Front disc coversion problems

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Ironmike

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Finally drove my Demon around the block after installing a manual front disc conversion and found 2 problems. Hope you guys can help me out a bit!

I installed a brand new disc/drum master cyl and also a disc/drum distribution block. Thought all would be fine. Apparrantly I'm wrong.

Problem 1. Pedal feels a bit spongy....at least to me. I heard I should have a nice hard pedal. Bench bled the master cyl and bleed my brand new lines,, twice. Still feels a bit spongy.

Problem 2. Rear brakes locking up with moderate braking. Darnit, I thought the new master cyl and distribution block would create the right pressure, front and rear. Do I need an adjustable proportioning block for the rear line?

Maaan, this thing's been "under restoration" since October and I really need to get on the road! Driving to alignment shop Monday one way or another...
 
How did you connect the brake lines on the MC?
Usually the rear port is for the front brakes and vice versa.
 
Manual brakes, spongy pedal means air in the lines. Visually look over your cylinders/ calipers carefully, and visualize where the internal cavity is, and the bleeder screw. You want the bleeder at the very top. On some cars, you can reverse the calipers and end up with the bleeders down

In extreme problems, one thing that might help is "rig it."

"Rig" C clamps into the calipers to control how far out the pistons travel. Bleed as best you can, and allow the pistions to come out into the clamps. Then disconnect the hoses and remove the caliper. Let them sit, "hose up" then gently close the clamp to force air/ fluid back up the hose. This should clear the caliper. Then reconnect, and bleed at the hose/ tube connection rather than the bleeder port

Proportioning is a matter of getting the correct valve/ adjustment. Some switch/ dist. blocks do NOT really meter/ proportion, and used a separate valve. Probably the easiest "out" is a Summit/ other aftermarket prop. valve.
 
Listing your set-up would help.

Kelsey hayes front disc brakes ?
Later 73 on disc brakes ?
9" or 10" drums in the back"
Give us an idea what your working with and it will help.
 
x2 on parts info. Is this a generic kit? Home brew kit? Gotta know where you are before we can tell ya where to go. (In a friendly way).
 
Scarebird. Nice set up. All my lines are brand new and connected correctly. Bleeders all face up. Bled a bunch of brakes in my old life.....I SHOULD have a nice pedal feel by now. I'm wondering if I should re-bleed the master cyl and start fresh from there. I recall bench bleeding it with 4 guys in my garage, all yappin'.........

Far as the proportioning issue, I've heard that some Mopars came from the factory with a proportioning valve in the rear line. I will probably fix that issue through Summit. I really hate a mushy pedal though. Our local track has a pretty short shutdown. Kinda makes me really want to get this resolved.

Factory 340 car that came with 10" drums up front and I guess 10 in the rear. Not sure though. Never paid the rear much attention.
 
Good deal, no real suprises as far as components go. You could try to narrow down where the air is. (and help on bleeding) Get the appropriate inverted flare plugs for the master cylinder and block off both ports. Pump the pedal until it gets high and hard. Wait a few minutes and press the pedal down again. It should still be high and hard. If it's not, the master is bypassing and needs to be replaced. If you pass this stage, connect one line and bleed the air out at that port by cracking that line open and having one of them yappers push down on the pedal slowly. Close the line before the pedal gets to the floor. Have the yapper release the pedal, crack the line open again and re-apply the pedal pressure. Do this a couple of times until you get a clear stream from the cracked open fitting. Test the pedal for feel and bleed whichever end is hooked up if the pedal is still low/mushy. Get a good pedal? Move on to the other line/system.
Do it this way and I bet you'll find your problem.
 
we do wilwoods on our SS cars and we bleed them and let them sit for a day or to and them more air comes out...

never have pedal on the first bleed...
 
Man! You got me real confused now. Sounds like you really know your stuff!
Wish I could comprehend what part of the line you're saying to crack open.
You mean the bleeder?
 
I ran into a similar problem a few months ago. I had the rear rubber line on the back proportion valve collapsing. I replaced it, and the 2 up front and solved problem and was alot safer.
 
Ironmike said:
Finally drove my Demon around the block after installing a manual front disc conversion and found 2 problems. Hope you guys can help me out a bit!

I installed a brand new disc/drum master cyl and also a disc/drum distribution block. Thought all would be fine. Apparrantly I'm wrong.

