Hey guys,

So i have replaced my master cylinder, all front brake lines and rear wheel cylinders. I have bled to system by both gravity bleeding and pumping the pedal style bleeding. It is still very soft and spongy and if you pump it once it gets harder. Do you think this is still air in the lines or could my new MC still be bad?

Thanks!

-Jon

 

Did you bleed the master cylinder? If you didn't you got air in the master cylinder and it isn't coming out unless you take it off and bench bleed it..

 

If you can pump and the pedal gets stiffer, then you still have air in the system. I disagree about the bench-bleeding - that is done to give you a head start but if not done, you can still bleed the conventional way, it will just take longer for the air in the MC to work it's way all the way down to the wheels where the bleeder screw is.

 

I always prefer to bench bleed the mc, but this one did not come with the tubes to do it. I will rebleed it this week and see what happens. So you don't think the master is bad again?

 

You still need to bench bleed it. You'll pull your hair out trying to get the air out once it's bolted up.

 

Pretty sure the NAPA ones don't use tubes for the bench bleed any more... Just put in the plugs and pump it a handful of times. At least that's how the last 3-4 I've put in were....

 

You can bench bleed it on the truck if you make yourself a little kit.
Just take old short pieces of tubing and bend them to empty back into the reservoir. So they attach at the outputs and curve up to the reservoir.
That way you can pump away and make sure no more bubbles. Better that they are long enough to be submerged. It's easier to tell when you're good.
Easier than the bench.
Then re bleed your lines and it should be good.

 

Oreilly's sells the kit, if there's one near you... Dorman® Help!® 13911 - Mstr Cyl Bleeder Kit | O'Reilly Auto Parts
I tried bleeding it on the truck and it didn't work.. Maybe I wasn't lucky or had the right touch. You'll be saving yourself alot of time and aggravation by getting the right tools and bench bleeding the hell out of it. When you get it back on the truck make sure your rear brakes are adjusted correctly and re-bleed them. If the pedal is still soft, open the master cylinder and have someone slowly depress the brake pedal while you watch for air bubbles. If you see any, then you still have air in it. If not then look to see if only the forward part of it shoots up a little fluid as someone depresses brake pedal. If this is the case, then you more than likely have a bad master cylinder. Especially if was a reman. I went through 3 to get a good one although the first one just had jacked up threads...

 

I've done it both ways. On my last truck, I used a vacuum pump to bleed an entirely new system.

On my crew, I just put on a new F350 MC and I bench bled it Then to make bleeding easy, I took the calipers off the rotors and filled them with fluid from the old MC before removing it. Then, I installed the new MC, and then took a C-clamp and squeezed the fluid back to reverse bleed it. Nice and tight.

 

If you haven't bench bled the master cylinder, then you need to start over, take it out of the truck and bench bleed it. No one can tell you if they think your master cylinder is bad because you're not setting it up correctly and the observations you are making right now are invalid. Anything else you try between now and then is wasted time.

This is not true. Bench bleeding is standard procedure that you will find set forth in any shop manual, or instructions that come with a new MC. The bore does not travel far enough when actuated by the brake pedal to push all of the air out; furthermore the MC is not level when in the truck. The only way to completely purge an MC of all air is to actuate the bore by hand with it on the bench, hence the name. If you have experienced otherwise, then you are getting lucky, or are used to spongy brakes.

Bench bleeding needs to be at the forefront of the mind of anyone replacing an MC. When it's not, threads like this are started.

 

I've always "bench bled" mounted in chassis with return lines to the MC. In addition there is a trick with the prop valve (pull the pin out?). I didn't know the "trick" and used a lot of fluid (several quarts) to get mine bled after MC replacement ('78 F250). I started with a vacuum pump and finished with conventional pump type bleeding. It did turn out OK though.

Once, on a newer model Jeep with ABS, I took it to a garage for pressure bleed when I couldn't get the air out. Pressure bleed fixed it.

 

It's in the manual because it's the best way to get the brakes bled the fastest - what we today call a "best practice". But to say it's the *only* way you will get the air out is not correct and these other folks on this thread telling of several different methods that worked for them is testament to that. I think you are crediting bench bleeding with some magical quality that it does not posess - if it were that critical, we'd have a whole lot more such threads and folks running into walls because their brakes did not work. It's not that exact of a science.

Please do not misunderstand - I am not saying bench-bleeding is bad or not needed. On the contrary, it is the best way, just not the only way, IMO.

 

While bench bleeding before installing in the truck IS the correct/preferred method.
In my experience, having done it both ways, it is my experience that both methods work without spongy brakes.
I totally understand the concepts in doing it on the bench.
Just saying in real world practice it works for me.
Guess I'm just lucky.

 

I am not crediting it with some magical quality. I credit it with two very quantitative characteristics, stated very clearly in my previous post:

1) The MC must be level when bleeding, which is not the case as it sits in the truck (this can of course be remedied at the expense of convenience)
2) The MC must be bottomed out to work all of the air out. This is not guaranteed to happen in all cases, and is exacerbated in the presence of power brakes.

But we do have a lot of these type threads. It's a moot point either way; the number of threads about a particular topic depends heavily on many other factors besides the general public's understanding of brake installation.

Understood.

That might be possible in some specific situations, but this cannot be made as a generalization, for the two reasons stated above.

 

I agree, you are! I wish I could have some