Spongy brakes (1 Viewer)

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Sep 24, 2012
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Just did a brake job and after a reinstall and bleed, I'm getting spongy pedal feel. I have to depress the pedal about 50% before getting much grab, and the pedal is almost on the floor before I can lock up the front wheels. Feels like air in the line. Some details:

I rebuilt the calipers (new seals, boots, pads) and replaced all the soft lines: the rubber was original and cracked. The discs were even and smooth so I did not turn them. Removing them looked like a PITA. I bled RR, LR, RF, LF. I did not bench bleed the MC. I was not aware of any other bleed points until I dug into the forum. Looks like I missed the MC bleed and the rear proportioning valve and reversed the order of the rear bleeds. I plan to re-bleed in the following order: MC valve, LR, RR, rear proportioning valve, RF, LF.

Does that sound right? Have I missed anything else? I inspected/cleaned, but did not change the rear brake shoes/drums. 75% meat on them. Do I need to adjust them? The parking brake will not lock up the back wheels on a downhill, even after adjusting the tension screw at the e-brake handle (currently 5-6 clicks).
 
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Hopefully this helps out!
 
Hey, long time no talky. I'd guess that you still have some air in your system. I've had to run a quart through my brake system to get all the air out after major brake work. Suggest channeling your inner anal retentive alternative personality, and doing 3 or 4 cycles through the standard bleeding system (LPSV, right rear, left rear, LPSV, right front, left front, LPSV)...or something similar. While the sequence seems important, I think the total volume of new brake fluid is more important. At least, that's been my experience. But as you know, I learn by doing, so be forwarned...
 
Doug, haha - you're awesome. Yes, I've been in stealth mode for a while. I switched jobs, which requires me to drive-commute, so I've been using my other-than-LC for a while. The brake job is a long awaited reconnect with my inner grease monkey.

and1111, that guide is perfect! I was actually wondering what to unscrew on the MC to bleed it. Can anyone walk me through a rear drum adjustment? I know there's a screw: it is on the inner portion of the rear wheels? (As the front calipers are on the inner portion of the fronts)? It's been ages since I've worked on drums.
 
The rear drum shoe tension setting is adjusted with the parking brake.

You can crank the parking brake handle a bunch of times till it gets firm, or pull on the cable at the rear axle by hand.

The rear brakes are supposed to be self adjusting if you use the parking brake.
 
So I bled the proportioning valve plus the master cylinder plus all 4 corners in every possible combination, and the brakes got spongier than ever. I must have flushed a full pint of new fluid through the system. I bled the MC by loosening the 2 hard lines, one at a time, and weeping fluid through the threads on the push stroke, tightening before the return stroke (just like you would a caliper bleeder). I think this prevented air intake.

After the initial 2 tries at this, the pedal went almost to the floor with almost no resistance. Successive bleeds improved that, to the point now where I have about 1.5" of travel before engagement - this took 5 bleeds at all 6 bleed points. About a pint flushed through, in addition to the 1.5 pints I replaced yesterday. No leaks visible anywhere, reservoir stays full between bleeds.

At this point, the brake feel is inconsistent but better than before the more comprehensive bleed today. It will be almost firm much of the time, yet spongy on a random stop. I can pump the pedal back up to firm. I cannot get the wheels to lock up on dry pavement even if I stand on it.

I considered a faulty MC (it's the original Aisin), but when the pedal is firm, it holds its position without slowly sinking. A bad seal in an MC will typically drop the pedal slowly.

Any thoughts? I hate to bleed it further - every attempt seems to soften things up.
 
The original is 27 years old. It's probably due for a change and sounds like it is the source of your problem. It could also be the proportioning valve.
 
Thinking out loud...spongy suggests air in the system, but you've bled it alot. Inconsistent suggests the MC, which is 27 years old and they do go bad. While in general I do not like throwing on new parts to see if it fixed a problem, when it's a wear part and it's old, then it's not such a bad idea. Especially when it's brakes. My vote is to replace the MC, bleed the heck out of the new one and the entire system.

Also, there's a thread on here somewhere about building a vacuum self-bleeding system. It involves a peanut butter jar, some jb weld, 1/4" tubing and vacuum hose. It's easy. I built one, and it works great. The engine vacuum powers it, and you can run alot of fluid through a system easily. Flushing a brake system every 2 years is recommended anyway, due to the hydroscopic (water absorbing) nature of brake fluid. I am happy to loan you mine if you wish.
 
Most of my brake bleeding issues have involved air in the master cylinder. Using short tubing and fittings to run from the outlets back into the reservoir is the only way to get all the bubbles out. Bench bleeding seems to be the only way to get the plunger all the way to the stops. I don't think you can get the last little bit using the pedal.

Sometimes they firm up from use over time. Wacky, but I've had it happen three times now on three different trucks. I wouldn't count on it.
 
Brake pedal rises when pumped = brake shoe needs adjustment.
Pedal doesn't rise, but remains spongy = air in system or balooning brake hose.
 
...there's a thread on here somewhere about building a vacuum self-bleeding system. It involves a peanut butter jar, some jb weld, 1/4" tubing and vacuum hose.
That sound like the start of a joke. The only thing missing is a duck. :lol:

My gut told me it's the MC. Driving it around for a bit, I noticed the tells: firm pressure on a sudden stop, but pedal sinks to the floor on soft stops. To me, that suggests slow blow-by around a seal.

