Crazy sliding problem?

[jdub]

I am in need of some suggestions on what to do for the sliding problem I'm having. My wife's Cj7 is being pretty funny when it comes to stopping on the isc/snow. It's a automatic, so when you put it in gear and drive a little say out of the driveway it easily locks up the front two tires and slides for a while. I just figured it was the front disks vs. the rear drums(amc20)

Tonight I went over a patch of slick snow and hit the brakes, it slid forever! The scary part was that the rear wheels, no matter how hard I try I cant get them to lock up. Even on snow/ice!

You're probably thinking that the rear shoes need replacing... They are actually about 5 months old. You see that's where I think the problem is. I believe that I let some air in the lines when I did the replacement. That was confirmed when the braking was terrible after the replacement. I checked the adjuster to tighten it up in the drum assembly and I eventually tightened it up too much that I had to unwind it and start over. That led me to believe that there was an issue in the lines. Granted that this was the first brake bleed I've ever done on a car. Any votes that I need to do it again? I know I should because there is quite a bit of sediment? clouding up the fluid in the reservior.

Just trying to narrow down the problem....

Problem is, who wants to bleed brakes out in this cold? What do shops charge?

Suggestions welcome. I'm concerned for the drivers safety.

 

[Hickey]

I would replace the master cylinder (They are cheap) and flush the lines while you are at it.

 

[jdub]

I would replace the master cylinder (They are cheap) and flush the lines while you are at it.

The whole thing? Speaking of, it's a non power set up. I hear its hard to convert to a power brake booster???

 

[Hickey]

Yup. They are about $20. If you have contamination in the fluid system it will be a beast trying to flush it.

 

[jdub]

That's cool $20 for the MC

 

[jdub]

I forgot to mention that when braking the fronts can be stopped in snow and the rear tires will spin in drive, yeah like power braking but the motor is at an idle! Am I not getting any power/fluid back to those drums?

 

[wr250]

things to check:
slave cylinders for leakage. if one leaks replace both, the other will start leaking soon.
master cylinder for leakage look under the master cylinder.
the master could also be bypassing internally.
brake pedal feel "weird" or have excessive travel ? if so then you have a leak somewhere, the bypass issue, or water in the system.
its also possible your proportioning valve is clogged or a brake line is flattened or pinched (rock encounter?)

 

[DaveB]

Speaking of, it's a non power set up. I hear its hard to convert to a power brake booster???

Converting to a power brake setup isn't that bad. I had a 77 cj7 and the first time I went out on ice I thought I was on a sled. I had the exact same problem you are describing. The fronts would lock up and the rears did very little, and with the front sliding you couldn't steer it. I swapped the proportioning valve, master cylinder, bled the lines and re-adjusted the rear brakes all of which helped, but I never could quite make it work as well as I had hoped. I ended up replacing the power brake booster and that helped the most. The booster would bleed off while the brakes were being applied. Even after all of that the brakes never were as good as I wanted on the 77. I think jeep proportioning valves are set up to not send a lot of pressure to the rear brakes, but I may be wrong. When I built my cj8 I used a GM dual diapragm brake booster and the jeep stops very well. I've been too chicken to take it out on the salty roads so I don't know if it has similar problems on ice.

 

[waynehartwig]

Proportioning valves don't start 'proportioning' until seeing a heavy breaking condition. Simply coming up to a stop sign won't work it, you need a panic stop or etc. However, if you had air in the lines, it might have taken the rear brakes out of the loop - a safety feature of the valve - and applying all of the pressure to the front (because it thinks the rear have failed). You can also cause this issue when bleeding the brakes.

The sediment is an issue, but it's not causing the rear brakes not to work. This should be addressed. Since you already think you have air in the lines as it is, now would be a good time.

To bleed them, go around and open all of the bleeder screws and close them when a solid streem of fluid comes out. If you can't get the fluid in the rear, try pushing down on the brake peddle VERY slowly with the screw open. Your prop valve may als be stuck, but you won't be able to get it opened back up until you get most of the air out of lines. Pressing on the brake peddle with both feet will get it free'd up.

Once all of the corners have fluid coming out, take a rubber line and a glass masonry jar. Take some of the fluid that just came out while doing the last step and fill about 1/4 of the jar, stick the rubber line on the bleeding screw and into the jar. Have a buddy pump the brakes until they feel firm (about 3-4 times), have him hold them to the floor while you open the bleeder screw. Keep doing that until you have no more air bubbles showing in the jar.

You need to start at the furthest point from the master cylinder and finish at the closest. So rear right, rear left, front right, front left would be the order.

To adjust the rear brake shoes you take the tire off. And adjust them until the drum is dragging pretty good and your done. Put the tire back on.

Also, when you replaced the brakes, make sure you have the secondary pad in the front and the primary (longer lining) in the rear of the car. The secondary should also have the e brake cable hooked to it. The adjusters are also left and right only, and if they are swapped, when it self adjusts, it will get looser instead of tighter.

Hope this all helps!

 

[jdub]

No, thank you very much! What I've learned is that I need to go and re-blead the brakes, Be more carefull with the process and use the rubber hose/jar method for visual reference. If that doesn't work and I've isolated that air isn't the problem then I need to look into an upgradeed brake system.

I know that air is probably my problem. I'm still a bit unsure though. The master cylinder could be clogging up too, or just not functioning properly.
The brakes on my '52 were being funny, then went out all together. well the opposite they would compress all the calipers and you wouldn't be able to move the thing(air in the lines & expanding under heat?) I replaced the Master Cylinder, first I had to find it, not in the engine compartment, but now you can lock up those 33's in no time(4 chevy disks)!

To grasp all that's happening with the system, I think I have a pretty good idea now... I blead brakes on Mountain Bikes frequently and they're much more complicated. My question is with the old fluid, Should I try to cycle the old stuff through? Kinda do a flush?

 

[1993yj]

I beld my brakes on my YJ many times over, took out the proportioning valve, and put discs on the rear. This helped with the problem, but never entirely fixed it. From my experience, Jeeps are just so light that, with underpowered braking systems (especially if you have on tires that are bigger than stock), the front tires would always lock up in the snow while the rears would still just turn.

I would try re-bleeding them, replacing all of the old fluid with new stuff, but I would also reccomend a brake booster and if possible, larger brakes. Bigger tires and wheels theoretically require bigger brakes to slow them down.

I just don't drive my YJ in the snow anymore, but I know that is not always a possible solution.

 

[jdub]

Makes sense!

 

[waynehartwig]

Don't put the fluid from the jar back into the master cylinder. Or were you asking if you should drain all of the luid from the master and put fresh in? If so, I wouldn't worry about. Bleeding the brakes this way you might drain half of the fluid out anyway.

The reason for the jar isn't so much to see the air bubbles still, although it helps, but to keep from pulling air back in.

 

[jdub]

yeah, Cool. I'm interested in using this method. Seems less messy too. Grandmas' got some of those canning jars that i'm sure I can borrow.

 

[1993yj]

I use the jar method as well. Didn't know there were other ways to do it myself.

 

[waynehartwig]

When I do them, I just open the bleeder screws and wait for the air to stop and I'm done. I don't do the second step unless the first way doesn't work. Not the right way to do it, but more often than not, satisfactory.

 

[jdub]

Other method meaning just let the brake fluid spill. I'd like to keep it in a catch basin. With MTB brakes I like to use a larger medical type syringe and either push fluid up the lines. Or in this case use gravity as your friend and pull fluid out trying to pull all of the bubbles out. Then you invert the syringe with the bubbles in the top of the cylinder part of the syringe, you push back enough fluid to replace what you took from the caliper. Clear?

 

[Jay5.9L]

Fisrt off its not a good idea to use old brake fluid. Its hydroscopic by nature which means it like water and over time it can get contaminated with moisture. When you start braking hard, the water can boil creating gas pockets in your lines. It also can promote brake system corrosion. Brake fluid is cheap so always use new stuff

On my '86 CJ-7 the stock power brakes were terrible. I bought the Vanco power brake setup that uses a coret MC and a duel diaphram booster. It help a lot but I had a sneeky rear cylinder (think that what the little thing is called that pushes the pads out) that would allow air in the system after a few days. Got that taken care of and now it brakes like a car I can't lock them up on pavement but can lock the front on dirt. I think I need to readjust the rears. A lot fo people gave me crap for buying a system when you can hit the junk yard and make you own for a fraction of the cost. I did not have the time or the energy to reasearch and find everything. It was a bolt on and was cake to install . Good luck.

 

[BlackDog]

Had no idea Mountain bikes ran a hydraulic brake system.
Learn sumpin' ever day.

 

[waynehartwig]

Other method meaning just let the brake fluid spill. I'd like to keep it in a catch basin. With MTB brakes I like to use a larger medical type syringe and either push fluid up the lines. Or in this case use gravity as your friend and pull fluid out trying to pull all of the bubbles out. Then you invert the syringe with the bubbles in the top of the cylinder part of the syringe, you push back enough fluid to replace what you took from the caliper. Clear?

Not real clear, but it doesn't sound like a good method to use. You've gotta always go from the reservoir out, without pushing back in. Pushing back in will add air, push the contamination from the cylinder back into the lines, and etc. If it won't drip on it's own, I could see using the syringe as a suction device, but I wouldn't advise using it to push fluid in.