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HELP..... Disc upgrade problems

I had a parts store order a bunch of MCs for me and I found one that will physically fit(not hit the vacuum elbow) and it has a 1 and 5/16 bore. I don't know if I will mess with it tonight or tomorrow. I will post a part number later. I will also change the title of this thread when the truck is fixed so that others can look here for problems with a disc conversion. There is a wealth of knowledge in this thread. Thanks to everyone who has posted ideas and thoughts here.

On a side note. If your battery holddown breaks and your battery hits the heatercore lines and it breaks one of the pipes for the heater core, the hoses can be plugged with the pin out of a shackle. Keep a couple different sizes with you. I needed a break from the brakes(get it) and went wheelin for a little while today.
 
Well, we got the new 1 ton MC into the truck. For a brief second the pedal was hard. Then came the foam. And the bubbles in the MC. So tonight, we will be inspecting every connection and making some new lines. I don't know if the little wave in the line at the MC is the problem or mabey a line going into the proportioning valve is messed up or there is a leaking piston seal at one of the calipers. I will be pressure bleeding the fluid tonight. I figure that 10psi or so should push fluid out wherever it is sucking air. It is just odd that now is the first time to se foam. I expected to see it the entire time if it has been sucking air. Mabey moving the lines around so much finally caused the gap to get big enough to foam the fluid. But I think it is bad enough now for us to find it.
 
I had similar problems with the m/c not getting pressure. Felt spongy after bleeding a dozen times. What worked for me is all the 4 wheel disc vehicles i have seen use a 3/16 inch line all the way to the back from the m/c to the rear brakes. I had to change my 1/4 inch rear drum line with a 3/16 line because of fluid volume pressure. Btw i run the 1 ton master with a willwood rear prop valve and all new 3/16 lines (all brand new). The front was hooked into a T fitting straight to the front. The rear was one line with an inline prop valve. I also ran all new stainless steel flex lines. If you still have that 1/4 inch line with the stock prop valve (brakelight switch) necking down to 3/16 to the disc in the rear that may be your problem.
 
ok... lets go back to the beggining... this is just a puzzle and you have to make all the pieces fit
1) The truck stock worked well... no brake problems.. everythig was in good shape when you started
if yes proceed... if not replace /fix what was questionable

2) You began adding pieces into the system and now it doesnt work
soooo one of those pieces isnt working right...or the combo isnt working right
I know this sounds simplistic but this is the way you have to start
look at each individual piece..are they all operating like they are supposed to..
the answer is probably not

the remn'd calipers?
unbobstructed brake lines?
the booster ( a definate possible)
the proportioning valve (a definate possible)
the rod length.. you said is good
the master.. you said is good ... but Im suspicious( the p30 master as you found out likes to work with hydroboost and not your booster)... um as an aside hyrdoboost 4wdb would solve this problem

there are too many 4wdb conversions out there that work so we know its your truck and not systemic... but we also know that many people complain of having to power bleed their systems.. having proportioning valve problems etc...
I have an article on hydroboost in the tech sction... Imsorry your having such a hassle....stickwith it
 
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I think it is now a sealing issue with the line at the MC. I am gonna make some new lines. Either that, or the MC has a bad internal seal. The next thing I will do is to remove the lines from the MC and try bench bleeding in the truck. That will let me know if the insides of the MC are good. I am thinking that I wasn't pushing the piston all the way in while it was in the vise. I will use the truck to make sure the piston goes all the way in.
On a side note, I had to tighten the hell out of the bleeding kit to keep air out. I have never had to do that before. Is it possible that the MC hole for the line is distorted? If that was the case it would be sucking air right at the MC.
 
It would be possible for the master cylinder to be messed up in the fittings but I would make that the last item on the list of thisgs that might be wrong. At the same time I would make it the first item on the list of things to look at and verify good.

I have had to tighten brake line fitting tighter than I ever thought the should be to get the to seal. I would guess that a little extra tightness might be in order but your theory on the master not being bench bled well is a very good one and I would go with that.

With a 1 5/16 master cylinder you should have the hard pedal real quick.
 
The foaming just started with this new MC. That is why I think it is the main concern. I have replaced everything but the lines off of it.
 
Let us know your results, and if it works out good post the part number so I can go pick one up for myself.
 
