Ender

Get rid of your ABS... ABS is dumb

freegdr

do this two and really be done with it

TheDale

If you need to lock up the brakes going that slow, put it in Nuetral. Or press the damn pedal harder. Doesn't sound like ANYTHING is wrong. That is how the brakes are suppose to work.

Did you try bleeding them? Start at the furthest wheel away first. And then work your way closer to the Master Cylinder.

Northwoods Snowman

They have been bleed already. ABS stays. It's a DD and the insurance company likes the ABS. The brakes are adjusted already, the parking brake wouldn't work either if they weren't.

I'm not an idiot, I know you have to push the pedal to get the brakes to work. Arnold Schwarzenegger could push the pedal and it wouldn't make the rear brakes grab any better. Trust me, I've tried pushing the pedal harder. I don't "need" to lock the brakes up normally going that slow, but that's how you test them to make sure they're working. Don't you guys know this? I thought it was common sense, but I guess not! And NO they're NOT working how they're supposed to work. Do you REALLY think the parking brake should be stronger than the hydraulics???? Why even bother with hydraulics then, why not run a simple cable back from the pedal and be done with it? The hydraulic system is used because of it's force multiplication abilities and should be stronger than the mechanical parking brake. As I've said before if you read through the whole post, the hydraulic service brakes are designed to STOP the vehicle. The parking brake is only designed to keep it from moving, that's why it's called a "parking" brake. Which do you think should be more powerful? (Don't answer that, just think about it.)

Does anyone know how to test the master cylinder and/or proportioning valve?

freegdr

wrong the ebrake has nothing to do with the adjustment its cable operated the e brake willlock the tires if pulled b4 the hydros will

freegdr

did the brakes work correctly according to you b4 winter came

mjs302

Did you change the wheel cylinders also? If the brake fluid has never been flushed before, the rear wheel cylinders could be binding. (New ones should be $10-$15 each). Also, some vehicles with ABS are difficult to bleed without a power bleeder. The ABS units can trap pockets of air that are almost impossisle to get out by gravity or manual bleeding.
Your master cylinder and proportioning valve can be tested with a brake pressure gauge(www.otctools.com/products/brake_pressure_test_kit) but good luck finding a shop with one. A race fabricator is probably your best bet. Most will suggest just replacing those parts if they are suspect. A new master cylinder should be about $100 and a new prop. valve (which can only be purchased from the dealer) will most likely be about the same.

Northwoods Snowman

No, I'm right, the parking brake uses a lever action to spread the top part of the shoes (lever pulls forward on the bottom, pivots against the bar that runs between the shoes, and thus pushes outward on the top of the shoe where it's connected) the same way the hydraulics do. If the bottom is not adjusted, spreading the top will just push the shoes "around" and to the bottom and not actually force them against the drum. If they are not adjusted neither system (parking or service) will work properly. You should actually learn how the rear mechanism works.

To answer your other question, no the rear didn't work correctly when I bought it, I was expecting it just needed an adjustment....WRONG.

Looks like I found the problem: proportioning valve. I took it apart today to look at it and see if I could identify anything wrong, which I couldn't visually. Just as a test I took the rubber seal off the valve and reassembled it and bled the system again. Works like a champ now! It's not really the correct fix so I will probably need to find another in the JY or get a new one, as I effectively disabled it all together, but they rear works like it's supposed to now! I took it out in the snow and all four wheels will lock up at the same time now when going slow enough to keep the ABS from activating. When I'm on dry road, the thing stops WAY faster than it did before, with better pedal feel too. When hitting the brakes harder on slick surfaces (snow), the rear tries to lock up about the same time as the front does and the ABS kicks in for both ends (can tell by leaning out the door and watching the rear wheel, don't worry it was in a parking lot). It's amazing how much better the Jeep stops when both axles are trying to stop it! This also tells me the master cylinder is fine.

freegdr

maybe you should be a little more friendly to people who are trying to help you you will make a lot more friends on here glad you found the problem

Northwoods Snowman

Point taken. My original response was very sarcastic, but I toned it back to be less of an ***.

freegdr

so was my reply ,i edited it because i remembered what the warden told me about hunting people down that made me mad ................

