I'm looking for the prop valve that goes under the master cylinder but not on the frame for a 70 GS with disc brakes. Does anybody repo this? If not, any used ones? Thank you.
Excellent, thank you very much! I made a mistake, I also need the frame mounted prop valve. Is it the same as 71-72, I'm assuming not. Any idea on where to get one of those?
Rob, Be careful if you think these are both for the same car. '71 & later used the combination valve on the frame. Available at many vendors. The mounting bracket is available too, check E-Bay. I'm not sure who has them. I've seen them there new for +/- $20.00. The hold-off valve mounted at the booster was for '70 & earlier.You need only one of the two.
Thank you, I am aware of some of the differences between the different disc brake years. I'm converting a 70 GS with power drums to power disc. Is the frame mounted prop valve different different for 70 drum vs. 70 disc? Thank you again.
The frame mounted valve is the same, the valve at the booster was added to the disk cars to hold off pressure to the front until the rear shoes started to engage for even braking. At least that's the way I understood it's function.
A '70 drum brake car had no proportioning valve. The steel block on the frame is a distribution block & switch for the dash light. Equal pressure to all 4 drums. A pressure metering switch or hold-off valve was added to disc brake cars. The amount of pressure required for disc. vs . drums is different & this valve accomplished this. The proportioning valve on the frame for '71 & later was a combination valve. It provided proportioning(metering), distribution & a switch. A '71 drum brake car was the same as the '70. No proportioning valve, only a steel distribution block.
Thanks for clearing that up. In summary, adding the hold off valve to the existing 70 drum brake distribution block will work correctly for disc brakes. Please correct me if I misunderstood something. Thank you again.
I have to confirm whether the distribution block on the '70 will work for both disc & drum. I think it will, but I need to be sure. Found it: Brake Valve, Combination Gr.4.690 #1234388 70 All & 71-72 With drum brakes. This is the distribution block on the frame. Gr.4.690 # 1233464 '70 Disc Brakes - Pressure metering This is the valve mounted at the master cylinder.
Rob, I just sold a complete 70 set on Ebay about 6 months ago. There are actually 3 valves in a disc brake set for 68-70. 1. Hold-off valve mounted to master cylinder, those are no repro'd 2. Distribution valve, mounted on frame rail, same as drum version 3. Rear delay valve, L-shaped, mounts on rear crossmember directly above rear axle, on the driver's side. You can get away with just the hold-off and you should be fine. If this is not a concours car, get the 71-2 combo valve. I have them for sale below and a whole lot cheaper than $140 for the hold-off valve. Here is the info:http://www.buickperformance.com/discbrak.htm
So now what......... So what do you do when your hold-off valve works to good. I mean now that you have explained it, I think that is my problem. My rear brakes lock up . I have changed almost everything in the system except for the hold off valve. My front discs only seem to come on after my rear has locked up.......any thoughts on how to correct it.
Me too! Thanks George. :TU: Bandit, when you bled the brakes did you hold in the button on the valve at the booster? When I converted mine from drum to disk in the front. The first time I bled the front, I didn't hold that button in to see if it made a difference and sure enough the rears would grab and hold long before the front did.
Interesting...my 70 in my avatar came with disc brakes from the factory and I don't recall the dealy valve. I'll get under it this weekend and see. I wonder it that was for 68-early 70 as my car is late. I'll report out this w/e. Thanks for the info.
3rd valve Rob I am in the midst of a body off restoration and have encountered the same issue. My 70 Stage 1 car originally equipped with Disc brakes does not have the third valve on the rear cross member. I have been led to believe this may be a mid year change. It appears mid 70 and up cars have the one piece front to back brake line and do not have a valve on the cross member.
Both of my big block 70's are factory disc brake cars and neither have this valve. Are they all supposed to have it? If so, Anybody got a couple to spare?
as mentioned before check ss396.com as they DO repro the valves that mount under the master cylinder now.
