This is foreign territory to me, so I will share what I know has been done so far. The car had a disc brake conversion before I bought it, and when I took delivery, it would not lock up the brakes. I bought a booster and master cylinder from Auto Zone that was for a disc brake car. Installed and it feels the same (maybe a hair better) than before. Does the 70 need a separate proportioning valve even though the master cylinder has the bigger front reservoir? I have bench bled the MC and bled a half pint of fluid from each corner of the car. The pedal feels like it travels quite a bit before I actually feel it want to stop the car.
It appears that I am missing the hold off valve that hangs below the MC? If I install this, will I need to find a 70 MC? The one I am using right now is the 71+ with the larger front reservoir. I guess I need to make an order to Inline Tube.
I have a 71 disc setup on my 70 car(maggot) and the only issue I have is loss of vaccuum due to the cam.I have stopped many times very well over 110 mph too..
Try adjusting it to max which work the rears more, pedal feel comes from the rear, I messed with the rears one day for a few min and never got nothing more than a dribble of fluid when released, they should have a pretty strong stream when functioning correctly
I saw that, but what I am reading on some other threads is that if I don't have this hold off valve in addition to the proportioning valve on the frame (the brass factory one just below the cowl), the disc conversion will not work. This thread in particular is the one I was reading, an explains exactly what I am experiencing... http://www.v8buick.com/showthread.php?302047-Disc-brakeconversion&highlight=proportioning+valve
OK I just adjusted that manual valve to max, and adjusted he drum brakes. Improved feel a little bit, but I still cannot lock up brakes.
I myself would remove adjustable valve and get one of the brass valves and mount it on the rail . more than likely gonna make life easier.
Adam, Even though the brass valve mounted on the frame is BOTH a proportioning valve & a pressure switch, which will sense a loss of pressure to the front or rear & turn on the brake light, & ALSO acts as a place to conveniently mount needed brake lines from the M/C to ALL the wheels front & rear, it is REALLY NOT NEEDED. All that's NEEDED is the brake hold-off valve. What the hold-ff valve does & the proportioning valve does is hold off the application of the front disc brakes from applying until there is 300lbs. of pressure on the rear brakes. Give me a call. I could explain it MUCH faster over the phone rather than typing for hours. It is NOW 1:50pm EST. I will be at the number below for a couple more hrs. Or PM a number I can call when convenient. Tom T.
I don't understand why if you replace every component from a 71-72 car onto a 70 car why people seem to have issues.I could see if you replaced and mis matched parts but I did the complete thing,plus used a Pontac 8.5 rear and my 70 car knows absolutely no difference and brakes well..Did you use the square prop valve instead of the longer one??
I did not change the original 70 prop valve on the frame. So, in my reading, if I have the 70 prop valve, I need the hold-off valve in accessory. If I use the 71+ prop valve, then the problem is taken care of without the hold off valve. Tom, I am going to table this issue until I finish the paint on the car. Will revisit this later. Thanks for the replies!
OK I see time to get a different prop valve..George N probably can hook you up with a good one.. I would definitely swap to that and remove the other style.If you have 2 valves,twice as much to go wrong.
The 70 had a separate hold off valve alongside the MC. In 71, they combined the hold off, proportioning valve, and brake warning light function into a Combination valve mounted on the frame.
if you have a 70 set up with no hold off valve the rear will lock up too quickly there for with your complaint of low pedal i suspect the rear brakes are too loose try adjusting the shoes out. also need to see if the rear drums are over max size this too can cause the low pedal
I did a disc conversion today as well and I too have low pedal. I did a conversion kit upgrade by Wilwood. Would I need to order a combo proportioning valve or a brake hold off valve? Or is there something else that I need to check in order to resolve this? Thanks, Jason
I like to use the 71 and up proportioning/hold off valve combination but the 2 piece 70 works fine too. I second the opinion of checking and adjusting the rear brakes. You will have pedal issues if they are not adjusted up correctly.
See your thread. http://www.v8buick.com/showthread.php?314278-70-Skylark-Disc-Brake-Conversion-Low-Pedal-Problem
