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Author Topic: 67 68 Camaro manual drum brakes  (Read 55813 times)
Steve68
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« on: November 13, 2007, 09:51:49 PM »

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.   Smiley Cry  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.
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JohnZ
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« Reply #1 on: November 14, 2007, 10:12:37 AM »

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.
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jeff68
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« Reply #2 on: November 14, 2007, 04:10:46 PM »

^^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?
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Steve68
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« Reply #3 on: November 14, 2007, 04:51:59 PM »

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
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jeff68
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« Reply #4 on: November 17, 2007, 06:06:20 PM »

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
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« Reply #5 on: November 17, 2007, 07:19:13 PM »

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
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jeff68
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« Reply #6 on: November 17, 2007, 07:56:35 PM »

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
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« Reply #7 on: November 17, 2007, 08:38:22 PM »

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
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jeff68
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« Reply #8 on: November 18, 2007, 06:48:24 AM »

Steve-
Thanks for the info.  I'll give it a shot.
-Jeff
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« Reply #9 on: November 18, 2007, 10:08:12 AM »

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
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jeff68
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« Reply #10 on: November 18, 2007, 01:24:47 PM »

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.  Huh  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.
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« Reply #11 on: November 18, 2007, 01:55:38 PM »

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
« Last Edit: November 18, 2007, 02:00:08 PM by Steve68 » Logged
KevinW
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« Reply #12 on: November 18, 2007, 02:19:19 PM »

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.
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jeff68
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« Reply #13 on: November 18, 2007, 02:22:23 PM »

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
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« Reply #14 on: November 18, 2007, 02:25:01 PM »

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
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« Reply #15 on: November 18, 2007, 02:41:31 PM »

Kevin

It would be difficult to see them.  They are behind the valve seat in the outlet holes.  You might be able to see them if you used a strong light but what you would likely observe would be a black edge.  I think this would be difficult especially if you didn't know what to expect to see.  Take a fine wire and VERY gently probe the hole to see if you feel anything.  Don't "push" it because you don't want to take a chance of rupturing the valve.  The valve has a slit in the top of it so, as I said in the above post, you could hit it just right and go past the top of it thinking you didn't have a valve there.  But if you are careful and move the wire from side to side you should feel the rubber valve.  Be careful.

Steve
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JohnZ
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« Reply #16 on: November 19, 2007, 02:15:52 PM »

There's an illustration on page 5-17 of the 1969 Chassis Service Manual that shows an exploded view of the seats, valves, and springs in the drum brake master cylinder outlets.
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« Reply #17 on: November 21, 2007, 03:56:32 PM »

OK, I can confirm that the NAPA UP472 rebuild kit comes with the RPVs.  It also comes with what I assume are the self-tapping screws needed to pull the original seats.  However, the kit that came in from the warehouse has brass seats that were all corroded.  I didn't dare use them, so they ordered another kit for me. 

I wonder if it is possible to pull the existing seats without damaging them and then re-install them.  The new seats had a counterbore on the back side that the RPV sits in.  Maybe the existing seats don't have this since there are no RPVs in there.  Anyhow, I'll try to keep you posted on my progress.
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« Reply #18 on: November 21, 2007, 04:26:53 PM »

Jeff, I can't imagine how you would remove the existing ones without damaging them.  I would not risk reusing them even if you could pull them as they might "loose the fit" if you know what I mean.  As for myself I would use the new ones.....just my 2cents.  BTW, if the next NAPA kit has corroded ones in it and there is an Advance Auto near they carry the kit as well, however, the supplier may be the same as for NAPA.  http://www.partsamerica.com/ProductDetail.aspx?MfrCode=RAY&MfrPartNumber=MK472&PartType=229&PTSet=A


Steve
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jeff68
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« Reply #19 on: November 21, 2007, 07:37:48 PM »

Steve-
Yeah, you're right about re-using the seats.  I came to the same conclusion after thinking about it for a little bit.

Funny, I actually called the local Advance Auto right after I posted and they told me they didn't sell the Raybestos kit, even after I gave them the part number.  I ended up ordering the Raybestos kit through a local CarQuest.  They will have it on Friday.  I hope that the quality will be better than the NAPA kit, but, like you said, they are probably the same manufacturer.
-Jeff
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« Reply #20 on: November 22, 2007, 08:04:09 AM »

I just checked my 67 camaro with manual disk brakes and the MC  has the check valve.
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Steve68
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« Reply #21 on: November 22, 2007, 10:18:11 AM »

red67|78 I'm curious, is the mc original to your car, has it ever been overhauled (if so by who), and how did you determine if it had the check valves?  Thanks for the feedback.  Smiley

Steve
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red67l78
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« Reply #22 on: November 22, 2007, 11:13:39 AM »

Yes it is original and i overhauled it myself 3 times allready.  The bore is pitted and last about 2 to 3 yrs until i have to rebuild it.
I have since then purchased 1 in California last year at a swap meet for 5 bucks.  The guy i think did not no what it was worth to me. Also if you use a small drill bit on the flat side you can feel the check valve spring back n forth. Only on the rear port.
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Steve68
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« Reply #23 on: November 22, 2007, 11:54:45 AM »

red67|78

Great idea on the drill bit!  Odd that it only had the check valve on the rear only.  To the best of your knowledge then no one had replaced the seats before?  We are talking about your original mc and not the one you bought at the swap meet right?

