69 Chevelle SS front brake bleeding

[mockingbird812]

Lately I have been going through the brakes on my Chevelle including flushing the brake fluid with fresh DOT 3. When I went to bleed the front brakes I never got what I would characterize as acceptable flow without bubbles. I used a hand pump Mighty Vac bleeder. When I finished as best I could with the bleeding I had an acceptably firm pedal. The front wheels spun relatively freely after several cycles of applying the brakes. When I test drove the car (did not exceed 30 mph) it drove and coasted nicely........for the first 10 minutes, then the front calipers began to bind increasingly worse as time went on. They were not overly hot by the time i got back to the house, i.e. I do not think that I "boiled" the brake fluid. I had my master cylinder rebuilt recently by White Post. I rebuilt my pressure metering valve (located next to and below the master cylinder) myself with a rebuild kit. I also lubricated the bushings and pins on the calipers to ensure that they were not binding. I learned something new when I read the chassis repair manual (see attached photo) where they recommend depressing the plunger on the pressure metering valve when bleeding the front brakes. I haven’t tried this yet but wanted to get input from some of the Masters out there on things I might have missed. Thanks

[Lynn]

I have no personal experience with White Post, but have heard nothing but good things about them.

Hard to diagnose without being there, but my first thought was the a residual pressure valve was installed under the brass fitting on the disc brake port on the master.

The first thing I would check though (because it is easier) would be to make certain there is sufficient free play at the pedal, AND make certain the pin between the booster and the master is not too long. If it is just 1/8 inch too long, it is pre-loading the master.

You can check both of those without breaking into the hydraulics.

[PeteLeathersac]

'

What brand and how recent are the Flex lines...collapsing inside?
:hmmm:
~ Pete

.

[mockingbird812]

Lynn, thanks for chiming in. Yes, I checked the pedal for free play and have confirmed that the pin coming out of the front of the booster is not preloading the master cylinder.

Pete, until recently I had the original flex hoses on this car. But, I replaced those with In-Line brand and am confident that they are not collapsing. Thanks

[Postsedan]

Sam,

"Recommend depressing the plunger on the pressure metering valve when bleeding the front brakes."

Absolutely.....this is a must.

Dan

[mockingbird812]

Well, I bled the brakes again and decided to follow the manual and depress the plunger – imagine that! Well that certainly is a new one on me, but then again I have only owned this car for 12 years now! Yeah Dan, I expect you bled a few 69 SS front brakes before. Took the car out for a 25 minute spin using the brakes frequently and no binding of the front calipers! Yippee! Thanks all.

[DW31S]

Learned long ago about depressing the plunger on the valve. I had a ‘69 Pace Car that “taught” me.

[mockingbird812]

I guess that I am curious why my initial NOT depressing the plunger on the pressure metering valve led to the front calipers to clamp down on their own while driving.

[PeteLeathersac]

I guess that I am curious why my initial NOT depressing the plunger on the pressure metering valve led to the front calipers to clamp down on their own while driving.

This is why I questioned the flex lines.
Glad things worked out, hope all's good from here!
:beers:
~ Pete

.

[Mr70]

Too Late to add anything to this,but just went through bleeding my own brakes recently with a similar outcome.

[mockingbird812]

Too Late to add anything to this,but just went through bleeding my own brakes recently with a similar outcome.

70s have the same plunger? Do you know how this pressure metering valve actually works?

[Kurt S]

http://www.camaros.org/brakevalve.shtml#mv

[mockingbird812]

http://www.camaros.org/brakevalve.shtml#mv

Perfect Kurt - Thank you!

[Kurt S]

You should know that I edited/created that page (JohnZ wrote it), and I *still* didnt' remember that I need to depress that plunger. So thanks for bringing this back up!

[Jonesy]

I have had a hell of a time with bleeding brakes since I restored my car. Never depressed the plunger. Guess I may now know why. Its only been 12 years:blush:

[mockingbird812]

You should know that I edited/created that page (JohnZ wrote it), and I *still* didnt' remember that I need to depress that plunger. So thanks for bringing this back up!

