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Discussion Starter #1
I have a 69 Camaro that has been causing me fits. I put in a new master cylinder. A Dorman 13-1423, supposedly for 67-69's with front disc brakes. It is what they call a Z28 type. It acts like there is air in the lines. I bleed all 4 brakes and the pedal feels great, until you start the car and the pedal drops almost to the floor. This car is a factory LM1 car. Stock front disc brakes and a 12 bolt rear end. It does not appear to have a proportioning valve ! It only has a distribution block. If this is all that is required, I assume that this master cylinder will not work ? If this is the case should I just install a combination proportioning valve/distribution block (PV 2) ?

The first image is my original master cylinder.
The 2nd image is of a pv 2 proportioning valve.
The 3rd image is my new master cylinder installed
 

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Did you fully bench bleed the new MC?
 

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Discussion Starter #3
Yes, I did bench bleed it.
 

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A factory disc/drum setup would have had a metering valve, which holds off pressure to the front discs until enough fluid pressure has built up to expand the rear shoes to contact the drums. However, metering valves have a little plunger valve that you have to depress manually to open the internal valve for bleeding purposes, so without having one, that's not your issue. I would revisit the new master cylinder and see if it has a residual pressure valve in each chamber outlet, there should be one in the rear for drums but not the front for discs. Also I would check the flexible hoses to each wheel, if you are reusing older hoses they can look fine but may have collapsed internally.
 

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When I did my manual drum/drum to power disc/drum I had a similar issue.
I think (been 20 yrs.) it was the rod was wrong (plunger) at the MC ????

I would start the car and the pedal would go to the floor and return without even touching it.
 

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Discussion Starter #6
Doug - Thanks for the reply, Yes I measured the depth of the master cylinder to the mounting surface and then made sure the rod was out from the power booster that distance, with about .060 clearance. I fine tuned it by pedal feel after that.

Tim - I think you are on to something. The 67-68's when they had disc brakes, there was a proportioning valve added. My 69 does not have a proportioning valve, so from what you are saying is that the 69's are different and it should have a residual proportioning valve in the master cylinder. This would answer my question and not all 67-69 Camaro's use the same master cylinder as the parts books try to tell you. To fix my problem, I think I will just install the PV-2 proportioning valve and remove the distribution block. The car is far from stock so I am not concerned with keeping it original. GM even went back to a proportioning valve on the 2nd gens, I am thinking in '71 ? Also, I have stainless steel flex lines, so no all rubber hoses.

Thank you for all your help !
 

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Tom I was referring to the metering valve that sits up under the brake booster, rather than a dedicated proportioning valve that prevents locking up rear drum brakes before the front discs have become fully effective; there's a great explanation of the various valve terminology and function over at the CRG here: Camaro Brake Valves
 

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Tim - I think you are on to something. The 67-68's when they had disc brakes, there was a proportioning valve added. My 69 does not have a proportioning valve, so from what you are saying is that the 69's are different and it should have a residual proportioning valve in the master cylinder. This would answer my question and not all 67-69 Camaro's use the same master cylinder as the parts books try to tell you. To fix my problem, I think I will just install the PV-2 proportioning valve and remove the distribution block. The car is far from stock so I am not concerned with keeping it original. GM even went back to a proportioning valve on the 2nd gens, I am thinking in '71 ? Also, I have stainless steel flex lines, so no all rubber hoses.
!
The one in your second picture is a combination valve, not a proportioning valve. Read this and it will tell you all about the components and their correct names: Camaro Brake Valves
 

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Discussion Starter #9
My bad on calling the metering valve a proportioning valve. My 69' does not have a metering valve or a proportioning valve ! I am thinking GM thought the residual valve would be enough ? Also, I understand that I called combination valve a proportioning valve... almost all of the brake companies do. GM also calls the Distribution block a switch.
 

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My bad on calling the metering valve a proportioning valve. My 69' does not have a metering valve or a proportioning valve ! I am thinking GM thought the residual valve would be enough ?
Doubtful the factory installed the wrong system on a disc/drum car. Drum brakes were standard on LM-1 cars. Power drums and disc/drum were options. LM1 info here:CRG Research Report - LM1 – The 69 Budget Performer Don't toss your original MC, someone will want it.
 

