69 Lemans with disc brake conversion - Pontiac GTO Forum
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post #1 of 6 (permalink) Old 10-23-2017, 12:41 PM Thread Starter
 
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69 Lemans with disc brake conversion

Hey guys so my 69 Lemans has a disc brake front conversion with booster and my master cylinder went bad so I am replacing it and lines at the calipers, and was going to do the booster too. I cannot for the life of me get enough torque to break those nuts free. So I'm thinking I'm going to just clean it up and paint it in the bay. My question is...see pic...wtf is that smaller object circled in yellow? It runs from my front port on the master with that line then down to the proportion block or whatever on the frame rail. Do they make new ones? What does it do?
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post #2 of 6 (permalink) Old 10-23-2017, 05:57 PM
 
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The part is the metering valve. the style with the big nut on the front was used from '67-69. A, F, & '69 GP with factory disc brakes can use the same metering valve. B series used a slightly different rate metering valve. '70 model metering valves lost the big nut feature, '70 factory disc models also gained a hold off valve on the rear frame crossmember in front of the rear brake hose.

In the late 80's & '90's I pulled the various '67-69 styles in yards as a specialty core. Wholesaled the weathered ones to be rebuilt, & retailed the best. Years ago on eBay, nice used early disc metering valves were up over $125 for many years. Several years ago, Inline Tube brought out a repro of the style with the big nut, then dropped the price on them. Doing anything short of a true Concours restoration, if ones staying with this style of original appearance style front disc set-up, one's better off buying a repro of the early metering valve from Inline for $59.
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post #3 of 6 (permalink) Old 10-23-2017, 06:16 PM Thread Starter
 
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Ok thank you. Now is there any reason I couldn't just clean it up, paint and reuse it? Everything was working fine till my brake pedal started to lose pressure and eventually went to the floor before getting any brake feel. This all happened in two days time.
Does that meeting valve have anything to do with that or is that mainly master cylinder sounding, which I'm replacing anyways along with lines to the callipers.

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post #4 of 6 (permalink) Old 10-23-2017, 07:55 PM
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I've also seen that part referred to as a hold-off valve. On disc brake cars its function was to prevent the front brakes from engaging until the rear brakes started to engage (I think, I may have that backwards - it's been awhile). It's sort of a safety feature to keep the car stable under braking.

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post #5 of 6 (permalink) Old 10-23-2017, 09:15 PM
 
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Below is a fairly good explanation of factory disc brake valves on factory disc brake '69 Camaros.
Camaro Brake Valves

The '69 Pontiac A-body factory disc setup uses a very similar system. I can't remember pulling the brass block off the rear crossmember of a '69 GP or disc brake GTO, but know that piece which the author of the Camaro article refers to as a proportioning valve (disagree on the name) was definitely used on '70 model factory disc brake installations,mthen went away for '71 models. Have pulled quite a few over the years.
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post #6 of 6 (permalink) Old 10-24-2017, 09:33 AM Thread Starter
 
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Nice info PH! That helped a lot. Makes me think this car actually came with disc fronts since it's even go the correct 69 Metering Valve...here I thought it was upgraded from drum. So to me with the condition I have happening it doesn't sound like this thing was part of my problem so I should be able to just clean it up paint it and reuse it. Again...budget is my issue and if I can reuse I will.
Anyone have a good idea how to get the booster off the firewall? Those nuts are impossible! I want to clean that up and paint it while I'm at it and being out of the car would be nice.

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