For almost two months I've been working on the brake system on my '76. I've changed out virtually every component - booster, M/C, all four calipers, lines (including one I broke in the early stages of repair). I've bled the system numerous times - gravity, 2-person push-pedal/bleed, and vacuum bleed. Every conceivable bubble within a universe of those brakes has been eliminated. But...THE PEDAL IS STILL SOFT, and the system is NONFUNCTIONAL.

If only I'd listened to several of the wise dudes on this forum - at the very beginning of this ordeal - I'd be driving today, not bitching about what has to be done next. The advice was simple: GET THE RIGHT BOOSTER FOR THE YEAR! Instead, despite being ASSURED I'd ordered the right part from [company name withheld to protect the guilty], I gerry-rigged the M/C pushrod, adapting it to 'work' with what apparently is a booster for a later series 'Vette. The result: BAD AIR SEAL!!!!!!!!

Now - I have to remove that &*^^ing booster, re-injure my tennis elbow - cranking those g&^^*@## bolts off the firewall, then reinstall a proper, correct power booster. To be perfectly honest: I DON'T WANT TO DO THAT!! I'm ready to turn this over to a local shop to complete. I've got other projects needing attention and this one has taken its toll. Yes - I'll no doubt have to peel off another 'boat buck' ($1k minimum in US dollars), but at this point I don't think I can do anything else and retain what's left of my temper.

Moral of story: believe NOBODY you buy stuff from unless you've verified, re-verified and verified AGAIN the parts are correct. And if they're not the right ones -SEND 'EM BACK!!!

Thanks for hearing me out. Some people like me have thick skulls.

 

Remove the drivers seat, yank out that booster and replace it with Hydroboost unit. I plan on doing mine one day. A ratchet, socket with a swivel and long extension is your friend.

 

Been there, done that. Seat removed, head on a pillow - "coal miner's" light on forehead. Heater duct removed; Universal joint, extention(s), long, short. Twisting, turning; reaching around, getting up, getting back in; stretching, pretzeling, cussing and groaning. And that was just the removal part; reverse the previous for the install.

Really not sure I'm up for that - again. Plus, there's always the possibility I could be wrong, and something ELSE is screwed up. (The P-valve is the only unreplaced component, but from all I've read, they rarely go bad. And wouldn't it be great if it IS the P-valve, and I subjected myself to those acrobatics a third and fourth time?).

I'm ready to pony up and let the boys down the road take it from here. I take solace in this: three of the calipers were leaking, so at least I got some of this right.

I think.

 

Follow this brake bleeding sequence...

Left rear inner
Left rear outer
Right rear inner
Right rear outer
Left front
Right front

I verified it with a Chevrolet Service Manual
Very weird but when I did it this way it worked great on my 78!

 

Is it possible it is the vacuum booster check valve? I have seen quite a few of the cheap little valves that wouldn't hold the vacuum and it seems like you didnt have power brakes.

 

Thanks for reminding me why I'm sticking with "foot-powered" brakes on my '68 rescue!

 

Roger that, sir. If I had a nickel for each time I completed that figure-8, I could buy a round for the entire 49ers team.

 

I wish that were the case. I tested the original blown booster's valve - it was totally functional. Did the same (blow/suck) test with the new unit. Same thing. The issue is, the pedal goes all the way to the floor - even with the booster offline and the hose plugged to prevent vacuum leak.

In any event, on Wednesday, the car's being towed to a shop a mile down the road. The place is pretty savvy with classics. Had a discussion with the manager this morning; told him everything I did. He suspects the booster rod too. They have a measuring device for setting those things up, and as he says, the measurement is 'critical.'
But, at this point, I'm just guessing. I'll report back when the surgeon returns from the ICU.

 

If I were you, I'd do the same thing.

 

Take out the steering column. Makes the job a piece of cake. I have mine out to swap the pedals for the trans swap and I'm dong the booster at the same time and a blind guy with one arm could do the booster.

 

Actually, a blind guy with one arm would have an advantage doing that job.

Seriously, I'm turning the rest of the job over to a shop I trust. Because this is the first major brake job I've ever done, I'd want it to be checked over anyway.

