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Author Topic: Good God In Heaven ... Please Help Me With These Brakes!!  (Read 8697 times)
no69x-44
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« on: August 28, 2008, 08:45:46 PM »

I don't know what else to do or where else to turn anymore.  I have a '69 and after 5+ years of restoring this blasted beast, it wants to fight me to the bitter end!  I have replaced EVERYTHING in the brake system.  Some parts several times.  This is the deal:

All new brake lines - complete front to back.
All new brake hoses
New Front Calipers
New Power Booster
Re-built Original Master Cylinder
Original Proportioning Valve
Original Distribution Block
Long Rod in the Power Booster to the Master

I think that covers everything.  This is an original Big Block Car and original front disc brake car.  The problem I'm having is with the front disc brakes.  What was happening is that I had to pump the brake pedal 6 times before the front brakes would actually grab enough to stop the wheel.  Each pump of the pedal added a bit more restance ... the about 6 pumps of the pedal is what it took before you could not spin the wheel.

I switched out the repro master cylinder and repro proportioning valve and installed a original master cylinder (re-built) and the original proportioning valve.  Now it is 3 pumps of the brake pedal to completely stop the front wheel.  Better, but still not quite right.  I have bleed the master cylinder and the front brakes a million times and the fluid comes out in a nice steady stream ... No air at all.
The back Drums have never been an issue and work fine.

So I'm done here.  I have nothing left to try.  I'm out of bullets.  If anybody out there that is a brake expert and has any advise at all ... I'm all ears.
Thanks in advance for any and all help.
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--Rob
----------------------------
'72 SS Nova - Gone
'68 Chevelle - Gone
'67 Impala - Gone
'65 Belair - Gone
'00 Corvette - Still got it
'69 Camaro - Keeper
KevinW
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« Reply #1 on: August 28, 2008, 09:24:48 PM »

Rob, you are testing the brakes with the engine running, correct?  I dont think I am doing anything on Monday and can come over to look it over if you want. Kev
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no69x-44
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« Reply #2 on: August 28, 2008, 09:34:40 PM »

Kevin - You know ... As I was writting this - I was thinking to myself that I have never tested the brakes with the car running. I was wondering if the power booster/vaccum would make any differance here.  I'm going to give that shot in the morning.  Do ya' really think that could be it?   Stay tuned ...
« Last Edit: August 28, 2008, 09:43:55 PM by no69x-44 » Logged

--Rob
----------------------------
'72 SS Nova - Gone
'68 Chevelle - Gone
'67 Impala - Gone
'65 Belair - Gone
'00 Corvette - Still got it
'69 Camaro - Keeper
hotrod68
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almost finished

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« Reply #3 on: August 28, 2008, 11:29:27 PM »

I've gotten bad rebuilt master cylinders--that's possible. But if you have ANY air in the system, front or back, it can cause problems. If it were me, I'd bleed the whole brake system once again to make double sure there is no air in it. Just a thought and good luck!
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HotRod'68  1968 SS350 coupe undergoing frame-off resto/rod. 386/350/4.11s
Butternut Yellow    black standard interior
melav8r
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« Reply #4 on: August 29, 2008, 12:29:15 AM »

The 69 Chev Chasis Service Manual says: "The spring loaded end of the pressure metering valve must be depressed while bleeding. This can be done by depressing and holding in the plunger in the end of the valve either by hand or by clamping."
They are referring to the proportioning valve mounted under the master for the front brakes.
Since you swapped out the master cylinder you should re-bleed the entire system if you haven't already done so. Also does the rear port in your master cylinder have a check valve installed? This keeps residual pressure to the rear brakes and can cause a spongy brake pedal.
I personally have had good results using a Mityvac Brake Bleeder without having to touch the proportioning valve. Uses a handheld vacuum pump to bleed the brakes. Available at Napa, Harbor Freight, etc...
good luck.
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KevinW
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« Reply #5 on: August 29, 2008, 05:37:38 AM »

Rob, power brakes need the vacuum to work properly.  I can also bring my homemade power bleeder with me to see if that helps.  I can think of a couple things to try to test, but take 2 people.
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jdv69z
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« Reply #6 on: August 29, 2008, 10:52:48 AM »

I had had good results using gravity to bleed my brakes. Just keep bleeder fitting at the wheel attached to hose submerged in brake fluid to prevent air from backing in to the system, and leave master cylinder cover off, Also make sure master cylinder does not empty out, or you'll have to start over.

