Brakes! Brakes! Brakes!!!!

[Jaycenk]

Hey guys. I will give you a little back story here. I have changed on the fronts the pads, rotors and ruber lines, calipers where in good shape. On the rear I have changed Drums, shoes, single hose, and slave cylinders. I have also changed the master Cylinder to a new Napa one.
Here is my problem and it has not goten any beter with the fresh parts, I have a fully firm pedal when the truck is NOT running. It is a firm pedal and it feels good while it is running to about 1/8th to 1/4 the way down and then sponge for another 1/4 to 1/2 and then down at the last 1/4 it firms up again. I bled the system from the furthest back around to the shortest on the driver front. No air comes out and no foamed or frothed fluid. I have great vacum on the booster and it holds for days after I shut the car off. If I pull the line on the booster you hear the air rush in very fast. Why the hell can I not seem to fix that sponge feeling in the middle of the pedal? This is another thing some times I don't have the problem but if I have to jump on them hard most times it goes sponge in the middle of braking. I had a close call last friday in the rain towing my boat where I went straight through a red light just un able to stop. I also had it happen a few miles later but that time the fronts did lock up and I did not have that sponge feeling and abs kicked in and stopped in time. My trailer has 4wheel disk surge brakes and they do work but I am just not getting enough stopping power out of the truck for them to help. This was in the rain and I was going only 45 to 50mph. I have got to get this thing to stop before I kill someone or my family. I tow alot with this thing so I am at about 9 to 10 klbs fully loaded boat, trailer, gear and truck and again trailer has surge brakes. Help me come up with an answer.

 

[97yukon]

Hey guys. I will give you a little back story here. I have changed on the fronts the pads, rotors and ruber lines, calipers where in good shape. On the rear I have changed Drums, shoes, single hose, and slave cylinders. I have also changed the master Cylinder to a new Napa one.
Here is my problem and it has not goten any beter with the fresh parts, I have a fully firm pedal when the truck is NOT running. It is a firm pedal and it feels good while it is running to about 1/8th to 1/4 the way down and then sponge for another 1/4 to 1/2 and then down at the last 1/4 it firms up again. I bled the system from the furthest back around to the shortest on the driver front. No air comes out and no foamed or frothed fluid. I have great vacum on the booster and it holds for days after I shut the car off. If I pull the line on the booster you hear the air rush in very fast. Why the hell can I not seem to fix that sponge feeling in the middle of the pedal? This is another thing some times I don't have the problem but if I have to jump on them hard most times it goes sponge in the middle of braking. I had a close call last friday in the rain towing my boat where I went straight through a red light just un able to stop. I also had it happen a few miles later but that time the fronts did lock up and I did not have that sponge feeling and abs kicked in and stopped in time. My trailer has 4wheel disk surge brakes and they do work but I am just not getting enough stopping power out of the truck for them to help. This was in the rain and I was going only 45 to 50mph. I have got to get this thing to stop before I kill someone or my family. I tow alot with this thing so I am at about 9 to 10 klbs fully loaded boat, trailer, gear and truck and again trailer has surge brakes. Help me come up with an answer.

ok..this may seem like a dumb suggestion but i had the same problem and miraculously noticed this getting under my truck one day...i had the spongy feeling after dropping the front of my truck and i had bled the brakes because the lines had to be disconnected from the caliper. well i developed the spongy feeling the next day so i went home and bled them again. didnt fix it. i got underneath my truck to grease the fittings and i noticed my caliper was wet. after unbolting the line i realized the little copper ring that goes on the brake line was flipped around...if you look closely the ring is seated to the caliper and i had a very slow leak....i unbolted it bled the brakes and flipped the ring around...no leak and no more sponge...just a thought man.

 

[grimm]

Yeah, what 97yukon says sound like a good thing to check. If you're getting a spongy feeling its most likely because air is entering the system somehow. If what 97yukon says turns out to be okay or doesn't fix it, I would check all connections throughout your brake systen. Make sure you don't have a pinhole leak in your brake hoses. Make sure your hard lines are attached to the master cylinder properly and not over or under torqued. Also make sure the master cylinder itself isn't leaking at the brake booster.

