brake bleeding..WTF?

-
pishta

pishta

I know I'm right....
Joined
Oct 13, 2004
Messages
23,821
Reaction score
13,677
Location
Tustin, CA
OK, so I converted my single pot to a dual disc/drum setup. straight forward setup, only 2 new lines used to feed the Prop valve from the M/C, all other lines are stock. Large reservoir for the front disk, smaller front reservoir for the drums, check. So I bench bleed the M/C so there are no bubbles, nice smooth action through the clear tubes. Install the full dripping M/C, slip new rubber chinga over old pushrod tit and get it seated (I think, how else would it seat if I can give it a full stroke to the floor?) and start using my mightyvac to draw fluid into pass caliper from the bleeder valve which IS on top. I finally (maybe 30 40 strokes at 1cc each time???) get no bubbles so I cap it and then do the driver side. Same deal, refill the 3/4 empty M/C and then figure that Im pretty good on the fronts. so i give it a stroke and its like nothing...straight to the floor? Wait: if the systems are seperate, I should be getting a hard pedal even with nothing in the rear lines (which is still empty) do I have to pump bleed them, (hard with no help) or can the one man brake bleeder work (hose into a 1/4 full bottle) still hard with no eyes on the passenger line? Im wondering if the piston is not getting back all the way to uncover the port inside the M/C? Maybe because the pushrod is too long or is not seated? Anyone know offhand if a 65 manual pushrod will work with a 67 manual M/C? maybe too long? M/C is good, I got a hard pedal on the bench with the plug bleeders...and no leaks anywhere. Baffled....
 
You need to fill the rear system, or brake pedal will go almost to floor with every stroke. Did you retrofit a two pot distribution block from a 1967 & up car?
 
Open both rear bleeders, and let it drain, till you get fluid comming from each bleeder. Do not let the resovoir go empty. Then bleed as normal.

barracudadave67
 
x2, and you should start the bleeding at the wheel farthest from the m/c, which would be right rear.

With nothing in the rear system, the brakes will work, and stop the car using only the fronts, but the pedal will go to the floor, and may not keep enough pressure to hold the car from moving once it's stopped.

I believe the prop valve will have the internal piston all the way to one side and trying to send more fluid to the rear, since it is starved.
 
didnt make lines, only bought them premade.
used distribution block out of disk/drum car
Ill gravity bleed rears as advised but still questioning why a dual system doesnt give a hard pedal when one is working properly and the other is shot (never happened to me, is that just how it works when one is down?) thanks.

ok just saw last post. Ill do rears and see if that helps.
 
pishta said:
didnt make lines, only bought them premade.
used distribution block out of disk/drum car
Ill gravity bleed rears as advised but still questioning why a dual system doesnt give a hard pedal when one is working properly and the other is shot (never happened to me, is that just how it works when one is down?) thanks.

ok just saw last post. Ill do rears and see if that helps.
Click to expand...

Yes, it is the way it works.
 
Cool. Will do. Thanks all. I tell you that mityvac is pretty cool for getting brakes set up, so far so good, I think? ;-)

Gravity bleeding: I know it works, but why didnt the fluid just flow out when I had the bleeder valve completely out? Must take a while, small passages?
 
To understand why you don't have a hard pedal, with only one system bled, you gotta understand the workings of the M/C, the use of the springs and valves, it's pretty cool...
 
inertia, you nailed it! I looked into the mysterious "combo valve" http://auto.howstuffworks.com/auto-parts/brakes/brake-types/master-brake2.htm
and found this..."The metering valve compensates for this, making the drum brakes engage just before the disc brakes. The metering valve ---does not allow any pressure to the disc brakes---- until a threshold pressure has been reached. The threshold pressure is low compared to the maximum pressure in the braking system, so the drum brakes just barely engage before the disc brakes kick in."
So that explains why The pedal goes to the floor, it is compressing the rear lines that are empty, never being able to overcome the threshhold pressure to allow the fronts to kick in. 'Course that doesnt explain how the fronts are suppose to work at all if the rear lines blows, but I dont have to understand everything, only what I can control. Knowledge is power....!
 
Hey!

That's what I said 4 posts earlier, only in not so technical terms.
 
YY1, Ok, I see it now. Sometimes the simpleton approach doesnt click with me.
 
'Course that doesnt explain how the fronts are suppose to work at all if the rear lines blows said:
the pedal side of the piston compresses a spring, (in the absence of hydraulic pressure in the rear reservoir/system), till it bottoms on the second piston, and compresses the fluid in the front system,.. thus the pedal seems to "go to the floor",, but actually just travels till it reaches the second system... cheers
Click to expand...
 
OK, consider this one closed. Attempted to bleed the back brakes with the mityvac and I wasnt pulling **** through the slave cylinders. Disconnected the hose from the pressure line (gravity bleeding started so I was on the right track) and still couldnt pull anything, flex hose was solid plugged with crap, couldn't even push a welding rod through it. $20 bucks later, I got a firm pedal. Thanks guys!
 
You must log in or register to reply here.
-

Back
Top