Kurt - Ha, does my heart good that a details guy like you can forget some of this stuff too!

['69Novajoe]

Hi guys, first of all, I hope all of you are taking care and keeping safe with all of this virus stuff around!!

I know this is an "old thread" but I'm hoping that some of you might still be getting notifications when someone posts here. I have a '69 Nova SS with drums in the rear and discs up front, all stock. Here's my dilemma.....I had been experiencing a low pedal for awhile so, even though I had the whole system rebuilt about 10-15 years ago, I decided that maybe the master cylinder was at fault. I brought it to the guys who rebuilt it (they sleeved the master, wheel cylinders and calipers with stainless back then) to have them redo the master. They said it really didn't look that bad but put in a new "kit" anyway. I started the installation yesterday, bench bleeding the master, installing it and then proceeded to bleed the whole system. I'm using a "one-man" vacuum pump style tool. I was doing pretty good until I got to the front brakes. Very little fluid (I thought) was coming out from the passenger side caliper. When I started on the driver side, nothing was coming out!! I even took the bleeder screw out of the caliper completely and stepped on the brake pedal. Still nothing, not even a drop!! Then I remember searching different sites for pointers on bleeding brakes and ran across this thread. I called the brake guys and mentioned the plunger on the metering valve to allow the fronts to be bled and he said that it shouldn't be necessary. He said to just start checking for a blockage. The first thing I did was disconnect the metering valve. When I tried to push in the plunger it wouldn't budge!! My question to you guys is, how much pressure does it take to push that in? Also, in normal operation, does that plunger go in and out every time you apply the brakes?? The reason I'm asking the question here is, I'm having a hard time getting a call back from the brake guys right now. Thanks in advance for any help you can provide!!

[ScottG]

That plunger senses pressure differential and moves the plunger in respect to the difference. If you have a total brake pressure loss the plunger would go fully into a failure position and that turns on your red BRAKE dash warning light. If it gets partially tripped it would limit brake fluid flow and you would see very little fluid volume when bleeding the brakes.. I always gravity bleed after a test drive, take off the master cylinder cap and put a section of vacuum line on the bleeder when it is open. The vacuum line keeps the fluid from chewing paint and you can watch the fluid to see if there is any air in the fluid..

['69Novajoe]

Hey Scott, thanks for the reply. I think you might be talking about the "distribution block" that has all the brake lines going to it and an electrical connection that would do exactly what you said, turn on the "red BRAKE dash warning light". The metering valve is what's described in a previous post. Here is a link to what it looks like...
http://www.camaros.org/brakevalve.shtml#mv

[mockingbird812]

Hey Joe. You can save your effort in telling us that you have “69 Nova SS”. We all know that you are the original owner of a very special 69 Nova SS and that is just super cool! So, not to be a smart aleck but what does your manual say? I would probably never have figured out about depressing that plunger on the pressure metering valve without checking my manual (and checking with the smart dudes around here). Do your brakes have the metering valve with the plunger (edit: I just checked yr CRG link and I think it says all 69 rear drum front disc brake cars have them)? If it does have the plunger then I’d clamp it down and give the bleeding another try.

If you don’t have a manual maybe someone (hey Wilma!) can provide a peek at one.

['69Novajoe]

Hey Sam, thanks so much for the kind words!! Believe it or not I don't have a "manual" for the car!!:dunno: The only question I have is how hard do you have to push to get that plunger to move?? It looks to be stuck and I'm pretty sure that's why the front calipers aren't receiving any fluid?? From what I'm hearing here and elsewhere, you just push the plunger and bleed the fronts. Sounds like it doesn't take much effort to push it??

Sam,
"Recommend depressing the plunger on the pressure metering valve when bleeding the front brakes."

Absolutely.....this is a must.

Dan

And.....

