Technical Bleeding a stubborn brake system

@kabinenroller how did you resolve this issue? I recently replaced the master cylinder, added a rear proportioning valve, entire new rear drum assemblies (minus backing plates) and rear no/cop lines since the original ones started leaking with the new wheel cylinders and now I can’t get a strong pedal.

to confirm it wasn’t the master cylinder I bought 3/8 flare nuts end caps/blank offs and capped off the master cylinder and got a fantastic pedal (obviously). I also performed all of the things that you did, two bench bleeds even. I am more concerned about the rear brakes, but I have them plugged off and I’m trying to bleed the front system for now and still get a pedal that is not nearly as stiff as when there were blank offs, but it is also front disc. I have done everything other than reverse bleeding to the master cylinder, but that seemed odd to me since there are more high points, including the bleeder screws are all higher than the master cylinder so I bought a pressure bleeder and still have no luck. Once my wife is able to help I’m going to try GaryF’s. Finally got the car PA legal almost 2 months ago and it’s been up on blocks because of a rear drum hanging up and evolved into replacing a lot of the brake components, the year is about over and I want to get it out at least one more time!

not only as it taking me literally forever and multiple brake lines to get non-leaking brake lines, but I still can’t confirm that they are all not leaking because I can’t get a stiff pedal and put a lot of pressure to it. Don’t have the money to pay someone to do the brake lines, but I will say I don’t want to do them again, ever if possible!

thanks for your help and hope you have the magic solution!

 

I would be gravity bleeding the system while your waiting for your wife.

 

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If you blocked off the MC and it had a hard pedal, the MC is good. If you still have the rear circuit blocked off (rear drums) and had a soft pedal when applied, the problem(s) is in the FRONT disc circuit.

What calipers are you using and what type of 'proportioning valve'? Is it a stand alone PPV (adj or fixed) or is it a COMBINATION VALVE of some sort? The MC piston bore is beneath the caliper/rear wheel cylinders bleeding screws?

 

@McMac 31
I eventually solved the issue. I had a friend pump the brake pedal, I had clear bleeder tubes hooked up to each wheel cylinder, instead of bleeding into a container I connected to my vacuum bleeder. When he depressed the pedal I opens the bleeder and the vacuum bleeder pulled the brake fluid from the system. When I closed the bleeder he let the pedal return to its normal position.
After doing each wheel with this process I then had solid pedal. Although even with a nice firm pedal I could not lock up the brakes. I tried everything and finally decided to remove the combination valve and install an adjustable proportioning valve in the rear line and plumb a 2lb residual valve in both the front and rear lines just after they leave the master cylinder. I now have a very solid pedal and great brakes. I am not sure why the system was so difficult to bleed but the combination of the pedal pumping and using the vacuum bleeder made a difference.

 

Glad its fixed, running a lot fluid through them isn't cheap anymore!
I recently had to bleed a whole new system on a TA, four wheel disk, all factory stuff. I couldn't get the air out, went through a lot of fluid with no luck. I finally made a 1/4" clear lid and cork gasket for the master cylinder with a hose port over the fluid. I used my late model pickup and a long vacuum hose from the running engine. With vacuum in hand I slowly touched the nipple to apply vacuum to the master cylinder. It wouldn't take full vacuum as it started sucking fluid up the line, but I could see it was pulling air out. I moved to the back half and got air immediately coming up out of the fluid. Whole process took about two minutes to fully bleed the whole system. It a cheap and easy way if someone is having trouble. I think this car had air in the rear flex hose from body to axle.

 

@garyf - could you describe how you gravity bleed yours? Just open all of the bleeders with MC lid on (or off)? This will probably be a good thread for many frame/chassis master cylinder mounted people to review when they have the same luck I and others do so I appreciate any detail to the full scope of what you would do for a frame mounted master cylinder and essentially new brake line set up.

@kabinenroller - did you keep an eye on what the vacuum pressure was when you were doing it? I have a fluid extractor that I modified and tried that, but I did not have the brake pedal depressed in a fashion of the classic brake bleed. I tried the vacuum first since all of the bleeders are above the master cylinder and air rises so that seemed like the logical step. Did you leave the pedal depressed the whole time or did you have the second person yell when it was about to bottom out and you shut the bleeder valve as it bottomed out?
Did you also do this with the master cylinder lid on or off? I’m assuming on if you were having someone depress the pedals so the brake fluid didn’t come shooting out the top?

I had to wrap the bleeder screws in PTFE tape as I was getting a vacuum leak from them and that helped the vacuum process but still did not yield stiff pedal results. PTFE thread sealant brush/liquid did not work where the tape did.

@MOONRNR - all bleeders are above the MC piston, I may need to Jack up each end of the car so the master cylinder is above the bleeder, but this could get a little sketchy because of the height difference.

• Master cylinder, CENTRIC 13061011

1” bore , 1.41” stroke or pushrod length.

https://www.summitracing.com/parts/...XGlUC_x87wL_jCk1dOBct0AvdCu068SZ1E3As4rSQOmVT

Used on 67-72’ mustang and cougar, I think the bore stroke is barely too long as I hit the firewall before bottoming out when bleeding the old-fashioned way.

