[lincoln31]

Man, I'm tearing my hair out! I've posted a couple of other times on my disc brake conversion and appreciated the tips, but I'm still stuck. I can't get the front discs to grab. When I bleed them, there isn't good pressure. I get kind of a spurt, then a dribble. The rears have a good stream of fluid.

I also have a bad power booster, which I got replaced today. The guy I bought the system from told me two things- that I can't use an adapter nut on the bigger size outlet port on the m/c. He said I needed to use the size line that will screw into the outlet. In other words, the two out lines from the m/c are different sizes and I need to use different size lines, not use an adapter nut on the m/c and use the same size lines.

Second- that I needed the power booster activated when I bleed the brakes.

I then went to a hot rod shop where they do all mechanical work. He told me the exact opposite. He said he always uses an adapter nut on the m/c and you can bleed the brakes w/o having the engine/power booster on.

Steer me straight! I'm trying to diagnose why I don't have adequate pressure to the front calipers.

Thanks

[Olle]

Can't see why you can't use a reducer on the line, even if it would be better and easier to use the correct lines and fittings. The fittings on the master cylinder and prop valve are usually different, with 3/16" line to front brakes and 1/4" to the rear. Note that the fittings on each end of a line of a certain dimension can be different, and I guess this is what you are seeing. No adapters should be needed, as long as you use the correct fittings. Go to a good part store and find the correct fittings and make your own lines, or have someone flare them for you. I usually try to bring brake cylinders, prop valves etc to the store, to make sure that I get parts that fit.

And I really don't know what he's talking about when he's saying that the booster needs to be "activated". If he's saying that you should bleed the brakes with the engine running, you really don't need to ask him for advice again.

IMO, none of above can cause the problem you have, but you could have a bad master cylinder. If you are going to disconnect the lines from the master cylinder, you could try to hook up your bench bleeding kit to see if you have any fluid coming out from the master cylinder. I read your previous thread, and can't help thinking that you overlooked something simple, like the pedal not travelling far enough, pushrod not adjusted etc.

[lincoln31]

Olle,
Thanks for the reply. When you wrote, [COLOR=Navy]"

The fittings on the master cylinder and prop valve are usually different, with 3/16" line to front brakes and 1/4" to the rear. Note that the fittings on each end of a line of a certain dimension can be different, and I guess this is what you are seeing

, that brings up another question. When you say 3/16 line to front brakes, you're saying from the prop valve to the calipers, right? What about from the m/c to the prop valve? Can the fitting at the m/c be different than the fitting at the prop valve on the same line? The reason I ask is because I went to a couple of different auto parts stores ie. Schucks, Autozone, and they only had brake lines with the fittings already on them. Therefore, if I needed a different size fitting, I would have to cut the line, put the new fitting on, and reflare it.

Bottom line, the line from my rear reservoir on my m/c goes to the inlet port on the prop valve for the front brakes. At both the m/c and at the prop valve, I used a reducer nut on that line. I then used the same size of hard line as comes out the other outlet port from the m/c to the prop valve. Am I reducing pressure or flow to my front calipers (through the prop valve) by using those reducer nuts? Should I get rid of them and buy a brake line with the proper size connecting nut so that it screws directly into the m/c? The only problem is if it is a different size thread at the prop valve. I would then have to cut the line, re-flare, etc..

[Olle]

Originally Posted by lincoln31

When you say 3/16 line to front brakes, you're saying from the prop valve to the calipers, right? What about from the m/c to the prop valve?

On factory brakes, it's 3/16" all the way from the m/c, through prop valve, distr. block and down to the brake hoses on the calipers.

Originally Posted by lincoln31

Can the fitting at the m/c be different than the fitting at the prop valve on the same line?

Yes, that's the way it normally is on a factory setup. Don't know why, I think it's just to make sure they only could be installed the right way at the factory. Look at your stock master cylinder, and you'll probably find fittings that are pretty large for their line dimension. All I have been able to find at Auto Zone is reducers, you'll need to find an old fashioned parts store where they keep these fittings in stock. I'd say you can get them from places like MP brakes too. Reducers are ok to use, but I don't like them personally (just another place where it can leak).

Originally Posted by lincoln31

Bottom line, the line from my rear reservoir on my m/c goes to the inlet port on the prop valve for the front brakes.

This was done because the guy at the brake place told you so, right? If that was the same guy who recommended you to bleed the brakes with the engine running, I would definitely double check with someone else, preferably the manufacturer.

Originally Posted by lincoln31

Am I reducing pressure or flow to my front calipers (through the prop valve) by using those reducer nuts?

Can't see that this would happen. Even if they may cause a small restriction, it shouldn't affect the pressure or flow. The inner diameter of the line should still be the same.

[BluEyesIDFN]

Is your prop valve also a brake light switch? Just a dribble from the fronts really sounds like you tripped the valve in there. It is designed so that if you have a leak in one of the circuits, it seals that one off. I forget how to reset it though.

Oh yeah, definately do not have to have the engine on to bleed the brakes - bloody waste of gas!

[lincoln31]

I'm suspecting the prop valve too. There is a black rubber hood that covers a little button on the front of the valve. I have checked it repeatedly and it doesn''t seemed popped out or like like it needs to be reset. It is flush with the valve, so I think it's fine.

I re-did new lines from the m/c to the prop valve again today. I'm gonna try again to make it work.