Brake Bleeding

[Bruce Edwards]

Bob,

What I said was that by going to a larger caliper the brakes should not work better than before you changed them. The amount of fluid needed to fill and thus move a larger caliper piston would be more than before your swap. Thus the brakes should have felt better before the swap not after.
You can pinch off the brake hoses one by one to see when the pedal gets firm. I have seen some flex hoses swell and that will give a soft pedal but I would figure you have new hoses on the car you are building.

[Rick Parker]

If you use a Mighty Vac, try putting some grease on the threads of the bleeder screws it should eliminate the air path and the constant source of air entering the system.

Rick

[Art Burtt]

Did you "bench bleed" the master cylinder?

[sideoiler10]

Art,

Sorry I took so long to reply but we have been gone. I have not removed the master cylinder and there is no bleeder valve fitting on the casting. I am using the Girling master cylinders that do not have a bleed fitting.

Bob

[rdorman]

Heh Bob I to have the Girling with no bleeder. I just bought a length of premade brake line and bent it so that I screw it in the master cylinder and the other end down in the bottom of the reservor. Then pump away. I do it on the car and it just pumps the fluid back into the reservor. Works great!
Rick

[Dominik]

rick d,

I learned that the inside needs to be bled first, having two bleeders at one caliper. Does that depend on the calipers?

when using a brake bias bar always bleed front and rear at the same time, start with the one farthest from the master cylinder (passenger side).

you may want to tap the calipers lightly with a plastic hammer to untrap little air bubbles and don't push the pedal too fast, which may lead to cavitation and even more bubbles.

are your bleeders pointing up?

a common mistake when using Jaguar XJ calipers is mounting them left to right and the bleeders point down.

good luck,

dominik

[sideoiler10]

Rick,

Duh! I don't know why I didn't think of that...sounds like common sense to me. Thanks Bob

[rdorman]

Dominik, I don't think it depends on caliper. I always bleed the inner bleeder first and the outer last.

All, Yep, always a good idea to bleed front and rear at the same time.

I use a jar and a tube placing them so that the bleeder is always covered in fluid and just pump away! Also be sure to only open the bleeder enough to let the fluid out, to much will draw air in around the threads.

Bob, no problem! Happens to me all the time! I took one premade line and cut it in half that way I can bleed both at the same time.

Rick

[GUMBALL928]

Some thoughts on brakes and bleeding:

- dual master cylinder assemblies are designed to apply equal pressure (via the balance bar) to front and rear calipers. This configuration only works if it is adjusted properly, and has regular maintainance. Trying to drive a car fast with incorrect front/rear balance is always exciting, and will sometimes get you extra TV time......occasionally even the 11 o'clock news.......
Replacing a dual master assy. with a single is a large step backwards.....

- when changing caliper / piston size, it is necessary to change master cylinder size at the same time - you must keep the same master piston - to - caliper piston ratio. Obviously, if you change from a 2 piston caliper to a 4 piston caliper, some calculations need to be done.....(Tilton's website has formulas)

- a larger master cylinder piston will pump more fluid, therefore giving a firmer pedal/shorter stroke. A smaller one just the opposite. If a driver likes to modulate braking by pressure, he will like a "rock hard pedal" with little travel, but if a driver prefers to modulate braking by travel, then he will like a softer pedal.

- Tilton makes a neat bleeding kit, containing 2 plastic bleed bottles with attaching cables, tubing, etc.....

- bleeding procedure:
> pump pedal 3-4 times, (not fast) then hold pressure (person in car says "hold")
> both people at calipers open bleed screws
> when pedal bottoms, person in car says "down"
> both people at calipers close bleed screws, and say "closed"
> pump again, repeat.....

- when bleeding a dual system, whether it is a "race" system with dual masters and a balance bar, or a "street" system with a dual piston master, it is necessary to bleed a front and a rear at the same time. If the calipers have an inner and outer bleed, do the inside first, then the outside.

- be very cautious when using a vacuum bleeder, as too much vacuum can draw air past caliper seals...

- when tightening bleed screws, use a torque wrench, as 10-15 inch pounds is usually sufficient

- clean all fluid from bleeder and caliper body, otherwise it will attract dust and grunge, jamming threads, and plugging bleeders, etc...etc...

- for competition, use a good 600 degree fluid - AP, Motul, Wilwood, etc. Also, use a fresh bottle. Brake fluid has a severe inclination to absorb water - a bottle opened and sitting for a couple of weeks(even closed tightly) may have absorbed enough water from the atmosphere to become useless.