many years hence causing the same problem.

I would buy it John but with a thorough bleed with no air coming out..... And it would have to be sucking air into both sides??? It wasn't described as a slow starting problem that got worse, it was all at once. Just doesn't sound right for air getting in through the switch sleeve.

I don't understand your point about it having to suck air from both sides.

Looking at the diagram you posted (which is accurate enough for argument's sake), if there were a slug of air from the switch to the end of the block it would easily be trapped there during bleeding. Why? Because it's in a dead part of the circuit. If Joe and Dennis are gently bleeding the brakes as advised, there would be little pressure in the system to push the air out through the switch. Once the brakes are bled with the air slug still present, pressing on the brakes would let the pedal drop because the air would be pushed back out through the switch threads. Let go of the pedal and it gets sucked back in. Hence, you could bleed the system with little or no air coming out yet experience a soft pedal or no pedal.

I've had my share of weird brake problems and this is completely possible within the realm of my experience. I wasted over a week with a customer's car once because no one, not even the dealer, could tell me how to trouble shoot GM's new quick-take-up brakes (remember those-people still don't know that you can't manually bleed them). That was around '81 and that's when I bought my pressure bleeder. Year's later I had a similar problem with an '86 Grand National that I owned. After taking it to three Buick dealers, the last one (who employed a regional GN guru) wanted to replace the whole brake system and though it was under warranty, I wasn't about to trust the car to these guys. Using methodical troubleshooting techniques I determined it was a $49 accumulator that took 15 minutes to replace. Just because these systems are simple it doesn't mean that they are easy to troubleshoot and anything with moving parts or seals should be suspect when troubleshooting them. I don't think we would be belaboring this if it had been the front wheel cylinders or master cylinder.

If a small leak at the wheel cylinder could cause the symptoms that Joe experienced then why can't the same leak at the distribution block cause it?

It would be best to take a look at the block.

Jim, why did you suggest the replacement of a master cylinder and wheel cylinders without evidence of failure and state that master cylinders are often "bad" out of the box, then discredit the possibility of failure in another hydraulic/mechanical component?

I am quite certain what Dennis will find when he pulls the seats, and I know why the system was unable to pump up and bleed properly.

And yes, loss of hydraulic fluid from one wheel cylinder can indeed result in the loss of all braking in certain conditions. I've had that happen twice over the years. Once in rush hour a.m. traffic, once in the garage after winter storage. There is a reason that "parking brakes" have also been called "emergency brakes".

After tearing down several "good" master cylinders recently and seeing how much sludge accumulates in the pistons and bottom of the reservoirs, I will now flush the entire brake system every time I service any hydraulic component.

Quote;
"Jim, why did you suggest the replacement of a master cylinder and wheel cylinders without evidence of failure and state that master cylinders are often "bad" out of the box, then discredit the possibility of failure in another hydraulic/mechanical component?"

The answer is very simple and I'm surprised you ask such an obvious question. Answer; 99% of the time it is one of these two components.

Quote;
"And yes, loss of hydraulic fluid from one wheel cylinder can indeed result in the loss of all braking in certain conditions."

It can, but again, 99% of the time you either loose your front or rear brakes, not both. The system was designed that way. The only way you loose both is to have two things go bad at once or you have neglected one of the systems.

The biggest reason that it most likely was not the distribution block that caused Joe's problem is that it does not make sense with the story he told.

Now I have a question for you, Vikki;

With your knowledge of how the distribution block works, describe how you can go from a hard pedal, then you just attempt to bleed the front brakes one time, at one corner, and you totally loose front and rear brakes? This is the exact info we were given. It just does not make any sense that it was the dis block alone.

I don't subscribe to the theory that if it usually breaks, it's probably broken. I find out what and why before replacing parts. Perhaps that comes with 20+ years in IT...I work on site and customers don't appreciate guesswork.

