Brake issues

[Jenny Gladden Brackin]

I've got a 1978 CJ5. I started having issues with the brakes. It started slowly with me having to pump the brakes to stop. I checked the fluid and it was a little low, but I haven't found any leaks. Now when I drive it, the first time I push the pedal, it goes to the floor. The second time, I have pressure. 7 months ago I replaced all the hardware in the rear drums, changed a few lines, and bled the brakes. Took a look at the front brakes today. It needs new pads and rotors. The calipers are working but I don't know if it's putting out enough compression. I also adjusted the rear drums again. Fluid level was still good. Any ideas where to look for the problem?

 

[greg92jeepxj]

Welcome to jeepz.com . If your confident that the entire system is properly bled and no air exists in any line from fromt to rear , it may be time for master cylinder replacement. Even if there is no sign of a leak from the master cylinder's rear seal where it mounts to the power booster or firewall if not equipped with power brakes , the internal rubber plungers are most likely worn. This is not only due to wear but from the bleeding process . Since the brakes were fine not too long ago before the brake bleeding was performed , I suspect that is key .
normal travel for the internal piston is a short stroke and any rust that eventually builds up in a cast iron master cylinder or corrosion inn aluminum master cylinder is the cause.
the bleeding process involves long pedal strokes ( if bleeding has been performed in this manner ) and the piston travels further in the master cylinder bore .
when this occurs , the rubber plunger seals ride over the rusted or corroded part of the bore causing damage to the plunger seals . This in turn leads to an internal leak.
Althoigh there may be no signs of external leaks , the internal piston isn't producing the needed pressure to apply the pressure to the rear wheel cylinders and the front calipers .
A simple test is to spin a tire on the front and on the rear to see if the brake in the wheel being spun is grabbing very well. You will have to really apply force to confirm this . Since the first pedal stroke is weak , the loss of the brakes ability to grab hard would be noticed as opposed to a stronger pedal stroke . Admittedly , this is not an accurate test since trying to spin a tire with your hands dosen't compare to trying to stop against the force of the weight of the jeep at any road speed . This test is only valid to see if there is any pressure at all .
youll likely find not much of a difference and not prove anything but if you find yourself bleeding brakes one more time to rule out any air in the system that may not have gotten out , you may want to try this to see if there is any difference between a weak pedal stroke or a stronger one.

 

[greg92jeepxj]

Re-reading your post raises a question ; the brake line replacement.
although this likely didn't occur , did the master cylinder run dry at any time ?
i ask because if no one was aware this occurred , there may be air trapped in the master cylinder bore chamber and causing the same effects as air in the lines . It couldn't hurt to bench bleed the master cylinder to rule out air in it. Unfortunately , it isn't very effective to try to bleed a master cylinder on a vehicle since your not guaranteed a full , proper stroke . Bench bleeding is the only effective way .
i realize that if your going to remove a master cylinder to bench bleed it , you may as well just replace it and be done with it. Has a master cylinder ever been replaced on this jeep ?
If so , how long ago ? I ask because if the brake fluid that was in the system before the lines were changed was old and nasty , this may be indicative of corrosion or rust in the master cylinder as well.
Between the plunger seals possibly being worn or air trapped in the master cylinder bore chamber , this may be the cause of the condition if not trapped air that may not have escaped from the lines themselves . I have found that when lines are replaced , the only effective way to rid all air from the line(s) is to gravity bleed the system .
to do this , you must keep the bleeders open on all four wheels at once . When brake fluid starts running out of the bleeders , close them and bleed the whole system starting with the right rear wheel first if unsatisfactory pressure is found.
Its going to come down to whether the master cylinder is in good condition and can make satisfactory pressure or if there is possibly still air in the system . The only way to be sure with the minimal amount of work is to place pressure gauges in the bleeder ports and measure pressure when pressing the brake pedal . I know , who's got one of those sets ? $$ .
it is unfortunate that us regular folks got to go at it the hard way . Tough on us .
i hope that this information is helpful and helps to find the cause .
Your welcome to post back your results . Wishing you luck and thanking you for your membership here at jeepz.com .

 

[Jenny Gladden Brackin]

That information is helpful. The master cylinder was replaced about 20 years ago. Probably time for a new one. After replacing the brake lines, I bled them. I had also taken it to my mechanic to adjust the carb because I was on a time crunch and my husband and I aren't great with carbs. My mechanic bled the lines again and said they were fine. When I was first working on it, it so had brake fluid in it. I ran it low during the bleeding process, but never completely out. Also, while bleeding, we used a pump to pull the fluid and also did it again by pumping the brakes. I guess it's going to boil down to replacing the master cylinder.

 

[JPNinPA]

I've seen upgrades that integrate a vacuum booster. Just a thought while you are at it.

 

[Jenny Gladden Brackin]

I'll look into that. Thank for all y'alls help. I like to get a few opinions before I work on something major. I was figuring it would be the master cylinder. Unfortunately, I didn't learn enough from my dad before he died last year. I really do appreciate the help. I'll try to remember to post the results when I get it fixed.

 

[greg92jeepxj]

Sorry to hear of the passing of your dad .
If you decide to take on the master cylinder replacement , your welcome to post back for advice.
The new/rebuilt unit should come with bench b,Eder hoses and instructions . I believe you'll have no trouble with it. Only drag is you'll have to re-bleed the system again since the lines will be open again at the master cylinder connections .
I agree about the power booster upgrade , now would be an ideal time .