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Discussion Starter #1 (Edited)
Quick question for the collective wisdom here. I just finished converting to front disc brakes on my 63. I bench bled the MC and pressure bled the whole system, clear fluid and no bubbles at all four brake bleeders. My pedal is down about 1/2 way to the floor from usual and the brakes do not bite until the pedal is all the way down. Am I just dealing with some air somewhere and need more bleeding, or something else? (The only other thing I can think of is, are the manual and power MC's different? If they are, and I have power brakes but ended up with a manual MC will that be causing this?) Oh and the MC / prop valve seems to be typical one I see in pictures of these converions, dual MC front disc/rear drum.

Thanks for any thoughts or suggestions.
:confused:
 

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I'd have to say as long as you have the correct parts, then bleed it more. Sometimes it takes a while to get rid of all of the air in the system.

On another note, as discussed in another thread, are your bleeder nipples up or down on the calipers. If they are on the bottom you won't be able to get rid of all of the air.
 

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Will the pedal come up if you pump the brakes? If so and you have no air you may want to add a residual valve to the disc line. That is recommended on most disc brake applications. If they pump up the M/C may be too small on the bore. It could be 1 inch bore and you may need a 1 1/8 bore to move more fluid per stroke. RM
 

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Real McCoy said:
Will the pedal come up if you pump the brakes? If so and you have no air you may want to add a residual valve to the disc line. That is recommended on most disc brake applications. If they pump up the M/C may be too small on the bore. It could be 1 inch bore and you may need a 1 1/8 bore to move more fluid per stroke. RM
Too small of a bore caused me to have a low, spongy pedal. Also some m/c's have a higher volume ouput on one port as compared to the other. Obviously you want the most volume going to the front discs. You can check this when bench bleeding; put your bleeder line in a small clear jar and give one full stroke. Mark the jar and compare to the other port. You'll probably suck air back in so you'll have to bench bleed inbetween tests.
 

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The power brake M/C has a shallower hole in the piston than the manual M/C does. If you have a manual M/C with a booster the booster rod will have to travel farther to contact the piston, causing a low brake pedal.
 

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Discussion Starter #7 (Edited)
Mike Goble said:
The power brake M/C has a shallower hole in the piston than the manual M/C does. If you have a manual M/C with a booster the booster rod will have to travel farther to contact the piston, causing a low brake pedal.
Hmmm, that is what I was worried about. How can I tell if I ended up with a manual MC?

Thanks again
 

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Are the rear brakes adjusted properly? I kept bleeding mine after we put the new rear end in the car and couldn't get the pedal up--I went back and tightened up the rears and the pedal came right up. The master I use(Mopar aluminum)doesn't seem to have enough volume to push the rear wheel cylinders as far as I was trying to make them go.( I keep the adjustment loose to lessen drag at the track)
 

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bowtie0069 said:
Are the rear brakes adjusted properly? I kept bleeding mine after we put the new rear end in the car and couldn't get the pedal up--I went back and tightened up the rears and the pedal came right up. The master I use(Mopar aluminum)doesn't seem to have enough volume to push the rear wheel cylinders as far as I was trying to make them go.( I keep the adjustment loose to lessen drag at the track)
you can test botie's way by simply seting the E-brake a little to tighten up the rear brakes. then see if the pedal is where u want it but it sounds like u got the wrong length brake push rod. give it a try BRO!
 

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Discussion Starter #10
The saga continues....

I tried the suggestion about setting the parking brake and checking the pedal, with no luck, the pedal did not change. Still soft.

I pulled the MC and checked the hole in the piston against the old single drum/drum MC and they were the same depth. So I am assuming my MC is correct.

So I bench bled the MC again and reinstalled. I pressure bled all four corners then manually bled with a partner pumping the brakes. Went through 2 and a half of the big bottles of fluid. All to no avail, the pedal is still really soft, I can stop but my foot is in the floor.

The calipers' bleeders are on top. I made sure that little spring loaded pin on the prop valve was held down while we were bleeding. I have gone over all the connections checking for leaks. Triple checked everything (again). I just feel like I am missing something painfully obvious that is causing me so much trouble....

Well I am grabbing at straws here now, not really sure what to do next. So anything else anyone has for me, please I'd love to hear it.
 

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You've gone from drum/drum to disc/drum conversion, right? When you installed the new master cyl. and booster, did you also change your clevis rod that attaches to the pedal arm? There's two holes on the arm, and drum brakes uses the upper hole, but discs use the lower hole in the pedal arm for more through. Check it out.
 

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There are many questions that must be answered:
1. What is the bore size of the master cylinder?
2. Do you have disc/disc or disc/drum?
3. Do your calipers slide smoothly into the caliper brackets or are they very tight?
4. Do you have a disc/drum or a disc/disc master cylinder?
5. How much free play do you have from the pushrod to the piston?
6. Does the pedal pump up after several quick pumps?
7. Does the pedal get stiffer after pumping?
8. Pump the pedal to max pedal height,and watch the fluid in the master cylinder. Does a lot of fluid rush back into the resevoir when you release the pedal?
Let me know.
Tim
 

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Discussion Starter #13 (Edited)
Thank you everyone for putting up with my inquisitiveness

brickyardboy said:
did you also change your clevis rod that attaches to the pedal arm? There's two holes on the arm, and drum brakes uses the upper hole, but discs use the lower hole in the pedal arm for more through. Check it out.
Hmm, I went out and checked and the clevis rod was already attached to the lower hole. (From the looks of that nut and cotter pin, it came from the factory like that :) )

You've gone from drum/drum to disc/drum conversion, right? When you installed the new master cyl. and booster,
I have a bad feeling this is going to be a really stupid question, but did I need to change the brake booster too. (I had power drums before.)

EDIT: (Also, I should mention, after reinstalling the MC and bleeding again today, the pedal height seems to be fine, but soft does not begin to describe it. I have been seaching more on the site and it sounds like it is really tough to bleed. However, I am getting clean fluid and no bubbles whatsoever at all four corners, so I believe I have bled all the air out.)
 

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Is this a new m/c that came with the conversion kit? I know of someone that did a conversion and couldn't get the pressure. Turns out the new m/c had the piston cups on backwards therefore creating a little pressure but nowhere near enough. It might be worthwhile to check the pressure with a gauge at the m/c to be sure it can develop the needed pressure. Without a gauge, plug the ports at the m/c and check your pressure by brake pedal feel. Is it much improved? If it is then the problem isn't the m/c but futher downstream. This will be the start of the trouble shooting process. You can later isolate the wheel cylinders and calipers later by plugging the line with a plug on the line just before the wheel cyl or caliper. Hopefully you are running a 10 psi residual valve in the line running to the rear drums(2 psi if it's dics at the rear). This maintains some pressure in those lines to minimize the amount of pedal movement needed to stop without making the brakes drag. This is because the pads are now close to the drum/disc and you aren't haveing to waste pedal movement on refilling the lines to the rear.
 

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All of the info provided would cover the various issues that can cause this problem. You need to do some basic research (ibuildm's list) and that will give you a base to start from. Then you need to proceed in a step by step manner to rule out the problem. Otherwise you will be chasing your tail on this for a long time.
 

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I had a similar problem on my 64-turns out the rear brake hoses collapsed when pressure was removed. Replaced teh old brake hoses and problem was solved.
 

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Discussion Starter #18 (Edited)
got it

Sorry for the delay guys, was out of town for a bit. Got it all taken care of, just needed some more bleeding, plus my booster had given up the ghost while we were rebuilding the front end. Just got her aligned and back on the road. :D Thanks for all the suggestions and help.
 
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