1968 GTO Front Disc Brakes don't work after new pads installed??? - Pontiac GTO Forum
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post #1 of 15 (permalink) Old 06-15-2018, 06:52 AM Thread Starter
 
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1968 GTO Front Disc Brakes don't work after new pads installed???

Hello All: I got a big problem. My 1968 GTO needed new front disc brake pads. My Micanic installed new Rotor and Pads. When he went to bleed brakes no brake fluid came out of the bleeder valve??? I was pumping the brake pedal. He seemed confused, and said, I need a new master cyclinder. I said, it's all brand new now?? He pulled the reservoir, and did something. He says now I need a new resivoir?? I can't see how the brakes where working great before, and now I need a rebuild. He had to do something. I would think he got air back into the system? My 68 GTO has we believe 1969 disc brakes in the front with drums in the rear. Rear brakes bleed just fine. Car is only working on back brakes. Is there something we can do with the Metering valve. I'm now reading one of my Maintenance Manuals that says. "The bleeding operation for disc brakes is the same as for drum brakes. The only exception is that the metering valve must be held open. This is done by depressing and holding the plunger in the end of the valve either by hand or by tapping. Tool J-22793 may also be used to aid bleeding." What does this mean, and how to do it... The brake pedal to me seems very had to push down. Not like it used to be. I need some real help here. My Mecanic isn't as smart as he says he is. He just wants to start changing part's at my dime.... :-(

Bobby :-)
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post #2 of 15 (permalink) Old 06-15-2018, 08:01 AM
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Hey Rob

Pretty sure he should have cracked the bleeder valve before pressing the piston back in.
Not sure, someone with more experience with your system will chime in now that I have moved your post from the 2002-2004 GTO page to the proper 1964-1974 Pontiac Tempest, Lemans & GTO forum page.
Personally whenever I do disc brakes I never force old fluid back up the line but prefer to bleed it off and add fresh to the reservoir.
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post #3 of 15 (permalink) Old 06-15-2018, 12:33 PM
 
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I would...

replace the hose at the caliper first ... buy good ones from napa

see if any fluid drains while replacing ,,,, if it drips master is probably good

he probably/may have not hung the calipers by a wire to take the load off the hose and damaged them or twistem wierd

just a cheap place to start ....

then just let the new hose drip for a couple teaspoons install on caliper and re bleed

NEVER go to the floor with a used master cylinder always put a block under pedal for 1/2 way travel

the seals on the bore on the inside of the master dont like that... kinda like ring ridge in a used cylinder of engine

Scott
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post #4 of 15 (permalink) Old 06-15-2018, 12:35 PM
 
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I would...

replace the hose at the caliper first ... buy good ones from napa

see if any fluid drains while replacing ,,,, if it drips master is probably good

he probably/may have not hung the calipers by a wire to take the load off the hose and damaged them or twistem wierd

just a cheap place to start ....

then just let the new hose drip for a couple teaspoons install on caliper and re bleed

NEVER go to the floor with a used master cylinder always put a block under pedal for 1/2 way travel

the seals on the bore on the inside of the master dont like that... kinda like ring ridge in a used cylinder of engine

Scott

maybe the bleeders could be plugged with debris .... pull em out ...run a wire thru em

the caliper should drip fluid .... with no bleeder

keep the master 1/2 full dont let it go dry
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post #5 of 15 (permalink) Old 06-15-2018, 05:21 PM
 
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It could be the master cylinder, BUT, odd that it was working before and now after the replacement parts it is not.

I would begin at the master cylinder and crack the line that goes to the front discs. Then have you depress the pedal slowly & steady. Put a rag under it to catch the fluid. If brake fluid seeps out, then probably not the master.

The fact that you said the pedal is "hard" would mean to me that pressure is building up, just not actuating your front discs. Generally when a master goes bad, the pedal will go to the floor.

If the master pushes fluid, then tighten the line back up and go to the line at the junction block and crack it open. Repeat the pedal push and see if any fluid seeps out. If so, then the junction block is probably OK. Keep doing this process right down to the hoses which attach to the calipers.

