4-wheel disc brakes on an "A" Body...???

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62BT409

62BT409

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Got 4 wheel disc brake system setup on the car. Thought to be a good idea but have had problems from moment one. Three master cylinders and still do not have very good brake at the pedal. Anyone have any suggestion? OR even things I need to mention to get a better idea?
 
what master cylinder are you using?
what brakes are you using? front and rear
more info needed
 
Also who made the brake system? Wilwood, Baer, ssbc??
 
caferacerx said:
what master cylinder are you using?
what brakes are you using? front and rear
more info needed
Click to expand...
The person who is the know to exactlly what is on the car is on the road. I just spoke with him....he can not recall how's MC it is but the fron brakes are the ECI brand:
[FONT=Verdana, Arial, Helvetica][/FONT][FONT=Verdana, Arial, Helvetica]Mustang II Disc Kits[/FONT][FONT=Verdana, Arial, Helvetica] - [/FONT][FONT=Verdana, Arial, Helvetica, sans-serif]ECI introduced the first Mustang II/Pinto "BIG BRAKE" conversion kit in 1981 and we still offer the largest selection and the best value in the industry. Our 11" diameter rotor kits use the early GM "BIG" piston calipers and provide 65% more braking capacity than the stock Mustang II, and more than twice as much as other so called "Big Brake Kits" using the later smaller piston GM calipers. Our Granada rotor/GM caliper kits are supplied with inner brake pad spacers to compensate for the difference in rotor thickness and are vital to prevent caliper piston over extension and subsequent loss of brakes. NO OTHER MANUFACTURER PROVIDES THESE SPACERS. That's the "ENGINEERED" difference in an ECI kit![/FONT][FONT=Verdana, Arial, Helvetica] [/FONT]

And the rear are the Right Stuff (that came with the Dana rearend set-up) And I am working the name of that system. I know that it is a single piston setup
 
sounds like the problem is finding a master cylinder "M/C" that will work with your set up
a m/c that displaces to much fluid will have a hard pedal but no stopping power
a m/c that does not displace enough fluid will have a soft pedal
a bigger bore = more fluid displaced
smaller bore = less fluid displaced
more fluid displaced = less braking power due to less mechanical advantage
less fluid displaced = more mechanical advantage (think leverage, like a long handle wrench tightening a bolt) but the pedal needs to travel further in order to displace enough fluid so you get a soft, mushy brake pedal
 
caferacerx said:
less fluid displaced = more mechanical advantage (think leverage, like a long handle wrench tightening a bolt) but the pedal needs to travel further in order to displace enough fluid so you get a soft, mushy brake pedal
Click to expand...

This seems to hit right on the head. Along with we have come to the conclusion the MC is the source of the problem. I don't even want to go to how many MC's we have tried. Thanks for the heads up.maybe we can move on once we decide on which MC.
 
caferacerx said:
a m/c that does not displace enough fluid will have a soft pedal
Click to expand...

Everything you say is correct except this. A smaller mc will have DECREASED pedal effort, and your foot will mover FURTHER.

If it gets small enough, the pedal may hit the floor before both sets of calipers engage enough to do much.

However, if the pedal is SOFT, that is mushy, you STILL HAVE AIR in the system.
 
67Dart273 said:
Everything you say is correct except this. A smaller mc will have DECREASED pedal effort, and your foot will mover FURTHER.

If it gets small enough, the pedal may hit the floor before both sets of calipers engage enough to do much.

However, if the pedal is SOFT, that is mushy, you STILL HAVE AIR in the system.
Click to expand...

I am only talking about a properly bled air free system, as air in the system will cause more problems
to displace the same amount of brake fluid
a larger bore m/c will require less pedal travel but more effort
a smaller bore m/c will require more pedal travel and less effort
and as you said " If it gets small enough, the pedal may hit the floor before both sets of calipers engage enough to do much." so that in this instance even in a properly bled air less system the brake pedal will feel soft or mushy like it has air in it even though it doesn't
 
I've used 2 PSI check valves in brake systems before to bring the pedal in line. It keeps pressure on the caliper but not enough to drag the pads.
 
67dart273 has a good point I was going on the assumption that the system was bled thoroughly, but perhaps you still have air pockets?
 
I started out with the smaller Strange 1.o32 bore per their advice, FULLY bleed system....result...no pedal unless I pumped the crap out of it...called Strange and they advised they "had some production problems" and sent me another one,confirming the smaller size bore was the correct application....result---same thing as before. they then sent the larger bore..1.125.....same result. I then replaced the master cyl with a #220669634878 Mopar lightweight aluminium master cyl swap kit that Hemi Mark found for me on E-Bay..this master cyl looked identical to ones I had used previosly on my car and Hemi Marks duster. Upon installation and bleeding I immediatly had a very hard pedal...but when the car had the rear off the ground ,running in gear, at a idle RPM the rear wheels continued to spin unless the brakes were pumped and the pedal depressed HARD...it appears to me all the pressure is somehow going 99% to the front discs...it stops, but we obviosly are not getting anythig out of the rears. also switched to the distribution block used on models with front discs...same result...and switched back to dist block wit no proportioning valve built in it...any help would be appreciated

thanks...Hemidenny
 
O.K. so the front's are working fine? and the problem is with the rear brakes? and the front and rear brakes are kits from different company's, what M/C does "right stuff" recommend, are you sure the one you are using is compatible with the rear kit you are using?
disk brake calipers often require more fluid displacement than drum brake wheel cylinders, so a front disk, rear drum M/C may not work on a disk disk car
how were the rear brakes bled? gravity, vacuum, pressure? if a brake line is higher than the bleeder you may have air pockets that can be very difficult to get rid of
 
i put cordoba rotors up front and explorer discs on the back of my duster and it took some getting used to at first and it was hell to get all the air out. but after i did and now that im used to them, WOW! it will put you into the dash and will stop nice and straight. at first i just used the disc drum mc that my duster cam with, when it started losing pressure i switched to the mopar aluminum one eberg sells. for factory discs with regular parts store pads i think it stops awsome.
 
the m/c we now have on is the Eberg (I beleive it is a knockoff of the Mopar piece no longer available thru Mopar)...the brakes were bleed the old fashion way..someone pushing on the pedal while I loosed the bleeder when pedal was at top and closed as we reached near bottom..I even loosened the u bolts on the rearend to allow me to rotate the rear and get the bleeders perfectly horrizonal per "Right Stuff" instructions...I must have gone thru acouple of gallons of dot 3....I bleed so much a needed a transfusion(of sanity!!!) I've bleed the brakes on many of my "hot rod Mopars " over the years and it really bothers me that I cannot figure this out...I hope I'm not missing something obvios
Jim and his friend are going to read the pressure and confirm what we suspect....just not sure what the best remedy will be.......thanks for all your input and suggestions
Mopar to ya!!!
Denny

P.S. Please remember to vote Tuesday...Vote like your Liberty and Freedom are on the line....just in case your not paying attention....IT IS !!!!!!
 
HemiDenny said:
.......................Upon installation and bleeding I immediatly had a very hard pedal..........................rear off the ground ,running in gear, at a idle RPM the rear wheels continued to spin unless the brakes were pumped and the pedal depressed HARD.......................it appears to me all the pressure is somehow going 99% to the front discs......Hemidenny
Click to expand...


Unless you have the rear brakes on the front section of the master, and have managed to bottom out the piston in the master, this is a pressure problem to the rear OR a restriction. If you had free flow during bleeding, this pretty much eliminates something like a restriction, so now we get down to proportioning

I don't believe you can simply compare caliper bores to one another in order to determine ratio. It will depend not only on bore, but how far the radius is of the caliper to the axle centerline---a caliper out away from the axle on a larger rotor, even though it has less surface will have more braking "leverage." Of course the size of the pads will affect this as well, just like the size of drum brakes

What I'm getting at is, you may have created a massive front rear ratio problem. I would think a proper proportioning valve (adjustable) in the "right place" should go a long way.

Have you tried NO valve of any kind, equal pressure front rear?
 
Yup get an adjustable proportioning valve if you dont already have one.Also fully depress the brake pedal first and then crack the bleeder valve.It helps remove any trapped air pockets better. You could also try a reverse bleeder. But I think it's more to do with your p valve and master.
 
HemiDenny said:
I even loosened the u bolts on the rearend to allow me to rotate the rear and get the bleeders perfectly horrizonal per "Right Stuff" instructions...
Click to expand...

I may have found your problem right here! Bleeders should be at the highest point in the caliper, and therefore VERTICAL. Air is lighter than Brake fluid and therefore goes to the highest point accessible to it. If you have them horizontal, you can go through a 55 Gallon drum of brake fluid and you will still have air in the system. Also try tapping the calipers a couple times to get the air bubbles to release and float to the top.

Check this, and the only other thing I can think of is try something in between the 1" and the 1.3" MC or change your pedal ratio while using the bigger one.
 
After the BRAKE SYSTEM DIAGNOSTIC KIT arrives, Tod and I will get the pressure readings at each wheel and the master cylinder. This should with no doubt give as a good idea as to where the weak spot is.

Does anyone here have a setup with the Right Stuff brake system and if so have you had any issues with them???
Thanks
Jim
 
the distribution block we are using is the stock block for 4-wheel drum brakes...it is suppose to distribute the pressure evenly,while the block for disc brakes(we tried this one also) front disc/rear drum has a proportioning valve within it that I believe limits pressure to the rear...thats why I switched back to the stock one....the m/c is threaded almost idiot proof ...using stock line from the m/c to dist block..they only go on one (correct) way.......I wonder if the flexible lines(appx10'')with the banjo fittings used to connect the rear calipers on each side to the hard lines could be adversly affecting the performance of the rear calipers???...what do you think...

Denny
 
62BT409 said:
After the BRAKE SYSTEM DIAGNOSTIC KIT arrives, Tod and I will get the pressure readings at each wheel and the master cylinder. This should with no doubt give as a good idea as to where the weak spot is.

Jim
Click to expand...
well, what's the prognosis???
 
I tried to answer this yesterday and got a paragraph and a half when I hit a button to make a sign and lost what I had types....so that pissed me off and I quit.

SO I will try it again.

After obtaining the new Brake Diagnostic Kit and some of the fittings and lines missing :angry5: ...called the supplier and they sent more fittings and lines. We hooked up to the brake lines and check pressures. Got pressures between 600# in the front and 700 - 800# reading at the rear "T"...to try to get to the calipers was a real feat. And they came in at 700#. The disc brake people said to make sure the rear caliper bleeders are level with the ground (they come and are installed at a 15 degree angle down).....so we took the rear calipers off and made sure they were parallel with the ground and re-bled the lines with the rotor bungee corded into place to have something to expand to. Things look better now but we are in another situation with the wheel spacer. (we noticed that the wheel is wobbling) so before we put everything back together....we are attacking this problem also. So we are in a holding pattern at the time.:(
 
I used the 13" front, 11.75 rear Dr. Diff Kit, with MP 1.032 master, stock disc/drum prop valve and HYDROBOOST. Pressure checks reveal exactly 50% of the brake pressure to the rear (perfect bias for these cars), modern feel and absolutely outrageous brakes.

Guys, there is no substitute here for spending $$ on the right parts. Dr Diff Kit and hydro unit is a $2500 investment period. If you aren't willing to go the distance for OE style (PBR calipers), properly engineered parts, stick with the 11.75s up front and drums in the rear. Quality Carbon pads are available for the single piston calipers, good fluid, braided hoses and you have a good package.
 
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