Hi !! I have build a tbucket , and the brakes are spongy , the specs I used was from T.P.. drawings the master cylinder is from a 1975 mustang from speedway motors. used a 10 psi residual valve for the back 11 inch drums, and 2 psi residual valve for the front with chevy disk brakes.. and a proportional in the back....I have bled them, numerous times and I can not get good a good brake pedal... .what am doing wrong !!!!! I replaced the master cylinder ,and getting same results....Darn!!!!!!!
Hello ,Tim !! thanks for responding, I bled them starting with the left front than right front , than right rear than left rear, I must have this 10 times at ea. wheel ..than I used a small vacuum pump did that a numerous times with same results , a little pedal 1st pump ,2nd pump a pedal 2/3 down..
Bleed farthest wheel from master cylinder first, closest wheel last. That should get all the air out.
I think I did that , but I will do that tomorrow just to make sure , I have been working on this for than more a week now , even replaced the master cylinder.. so bleeding the normal way should do it ..
when they say to bleed the furthest first it means the one that has the longest line, if you already didn't know....
You say Chevy Disc brakes...are you sure you don't have low drag metric calipers? They pull farther back when the brake pedal is released and require a special quick take up master cylinder to push them back to the rotor quickly. Using a normal master like the Mustang one you have will mean the brake pedal will always seem very low. I forget the exact cars you need to specify to avoid the low drag versions (late 70's Malibu is one I think), but a Google search for something like "low drag caliper" should get you the info you need.
Two things important for a good pedal and bleed; minimum push rod clearance of about 1/16" when the pedal is fully released by it's return spring, and being able to fully stroke the master. Bleeding sequence with a dual master is not important, and in fact will let you know if each system in intact with the other failed while bleeding. Also, the 15/16" Mustang 2 master may be too small for a high pedal, depending on ratio and your brakes. Make sure the drum brakes are properly adjusted.
a lot times improperly adjusted drum brakes will seem spongy especially if you didn't turn the drums Tom
If the calipers are on the wrong side the bleeders will not be in the right place to fully bleed the air out.
I bought the chev brake kit from Ron pope, intermediate chev brakes. I bought the whole front end from Ron.
Do you have a square tubeing frame and use through the frame brake line fittings? Some have a large passage and are hard to all the air out.
Here are a couple pics of the car took a few years but getting closer. View attachment 3201283 View attachment 3201284 View attachment 3201286 Sent from my SCH-I545 using H.A.M.B. mobile app
Also is the master cylinder lower in the frame than the the calipers and wheel cylinders? That can make bleeding a real pain. I agree with @V8 Bob that mustang master may not move enough fluid for your brakes. I personally dont like the mustang ones and have always used a gm one, and replaced Mustang ones with a chevelle or vette type.
See if you know someone with a pressure bleeder that attched to the top of the master and pushes all the air out at the same time. I had a similar problem and borrowed this tool from a friend and it totally got all the air out. I also use speed bleeders but you still have to get all the air out http://www.ecklersfirebird.com/brake-pressure-bleeder-dual-master-cylinder-10058.html
The Jalopy Journal
