New calipers and now brake problems.

[Houston Ben]

Hi all, 1986 C10 with 1" rotors. I did search, but had additional questions as well.

Last week I changed out my brake calipers and now my pedal goes to the floor. I can hold the truck, but I do not trust it to drive. One mistake I made was I left the RF bleeder loose and stepped on the brake. I heard the fluid squirt and panicked and released the brake pedal and it sounded like it sucked in air.


After that, I did the following:

First I bled just the fronts with no luck

Gravity bled all 4 starting with the RR LR RF LF method and still bad braking.

Pressure bled in the above same manner and still no luck.

I did accidently press on the pedal with the lid off of the MC, I did bleed again, but will this introduce air?

When bleeding the LR, there was a lot of air that came out. I would pressure bleed and pressure bleed, but the same amount would rush out every time. I have a hose attached to the bleeder screw which would suddenly jump at the end of the travel of the pedal.

I am at a loos and am running through brake fluid quickly. I can't find a lead, but I can hear the fluid squishing around when the pedal is pressed.

Pedal gets pressure when truck is off, but when I start it, mush...

I did not have these issues before the caliper swap.

Any ideas???

[mongocanfly]

Did you use the little tool to hold the proportioning valve centered?...
Lid off master will not put air in system ...

[Houston Ben]

Thanks for the reply,

Nope, don't know about it till now. This is necessary for bleeding? Your talking about the plastic thing that screws into the valve yes?

[mongocanfly]

Yes...mines aluminum but they do make plastic...if you dont use it the proportioning valve will think you have a blown brake and it trips... if your proportioning valve has the rubber plug on the end ,you can use a small screwdriver to recenter it..
This may or may not be your issue...but I learned the hard way on mine

[Houston Ben]

I will get one, thanks!

[Bluestep]

I would guess that you installed the calipers on the wrong sides. If the bleeder screws are not at the top you won't ever get the air out. After correcting it get someone to assist you in bleeding it, have them depress the pedal gently and you crack the bleeder to let the air out. It goes much faster and doesn't have the problems of messing with a hose and container.

[RUN GMC]

....also I had a problem with my brakes after rebuild/replace all the way around.....realized later I had to replace vacuum check valve and rubber gasket on brake booster and some vacuum lines including the one to the vacuum ball on my driver side fender......there was also a 3 way check valve that just fell apart when I touched to remove the lines...........

https://www.summitracing.com/parts/r...RoCV3QQAvD_BwE

https://www.summitracing.com/parts/rnb-80189?rrec=true

[lilpoindexter]

It sounds like the proportioning valve. I had a similar incident. i didnt know about resetting the little valve, so i bled and bled and bled and bled and bled, and eventually it moved back.

[akart]

Here's what I do: Button on top of proportioning valve has to be pressed while you are bleeding.I've fiddled in a clamp. Start from the back brake furthest away. Get a jar and put some clean brake fluid in it. Barely crack the back bleeder and attach a clear hose/tubing to the bleeder,nice tight fit. You have the end of the hose submerged in that jar of brake fluid.Open the bleeder just a bit more. Now pump the brakes not all the way to the floor like about 3/4 of the way. Watch the tube till it flows clear. I have actually pumped the brake by hand and watched the flow.Tighten bleeder without disturbing the hose. Other back bleeder next then move on to the front doing the furthest from the master first. So...The hose is in the brake fluid and it can't suck air back only fluid. Make sure to watch your fluid level in the master as you go. Another thing you can do if the fronts are being hard to bleed is get a pump type oil can,attach the hose from can to the bleeder and pump the air bubbles out/up from the bottom. Might have to drain some fluid out of the master as you go. This works really good w/a Hyd clutch. Sounds a little complicated but this has always works for me while I bleed them by myself. But a helper would make it easier. That was a mouth full !!!!

[Houston Ben]

Well, I ordered the prop valve bleeder tool...but it does not fit. I have decided to just buy a new prop valve (mine looks to be original) but not sure which one to get. POL has one that looks like it will work which is the AC Delco 172-1353 & 172-1361. Does anyone know if this is a direct swap? If not, does anyone know which one is?

Thanks for any help,

Ben

[Sabaka454]

Did you confirm you didn't mix up the calipers? Are the rear brakes properly adjusted and did check the wheel cylinders for leaks? If all checks out, then replace the master cylinder.

[Houston Ben]

Hi Sabaka,
Thanks for responding. Yes, calipers are on correct side, bleed screw is facing up. Have not take off the rear drum as there is no signs of leaks. The wheel cylinders are approximately 4 years old along with the master.

The brakes were working fine prior to the caliper replacement, how would it go bad just from replacing calipers? I don't know much about brakes in general so all help and knowledge is appreciated. If it is bad, guess I could do the late model MC swap??

Ben

[Dead Parrot]

One way the MC could have failed: When you bled the brakes, the MC was pushed into a part of the cylinder it didn't normally operate it. Possible that part was pitted with rust. Operating in the pitted area damaged the seals inside the MC. Now they won't hold pressure.

Discovered this failure mode shortly after hooking up the new to me boat and driving home from the lake. Had to do a couple of hard slow downs to avoid highway silliness. Those went fine. The boat required just enough extra pedal pressure to nudge the MC into long unexplored territory. Next hard slow down attempt, pedal went to floor and brake fail light came on. Was an interesting next few miles home.

[mongocanfly]

Give POL a call about your prop valve....you'll need one for disc/drum..that's who I got my hydroboost from....very helpful folks...