• Rear wheel cylinders are Napa 17508 and 17507, .875” bore and

Super common on Fords, Jeeps, Dodge, etc. to fit on a small bearing Ford 9 inch rear.

• Front brakes

Early 70s Camaro? Based on my research I found a good example from Rock auto, pictures attached.

70-76’ Camaro if it is correct and a bunch of other GM cars from the mid 70s.

• Speedway Compact Adjustable Brake Proportioning Valve for rear drums

https://www.speedwaymotors.com/Speedway-Compact-Adjustable-Brake-Proportioning-Valve,1979.html

Not sure how confident I am in this, but it seems to work based on the reviews and I can pull fluid past it for bleeding. Chose this as I was not looking to make up special brackets or mounting to the frame. If I knew I was going to be replacing as much as I have, I probably would’ve just gotten the speedway below master cylinder mounted adjustable proportion valve with brake light switch, but I saw reviews that it leaks.

Honestly, I was trying to do things right, but on a budget, and this has gotten wildly more expensive than I anticipated for a simple master cylinder and drum equipment replacement. At this point, I probably should’ve went to disc brakes but I was trying to keep it relatively traditional, and true to my godfather who built the car. I am keeping an eye out on the classifieds for a small bearing for 9 inch rear disc with emergency brake disc conversion kit for sale but I just missed one a couple months ago. I’ve replaced Master cylinder, flex line to axle, both rear brake lines from flex line T, both rear cylinders, drums, shoes, all of the springs and other internal drum components. I added the proportioning valve as it was missing, but the car does already have the proper residual valves.


Next thread that I still might make is knowing in the magic secret of getting new brake lines/fittings not to leak even with the good on-car double flare tool from speedway. Apparently the expensive hydraulic flare tools are the way to go. Also, if you were taking non leaking brake lines off, (to say replace a wheel cylinder) how hard should you tighten them so you don’t create a leak. I’ve done tons of research on this issue and have made several calls to places like in line tube and others but it’s the hot rod shops and mechanics that truly have the know how and I’ve heard several different methods.

 

Yep, same thing happened to me on my Corvette.

 

Where did you source the calipers, from a 'kit maker'? If so, they are usually off-shore and are a copy of the GM low drag caliper (D-154) requiring a step-bore MC or the ever popular CORVETTE style MC (more initial volume movement).

Do you have a 2# RESIDUAL PRESSURE VALVE(S) plumbed into the front disc circuit?

Do you know if the MC (CENTRIC is good quality) has an internal rear circuit (rear drum) 10#
RPV? Most service replacements do not as the RPV was eliminated in the mid-seventies and went with wheel cylinder cup ex-panders. You need one of the two.

You also have to verify you have the correct pedal ratio and MC piston travel.

READ THIS - https://www.performanceonline.com/blog/2009/02/master-cylinder-bench-bleeding/

https://duckduckgo.com/?q=bench+ble...i=https://www.youtube.com/watch?v=dMB4l-Q4zsA

 

Forgot-

If the brake line fittings are leaking, you are fighting a losing battle.

 

I’m not sure where the calipers are from, my godfather built the car starting in the late 80s and we lost him just before he finished it a couple years ago so I have to dig and do research on everything on the car. These look like remanufactured GM calipers but I’m not 100% sure.

The master cylinder that was on the car worked great before the seal blew out, it had a casting number 29867-c and looked extremely close to this new centric model meant for mustangs and cougars with front disc, rear drum brakes.

The new centric MC #130.61011 does not state if it has an integrated RPV, I don’t think it does.

I do have the proper Willwood #2 and #10 RPVs, they could be a little closer to the MC (1-2ft of line from MC connection) but I don’t think that is an issue.

And when I say leaks, I mean I have to check two connections with a rubber glove at the base of the flare fitting threads as it would be such a small leak or seap I could not identify it with a flashlight, only a shimmer off a nitrile glove. None of them technically drip but I need to make more new lines I guess.

I roughed my pedal ratio but it may be under 5:1 which isn’t ideal for manual all disc and a 1”bore. I will fully remove it soon and get an accurate measurement. I will have to post pictures of the pedal and pushrod set up as it is a mid 90’s @the flatlander’s frame and is not very common using a 16-17” long pushrod, I can’t just snag a pedal from speedway (I don’t think).

I have this MC from Speedway I was going to use but something tells me it is not right? I got it since it is meant for disc/drum but was also verified to work with disc/disc if I upgraded the rear brakes, but I may need a smaller bore MC. Once I have the actual pedal ratio and front disc bore size, I will do the proper break calculations if I go rear disc.

 

Sometimes the leak is so minute that they don't leak noticeable fluid but will let air into the system over night or a few days. I had that happen on an OT rig that I had a few years ago and finally replaced the line.

