Brakes won't bleed - Chevelle Tech
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post #1 of 9 (permalink) Old Sep 21st, 14, 2:49 AM Thread Starter
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Leadfoot
 
Join Date: Mar 2012
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Brakes won't bleed

Basics: 1971 Chevelle, disc front drum rear. So far as I know, stock setup - was this way when I acquired it.

Background: Few months back, hard line to right front developed a hole (improper routing by a PO, was rubbing on the control arm mount below the valve) while driving. Lots of brake pumping insued but it didn't do a damn thing, zero brakes - stopped it with the parking brake. Got it towed home, let it sit.

Current Problem: The damn brakes won't bleed. Finally went to fix it today. New hard line, bent it up so it cleared any chaffing points. Went to bleed the fronts and the bleed screws were so jammed up one broke, the other stripped completely to the point that a torch and vice grips were useless. Luckily the local parts store had new calipers in stock cheap, so I picked them up. Threw them on, cracked the bleed screws and let it sit for a while keeping an eye on the reservoir. Had a buddy come over to help bleed.
For the longest time, nothing happened to the pedal and there was very little fluid flow, as in a dribble and a small gush of fluid, but that wasn't even enough to make it down the drain tubing. I tried filling the tube and leaving the valve open while he pumped, and the fluid just moved back and forth maybe a 1/2 inch in the tubing (1/4" tube). Same thing with the driver front. Did some research on here, found out about the little plunger on the distribution block so I had at it. It was quite stiff, so I used a C-clamp to depress it and hold it closed. Still nothing on the fronts, only now there was zero fluid flow and the pedal was rock hard - no brake action in the calipers either. I was under the impression that since it is a dual reservoir master, that the rears didn't need to be bled.
Ended up leaving the clamp on the valve and starting in the rear (normal bleed sequence), and then the damn bleed screw sheared off with hardly any pressure on the 1/4" ratchet. While I was in there, I had him hit the brakes and the rears don't engage either, just like when the line failed. I thought that distribution block was supposed to catch that and send full pressure to the rears as a fail safe? It most certainly didn't.

Kind of at a loss of where to start. I've gone through several threads on here but it varies widely and I'm fairly strapped on cash now (thank you divorce), and school makes it difficult to find time to just go at this willy nilly.

Any help, guidance, etc would be much appreciated. I was completely stoked to finally drive her again after three months of sitting, and after hours of work just to get slapped in the face at the last minute really sucked.

Cecelia: 1971 Chevelle / mild 357 SBC, Summit St2 manifold w/Edelbrock 750 / Blueprint heads, Isky 292 mega cam w/ 1.6 rollers, MSD-6, cheapo headers and exhaust / built TH400 / 3k Holeshot / 12-bolt, 3.73's, Detroit
Stay Puft: 2001 Excursion 7.3 Lmtd 4x4 / Triple pillar / DP F5 tunes / 4" turbo back / 4" on 35's / few other "goodies"
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post #2 of 9 (permalink) Old Sep 21st, 14, 3:08 AM
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Derrick
 
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Re: Brakes won't F'ing bleed

pretend it's an all new install- pull the master cylinder and bench bleed it... then put it on, top it off, and open all the bleeders and let it gravity bleed for a while... if everything goes as it should, you shouldn't need to do much bleeding at all.

"Detroit hasn't felt any real pride since George Bush went to Japan and vomited on their auto executives, I tell you whut"

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post #3 of 9 (permalink) Old Sep 21st, 14, 6:38 AM
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Sergio
 
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Re: Brakes won't F'ing bleed

I know you said it was a stock setup but for the longest time i had trouble getting my brakes to bleed because i chose to install one of the Corvette MC. I got two of them and had the same issue until i just got a stock replacement and the moment i did that fluid was rushing out of all four side when bleeding them. The bore was the same for all of the MC but the Corvette style one just did not work for me.Did you replace your MC also recently?

It seems like there is something going on here more than what a right front brake line would cause. Seems like it was working before just fine before the hole was made. Wondering if your distribution block is damaged somehow,not letting fluid go to any lines.
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post #4 of 9 (permalink) Old Sep 21st, 14, 11:10 AM Thread Starter
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Leadfoot
 
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Re: Brakes won't F'ing bleed

Quote:
Originally Posted by novaderrik
pretend it's an all new install- pull the master cylinder and bench bleed it... then put it on, top it off, and open all the bleeders and let it gravity bleed for a while... if everything goes as it should, you shouldn't need to do much bleeding at all.
Thanks bud, I'll give that a shot hopefully later today. With my luck and this car all the lines and going to shear off as will the bolts on the master, hah.

Quote:
Originally Posted by Delta
I know you said it was a stock setup but for the longest time i had trouble getting my brakes to bleed because i chose to install one of the Corvette MC. I got two of them and had the same issue until i just got a stock replacement and the moment i did that fluid was rushing out of all four side when bleeding them. The bore was the same for all of the MC but the Corvette style one just did not work for me.Did you replace your MC also recently?

