Brake Wars..Episode 3.. The mechanic strikes out..again

[midnight sun]

Well the symtoms are common for a residual valve, but if it's still doing it with a new valve, the only thing left are the front hoses and calipers. See how far the caliper pistons are retracting, it should be just enough to release the rotor.

I hate to ask this, but are you sure you installed the valve the correct way? Arrow points to the brake calipers.

Yup, the arrow wuz/iz pointing correctly.  The calipers are retracting just enough to release the rotor.  Today I made a new brakeline without any residual valve at all.  Still the same.  Another funny thing I noticed today was that when I bleed the rear brakes, the pedal goes all the way to the floor.   When I bleed the front, the pedal goes about half way down and then its as if it is hitting something.    It just stops hard against whatever! FWIW I am using speed bleeders.  A friend of mine is coming over tomorrow and we are going to start from scratch.  Maybe he can see something I have been overlooking.

[midnight sun]

Here's one way to do it at home . . . no worse than a regular driveway bleeding job.

Make a plate - 1/2" aluminum works well.

Drill and tap it for a couple of Schrader Tank Valves.
One over each reservoir.
(Schrader Tank Valves are a fitting with a tire stem on one end and 1/8-NPT on the other.  Available most real parts houses.)

Use copper coat to glue a thick piece of Vellumoid gasket paper to the plate bottom.

Bolt or clamp - as the case may be - the plate to the M/C.

Set your regulated dry air supply to 35# or so.

Bleed one wheel.

Refill the reservoir.

Repeat as necessary.

If you don't get carried away there's plenty of fluid in the M/C reservoirs to bleed a wheel.

The obvious problem is pumping air from the air supply into the lines so be careful.

Thanks Jay, I may just try this.  Besides it will give me something new to build a try instead of just incessantly bleeding the brakes and going through brake fluid!!

[Bruce Dorsi]

Another funny thing I noticed today was that when I bleed the rear brakes, the pedal goes all the way to the floor.   When I bleed the front, the pedal goes about half way down and then its as if it is hitting something.    It just stops hard against whatever!

I may be mistaken, but I think the reason the pedal only goes half way down when bleeding the front brakes, is because the rear shoes have expanded against the drums, and there is no further movement possible.

The fact that there is no resistance while bleeding the rear brakes seems to indicate the front brakes are not working properly, but you already know that!


Is the m/c port which is closest to the booster (pushrod end) connected to the front discs or the rear drums?

When all lines are connected and bleeders are closed, does a second pump of the pedal create a firm pedal, or does it stay soft?

Is there a possibility that the speed bleeders are ingesting air into the calipers?

It seems I have more questions for you, than answers!

[MrMopar64]

Another thought..... Are you sure that all the speed bleeders are working
maybe one is not doing what it should. I'm guessing your doing this by yourself sense your using speed bleeders so no one there to see that fluid is coming out

MM64  

[Bob Paulin]

Another funny thing I noticed today was that when I bleed the rear brakes, the pedal goes all the way to the floor.   When I bleed the front, the pedal goes about half way down and then its as if it is hitting something.    It just stops hard against whatever! FWIW I am using speed bleeders.  A friend of mine is coming over tomorrow and we are going to start from scratch.  Maybe he can see something I have been overlooking.

It actually IS hitting something!

The rear piston in the master cylinder is bottoming out against the front piston.

Under normal conditions, the pedal pushrod has a mechanical connection against the rear piston in the Master Cylinder while the front piston is driven hydraulically by pressure developed by the rear piston.

If you lose pressure in the front brakes hydraulic system (rear piston), the piston hits the front piston and mechanically drives the front piston (rear brakes) in order to still have brakes.

The question in my mind is how come the front MC piston (rear brakes) isn't bottoming out against the end of the bore and allowing the rear piston (front brakes) to build pressure when you open up the rear brakes?

That's what should be happening when a "leak" (opening the bleeder) develops in the rear hydraulic system.

Without going back through all the posts.....did you bench-bleed the MC before bolting it on?.....and, I mean _bench-bleed_ - not disconnecting the lines and bleeding it with the pedal.

When you bench-bleed you can actually force the pistons all the way to the end of the bore.

B.P.


PS - I used to sell the "speed bleeders" when i managed the NAPA store. I wasn't impressed by them.....but, then again, I have a pressure bleeder.

[exsedan]

Is the parking brake functional and adjusted properly? If the levers in the rear system are not held in the correct position by the cables, it creates excessive travel in the wheel cylinder and the front master cylinder piston may be bottoming out prior to complete application of the brake shoes to the drums.