It's one thing when a car refuses to start; it's another if it refuses to stop.

 

He's a smart man. You most definitely will not get a hard pedal if the rod is too short. In fact, that may be (and probably is) the only problem.

Ask me how I know...

 

I will: tell me what your experience was. I wouldn't mind hearing another's horror story.

 

Welp, here's the update from the 'hospital:'

According to them, one of the new calipers is defective; and the booster - even with the M/C piston rod adjusted - is too. A couple of connections weren't completely tight (my fault; I was afraid of knackering a line.) So - bottom line: hard pedal; no assist - leaky caliper.

Spoke with the parts suppliers and they're making good on the Q/C-challenged gear. Still, I'm not inclined to do that booster swap - likely a $700 decision. Oh well; like I said, I've got a bunch of other projects I'd rather tackle. This ain't one of 'em. You know that Golden Triangle Theory: Good - Fast - Cheap. Pick any TWO sides.

 

Well, my experience was similar to yours - replaced the booster, put the driver's seat back in, bled the system and couldn't get a firm brake pedal. Bled the system again and again, no dice.

So out comes the driver's seat, disconnect the M/C, out comes the booster, returned it, got a replacement, put it on the firewall, bolted the M/C back on, re-installed the driver's seat (although this time I only used two bolts instead of four "just in case"). Same problem - couldn't get a firm pedal. Bled the system a few times, no dice. So out came the driver's seat, disconnected the M/C, and removed the second booster from the firewall.

Took the second booster back for another exchange and the guy looks at me like I'm crazy. He quizzed me on the calipers, the M/C, all of the brake line connections, and the proportion block. But I had gone over everything (I had pretty much replaced everything with new parts). Finally he just shook his head and said sometimes the boosters are bad, so he gave me a third booster.

On goes the third booster, on goes the M/C, in goes the driver's seat. And, of course, same results. So this time I knew it wasn't the booster, it had to be something else. A friend of mine was helping me do the rebuild, and we went over everything in the system again. The only other part that we had replaced and had not yet checked carefully during this exercise was the booster rod (it came with the new booster, so we used it). I had already disposed of the original one, and we just didn't think to compare the two of them side-by-side. So out came the driver's seat, we lengthened the rod a bit, in went the driver's seat (thankfully for the last time) and voila, problem solved!

So, after that experience (along with having replaced the M/C in a manual brake system in my other C3), I've gotten pretty good at R&R of the booster and M/C (and driver's seat ) - at least I was a few years ago when I did all this. And I think my back has just about healed up now too...

 

I got real good at getting 3 out of the 4 nuts off the booster. That top left one is the killer. I say get in there again yourself and save the $$.

 

Wow. You're a focused guy - or - a glutton for punishment.

My situation is, I seriously strained some ligaments in my right forearm/elbow from the upside down, side-to-side ratchet work in that tight space. Even removing the steering column wouldn't affect that much, other than to remove a barrier between my nose and the target. I ordinarily lift hand weights, but I've had to put that aside for a few weeks because I could barely lift the 20 pounders after doing that booster job.

Yeah, I realize I'm a wimp. But - like Dirty Harry Callahan opined - "a man has to know his limitations..."

Thanks for the detailed post; if nothing else it explains quite a lot.

 

Well, I'm picking up the replacement parts this morning. If for some reason the shop tells me it'll be a week or more to get the job done (not unlikely because of the holidays), I may bite the bullet and do just that.

Or not.

 

She runs, she rumbles - she STOPS! Brakes be done; and it didn't cost an arm and a leg.

Now, I can focus attention on the myriad other projects. On second thought, I think I'll drive the car for awhile and enjoy it.

Merry Xmas to ya all!

 

Wait, wait, wait.....dont put away the eggnog just yet..........
Does anyone know how to calculate the exact pushrod length?
I know I read an article on this a loooong time ago somewhere.
The article was about switching from a vacuum powered brake system to a full manual system by switching out the master cylinder to a larger bore and either lengthening or shortening the pushrod. (it has a threaded end which allows an adjustment)
I remember the adjustment was relative to the brake pedal pivot point....or something like that.