When they opened the front bleeder valve with the rear system pressurized the shuttle moved to the front. My guess is that the shuttle return spring is broken or corroded, or that the distribution valve accumulated a layer of "mud" that the shuttle stuck into. In either case, the shuttle did not return to the center position and the fluid from the reservoir could not build pressure on the FRONT of the shuttle to recenter it. If you look at the brake line diagrams posted on my site, or under your hood, you will see that the front port on the distribution block goes to a front brake line, not to the master. The master feeds the front driver's side port on the distribution block. Without pressure on the front of the shuttle and with high pressure against the rear of the shuttle, and with suspected internal interference, the shuttle was not going to return to center. The pedal was low because there was no pressure to the front wheel cylinders.

If, however, they had opened a rear brake bleeder and removed the line from the front port of the distribution block and used a very narrow pin punch to recenter the shuttle, there is a good chance it would have been able to be returned to service.

If the line from the master cylinder was routed to the front of the distribution block rather than the side, I do not believe this condition would occur as the pressure from the master cylinder would serve to push the shuttle back into place.

And as to that 1% when the brakes fail totally...the majority of cars on the road today are maintenance-deferred or neglected. I see it every day, even on newer cars. Since we don't have safety inspections, how many cars do you see every day with bad shocks or struts, hanging exhaust systems, squealing brakes, burned out headlights, or burned out brake or tail lights? It's not just older cars. In this case, though not intentional neglect, failure to flush the brake system on a periodic basis likely contributed to the situation and compounded the problem. Hydraulic systems are not designed to be maintenance free for 35+ years.

Quote:
"I don't subscribe to the theory that if it usually breaks, it's probably broken. I find out what and why before replacing parts."

This seems sarcastic and serves no purpose here. You suggest changing the dis block without knowing it's broken????

Quote;
"The pedal was low because there was no pressure to the front wheel cylinders".


I read it that there was no pedal at all. Big difference for the trouble shooter.


So, you are saying the shuttle moved over and stuck? The block, as I see it, can either have the front brake passage open, blocked or partially blocked.
Open: Normal operation
Closed: Hard pedal
Partially blocked: Not much change to speak of.

That's the way the block was designed. It was purposefully designed so that if the sludge made the piston stick you would not loose your brakes. Your post on the foreign car block sums this up. They do not even recommend replacing the block unless there was leakage at the switch. Where did the step go where you look for a leak at the switch? I think it's probably very common to have the sludge in the block. A good flush would solve it. Sounds like this block had a very good flush before the said problem occured.

I'm skeptical and this is all BS! Just take a look at the block. Why sit here and type all day when a cursory inspection of the block, which I can't believe wasn't done, will answer the question.

It all boils down to, "Where did the hydraulic pressure exerted by the master cylinder go???? There is no loop in the system. We are taking about MASS AMOUNTS OF AIR! Where did the mass amounts of air come from so quickly. Most definitely not from the block...

Jim, they followed your suggestion to change the master cylinder first. It didn't fix it. It couldn't.

If you read the posts, even though they were pulling brake fluid through the front bleeders the wheel cylinders were dry. Why? Because the front of the master cylinder was not pushing fluid into the lines. Without fluid, there is no hydraulic pressure. With no hydraulic pressure, the pedal goes to the floor. And if there are no leaks, why is there no pressure? Because the fluid is not under pressure going into the brake lines. And the only place that can happen is in the distribution block.

They fixed the problem, and that's what is important.

Quote;
"If you read the posts, even though they were pulling brake fluid through the front bleeders the wheel cylinders were dry. Why? Because the front of the master cylinder was not pushing fluid into the lines. Without fluid, there is no hydraulic pressure. With no hydraulic pressure, the pedal goes to the floor."

This logic is severely flawed. Piston in block moves over and there is no flow. That would make the pedal hard not soft. That's one of the problems with this theory, it doesn't hold fluid!!

Did I say that fluid was blocked? No, only that pressure was not applied to the end of the piston with the shuttle off-center.

If the fluid wasn't blocked why was there no flow. Come on, it's easy to see. It's either blocked or not. Not blocked, it's normal, blocked, hard pedal.

Strike three, you're out. And as Joe's problem is solved, I'll move on to more productive things.

Yeah, like learning a little about hydraulics. Dahhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh!