BRAKE HELP needed asap, tnx

[BrockGrimes]

Ok I was sitting at a light with my foot on the brake, when all of a sudden the pedal just eased on down to the floor and I started rolling forward, so I let off the brake and mashed it again and had full pedal. Drove it around somemore going where I needed to go then back home, with no further incident. Today was gonna take the wife out to grab a burger, had my foot on the brake and when I started it up the brake pressure bleed off on the pedle went to the floot, let off and mashed it got my pedal back, so I took it for a short drive to see if it would hold, near the end of the drive it seemed like I was starting to loose brake pressure. WTF?

When it first happened I stopped in a parking lot and looked underneth and didn't see any brake fluid leaks or spray on the inside of the tires. This time well It's dark and wet outside and I'll have to check it out tomorrow after I get off work. Driving the wifes vehicle in. Jeep in Garage.

What do you guys think? Searched post couldn't find anything, looked at my chiltons no help there, need help miss jeep already, yes sad I know.....
Help please!

Oh one more thing when it happened both times the Brake light in the dash came on, when I mashed the pedal and got pressure again the light went out.

[Dukes69]

bad master cylinder

[avnative]

bad master cylinder

<<<<X2

[goodtimes]

X3.

Be sure that when you buy a new master cylinder, you get a NEW master cylinder. For your own safety, and that of anyone who rides in your jeep or on the road while you are driving your jeep, do not buy a "reconditioned" or "remanufactured" master cylinder. I'm running late for work, so no time for a long explaination, but lets just say that I used to work in the chassis division of a large corporation who supplies a very large percentage of braking components for the automotive aftermarket, and I will walk before I use anything but NEW master cylinders.

[nagal]

Not to :hijack: but does this apply to calipers as well?

I am noticing while checking prices on WJ stuff no one is listing new just remanufactured.

[D4x4Fish]

bad master cylinder

x4

Not to :hijack: but does this apply to calipers as well?

The master cylinder is a pump which leaks interal, not holding PSI, no signs outside. Thats why when you pump the brake pedal you get psi for awhile intill it bleeds down and no brakes.

Calipers are a piston or Ram, when leaking has fuild showing outside, and no PSI.

[Dukes69]

Not to :hijack: but does this apply to calipers as well?

I am noticing while checking prices on WJ stuff no one is listing new just remanufactured.

Probably. IIRC, the reman. units are basically cleaned and fitted with oversized parts. The tolerences are rather iffy.

[sam 15]

X5

[goodtimes]

Probably. IIRC, the reman. units are basically cleaned and fitted with oversized parts. The tolerences are rather iffy.

I wish that was the only problem.

Here's the deal. A master cylinder or Caliper comes in as a core (what someone returned to the parts store to get their "core charge" back). The snap rings get pulled, seals and piston blown out, the bleed screw (as applicable) gets removed. The piston (calipers only, master cylinders usually get new pistons) gets tossed in one box, the cylinder gets tossed in another. Both crates get shipped to Mexico where they get dipped in some cleaner that is illegal in the states. Parts get shipped back.

Here is where it gets scary. Master cylinder bores are cleaned with a wire brush on the end of a drill. Calipers get sent out to plate (as applicable), then treated with the same wire brush. New seals are put on the pistons, they are sprayed with a assembly fluid (which is compatable with brake fluid), the whole thing gets pushed together with a air cylinder, then pressure tested (with air), and vacuum tested. Then box and ship.

So what was the scary part? You engineers and machinists and mechanics probably picked it out. A good majority of people don't. The problem is with the wire brush. The brush removes the rust, dirt, etc., but does nothing to address any burrs, nicks, scratches, or pits in the surface of the cylinder. Any of these will cause the seal to wear out very rapidly (sometimes in a matter of 5 - 10 cycles). But since the seals held for the first cycle (when it was tested), it is considered good, and it gets shipped.

A few years ago, I bought a re-con master cylinder for my '80 GMC. It lasted about a month. I exchanged it (lifetime warranty). This one lasted less than a day. I exchanged it. The third one lasted a week or so. I exchanged it. The 4th one lasted a little longer, but not long enough for me to not get pissed off about it. This one I didn't return, I pulled it apart, and found the seal was torn, and the surface finish of the bore was rough (pitting from rust), and had 2 or 3 small burrs on it. The next cylinder I bought was new, it is still in the truck and working fine.