This is just a long shot, but I did neglect to complete the parking brake system on a car many years ago, and had similar brake problems. Just recently had problems on a system where the adjustment was too tight and created a "lock-up" in the front brake system..................jb EXSEDAN

[Mikej]

Did you have a hard peddle when you unhook the flex line and plugged then at the calipers. Front.  If you are getting bubbles every time you bleed the front brakes, you are not getting the air out or air is coming back in around the bleeder or pistons or line connections. I would think the lines and bleeder would show up as a leak under pressure. Also is the peddle better if you pump the brakes? Does it go down after it sets for a minute? You can compress air( spongy brakes). You can't compress fluid but you might not be getting on one sroke either. Luck

[midnight sun]

Is the m/c port which is closest to the booster (pushrod end) connected to the front discs or the rear drums?

When all lines are connected and bleeders are closed, does a second pump of the pedal create a firm pedal, or does it stay soft?

Is there a possibility that the speed bleeders are ingesting air into the calipers?

The port closest to the booster goes to the front system

Second pump of the pedal still results in a soft pedal.

Am going to try regular bleeders today.

[midnight sun]

Without going back through all the posts.....did you bench-bleed the MC before bolting it on?.....and, I mean _bench-bleed_ - not disconnecting the lines and bleeding it with the pedal.

.

I did bench bleed the MC before installation.  I also did it again yesterday on the car.  I modified some brake lines and curled them back into the top of each reservoir from the outlet ports and pumped the pedal several times to remove any air.

[midnight sun]

The question in my mind is how come the front MC piston (rear brakes) isn't bottoming out against the end of the bore and allowing the rear piston (front brakes) to build pressure when you open up the rear brakes?

That's what should be happening when a "leak" (opening the bleeder) develops in the rear hydraulic system.

Regarding your above question, what would that indicate to you i.e. the front piston not bottoming out against the end of the bore?

Just curious as usual!!

[enjenjo]

Jsck, this isn't brain surgury. If shutting off the front calipers cures the problem, then the cause is there. Correcting it can be the hard part. If the  pistons are not retracting too far, then it has to be air in the calipers.

[Bob Paulin]

The question in my mind is how come the front MC piston (rear brakes) isn't bottoming out against the end of the bore and allowing the rear piston (front brakes) to build pressure when you open up the rear brakes?

That's what should be happening when a "leak" (opening the bleeder) develops in the rear hydraulic system.

Regarding your above question, what would that indicate to you i.e. the front piston not bottoming out against the end of the bore?

Just curious as usual!!

Actually, it just might be bottoming out okay, but there is enough air in the front system to allow the pedal to drop.....

.....I'm reading that blocking the front hydraulic system off at the M.C. tightens things up nicely, so that would point to the problem being in the front hydraulic system.

I know it has been pointed out earlier, but I'm going with the way the calipers are mounted.

On many calipers, the bleeder passage is drilled in such a way that the bleeder is NOT at the top of the caliper when the bleeder port opening inside the cylinder bore IS. The bleeder screw could be rotated nearly 90° from the 12 O'Clock position.

It's a little different from drum brake wheel cylinders.

B.P.

[midnight sun]

I made a little progress today on the brake saga.  First I made up a new line going to the front without any residual valve.  Then I removed the speed bleeders from the from calipers and installed the stock bleeders.  Then I bypassed the T where the fluid goes to the drivers side caliper so that I was only getting fluid to the passenger side caliper.  I then called upon my able assistant (wife) and we bled the passenger side.  Voila!! Good hard pedal.  Then I reversed the process and blocked off the T to the passenger side and bled the drivers side caliper.  Again, good solid pedal.  I then hooked up everything back normally and lost about half of the good solid pedal I had.  Re-bled both sides again.  It is a lot better than it was but it still puzzles me why they will bleed good separately but when everything is hooked together I lose some of the good pedal.  Almost like there is not enough pressure/fluid to activate both calipers at the same time. Sooner or later Im gonna get there.  At least Im making progress!!

[C9]

I've been following this - as I'm sure many of us are - for the educational value.

This latest is most interesting.

Is there any chance the brake line runs up and then down again so that an air bubble could be trapped in the line with no way out?

A shot in the dark, I know, but....

[river1]

i've also been following this for educational reasons.

you've isolated everything down to the calipers.

are your calipers new? used? rebuilt?

used i think you got a couple of bad ones.

new/rebuilt i'm thinkin when they were put together (by humans) they got bad parts in them.

replace the calipers i think the problem will go away. if you have already tried that, try getting them from a different source.

good luck

jim