Learned long ago about depressing the plunger on the valve. I had a ‘69 Pace Car that “taught” me.

[mockingbird812]

Been a while since i did the bleeding but I remember it was firm and I think I used a clamp to depress it and free my hands up to do the bleeding at each front wheel. I would put something (piece of wood) between your clamp and the plunger so as not to harm it.

[mockingbird812]

Hey Joe, I reached out to Tom, WilmasL78boy, and he should check in soon.

[WILMASBOYL78]

69 Chassis Service Manual states this regarding bleeding front disc brakes:

"The spring loaded end of the pressure metering valve must be depressed while bleeding. This can be done by depressing and holding the plunger in the end of the valve either by hand, or by clamping.

This is all on page 5-29....there is additional information on pages 5-3 thru 5-5

If the plunger won't move, it may be stuck due to age/corrosion...I would check it and service as needed.

I double checked the 70 manual as well...same instructions.

Good luck.

_wilma

**you just reminded me I have to look at the front brakes on the 70 4 spd...I had a collapsed hose and changed both of them...pedal is still a little soft...

['69Novajoe]

Been a while since i did the bleeding but I remember it was firm and I think I used a clamp to depress it and free my hands up to do the bleeding at each front wheel. I would put something (piece of wood) between your clamp and the plunger so as not to harm it.
Yep, that sounds like the proper way to do it!!

Hey Joe, I reached out to Tom, WilmasL78boy, and he should check in soon.
Thank you so much Sam!!

69 Chassis Service Manual states this regarding bleeding front disc brakes:

"The spring loaded end of the pressure metering valve must be depressed while bleeding. This can be done by depressing and holding the plunger in the end of the valve either by hand, or by clamping.

This is all on page 5-29....there is additional information on pages 5-3 thru 5-5

If the plunger won't move, it may be stuck due to age/corrosion...I would check it and service as needed.

I double checked the 70 manual as well...same instructions.

Good luck.

_wilma

**you just reminded me I have to look at the front brakes on the 70 4 spd...I had a collapsed hose and changed both of them...pedal is still a little soft...
Hey Wilma, thanks for checking in!! I actually clamped the metering valve in a vise this morning and the plunger still won't move!!:ooo: Guess I've got a faulty valve after all. Gee, it's "only" (almost) 51 years old so what do I expect??!!!:confused2: It will be nice to get her back on the road, especially since I hear gas prices are coming way down!!:burnout: But, then again, we aren't supposed to go out (in California) anyway!!:frown:
Take care, be well and thanks again for all your help everyone!!

[m22mike]

Does this help at all ? I would like to understand how pushing on ,(DEPRESSING ) the exposed piston rod moves anything when the valve seal is already seated ?
Joe , your valve is most likely OK. They are easy to take apart, just used the correct socket. Most I have restored I cleaned and re used the seals.

['69Novajoe]

Does this help at all ? I would like to understand how pushing on ,(DEPRESSING ) the exposed piston rod moves anything when the valve seal is already seated ?
Joe , your valve is most likely OK. They are easy to take apart, just used the correct socket. Most I have restored I cleaned and re used the seals.

Hey Mike, you've raised another question!! I hear that the plunger needs to be "depressed" in order to bleed the front calipers.:dunno: That has come from a few sources now. With all due respect, since you've actually taken one apart and know how they work, do you think the plunger actually moves but maybe just a very small amount??:hmmm: In this case, I'm gonna be a "parts replacer" and see what happens.:tongue: I think something is blocking the flow of brake fluid and this looks to be a good place to start?? The way the pedal was acting (going almost all the way to the floor!!) and the actually braking was performing (not coming to a stop very fast!!) it all points to just the rears doing all the work??!! Anyway, I found a new replacement on ebay for $54.50. I'll keep you all posted.