Problem 1. Pedal feels a bit spongy....at least to me. I heard I should have a nice hard pedal. Bench bled the master cyl and bleed my brand new lines,, twice. Still feels a bit spongy.

Problem 2. Rear brakes locking up with moderate braking. Darnit, I thought the new master cyl and distribution block would create the right pressure, front and rear. Do I need an adjustable proportioning block for the rear line?

Maaan, this thing's been "under restoration" since October and I really need to get on the road! Driving to alignment shop Monday one way or another...
Click to expand...


Mike,

Bleed your brakes one more time, starting with the rear passenger,rear driver,front passenger,front driver, in that order. Hopefully this will get all air out of the system, and give you a better feel.

The different m/c and brake system will give you a different pedal feel. If you think its going to stop like a modern car, well its not. As long the fronts are working (we know the backs are) I say drive it. Give it a chance to seat/settle. Hopefully this helps.

PS: An old HotRod trick to proportion rear brakes is to put
9" wheel cylinders in 10" brakes. :thumrigh:
 
Ahaa. Now I read an old post that says I have to bleed the distribution block/proportion block.....whatever you want to call it, seperately before bleeding the lines. To get specific, the guy said "bleed the dist. block and get it centered" before bleeding the lines. Get it centered?

Makes sense, I guess....anybody know how, or why? I'm tired of this spongy pedal.
 
Ironmike said:
Man! You got me real confused now. Sounds like you really know your stuff!
Wish I could comprehend what part of the line you're saying to crack open.
You mean the bleeder?
Click to expand...

Oops, been away for a day or two. Sorry for the confusion. When I said crack the line, I meant the line nut that goes into the master cylinder. Just a small turn or two and when pressure is applied, fluid will escape around the flare. It's why you want someone to apply slow, light pressure on the pedal when the line is "cracked" open. (Can get messy if the pedal gets stomped on). It's the same way you would bleed the distribution block.

By starting with the master blocked off, and breaking it down to two brake systems (Front/Rear), it's the fastest way I've found to find where a problem is in the brakes.
 
Another way to localize the issue.

Wrap the rubber lines with a rag and vise grip them closed. Don't go crazy on the pressure you use to clamp it. I usually do the rear first. If the pedal gets solid when the line is clamped, the issue or at least one issue is in the rear lines, after the clamp. Can do the same deal with fronts.

Block off all 3 rubber lines and it's before the clamps if still mushy.

Yes crack the fittings right at the master and prop/distribution block when bleeding. One of the highest elevation points in the system is at your bends coming out of the master. Real easy to get air trapped in the bend. Make darn sure the line isn't going uphill out of the master before that turn down.
 
crackedback said:
Another way to localize the issue.

Wrap the rubber lines with a rag and vise grip them closed. Don't go crazy on the pressure you use to clamp it. I usually do the rear first. If the pedal gets solid when the line is clamped, the issue or at least one issue is in the rear lines, after the clamp. Can do the same deal with fronts.

Block off all 3 rubber lines and it's before the clamps if still mushy.

Yes crack the fittings right at the master and prop/distribution block when bleeding. One of the highest elevation points in the system is at your bends coming out of the master. Real easy to get air trapped in the bend. Make darn sure the line isn't going uphill out of the master before that turn down.
Click to expand...


Sometimes I get the impression you and I might have done some of this **** before.
 
Did you happen to bleed the master cylinder before bleeding the wheel cylinders?
 
Think I got it all down, guys. Gonna try everybodies suggestions tomorrow night. Might as well plumb the rear proportioning valve in before I try for the perfect bleed. I'm gonna start fresh, with Revhendo's instructions. Hope it works.

Had to trailer it to get lined up today....all good there, brand new 520 horse stroker and I can't drive the damn thing because of this brake issue.

All the grinding, welding, bushing pressing, engine swapping I've done over the last 6 months, I NEVER though brake bleeding would hold me back...unbelievable. I have the worst luck :)
 
All your problems may be inside the rear drums.
 
I have been in your position a few times. All of the above is great advise. Look for the simple things, double/triple check to make sure your calipers are on the correct side. I had the this same issue on a B body and it was because I had to switch the calipers from the front of the rotor to the rear to clear the sway bar and I had the calipers on the wrong side. The bleeder was on top of the line but not on top of the caliper. I looked at those calipers for days before I switched them. I was chasing my tail and the problem was right in front of me. I would defenitly clamp the lines off, that will tell you if the air is in the front or the rear. As far as the prop valve, I have done it every witch way, In the Super Bee, I have the Drum/drum dist block and no prop valve and it works fine (no lock up) in my duster I have the drum/drum dist block and a adj prop valve and no lock up. The last thing you may want to look at is your rear wheel cylinders. I am not sure of what master you have or what wheel cylinder you have but in the disc master there is a take up valve inside it and on a drum master the take up valve is in the wheel cylinder. If you have two take up valves you will have rear wheel lock up. I would swap out the rear wheel cylinders to a disc/drum wheel cylinder. That could be causing the lock up. Hope this helps.
 
siuauto said:
I have been in your position a few times. All of the above is great advise. Look for the simple things, double/triple check to make sure your calipers are on the correct side. I had the this same issue on a B body and it was because I had to switch the calipers from the front of the rotor to the rear to clear the sway bar and I had the calipers on the wrong side. The bleeder was on top of the line but not on top of the caliper. I looked at those calipers for days before I switched them. I was chasing my tail and the problem was right in front of me. I would defenitly clamp the lines off, that will tell you if the air is in the front or the rear. As far as the prop valve, I have done it every witch way, In the Super Bee, I have the Drum/drum dist block and no prop valve and it works fine (no lock up) in my duster I have the drum/drum dist block and a adj prop valve and no lock up. The last thing you may want to look at is your rear wheel cylinders. I am not sure of what master you have or what wheel cylinder you have but in the disc master there is a take up valve inside it and on a drum master the take up valve is in the wheel cylinder. If you have two take up valves you will have rear wheel lock up. I would swap out the rear wheel cylinders to a disc/drum wheel cylinder. That could be causing the lock up. Hope this helps.
Click to expand...

LOL, reminds me of a time I couldn't get a guys brake pedal right. Went over that thing for an entire day before I figured out the wheel cylinders were somehow installed upside down from a previous brake job. Lost my a$$ on that job.
 
I'm pretty sure I bought a disc/drum master. I know it was a 71-73 Dart cylinder. You tellin' me they even made a Dart with 4 wheel discs?
 
Ironmike said:
I'm pretty sure I bought a disc/drum master. I know it was a 71-73 Dart cylinder. You tellin' me they even made a Dart with 4 wheel discs?
Click to expand...



does it look like this?


71-72-73-dodge-dart-duster-scamp-brake-master-cylinder_140435607892.jpg
 
siuauto said:
I have been in your position a few times. All of the above is great advise. Look for the simple things, double/triple check to make sure your calipers are on the correct side. I had the this same issue on a B body and it was because I had to switch the calipers from the front of the rotor to the rear to clear the sway bar and I had the calipers on the wrong side. The bleeder was on top of the line but not on top of the caliper. I looked at those calipers for days before I switched them. I was chasing my tail and the problem was right in front of me. I would defenitly clamp the lines off, that will tell you if the air is in the front or the rear. As far as the prop valve, I have done it every witch way, In the Super Bee, I have the Drum/drum dist block and no prop valve and it works fine (no lock up) in my duster I have the drum/drum dist block and a adj prop valve and no lock up. The last thing you may want to look at is your rear wheel cylinders. I am not sure of what master you have or what wheel cylinder you have but in the disc master there is a take up valve inside it and on a drum master the take up valve is in the wheel cylinder. If you have two take up valves you will have rear wheel lock up. I would swap out the rear wheel cylinders to a disc/drum wheel cylinder. That could be causing the lock up. Hope this helps.
Click to expand...

By the way, are you confusing take up ports with pressure check valves?
 
Ironmike said:
Might as well plumb the rear proportioning valve in before I try for the perfect bleed.
Click to expand...

Be sure you fully open the valve when you bleed. I had to bleed the crap out of my car when I redid all the brakes, then had to go back a do it again after it sat. Good now.
 
Looks just like abodyjoe's pic. Raybestos #MC36406. What's the diff between mine and MC36426?

Went through the whole bleeding process again after installing my rear proportioning valve and things feel better, but still not that great. The car stopped better with the old drums up front. Sumpin' ain't right somewhere.
 
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