I've just finished converting the front of my truck to disk brakes, using the
conversion kit from ChevyDuty and rotors and calipers from a '73 Chevelle
wagon.
My plan has been to also convert to a dual master cylinder as part of this
process, though I didn't get that far today.
Because I've not driven the truck in weeks, I wanted to take a drive with the
new brakes in place. I also wanted to learn for myself if disk brakes
operated by the original master cylinder will work or not. I've heard
conflicting answers to the question.
So, with the new brakes in place, I bled the brakes. Before bleeding the
rotors would turn with just a tiny bit of drag. After bleeding I can't turn
the rotors at all unless I use a tool or tire to gain some leverage, and then
I have far more drag than seems appropriate.
As I prepared for this project I talked to a lot of people, and read several
books that talk about disk brake conversions. One of the things I read is
that if your master cylinder is lower than the top of your calipers or wheel
cylinders you need residual valves in or near the master cylinder to prevent
your brake fluid from draining back into the master. For disk brakes this
residual valve should hold two pounds of presure and for drum brakes it should
hold ten. And I bought those valves to install when I put in the dual master
cylinder.
Until a few minutes ago it never occured to me that the original master
cylinder might have a ten pound residual valve, for the drum brakes. If it
does, that would explain why my disk brakes are lightly applied once I've put
any pressure to them at all.
Does anyone know if that is the case? If it isn't the case I may have some
other problem, though since they seemed fine before I pressed the peddle the
first time, that seems unlikely.
Any ideas?
I may do the master cylinder job Sunday. If not it might be a couple weeks
before I can focus on this again.
Oh, and I didn't even attempt the test drive because I discovered I don't have
enough inflated tires mounted on five-hole wheels. But that's a different
problem, and I'm pretty confident I know what to do about it...
Steve@OldSub.com
www.oldsub.com to see all three of my old trucks...
oletrucks is devoted to Chevy and GM trucks built between 1941 and 1959
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