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Discussion Starter #11
No, I am not saying that GM installed the wrong parts. I was stating that My LM-1 car does not have a metering valve or a proportioning valve and now, with a NEW master cylinder from DORMAN it does not function properly. They claim that the master cylinder fits 67-69 Camaro's.
 

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To fix my problem, I think I will just install the PV-2 proportioning valve and remove the distribution block. The car is far from stock so I am not concerned with keeping it original.
If you've installed a combination valve as your picture suggests, it contains/provides all the functions of the multiple valves originally installed on a '69 with front disc/rear drum. I'd stick with that. My bets are your MC is not fully bled even though you did already bleed it since you've verified you have the correct push rod length for your MC/booster combination. Others on this site from time to time have bled their MC multiple times only to do it again and find air trapped in the system. Did you bleed the MC on the car in the tilted orientation or horizontal clamped in a vise? You can get air trapped if the MC is not bled horizontally.
 

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Discussion Starter #13
Thanks for replying Chris. I bled the master cylinder in a vise horizontally level. The picture of the combination valve is what I am considering using. Your suggestion on leaving it as it was, is where "the problem" is. My car does not have a metering device or a proportioning valve or a combination valve ! It only has the distribution block, that GM just calls a switch. It has been this way for me the last 20 years, and I assume since new - 50 years ago. I needed a new master cylinder and installed the NEW Dorman master cylinder that is for a 67-69 camaro with front disc brakes.
 

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Tom, It's a bit surprising and puzzling why your car didn't have the normal valves as has been mentioned. A few things to check: are the rear brakes adjusted properly, is the pedal rod in the correct lower hole (power brakes) and is the push rod/pin set for the correct length ? Another item is verify you have a disc/drum master cylinder. It could have been packaged wrong. You may have a drum/drum MS. See the CRG info above for part(s) identification. I also believe you will need to add a combination valve as that would be expected by the master cylinder builder/remanufacturer. Also when bleeding the brakes I normally use the pump up/hold release method (2 person) in the order of RR/LR/RF/LF. Don't let the MS run dry.
 

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Discussion Starter #15
Another interesting note. I have looked in the 69 AIM and the valves are not shown or mentioned either ! (That I could find)
The inside rod that you are speaking of has never been touched or changed either.
 

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Discussion Starter #17
Al,

Thanks for your suggestions. The rear wheel cylinders are new and the calipers are new. (for your information) I adjusted the master cylinder to power booster rod. (see post 6) I have bled the system in the method and order the same as you suggested. The brake shoes and pads have maybe 500 miles on them and the rear shoes are adjusted properly. (Drums barely slide on and off)

-Tom
 

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Another interesting note. I have looked in the 69 AIM and the valves are not shown or mentioned either ! (That I could find).
Metering valve under the MC is shown in UPC J52/A2, have not yet come across a detail in the AIM showing the proprtioning valve on the subframe rail under the driver's side.....
It sounds as though you haven't really changed anything fundamental in the way the car was previously set up, and (presumably) the brakes functioned correctly then, except now you have replaced the master cylinder and the rear wheel cylinders, and have a pedal that goes to the floor; is that correct? If so, then the issue has to be either the new MC or somehow the process of bleeding isn't purging all the air.
And just to understand clearly, what was the reason for replacing the previous master cylinder?
 

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Discussion Starter #19
Yep, you are right... the valve is shown if you ordered the J52 option (front Discs). They also show a metering valve in UPC 5 B6. One interesting thing is that the part is only called a valve in UPC J52 and looks a lot different in UPC 5 B6 where they call it a metering valve. They really don't show a page for the LM-1 or z28 that were Standard discs.

I changed the master cylinder as the rear seal was very slightly leaking into the Power booster and it would not build up any pressure when trying to bleed the brakes. I confirmed that it was bad by trying to bench bleed with the small hoses like in the pic and it continually sucked in air. I am starting to think that I should have my original Master cylinder rebuilt.

This picture is NOT mine, I only show it because they used the same hoses and port adapters that I did.
 

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Yep the appearance of the metering valve is much closer to the real thing in the UPC5 diagram!
Did you confirm if the new master cylinder came with a residual pressure valve in both chamber outlets?
 
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