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Brake pedal pushes back??????

K85 Octane

K85 Octane

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Question:

If I hold the brake pedal while turning off my truck, it pushes back against my foot.

Anyone know what that means? :dunno:
 
K85 Octane said:
Question:

If I hold the brake pedal while turning off my truck, it pushes back against my foot.

Anyone know what that means? :dunno:
Click to expand...

It's losing power assist. I would check the one way valve on the vacuum line going to the booster, if its bad it'll do that.
 
Will do, I will be checking the booster hear shortly too.

Would this also give the truck a soft pedal? Cause I am in desperation mode right now, getting ready for Moab and I don't have reliable brakes. In a panic since getting my truck back tonight. My stomach doesn't feel good.
 
Spongy pedal is usually air in the lines........is it spongy or does it just have too much travel, then solid at the end?
 
travel, then solid. If I crack a line, the pedal will hit the floor...otherwise it comes to a very abrupt end when connected.

But, I'm all over the place as to what I'm using. My brakes have plagued me from the beginning. I just recently tried another set up today and it started pushing back tonight. 60/14 with disc
 
Ok, too much travel with a solid pedal at the end means the master cylinder doesn't have enough volume ( too small of a bore). Ive got the same setup as you (I think). I just got the master and booster from a 77 or 78 K30 IIRC, and I'm not using a proportioning valve. Pedal isn't perfect, but it'll hold the truck stopped at any angle, aand doesn't have excessive travel.
 
Mc39017 is the part number for the master at rock auto. Got mine at napa but it's the same one. 1 5/16" bore and I'm using the vacuum booster that is for the same truck
 
Gunna make a list of stuff I've tried. If I can't get my brakes any better before BB, I'll have to leave it at home. No point in towing it all that way and not trusting it.


I'm running the original booster. It's been tested in the past and had a valve replaced. It's current condition is unknown. I hope to test it in the next of couple days.

I drove it with the D44/14b combo the truck came with when I bought it. Brakes were good, much better than they are now.

Then swapped in a D60 and discs for the rear. Complete garbage and always has been.

I will list off, in order, the combinations I have tried thus far. These are all on the D60/disc 14b, original booster, new braided drop lines. 1985 K5

1) 1985 K30 master cylinder, all else stock. Ended up with a very soft pedal. Much like now but a little worse. (pressure bled)

2) 1999 master cylinder with 4wdb, all else stock. I swapped this in the day after I finished #1 setup. Ended up with a very hard pedal. Stopped worse. (pressure bled)

3) Back to 1985 K30 master, bypassing factory prop valve, running straight line to front brakes. Rear line has an adjustable prop valve put in place. Still ended up with a soft pedal. Rear prop valve never felt like it did anything. (vacuum bled)

4) Some local brake company that "builds" systems for trucks/ cars/ hotrods tried to fix my problems. Ended up with some small "vette" master cylinder, bypassing factory prop valve, 2lb check valve on fronts, adjustable prop valve to rear with 2lb check valve. Ended up with the best setup so far, which doesn't say sh1t cause I still can't stop. Guy at the shop says it's the best I'll get without going hydroboost. Bullsh1t. I should be able to hold my truck on an obstacle, hydroboost isn't needed for that. (manual bled)

5) Tonight's work. I thought I had it this time. Picked up a 2003 Suburban 1500 master cylinder and matching prop valve from a crashed truck. It had a vacuum booster, not hydroboost. Got rid of all the previous crap. I have brand new hardlines on the rear axle. My lines go from the 2003 prop valve directly to the calipers (well, junction blocks) Nothing else on the truck. All corners bled nicely. (manual bled)

I'm at a loss.
My cousin has a k20 with D60 swapped in. He is running the factory booster and MC. At first it didn't stop well. He was told by a friend who worked for Chevy, to change the prop valve to XXXXX (prop valve unknown, need to check for any #s, might be K30 prop valve) Now his brakes are great. All he changed was the valve. I don't understand how that helped flow more to the larger D60 calipers but apparently it did. He is running factory drums in the rear though. It this point, I wouldn't mind constantly locking up the rears with my discs.
 
