Problem with disc brakes after swap

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khaley71

khaley71

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I did a disc brake swap on my 71 Swinger. The car originally had 9 inch drums all the way around. The donor car was a 74 Dart Sport with big bolt pattern manual disc brakes. The problem after the swap is I have to push really really hard on the brake pedal to get my Swinger to stop. This is a list of used parts I installed from the Dart Sport...spindles, proportioning valve, upper control arms and the brake pedal push rod. This is a list of new brake parts I installed when I did the swap...rotors, calipers, pads, all rubber lines, all steel lines and master cylinder. When I ordered the master cylinder I ordered one for a Dart Sport with manual disc brakes. The rear in the car was also swapped from the 7 1/4 to an 8 3/4 with big bolt pattern axles from Doctor Diff. All the brake parts on the rear are also new...drums, shoes, wheel cylinders and hardware kit. The shoes in the rear are adjusted up until they just start to drag slightly. I have bled the system several times and have plenty of fluid coming out at all four wheels. I'm not sure what else to check. There really isn't much difference between the drums that where on my Swinger and the manual disc's I have on it now.
 
What is the bore size of the Master?

The rebuilders and after market will cross list them for multiple vehicles.

You want a bore size 1" or less most likely.
 
To be honest I don't know what the bore size is. I'm guessing the only way to tell would be to disassemble the one I have now and mic it?
 
1969383S said:
What is the bore size of the Master?

The rebuilders and after market will cross list them for multiple vehicles.

You want a bore size 1" or less most likely.
Click to expand...

X2!! Also a GOOD set of pads make all the difference. How much peddle travel do you have? The smaller bore MC's will give you more peddle travel.

Just one more suggestion, I use EBC red pads, they are hard on the rotors and make some dust but they stop! I had them on my daily driver and found them too touchy but on the Barracuda they are just right. They ain't cheap! If all else is working correctly and in good shape they will make a big difference once they get seated. FOLLOW their directions and I think you'll like them. Not all pads are the same. I found out what works on one car might not be the best on another.
 
The pads I used are ceramic, I forget the brand name. I'll have to check on the pedal travel tomorrow. I guess I'll try a master cylinder with a smaller bore, hopefully it won't be to much trouble to find one. Thanks for your help gang, I'll let you know how things work out.
 
If you have the part no of the Master you should be able to reference that to bore. "Used to be" you could also look 'em by the casting no.

I don't know a thing about ceramic pads. They may be part of the problem
 
When I can find the time I'll look to see if the master cylinder has any numbers on it. I just wanna get this thing sorted out so I can drive the old girl again. Maybe I'll try switching to semi metallic pads too.
 
I wish I could remember exactly what I put on mine. They work well. Hell I'm just using the original 67 drum master, and I believe they are NAPA semi metallic
 
No, ceramic pads are better for initial bite than semi-metallic. Metallic pads need to warm up a bit, ceramic is good when cold. Keep the ceramics. My guess is that you just aren't used to the feel of Mopar non-assisted disc brakes. My 67 Barracuda came with a 1-1/16" bore, and the pedal effort could be described as enormous. The pedal is rock hard, and guests feel they need to use both feet. Now that I am used to it I like it -- the response is extremely linear and easily feathered. I'm guessing this size is what you now have.

There is a 15/16 bore MC -- it is listed as correct for power disc brakes, but it is a bolt-in swap -- it increases the pedal travel but decreases the effort, basically giving your foot more leverage. You might like this better -- a lot of people make this swap.

Overall, drum brakes require less pedal pressure because they are designed so that the shoes "grab" the drum and pull themselves tighter once they make contact. Disc brakes don't do that -- it's strictly linear -- more push, more squeeze.
 
If you installed "racing pads", they give little friction when cold and only work once heated up and staying hot, like in road-racing. "Ceramic" is a squiggly term, more of a marketing term than a technical description.

