Low Brake Pedal- finding resolution

[termite]

What am I missing?

Throwing this out there, we've all done it at least once. Bleeder is mounted on top of the caliper, correct?

Possibility the caliper the caliper is now weeping fluid into the dust boot as well. Don't discount it since you just disassembled and cleaned everything.

 

[Reega]

Throwing this out there, we've all done it at least once. Bleeder is mounted on top of the caliper, correct?

Possibility the caliper the caliper is now weeping fluid into the dust boot as well. Don't discount it since you just disassembled and cleaned everything.

Okay, I’ll check the weeping. Yeah bleeder is definitely on top. Thank ya!

 

[Schurkey]

Okay, so back in the same boat…maybe a marginally better pedal. Line lock the front right and it’s way better.

If you clamp the front LEFT hose, does it also improve as much? How about the rear hose?

Perhaps the caliper piston is not sliding properly on the square-cut seal (old seal, damaged piston) or the caliper isn't sliding on the mounting pins/sleeves.

Might be time for a replacement caliper.

@Schurkey may frown on this, but on occasion I've pumped fluid UP, from the caliper to the MC, to aid in purging air bubbles. Air wants to rise... so push the fluid in bottom-up.

Reverse-bleeding can be done, it works, but has three caveats.
1. DO NOT push dirty fluid backwards through an ABS unit. Generally-speaking, the most-contaminated brake fluid is found at the lowest points in a hydraulic system--the wheel cylinders. You MUST flush the old fluid out in the usual direction, or start with a clean, empty system before forcing clean fluid UP to the master cylinder.
2. Don't over-fill the master cylinder reservoir. At some point, you'll probably have to suck some fluid back out of the reservoir or it'll overflow.
3. The bleeder screw is higher than the brake hose/brake tube connection on the caliper/wheel cylinder. Which means, there's likely going to be a small air-bubble trapped in the wheel cylinder/caliper that will not bleed back to the master cylinder. So the LAST thing you do when "reverse bleeding"...is to bleed in the normal direction to assure that all the air is out of the wheel cylinder/caliper.

So here's the process:
1. Flush the fluid in the normal direction, to remove all the contaminated fluid.
2. Reverse-bleed the system with clean fluid.
3. Bleed in the normal direction just a little, to assure there's no tiny air bubble between the bleeder screw and the brake plumbing.

By the time you do all that...you "probably" got all the air out in Step 1, making Steps 2 and 3 unneeded.



You've invented an inexpensive plastic-bottle reverse-bleeding tool. There's at least one company (plus twenty Communist Chinese bottom-feeder knock-offs) selling unreasonably-expensive "special tools" for "Reverse Injection Bleeding".
brakebleeder.com/pages/brake-bleeders

Best Brake Bleeding Kit for Your Car | Phoenix Systems

Stop searching! Find comprehensive reviews and comparisons of the best brake bleeding kits for your car. Bleed your brakes like a pro! Shop Now!

brakebleeder.com

But in the end, all you need is...the disc brake caliper. (Doesn't work well with drum-brake wheel cylinders...sorry.)

Pump the brakes so the piston is 2/3 the way out--not far enough to push it past the square cut seal. About like it would be if the pads were worn-out. Bleed the brakes in the usual way, so the caliper now has clean fluid inside.

PUSH THE PISTON BACK IN. You've just shoved almost the entire caliper's worth of fluid back through the plumbing, up to the master cylinder...taking any remaining air with it.

Throwing this out there, we've all done it at least once. Bleeder is mounted on top of the caliper, correct?

My friend's son was doing the brakes on his Avalanche. Installed rebuilt calipers. Bled the brakes several times, had a low-squishy pedal. He calls his Dad...who calls me. I asked if the bleeder screws were facing up or down.

Yup. Left caliper installed on the right side, right caliper installed on the left side.

Possibility the caliper the caliper is now weeping fluid into the dust boot as well. Don't discount it since you just disassembled and cleaned everything.

Good call. Given enough weeping, you might see the dust-boot inflating with fluid. If the dust boot were CAREFULLY pulled away from the piston, (do not tear the dust boot) the fluid would leak out.

 

[Reega]

Did you already say: Was the right-side hose replaced?

Another tack:

@Schurkey may frown on this, but on occasion I've pumped fluid UP, from the caliper to the MC, to aid in purging air bubbles. Air wants to rise... so push the fluid in bottom-up.

I'm not saying this'll fix you, but...

And all your lines have clean fluid in them already, so pumping backwards doesn't sound so bad (does it?).

I used a "ZEP" sprayer bottle from Home Depot, removed the "twisty" blue spray nozzle and jammed a length of hose over the end of what remained. Tie-wrapped it on. Filled the bottle full of brake fluid, purged both the sprayer's pump and the hose I attached so they're full of fluid, then attached the end of the hose to the brake bleeder on the caliper / wheel cylinder.

Use your head and it can be done.

As you pump the ZEP handle, watch for air in the hose. If you get air, stop; remove hose from bleedr, re-purge, re-attach to bleeder and then slow your action on the hand pump.

And maybe this is a $h!t idea, but AFAIK it's never caused a problem for me. Then again, I've only done it maybe half-a-dozen times in the last 20yrs.

This is an interesting idea. I’ve always been a never “upstream” kinda guy. I open the bleeder when compressing the piston on a brake change, but if there’s a chance. What about just cracking the banjo bolt? Wouldn’t that serve the same purpose? Gravity would force fluid out from the top as I pump fluid/air through the bleeder?

 

[Reega]

If you clamp the front LEFT hose, does it also improve as much? How about the rear hose?

Perhaps the caliper piston is not sliding properly on the square-cut seal (old seal, damaged piston) or the caliper isn't sliding on the mounting pins/sleeves.

Might be time for a replacement caliper.


Reverse-bleeding can be done, it works, but has three caveats.
1. DO NOT push dirty fluid backwards through an ABS unit. Generally-speaking, the most-contaminated brake fluid is found at the lowest points in a hydraulic system--the wheel cylinders. You MUST flush the old fluid out in the usual direction, or start with a clean, empty system before forcing clean fluid UP to the master cylinder.
2. Don't over-fill the master cylinder reservoir. At some point, you'll probably have to suck some fluid back out of the reservoir or it'll overflow.
3. The bleeder screw is higher than the brake hose/brake tube connection on the caliper/wheel cylinder. Which means, there's likely going to be a small air-bubble trapped in the wheel cylinder/caliper that will not bleed back to the master cylinder. So the LAST thing you do when "reverse bleeding"...is to bleed in the normal direction to assure that all the air is out of the wheel cylinder/caliper.

So here's the process:
1. Flush the fluid in the normal direction, to remove all the contaminated fluid.
2. Reverse-bleed the system with clean fluid.
3. Bleed in the normal direction just a little, to assure there's no tiny air bubble between the bleeder screw and the brake plumbing.

By the time you do all that...you "probably" got all the air out in Step 1, making Steps 2 and 3 unneeded.



You've invented an inexpensive plastic-bottle reverse-bleeding tool. There's at least one company (plus twenty Communist Chinese bottom-feeder knock-offs) selling unreasonably-expensive "special tools" for "Reverse Injection Bleeding".
brakebleeder.com/pages/brake-bleeders

Best Brake Bleeding Kit for Your Car | Phoenix Systems

Stop searching! Find comprehensive reviews and comparisons of the best brake bleeding kits for your car. Bleed your brakes like a pro! Shop Now!

brakebleeder.com

But in the end, all you need is...the disc brake caliper. (Doesn't work well with drum-brake wheel cylinders...sorry.)

Pump the brakes so the piston is 2/3 the way out--not far enough to push it past the square cut seal. About like it would be if the pads were worn-out. Bleed the brakes in the usual way, so the caliper now has clean fluid inside.

