I'm at my absolute wits end- Fading Brake pedal despite best efforts

[Chester]

What we were doing with the not so pretty custom special service tool was sufficient, like Pin_Head said, modulating all 3 segments together vs one at a time yielded the same result, flushed the contents of the ABS reservoir and replenished with fresh fluid. Thanks Pin_Head.

 

[DARKNESS]

So the master cylinder got messed up from pushing the brake pedal too far while bleeding?

 

[Chester]

A few points worth taking away from this; cliff notes?
The ABS unit has fluid in it that might be as old as your truck. It's not too difficult to put together a test jig, or you could just force the ABS to modulate with hazardous driving (easier), but the contents of the ABS modulator should get flushed out (fluid, air), might be the cause of spongy brakes.
Just because you've replaced the master cylinder, with a rebuilt, it could be bad. And just because you replaced the replacement with a brand new one, it could be bad too. Where we screwed up was not fully closing off both ports. We now have plugs to fully block them off, and the new master cylinder pushes on through even with the ports closed, whereas the rebuilt doesn't. However, the rebuild unit appears to have had a folded sweeper on the front piston assembly, it had a crease on inspection, which may have been letting fluid by. It was fixed, or unfolded and is now the functioning master. Had we had plugs at the time, we would have discovered this, but at the time, we were feeding the outlet of the ports back into the reservoir, making sure there was no air, assuming the assembly was working fine, as it appeared.
EDIT The method we use while bleeding involves pulling a vacuum on the bleeder before it's opened, and kept it on until we were finished with that bleeder. We use a hand held aspirator (Snap-On, but similar to a mighty mac) and draw vacuum on a clear vessel which is connected to the bleeder valve. Vacuum above about 5"Hg. will draw atmosphere air through the threads of the bleeder valve. The air comes out the tube and not into the brake system, but the air in the tube flowing to the vessel could get drawn back when the pedal is released with the valve still open. Teflon tape on the threads of all the bleeders solves this.

After a while, brake fluid doesn't burn your hands.

 

[Chester]

So the master cylinder got messed up from pushing the brake pedal too far while bleeding?

I don't doubt that might happen, but it didn't happen in this case, I don't believe.

 

[Pin_Head]

What we were doing with the not so pretty custom special service tool was sufficient, like Pin_Head said, modulating all 3 segments together vs one at a time yielded the same result, flushed the contents of the ABS reservoir and replenished with fresh fluid. Thanks Pin_Head.

Is think it would be helpful to post the details of your SST along with pictures in case someone else might need one.

 

[Chester]

The resolution was a master cylinder. There is still some work to be done but at least I have brakes now.

By no means do I regret all of the other parts that were purchased as they were all necessary.

I essentially have an almost entirely new braking system every component except the ABS actuator.

What about the rear wheel cylinders? And so what you used a case of brake cleaner on every inch of hard lines while laying on your back with a brass brush looking for damage, they're shiny like new, but they're still 18 years old.

 

[DARKNESS]

I don't doubt that might happen, but it didn't happen in this case, I don't believe.

It's hard to believe you got two faulty MC's in a row and were not the cause of it, but I suppose it's possible.

 

[scrowley]

It's hard to believe you got two faulty MC's in a row and were not the cause of it, but I suppose it's possible.

It's happened to me. They sit on shelf for yrs and dry out. Then get damaged from being cycled dry. how many ppl buying 80 mc's. From mid 90's ...who knows how long it's been sitting there.

 

[Chester]

It's hard to believe you got two faulty MC's in a row and were not the cause of it, but I suppose it's possible.

Yeah, surprisie surprise surprise. I went ahead and honed the bore, used a triax with #1200 Al2O3 paste, finished the ends with a split sphere hone, didn't want to maybe bell mouth the front and rear. I've never seen a bad one either, and I probably rebuilt my first around 1967.

 

[DARKNESS]

It's happened to me. They sit on shelf for yrs and dry out. Then get damaged from being cycled dry. how many ppl buying 80 mc's. From mid 90's ...who knows how long it's been sitting there.

Good point, didn't think about them drying out on the shelf. Looks like I'll be rebuilding mine rather than buying new or reman if the time comes.

 

[musthave]

What about the rear wheel cylinders? And so what you used a case of brake cleaner on every inch of hard lines while laying on your back with a brass brush looking for damage, they're shiny like new, but they're still 18 years old.

The insides of the hard lines are glistening in their 9th lathering of new brake fluid. Yea, 18 years old. If you get that bender we'll put in some new hard lines too. Does that bender work well with beryllium? I want something that will last. Rear wheel cylinders, yea, hey @beno...

 

[musthave]

Is think it would be helpful to post the details of your SST along with pictures in case someone else might need one.

Good point, someone else will benefit from that. We'll get some pictures and explain, though rudimentary in design, it worked great.

 

[Chester]

Good point, someone else will benefit from that. We'll get some pictures and explain, though rudimentary in design, it worked great.

It might be worse. That wire I found and stripped for stranded conductor,, I think it's the missing link up or charge port something to the Granddaughter's iphoner blue teeth thing, big trouble on scrap wire cannibalism here..

 

[70Cruza]

Awesome!!!! read to the end.......Almost sad its over...........

Thank you all for sharing. I think I have all the info I need to trouble shoot mine now. Thanks guys for the Diagrams as well. Will be looking for this Custom SST as well..................

Ill drink 6 for ya'll tonight! .

 

[OGBeno]

It's hard to believe you got two faulty MC's in a row and were not the cause of it, but I suppose it's possible.

I'm going to check the date stamp for production when I get it back and warranty it.

Apologies for a bad part.

Glad this has been remedied

 

[1973Guppie]

I was right! what's my prize?

seriously though I have had several master cylinders bad right out of the box, oem and non oem, they are all rebuilt anyhow.

 

[Pin_Head]

I was right! what's my prize?

Hey! Your prize is to go to the back of the line. The first post on page 1 said it was a bad master and it was the first thing I mentioned on page 1.

 

[Chester]

I was right! what's my prize?

Hey! Your prize is to go to the back of the line. The first post on page 1 said it was

Thanks to all of you who posted, even the numb nut stuff was helpful, and NLXTACY for the wits end in the title!

 

[NLXTACY]

Wits' End seems to be a problem solver

 

[DSRTRDR]

just for the record: when we got an OEM replacement master cylinder for our 80 from CDan last year, it was NOT defective

we installed it, we bled the system, and the brakes have worked fine ever after