Potatowalker

I looked at this thread because my rear brakes feel weak as well... didn't figure I'd have to skip every-other post to see the outcome!

Good job OP on tracking that down!

It's amazing how often the simple act of taking something apart and staring the pieces down individually before reassembling will make a difference! I've found this to be true with most things mechanical, not just my jeep. I think it has to do with miniscule irregularities in fitted parts, like seals & threaded fittings that seat flush. Chainring bolts on my Mtn.Bike is another good example!

jeans

Not to be a naysayer, but that is a band-aid fix, and really isn't safe. There is a o-ring around the valve to seal it to keep pressure from going where it isn't suppose to go. Sure, your brakes feel great, but are they working correctly...not a chance.

With that seal gone, you may have diminished the pressure going to the front brakes. Front brakes are your primary source of braking, and anything that makes them less functional isn't safe. Its a bigger safety issue the way it is now.

To check if your valve is faulty, look for little scratches, wear marks, etc. That would indicate that its worn out.

Id put that o-ring back on, and keep looking for the real problem, IMO.

Northwoods Snowman

I learned a couple of things about that little valve, that may surprise you guys, it did me. I spent probably an hour playing with it trying to figure out how it actually works. First off, it has no bearing on the front brakes. The front and rear are completely separated and the only "connection" between them is the little piston that move back and forth to activate the brake light switch. Even if that moves one direction, the front and rear brakes are still sealed off from each other. The other thing I learned is that the proportioning valve doesn't regulate pressure, it regulates FLOW. The way it's designed, you can "slowly" apply the brakes and end up pushing on them as hard as you possibly can, and you will have full pressure on the rear brakes. Now, if you suddenly jam on the brakes, the pressure wave traveling through the fluid from the quickly flowing fluid will expand the "seal" on the proportioning valve and restrict flow, thus limiting the rear brakes only when you hit the brakes really FAST.

I drew up cross section view to try and explain how it works (or at least what I figured out of it). Keep in mind it's not to scale and the seal fits tighter than it shows in my pictures. The green is the fluid path around the valve for the rear brakes. The blue is the seal, and the red parts on the seal are little bumps and ridges made on the seal to keep it from 100% sealing. The pink is where the seal expands to actually seal when it sees a high volume surge of fluid. The raised parts on the seal keep it from completely sealing to allow "normal" brake operation. I also found a picture to show the raised parts of the seal on the internet (not my picture).




I don't really want to leave the seal out of the valve, but I'm not to worried about it either if I can't find cheaper parts to replace it. The valve isn't supposed to do anything under normal braking anyway, just under extreme braking. If I do end up locking the rear, the ABS will kick in and not let it lock. I know it's only a band-aid, that's why I said "It's not really the correct fix..."

jeans

^ Sorry, your wrong. I cant say it any nicer. This is a simplified explanation:
Proportioning Valve
The proportioning valve reduces the pressure to the rear brakes. Regardless of what type of brakes a car has, the rear brakes require less force than the front brakes.
The amount of brake force that can be applied to a wheel without locking it depends on the amount of weight on the wheel. More weight means more brake force can be applied. If you have ever slammed on your brakes, you know that an abrupt stop makes your car lean forward. The front gets lower and the back gets higher. This is because a lot of weight is transferred to the front of the car when you stop. Also, most cars have more weight over the front wheels to start with because that is where the engine is located.
If equal braking force were applied at all four wheels during a stop, the rear wheels would lock up before the front wheels. The proportioning valve only lets a certain portion of the pressure through to the rear wheels so that the front wheels apply more braking force. If the proportioning valve were set to 70 percent and the brake pressure were 1,000 pounds per square inch (psi) for the front brakes, the rear brakes would get 700 psi.



Link for this info: http://auto.howstuffworks.com/auto-p...ter-brake2.htm


Taking that seal out has allowed full pressure to all four brakes. Its unsafe to drive your jeep like that, and its a safety hazard to others on the road.