I THOUGHT I KNEW BRAKES.....

The Big Comets

I THOUGHT I KNEW BRAKES.....

Postby Boatmangc » Tue Sep 04, 2018 4:53 pm

Did a rear disc conversion and couldn't get fluid to the rears, no brake light. Horrible pedal. I found what I assume was the proportioning valve on the front subframe on the passenger side. I disconnected the line coming out of it and got rusty muddy stuff out of it. As I was in the middle of an emergency evacuation I just made up enough fittings to bypass the valve and proceeded to bleed the brakes. I had fluid flow to the rears but not a lot. 10 months later and a 1000 mile relocation I was finally able to get back to the car. I bought a Jegs adjustable proportioning valve and stuck it in. Still no good fluid flow and crappy brake pedal. Even though I thought the master cylinder was good I went ahead and replaced it. Same thing.
I pulled the distribution block under the master cylinder and tried to get it cleaned up with brake cleaner and managed to get the valve stuck way back in it so now I have no pedal, what I assume is no rear brakes and a nice brake light on the dash.
The car stops but I wouldn't dare drive it anywhere. The pedal goes almost to the floor.
Frustrated, anyone have any insight on what I am missing? I have ordered an o ring kit for the distribution block and pulled it off, I just need to figure out how to get the piston out of it, it seems to be stuck pretty good although I have my doubts it's where my issues are.

Rant over LOL.
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Re: I THOUGHT I KNEW BRAKES.....

Postby Lou's Comet » Tue Sep 04, 2018 9:01 pm

Boatmangc wrote:Did a rear disc conversion and couldn't get fluid to the rears, no brake light. Horrible pedal. I found what I assume was the proportioning valve on the front subframe on the passenger side. I disconnected the line coming out of it and got rusty muddy stuff out of it. As I was in the middle of an emergency evacuation I just made up enough fittings to bypass the valve and proceeded to bleed the brakes. I had fluid flow to the rears but not a lot. 10 months later and a 1000 mile relocation I was finally able to get back to the car. I bought a Jegs adjustable proportioning valve and stuck it in. Still no good fluid flow and crappy brake pedal. Even though I thought the master cylinder was good I went ahead and replaced it. Same thing.
I pulled the distribution block under the master cylinder and tried to get it cleaned up with brake cleaner and managed to get the valve stuck way back in it so now I have no pedal, what I assume is no rear brakes and a nice brake light on the dash.
The car stops but I wouldn't dare drive it anywhere. The pedal goes almost to the floor.
Frustrated, anyone have any insight on what I am missing? I have ordered an o ring kit for the distribution block and pulled it off, I just need to figure out how to get the piston out of it, it seems to be stuck pretty good although I have my doubts it's where my issues are.

Rant over LOL.


Did the brakes work ok before the conversion? Are the brakes power? What conversion did you use for the rear? When you did the conversion did you convert the MC to a 4 wheel disc master cyl, or still use the disc/drum master cyl? A master cyl for 4 wheel disc should have two large reservoirs the same size where a disc/drum MC will have a large one for the front disc and a small one for the rear drums.

Disc brake calipers take more volume than drum brake wheel cylinders, maybe your MC isn't giving the rear calipers enough volume, esp if the MC is for rear drums?

Do you know the bore of your MC?

What you are calling a distribution block under the master cyl is the proportioning valve if it has a valve in it. A distribution block will shouldn't have a valve in it.

Since you have a new adjustable proportioning valve I would use that in place of the factory one. And then go from there.

Also if you are still using the factory type disc/drum MC it may have a residual valve for the rear drum built into it that when you do get brakes working correctly may create drag on the rear brakes when no pressure is applied.

First thing I would do is replace the orig proportioning valve with the new adjustable one, the bleed the brake real good and see where you stand.

Lou
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Re: I THOUGHT I KNEW BRAKES.....

Postby Boatmangc » Wed Sep 05, 2018 4:19 am

I did not upgrade the master cylinder. I replaced with an O'reilly auto parts unit
The car was originally power front disc/drum rear and after taking it apart even though it had a good feeling pedal I really doubt it had much if any rear brakes.
There were 2 valves? on the car. One under the master cylinder with multiple fittings and the brake light connection and another inline with the rear brake line mounted to the right front subframe aft of the firewall, that's the one that was plugged up. I have replaced all the brake lines with SS as well minus the ones that cross the firewall behind the motor, I will get to them when I pull the motor.
I bled the new master cylinder when I installed it. Then vacuum purged the brakes then did them old school. I have fluid flow to all 4 now ( enough I can't say) but the pedal goes way down before I get brakes.
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Re: I THOUGHT I KNEW BRAKES.....

