Newly installed aluminum master cylinder spongy brakes

[Bronk74]

Hello,
Installed new Aluminum master cylinder, bench bled it. Installed, I do have aftermarket front discs (power) installed. Bled all 4 wheels brakes still very crappy and spongy, will do some more today. maybe I may have over looked something any pointers appreciated.

 

[DirtDonk]

Did you already have the brakes set up this way and working?
Or did you just install the front discs at the same time?

What about the booster?
Always there, or recently installed as well?

 

[Bronk74]

Yes the

Did you already have the brakes set up this way and working?
Or did you just install the front discs at the same time?

What about the booster?
Always there, or recently installed as well?

discs were installed previously about 20 years ago they worked but…. They were very slightly spongy also was never fully satisfied with them, but the wheels would lock up and the tires would skid … I do not get that now i speed up i slam the brake and it almost goes to floor and slowly comes to stop.

 

[73azbronco]

Sponge=air. Make sure each line is free of air.

but first....., double triple quadruple check, front calipers are on correct side, ie, bleeder on top. Don't ask me how I know this.

 

[Wild horse 75]

Incorrect master size can create a spongy pedal. Ensure the new one is the same size as the old one.

 

[Bronk74]

Sponge=air. Make sure each line is free of air.

but first....., double triple quadruple check, front calipers are on correct side, ie, bleeder on top. Don't ask me how I know this.

Yes front calipers have bleeders pointing up.

 

[Bronk74]

Incorrect master size can create a spongy pedal. Ensure the new one is the same size as the old one.

I don’t think wild horses would do me like that!

 

[DirtDonk]

Well, not on purpose we wouldn’t anyway!
It’s not impossible for the manufacturer to ship us one with the wrong size piston, of course.
but as far as I know that has never occurred.
So far…

And if the piston was too small, it wouldn’t be spongy. It would simply have longer travel.
Spongy is air, or an expanding faulty hose.
Excess travel but firm is either improper adjustment, or too small of a piston.
Too hard to push, but still firm, would be too large of a piston.

These are typically 1 inch, or 1 and 1/8th inch piston diameter, so I believe that’s what you should have.
Either is fine for use with the booster, but without a booster, the larger one is pretty hard to push.
But moving all that fluid with the large piston, it would never be spongy. Again, unless you had air in the system. Or a hose was expanding.

I don’t remember if we talked about it already and don’t have time to re-read it all yet, but do you have an aftermarket proportioning valve?
If so, does it have the little valve that you’re supposed to pull when bleeding the front brakes?

 

[Wild horse 75]

I don’t think wild horses would do me like that!

It’s not that they would’ve done it deliberately. If they don’t know what master you originally had they could’ve given you a different one. Also you said they’ve always felt slightly spongy so it’s possible you never had the right size and changing it has just magnified the problem.

 

[nvrstuk]

Incorrect master size can create a spongy pedal. Ensure the new one is the same size as the old one.

Incorrect m/c won't create a spongy pedal. If the system is bled properly then the incorrect mc will be hard as a ROCK but you might have to push the pedal all the way to the floor or 2+ times to move enough fluid to fill the calipers/wheel cylinders. Sizing has nothing to do with sponginess. You might be mistaking long pedal travel for sponginess but they aren't one and the same.

 

[73azbronco]

^^^what this guy said.

 

[Bronk74]

Well, not on purpose we wouldn’t anyway!
It’s not impossible for the manufacturer to ship us one with the wrong size piston, of course.
but as far as I know that has never occurred.
So far…

And if the piston was too small, it wouldn’t be spongy. It would simply have longer travel.
Spongy is air, or an expanding faulty hose.
Excess travel but firm is either improper adjustment, or too small of a piston.
Too hard to push, but still firm, would be too large of a piston.

These are typically 1 inch, or 1 and 1/8th inch piston diameter, so I believe that’s what you should have.
Either is fine for use with the booster, but without a booster, the larger one is pretty hard to push.
But moving all that fluid with the large piston, it would never be spongy. Again, unless you had air in the system. Or a hose was expanding.

I don’t remember if we talked about it already and don’t have time to re-read it all yet, but do you have an aftermarket proportioning valve?
If so, does it have the little valve that you’re supposed to pull when bleeding the front brakes?

So I have an after market front disc conversion from wild horses that I bought and installed like in 2005 -06 time frame. It could be a faulty hose just getting old, What’s the best way to diagnose an expanding faulty hose? Would it be visible to the eye as you pump it?

 

[73azbronco]

Hose should be OK. I have never seen a hose deteriorate to mushy feeling. Thats about 75 years of looking at brakes. Stainless lines? should be fine. Was it bleed when installed? Can we get a picture of brake caliper and bleed valve?

 

[nvrstuk]

I have seen 'em mush up & expand... Course I was working at a dealer before the age of modern internal combustion engines... lol

 

[Bronk74]

Just bled all 4 wheels. The front compartment on MC seems to be foaming up not sure why I did bench bleed it. Not seeing any leaks anywhere
Any help appreciated

 

[Brush Hog]

Foam means tiny bubbles means you are sucking air some where.

 

[Bronk74]

Foam means tiny bubbles means you are sucking air some where.

I went through and tightened everything on the MC fittings and hose fitting ,,,will test tomorrow

 

[Bronk74]

Ok no more foam in brake fluid. brakes are better (basicly back to where they were with old MC. The brakes work but just not rock hard very spongy just like from Day one of the Wild horses front disc conversion. Starting to wonder if I should just disable the power boost and go manual! Because with motor not running brakes are very hard and stiff.

Another issue…..
now the brakes (Front) pull to the right and seems like the left rear want to swing around to the left . Very dis hearting at this point. Any advice or help appreciated

 

[nvrstuk]

Did you bench bleed the mc again AFTER you tightened and fixed the air leak that was causing the bubbles? You can't skip steps (sorry).

Air in lines will make some individual corners work slightly better and you might experience pulling.

Start from scratch and follow every single step mentioned earlier. We don't know if you have the calipers installed correctly or not. More than a few little things that add up and make it hard to diagnose.

Wish ya the best. I did brakes at a GM dealership 100 yrs ago... every step has to be done right or you will have symptoms. Once you finish it up you will be SO glad you did all the conversion work.

 

[73azbronco]

This guy^^^