K5er4Life said:
Let us know your results, and if it works out good post the part number so I can go pick one up for myself.
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I will post the part #.
I am taking the MC back and getting another one. The hole for the front brake line is oval or something. I had to use a wrench on the bleeder plastic fittings to get it to seal. The air is coming in at the master cylinder port. I am going to take the other end of the line off at the proportioning valve and run a hose back to the MC to verify this. That has to be the problem now.
 
Word of advice, when you bench bleed a MC, don't push the piston ALL the WAY IN...use shorter strokes, around one inch to get it done. Although I've not had issues with this, there are warnings in repair manuals about it.

---application specific---does not apply to yours!
 
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mouse said:
Word of advice, when you bench bleed a MC, don't push the piston ALL the WAY IN...use shorter strokes, around one inch to get it done. Although I've not had issues with this, there are warnings in repair manuals about it.
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Where did you see that? I would like to read what it says, any why. The only issues I know of in regards to bleeding with a short stroke, refer to an old MC that has been exposed to the elements for a while. Corrosion and rust can build up on the part of the shaft that never sees fluid. If you push it to the floor in an older MC the junk on the shaft can mess up the seal.
 
Well, after referencing my brake books, I can't find a source stating this concern...actually quite the opposite. Most say "full, deep strokes." I remeber seeing this when going to manual brakes on a race care around 10 years ago, with a specialty brake manufacturer, and apparently this may have been an application-specific warning. The note stated that compressing too far could cause a seal to be rolled inside the MC...or something similar.

I guess I should have double checked before recommending it. Thanks for the challenge..you seem to have done it correctly!
 
you use short stokes so you dont cavitate it and create air bubbles internally... exactly what you are trying to get rid of....
or at least thats what I recall from doing google searches when I was doing brake research

With ALL the problems you are having I would say go back to square one... but I am suspicious (again) of the M/C or booster.... (if you didnt change the rod length).. a slightly larger bore would push more fluid... but also other problems would be enhanced as well..... like a bad booster... bad caliper.. etc...
I went thru 4 calipers from raybestos on my project tuggy... to the point my parts man thought I was doing something wrong.... then we found out that during the reman process they were blasting off the sealing rings... found a good one and end of story
 
A little update. I got another MC under warranty. When I was about to put the lines on I noticed that the line for the front brakes looked funny. Upon closer inspection, I realized that the double flare was completely gone. It just looked like a single flair. I thought I had found the problem. WRONG. Mabey part of the problem, but not THE problem. I pulled some lines off of a suburban and put them on and bled, and bled, and bled. Same problem. I talked with my son for a while and realized he was using 3/4 ton calipers. I saw no need for this, and after talking for a while we decided to try some 1/2 ton calipers instead. We replaced the 3/4 with the 1/2 in the rear(but used the same pads, they fit I guess they are the same) and bled and bled and bled. We got some resistance on the pedal. So finally some progress. It was 10 pm so we decided to quit while we were ahead. Tonight we will start the truck and drive it and see how they actually stop the truck.


BTW, if anyone needs about a dozen empty 32oz. brake fluid bottles, let me know.
 
There should be no difference between the 3/4 and 1/2 ton calipers. The part numbers show to be the same. Is the mc your using from the 1 ton "k" trucks for the hydro assited brakes? You know, the ones with the metal cap on top, the none vaccum boosted? I really want to get my brakes worked out, so far I have removed the pv and I have still have the dropping pedal with low pressure. I can still lock the brakes but I have to take the pedal to the floor. I double checked all my lines and I have no leaks, I even put a wrench on the fittings that I installed. I am starting to think that the 3/4 ton mc bore is too small and a bigger bore would remedy the problem. Does anyone know what size the 3/4 bore is? The 1 ton is 1 5/16" right? Damn, I want to get these bugs worked out, these brakes need to work. I have been running with my brakes the way they are and being very careful to give myself enought time to stop. I have not had any fluid loss in my resevior. I really hope that mc works out for you so I can give it a shot also.
 
I will post the MC part number tonight. It is not the one for hydroboost. The one for hydroboost hits the check valve for the vacuum on the booster. The 1/2 ton calipers we ended up using, were the ones for the front of a 79 Blazer.(his truck) the ones we took off had a bigger piston in them. We measured them. I am also using a proportioning valve from inline tube. I found another one from gmpartsonline(or something like that) that is supposed to be the same and it is only 56.00 shipped. When it gets to me, oin a few days, I will let you know if they are the same. Also, the MC is a new unit. A hundred bucks. I was done taking chances with the reman stuff.
 
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