Example of how bad my brakes are.

My claim to fame, the Calender back cover, is a good example.
If I don't pop the trans into Neutral and stay in Reverse while coming off this pole in 4L, I will NOT be able to stop and will come down hard. I have lived with this and just gotten used to playing with Reverse/Neutral while on obstacles. :( It is not a controlled feeling. I can't have this while at Moab.



 
Also, if I push the gas and brake at the same time....the truck will roll faily easily forward AND reverse. This is 2wd and smooth concrete. Nothing skids, chirps, or spin. It just rolls :(
 
I've never tried to lock up the tires on pavement on mine, but in 2 high I've power braked it and it'll spin the rears without pushing through the front brakes:dunno:. Maybe you need better pads in the front.
Wish I was a little closer I'd like to stop by and help. I'll be out in Palmdale on Wednesday night or Thursday to look at a trailer. Maybe I could head down after, dont know what your work schedule looks like.
 
I think the pads are all "Posi-quiet" brand pads, which I've used on other vehicles and my DD S10. Seems to be ok. I also ran my fingers over all the discs and then checked some random truck at the shop. What I was looking for was a clear sign of glazing. I didn't find mine to be any different but it's probably not the approved method for checking lol.

If it means getting this fixed, or at least on a path.....my schedule is completely flexible. I'm fine at work and getting to BB has become top priority. hahhaha

Afterall, Babaganoosh needs his door stuff. Only been waiting a year, haven't you Ben :D
 
I'll send you a PM on Tuesday night when the guy with the trailer get back and let you know when I'm gonna be in Palmdale. You're like 40 miles or so from the i5/14 interchange, aren't you?
 
Hope you like beer and a burger, cause you'll get both. Plus I wouldn't mind helping with gas. It's quite the distance. :waytogo:
 
Im not worried about the fuel, and beer is good.:thumb: I better call it a night gotta be back at work in 6 hrs.:doah: I'll PM you Tues evening.
 
If you want, I'll give you my booster and master cylinder so you can rule that out. It worked great in my truck, no issues at all.
 
It sounds like it might be a lack of movement in the calipers or not getting full contact with all 8 pads:dunno: 2nd set of eyes is always good:waytogo:
 
When you say pushes back, does it move your foot, or you just feel increased pressure?
Its fairly normal for you to feel increased pressure. When the engine is running, the booster is pushing the master harder than you are, so to speak.
While the booster is supposed to hold vacuum when you switch the engine off, that is when its not being used.
If you hold the pedal down when you switch it off, you will bleed off the vacuum, I think.
With no vacuum, you get the full feel of what the booster was doing. To check the booster vacuum hold, crank the engine, run it a few seconds, turn it off, wait a minute or so, then try the brakes.
You should still have boost.
I suspect what you are feeling is normal. Not to say you don't have a problem, you obviously do, but that might not be a symptom.
I would walk outside and check my truck, but I am in the middle of one of our famous Florida thunderstorms, and it might literally kill me to go outside right now.
A tree across the road took a hit a few minutes ago. I checked out the window, no fire, but it looks like part of the top may be gone.

If your foot actually gets pushed back, then I suspect air in the system somewhere, no matter how many times you bled it or how.

A full hydraulic system, deadheaded, can have lots of pressure, but no flow. When you press the pedal, the shoes and pads move out to their stopping point. After that, the harder you press, the harder they press, but almost no fluid moves, because they do not move more than a tiny amount.
The rubber lines expand slightly, the friction material compresses a little, and the drums expand slightly and even the disks compress a very tiny amount.

But there should be very little movement. When you release the pressure, nothing should push back much.
If there is air, it will compress a lot when you press the pedal, and then expand back to its original size when you release the pressure.

Quick and dirty way to check, especially if you have the old steel top master, is to press the brake pedal down hard with the top off.
Usually without the booster helping.
Then release the pedal suddenly.
You might see a small movement in the fluid. If you see a jet of fluid shoot up from the master, you have air in that side of the system.
 
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