67 68 Camaro manual drum brakes

[Steve68]

A story to set the stage:  A few years back one of my sons wanted a 1st gen Camaro for his graduation from college.  One was for sale in the next neighborhood for a very reasonable price.  Bought the car and did some refreshing here and there.  He loves his car and it is his daily driver.  The only complaint has been the braking.  The car has always passed state inspections.  About a month ago the braking started to become very bad.  Pedal almost had to pushed to the floor to get it to stop.  I told my son to drive my old truck for now, pull the Camaro into my garage and I would try and fix this problem once and for all.  After replacing a couple of wheel cylinders that were "suspect" it still had little to no front brake action and some rear brakes.  Checked and re-checked everything a million times for leaks, air in the lines, replaced the master cylinder (mc) several times (even tried two different suppliers), and so on.  All to no avail.  Even took it to a nationally recognized brake shop and had them look at it....they too could not figure it out.  I finally called the tech people at Cardone and NAPA Brakes and asked them if their master cylinders for a '67 4 wheel drum with no power assist had check valves in them.  Both said no.  The factory manuals for both the '67 and '68 show check valves in the drawing and in the discussion for replacement/overhauling of the mc talk about how important it is to get the check valves seated in the outlets etc.  The manuals go on to say that if you don't you will not get the proper amount of pedal.  Exactly my problem.  When I asked the suppliers Cardone said that they would be willing to build me one with check valves and exchange it for the one I currently had however NAPA insisted check valve were not needed and stated that they had installed many on 67/68 Camaro's without a problem.  NAPA said it would not be a problem because the mc was above the wheels.  I took Cardone up on the offer and installed the new one (mc with check valves in both outlets) on the car.  Problem fixed.  Pedal is high and firm.  Car has GREAT breaking and almost feels like it has power assist it is so good.  I am planning on passing this info back to both the suppliers tomorrow.  I just wanted to pass this on to you all as this problem was one of the most confounding ones I've dealt with and I've been working on cars since I was a teenager.....I'm old now.      I would like to know how many of you have tried to fix your brake system at one time or another because you felt the mc was bad and just either gave up and accepted the situation or tried replacing the mc several times before getting acceptable results or went to a front disc system to get good braking.

[JohnZ]

ALL factory drum brake master cylinders have RPV's (Residual Pressure Valves) behind the seats in the outlets, as do the rear outlets on disc/drum master cylinders. The RPV's maintain 10psi at the wheel cylinders to overcome the initial tension of the shoe pullback springs and get the shoes out close to the drum surface to minimize pedal travel when depressing the pedal. Any master cylinder supplier that doesn't understand that shouldn't be selling them.

[jeff68]

^^Good stuff to know.  I have a 4-drum manual brake car.  I had my original master cylinder rebuilt and stainless-sleeved.  I hope they kept the original RPV set-up.  I haven't installed the MC on the car yet.  Is there any way to check for the correct RPVs by examining the master cylinder?

[Steve68]

I hate to tell you John but I had direct contact with the tech people at Cardone and NAPA Brake systems and both are not currently building them with check valves.  I suspect that Cardone will be soon.  I believe these guys are major suppliers to most of the retail car supply stores.  I guess the best thing to do when buying is just ask to make sure.  I had bought/exchanged several mc's before the thought of this being the problem came to mind and I started to inquire with the suppliers.

Jeff, I would say that you could insert a very blunt object in the hole very carefully and see if you feel any "spongy or rubbery" resistance.  The check valves have a slit in them and it would be possible for you to hit them just right and go through them and think that they were not there.  There should also be a spring behind the check valve.

Steve

[jeff68]

Steve-
I checked my MC for RPVs and didn't find anything.  I took a piece of paper towel and rolled it into a very small 'tooth pick' shape.  I could easily insert it at least 1/2" - 3/4".  The MC was rebuilt by SSBC (Stainless Steel Brakes Corp.).  I would have thought that they knew what they were doing.

Now, How do I fix this?  Can I buy a MC rebuild kit and install them myself?

Any input is appreciated.
Thanks,
Jeff

[Steve68]

Jeff

I think you would have felt something at that depth below the valve seat.  Yes, automotive stores do sell the mc kits that have the check valves in them.  You will have to get a couple extra tube nuts that go into the outlets.  They are used to both extract and install the new valve seats.  Make sure you can find these before proceeding with the repair job.  Do you feel you can't go back to SSBC and ask them why they failed to install the check valves?

Steve

[jeff68]

Well, I looked up my paperwork from the rebuild, and it was done back in August of 2001.  (Man, I've been working on this project waaaaaay too long.)  I figure that I would rather just install them myself than risk having something happen to my original MC.  Plus, I'm not sure that they are still in the rebuild business.

I tried blowing back through the 2 MC outlets by mouth, and I can easily blow air back through them.  I can't believe that there is a 10 psi valve in there.

It looks like the NAPA UP472 rebuild kit comes with the valves and new brake line seats.  I think that I'll just go that route.

I understand the process for removal of the seats, but I have a question about installation.  Should you install the new seats using only the tube nut to press them into place?  It seems like this could possibly score the surface of the seat that mates with the brake line.  Would it be better to install the seats using an actual brake line & nut instead of just the nut?  Should anything be used on the new seats, such as Loctite retaining compound or brake fluid for lubrication?

I really appreciate all your help on this, Steve.

-Jeff

[Steve68]

Jeff

No lubrication is needed and using the nut only is the method the service manual calls for.  The contact area of the nut is greater in diameter then the contact area of the brake line flare area so it should not be a problem if the valve is slightly scored.

Steve

[jeff68]

Steve-
Thanks for the info.  I'll give it a shot.
-Jeff

[Steve68]

Jeff

I don't think you will find it too difficult.  Just take it slow.  By the way, the springs fit up into the bottom of the check valves.  Let us know how it goes.

Steve

[jeff68]

I had to order the rebuild kit at NAPA.  I found the tubing nut for the forward hole no problem.  The rear hole appears to be some size that nobody at NAPA has ever seen before.    Luckily, I was searching around in a bunch of plumbing 'stuff' that I have and I found a nut with the correct threads (it was part of a shut-off valve for a pressure washer).  It's not quite deep enough to install the seat, but it has internal threads, so I can install a bolt/jam nut into it and grind down the outside hex of the nut to make a nice little installation tool.  I hope it works.

[Steve68]

Jeff

You might want to take a measurement, if you have not pulled them yet, from the top of the seat to the top of the hole so when you install the new ones you will know for sure you have them (valve seat) seated.  If I remember correctly it is around 1/4".

Steve

[KevinW]

Does anyone have a pic of the check valve?  I do not know what one looks like, so I cant tell If I have any.

[jeff68]

Steve-
Yes, I measured and it's 1/4".  I haven't pulled them yet.  I don't want to take anything apart until I have the replacement parts in-hand.
-Jeff

[jeff68]

Does anyone have a pic of the check valve?  I do not know what one looks like, so I cant tell If I have any.

Check out the picture of the NAPA rebuild kit.  They are the 2 small rubber 'caps' with the springs:
http://www.napaonline.com/masterpages/NOLMaster.aspx?PageId=470&LineCode=UP&PartNumber=472&Description=Brake+Master+Cylinder+Kit