Double pump brakes

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diymirage

diymirage

HP@idle > hondaHP@redline
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The car is a 71 duster with a hodgepodge of brake parts on it, scarebird conversion up front, 68 dart 8 3/4 on the rear (with the associated brakes) and a newer master cylinder (I believe it's a double reservoir or whatever it's called)

When I'm driving it, often times the first pump of the brakes goes to the floor, the second is nice and solid

I bench bled the master when I swapped it out (a few years ago)

What should be the first thing to do...bleed all 4 brakes ?
 
You have a disc master?

Screenshot_20230811-202854_Chrome.jpg
 
I have been having brake issues since swapping out to an 8 3/4.

I reused the old drums (over the cut limit) and new shoes. the arcs are very different. It will take a lot on miles till the pads ware into the drums.

I changed the cyls at the same time.

I thought I had bleed the brakes enough, not by a long shot!

I ended up putting a pint of fluid through the lines and now have a firm pedal, but the braking effort is slightly greater due to the arcs of the drum / shoes


Bleed baby bleed
 
OP how does the pedal feel? It should be rock hard almost. If not you have air in the system. Otherwise I'd look into bleeding the brakes

For those claiming you "must" have a disc brake master, I have 4 wheel disc. My pedal, always one stroke, goes down just less than half way and is ROCK hard. My car has 73/4 Duster/ Demon front brakes and a Ford/ Lincoln Versailles factory disk brake, 9" rear axle
 
I am wondering when you changed the rear wheel cylinders, that the diameter of the cylinders somehow changed.
 
67Dart273 said:
OP how does the pedal feel? It should be rock hard almost. If not you have air in the system. Otherwise I'd look into bleeding the brakes

For those claiming you "must" have a disc brake master, I have 4 wheel disc. My pedal, always one stroke, goes down just less than half way and is ROCK hard. My car has 73/4 Duster/ Demon front brakes and a Ford/ Lincoln Versailles factory disk brake, 9" rear axle
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When it doesn't go through the floor, it feels fine, solid
sireland67 said:
I am wondering when you changed the rear wheel cylinders, that the diameter of the cylinders somehow changed.
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Not sure, I changed the rear end ages ago, long before this pedal feel became an issue
 
This has just developed? If so I'd say your master is bad. What happens when you panic hit the peddle? Is it hard then?
 
Bodyperson said:
This has just developed? If so I'd say your master is bad. What happens when you panic hit the peddle? Is it hard then?
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No, it's been a bit of an ongoing condition
After dragging my feet for years I finally got my transmission rebuild this month and now I'm able to drive it...so it's something I want to address now

Honestly not sure what happens when I stomp on it

I will look into it and report back
 
It was in there, but it had broken off
As soon as I took the drum off (which was entirely too easy, huge clue right there) it simply fell on the ground

I adjusted the shoes untill the drum started to catch on the way off and it feels way better

I ran into an issue on the driver side, (one lug nut seized up and the stud spun loose) so when i get that fixed I'll have a look on that side
 
Did you bleed the lines at the master cylinder after you installed it?
 
diymirage said:
The car is a 71 duster with a hodgepodge of brake parts on it, scarebird conversion up front, 68 dart 8 3/4 on the rear (with the associated brakes) and a newer master cylinder (I believe it's a double reservoir or whatever it's called)

When I'm driving it, often times the first pump of the brakes goes to the floor, the second is nice and solid

I bench bled the master when I swapped it out (a few years ago)

What should be the first thing to do...bleed all 4 brakes ?
Click to expand...
Adjust the rears and bleed all 4. Start bleeding furthest from the master cylinder. RR LR, RF, LF. After bleeding at the wheels, I would crack the lines at the master just in case.
 
There is an easy check for air in the systems .
If the pedal is hard, and near the top, do the "air test".
Set the emerg to move the shoes out to the drum, so they can't return by the springs.
Have the brake pedal pumped a coupla times and held down, remove the m/c cap and watch the fluid surface for fluid return.
Have the pedal released, - with the shoes pegged against the drums, and the calipers pads that merely "relax", - there should be barely any return, if there is a heavy return, or " fountain" the only thing that can cause that return is air that you compressed with the pedal.
Bleed whichever system has the return .
Brake fluid is excellent paint remover, flush with water immediately if any gets on your paint.
Cheers.
 
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RustyRatRod said:
Did you bleed the lines at the master cylinder after you installed it?
Click to expand...
you know, i must have, but i couldnt tell you for sure i did
i went back through the paperwork and i changed that master cylinder back in 2017

i remember bench bleeding it, and im sure i bled the lines, i just dont remember it

after i adjusted the rear brakes yesterday i was able to slam on it and lock all 4 of em up with half a pump (in the drive way of course, not going terribly fast)
so i think that solved the issue, but i will bleed all four corners, just to be sure
 
If the same fault shows up again, buy a master cylinder. They do bypass internally at random. Works fine for days then suddenly the pedal goes to the floor. A quick "pump again" response makes brakes. I've aways called this event "warning shots" fired by a failing master cylinder. I don't believe this is an engineer's brainchild safety feature either. I believe its a unexpected blessing for all of us.
The ones that sticks in my memory the most was a big ol' green 73 Impala we owned. Wife complained that it had happened a couple of times while she was driving it to and from, so we traded rides. I drove the thing to and from almost a week before it happened to me.
 
My 74 Valiant, which is a long story, always "starts out" with a great pedal, but as you drive it, the thing gets more and more mushy. It needs a master
 
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