Brakes have me baffled!

[mikelbeck]

I can't figure out what's up with my brakes.

Here's the background. The brakes in the car have always sucked. Until recently I had a stock cast iron master cylinder and drums all around. I upgraded the front to Wilwood discs, replaced the master cylinder with an aluminum unit I bought from GregZ @ MagnumHP a while ago, replaced both real wheel cylinders, replaced the line lock with a brane new unit and replaced all of the lines between the master, line lock and distribution block.

I've adjusted the rear brakes, bled them over and over, bled the fronts, and bled the master before I installed it. I replaced the line lock today, and when I did I re-bled the fronts. Nothing but pure fluid coming out, no air.

When I step on the pedal, it has about 3 inches of travel before I get anything. When I do get something, I hear and feel a "clunk" like I've hit something solid. And it doesn't stop at all while it's within that 3 inches. Once I get past that point, I have only about 1 inch of travel before I can't move it anymore, but it's not to the floor. In that 1 inch, I've got a little brakes or more brakes, but not enough to lock up the wheels. If I go in reverse about 30 MPH and jam on the pedal it'll lock up the wheels, but I don't think it'll do it going forward.

If I pump it up 4 or 5 times it'll get a little firmer - but not much. It'll give me about 1/2 more travel before I hit that solid stop. After I let off of it (after pumping) I hear the sound of fluid moving around, but I can't tell where it's coming from, but it's somewhere in the area of the master cylinder, the lines to/from it or the line lock.

Any ideas? Suggestions?

[mikelbeck]

If it makes any difference, here's the master cylinder I've got:

http://www.magnumhp.com/showdetails.php?ITEM=MAG-1

It's an aluminum unit with a 1-1/16" bore.

One other thing - I had to use a 4 to 2 bolt adapter (this one: http://www.magnumhp.com/are-02.jpg ). Is it possible that my pushrod is too short now?

[onehellofadart]

I believe the clunk is the Master. Maybe that home made o ring is not working. See if there is any fluid on the push rod that is in there now.
The adapter plate is what 1/2" total thick?
Maybe you need an adjustable push rod to cure the long travel.

[sickt7cuda]

It sounds like you're not getting full travel of the piston in the Master and that's why you gotta pump it a couple of times to build up the pressure. I would check the line pressure first. PSI range can go up to 1700 but you'll never get that high without a booster. You should get 600psi or so.

If line pressure is low, you may need to extend the rod into the MC. Before you go out and buy one, try juryrigging an extension to ensure full travel and see if line pressure increases.

[mikelbeck]

I believe the clunk is the Master. Maybe that home made o ring is not working. See if there is any fluid on the push rod that is in there now.

What does it mean if there's fluid on the pushrod?

The adapter plate is what 1/2" total thick?
Maybe you need an adjustable push rod to cure the long travel.

Yeah, that's what I'm thinking...

Once I have an adjustable pushrod, how do I know how much to adjust it? Should I just pull the old one, measure the thinkness of the adapter plate and make the new one that much longer than the old one?

[mikelbeck]

It sounds like you're not getting full travel of the piston in the Master and that's why you gotta pump it a couple of times to build up the pressure. I would check the line pressure first. PSI range can go up to 1700 but you'll never get that high without a booster. You should get 600psi or so.

If line pressure is low, you may need to extend the rod into the MC. Before you go out and buy one, try juryrigging an extension to ensure full travel and see if line pressure increases.

Unfortunately, I don't have any way to check the line pressure.

If the pushrod is longer, wouldn't I have to push the brake pedal more to get the same effect? I'm thinking if it's longer, when I'm off the brake it's going to move the pedal up the difference between my current pushrod and the longer pushrod. Then I'd have to move it that much more? Or is that wrong?

[onehellofadart]

I believe the clunk is the Master. Maybe that home made o ring is not working. See if there is any fluid on the push rod that is in there now.

What does it mean if there's fluid on the pushrod?

Fluid would be pushing through the seal.

The adapter plate is what 1/2" total thick?
Maybe you need an adjustable push rod to cure the long travel.

Yeah, that's what I'm thinking...

Once I have an adjustable pushrod, how do I know how much to adjust it? Should I just pull the old one, measure the thinkness of the adapter plate and make the new one that much longer than the old one?

I would think so.

[onehellofadart]

It sounds like you're not getting full travel of the piston in the Master and that's why you gotta pump it a couple of times to build up the pressure. I would check the line pressure first. PSI range can go up to 1700 but you'll never get that high without a booster. You should get 600psi or so.

If line pressure is low, you may need to extend the rod into the MC. Before you go out and buy one, try juryrigging an extension to ensure full travel and see if line pressure increases.