[homemade87]

Originally Posted by Houston Ben

Hi Sabaka,
Thanks for responding. Yes, calipers are on correct side, bleed screw is facing up. Have not take off the rear drum as there is no signs of leaks. The wheel cylinders are approximately 4 years old along with the master.

The brakes were working fine prior to the caliper replacement, how would it go bad just from replacing calipers? I don't know much about brakes in general so all help and knowledge is appreciated. If it is bad, guess I could do the late model MC swap??

Ben

how would it go bad just from replacing calipers?

This is a good question . I usually use common sense when I have a fail after I just touched something . 9 times out of 10 its usually something I have done .
The one thing that can happen is the fluid can leak low enough that the master an suck in air when the pedal is depressed if not paying close attention to the level when dissembled . If this happens the master will have to come off and bench bleed . The master is a step down type on your 86 and they are a real pain to get the air out .

I would hold off on the prop valve . Most likely not the problem . Take the master off and get some bleed fittings and hose and bleed the master .

Bleed , bleed , and bleed some more . Bleed it at a angle both ways as well . I cant stress enough how hard the step master is to get all the air out .

I believe in you situation this is most likely the problem . I would try this first as it does not cost anything to do . After that bleed both sides completely so any air that made it in the lines can travel to the caliper and escape .

[truckin 79]

Bleed the brakes the good old fashion way. Have someone in truck push on pedal 3 times hold and then open bleeder. Then watch and see how much air comes out. Then keep bleeding till all are is gone

[homemade87]

Originally Posted by truckin 79

Bleed the brakes the good old fashion way. Have someone in truck push on pedal 3 times hold and then open bleeder. Then watch and see how much air comes out. Then keep bleeding till all are is gone

I have not ever been 100% successful bleeding the step type master this way . You may get it close and always feel the brakes could be better .

[Houston Ben]

Damn it... Bought new MC, bled with bleeder tool and saw all air come out with good stream out both holes. Bled brakes and same crap. Driver rear shoots out air and driver front keeps having bubbles come out even when not pressing on pedal.

Started truck and same **** feel. I bought a proportioning valve bleeder tool, but it didn't fit my valve OR it was just a PIA to get in as I could not screw it all the way in.

https://youtu.be/-vzcQh8FdxA

https://youtu.be/9qVm4crPqm0


Any clues???

[74CustomK20]

You're getting are in somewhere. It might be your calipers? Just because something is new, DOESNT MEAN it's good. Or you have developed a leak in a line. My prop valve tripped one time. I opened all 4 screws and mashed my brake pedal 3 times n it reset. Made a mess, but it worked.

[Houston Ben]

I barrowed a friends pressure bleeder and will work on it today or tomorrow. If that don't work, then I will buy a new P valve...

[hatzie]

Shouldn't need a combination valve. They're pretty tough and they last darn near forever.

Here's what you're dealing with internally...

There are two tools you need if you've managed to make the combination valve confused or angry with you.

This tool pulls on the bleeder rod so that it opens the metering valve to the front brakes.


The differential pressure valve has to be centered when you're bleeding the system. Locking it down in the centered position helps immensely.

If the differential pressure valve is out of whack you can re-center it by opening bleeders on the opposite end of the vehicle from the direction it tripped and pushing the brake pedal down just til the BRAKE light goes out.
If you overdo it just close the open bleeders and open the ones that you left closed and push the pedal carefully down til the BRAKE lamp goes out.
Once the differential pressure valve is centered you unscrew the warning lamp switch from the combination valve and screw in the differential pressure valve tool like this cutaway shows.


Pressure pot bleeding is IMHO the best way to fully bleed the system when you have no assistants... and when you don't want to replace or re-build the master cylinder.
Why do I mention the master cylinder???
The pedal push method almost always pushes the old piston seals that are stiff, since they aren't in their first flush of youth, into an area of the master cylinder bore that's not worn, so it's smaller, and the stiff cups don't rebound to the diameter of the worn bore quickly if at all. That section of the bore can also have more than a little corrosion that'll sand the seals as they grind past it... That's why your master cylinder sometimes blows out soon after a brake line failure.

[mongocanfly]

yep..the valve has to be centered before you put the tool in

[Houston Ben]

Little update,
Had my boy help me bleed again. Bled the LR for a while and it finally stared to not sound like there were bubbles in it. I pushed the brake pedal which also did not feel "bubbly" anymore. I took it for a drive and she stops pretty good now. Is it just my truck, or do all these trucks have an initial hard push when stomped on where it does not feel like the brakes are applied until the pressure releases a little then the braking begins?



Looking at my prop-valve, it appears someone put a piece of clear plastic with the bleeder rod. When I was bleeding, I could hear what I assumed was the prop-valve tripping and resetting. It would make a sound when I bleed the brake, then make another sound when I had my boy build the pressure back up after I closed the bleeder screw. Do you think this was the prop-valve?




Also, if the prop-valve is tripped, shouldn't it be cutting off fluid to front or back brakes? I can get fluid out of both no problem.


Thanks for your time an patience on this. Not totally positive it is solved, but it is better.

[homemade87]

Good your making progress . It sure sounds like you introduced a lot of air in the system when the calipers were off . Easy mistake to make if not paying attention .

Since you made some improvements I would do a 4 corner bleed starting with the farthest point and working closer to the master . Its hard getting all the air out but keep working on it , it will come out . When I do a full flush it usually takes a qrt of fluid or more . Brake fluid gets old as well and does not hurt to change it .

I still say you prop valve is fine. Dash brake light would be on if it was tripped . Just keep working on it .