Spongy brakes after replacing shoes

[pickupman]

A few weeks ago, I replaced the rear shoes (in attempt to fix the e-brake issue that I was having: http://www.oilburners.net/forums/showthread.php?76155-Drum-brake-question-Why-would-this-happen). After replacing the shoes, I noticed a big decrease in stopping power and a general spongy feeling when applying the brakes. Interestingly, when I applied the brakes the pedal would start spongy and firm up as it moved through it's range of travel. I tried to lock the brakes and couldn't do so. The shoes were adjusted so that there was just a slight amount of friction on the drum if I were to spin the wheel. At no time during the initial shoe replacement were the brake lines or bleeder valves disturbed, so there was really no opportunity for air to get it.

After pulling everything apart again, I double checked my work and I didn't see anything wrong with the installation of the shoes. One both sides, the shorter shoe is in the front, and the longer shoe is in the back. I also checked the wheel cylinders and noticed that one of them had a tiny bit of brake fluid under the boot, so I went ahead and replaced both wheel cylinders, figured that perhaps I had disturbed them when changing the shoes and caused one to fail. After I put the new wheel cylinders in and bled the brakes, I asked a helper to apply the brakes with the truck running and rear wheels off the ground. I was not able to turn the rear wheels by hand with the brakes applied. When I went out for a test drive, I still observed the same lack of stopping power and sponginess feel to the brakes. I bled the brakes multiple times, and didn't see any air in the lines. There is also no ABS system to worry about.

I really can't figure out what to do next. I have read that the master cylinder can fail when trying to seat brakes, so I'm wondering if it might have failed for just the rear brakes. It is only a few years old. Other than that, I am running out of ideas really fast.

 

[79jasper]

If you've never done so, flush your brake fluid.
A new master wouldn't be a bad idea.

Sent from my SAMSUNG-SM-G935A using Tapatalk

 

[ironworker40]

I never have the vehicle running when I bleed brakes. Re- bleed ALL, front and backs and readjust rears. Make sure you have no leaks, I have had many of old lines pop while bleeding brakes.
Is the red brake Light on? I have seen the proportioning valve get out of sync when only bleeding one side,which sometimes will cause the brake light on dash to come on. This is usually cured if you bleed all of the wheels and the light will go off.

 

[pickupman]

I never have the vehicle running when I bleed brakes. Re- bleed ALL, front and backs and readjust rears. Make sure you have no leaks, I have had many of old lines pop while bleeding brakes.
Is the red brake Light on? I have seen the proportioning valve get out of sync when only bleeding one side,which sometimes will cause the brake light on dash to come on. This is usually cured if you bleed all of the wheels and the light will go off.

I didn't have the engine running while bleeding the brakes. The brakes were bled multiple times, and the fluid coming out is clear when I finished.

The whole thing with the engine running was just so I could confirm that when the brake pedal was applied that the rear brakes were actually engaging. After the initial test drive, I wasn't sure that they were even working. Now I know that they are working, probably just not well enough, when driving it seems like the front brakes are doing all the work.

 

[pickupman]

Is the red brake Light on? I have seen the proportioning valve get out of sync when only bleeding one side,which sometimes will cause the brake light on dash to come on. This is usually cured if you bleed all of the wheels and the light will go off.

The light doesn't come on at all. I have seen it come on in the past like when the master cylinder failed.

 

[ironworker40]

Okay I misunderstood your post. So assuming you bleed all the wheels and have no air. Soft deteriorating rubber lines cause a spongy feel also. Did you check the front rubber lines? Also did you cut the drum when you did rear shoes? When replacing any brakes it is best to cut rotors and drums, if you don't the brake pad is not contacting the complete surface of the drum. If this is the case it will get better as the shoe wears in, but will require readjusting maybe a time or two until they seat. Even when cutting the drums this happened but to a much lesser degree. Old shops use to have a machine that would ark (or arch some people called it) the new shoes to each drum.

 

[pickupman]

Okay I misunderstood your post. So assuming you bleed all the wheels and have no air. Soft deteriorating rubber lines cause a spongy feel also. Did you check the front rubber lines? Also did you cut the drum when you did rear shoes? When replacing any brakes it is best to cut rotors and drums, if you don't the brake pad is not contacting the complete surface of the drum. If this is the case it will get better as the shoe wears in, but will require readjusting maybe a time or two until they seat. Even when cutting the drums this happened but to a much lesser degree. Old shops use to have a machine that would ark (or arch some people called it) the new shoes to each drum.

The drums are brand new. I went that route instead of getting the old ones cut, since rock auto had a good price on new motorcraft drums. Also, the rubber lines feel firm to me.

 

[ironworker40]

Did you cut the new drums? Even new drum can be slightly out. Most manufacturers require they be skim cut prior to installation. If all else checks out have them cleaned up and you should get better braking on the rear. Lightly sand shoes to clean them up with 100 grit prior to re installing cut drums to remove greasy finger prints and such.

 

[pickupman]

Did you cut the new drums? Even new drum can be slightly out. Most manufacturers require they be skim cut prior to installation. If all else checks out have them cleaned up and you should get better braking on the rear. Lightly sand shoes to clean them up with 100 grit prior to re installing cut drums to remove greasy finger prints and such.

The new drums were not cut. I didn't think that they would need to be.

 

[Kainoa]

I had this very problem when I replaced the parking brake cables on both rear wheels a week ago. (sticking per previous owner) So on the advice of one of the members here, I went back to the rear tires and adjusted the stars inside the wheels to grab the drums until they wouldn't turn at all, then backed the stars off until the wheels turned, but were still creating friction on the drums. Previously, the brake pedal was going all the way to the floor, now it's nice and firm, and I feel a lot safer driving the rig. Now I just have to determine why the parking brake doesn't grab enough to keep the truck for moving on an incline! Good Luck!

 

[pickupman]

I had this very problem when I replaced the parking brake cables on both rear wheels a week ago. (sticking per previous owner) So on the advice of one of the members here, I went back to the rear tires and adjusted the stars inside the wheels to grab the drums until they wouldn't turn at all, then backed the stars off until the wheels turned, but were still creating friction on the drums. Previously, the brake pedal was going all the way to the floor, now it's nice and firm, and I feel a lot safer driving the rig. Now I just have to determine why the parking brake doesn't grab enough to keep the truck for moving on an incline! Good Luck!

I think this was exactly the issue. I had some time this evening to take another look at it, and I adjusted the drum brakes until I couldn't turn the wheels, then backed off on the adjusters until it was just slightly rubbing (the wheels woulds spin almost a full turn).

After going out for a test drive, no more mushy pedal, and I could actually get the brakes to lock up. I guess they just hadn't seated right. I still intend to replace the master cyl in the near future, but at least I know I wasn't going crazy.