Ordered an MC from the local O'Reilly's. Was surprised to find it was a reman Aisin. Even has the TEQ mark in the casting. Installed and bled, and problem 90% solved. I think the last 10% is in the few bubbles I got swapping in the new MC. Yes, I can re-bleed the whole system, but won't the air stay up by the MC? Will bleeding out a wheel push all those bubbles downhill?

What's the right way to fully bleed a new MC? Before I connected the 2 hard lines to it, I slowly circulated fluid through the MC using 2 short tubes into the reservoir (on-car bench bleed). However, there's a moment when you have to disconnect those 2 little tubes and reconnect the hard lines. I worked quickly, but undoubtedly introduced a bit of air at the hard line fitting. I even backed off the hard line threads a bit and let some fluid ooze out under pressure, hoping the air pocket would get squeezed out.
 
F:censor:ing hell. I CANNOT get these brakes to firm up! Recap: new pads on rebuilt calipers, existing rear drums/shoes, all new soft lines, new OEM master cylinder, no visible leaks (no loss of fluid). I've bled all points in every order possible, but generally from the farthest point first. MC has been on-car pre-bled using the "2 tubes" method, circulating the fluid through the reservoir until bubbles are gone from inside the clear tubing.

At this point, I can max out the pedal on the floor at full brake. It was actually better last night when I installed the new MC. Today's attempt at trying to bleed out the air pockets I thought I introduced during that install actually made things worse, so I "reset" by de-installing and re-installing the MC the same way as last night. Still too soft. Help?
 
If the calipers are installed upside down, they will trap air that never can be purged. Just something that came to mind.
 
If the calipers are installed upside down, they will trap air that never can be purged. (Not to say that happened).

Was gonna ask the same thing right before you posted. Could the calipers be on the wrong side?

The bleeder valve should be above the brake line.

T
 
I originally had really soft brakes on my HJ61. I replaced everything and they were still really soft. Took it to Midas and they adjusted the rear drum brake settings. E-brake is much stiffer now and pedal is about 50% better. The mechanic mentioned something about diesel engines having lower pressures that make the brakes a bit softer. NOT sure if this is true or not, but at least adjusting the rear drum brakes did make it better.
 
If the calipers are installed upside down, they will trap air that never can be purged. Just something that came to mind.
Yeah, that was one of the first things I reviewed. The calipers are mounted with the bleed screw correctly up.
 
The last Cruiser I bled the brakes on refused to offer a firm pedal. I put on 3 different bench bled masters, 2 different bench bled proportioning valves, 2 different boosters, replaced and adjusted the rear drums, and bled at least 3 quarts of fluid using both vacuum and pressure methods. The pedal never felt firm enough to drive. It even sunk when the engine was running.

In frustration and disgust, I just left the problem and didn't drive the 60 for nearly 2 months. When I finally returned to address the issue, I started the truck and it had firm brakes. It has been fine since. I have no explanation other than suggesting the possibility that over time air bubbles rose to the reservoir. I wonder if the bleeding process tends to cause turbulence that breaks up air pockets into foam and it takes time for it to stratify.

If its not on your DD, maybe give yourself a break and let the problem sit for a few days.
 
I'm wondering whether the brake booster might be the culprit. Again, probably the original @27 years old. I've never had one go bad on me, so I'm not sure the symptoms. Online search says symptoms include:

-hard pedal (No)
-hard to stop vehicle (Cannot fully lock up the wheels on dry pavement unless I stand on the brakes, but they're new pads and not fully bedded in)
-pedal sinking to floor (Not SINKING like with a bad MC, but just spongy enough to touch the floor while maintaining resistance)
-hissing (There is a slight hiss when I release the brake)

Funny thing is: everything worked fine before I started any of this. The only reason I did it was to replace the old soft lines, which were cracked and brittle. The master cylinder even seemed to work fine, so I don't get why now it started blowing by, and if/why problems with the booster would appear. Maybe marginal parts were all in stasis?
 
A couple of thoughts...

1. You are not a trained mechanic in a well equipped garage. You do this by choice, and one of the consequences of that choice is the possibility that the problem will take longer to solve and will be frustrating. When this happens to me, I try to remind myself that I made this choice and therefore I need to find peace with the process no matter where it leads me. That works, mostly, sometimes a bike ride works better.

2. It made sense to replace the old soft lines, and the MC. And anyway that's done. No point in re-thinking that one.

3. I don't think a booster suddenly goes bad. Air in the master is still my personal vote, and it's been noted by others that it can be tough to get the air out fully. Maybe leave the resevoir cap off and recheck on Saturday? Maybe the air will find a way out and it will fix itself...
 
Against my better judgment, got both Mity Vac and a venturi valve suction bleeding device from Harbor Fright. Both were complete garbage, of course, so I ended up under the truck with a wrench yelling "press!" and "release!" to my son at the brake again. After about another quart's worth of fluid, the brakes started to firm up. I'd say I'm at about where they were when I started this whole process, which is safe and OK, but not ideal. About 1-1/2" of pedal travel before they bite. I hesitate to do any more.

I wish the new pads (Wagner) had a bit more grab. I followed the bed-in procedure, but they really only lock up the fronts when hot. Any thoughts?
 

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