Now I have seen bleeders which are solid and not drilled with the hole that generally allows you to bleed the brakes through them. Verify that the bleeders do indeed have the holes drilled through to allow the system to bleed. If not, you will have to remove them to get the fluid to escape, and while you still have your foot to the floor, insert the bleeder screw and tighten up before you release the pedal.

Just go step at a time and see what turns up and this should identify where in the system the blockage/problem is occurring.

Does not sound to me like you have a mechanic who knows his stuff.
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1968 gto front disc brakes don't work after new pads installed ????

Hello Guys: First Thank you for the Help..... :-)

Today Saturday 16 June he is going to install a new Master Cyclinder. He really believe it went bad????? I can't believe that a system working great this would fail. He said, he did a bench test, and no fluid coming through the front brakes resivour. He calls it the Master Cyclinder. I call it the brake resiviour.

Under the car is where the warning lite value is. I don't have the warning lite wire connected to the brake warning lite in the car. Don't that warning lite value have a reset ability???????? Back brakes bleed just great, and work...

He's a old Mechanic and been around for awhile, but he jumps before he thinks.
I like reading up on stuff and learning before I jump. I'm an old retired Helicopter mechanic, and I work very slow on the Aircraft. Different animal. I will for sure let you all know what happens. I'm going golfing today.
Pray for my CAR... LOL LOL Have a great weekend. (I'll be back) LOL LOL
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post #7 of 15 (permalink) Old 06-16-2018, 03:26 PM Thread Starter
 
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1968 gto front disc brakes don't work after new pads installed ????

Hello All: Update. Well, I started some research, and came up with the
porportioning valve has gone into the safe mode. This is why only my back brakes work. Front Disc we can't bleed brake fluid. Can this Proportioning valve be re-set????? Do I have to buy a new one and where???? I read that maybe if I press real hard on the brake pedal the valve will go back to nuturel? Is this true....
Any Ideas?????????

Thank you, Bob :-)
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post #8 of 15 (permalink) Old 06-16-2018, 06:38 PM
 
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...............

https://www.inlinetube.com/brake-fuel-lines

so you have presssure coming out of the master but the stay off valve is stuck .. pressure at but
not thru the valve /.. once they are sticky guess what will happen one day ... yup rears only again...


it happens

buy a new one .... it mounts under the master cylinder nut correct ? pictures really help too..

you mentioned its a 68 that would have had 4 piston but has single piston 69 n up calipers/conversion now ?

Scott put some hoses on the front now too maybe ....
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post #9 of 15 (permalink) Old 06-17-2018, 01:23 AM Thread Starter
 
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1968 gto front disc brakes don't work after new pads installed ????

Thank you all for the greast Info:

Getting new Porportioning Valve. This should fix it. My Mechanic is milking this
job. He's FIRED.....

Tks, Bobby :-)
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post #10 of 15 (permalink) Old 06-17-2018, 08:23 AM
 
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Quote:
Originally Posted by rob40999 View Post
Thank you all for the greast Info:

Getting new Porportioning Valve. This should fix it. My Mechanic is milking this
job. He's FIRED.....

Tks, Bobby :-)

Good for you. Another example where your mechanic is a "parts changer" which cost you $$$ until he changes out the part that was the problem in the first place - and then thinks he's done something. Correctly diagnosing & identifying the problem can be time consuming and can cost you $$$ in labor and could cost you more than the bad part itself.

These older cars are not really all that difficult to work on and when there is a problem, it is just a matter of steps to be taken to identify or narrow down where the problem is. Sometimes you can rebuild the original part or sometimes it needs to be replaced - just as you would have done 40 years ago, these mechanical & consumable parts don't last forever and were not intended to.

With this, sometimes is is faster, cheaper, and safer to simply replace & install new replacement parts (whether it be an NOS part, rebuilt part, or aftermarket part) when a system such as brakes begin to give a problem and you are not sure where the problem is. The way people drive today, brakes are the #1 priority in my book and I always inspect and typically replace/rebuild all moving parts - for my own peace of mind & because I'm going to be keeping the car long term anyway.

We all want to save $$$ and get the repair done as inexpensively as possible, but you do get what you pay for and its simply better to accept the fact that old car ownership is a hobby where spending money on upkeep is not a matter of "if", but a matter of "when" you will have to drop the next dollar to keep it up and running.
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