I'm still having issues with the brakes on my '72 Dart...

It acts like it needs to be bled... again...

Before I just start replacing parts, isn't there a way to verify brake line pressure with an inline gauge or something similar?

Thanks!

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Rob

I’m Mater
The Kentucky Poser

Have you ever used SPEEDBLEEDERS? Once you do you'll never go back.

http://www.speedbleeder.com/

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1964 Dart GT

When I was autocrossing a lot and being very hard on brakes I thought about swapping to speed bleeders, but I hardly ever do any aggressive driving anymore...

I don't mind bleeding them... I just wanna figure out what the dang problem is so I can drive this thing a little before I leave!

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Rob

I’m Mater
The Kentucky Poser

I would suspect blow by in master cylinder.

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67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

I'm one of the mellowest drivers you'll ever meet. I out grew my lead foot long ago.
Speedbleeders just make the process of bleeding your brakes easier.(In My Opinion)

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1964 Dart GT

You can tap a pressure gauge into the brake system like the pro stocks do for staging purposes. They make gauges that go as high as 2000PSI.

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If you didn't drive it there, it's not a street car.

wjajr, it does seem like the master cylinder, but it acted this same way when I had a cracked bleeder in one of the Wilwood calipers. I also have a line loc and adjustable proportioning valve.

These brakes have had this intermittent issue since they were installed. I just don't want to start replacing parts and have them not be the real issue.

Danarchy, it isn't that I don't WANT to drive aggressively...

I just haven't had the opportunity in quite awhile...

Exner Geek, that is what I was hoping. I've asked a couple brake shops and they don't have any gauges like that. They just replace parts I guess.

I'll look at getting a gauge myself and do some testing.

Thanks all!

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Rob

I’m Mater
The Kentucky Poser

My thought is that if I start at the master cylinder with the gauge and the problem is the same... I've confirmed that the master is, indeed, the culprit. I would cap the line after the gauge...

Is that not the right way of thinking? Does there NEED to be a moving part beyond the gauge for it to read the pressure..?

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Rob

I’m Mater
The Kentucky Poser

Rob, the gauge itself is the only 'moving part' you need. Doesn't matter what else is hooked up - if there's pressure in the system, it'll read it.

Usually if air can get into a system (15psi), fluid can get out (100's of psi). So you should be able to find some evidence if that's what's happening.
Internal M/C bypass can mimic an airy pedal, but leaves no external trace.

Pads sticking in their ways and soggy hoses also do weird things to pedal feel.

Especially since it's "intermittent", I also vote for a bad M/C, FWIW.

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O==\=/==O

"A mechanic is Somebody."
- Jim Preston

Thanks.

Most folks I've asked say it's the master... I just wanna make sure first, if possible.

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Rob

I’m Mater
The Kentucky Poser

For this type of problem, a gauge won't tell you much. Think about it, you know you don't have high pressure until the pedal gets firm, & that's what the gauge will show. There are two ways to go about checking the system for "source" of pedal drop.

The hard way is to get or make plugs for the various hard line connections- start at one port on the M/C & block it off. If the pedal is significantly better, go down the line towards the wheels to locate the fault. If not then block the second M/C port & repeat. If both ports are blocked & pedal is bad then it's the master itself.

The "easy" way is to (gently) clamp off all three bks hoses & check the pedal. If you have a bad pedal then it's likely to be the master. If good pedal then release one hose at a time to find the bad corner. I generally don't like to clamp off hoses as there is a slight possibility of causing internal damage to the hose (which would show as a restricted hose).

FWIW, the most common cause I see for an intermittant low pedal is a bypassing master cylinder.

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63 Valiant Wagon
225 - 4 bbl

Thanks for the reply. I looked the other night and what I plan to do is just what you recommend.

I will start at the master by plugging the main lines. That will likely ID the master as the issue. If not, I'll go down the system one fitting at a time.

I have braided lines, so also don't like the idea of pinching them off.

I'll report back if/when I figure it out and likely confirm most of your opinions that I need a new master cylinder.

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Rob

I’m Mater
The Kentucky Poser

It does appear that the master is bypassing on the rear reservoir (front brakes). In fact, you can even hear air being pushed with each pedal stroke until it builds pressure.

I got a new master cylinder from O'Reilly's for $21.

The adjustable brake push rod is on the way from Mancini. (The brake pedal is much higher than the gas pedal, which is awkward and makes aggressive autocross type driving nearly impossible.)

I'll get some speed bleeders for the Wilwood calipers once I confirm the correct size.

I'm hoping to do some autocrossing and drag racing with this thing before it goes into long term storage with everything else.

Chase and I are taking his SRT-4 to an SCCA autocross in Louisville this weekend. IF I get these brakes fixed by then I MAY take the Dart too...

This is the car in question: http://slantsix.org/forum/viewtopic.php ... light=hate

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Rob

I’m Mater
The Kentucky Poser

Well, this ain't gonna lower my brake pedal at all!

This adjustable pushrod will put my brake pedal up by my knee!



Are there different length pushrods for power versus manual brakes perhaps? Maybe the wrong pushrod was installed when we swapped to the newer aluminum master cylinder...

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Rob

I’m Mater
The Kentucky Poser

Can you screw the adjustable all of the way in to the end of the male threads, or is there some left over when it bottoms out?

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Thom

Cross-threaded is tighter than Lock-tite