I need some advice. I just installed front disc brakes and the instructions stink and Im just wet enough behind the ears to ask a dumb question. My kit has a new proportioning valve that came with it. Does the old have to be removed? Can I use the old one instead of the new one? I think two would not be good but what do I know. Im still running drums on the rear of the 72 Skylark. o No:
If you changed from all drums to discs at the front, you need the new proportioning valve. What you had on the car (with 4 drums) is a distribution block instead of a proportioning valve. There is a button under the little rubber boot on the valve, you need to press that in when you bleed the brakes.
The new proportioning valve should replace the existing distribution block as long as it has outputs to all four wheels. No need for both. Devon
I just talked with some old timers about doing my front pdb conversion, I bought an PDB set up off a 70 monte carlo and the old timers said I didnt need to swap the Distribution block for the proportioning valve, "I've done it both ways, with the Distribution block and with the Proportioning valve, and they both work fine, save yourself a step, unless one is no good." is what was said to me. These fellas have been doing ground up restos for 35 years now, and have not steered me wrong yet. Although I will admit Id like to put that P valve in anyways ;p
Your first skid test will tell you whether you're ok or not. Even a proportioning valve may not work properly if designed for a car with different front to rear brake bias than yours, making an adjustable valve about your very best bet. Personally, I'd do it once and do it right. Devon
I hate to keep beating a dead horse but I need some advice on how to plumb my brakelines. If I understand correctly the old proportioning valve needs to go away in favor of the new valve. How do I plumb to the new one from where the old one was located? The old one is located below the driver seat while the new one is at the master cylinder. Do I just use some sort of brake line connectors at the old valve to run up to the new valve? Im so lost.....the conversion has been easy up until now.
A proportioning valve simply biases braking power to the heavier end of the car (front) When you have disc brakes on the front and drum on the back, you actually need anothert type of valving. Disc brakes are inherently fast acting, where as drums have clearance and spring tension to overcome before braking occurs. In a disc/drum car, the factory incorporated a hold off valve. That valve delays front brake pressure until pressure is built up in the rear brakes. In early cars, the proportioning valve and hold off valve were separate, but in 1972, they were combined into a combination valve. I would just get the right combination valve for a disc/drum A body and use that. This is for the 71-72 Chevelle. http://www.ss396.com/mm5/merchant.m...ino&Product_Code=FPR-102&Category_Code=VALVES You will probably have to modify your existing lines to install the right valve.
in 72 it a combination valve - lots of info/diagrams in the manuals (be sure you use A body sheets when looking at the assembly B_C_E ARE different plumbing ) <center> </center> 1972 Full Line - Buick Assembly Instructions - sent in by Glenn Tangen 1971 GM Corp <center> </center> 1972 full Buick Chassis Manual - GM Corp <center> </center> 1972 full GM Body Service Manual - - GM Corp <center> </center>
You need a flaring kit and new brake lines :TU: Here's a video: <iframe width="640" height="480" src="http://www.youtube.com/embed/qNePrGR1D-s" frameborder="0" allowfullscreen></iframe>
looks easy enough...still not sure about the brake lines. It seems to me that the rear brake lines will need to be extended or replaced so that they can reach the new proportioning valve which is located next to the master cylinder. I make this assumption because the old proportioning valve is going away and it is located underneath the driver seat. So I guess I need all new brake lines front and rear? Man do I feel like an idiot.
I'm reading this thread, but nothing directly fits my situation. I have a 67 Buick Lesabre with a distribution block on the driver frame rail, obviously splitting one line from the MC to 2 lines to the front and 1 line to the back. It has an electrical boot in the middle. The new MC / Booster kit i am getting is this one: http://www.summitracing.com/parts/rsd-g91210971/media/images/make/buick It comes with a proportioning valve mounted to the bottom of the MC. http://www.getdiscbrakes.com/media/wysiwyg/pdf/PV71_Fixed_Combination_Valve_Supplement.pdf There are 5 ports total 2 to the front (independent lines) 1 to the back 2 in from the MC My Question: Can i plug off one of the Front ports and put in my factory line to the remaining front port? Which then runs to the distribution block and to both front calipers. Can i just put in my rear line to the rear port and call it done?
So you want to run the new proportioning valve in series with the original distribution block? I just finished this exact conversion yesterday, while it may seem like a pain to re plum your front lines and extend your rear line I highly recommend replacing every line you can and mount the combination valve on the MC as outlined in the instructions. I spent maybe an hour total to replace both front lines, the MC to combination valve lines and extending the rear line. Now I know I have fresh brake line and fittings to compliment my overhauled brake system. The only out of the box thing I had to do is this: The combination valve takes a 9/16"-18 fitting for 1/4" line, the fitting for the rear line is the same. I could not find a 9/16" union for 1/4" line. So I cut and reflared my rear line with a 7/16" fitting and used a union to join that to a new line that terminates at the combination valve through a 9/16" fitting. I say this because you wanting to use both valves (this is what I am assuming) means factory looking isn't a direct concern so I think keeping it simple is the safest way to go. Less to go wrong and in the end much easier. Or I believe you can use a factory style combination valve found on 71,72 cars that will mount on the frame and you can forget about the included valve with the kit. But you may find when taking the original valve off that many lines will twist and break since the fittings seize to the line.
Is a combination valve the same as a proportioning valve? I know that there was a 3 piece valve in the 70's, is that a combo valve? I thought that the distribution block only split the fluid not add pressure to the system, in a sense, the distribution block acts as a T-fitting splitting the singular line into 2. where did you get your brake line from?
Im sorry let me back up for a second. I am mixing your situation with that of the original poster. Reading this on a smart phone earlier I missed some details. First, was your car originally equipped with front disc brakes? I am not familiar with the brake systems of the larger Buicks.
