New master and now no power brakes
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Ok I did a disc brake upgrade to my 68 swb. I already had a power booster and now it feels like it isn't working. I used a 1975 Corvette style master cylinder and the truck stops ok but the pedal is hard. Any ideas?
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Re: New master and now no power brakes
How do you Upgrade to newer style Brakes ?
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Re: New master and now no power brakes
Oh simple as that then :lol:
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Re: New master and now no power brakes
Just the front disks, upgraded? I'm guessing that you got a CPP master and prop valve combo for disk/drum or disk/disk, which ever you have? Bore size on the master, did you change the pushrod, bleed the brake system correctly?
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Re: New master and now no power brakes
I used a rebuilt 75 Corvette master with a 1" bore. Stock rebuilt booster that is workiń properly and I believe I bleed the system good. Nice firm pedal. Front disc upgrade only with new CPP disc/drum prop valve
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Re: New master and now no power brakes
Also since you had the booster already, did you look to make sure it didnt have fluid in it? I had to replace mine due to this. And another is poor vacuum pressure. Where are you porting the vacuum for the booster from?
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Re: New master and now no power brakes
My concern was maybe I should of used the 1 1/8 inch bore master but I figured the smaller bore would cause higher pressure.
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After reading this I'm thinking I may need to switch to the larger 1 1/8 bore
http://67-72chevytrucks.com/vboard/s...d.php?t=561809 |
Re: New master and now no power brakes
Did you properly bench bleed the master ? Not sure if that is a brand new (looks brand new from the pic). All the brand new master cylinder I get has a note saying to you have to bench bleed it or at least comes with 2 lines where you can bleed it in the car before installation of the hardlines.
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Driving it to work this morning made me realize that I will get used to the firmer pedal and that there is like a half pedal that feels like power and then it hits a point where it feels like manual brakes. I was thinking that with the larger bore that there would be less stroke and maybe that would keep it in the power brake feel realm? |
Re: New master and now no power brakes
I have done drum to disc on the front of my C20. I have a prop valve that looks like the one on your truck. I am told that the lines have to be reversed to work.... Could this be the issue?
Have you called CPP? I am sure they have run into a question like this before. I have not hooked it up YET. That comes this weekend. I went back to the distribution valve for now and it feels spongy. |
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Re: New master and now no power brakes
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I would try a stock 71-72 M/C.
They have the 1-1/8" bore. http://www.oreillyauto.com/site/c/de...01292&pt=01292 |
Re: New master and now no power brakes
Thanks Keith no actually got one of those yesterday :lol: was already headed down that path. Plus I have this relationship with Oreillys so they will swap it no questions asked. :D I will post updates this weekend. Thanks guys and let me know if you have any other suggestions til then
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Re: New master and now no power brakes
Shawn, after reading the link you posted, I think the larger bore is what you need. I think you're heading down the right path. :D
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Well the silver lining in all of this is I will be able to pre paint the new master :lol: Thinking of just going with a flat clear or some aluminum paint that I already have.
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No painting that will eventually rust anyway. I painted my '69 M/C with cast look caliper paint,... but now it's starting to look like crap. (with almost no miles on the truck) |
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Re: New master and now no power brakes
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I believe the discussion above regarding which line from the mc goes to which port on the prop valve is valid - but only for a 3/4 ton truck (pic of my 3/4 attached). Note rear mc res attaches to the front port of the prop valve and vice versa. You can see the 1/4 (rear) lines and figure out which ports/reservoirs feed the rear brakes and which other ones feed the fronts.
My inline tube purchase matched the old lines between mc and prop valve. BUT, your truck is a 1/2 ton - so my point is dispel the confusion between 1/2 and 3/4 ton. Your mc to prop valve lines are right for a 1/2 ton and the pic below is right for a 3/4 ton. |
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