It seems like there is something going on here more than what a right front brake line would cause. Seems like it was working before just fine before the hole was made. Wondering if your distribution block is damaged somehow,not letting fluid go to any lines.
I have not replaced the MC while I have had the vehicle. Having said that, it seems somewhat apparent that the guy I got it from didn't really know WTF he was doing, or how to do it properly. Case in point, he lowered the car by cutting three coils off the springs. Then the tires rubbed so he put smaller tires. Then those rubbed so he just cut the fenders wells out and radiused the outers. Just the tip of the iceberg.

Everything was indeed working perfectly fine prior the to the right front line going bad. The hole that developed was maybe an inch, inch and a half from the distribution block - could air have gotten inside that and wreaked some havoc? That was one of the other reasons I left the bleeders open after the new calipers were installed, but apparently it seems to have done nothing. Ugh.

Cecelia: 1971 Chevelle / mild 357 SBC, Summit St2 manifold w/Edelbrock 750 / Blueprint heads, Isky 292 mega cam w/ 1.6 rollers, MSD-6, cheapo headers and exhaust / built TH400 / 3k Holeshot / 12-bolt, 3.73's, Detroit
Stay Puft: 2001 Excursion 7.3 Lmtd 4x4 / Triple pillar / DP F5 tunes / 4" turbo back / 4" on 35's / few other "goodies"
post #5 of 9 (permalink) Old Sep 21st, 14, 12:37 PM
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Re: Brakes won't F'ing bleed

I have had great success using a reverse bleeder, but it won't be of much help if you don't have access to one.

Are you bleeder screws facing up? Many folks have had a heck of a time bleeding their brakes simply because the bleeders were facing down.

I would start by popping the line off at the caliper and checking for fluid flow there, and work back as necessary.
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post #6 of 9 (permalink) Old Sep 21st, 14, 2:13 PM Thread Starter
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Leadfoot
 
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Re: Brakes won't F'ing bleed

Quote:
Originally Posted by 68Malisport View Post
I have had great success using a reverse bleeder, but it won't be of much help if you don't have access to one.

Are you bleeder screws facing up? Many folks have had a heck of a time bleeding their brakes simply because the bleeders were facing down.

I would start by popping the line off at the caliper and checking for fluid flow there, and work back as necessary.
Bleed screws are indeed facing up, with the caliper soft line on the bottom. I made that mistake way back with my Cherokee and it drove me nuts until that 'Oh....duh' moment
When checking for fluid flow for the front system while working my way back, the plunger on the distribution block needs to remain depressed with a C-clamp correct?

To reiterate, initially it wouldn't budge at all. A few light taps with a small hammer didn't do much, so I used a C-clamp to depress it. Initially it did not want to move, I had to get a decent amount of squeeze with the clamp before there was a light 'pop' of sorts, then the plunger depressed. I just ran the clamp down until it was snug enough to hold itself in place. Was this correct?

Can someone confirm that since the master cylinder has two reservoirs, I should be able to focus on just the front brakes as far as bleeding? I know the entire system should in theory be bled and is a good practice, which I normally follow. I'd just like to resolve this issue then branch out from there. I don't know if its possible to do so without doing the entire system in the standard RR, LR, RF, LF order.

I'm fairly mechanically inclined, but I haven't worked on something this old before. I also just got out of the Navy after 8 years, and the movers lost ('lost' rather, all garage items go figure) a bunch of my stuff including all my shop manuals for the car so I'm flying blind and relying on the forums and internet.
post #7 of 9 (permalink) Old Sep 21st, 14, 4:17 PM
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Denny
 
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Re: Brakes won't F'ing bleed

I think you should make sure your pressure differential valve is centered. Here is the procedure to do it. And yes, the front and rear are totally separated and, in theory, you shouldn't have to bleed the rear if you only changed a part in the front.

What I think happen with your situation

You probably have the cast iron combination valve. Normally, you should have the brass version as the cast iron one is only listed for 71-72 GM trucks, but I know one member here had one on an El Camino 71 and the one below was found on an 87 Monte Carlo SS (and was replaced by the one from the right found on another Monte Carlo SS of the same year). Does the workers on the assembly line take one model when they ran out of the other or was it replaced afterward by a «careless» mechanic? I don't know. But, anyway, they work the same.


The reason I'm telling you this is because the valve stem doesn't work the same on both. For the brass combo valve, it has to be pushed while bleeding the front brakes like it says on this figure from a 72 Buick chassis service manual:


But with the cast iron combo valve, it has to be pulled. The next figure show 2 special tools that can be used to do so:


So if you have the cast iron version and you pushed on it while bleeding, you actually closed the valve, hence why you got the hard pedal and no fluid flow. The difference between the two valve stems is that the one that needs to be pulled have a little knob at the tip for the tool to hold it.