PUSH THE PISTON BACK IN. You've just shoved almost the entire caliper's worth of fluid back through the plumbing, up to the master cylinder...taking any remaining air with it.




My friend's son was doing the brakes on his Avalanche. Installed rebuilt calipers. Bled the brakes several times, had a low-squishy pedal. He calls his Dad...who calls me. I asked if the bleeder screws were facing up or down.

Yup. Left caliper installed on the right side, right caliper installed on the left side.


Good call. Given enough weeping, you might see the dust-boot inflating with fluid. If the dust boot were CAREFULLY pulled away from the piston, (do not tear the dust boot) the fluid would leak out.

Thank you for the thorough reply. I definitely have some more avenues to pursue! Really appreciate everyone’s thoughts and ideas.

 

[Reega]

Thank you for the thorough reply. I definitely have some more avenues to pursue! Really appreciate everyone’s thoughts and ideas.

Also, bought this today for $11. Maybe a little too much, but I’m excited. Kent Moore Tool dust boot installer

 

[1998_K1500_Sub]

You've invented an inexpensive plastic-bottle reverse-bleeding tool. ...

But in the end, all you need is...the disc brake caliper.

^^^ Elegant.

 

[1998_K1500_Sub]

What about just cracking the banjo bolt? Wouldn’t that serve the same purpose? Gravity would force fluid out from the top as I pump fluid/air through the bleeder?

Yeah, I get what you're saying.

You might crack the hose connection at the hardline near the frame. I might "go there" if I was you... open the connection, allow it to gravity bleed from the MC and, while that's happening, compress the caliper piston (like @Schurkey suggests) to force fluid / air(?) back up to the same junction.

The context of my post was a bit greater... when installing new hoses and/or MC, such that extensive areas of the system may harbor an air bubble, that's when I'll consider the reverse bleed.

There's also a wierd curly-cue in the hardline from the MC to the ABS (at least on my 1998) that I always thought would be a 8itch to bleed and might readily harbor a pesky air bubble. So instead of trying to work any air from the MC down to the caliper, I go backwards.

In your case, it seems the "air" bubble's downstream from the hose (since when you pinch-off there, the pedal's good), so your focus would logically seem to be limited to the caliper or at most the hose and caliper.

I think the last time I used my reverse-bleed tool, I had been gravity-bleeding a front caliper and my attention got diverted and the MC went dry. Maybe I got lucky, but I put the reverse-bleed ZEP bottle on the caliper and pumped fluid back up to the MC until I saw no bubbles, and voila(!) the brakes had a good pedal.

 

[1998_K1500_Sub]

Also, bought this today for $11.

You must be registered for see images attach

Yeah...

Maybe a little too much, but I’m excited.

Uh huh...

Kent Moore Tool dust boot installer

Oh.

<whew>

 

[Reega]

If you clamp the front LEFT hose, does it also improve as much? How about the rear hose?

Perhaps the caliper piston is not sliding properly on the square-cut seal (old seal, damaged piston) or the caliper isn't sliding on the mounting pins/sleeves.

Might be time for a replacement caliper.

I didn’t clamp the rear hose. I thought that was the problem after the caliper rebuilds. So I did both front and the pedal was really nice. Removed left front and it lost a little something. So with the right still clamped, I changed the bleeder and gravity bled. Nothing new, just brand new fluid coming out. I then removed the caliper and continued gravity bleeding while changing its orientation and got some of the most minuscule bubbles. Everything back together pedal was good. Tried the same on the right side, no new air and pedal was soft. Clamp the left front no change.

When I rebuild the calipers, I ended up using new square cut seals and pistons. I messed up installing the piston with the old boot and tore it. I figured why use part half of the kit. Piston was harder to seat than I thought it would be, even all lubed up. I’ll check the dust cover for fluid, I could have torn the seal being too forceful.