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Brake Woes (pedal to the floor!)

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Deaol

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Hoping I am posting in the right section, and maybe someone can help.. situation is driving me bonkers.

Recently swapped some 4.10 axles under my 84 k10 (dana 44/14bff from a 76 3/4) No lift, stock height.. just a firewood rig.

New rear brake cylinders/shoes & lines, new front calipers/soft lines, new master cylinder (removed the 1/2ton master cylinder and used the same stock/new master that the 3/4 had, vacuum no hydro)

Bench bled the master cylinder, have bled and bled the system numerous times now no air from any corner.

Pedal still goes to floor, brake light on, but the rears are locking up no prob when hitting the floor, fronts are not. Can pump up the system and get a hard pedal when truck not running.

Any ideas? Is there still air in the system that I can't get out? I have heard of issues with the banjo bolts/washers on new calipers.. but the bolts are brand new 7/16-20s. Driving me nuts!

Thanks guys!
 
Do you get good flow of brake fluid from the front when you bleed the brakes or when you bled the master? I had this problem with my rear disc conversion and it ended up being a bad master cylinder. I was hardly getting any fluid. I cracked the lines at the master and had the same problem. Gravity bleeding can work well. just open the cap on the master and open the bleeders and leave it for a few hours or more. I accidentally gravity bled my rear calipers when I put them on. I didn't get it done in one day, and the next day, they were full of fluid and took very little bleeding if any.

If you get good flow when someone presses down on the pedal (with the truck running) and you open the bleeder, then your lines are probably good. I tried bleeding with the truck off, but I just don't seem to get as much fluid. It is possible to have an air bubble. I use a clear jar and a hose to bleed the brakes. I try not to open the bleed screw more than I have to. I want to see the air come out of the system. I also keep the hose under the used fluid in the jar, to see the air or fluid come out. If you open the bleeder too far, it will get air in the bleed hose.

The other thing you didn't mention was the proportioning valve. I replaced mine when I went to 4 wheel discs. The kit came with a new one. I don't know if the 3/4 ton proportioning valve is any different than the 1/2 ton trucks. It might be possible that you have a problem with it.
 
It always takes a while for my pedal feel to be good after doing new brakes. One the pads and shoes cut in, it gets more firm.
 
When you bled the brakes did you do the farthest from the master cylinder to the closest?
How's the condition of the rotors, are they too thin? If you jack the front end up do the pads make contact with the rotors when you first press down on the pedal and are you able to turn the tire by hand? What's the condition of the rubber brake hose going to the caliper?
Having the brake light come on makes me think there's still air in the system. Best thing to do is power bleed them.
 
Thanks for the replies guys.

Haven't touched the proportioning valve, it is the stock one. I get great flow from the front and rear bleeders, with the truck off they bled well when i did a gravity bleed. When bleeding I started with the passenger rear and worked my way forward, bleeding the drivers front last. The front rubber brake lines are brand new, and with the pedal to the floor I cannot spin any of the tires.

Think ill see if I can source a power bleeder around here or maybe see if a shop can do it for beer/cash. Hopefully that will do the trick.
 
Have you ever had good brakes on this truck since you put on the new parts?

If not, then you might need to consider there is something basic wrong. I'm real suspicious of the master cylinder.

A master cylinder for a drum/disk system will have one bore larger than the other to supply the disks with more fluid per stroke.
Its late, I'm tired, and mostly a Ford man, but I have read here about people changing types of MCs and finding the lines hooked up backwards.

In other words, one fitting is larger than the other and they are swapped on different cylinders.
If you have the drum port hooked to the disk brake line, you will never get enough fluid to extend the caliper pistons with one stroke.

I'm quite sure that the bore size and port location is available on the web somewhere for all MCs, but I have no idea where.

I suppose you could connect two short stub lines to the two ports, and catch the output in different cups for one full stroke, but that might get messy.
Then again, since you have bench bled it, you may already have the parts you need.

I want to say that there are adapters that let you swap the lines, but I'm not sure.

If the pedal is nice and hard after you get it pumped up, then odds are its not air. Air stays spongy a long ways.

As a real long shot, if you pump it up sitting still, take your foot off the pedal, wait and then have a good pedal every time until you actually move the truck, then there is one other odd possibility.

A really warped rotor, or a wheel bearing about to fail can cause the caliper to get pushed back farther than normal and take more than a full stroke to move it back.

Saw that on one years ago. Guy had actually warped his rotor by hitting something, and as he drove, it beat against the pads and pushed the calipers back.
None of us could figure out why his pedal went to the floor until I happened to drive it.
Unbelievable vibrations when you hit the brakes.
Of course, he never bothered to mention that............
 
Check all the things Fordum just listed,like the lines at the master-they can be swapped around on some masters and there are adapters available to let you put the right lines in the correct ports...I had swapped a Delco master onto my truck that originally came with a Bendix style cylinder and the lines would only screw in if I swapped the one formerly in the rear port to the front one..

I was able to bleed the brakes OK,but all I had for brakes was rears that locked up instantly with a feather touch to the pedal,and the fronts barely did anything...bought two brass adapters at Auto Zone for 1.69 each and put the lines back where they belonged and re-bled the brakes and now they work perfect..

It's possible the master is fine though,maybe your rear shoes still need to be adjusted tighter to the drums,you should turn the star wheel until you can barely turn the drum by hand,then back them off a bit until they barely drag..if there is too much clearance between the drum and shoes you'll have to pump up the pedal more than once before they even touch and it'll be hard to bleed them...


