Help with brakes!

[CFster]

I just can't get a decent pedal and I don't know why. I have a TCI chassis under a '40 Ford coupe. It came with 11" front discs with the typical 2.38" bore S10 calipers and 11" x 2.25" rear drums. Also has a 7" dual diaphragm booster with a Corvette style 1" master. Since the master is lower than the brakes it had the required 2lb front and 10lb rear inline residual valves, and an adjustable prop valve in the rear line.*

I could never get what I would call a high pedal, and under hard braking wondered if I was going to run out of pedal travel before running out of brakes. I'm aware of the issues with bleeding a master under the floor and have used a power bleeder and also gone to the trouble of jacking each end of the car way up to get the low side brakes lower than the master while bleeding. *I'm fairly confident I got all the air out of the system.*

I've also replaced the master - three times.*

I've adjusted the pushrod between the pedal and booster. There's only about 1/8" of travel from being adjusted all the way out, to the point where the brakes start locking up after driving for a few miles (I believe the fluid is heating up and applying the brakes because there's no free play in the linkage).*

I thought I'd just have to live with this seeing as it appears that the way the linkage is designed means a lot more brake travel is required than normal to push the pushrod into the booster due to the cantilever design.*

So, I thought I'd try another approach - increase braking force for given pedal travel. I upgraded to 2.75" calipers up front, and a rear disc setup in back (11-1/8" rotors with 2 - 1/8" calipers). I changed my rear 10lb residual valve to a 2lb. I also went up to a 1-1/8" master cylinder. All else being equal the master should have raised the pedal and required more effort to press. *This is not the case. I think it's even lower than before.*

I investigated installing a 8" dual diaphragm booster, but there's just no way no how it's going to fit in the frame.*

I figured I'd ask if anybody has any tips, seeing as a good number of cars here have the same style brakes.

Help!

[jerry clayton]

If you have power steering in your car change the brake system to the system like on the 2004 years Mustang-gets rid of those vacume boosters

[HOSS429]

someone will probably hit the nail on the head but if i had a problem that was driving me nuts i would start at the beginning of the system and block off everything till i duplicated the results .. unhook and close the lines coming from the master cylinder and see if the pedal is firm .. if so step to the next section of the system and block it off .. etc etc ....

[34_40]

You mentioned a adjustment to the brake rod.. is this the one from the pedal to the booster? Or the one in the booster to the master?

Another thing a lot of folks have trouble with is some of the older bulkhead fittings, they pass through the frame rail, to join the line on the inside (or the inner side) to the outer line or hose. there were some made some years back that had a larger I.D. that will actually capture air and will be near impossible to remove. Perhaps you can remove a line and see if there is a larger I.D. that could capture air.

Another thought is if you have a power bleeder, go backwards, that is, push fluid from the caliper, slowly to the master.

[Dave Severson]

Yup on what Mike said!!! I got one of the Phoenix backwards bleeders when they first came out, no problems bleeding any kind of brake system since!!!!

[CFster]

Yeah I pushed the fluid backwards through the system. There's no sir bubbles coming out of anywhere...

[Dave Severson]

Ok, back to the master cylinder, is it one designed (ports are different) for a disc-disc brake system?

You mentioned the long travel on the pedal---is the pedal ratio goofed up and not pushing the pushrod far enough into the cylinder???

Never have figured out why the people building these pedal systems use such long pedal travel and power brakes. I've just never been a big fan of power brakes on Hot Rods, I'd rather have to push the pedal a bit harder and eliminate one more problem prone component from the system (the booster). A lot of the 7" power boosters barely qualify as "junk" IMO.........

[daveS53]

What about the pushrod between the booster and the master cylinder? I've got a similar setup with a 7" dual diaphragm booster and Corvette style master, but it's operating Willwood discs. It's seems to be common for the sellers of these items to not give you the proper pushrod to fit between the master and the booster. I'm using one that I made myself because I've never got the right one from a seller. The Corvette style master cylinder has a deep recess in the piston and requires a pushrod that's about an inch long. Some boosters come with a much shorter rod the barely protrudes from the booster. I've been sent a longer pushrod, that was supposed to fit the recessed cylinder, but it was too long. My solution was to use an allen head bolt, with a jam nut. My booster had 6mm threads.

The pushrod between these two parts is supposed to have a small amount of clearance, after the two are bolted together. If there's no clearance, pressure will build up and lock up the brakes, or at least cause some drag after awhile. You must also have a return spring on the pedal, or the same thing will happen.

My car requires a very small amount of pedal travel to produce a hard pedal, certainly less than an inch and a lot of that is just free play.

[34_40]

When you pushed the fluid in, was the bleeder on the bottom and the line on the top? If not did you then "burp" any air ouut of the bleeder?