There is a alternative though.....you can buy rebuild kits for most master cylinders. That plus a brake hone will go along way towards fixing your problem. Just pay careful attention to the bore dimensions, and make sure you get the surface finish at least close to what it is supposed to be.

[mrblaine]

I wish that was the only problem.

Here's the deal. A master cylinder or Caliper comes in as a core (what someone returned to the parts store to get their "core charge" back). The snap rings get pulled, seals and piston blown out, the bleed screw (as applicable) gets removed. The piston (calipers only, master cylinders usually get new pistons) gets tossed in one box, the cylinder gets tossed in another. Both crates get shipped to Mexico where they get dipped in some cleaner that is illegal in the states. Parts get shipped back.

Here is where it gets scary. Master cylinder bores are cleaned with a wire brush on the end of a drill. Calipers get sent out to plate (as applicable), then treated with the same wire brush. New seals are put on the pistons, they are sprayed with a assembly fluid (which is compatable with brake fluid), the whole thing gets pushed together with a air cylinder, then pressure tested (with air), and vacuum tested. Then box and ship.

So what was the scary part? You engineers and machinists and mechanics probably picked it out. A good majority of people don't. The problem is with the wire brush. The brush removes the rust, dirt, etc., but does nothing to address any burrs, nicks, scratches, or pits in the surface of the cylinder. Any of these will cause the seal to wear out very rapidly (sometimes in a matter of 5 - 10 cycles). But since the seals held for the first cycle (when it was tested), it is considered good, and it gets shipped.

A few years ago, I bought a re-con master cylinder for my '80 GMC. It lasted about a month. I exchanged it (lifetime warranty). This one lasted less than a day. I exchanged it. The third one lasted a week or so. I exchanged it. The 4th one lasted a little longer, but not long enough for me to not get pissed off about it. This one I didn't return, I pulled it apart, and found the seal was torn, and the surface finish of the bore was rough (pitting from rust), and had 2 or 3 small burrs on it. The next cylinder I bought was new, it is still in the truck and working fine.

There is a alternative though.....you can buy rebuild kits for most master cylinders. That plus a brake hone will go along way towards fixing your problem. Just pay careful attention to the bore dimensions, and make sure you get the surface finish at least close to what it is supposed to be.

Since you have a TJ, this will apply to you. I don't know if it applies to YJ's or not. At last check at my very reputable undercar supplier, you could not get a reman TJ master. Only new ones were available. Been that way since the TJ was intro'd.

[BrockGrimes]

Popped the top off the master cylinder, and the front part is full to the top with fluid but the rear is half way if not almost empty. Crawled around underneth and don't see any signs of leakage, nor do I see any around the mastercylinder. I had the wife mash the brakes while it was running the front brake calipers barely moved, couldn't really tell ont he rear drums, I got in and mashed the brakes and it's like nothing is there, little or no brakes, even after pumping them. No sign of leakage, but the rear part ot the master cylinder is low or almost empty and the front is maxed out full to the brim. Thoughts? Mastercylinder or brake booster or both?
If it's the master cylinder, would one pulled from the junk yard be ok, what would I need to look for? Money is minimal right now, driving the wifes PT. Thanks for the info so far what you think now from the looks of the above?

[mrblaine]

If it's the master cylinder, would one pulled from the junk yard be ok, what would I need to look for?

There's a few things in life you don't skimp on. Don't buy cheap condoms, worn out tires and junkyard parts for your brake system unless it was out of a less than 10,000 mile recently rolled vehicle.

You already own a used master cylinder, why do you want another one?

[goodtimes]

Since you have a TJ, this will apply to you. I don't know if it applies to YJ's or not. At last check at my very reputable undercar supplier, you could not get a reman TJ master. Only new ones were available. Been that way since the TJ was intro'd.

That is very possible. IIRC all of the master cylinders we re-manned were the cast pieces. I have not had to replace the master in my jeep.

Your not buying from "undercar parts" are you? We used to supply them with parts......

[mrblaine]

That is very possible. IIRC all of the master cylinders we re-manned were the cast pieces. I have not had to replace the master in my jeep.

Your not buying from "undercar parts" are you? We used to supply them with parts......

Not undercar, South County Brake Supply. South Orange County CA.