Spongy brakes

[recian]

So my 81 has a spongy brake pedal. I drove a couple other trucks prior to this one and they were the same way. This truck was the first one I drove with an alum/plastic master. Rest had solid cast ones. So far I've changed the black brake fluid and bled the brakes along with replacing leaky rear cylinders + lines and adjusting the new rear shoes out. Its a little stiffer but still goes half way down before grabbing. I'm leaning towards the proportioning valve or front brake hoses next. I was reading up on the brake diagnosis on the sticky to get a few ideas. Anyone here seen something that's common?

 

[Swims350]

when you bled how did you do it?

sometimes that's your biggest problem. I preffer 2 person, one pumping and holding, and not quickly stabbing the pedal either.

ps rear frist, then ds rear, ps front then ds front of course.

first off you covered some good ones, I fought mine over and over on my 88. parts are cheap enough I say go ahead if you got the cash, buy the front lines, the flexible ones, rear if you have not bought it, then change calipers and pads too.

I found brake hoses dirt cheap online, rockauto with a discount code or amazon even. calipers only cost about $12 or so a piece last set I bought also.

rebleed and see if it's gone, because if not I say it's in the rear. Mine was kept having it go halfway down or more and drop off, I changed everything, except for the booster. Mine was rears needing adjusted out and the rear hose needing changed.

 

[recian]

I always use 2 people to bleed. When I was done there was clean fluid in a steady stream coming out. I prefer not to change the rear hose since where it connects to the line is a solid ball of rust. I don't want to try and change the F to R lines even tho they have a joint in the center and I can get pre-bent stainless ones from LMC. My truck isn't too rusty since it's spent it's whole life here in NC but it was a farm truck and I've never seen a 100% rust free original square body lol. For a 100% original truck it's holding up pretty well. Just needs a fender and doors due to rust.

If i do the brakes I'll have to buy all new lines from LMC and pick up some hoses and do it all at once. LMC sells the whole stainless set (8pcs) for 220 and all 3 flex hoses in stainless for $100. So for around $400 (shipped) I can get all new brake lines.

 

[bucket]

If there's no air in the lines and the rear brakes are properly adjusted, I'd check the front caliper pins and bushings to make sure the caliper is moving properly.

 

[chengny]

So far I've changed the black brake fluid and bled the brakes along with replacing leaky rear cylinders + lines and adjusting the new rear shoes out.


I don't see the master cylinder among the components you've changed. Before getting into the cost and time of installing new brake lines I would try a new M/C.

Excessive pedal play is a textbook symptom of worn cups (seals) within the M/C.

 

[recian]

I was saving the master for last. It looks like it was replaced at some point. It's the cleanest thing on the truck even tho the fluid in it was black. I need to check the calipers and hoses next to make sure they're not cracked up or having any other issues. The rear flex hose was a little dryrotted but not too serious but I know the fronts get more abuse.

 

[chengny]

By any chance did the truck sit unused for some length of time?

That will accelerate loss of sealing between the cups and cylinder walls.

 

[recian]

I'm not sure but would I assume it did judging by the black fluid. The original owner drove it occasionally, he passed then the family enherited it, rebuilt the engine, got it running and sold it to the guy I bought it from who drove it for over 3 years and put 60k on it.

I plan to replace the rubber hoses next but to do so I need new brake lines since they're all rusted together. I ordered those parts from LMC today. I'll get calipers and a master from the local auto store and do the whole system at once. My fronts are squeaking so I"ll probably do pads and rotors just to be done with the whole system.

 

[Swims350]

I never said change hard lines, I never do, not unless they are rusted, leaking or the ends twisted off.

I meant the rear flex line and if you have not changed it, DO IT. TRUST ME.

I fought mine over and over, new master, new flex hoses up front, calipers, wheel cylinders, still had a crap pedal, changed that rear line, instant improvment, then I adjusted mine out since one wasn't right and it was fixed.

I know you adjusted yours out, I read it. That's whay I said if you have not done so change the front flex lines, and maybe the calipers, rebleed and see if it's fixed, if not then change the rear line, flex line. If it's rusted one big ball all the more reason to change it. If those lines rust or break any parts store has some lengths you can buy, bend by hand and replace both rear axle hard lines very easily. I've had to do that on every vehicle I've owned I think.

 

[recian]

Yeah I managed to get the axle lines replaced. I had to cut the lines and put a socket on the fittings due to the rust, otherwise they just wanted to strip. I left the lines on the cylinders and pulled them all out together. There is no longer anything to put a socket on at the flex hose side so I need the hard line too. Same thing for the fronts. I've got parts on order, just have to wait til they get here and then get the time to take it to she shop and do it on a saturday that I don't have to work.

 

[dhamp]

Mine has new front lines, new MC, new calipers and hoses, new fluid.....still a little spongy. It stops when I need too, so I just figured that's an old breaking system. Need to check my rear adjustment tho. Now would be a good time since I've got it in the garage already doing some tune-up stuff.

 

[recian]

I ordered new stainless lines, stainless flex hoses and joint from LMC. (I'll have to replace the lines in order to change the flex hoses since they're all rusted together) I've got a new master, new calipers, pads & rotors + wheel bearings. The rear wheel cylinders and shoes are new. Replaced last weekend. Next weekend I"m going to do it all at work since I'm off. I'm going to cut the drums too instead of replace since theyre $55 ea plus it'll allow me to get a better adjustment on the rear also. There's no hole for adjustment so due to the lip on the drums I couldnt do a good adjustment.

 

[recian]

Got everything put on saturday. I ended up having to cut 90% of the lines and put sockets on them since they tried to strip even with snapon line wrenches. I also found out there's one line from prop. valve to rear that is bolted under the engine mount. I ended up cutting it at both ends of the bracket and running the new one on top of it. Otherwise the job was pretty easy once I got the fan shroud out to get to the proportioning valve.
The auto store ordered me the wrong calipers so I ended up not changing them.

The pedal is MUCH stiffer now. At first it felt like non-power brakes. With the engine off the pedal doesn't move it's so solid. It's softened with the break in of the pads and shoes. Now after 10-15% pedal travel it grabs hard. I can lock the front wheels by putting about 50% pedal or more.
The line at the prop. valve that goes to the rear was a little loose and leaking slightly so I think the system may have sucked air into the rear and need to be re-bled causing that issue.

 

[dhamp]

Glad it worked out! Now you should have worry free breaking for a looooong time!

 

[recian]

I fixed that one loose line and haven't had a problem since. I haven't had the time to bleed them again but I'm hoping that fixes the delay.