Soft Brake pedal

[lonewolf]

Hi guys I have a 2002 2500HD Duramax and the brake pedal is sort of like stepping on a wet sponge. Just wondering if I may need to bleed the brakes or if there may be more going on than just air in the system. Any help would be great and thanks for your help.

 

[saratoga]

I would start by checking the pads for uneven wear which would indicate binding caliper slides and/or corrosion around the pad ears and retainer clips which these trucks are famous for.

Cleaning and lubing the caliper pins with synthetic disc brake grease as well as removing any rust from the pad ears and under the stainless pad retainer clips then making sure that the pads go back into the clips with no binding and that the calipers slide easily on the pins will most likely make your truck stop better than it did new.

If you have never flushed your brake fluid, that would also be a good time to do so. I know you technically need to cycle the ABS dump valves with a Tech II to get 100% of the old fluid out, but I never did. I just started at the RR, attached a hose to the bleeder and kept pouring clean fluid into the master cyl until it came out the tube. Then I went around to the other three corners and did the same thing. It takes a while for the RR to come clean, but the others go much faster.

 

[btfarm]

If you have never flushed your brake fluid, that would also be a good time to do so. I know you technically need to cycle the ABS dump valves with a Tech II to get 100% of the old fluid out, but I never did. I just started at the RR, attached a hose to the bleeder and kept pouring clean fluid into the master cyl until it came out the tube. Then I went around to the other three corners and did the same thing. It takes a while for the RR to come clean, but the others go much faster.

You were pumping the pedal at this time? If so, how did you keep from pulling air? Or did you do the submerged hose in the glass jar trick?

 

[saratoga]

You were pumping the pedal at this time? If so, how did you keep from pulling air? Or did you do the submerged hose in the glass jar trick?

Hose in the glass jar, cap off the master cyl, crack the bleeder and let gravity do the work. No pumping (it takes a while). I would siphon out the reservoir, fill it with fresh fluid, crack the bleeder, compress the caliper pistons so all the crud goes out the bleeder and not back up the lines then let it do its thing while I worked on something else. Religiously keep an eye on the fluid level and top it off periodically. Repeat Steps 2-4 on the other three corners.

 

[saratoga]

Found this example from when I almost died putting brakes on in the middle of July.

 

[THEFERMANATOR]

Keep in mind that the gravity bleed method will not work with all GM brakeing systems. I tried this with an 01 1500 here recently and it would NOT gravity bleed for more than a few seconds as the ABS unit had residual valves in it. That was a real pain to bleed them as I had to pump the brake pedal up, then go back and crack the bleeder and close it when fluid stopped flowing, then do back and repump the pedal, and so on and so on. Changing the brake fluid is a good idea, and should be done at least every 5 years to keep the seals in the system in good shape. Brake fluid is what is known as an aqueous fluid in the fact that it absorbs moisture from the air, and can actually pull moisture in through rubber brake lines. This is why brake fluid turns black and slimy over time is it absorbs moisture and then becomes acidic and actually eats your brake system seals instead of lubricating them. This is why most new vehicles have gone to DOT4 brake fluid as it is said to not absorb as much moisture over time, and is fully compatible with DOT3 brake systems.

 

[Big T]

I'm having the same problem on my '99. I completely redid the front brakes along with the front end last year. I've Bled the brakes several times, but the pedal is still spongy. Today I bled them again with my son working the pedal. I could not get the right rear bleeder cracked open. Maybe it's rusted in place? I shot it with PB Blaster. I was able to get the Left Rear bled along with the two fronts. I bled it with the engine running and those things squirt like a geyser. I'd close them before the shot was completely done and then instructed my son to let the pedal up. No improvement. I noted that the fluid has black silt in the reservoir.

I pulled the rear drums and the brakes looked fine. Did a test without the hub on and son slowly pushing down the brake pedal. They did not press out until the pedal was more than half way down. Rear brakes were poorly adjusted, as if the auto adjust is not doing its thing. I rotated the adjusters (a lot) until the drums barely fit on. The pedal definitely came up, but it's still spongy.

On another note, the ABS was working after redid the front end last year with new bearings. The driver's side sensor cable rubbed through and I lost the ABS. I bought and installed a new sensor for the driver's side, but the ABS is still not working. Can't figure out what is wrong, nor do I know what to test. It did work briefly after one heavy duty off roading adventure, but that was for like a couple miles before the light came back on again and the ABS has not worked since.

 

[WarWagon]

Pull the codes out of that ABS unit. May need a scanner to do so.
Rear drums are adjusted from the back as the drums wear and leave a ridge on the edge. So you can't put the drums on and have them 'tight'. Only way is to turn them so the drum surface is ridge free. You need to nearly lock the brakes up in reverse to get the adjustors to work or adjust the rear brakes every oil change. The adjusters never really work and this is why the rear shoes last forever. (You really need to go rear disc and get rid of the obsolete drums...)

I recall some ABS units with bleeder valves on them and others suggested a techII to be bled.

Rear proportioning valves do fail. They are supposed to put pressure to the rear before the front brakes start to apply. Master cylinders also fail. If the system is air free I would suspect the MC is shot esp with the seal debris you describe in the reservoir. As you can't open one bleeder you will need to replace the wheel cylinder because that is where the air would be.

1/2 tons are famous for soft pedal. This is a combination of rubber brake line flexing and the calipers flexing. Yeah, the 1/2 ton calipers flex a lot! You will notice this caliper flex after a stainless steel brake line upgrade.

 

[Big T]

Thanks for the response and sorry for the thread jack.

Are there separate aftermarket scanners for the ABS, or do I have to take that into the dealer?

Although I did not "flush" it the last time, I did run a lot of fluid through it. I was surprised at the amount of silt that billowed up when I went to fill the brake reservoir. This had me thinking that I had a master cylinder Problem.

I checks the rear drums for wear and they did not have a lip on them. It took a lot of turns on the adjusters to get them to where the fit was "snug". I will go at them from the back. Makes me wonder if I was getting any rear braking at all?

I had planned to replace the brake lines with stainless this winter as this truck came from Illinois and the lines are definitely rusty.

This is a 3/4 ton Suburban. Do they have rear disc brake conversions for them? If so, how much are they?

 

[Big T]

I was finally able to crack the RR bleeder. Used vice grips on an extra long 8mm box wrench to extend it. First pump of the pedal produced nothing, then finally a stream of fluid. Seemed as though the pedal came up higher, though it still finishes squishy, as opposed to like a rock on my son's '95. I'll do some test and further adjusting on the rear brake shoes.

Would also like to resolve the ABS. Could the ABS relay be out? That's a cheap part to test on.