Whons Posted July 5, 2023 Share Posted July 5, 2023 I put a master cylinder in my new 71. I bench bleed the master cylinder. bleed all wheel cylinders, starting from the passenger rear, driver rear, passenger front, driver front. Didn't have any problem bleeding. Pedal felt good. Started the engine backed out of the garage and pedal went to the floor. I noticed a drip of brake fluid on the proportioning valve, and not at a fitting, and where the little rubber boot is there was a little pin that pushed thru it. I ordered another proportioning valve. Has anyone ever seen this happen? I have bleed a lot of brakes and never had a problem. Please advise Thanks Wayne. Quote Link to comment Share on other sites More sharing options...
Whons Posted July 5, 2023 Author Share Posted July 5, 2023 I should mention that there was no loss of fluid in the master cylinder. Quote Link to comment Share on other sites More sharing options...
cny first gen 71 Posted July 5, 2023 Share Posted July 5, 2023 Seems like if pedal went to floor there would be more fluid than a drip. What did you use from master cylinder? It could be a seal in the valve I guess. Quote Link to comment Share on other sites More sharing options...
Scott S. Posted July 5, 2023 Share Posted July 5, 2023 Did you set the push rod between the master cylinder and the booster to the right length ?? There's an adjustable nut at the end of the rod and a special tool to set the correct length/depth. If it's too long, it may have pushed the valves too far ? Quote Link to comment Share on other sites More sharing options...
Whons Posted July 5, 2023 Author Share Posted July 5, 2023 the master cylinder looked exactly like the old one. I bench bleed it and bolted it on. I talked to a tech rep at Summit and he said to bleed the brakes with that proportioning valve you need to screw out the center where the electrical lead conectes and screw in a special threaded plug. bleed the brakes as normal, then take the special plug out, put the electrical peice back in and your done. never did that but will try it. the only time I had to worry about a different push rod is when I went from manual to power brakes. Quote Link to comment Share on other sites More sharing options...
Scott S. Posted July 6, 2023 Share Posted July 6, 2023 When I replace the brake system in my '70, I did it in pieces. In the booster instructions it tells you how to set the rod.... But these instructions weren't in the master cylinder instructions. I believe it's supposed to be 0.060 inch of clearance. Not a lot of tolerance if it's out to much. I didn't get it set right the first time, and had similar pedal response. Felt good until the car was actually moving, then had to use both feet to get it to stop. There are articles here that talk about the procedure and the "special" gauge/tool for the job. Hope that helps. Quote Link to comment Share on other sites More sharing options...
Scott S. Posted July 6, 2023 Share Posted July 6, 2023 It's 0.020 in. Here's a pic of the tool as well. Quote Link to comment Share on other sites More sharing options...
jft69z Posted July 6, 2023 Share Posted July 6, 2023 1 hour ago, Scott S. said: It's 0.020 in. Here's a pic of the tool as well. Those look like my pictures 😄 Quote Link to comment Share on other sites More sharing options...
MC1of80 Posted July 6, 2023 Share Posted July 6, 2023 Stop overthinking people. He only changed the master and bled the wheels properly. Push the pin back down to reset the proportioning valve. 2 Quote Link to comment Share on other sites More sharing options...
Whons Posted July 6, 2023 Author Share Posted July 6, 2023 thanks everyone. I am going to put a new proportioning valve in, then bleed all the brakes again. 2 Quote Link to comment Share on other sites More sharing options...
Scott S. Posted July 7, 2023 Share Posted July 7, 2023 On 7/6/2023 at 1:11 PM, jft69z said: Those look like my pictures 😄 That they would.... Just trying to share the knowledge. Quote Link to comment Share on other sites More sharing options...