 

@kabinenroller - did you keep an eye on what the vacuum pressure was when you were doing it? I have a fluid extractor that I modified and tried that, but I did not have the brake pedal depressed in a fashion of the classic brake bleed. I tried the vacuum first since all of the bleeders are above the master cylinder and air rises so that seemed like the logical step. Did you leave the pedal depressed the whole time or did you have the second person yell when it was about to bottom out and you shut the bleeder valve as it bottomed out?
Did you also do this with the master cylinder lid on or off? I’m assuming on if you were having someone depress the pedals so the brake fluid didn’t come shooting out the top?

Reply:
I used a fluid extractor/ bleeder, the vacuum was activated from the time I opened the bleeder until I closed it. The brake pedal was pumped once then held down when I open the bleeder valve, then released after I closed the bleeder valve. The cover was secure on the master cylinder. The only difference from a normal brake bleed was that the vacuum extractor was used instead of a normal tube/bottle.

 

I am fairly certain the problem is the having the low drag calipers without using the correct GM MC (whether GM STEP-BORE or the CORVETTE DUAL DISC MC) - which seems to be the out for these so-called 'KIT MAKERS' that is going to get someone killed one day.

LOW DRAG CALIPERS are fine, I understand the need. But they have to be matched up with the correct GM components (MC - METERING VALVE - PPV) to work correctly.

On the leaking fittings, spray them down with brake cleaner, let them dry and have someone hold down on the pedal to see if there are any leaks and the pedal height stays high (after proper system bleeding).

Also, you need to study proper MC piston size required (manual or power assist) and brake pedal ratio.

Another fear factor is if the car shown in your avatar is the one you are working on is BRAKE BIAS/BALANCE. Skinny tires on the front and fat ones on the rear (and I love the look also) are begging for it on either a dry or wet road surface. When you get around to adj the PPV, you will need to test the brake bias/balance on a large public parking lot when it is not busy. Try it on a dry day and most importantly on a rainy day.

Here is some more reading -

https://www.hotrodders.com/threads/test-for-low-drag-calipers.158523/

https://mpbrakes.com/support/troubleshoot/

FORGOT -

Your rear wheel cylinders are most likely off-shore also and are junk (metric bleeder screws). If the fitting is leaking, tighten ever so lightly until the leakage appears to stop. There is a torque value, but it requires a high dollar wrench.

Position both RPV's as close to the MC as possible, especially the front circuit #2 as it prevents siphoning of the fluid back into the MC due to gravity.

 

Hi Guys, I didn’t mean to hijack this thread so I am starting a new one soon regarding my own car with pictures, measurements, issues, thoughts etc.

@kabinenroller - thanks for the info I’m going to try it soon and also the gravity bleed as @garyf recommended

@MOONRNR - I have more research to do but I have a 5.5:1 pedal ratio, 2.93” front piston and .875” rear wheel cylinder diameters. Since I have the same dimensions front and rear as a 73 Camaro I assume I can use one of these manual 1”bore master cylinders from rock auto that is for a 73’ Camaro. I cannot confirm if the have the proper step bore though:

DYNAMIC FRICTION 35547036
Or
QUALITY-BUILT NM1751


Lastly I will add I have seen torque values for new brake line flare nuts around 120-130 in/lb. Rather than buying the special $$$ open/flare torque wrench I bought flare line crows feet and plan to use them with my smaller in/lb torque wrench. FYI the crows feet need to be 90 degrees (3 or 9 o’clock) from the torque wrench handle and you will get the same torque as a socket. If you have it at zero degrees or inline with the torquer, the torque value will be larger than anticipated.



I think I have been over tightening all of them especially being ni/cop!

 

... whew ...

You are correct in the crows foot flare wrench and torque. The torque value will not be 100% correct (the length of the crows foot will throw it off - there is a formula to allow for this but it should be close, especially if a short crows foot).

If you crank one down you can stretch and pull threads, especially with off-shore.

So you think the brake system used is from a 73 CAMARO donor? That should be before the low drag caliper was introduced (I am a FORD GUY so am unsure). But if the calipers were ever replaced for service, most likely they were low drag.

One way to determine what they are is to rebuild them. The seal type will tell you which caliper style you have. If the caliper has a metric bleeder screw, it will be a low-drag.

If you block-off one front disc circuit (brake hose crimp tool - be gentle here) at a time, depress the pedal and the pedal is hard (also bled correctly), the other circuit is good. If the other side is blocked off and the pedal stays hard, the other circuit is good. If either goes soft, the problem(s) will be in that circuit.

You've determined that a 73 CAMARO with manual disc/drum came through with a 1" MC?

https://shop.wilwood.com/blogs/news/pedal-ratios-and-how-to-find-them

I hope all that made sense.

Is it possible to show a photo of the MC-pedal install?

Don't worry yourself as to the repair. You are learning and the next go-around will be much easier.

A few years ago I had a TAURUS DISC/DRUM ABS that gave me fits. OEM parts are nonexistent. The brake fluid was mud as it had never been serviced. CENTRIC BRAKES finally pulled me through.

Parts quality now is dismal. You have to be very careful regarding aftermarket parts.