I remember my friend jeep having "Un-bleedable brakes" once after we replaced the front calipers..we were careful to match the old ones up to the originals because we had problems getting the right ones before--we installed them and tried bleeding it for 2 days,pumped a gallon or two of brake fluid thru them..replaced the master cylinder in case we trashed it from pumping so much..no change,all I got was a nice firm pedal after bleeding it--take your foot off it for 5 seconds,and it'd go RIGHT to the floor again..we got pissed,ended up towing it to a brake shop..

The guy took one look at the calipers,and said "huh"..took one off,flipped it over,stuck a 2x4 in between the brake pads,and had his helper pump the pedal...did the same to the over side too...ten minutes and 50 bucks later,the Jeep was driven home with perfect brakes!...ended up we put the left caliper on the right side,as did the previous owner,we copied his mistake!..so the bleeders were facing DOWN instead of UP,and we'd never have succeeded in getting all the air bled out!..:doah:

I remeber one other vehicle I helped bleed brakes on drove us batty..spent all day pumping the pedal on a '78 Camaro at my friends shop--all he replaced was a front hose that was all tattered and had fabric showing...had good brakes when it drove in!.
After a good hour of me pumping up the pedal and him opening and closing the bleeders,we were stumped..started blaming parts like the master cyl,etc,but they appeared to be good,and did work fine before we replaced the brake hose...we decided to try bleeding them once more before giving up and pushing it outside so another car could be worked on..and tell the customer to take it to the shop up the street and let them pressure bleed it..

Well,as I was pumping the pedal up,I noticed a weird squeaking-creaking noise...then realized the car was moving slightly side to side as I pumped up the pedal!....then when I finally got a firm pedal and my friend opened the bleeder,I saw the car move sideways back the other way about an inch,and I heard that creaky-squeaky noise again...then I thought of something..while reading a Motors manual troubleshooting chart under "brakes wont apply" I saw "defective or loose wheel bearings" listed..I though WTF,ow can a wheel bearing affect the brakes..:dunno:

Guess what!..

I got out and grabbed the drivers side at the 6 and 12 o clock position,and pulled and pushed on it--it moved in and out a good half inch!...the frigging outer wheel bearing was TRASHED,and so loose I was surprised the car could even be driven that way!...ten minutes later after replacing the worn bearing and adjusting them properly,the brakes bled in about 30 seconds!...:doah:..sometimes the stupidest things are the problem..
 
If you still have access to the '76 donor, look at where the brake lines are routed (front and rear) and compare that to the 84. I think these years are crossing the change from which line connects to the front and rear of the MC.

You could look up the specs on the masters. The 76 one may not be any bigger or any better than the 84 one. If so, you could swap the master back to solve the problem.

Can pump up the system and get a hard pedal when truck not running.
Click to expand...
You're probably just depleting the booster of vacuum and feeling the manual effort.
 
Master cylinder definitely could be an issue. As for port swapping, its common. I ordered a 3/4 JB7 master when I upgraded to 3/4 ton axles with the big brakes. I was a bit perplexed hooking it up until I saw that it was set up exactly opposite to my factory one as far as the location of the large/small port and big/small resevoirs. I used a vaccuum bleeder with good results.
 
paratrooper307 said:
Master cylinder definitely could be an issue. As for port swapping, its common. I ordered a 3/4 JB7 master when I upgraded to 3/4 ton axles with the big brakes. I was a bit perplexed hooking it up until I saw that it was set up exactly opposite to my factory one as far as the location of the large/small port and big/small resevoirs. I used a vaccuum bleeder with good results.
Click to expand...

Yeah the master I have is a 3/4 JB7 also, but the front/rear reservoirs were the same as the stock k10 master (small front big rear)

I will be taking everything everyone has posted into consideration tonight, I stopped on my way home from work and grabbed some get **** done juice and hopefully these brakes will be functionally before the box is empty!

Thanks again guys
 
The different size reservoirs might be in the same place, but the lines might still hook up backwards.
In other words, the front brake line might be hooking to the small reservoir.

There is one other possibility which I thought of, but did not mention because you said you used the MC off the other truck and it had power brakes.
But the masters for manual and power brakes have a big difference. The "dimple" on the piston where the pushrod goes in is shallow on a power MC, and deep on a manual one.
If you put a manual MC on a power system, you are not getting enough stroke.



Never had that problem personally.............:whistle:
 
I'm not sure if you could put one from a manual onto a power booster on a GM,the push rod clips into the piston with an o-ring thing,on the manual ones and goes all the way to the pedal...I dont know off hand it the seat in the piston is the same depth or not on a manual vs power masters..some boosters have adjustible push rods,but you dont see them very often..
 
Not sure where I got that info, may not even apply to GM, I work on so many different things.
But I'm sure that its true of some MCs, because I remember running into it before.......
 
Are the front calipers correct from side to side, meaning the bleeder screws are pointing up? Sounds simple and dumb but it happens a lot, you'll never get all the air out if they are like that.
 
A positive UPDATE; the brakes are now fully functionally and the stopping power is perfect.

I really want to thank everyone who contributed! :thumb::waytogo:
CK5 has an awesome community!

-------------------

Probably the main contributing factor was the passenger side caliper was indeed a drivers side, so the bleeder screw was pointing down. The calipers were new so the auto parts store must have boxed a passenger side caliper in a drivers side. I didn't even think/look twice when installing.

I pressure bled the brakes (pushing new fluid from the bleeders) this worked like a hot damn and highly recommend this method from the get go.

The rear shoes were not properly adjusted, so after a few rounds the rears were snug and braking great.

I did run into a issue with the check valve on the booster leaking, though I do not think it was contributing to the pedal to the floor, it is defiantly something that i missed.

All and all, shes safely back on the road and ready to haul some crap or get out camping.

mn0p.jpg
 
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