Whons Posted July 8, 2023 Author Share Posted July 8, 2023 Rockauto master cylinder is going back. I tried one from AutoZone that was aluminum but didn't like the bench bleeding instructions. I may have pushed the piston too far. Took that back. Just got another one from Napa. finished bench bleeding the old school way with the tubes going back into the front and rear sections. It's still in my vise. I will put it in the car tomorrow. I'm going to just barely crack the bleeder screws, I may have opened them too far before. I'll report tomorrow. 1 Quote Link to comment Share on other sites More sharing options...
cny first gen 71 Posted July 9, 2023 Share Posted July 9, 2023 Are you using new or rebuilt master cylinders? I will never use a rebuilt ever again I've seen way to many fail. 1 Quote Link to comment Share on other sites More sharing options...
Whons Posted July 9, 2023 Author Share Posted July 9, 2023 The one that I bought from Napa today is new. I will put it in tomorrow. The one I got from Rock auto was probably rebuilt. I will never get any thing from rock auto again except hoses and belts. 1 Quote Link to comment Share on other sites More sharing options...
cny first gen 71 Posted July 9, 2023 Share Posted July 9, 2023 I've never bought from rock auto so I have nothing positive or negative to say about them. I usually try to buy local in case there's some kind of problem. Advanced auto has always been good to me but I do get stuff from summit and jegs also. I fine doing some research saves time and money in the long run. A lot of people get stuff from Amazon to, I've gotten a few things but do plenty of checking first. Just my humble opinion. 2 Quote Link to comment Share on other sites More sharing options...
Whons Posted July 9, 2023 Author Share Posted July 9, 2023 I buy from autozne, advance auto, Jegs, Summit, Original Parts Group, and a lot on Ebay. I also sell on eBay auto parts and custom painted fishing 🎣 lures for steelhead and salmon. Quote Link to comment Share on other sites More sharing options...
Whons Posted July 9, 2023 Author Share Posted July 9, 2023 Well I put my new master cylinder from Napa (new one). Had the same problem, pedal to the floor with engine running. So I watched a you tube video on the power brake booster info. One thing that they said to test it was to start the engine with your foot on the brake pedal and when the engine starts the brake pedal will go down a little. Well I did that and mine goes down almost to the floor. I am thinking that the push rod length is not correct. If it is too short it may travel too far before it pushes on the piston on the master cylinder piston. So I ordered the special tool to measure the rod length. I don't think my booster is bad, I checked the vacuum line and the check valve, all good. It worked fine before I changed the master cylinder. But I wanted to change all the brake components because the front brake hoses were badly cracked. Any help would be greatly appreciated. Wayne Quote Link to comment Share on other sites More sharing options...
jft69z Posted July 9, 2023 Share Posted July 9, 2023 If you had a hard pedal when you were manual bleeding it, it's doubtful the rod length is that far off. You still have air in the system somewhere and need to pressure bleed it, like I mentioned on the phone the other day. 2 Quote Link to comment Share on other sites More sharing options...
MC1of80 Posted July 9, 2023 Share Posted July 9, 2023 Agreed 1 Quote Link to comment Share on other sites More sharing options...
cny first gen 71 Posted July 9, 2023 Share Posted July 9, 2023 Ditto 1 Quote Link to comment Share on other sites More sharing options...
jft69z Posted July 9, 2023 Share Posted July 9, 2023 Also, as I mentioned on the phone, to quick check that rod length, look down the holes in the bottom of the master cylinder with a bright light. As you're tightening the master cylinder to the booster, you should see NO movement of that piston and seal down that hole, if you do, the rod is too long. To check the opposite, too short a rod, look down there when actuating the brake pedal. If it seems to take a lot of travel to see that piston/seal move, then you need to look further. (It may be slightly more controllable if the booster/master was off the car). These are just quick and dirty tests, not meant to set the 0.020" gap. 1 Quote Link to comment Share on other sites More sharing options...
Whons Posted July 18, 2023 Author Share Posted July 18, 2023 Bought a pressure bleeder and finally got brakes. I was amazed how much more air I got out of the lines. 3 Quote Link to comment Share on other sites More sharing options...
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