Furthermore, by having a leak in the front brakes, you tripped your pressure differential valve which partially blocked your front brake lines, thus why you couldn't bleed the front at first.

Then, I suspect your rear brakes are not in perfect shape as well. I would check for a small leak (look also behind the dust boots of the wheel cylinders, there shouldn't be any fluid passing by the cups) because what I suspect happened is that by blocking your metering valve (the valve stem) while bleeding the front, the pressure increase in the front was larger than for the rear and the pressure differential valve went on the other side! Then you went to bleed the rear, which was now blocked off the same way the front was before!


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Jack Action is offline  
post #8 of 9 (permalink) Old Sep 21st, 14, 4:46 PM Thread Starter
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Leadfoot
 
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Re: Brakes won't F'ing bleed

Quote:
Originally Posted by Jack Action View Post
I think you should make sure your pressure differential valve is centered. Here is the procedure to do it. And yes, the front and rear are totally separated and, in theory, you shouldn't have to bleed the rear if you only changed a part in the front.

What I think happen with your situation

You probably have the cast iron combination valve. Normally, you should have the brass version as the cast iron one is only listed for 71-72 GM trucks, but I know one member here had one on an El Camino 71 and the one below was found on an 87 Monte Carlo SS (and was replaced by the one from the right found on another Monte Carlo SS of the same year). Does the workers on the assembly line take one model when they ran out of the other or was it replaced afterward by a «careless» mechanic? I don't know. But, anyway, they work the same.


The reason I'm telling you this is because the valve stem doesn't work the same on both. For the brass combo valve, it has to be pushed while bleeding the front brakes like it says on this figure from a 72 Buick chassis service manual:


But with the cast iron combo valve, it has to be pulled. The next figure show 2 special tools that can be used to do so:


So if you have the cast iron version and you pushed on it while bleeding, you actually closed the valve, hence why you got the hard pedal and no fluid flow. The difference between the two valve stems is that the one that needs to be pulled have a little knob at the tip for the tool to hold it.

Furthermore, by having a leak in the front brakes, you tripped your pressure differential valve which partially blocked your front brake lines, thus why you couldn't bleed the front at first.

Then, I suspect your rear brakes are not in perfect shape as well. I would check for a small leak (look also behind the dust boots of the wheel cylinders, there shouldn't be any fluid passing by the cups) because what I suspect happened is that by blocking your metering valve (the valve stem) while bleeding the front, the pressure increase in the front was larger than for the rear and the pressure differential valve went on the other side! Then you went to bleed the rear, which was now blocked off the same way the front was before!
Jack, that is indeed what I have is the cast iron combo valve - THANK YOU!

I had the drums off both rear wheels, there was no evidence of any leaks and they appear to be wearing and functioning properly.

So as I understand your information, I need to pull the valve out and keep it out (going to try needle nose and small vice grips), then I should be able to bleed the fronts. Time to call up a buddy and see if someone can help!

Cecelia: 1971 Chevelle / mild 357 SBC, Summit St2 manifold w/Edelbrock 750 / Blueprint heads, Isky 292 mega cam w/ 1.6 rollers, MSD-6, cheapo headers and exhaust / built TH400 / 3k Holeshot / 12-bolt, 3.73's, Detroit
Stay Puft: 2001 Excursion 7.3 Lmtd 4x4 / Triple pillar / DP F5 tunes / 4" turbo back / 4" on 35's / few other "goodies"
post #9 of 9 (permalink) Old Sep 22nd, 14, 9:37 AM Thread Starter
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Leadfoot
 
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Location: Houston, Texas
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Re: Brakes won't bleed

Just to follow up, the brakes now work and were bled. It may be that I haven't driven it in three months and I'm used to my truck, but it feels like there's more pedal travel than necessary. Either way, it stops perfectly well.

The rear brakes I couldn't touch, both bleed screws sheared off, and the line fittings are completely rusted and were stripped by a P.O. Didn't have the time or resources to get into all that mess, plus after bleeding procedures up front were completed, all four wheels were spun and brakes applied and they all stopped quite well. Test drive last night went very well too, and so I drove it the 37 miles to school today. Which I'll probably regret later this afternoon as I have no AC and it's supposed to be high 90's, hah.

I did run into an issue with the pressure differential valve as Jack was saying. Without being able to pop open the rear brakes, I ended up just kicking the sh!t out of the pedal several times and there was a 'pop' from the distribution block. After that the fronts bled down just fine.

Many thanks to all that helped me out, y'all made my week with the car on the road again!

Cecelia: 1971 Chevelle / mild 357 SBC, Summit St2 manifold w/Edelbrock 750 / Blueprint heads, Isky 292 mega cam w/ 1.6 rollers, MSD-6, cheapo headers and exhaust / built TH400 / 3k Holeshot / 12-bolt, 3.73's, Detroit
Stay Puft: 2001 Excursion 7.3 Lmtd 4x4 / Triple pillar / DP F5 tunes / 4" turbo back / 4" on 35's / few other "goodies"
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