Soft brake pedal - don't know where to go
 

Hi Everyone,

I've had quite a few Blazers (and Bravada's) over the years, so not new to them. Currently have a 2000 Bravada with a tad over 104K on it, we bought for our kids to drive around.

A few of the rear brake lines were rotted out, so replaced them and now, can't seem to get the soft pedal to go away. I've read lots of info on this fairly common problem, but I'm not sure what to do next.

What I've done -
Replaced all rear brake lines.
Both passenger side brake calipers are new.
On my 3rd Master Cylinder (the 2nd "new" one had a leak in the back of it.
I've bled the brakes multiple times (to include running the ABS bleed procedure on a scantool).

My process:

Bench bleed MC
Have assistant pump and press the brake pedal, and crack the MC lines open to get any residue air out, making sure to close them quickly while there is still pressure on the system.
ABS Bleed with scantool
Bleed brakes with assistant helping starting at RR, LR, RF, LF
Turn on engine
ABS Bleed again,
Bleed brakes again with assistant

We just can't get the soft pedal to go away. It just sinks to the floor. The brake light comes on when bleeding the brakes (as the pedal goes to the floor when releasing pressure at the bleeder screws (front brakes only)).

Pedal is firm and just fine when the engine isn't running.

I've checked multiple times for leaks, to include letting it sit overnight.

I'm out of ideas with this one. Never had this kind of problem bleeding brakes on other vehicles (mostly GM, and Blazers in the past).

I've read that people have ran down gravel roads and did hard stops a few times. Haven't tried that yet, since the Bravada is up on jacks I'm hoping to get this solved before I put it back on its tires.

Any advice would be appreciated.

Thanks!

Are you sure you got all the air out? I recently went through this with another vehicle and was surprised at how long it took to get all of the air out. I got a length of vinyl hose at ACE and connected it to the bleeder. I went up about 12" with it before turning it down into a container. The fluid in the line stopped air from being sucked back in and I sat and watched while someone else pumped the brakes. It's easy to see the air bubbles through the vinyl tubing.

No, I'm not sure. It feels like air in the line, but I've been through 3 bottle of brake fluid! Using vinyl tubing for bleeding them too, agree that it sure makes it easier to see air bubbles. Gonna give it a try again tomorrow morning though!

If you've got that much fluid through it, you are certainly working on new fluid. I would catch that in a clean bottle and reuse it.

Bleed the brakes again this morning and pretty much the same results.

I get a brake warning light when bleeding the front brakes, every time. The scan tool says the differential pressure/fluid level switch is reading low, of course, there is plenty of fluid in the MC.

If this switch is bad, can it be letting air into the system? I'm not even sure where this sensor is on the Bravada, I'm guessing it is the electrical connector in the proportioning valve?

Thanks

I can't help you with that but I would not expect the switch to let air in. If that switch is only on the front have of the MC, it would be logical for it to light while bleeding. How does the pedal feel? Is it possible that the pedal is good but you are being over-sensitive to it? Been there, done that more than once myself. At this point, I'd put it back together and take it for a short drive and see how it goes. Of course, I'd stay out of traffic and off of hills until it felt good to go.

MC bleeding requires very short pedal movement, which is why best done on the bench...hence the term, "bench bleeding".

Watch the MC and have another person do some very short pedal presses, watch for air bubbles in the reservoir.

Other than that, I have only had success with gravity bleeding my Blazer brakes...in the same order as you have listed above.

Pedal still sinks to the floor - spongy, but yea, it is a real possibility I'm looking too far into it, and need ot just take it for a drive.

Did the bench bleed, on a bench.

Did a bleed of the MC again (while it was in the Bravada) this AM just to make sure there wasn't any air trapped in it. Short strokes, no air bubbles.

I took the MC on my pickup truck apart and was surprised at how simple they are. Two-piece plunger with some rubber cups on it that seal in one direction and let fluid pass in the other so they can refill. And some fairly heavy springs to push them back into the start position. Very easy to disassemble too, if anyone else is curious as to what's inside.

Are you using a clear hose attached at the wheel caliper bleeding fittings into a jar of brake fluid? Do you get equal flow out of all four calipers?

The ABS modulator as well as the master cylinder can be the issue, both have to be fully bled. Some articles that may be helpful:

https://www.knowyourparts.com/techni...-installation/


https://www.brakeandfrontend.com/bleeding-abs-systems/


George

Here are the service manual pages for reference:

https://cimg6.ibsrv.net/gimg/blazerf...785ccbfa24.jpg
https://cimg8.ibsrv.net/gimg/blazerf...27bd8b42db.jpg
https://cimg9.ibsrv.net/gimg/blazerf...eb227eff46.jpg
https://cimg0.ibsrv.net/gimg/blazerf...77619ab9ff.jpg
https://cimg1.ibsrv.net/gimg/blazerf...d9222a23cb.jpg
https://cimg2.ibsrv.net/gimg/blazerf...aefc1c2fa8.jpg


George

Before attempting the automated bleed, all air MUST be bench bled from the master cylinder AND the steel flex lines going to the EBCM. The adage of "junk in, junk out" applies here. The automated bleed operates all of the solenoids in the EBCM. It draws fluid from the master cylinder, (and steel flex lines), and forces it into the steel lines exiting the EBCM. Each caliper must be bled to remove the air after doing the automated bleed. The automated bleed may need to be done several times. In the post above, refer to page 5-207, steps 10 through 13. One thing that is not clear in step 10, is that during the automated bleed, you must maintain constant pressure on the brake pedal. Once the scan tool confirms that the bleed is complete, then you can release brake pedal pressure.

Thanks. Yes, I've been using a clear hose into a jar to see what is happening. And yes, equal flow out of all four calipers (which tells me it isn't the proportioning valve).

I've put a couple miles on it, and, while it stops, the pedal feel just isn't where I'd like it to be. Thanks for the service manual pages. I'm gonna put it back up on jacks and make sure I follow them.

I have been wondering if the automated bleed in the ABS gets rid of the air, or just pushes it to the rest of the system. Gonna put it back up on jacks when I can, and go through all the steps one more time. Thanks for the assist.

Once I get this brake thing finalized, gotta fix an oil leak, then take care of a slight hesitation, and she should be good to go.

Sounds like your on the right track, you'll get there.

George

The procedure for my Ford pickup calls for bleeding of the brakes, bleeding of the ABS and another bleeding of the brakes. I can't figure any way for the ABS system to purge the air out of the system, just out of itself and into the brake lines. Then it's a pretty long ride to those rear brake bleeders.