Postby Lou's Comet » Thu Sep 06, 2018 6:36 am

Boatmangc wrote:I did not upgrade the master cylinder. I replaced with an O'reilly auto parts unit
The car was originally power front disc/drum rear and after taking it apart even though it had a good feeling pedal I really doubt it had much if any rear brakes.
There were 2 valves? on the car. One under the master cylinder with multiple fittings and the brake light connection and another inline with the rear brake line mounted to the right front subframe aft of the firewall, that's the one that was plugged up. I have replaced all the brake lines with SS as well minus the ones that cross the firewall behind the motor, I will get to them when I pull the motor.
I bled the new master cylinder when I installed it. Then vacuum purged the brakes then did them old school. I have fluid flow to all 4 now ( enough I can't say) but the pedal goes way down before I get brakes.


There should not be two valves, the one under the master cyl is the factory proportioning valve. I really don't know what the one on the right subframe is. Maybe someone added a residual valve??

If your proportioning valve is stuck that could very well be your problem. I would replace that first. But if you had the problem before you disassembled the proportioning valve and stuck the valve then it probably still has a issue.

The pedal going way down is typically a bad/weak/wrong master cylinder.

Since you went from drum rear brakes to disc you may have to upgrade master cyl. The rear calipers will take more volume than the brake wheel cylinders you had, and with the same bore size master, the pedal will need to travel more to give the volume. Upgrading to a master with a larger bore would help this.

Really need to check everything now, kind of start from scratch thinking.

Some questions/thoughts no particular order.

Do you know the bore size of your master cyl? If you still have the old one you could measure it.

If you have stock master I assume it has a large reservoir and a small one, do you have the front brakes plumbed to the large reservoir?

Did you change or modify any of the push rods from the brake pedal to power booster or power booster to master?

What rear disc conversion kit did you use?

Does the pedal get better if you pump it?

No leaks or seepage at any of the connections.

The rear calipers mounts good and strong? Calipers retract from rotor runout basically, if the rear calipers mounts are flexing the pads could be retracting more than should be and excessive pedal would be needed to take up the extra pad travel.

Brake power booster in good shape? Holding vacuum? Booster check valve good?

What I would do,,,, first I would eliminate the valve?? Thing on right subframe and replace it with hardline. Replace the proportioning valve with your adjustable one. Bleed the system. Check EVERY connection/fitting for leaks. I spray them good with brake clean then dry them with air or paper towels. Then work the brake pedal a bunch of times then go around with tissue to check the every connections, any fluid leaks and a Kleenex tissue will show it.

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Re: I THOUGHT I KNEW BRAKES.....

Postby Boatmangc » Fri Sep 07, 2018 3:56 am

Lou's Comet wrote:
Boatmangc wrote:I did not upgrade the master cylinder. I replaced with an O'reilly auto parts unit
The car was originally power front disc/drum rear and after taking it apart even though it had a good feeling pedal I really doubt it had much if any rear brakes.
There were 2 valves? on the car. One under the master cylinder with multiple fittings and the brake light connection and another inline with the rear brake line mounted to the right front subframe aft of the firewall, that's the one that was plugged up. I have replaced all the brake lines with SS as well minus the ones that cross the firewall behind the motor, I will get to them when I pull the motor.
I bled the new master cylinder when I installed it. Then vacuum purged the brakes then did them old school. I have fluid flow to all 4 now ( enough I can't say) but the pedal goes way down before I get brakes.


There should not be two valves, the one under the master cyl is the factory proportioning valve. I really don't know what the one on the right subframe is. Maybe someone added a residual valve??

If your proportioning valve is stuck that could very well be your problem. I would replace that first. But if you had the problem before you disassembled the proportioning valve and stuck the valve then it probably still has a issue.

The pedal going way down is typically a bad/weak/wrong master cylinder.

Since you went from drum rear brakes to disc you may have to upgrade master cyl. The rear calipers will take more volume than the brake wheel cylinders you had, and with the same bore size master, the pedal will need to travel more to give the volume. Upgrading to a master with a larger bore would help this.

Really need to check everything now, kind of start from scratch thinking.

Some questions/thoughts no particular order.

Do you know the bore size of your master cyl? If you still have the old one you could measure it.

If you have stock master I assume it has a large reservoir and a small one, do you have the front brakes plumbed to the large reservoir?

Did you change or modify any of the push rods from the brake pedal to power booster or power booster to master?

What rear disc conversion kit did you use?

Does the pedal get better if you pump it?

No leaks or seepage at any of the connections.

The rear calipers mounts good and strong? Calipers retract from rotor runout basically, if the rear calipers mounts are flexing the pads could be retracting more than should be and excessive pedal would be needed to take up the extra pad travel.

Brake power booster in good shape? Holding vacuum? Booster check valve good?

What I would do,,,, first I would eliminate the valve?? Thing on right subframe and replace it with hardline. Replace the proportioning valve with your adjustable one. Bleed the system. Check EVERY connection/fitting for leaks. I spray them good with brake clean then dry them with air or paper towels. Then work the brake pedal a bunch of times then go around with tissue to check the every connections, any fluid leaks and a Kleenex tissue will show it.