Unfortunately, I don't have any way to check the line pressure.

If the pushrod is longer, wouldn't I have to push the brake pedal more to get the same effect? I'm thinking if it's longer, when I'm off the brake it's going to move the pedal up the difference between my current pushrod and the longer pushrod. Then I'd have to move it that much more? Or is that wrong?

I would think if it is the problem that the push rod is to short that when you extend it you would not have to pump it up to complete the stroke of the Master. If the rod is too short now has it effected your pedal return position now?

[mikelbeck]

I would think if it is the problem that the push rod is to short that when you extend it you would not have to pump it up to complete the stroke of the Master. If the rod is too short now has it effected your pedal return position now?

I'm not sure if the pedal is any different from what it was with the old master, I never really took notice of where it was before.

I been thinking about this... If it's too short, it's not making it all the way into the master, so I'm not getting the full effect of stepping on the pedal, right? With a longer one, the pedal may sit a little higher initially, but when I step on it, it'll go further into the master, moving more fluid, and giving more stopping power. Does that sound right?

[mikelbeck]

Why is there such a big difference in the price of this part? (Mopar P5249316)

Jegs has it for $62.99.
Summit has it for $65.95, but no stock.
Mancini has it for $70.95, but they also have their own version for $39.95.
Moparts Racing has it for $55.00.

[onehellofadart]

I would think if it is the problem that the push rod is to short that when you extend it you would not have to pump it up to complete the stroke of the Master. If the rod is too short now has it effected your pedal return position now?

I'm not sure if the pedal is any different from what it was with the old master, I never really took notice of where it was before.

I been thinking about this... If it's too short, it's not making it all the way into the master, so I'm not getting the full effect of stepping on the pedal, right? With a longer one, the pedal may sit a little higher initially, but when I step on it, it'll go further into the master, moving more fluid, and giving more stopping power. Does that sound right?

I think thats what I said.
I don't know why there would be such a price diff in the same part.

[mikelbeck]

I would think if it is the problem that the push rod is to short that when you extend it you would not have to pump it up to complete the stroke of the Master. If the rod is too short now has it effected your pedal return position now?

I'm not sure if the pedal is any different from what it was with the old master, I never really took notice of where it was before.

I been thinking about this... If it's too short, it's not making it all the way into the master, so I'm not getting the full effect of stepping on the pedal, right? With a longer one, the pedal may sit a little higher initially, but when I step on it, it'll go further into the master, moving more fluid, and giving more stopping power. Does that sound right?

I think thats what I said.

LOL, I wasn't sure, I had a hard time wrapping my head around what you said.

[sickt7cuda]

I been thinking about this... If it's too short, it's not making it all the way into the master, so I'm not getting the full effect of stepping on the pedal, right? With a longer one, the pedal may sit a little higher initially, but when I step on it, it'll go further into the master, moving more fluid, and giving more stopping power. Does that sound right?

Sounds right to me.

[B3Cuda]

It is my understanding that when you change over to the new style master cylinder that you need to use the adjustable pushrod,

I am not sure how it works exactly but you need to watch out for the brake pedal ratio as well. You could wind up needing more foot pressure to make it stop.

As for the spongy pedal did you bench bleed the master before installing it ?? This is very important to do.

[mikelbeck]

It is my understanding that when you change over to the new style master cylinder that you need to use the adjustable pushrod,

I am not sure how it works exactly but you need to watch out for the brake pedal ratio as well. You could wind up needing more foot pressure to make it stop.

As for the spongy pedal did you bench bleed the master before installing it ?? This is very important to do.

I bled the master on the bench before installing it, and then again once it was installed.

[mikelbeck]

Ok, gentlemen... The verdict is in.

The master cylinder was no good.

Before I took out the stock distribution block, I bled all four corners again. The same result, a mushy pedal.

So I stopped in at AutoZone and picked up a new (not re-man) master for an '81 D150, bench bled it for 40 minutes - made sure not a single bubble was to be found anywhere - installed it and bled everything again.

I've got brakes! And a good pedal!

I'm still going to remove the stock valve and put in the Wilwood proportioning valve, but for the time being it stops just fine. Even the line lock works, I can hold the car up to around 3500 before it pulls through the brakes. I can lock up all four wheels without pumping the pedal.

[sickt7cuda]

"You Da Man"!

Now go do some Racin'!!!!

[mikelbeck]

"You Da Man"!

Now go do some Racin'!!!!

Sunday! Gonna win me a Wally @ E-Town!

That is, if I don't lose first round. #-o

[onehellofadart]

Glad you found the problem. =D>