Odd brake problem

Re: Simple physics

Scott, I have no idea what is going on with your setup, I was only commenting on the statement concerning the "fix" of using a larger bore M/C.

I really does sound like you have air in the system, or a flex line is ballooning under pressure, or something in that realm. Possibly even a leak under high enough pressure.

Backing plates can flex, brake shoes too if they are over powered.

The term "soft" ------ try putting it into different terms.
I am mentally translating your "soft" into spongy----

When you are stopped, put your foot on the brake pedal, push hard enough to get a good solid feel, and hold it there for 10 seconds. Now can you still push the pedal any more after it has been held down?? Do this both with the engine running, and shut off.

 

Re: Simple physics

The S-10 master cylinder has the same bore size as that of the Jeep. I am using the same master cylinder and booster. I am also using the S-10 combination valve.

The one thing that I have noticed that is different with yours than the S-10 is something Warlock touched on earlier. On the S-10, the front/rear brake line sizes are different. The line size from the front M/C port thru the rear combination valve ports and to the rear brakes is 1/4". The line size from the rear M/C port thru the front combination ports to front brakes is 3/16". In my case I did reduce the rear line size after the combination valve to 3/16". Brakes work fine.

 

Re: Simple physics

I noticed that too. And did the same. I'm thinking of taking the Master cylinder back off and bench bleeding it some more.

 

Re: Simple physics

Long shot here, but try bench bleeding with the output ports on top-----lay the M/C on its side-----make sure you dont loose all the fluid from the reservoir when you do this.

As it is, the top half of the cylinder bore is above the output fittings, possibly trapping air.

 

One more thought-------are you getting full pedal travel???

Due to the setup being from another vehicle, could be that the Jeep floorboard or firewall is preventing the pedal from making a full stroke-----this can leave air trapped in front of the piston in the M/C.

Disconnect the brake lines, push down on the pedal----it should be clear of the floorboard when the pushrod bottoms in the cylinder.

Even if this is occurring, a proper bench bleeding will remove any air.

 

Just thinking here trying to come up with ideas.

1. Proportioning valve. Since I'm not sure how those work, and there isn't one on my setup, I would suspect that it could be a problem. OK, that's pretty weak but just an idea.

2. If the front and rear were really mismatched, the rear (drum brakes) could "bottom out" before the front (disc) brakes. It's possible that this could cause poor pedal feel.

If you've ever had a leak in a brake line and ended up with only one pair of brakes working you know what I mean. It doesn't feel right and almost feels "spongy".

 

After bench bleeding the master cylinder again, with no change. I think I suspect the problem. 1) I think I need more pedal travel. Because if I hold the pedal almost to the floor. The pedal is hard. 2) If I stand on the brakes going down the road, it barley locks up the front wheels. I think the problem there is, the pads are contaminated. I think I'll try putting new ones on.

Shouldn't of used the old pads.

 

Scott,
use Organic pads too. They will make it stop better with less pedal effort. In a light weight Jeep they will be fine. They don't wear out the rotors like semi-metallics or ceramics do either.

 

If the pads are not perfectly aligned with the rotor, there will be a soft feel until they wear in. It sounds like the pedal travel issue is on the right track to solving the problem.

 

If that proportioning block has a bleeder valve on it, there could be air in there as it's laying on it's side. Just a thought.

 

I've had some that were a bastard to bleed.
If I think it's the master, I've taken the lines off, threaded in a fitting plug and see if the master hold PSI when I'm standing on it.
I've had a few old masters go when you pump them up, (the cups rub past where they were stopping before and there's crud there that scores the cups).
I always gravity bleed rather than "pump and release method".
More than once I've "reversed bleed" the system.
Start at the farest away, (rt rear).
I use a turkey baster or my brake syringe.
suck the fluid outta the master.
Leave the cap off.
open the RR wheel bleeder and force fluid FROM the wheel cylinder to the master.
It'll take 4-5 times to get fresh fluid into it. the go to the LR and repete
Some words on this...............
When you refull the turkey baster or the syringe, before you put it on the bleeder, MAKE SURE YOU HAVE ALL THE AIR OUTTA THE LINE, OR YOU JUST PUT AIR BACK IN!!!!!!!!!!!!!!!!!!!!!!!!!
I use a clear hose from Lowes for this.
I've done this on motorcyels and a few jeeps also.
Try that, it should work
Joe
If it weren't for my jeep I'd have plenty of time and money for my family!bunny with a pancake

 

This is how it is done in the aviation world, you just force the air in the direction it already wants to go anyway.

It is easy to make your own pressure bleeder from a cheap garden sprayer, or you can pay big bucks to buy one made for the purpose.



http://www.aircraftspruce.com/catalog/lgpages/hydraulicBleedertank.php

In addition, this turns the job into something that can be done by a single person.

 

Just something to try. Sometimes the the metering block gets airbound in the MC even after its been bled. When you've bled out all of the lines and she still doesn't get hard, try giving the MC a few swift taps around it. This sometimes will free up you're metering block. I have had to this many times on various vehicles. Again, probably not the problem by the sounds but it's easy enough to do and you might get lucky.

 

You didn't notice my power brake booster?

 

Went to put the new brake pads on. Found that one of my brake calipers were stuck.