Most people find a 15/16"D or 7/8"D MC bore best for manual disks. Since you have issues, I would go the smallest. I used an MC for a 95-99 Breeze ABS on all 3 of my 60's Mopars. Many others would work w/ a 2-4 adapter plate. Many here use a 90's Dodge truck MC (search). Lighter aluminum and no rust. But, there must be a reason why even the smallest cars today come w/ a booster. When the booster failed in my 65 Newport, I had to use 2 feet and it felt like stopping a train, and that is a drum-drum car (and big drums).
 
khaley71 said:
I did a disc brake swap on my 71 Swinger. The car originally had 9 inch drums all the way around. The donor car was a 74 Dart Sport with big bolt pattern manual disc brakes. The problem after the swap is I have to push really really hard on the brake pedal to get my Swinger to stop. This is a list of used parts I installed from the Dart Sport...spindles, proportioning valve, upper control arms and the brake pedal push rod. This is a list of new brake parts I installed when I did the swap...rotors, calipers, pads, all rubber lines, all steel lines and master cylinder. When I ordered the master cylinder I ordered one for a Dart Sport with manual disc brakes. The rear in the car was also swapped from the 7 1/4 to an 8 3/4 with big bolt pattern axles from Doctor Diff. All the brake parts on the rear are also new...drums, shoes, wheel cylinders and hardware kit. The shoes in the rear are adjusted up until they just start to drag slightly. I have bled the system several times and have plenty of fluid coming out at all four wheels. I'm not sure what else to check. There really isn't much difference between the drums that where on my Swinger and the manual disc's I have on it now.
Click to expand...

Sounds like your master cylinder is sized for drums, not discs. Call any of the brake companies , MPB, Wilwood, and they will help you.
 
I had to add an adjustable porportioning valve on the line to the rear brakes. Seems the rears were getting most of the fluid. Still have to push hard but it stops a lot better
 
You need a smaller bore MC. I also have 73-75 discs on my 68. I have tried MC's with the following bores, 1-1/8", 1-1/32 and 7/8" with no other changes besides the MC.
The 1-1/8" MC was just too hard. The car would want to creep at a light unless I used both feet on the pedal. I currently have an aluminum 1-1/32" bore on it now (vintage Direct Connection) and it is extra firm but manageable. IMO, the perfect MC for you is 7/8". It gives a nice linear pedal without a lot of effort and was my favorite but I try to save weight whenever I can, hence the aluminum on there now.

I intentionally left off the factory proportioning valve and safety switch and just plumbed in an adjustable prop valve in the rear line. (Summit but looks just like the Wilwood) The safety switch just turns on the red dash light when there is a leak in one of the two circuits. Believe me, when that happens you don't need a light to tell you something is wrong. My Neon did it just last week. (rear wheel cylinder went bad)

Order a MC from a 73-75 A-body. Not a manual disc car but a power brake car. This will get you the 7/8" bore and you will run it manually using a manual brake pushrod. Try it, I guarantee you'll like it!

FYI, you can measure the MC bore without disassembly because you can see the bore on the back side where the piston goes in and it's easy to measure.
 
I have factory disk brakes on my 68 dart, switched to manual with an aluminum MC and 2 to 4 bolt adapter. MC was off an Aspen/volare 79 model, 1 1/32 bore, rockauto has them on close out for $20, pedal is a little more firm but works just as good as it did with the brake booster installed. Are you sure the donor had the correct pushrod? Do the brakes drag at all?
 
Also make sure your bleeders on the front calipers are on top, if the are on bottom you will get fluid but air pocket will stay above bleeders
 
For comparison, I currently have a 1" bore master with booster. Factory Kelsey in front with all new 69 factory style pieces in the rest of the system. Front pads are organic. Pedal is still hard unless on deacelleration as I have a 509 cam in the 383. The car stops fine and seems to get a tad better every time I drive it. I was concerned at first but think like most I have gotten to used to driving newer vehicles.
 
Hey gang sorry I haven't been back sooner with an update....work, weather and the wife sometimes get in the way lol. Thanks everybody for your suggestions and help. Im going to work on it some this weekend and I will come back with an update. There really is a great bunch of people on here.


gtsdude said:
Are you sure the donor had the correct pushrod? Do the brakes drag at all?
Click to expand...

No the brakes don't drag at all. Im pretty sure the push rod was the original one from the donor car.
 
BillGrissom said:
When the booster failed in my 65 Newport, I had to use 2 feet and it felt like stopping a train, and that is a drum-drum car (and big drums).
Click to expand...

This is a more accurate description of how it feels when I'm trying to stop my Swinger. The pedal is firm but it feels like its not going to stop. I took it out last night to try a couple panic stops as I had not tried previously. There is no making a panic stop at all. I realize in an idea situation you don't want the wheels to lock up but they didn't even come close.
 
I "was told" ceramic pads require a break-in period, after which they grab better. I dont "know" if thats true, but customers used to say that. They also make a lot of black dust thats sometimes hard to get off.For those reasons, I have never, and wont, run them.

As others have said, theres only two reasons why a hard-pedal, non-boosted, fully- rebuilt, A-body is hard to stop; 1) a too-large M/C bore, and 2)the pad/rotor interface.
I myself have a booster, a 15/16 M/C, and organic pads. Awesome oem brakes( K-H & 10" drums)

If you cant lock up the brakes at sub 25mph or so, Somethings not right.I wouldnt take out in traffic.
.
 
AJ/FormS said:
I "was told" ceramic pads require a break-in period, after which they grab better. I dont "know" if thats true, but customers used to say that. They also make a lot of black dust thats sometimes hard to get off.For those reasons, I have never, and wont, run them.

As others have said, theres only two reasons why a hard-pedal, non-boosted, fully- rebuilt, A-body is hard to stop; 1) a too-large M/C bore, and 2)the pad/rotor interface.
I myself have a booster, a 15/16 M/C, and organic pads. Awesome oem brakes( K-H & 10" drums)

If you cant lock up the brakes at sub 25mph or so, Somethings not right.I wouldnt take out in traffic.
.
Click to expand...

This pretty much sums it up, I think
 
Something is wrong with the brakes, it's not just a "manual brakes are hard" problem. If I used 2 feet on the brake pedal of my duster the brakes would lock up before I even knew what was happening.

I have manual disks on my Duster, and prefer them significantly over the power disks on my challenger. All of my cars from here on out will be manual disks, they're infinitely better than the stock power brakes IMHO. I've run through pretty much all the combinations of manual disks on my Duster. Initially I had the stock 1-1/32" master cylinder and 73+ stock rotors, then upgraded to 11.75" rotors while still using the same m/c and calipers, and I now have Dr. Diffs 13" cobra style kit with a 15/16" master, also from Dr. Diff. The feel with the 15/16" master is better, but it was never hard to stop with the stock master cylinder or stock rotors.. Certainly not as hard as what you describe. If anything it's better with the 15/16" master because there is a little more pedal travel, so it takes a little more input to lock up the brakes.

If you installed the master cylinder for a Dart Sport with manual disks you should have a master with a 1-1/32" bore. That shouldn't give you the symptoms you describe. I prefer the 15/16", but that's not your problem.

If you have to use 2 feet and it still doesn't stop, something is wrong. It's possible that the brake pads haven't properly bedded to the rotors, or that they're somehow contaminated. I haven't used ceramic pads so I'm not familiar with their break in process. It's also possible that you have an issue with the proportioning valve from the donor car, or the push rod from the donor car.

The fact that the rear brakes don't lock up either kind of indicates that the problem is not just the front pads though. I would confirm that the master cylinder push rod is the right length, and then suspect that proportioning valve. It's also possible that your "new" master cylinder isn't working properly, it wouldn't be the first time.
 
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