Low Brake Pedal- finding resolution

[Reega]

Yeah...



Uh huh...



Oh.

<whew>

I didn’t even see it until your reply!!!!

 

[Reega]

So …IDK. I pulled the right front caliper and pumped the piston out enough that I could look behind the dust cover. There was some fluid, but that was only a day or so after the rebuild. I wasn’t sure if it was leaking or residual “lube” from driving the piston. Anyways, went ahead and pulled the caliper and broke it down again. Nothing obvious on square cut seal or piston. Put it back together and reinstalled and bled.
A few posts back I mentioned replacing the left front bleeder, this is non-related to the low pedal on the right front caliper, but added complications to the system. I didn’t clean the seat well enough when the caliper was apart and the left front was sucking air. The only way I found out was that I rubber capped the valve and it blew off. I had a sinking pedal at this point so I knew I had a leak somewhere. I had two, there was also a leak at the banjo bolt. I normally, torque to 33ftlb, untorque , retorque, untorque, torque. Well, that didn’t seat these copper washer. A lot more torque, but no leaks. All this to say the system had changed.
I replaced the front right with a new Raybestos Caliper. Seems well constructed slides nicely lubed with silicone. All back together and bled and clamping either front wheel will end in a better pedal. Both it adds more firmness(all without the rear clamped). Didn’t seem great, but I needed it today and drove around. Wasn’t bad, felt about like my Acura. Stopped well, didn’t seem especially low, minimal pedal to hold at a light, doesn’t feel alarming while driving. So idk. Way better than when I started, not as firm as my ‘89. I will say, not a fan of the aftermarket brake hoses. I don’t think they are as rigid as the original. They are also a mm less in diameter. I cut an OE hose open where I clamped it, it looked fine, no degradation.
So now, I’ll probably try to find some SS hoses( having trouble finding any online) or have some built. I wish there was a silver bullet but can’t point to one. I plan to get the brakes good and heat soaked one day and come back and bleed, I really think i still have a bubble or too hanging out, but they are probably 85-90% of what I expect. It stops really well.
Really appreciate everyone’s help. If something else turns up I’ll let y’all know.

 

[1998_K1500_Sub]

clamping either front wheel will end in a better pedal

I wonder what you would find if you put a set of dial calipers across the brake caliper (back to front) and then stood on the brake. Would you find that the caliper body "spreads" when heavily applied? If so, that would help explain a soft(er) pedal.

I would like to see someone do this.

I’ll probably try to find some SS hoses

You'll find a better pedal when you put SS lines on both front AND rear. @Schurkey and I both noticed, independently, that installing only the front two didn't make as much difference as installing them all around.

Some SS hoses are better than others; they fit the front calipers better. The ones I installed were very usable but they could have been better. See @Schurkey's remarks in this post:

Brakes for towing

The brake pad and rotors checked out and they are good. Did you ever bother to verify that the rear brakes work? Do you have access to a scan tool so you can flush the old brake fluid? How about the calipers? Pistons not "sticky"? Caliper body "floats" on it's mounting pins? Define...

www.gmt400.com

 

[Reega]

I had some Russell’s on my 89 and it really firmed it up. I just can’t find any for a k2500 96+ without a lift.

Yeah, I could see some “flex” with the calipers while my wifey was applying the brakes. That’s what made me wonder about “caliper fatigue”. The other thing I wonder about with the k2500 in particular is the lug studs hold the rotor to the hub. So if they are not seat properly there would be more movement then with the wheel on and the outside clamping forced of the lug nuts against the wheel and stud…kinda like a loose wheel bearing. When I put the new rotors I hammered with a brass drift from the back, but several wouldn’t seat completely and used a stud installer on the face. Could be my impact didn’t have enough torque, but there is no perceivable movement whatsoever.

 

[Schurkey]

When I put the new rotors I hammered with a brass drift from the back, but several wouldn’t seat completely and used a stud installer on the face. Could be my impact didn’t have enough torque, but there is no perceivable movement whatsoever.

A 20-ton press would flex and pop when knocking the old studs out. Did a nice job of putting the new ones back in, though.

 

[Schurkey]

I wonder what you would find if you put a set of dial calipers across the brake caliper (back to front) and then stood on the brake. Would you find that the caliper body "spreads" when heavily applied? If so, that would help explain a soft(er) pedal.

Absolutely, the caliper will spread some. If the caliper is designed properly, they don't spread so much as to genuinely sabotage braking, though.

Given a standardized caliper casting, the bigger the piston, the more it would flex.

You'll find a better pedal when you put SS lines on both front AND rear. @Schurkey and I both noticed, independently, that installing only the front two didn't make as much difference as installing them all around.

The SS/Teflon- (PTFE-) liner hose is pretty-much the gold standard for flex hose. I still think the big improvement is not from the SS/Teflon hose, but because a decades-old hose is being replaced with "new". The old hose probably has weak fabric reinforcement, and the new hose is still performing at it's peak.

That said...I've converted most of my fleet to the SS/Teflon hoses, at whatever point I'm replacing hoses anyway. I don't remove "good" rubber hoses to install new SS/Teflon hoses.

 

[Reega]

So to finish this thing off, I was shooting for the Factory Service Manual spec of 2&1/4inch travel(I can’t remember exactly) on the brake pedal. Even though I said it was fine, it wasn’t right and it frustrated me. I bought a Zep Spray bottle from Lowe’s to reverse bleed, but I also bought a pressure bleeder from OMT off amazon. Figured if it didn’t work I’d send it back. Anyways, the reviews were right on the Chevy specific one. I broke the chain. I used some DeWalt trigger clamps and proceeded anyways at 12+ psi on the chamber. Cracked the bleeders and let it go. I really wanted to see air being forced out, but I didn’t have my vinyl hose straight up and it sucked from the hose/bleeder. Lots of bubbles, got it straight, nice flow no bubbles. Anyways, both sides with pressure bleeder and pedal is right close to spec. Best it’s been in the few years I’ve owned it. Only thing I can conclude is that the velocity of the fluid travel under pressure helps to remove those minute pockets of air. For me, worth the $68 to have it right.