Jimmy V.
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Jimmy V.
fireZ
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« Reply #7 on: August 29, 2008, 03:26:29 PM »

I had the same trouble on a 68 car and it ended up to be a bad proportioning valve [large round one with large nut on front] The valve was not allowing enough fluid forward to operate front discs. Take off the line at the proportioning valve and pump the pedal lightly to see if any brake fluid is passing through the line.
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1968 Z28 LA Built
LIC # RPO Z28
no69x-44
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« Reply #8 on: August 29, 2008, 10:45:17 PM »

Guys - Thanks for the replies.  Keep them coming if some thing should come you.  I sent a good part of the day messin' with the front brakes and still nothing.

Kevin - I did start the car and tried the brakes, but the pedal goes down to the floor.  I tried creeping the car a little and the back brakes did grab, but felt like nothing in the front.  The paint guy has time this week to do touch up work and final buff on the car for me.  The car is there now and hopefully I will get the car back home in couple of weeks - I'm hoping maybe after next week.   I'll give you a call when I get the car back (if it doesn't end up in paint/touch up prison) and maybe you can stop over one weekend day and get this Voodoo spell off!

I'm so close to driving this car again, I can taste it.  Well, I guess I can actually drive it ...  But I just won't be able to really stop it!
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--Rob
----------------------------
'72 SS Nova - Gone
'68 Chevelle - Gone
'67 Impala - Gone
'65 Belair - Gone
'00 Corvette - Still got it
'69 Camaro - Keeper
KevinW
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« Reply #9 on: August 30, 2008, 07:46:44 AM »

Rob, OK.  What I was going to try was take the MC cover off and watch the piston movement through the vent hole as you push down on the brake.  We should see the MC piston start moving right away.  If it does not, then something wrong with the linkage.  If that is good, we take the tires off and check the distance of the pads and watch/feel them as the pedal is pressed.
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william
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« Reply #10 on: August 30, 2008, 09:59:16 AM »

I'm not trying to be insulting but there is a right and left caliper for 69. If they are reversed the bleeders will not be at the highest point and there will always be air in the system. I have seen several experienced people do this.

Also if you used stainless lines there may be a mismatch in the flares. We had a fitting at the distribution block that would draw air but not leak fluid.
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JohnZ
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« Reply #11 on: August 30, 2008, 10:24:02 AM »

Did you bench-bleed the master cylinder before installing it? If not, any remaining air in the bore is almost impossible to get out without pressure-bleeding.
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'69 Z/28
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Sauron327
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« Reply #12 on: August 30, 2008, 10:42:26 AM »

John,
 Wasn't onebad34 having similar problems. I couldn't find past post. And doesn't the piston in the MC have to return it's stroke fully to operate properly? Or would that affect the rears as well?
 I also had to give my friend my spare MC to replace his "new" one which also would not bleed. Fronts then bled straight away. Bench bled first as you say.
 I have been lucky but my days are numbered. Many are having replacement part problems. 
 
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KevinW
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« Reply #13 on: August 30, 2008, 04:07:50 PM »

If I go over to Robs, I will bring my pressure bleeding adapter.  I want to make sure his MC/rod and booster linkage is working properly first.  I will check his calipers too.  Thanks William!
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no69x-44
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« Reply #14 on: August 30, 2008, 04:39:22 PM »

Hey guys thanks for the help and please don't be shy with any additional ideas.  The Calipers are on correctly.  The Bleeders are on the bottom.  If the left one was on the right side adn visa versa - then the bleeder screws would on the top of the calipers and that would be an air issue.
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--Rob
----------------------------
'72 SS Nova - Gone
'68 Chevelle - Gone
'67 Impala - Gone
'65 Belair - Gone
'00 Corvette - Still got it
'69 Camaro - Keeper
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