Lou

Thanks Lou,
I replaced the OEM master cylinder with an identical replacement, I didn't give the Master Cylinder size much thought.
I believe the second valve or whatever it was to be OEM as well, it was in the original brake line headed back to the rear brakes.
Sigh... the rear disc kit was a fleabay purchase. although it appears to be well done. It uses early 80's Buick Century rear calipers with an E Brake cable that actuates the caliper for E brake actuation. The brackets seem pretty sturdy.
I have replaced as many of the brake lines with new SS lines. I have been over it several times and I cannot find any leaks.
I need to set up a new photo storage service so I can post pictures of what was on the car originally.
Other than a dual exhaust system my car is an apparently unmolested 74000 mile survivor.
I eliminated the second valve during my rapid reassembly just before evacuating for the hurricane
I purchased the Jegs adjustable proportioning valve after I moved to Ga. the 1st one was defective so right now I just have the original valve bypassed. I have a new one but haven't had time to install it.
Evidently my proportioning valve or distribution block (4 lines in/out with the brake warning light switch) is NLA. I found a repair kit via west coast cougar club and have not had the time to attempt to get it apart. I have to plug most of the fitting holes, adapt a zero fitting into the closed end and force it apart with a grease gun in order to clean it up and replace O rings etc.

Again, the car seemed to stop OK when I bought it and had good pedal but when I installed the rear disc kit I was unable to get any fluid flow to the rears as the unidentified valve was totally plugged. My gut is the original rear drums were merely ballast. LOL.

My 1st valve looks similar to this: https://www.summitracing.com/parts/rsd- ... 2TEALw_wcB

And the mystery one which was plugged up looks similar to this: https://secure.cougarpartscatalog.com/s ... stang.html
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Re: I THOUGHT I KNEW BRAKES.....

Postby 3154tm » Sun Sep 09, 2018 6:25 am

it's possible that if the car came with front discs the valve you found on the frame was an RPV, usually 10 psi
for the rear drums. that's what the one in the second pic looks like. to make things work it's possible you may
need to replace it with one for disc brakes, usually 2 psi. though they aren't always used and you may have
an unrelated problem. lottsa luck
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Re: I THOUGHT I KNEW BRAKES.....

Postby Boatmangc » Tue Sep 11, 2018 1:12 am

Update,
I rebuilt the front valve, (I believe it is actually called a differential valve on my car) and installed the Jegs proportioning valve. No matter where I set the valve I still have little or no fluid to the rears. I can crack the line in front of the valve and have flow but not after it. I'm starting to think the master cylinder isn't up to the task. last ditch I have a rebuild kit for the drum/disc PPV and will force it parts after this rainy weather passes.
But I think I need to re-bleed the master and look at it closer, just because it's new doesn't mean it's good.

On a sad note the SSHS event has been cancelled due to local sporting events using up all the available hotel rooms below $250.
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Re: I THOUGHT I KNEW BRAKES.....

Postby Lou's Comet » Thu Sep 13, 2018 7:08 am

Boatmangc wrote:Update,
I rebuilt the front valve, (I believe it is actually called a differential valve on my car) and installed the Jegs proportioning valve. No matter where I set the valve I still have little or no fluid to the rears. I can crack the line in front of the valve and have flow but not after it. I'm starting to think the master cylinder isn't up to the task. last ditch I have a rebuild kit for the drum/disc PPV and will force it parts after this rainy weather passes.
But I think I need to re-bleed the master and look at it closer, just because it's new doesn't mean it's good.

On a sad note the SSHS event has been cancelled due to local sporting events using up all the available hotel rooms below $250.


If you have flow before the valve but not after it then I would suspect the valve.

When you went to rear disc you changed the requirements of the system. Having rear disc and keeping all the factory valves, master cylinder, and such just may not work.

Disc brakes take more volume than drum. If you look at a master cyl for a early 80,s century it has 4 ports, each wheel has its own line which gives more volume.

For me I would start simple, basically from scratch. To start I would run the line for the rear brakes out of the master directly to the rear hose on the rear axle going to the splitter on the rear axle. Then run the line for front brakes from the master to the front brakes thru a splitter and then both front wheels. Eliminate all the valves.

Then see what you have. If it works then you can tweak the system with a proportioning/combination/differential valve if you want to or feel it needs one.

If it don't work then you know you need to address the master cylinder.

Most of the four wheel disc brake conversions I have seen/dealt with they run a corvette style master cyl which has a 1"+ bore size. And two large chambers in the master instead of a large for front and small for rear. Not sure what the bore size is on the master you are using.

But first I would eliminate all the valves and see what I had.

Lou
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Re: I THOUGHT I KNEW BRAKES.....

Postby Boatmangc » Tue Sep 18, 2018 4:41 am

Turns out the New valve from Jegs was bad, I did a quickie repair on the OEM valve and was able to bleed the brakes, get pedal and stop the car. I actually made a small car show Saturday!.
I will have to install a new valve as the OEM is now beginning to lose fluid through the weep holes.
I am going to Upgrade the remaining parts of the brake system when I do the 347 swap. but for now she goes down the road again!
Thanks for all the input!!!

By the way there is a small company called Muscle Car Research that has repair kits for a lot of our obscure brake parts. They are online..
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