You can also get a sudden spongy feeling when your brake hoses flex excessively, which is why many people go to stainless steel braided hoses. Additionally, if your brakes aren't properly bedded in yet (broken in) you can have an easier tendency to experience brake fade. Just some thoughts.

If everything checks out and you are 140 percent sure there are no leaks, try bleeding the brakes again as you may have too much moisture in the system causing your brake fluid to boil much earlier than the rated boiling point of standard fluid. This will cause brake fade which can also give a vague feeling. This will also create air in the system, which will also cause the sponginess. Anyways, good luck, hope it works out. Let us know if you solve the problem!

 

[Jaycenk]

Hey thanks for the reply's. I have been thinking about it for days now and I am am at the same conclusion that I have to have air in the system some where. I am going to get under it in the morning and I will look at all that stuff again. I changed the ruber lines so I will check to see if I have weepers. The brakes had alot of around town miles on them and it is not as touchy around town with no boat on the back but still there. I have around 600 miles on the new pads, rotors, shoes, and drums.

Another thought I had was with the ABS modual it's self. on my 98 it has no bleed valves on it and I did change the master cylinder due to blow by on the M/C piston. I more than likeley got air in the abs system and I don't know how it's internal plumming works so I wonder if there is a place for air to get trapped? just a thought as I am going to be pulling my boat down to the keys in a little over 2 weeks so I need to fix this. I also was told of a new bleeding system out there that bleeds from the calliper up to the master cylinder. I may have to give that a shot if I can't figure this out soon.

 

[grimm]

You can bleed the ABS valve/pump as well. One thing I forgot to mention. I believe on these trucks, air can in fact get trapped in the ABS system. Might be worth a shot to check.

 

[bowtiefreak]

try pulling the fuse for the ABS, the large fuse under the hood. try that, it elimiated the ABS system and reverts the the fail safe of standard brakes.

 

[Jaycenk]

You can bleed the ABS valve/pump as well. One thing I forgot to mention. I believe on these trucks, air can in fact get trapped in the ABS system. Might be worth a shot to check.

I didn't see any bleed valves on the ABS Modual is there one on it that I don't see? If not how do I bleed it? Also I was messing around with it today and it feels like my booster is late to give aid to the brakes. It feels like it has a 1 or 2 second delay before it helps with my input. I don't see any leaks and if I can figure out how to get the ABS modual bled and may need to change the booster It should be ok. I will try pulling that fuse right now and see if it makes a difference.

---------- Post added at 05:13 PM ---------- Previous post was at 04:58 PM ----------

Tried pulling the fuse and nothing changed still had good stops and bad stops so I am going to continue to try and figure out if I need to bleed this ABS mod some how.

 

[grimm]

It makes sense now that I think about it. You replaced the master cylinder, right? So air probably entered the ABS system that way. If you replace a component that sits before the ABS modulator in sequence, you are more likely to have air in the ABS mod. If you had only replaced something that sits after the ABS modulator, air probably wont get in that way.

I think I wrote something previously about bleeding the abs system. Basically get your car jacked up off the ground. Get your wheels going and then lock up the brakes. This will should trigger the ABS system which will cycle brake fluid through the ABS pump/valve which actuates the anti-locking mechanism. You may have to do this in between each wheel. You may also be able to bleed the ABS system using a scan tool, which can actuate the modulator via the computer, while you bleed.

 

[Jaycenk]

Anyone know how to make it cycle though some wiring? I don't have a scan tool but if there is a way to manualy make it cycle I could then bleed it while it is cycling. If I hot wire the physical motor on the ABS unit is that all that needs to be activated to simulate an ABS lock up cycle?

 

[bowtiefreak]

ABS on OBS = sucks.

I swaped the master cylinder on mine a while back and could not bleed the lines to get the air out. had to get it to a local shop who vacuumed the lines to pull the air out.