Mushy Brakes

[quinletc]

76 CJ5 with manual drum brakes. The brakes have been needing adjustment, but working.

Yesterday, I was at a stop, pressing on the pedal a little harder than usual (for no real reason), when I felt it give a little. Not a big thing, just a little twitch.

Since then, the brakes have been really spongy. Interestingly, if I pump them a couple of times, they work better. Next stop, though, I have to pump again.

The lines are not leaking. I have not checked the reservoir yet, but I pumped the brakes multiple times in the driveway, and no fluid dripped from any wheel or anywhere else.

I am assuming that the piston seal inside the master cylinder either tore or otherwise moved out of position when I was pushing on the pedal. Does that make sense to y'all?

Other possibilities I should check?

 

[Posi]

By pushing hard on your brake pedal you found your weak link.
I would suggest you inspect your brake lines, fittings, and wheel cyl chances are you will find a leak.
If your 100% sure there are no leaks test the MC
Good thing you found it at a stand still.

 

[Lumpy Grits]

Have you messed with the brake system other than a brake shoe adjustment?
If you find no leakage at the wheels--
New MC time. The separation seal is allowing fluid to flow between front to back reservoir.
LG

 

[quinletc]

Have you messed with the brake system other than a brake shoe adjustment?
If you find no leakage at the wheels--
New MC time. The separation seal is allowing fluid to flow between front to back reservoir.
LG

I have not touched the brakes at all.

I believe you are correct, as I looked in the reservoir, and the fluid level in the front was much lower than the level in the back.

 

[Posi]

Fill the front and pump the brakes.

 

[quinletc]

Fill the front and pump the brakes.

What brake fluid is recommended?

The TSM talks about a Jeep-specific fluid. Do I need that, or can I use DOT-3 (or something else) from AutoZone?

 

[Posi]

DOT 3 is fine

 

[Lumpy Grits]

Only DOT 3 is recommended for our OEM CJ systems.
Never mix brake fluid types.
LG

 

[quinletc]

Well, I don't know what the heck is going on.

I replaced the MC, after bench bleeding it, and when I went to bleed the first wheel with a vacuum pump, I got a thin stream of fluid and a WHOLE LOT of air.

The seal was good, as the vacuum held and some fluid did flow, but not like it should have.

If anything, the brakes are worse now. I think it may be time to engage a professional. Brakes are not where I am willing to take chances.

 

[Lumpy Grits]

You bleed the wheel farthest from the MC first.
Get a buddy to pump the pedal and try it the old-school. You may have 'tripped' the proportioning valve.
LG

 

[Posi]

Before you bought a new M/C I asked you to fill the front reservoir and pump the brakes. What happen when you did this?

 

[quinletc]

Before you bought a new M/C I asked you to fill the front reservoir and pump the brakes. What happen when you did this?

It didn't help.

 

[quinletc]

You bleed the wheel farthest from the MC first.
Get a buddy to pump the pedal and try it the old-school. You may have 'tripped' the proportioning valve.
LG

Well, since stopping is a non-negotiable requirement, and I felt like I was venturing into territory where I might be compromising my own safety, I went ahead and took it to the shop. Good news, OK news, bad-ish news.

The bad-ish news is that I spent $130 to get the brakes checked, bled, and adjusted.

The OK news is that all the brakes needed was a thorough bleeding.

The good news is that the Master Cylinder which I replaced was apparently the problem. Also, the service guy said I had pumped so much air into the system I would have killed myself trying to pump it out manually. And now I know my brakes are properly bled and adjusted.

 

[mtnwhlr]

Glad to here you got it fixed and now can stop when needed.

 

[Lumpy Grits]

Good to hear.
Remember to ck the level often. Find out what fluid this shop used and use the same for topping off.
LG

 

[Posi]

Disregard this post. I posted twice and lost both then posted this after you found your problem.

It didn't help.

Wasn't my point.

After adding fluid and pumping the brake pedal....
Was there a change in the fluid level?
Did it stay the same in both reservoirs?
How long did you pump the pedal?
Did you let it stand over night?
If so, was there a change in fluid level over night?