[m22mike]

IMO, pushing on the shaft only increases the pressure on the piston seal, that is under spring pressure and seated and holding off flow. As the brakes are applied the rear brakes see pressure first, as pressure increases to about 40psi it overcomes the spring pressure in the ROUND HOLD OFF VALVE. Fluid flows into the line at the big nut , passed the piston seal, out the side fitting to the distribution valve, to the front brakes. Sometime watch the shaft move out as the brakes are applied by a helper.
If you wanted free flow through this valve it seems to me one would pull and hold the shaft open to unseat the piston seal.
Open to learning more if this sounds incorrect to others.

Mike

['69Novajoe]

IMO, pushing on the shaft only increases the pressure on the piston seal, that is under spring pressure and seated and holding off flow. As the brakes are applied the rear brakes see pressure first, as pressure increases to about 40psi it overcomes the spring pressure in the ROUND HOLD OFF VALVE. Fluid flows into the line at the big nut , passed the piston seal, out the side fitting to the distribution valve, to the front brakes. Sometime watch the shaft move out as the brakes are applied by a helper.
If you wanted free flow through this valve it seems to me one would pull and hold the shaft open to unseat the piston seal.
Open to learning more if this sounds incorrect to others.

Mike

Okay, I see your point. So now I'm totally confused as to why it says in the manual....."The spring loaded end of the pressure metering valve must be depressed while bleeding. This can be done by depressing and holding the plunger in the end of the valve either by hand, or by clamping." Will doing that relieve the spring pressure somehow??:dunno: I've been trying to do this with a hand-held vacuum type bleeding tool which doesn't create enough vacuum (?) to overcome the spring pressure?? Some other instructions mention using a "pressure-type" bleeder. Not sure if that would make a difference or not?? I've ordered a new valve like I said and will let you know what I find. If it still doesn't work I'll have to find a "helper" to help me bleed the brakes the "old-fashioned" way by stepping on the brake pedal!!:grin: Thanks again for all your input Mike!!

[m22mike]

I have no comment on the directions in the service manual Joe.
Sorry I don't have any more
I can tell you. Maybe those that have had succes depressing the shaft during bleeding can explain what is happening in the valve.

Mike

['69Novajoe]

Hey Mike, I ended up buying a new metering valve (because I was convinced it was bad), pushed the plunger (which seemed to maybe move a little bit, if at all!!) and then proceeded to bleed the brakes. Actually, before I installed the valve, I checked it with my vacuum bleeder to see if it was allowing air through it and it was! Not sure if pushing that plunger did the trick or not!! I got good flow to the fronts now and the pedal has returned to the proper position and is rock hard!! Guess I got all of the air out of the system!! Everything seems to be working correctly at this point and I'm a happy camper!! Gonna go on a bit of a ride/cruise this Saturday to give it a good test. Thanks again for all your input and suggestions.

[mockingbird812]

Hey Mike, I ended up buying a new metering valve (because I was convinced it was bad), pushed the plunger (which seemed to maybe move a little bit, if at all!!) and then proceeded to bleed the brakes. Actually, before I installed the valve, I checked it with my vacuum bleeder to see if it was allowing air through it and it was! Not sure if pushing that plunger did the trick or not!! I got good flow to the fronts now and the pedal has returned to the proper position and is rock hard!! Guess I got all of the air out of the system!! Everything seems to be working correctly at this point and I'm a happy camper!! Gonna go on a bit of a ride/cruise this Saturday to give it a good test. Thanks again for all your input and suggestions.

Glad to hear you got it working Joe. We may need to see a photo of your sweet ride!!:laugh:

['69Novajoe]

Glad to hear you got it working Joe. We may need to see a photo of your sweet ride!!:laugh:

Thanks Sam!! I'm actually going to be doing a bit of a "test drive" this coming Saturday to take some pics with another Nova that is scheduled to be shipped to the owner by the end of next week. I'll try to post some pics. In the meantime, here's a pic I took a little over a year ago. Boy how time flys!!

[mockingbird812]

Looks great Joe! Thanks!!!!!!:biggthumpup: