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FOUND! Problem with poor pedal in my 65 Dart Disk/drum
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Author:  ppsi [ Wed May 13, 2009 6:28 am ]
Post subject:  FOUND! Problem with poor pedal in my 65 Dart Disk/drum
I posted scads of information and received a ton of helpful posts in my quest to get the front disks on my 65 Dart to behave. All along I was chasing , what I thought was, an air problem. I finally got a helper to bleed the brakes and while doing so noticed that the calipers were moving in an angular direction when squeezing the rotors. This made the piston have to travel farther which was making the pedal go so close to the floor. The caliper would sort of kick out at the top/inside and make the sorry a$$ clips flex. I sent pictures to Master Power Brakes because they wanted to see that it was all set up right and have not heard from them. I am going to see if the parts I got from them are square to the rotor and spindle etc. I can't think of any other reason the piston would be at an angle to the rotor. It was yesterday PM when I found this and have not done anything to any parts yet but am heading out this AM to look. If anyone else has some input on this symptom I'd love to know how it was fixed. All the surfaces are smooth and lubricated so there is nothing hanging up and both sides are doing the exact same thing WITH the second set of calipers as well. I know once I can get the piston to travel perfectly perpendicular to the rotor all the lost motion that is happening now will give me a good pedal.
Thanks-Howard
Author:  Dart270 [ Wed May 13, 2009 8:00 am ]
Post subject: 
Bent caliper mounting brackets or spindle, or bent caliper pins (if pin type), or something else bent in there...?

What type of calipers and rotors? Is this an aftermarket kit?

Am I misunderstanding your question?

Lou
Author:  ppsi [ Wed May 13, 2009 12:22 pm ]
Post subject: 
Quote:
Bent caliper mounting brackets or spindle, or bent caliper pins (if pin type), or something else bent in there...?

What type of calipers and rotors? Is this an aftermarket kit?

Am I misunderstanding your question?

Lou
The set up is from Master Power Brakes. It is their "B body disk brake conversion kit" and it came with upper control arms-w-the larger ball joint, lower knuckles, mounting brackets for the slide type calipers and the calipers and master cylinder. I did this conversion 6+ years ago and lived with it thinking that that is how the brakes are supposed to feel. They stop the car fine but with a low pedal that I've some to find out is an issue with the geometry of the bracket in relation to the rotor. Somewhere in the machining or manufacturing there is a flaw that, to make a long story longer, makes the caliper travel in a diagonal path because the piston does not meet with the pad backing plate square with the rotor. This is causing the caliper to kick up and takes up more travel than if it was pressing the pads against the rotor at exactly 90 degrees. Needless to say the spring holding clips (not pin type) are not designed to do anything other than give the travel some tension and I can see them flex as the pedal is depressed. When the pedal is let off I can see the amount of unrequired travel that is going on which translates into pedal travel. I've been talking with MPB and they are helpfull but keep asking for more photos of my set up and I really don't think they will be able to help. I am going to have to set the brackets up on my surface grinder and indicate the lands that are machined in the brackets where the bolts hold the bracket to the spindle and then indicate the wyas where the caliper and pads ride and I am sure there will be somthing other than a 90 degree angle. Hopefully I can just grind the ways a small amount to get them right and os course this will all depend on the lands that are on the spindle where the bolts /bracket mate. It is a little complicated for me to explain properly so I hope it is somewhat less than mud clear but I am sure that a QC issue will present itself. It is just going to take a lot of time on my part. I know it is not a problem with the pad backing although I wish it were that easy. I used some flat stock to take the place of the width of the pads and the calipers still get cocked out of alignment when the brakes are applied.
This sucks!
Thanks-Howard
Author:  Joshie225 [ Wed May 13, 2009 6:24 pm ]
Post subject: 
Mopar pin type calipers to the same thing. The calipers rotate around the bushings and soak up pedal travel. This is why I use sliding calipers on my disc brake swaps. My '66 Dart with late A-body brakes had a very firm pedal after about 1" of travel. About the only thing you can do it swap in a larger master cylinder so you have more fluid volume available, but it will require more pedal effort.
Author:  ppsi [ Thu May 14, 2009 5:38 am ]
Post subject: 
I have to disagree. It is not the design of these calipers to travel in a way that is not 90 degrees to the rotor. When the piston hits the backing plate of the pad on an angle instead of dead flush on the backing plate the caliper takes up travel due to excessive flexing of the clip. I can isolate this easily with clamps that make the piston not cause the caliper to kick out and the pedal is solid. The spongy feel and low pedal is coming from the caliper moving up and away from the rotor making the clips flex which feels like air in the lines. If I watch it I can clearly see this felxing of the clip and how it is transmitted to the pedal.
Thanks-Howard
Author:  Joshie225 [ Thu May 14, 2009 7:13 am ]
Post subject: 
OK, I think I understand, but a picture would make it much clearer.
Author:  sandy in BC [ Thu May 14, 2009 8:11 am ]
Post subject: 
I have been lurking on this thread. I am in the middle of a non slant rear disc conversion. Although I dont have the same symptoms I have been doing the same science .

I am using the hub /rotor to square the caliper mount to the axle.

I have a bolt on kit and a weld on kit to play with.

With the caliper mounted to the bracket and the wheel bearings adjusted how does the caliper mount interface with the axle?

Bolt on kit: With the caliper bracket bolts loose and the brakes pressurized is the bracket square to its bolt surface? Observe bracket as bolts are tightened.

Weld on kit: with brakes pressurized. If the bracket meets the axle in a way that can be welded: tack 2 places.....relax brakes and rotate Rotor. Repressurize brakes and watch for bracket deflection. If no deflection weld bracket. Repeat.

I think the caliper mounting bracket alignment is the key to brake swaps. I think a tool in establishing the alignment is the built in dial indicater (bearings/hubs/rotors).

Remember that rotors are finshed with a built in wobble ....so rotate early and rotate often.

PPSI are you seeing the built in rotor wobble?....or a missunderaligned bracket?


The axle Im working with: 14 bolt 10.5" ring gear full floater with GMC 8 bolt front calipers and rotors(3/4 ton 4x4 front axle) I have machined off one side of the rotor and vents to cut about 40% off the rotors weight. I double up pads on one side of the caliper .
Author:  ppsi [ Thu May 14, 2009 12:56 pm ]
Post subject: 
Image
This is a bad cell phone picture of the left side caliper. Obviously this is a front disk brake system. I doubt the photo and description will help explain the problem but if you picture the piston contacting the pad at a slight angle instead of dead perpendicular you might imagine how this would effect the travel of the caliper as it slides to squeeze the rotor but then once the pressure is built up in the lines it tries to make the piston contact the pad flush or should I say completely which causes this raising up of the caliper. If the piston contacted the pad completely-in other words with the full circle of the piston-then the only travel would be perpendicular to the rotor. Sort of like taking a cup and putting it top down on a flat surface but with the top of the cup at a slight angle to the flat surface and letting it go you will see the cup rim find 100% contact with the flat surface. Gravity will do this where in my brakes the hydraulic pressure is doing it at the cost of tilting the caliper and taking up travel. I hope this makes a little sense. It has rained all day so I've not been able to get outside to mess with it. In addition I am trying to formulate a way to attack the diagnosis. I could fabricate a set of hold down clips that don't flex but this is a bandaid at best. Maybe I will loosen the bracket bolts and see the caliper correct it's position by looking at the bolts and seeing where the out of square spots are located. I might also shim one side of the lands that are machined for the bolt bracket/spindle mating points. I think if I were to place a strip of shim stock either on the top half or bottom half of the bolt contact spots it would make the bracket square up to a degree. I first have to get another person to apply the brakes so I can remember if the caliper is kicking up on the inboard or outboard side. Keep the idea coming please or a tow truck?
Thanks-Howard
Author:  Joshie225 [ Thu May 14, 2009 1:03 pm ]
Post subject: 
Wow, bad brake kit. I thought you had the kit with the GM calipers rather than the Chrysler sliders. I'd take the caliper off it's mount and see if the caliper mount is square with the rotor. A regular carpenter's square should suffice. If the mount is square with the rotor then it has to be the caliper that isn't square. The caliper kinda looks like a Chinese knockoff.

If the mount is not square with the rotor then take the mount off the spindle and see if the caliper mounting area is square with the caliper to spindle mounting area. Caliper adapters and calipers are pretty easy to come by, but the kit supplier has a clear obligation to correct the problem.
Author:  sandy in BC [ Thu May 14, 2009 4:47 pm ]
Post subject: 
Quote:
but the kit supplier has a clear obligation to correct the problem.
....agreed!
Author:  ppsi [ Thu May 14, 2009 5:11 pm ]
Post subject: 
I would have to say that due to my own fault in not realizing there was a problem 6 years ago it will be hard to hold Master Power Brakes responsible. They have been great to talk with thus far and I've not asked nor have they offered to replace the adapter because I am still in the process of determining the exact cause of the problem without any doubt AND with the ability to show it is the adapter. I think they would replace the faulty part but maybe this will be a bridge to cross soon.
Just as a way to make sure I am not looking for more than I should expect and the fact that I am almost doubting myself at this point how much pedal travel should the caliper take up? In other words (yes I use that phrase a lot) when I pinch off the hoses I get a super hard pedal maybe 1" after pressing the brake. Where should this pedal sink to after incorporating the caliper, pads, etc. into the equation?
Thanks for the tips.
Howard
Author:  MI6 [ Tue Sep 22, 2009 6:58 pm ]
Post subject: 
Any updates/progress to report?
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