Steve
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red67l78
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« Reply #24 on: November 22, 2007, 01:50:25 PM »

Yes i am talking about original one.  The other one is identical eccept for casting date.  I am in the process of rebuilding the swap meet one to put in car. The MC turned out to be rebuildable and clean. I replaced the brass seat last time and left the check valve alone.  The rear line is still original and it tightened  the seat up.  When done i should not have to remove MC again.
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jeff68
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« Reply #25 on: November 22, 2007, 07:30:47 PM »

Yes, the drill bit is an excellent idea.  I just used the flat end of a small bit on my MC, and I'm now 100% sure that SSBC did not install the required RPVs.
Steve-  Wouldn't it make sense that red67l78's MC only has one RPV since it is a disc brake car?
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« Reply #26 on: November 22, 2007, 08:46:11 PM »

Jeff, you are absolutely correct.  I read right through the "disk" part of his post and saw only the manual brakes part.  Thanks for pointing that out, I appreciate it.   Smiley

Steve
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« Reply #27 on: November 23, 2007, 12:04:42 AM »

Steve... I wouldn't rule out a bad master cylinder, new OR rebuilt. When I started to reassemble my '68--manual drum brakes all around--I went through 3 before I got a good one. The first two would not bench-bleed right--perhaps the check valves were stuck or installed wrong, who knows--but neither worked as it should. The 3rd one was okay and works perfectly. Just a thought...
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« Reply #28 on: November 24, 2007, 10:26:34 AM »

hotrod

There is no question that the mc's that I tried did not have check valves in them.  I called the manufactures and both advised that they did not install them in their products.  After installing the one Cardone made for me with check valves in both outlets, the car has the best braking one could ask for.  The pedal is both high and firm and over the past two weeks has continued to provide great breaking.  BTW, before returning the replaced mc to the store I pulled the seats just to confirm for myself that there were no check valves (there were none) and the other mc's that I had tried did bench bleed very well, they just didn't have the check valves.

Steve
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jeff68
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« Reply #29 on: November 25, 2007, 12:23:18 PM »

I just finished installing the RPVs in my original MC.  Not too bad of a job. 
Here are a few diagrams showing the RPV (check) valves:



I couldn't get the supplied 6-32 self-tapping screw to 'start', so I drilled & tapped the existing seats.
A little grease (Permatex brake caliper grease that is compatible with all brake system rubber parts) on the drill to capture the brass chips:


Same goes for the tap:


Tapping the seat:


Install the tube nut, then install a 6-32 screw long enough to engage all the threads you just tapped:


Hold the screw from turning and back out the tube nut:


Here is one of the original seats after removal:


Clean everything thoroughly, then install the RPV, then the seat, then the tube nut, and tighten the tube nut until the seat bottoms out.  Do the same on the other port and you are done.  The finished project:


Sorry I forgot to take pictures of the actual valves.  When I got to that part I guess I got a little anxious to get everything installed.

Thanks again to Steve for all his help.

-Jeff
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« Reply #30 on: November 25, 2007, 03:12:37 PM »

Good post - excellent photos!
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« Reply #31 on: November 26, 2007, 01:37:29 PM »

nice work Jeff,thanks for all the good info!
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Sebastien 68  327 rag top
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« Reply #32 on: December 02, 2007, 09:13:42 PM »

Following 7 posts are pages from Delco Drum Brake Service Manual; 17D-11; January 1971; Dealing with Master Cylinder Reconditioning.  Note reference to check valves only being part of the drum brake master cylinder on pp 4-26 (4th post in this series.)
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« Reply #33 on: December 02, 2007, 09:14:46 PM »

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« Reply #34 on: December 02, 2007, 09:20:00 PM »

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« Reply #35 on: December 02, 2007, 09:20:30 PM »

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« Reply #36 on: December 02, 2007, 09:21:00 PM »

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« Reply #37 on: December 02, 2007, 09:21:27 PM »

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« Reply #38 on: December 02, 2007, 09:22:01 PM »

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Richard Thomas
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« Reply #39 on: December 03, 2007, 02:13:12 PM »

thank you for sharing Rihard!
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Sebastien 68  327 rag top
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« Reply #40 on: December 05, 2007, 06:36:40 PM »

So do power drum brakes receive the RPV?  How about the rears on a power disc brake set up?
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Steve68
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« Reply #41 on: December 05, 2007, 07:25:33 PM »

Question 1: Yes. Question 2: No.

Steve
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« Reply #42 on: December 05, 2007, 08:13:08 PM »

Question 1: Yes. Question 2: No.

Steve

That seems odd.  Given JohnZ's explanation of why the RPV is necessary it would seem that the rear drums on a Power front disc car would need them as well, escpecially since a power drum car needs them (which implies that the booster does not do the same job as an RPV).

I'm not saying your wrong, just clarifying the logic.
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Steve68
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« Reply #43 on: December 05, 2007, 08:31:31 PM »

I think I misunderstood your second question.  I thought you were indicating the rears were disk brakes.  If the front are disk and the rears are drum then the front outlet (to the disk brakes) does not have a check valve in the outlet and the rear outlet (to the drums) does have a check valve.  The check valves provide a residual 8-10 pounds of pressure on the line to hold the wheel cylinder internal cups against the wheel cylinder wall (to seal it around the cups perimeter).  Sorry if I misunderstood the question to start with and confused you.   Smiley

Steve
« Last Edit: December 05, 2007, 08:43:30 PM by Steve68 » Logged
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