rear brakes again

reborn55 · February 16, 2009, 10:47:51 AM

Back to the brakes again. Installed new rear brake hose--and low pressure brake switch. Went to bleed rear brakes--had wife pump brakes slowly 3 times--released the bleeder and pedal went down, but not all the way to the floor. Lacked about 2 inches frome reaching the floor. Neither rear wheel when opening the bleeder will cause the pedal to go to the floor. Bleeding the front brakes--the pedal does go to the floor. I have a good pedal--no air in the lines. Have not driven the car yet as curious as to why the pedal does not go to the floor when bleeding the rear brakes---anything to worry about or should I drive it and see what happens. Running in gear the rear brakes are applying a little sooner than before. Thanks

enjenjo · February 16, 2009, 11:25:58 AM

If you have a combination switch in the system, it may be stuck with the rear brakes shut off. I had one recently that was doing this, I had to disassemble the valve, clean it out, and install new Orings to get it to work right. When bleeding it, fluid would just dribble out of the rear brake bleeders.

reborn55 · February 16, 2009, 11:40:11 AM

Got a Wilwood vavle, 10psi residual valve in the system--cleaned them before assemble. Got a decent stream of fluid out of both bleeders.

enjenjo · February 16, 2009, 11:50:20 AM

OK then, you still have air in the rear brake circuit.

wayne petty · February 16, 2009, 03:03:41 PM

Quote from: "reborn55"Back to the brakes again. Installed new rear brake hose--and low pressure brake switch. Went to bleed rear brakes--had wife pump brakes slowly 3 times--released the bleeder and pedal went down, but not all the way to the floor. Lacked about 2 inches frome reaching the floor. Neither rear wheel when opening the bleeder will cause the pedal to go to the floor. Bleeding the front brakes--the pedal does go to the floor. I have a good pedal--no air in the lines. Have not driven the car yet as curious as to why the pedal does not go to the floor when bleeding the rear brakes---anything to worry about or should I drive it and see what happens. Running in gear the rear brakes are applying a little sooner than before. Thanks

my thoughts are the system is working correctly...

when you open the bleeder screws at one end... the pedal does not go all the way to the floor... this is why there is a split system.. so if one half goes... the other still works... at least enough to stop the car...

is the pedal firm when the screws are closed?

? (yes is good) will it pump up any from where the pedal is at after pushing it one time??? (no is good)

remember the rear piston pushes with hydraulic pressure the front piston in the master... so when your foot is on the brakes.. there are pressurized sections in the master bore.. the primary system pushes on the secondary piston to drive it forward...

the spring between the sections only returns the 2 parts to their normal retracted position...

this is why there are forward facing seals on the front of the rear piston... and a rearward facing seals on the back of the forward piston.

http://auto.howstuffworks.com/auto-parts/brakes/brake-types/master-brake1.htm

reborn55 · February 16, 2009, 09:01:34 PM

this is what I have--front port to rear shoes--rear port to front discs

wayne petty · February 17, 2009, 02:08:41 AM

i was not saying that there is anything wrong with your system... only that from what you posted... it seems to be working properly...

i put the drawing in there... to let people know what it looks like inside...

so there are two different pressure circuits.. the front of the rear piston pushes on the back of the forward piston... with fluid pressure unless the rear half fails...

so when you open the bleeder screws on one side of the system... the pedal should only go half way to the floor... expecting the pedal to go all the way to the floor when only one side of the system is opened... is incorrect thinking...

if when a bleeder screw was opened.. and the pedal went all the way to the floor.. why even bother with a split system...

are the pressures to the system are correct for even stopping power???

that needs to be adjusted if it is off...

i noticed on some fords... in the mid to late 60's that they had different sized wheel cylinders.. to adjust brake bias... larger rear wheel cylinders for heavier cars.. and wagons... so there was more force applied to the rear shoes.... but this is not possible with disc brakes on all fours... as minute size changes of disc brakes is not cost effective..

one of the parts store i used to by parts in had a bendix picture book... it not only listed the part numbers with images.. but also classified them together... so all with the same mounting and shapes were listed by bore diameter... much easier to interchange.. the few that are left... they hold on to tightly... this is off thread... so i will stop

setting up the brake bias so that a car with half a tank of gas will lock up all four wheels at the same time is what is optimal.. in my opinion...

reborn55 · February 17, 2009, 08:48:40 PM

It seems I have over diagnosed the problem as usual. Appears brakes are working the way they are supposed to. When I broke the fitting removing the brake pressure switch--I installed a pressure gauge in line to rear brakes--air in system but still had pedal as the front brakes were still working. Same as bleeding the rear--so car will come off stands Friday for test drive. Pretty sure all will be well.

Thanks again