Need Help With Disc Brake Coversion

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billkrz

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Hello to all. I need some advice regarding the brakes on my 1968 Dart. It originally came with power drum brakes. Somewhere along the line, a previous owner changed the bolt pattern to 4 1/2". At the same time, he swapped the front brakes for the 1970-1972 B/E body discs and 11" rear drums.
When I got the car, the brakes were pretty non-existent. First thing I did was ask you FABO folks to identify the calipers. That's how I know what they are. Next, I asked which M/C to use as the car still had a drum M/C (same size reservoirs). It was recommended that I swap to a 70-74 B/E body M/C with the 1 1/32" bore(new Bendix). That made sense as it matched the calipers so I did this.
Brakes were still lousy so I swapped the calipers with NAPA rebuilds and new front hoses.
It was also suggested that I install a delay valve in the rear line as per factory disc cars so I did this as well.
Now here is what I have: the braking is very poor and only the rears seem to be working. If I close off the rear brake line, I am barely able to stop.
I am using the Dart booster. According to NAPA, their booster works for 1968-1972 Darts. Though I am using the "B/E" master, shouldn't this still work?
I'm open to all suggestions.
Here are my questions/thoughts: could the brake distribution/junction be a problem? I don't think this was changed.
Can you use the same distribution block for drum and disc brakes?
Do I need to swap the distribution block for a "B" body one as this is where the brakes come from?
Help!
Thanks,
Bill
 
This isnt going to answer your question but it might get you headed in that direction. Im doing a drum to disk swap on my 66 Barracuda and what I learned is that the M/C, booster, proportioning valve setup is very specific to what was on the car and what you are swapping to (atleast thats how it is for my car). Id start with what the set up is at each of the wheels and work my way backwards to find out what M/C, dist block, proportioning valve, booster combination is needed. Hope this was even slightly helpful and good luck.
 
Are you sure the lines are plumbed properly? The front disc brakes will use the larger cavity of the MC (the rear most one) and the rear drum brakes use the smaller cavity (usually the farthest forward one).
 
I did a changeover from 10'' drum brakes to the Kelsey Hayes disc on a 68 Dart. the only thing I changed was a master cylinder to a 73-75 Dart with disc brake and a V8. The combination valve for disc and drum are listed the same in a mopar parts catalog for a 68. There is the valve going to the rears which I did not use and so far no problems. I have a 1970 Challenger also and the combination valve is totally diffreent. My 2 cents thinks that is where the trouble is. Did you gravity bleed the whole system? I understand if you push the pedal at all when lines aren't connected you can screw up the pston in the combination valve and there a real bear to correct.

You might try calling Stainless Steel brake. they have helpful people and parts for all swaps. Hope this helps.
 
Your '68 combination valve will work fine with the 4 piston KH calipers, but won't pass enough fluid for the single piston calipers. Sounds like your valve has tried to fill an open line and needs to be reset to boot. Just switched my '66 Valiant to '75 Duster upper A arms, spindles, brakes, and valve block. Using a '74 Charger manual disc brake master cylinder it will stop on a dime and give you 7 cents change. There is no delay valve or check valve in the rear line. I'm thinking that if you would change your combination valve for the one from a '73-'76 disc brake A body you should be OK. Be careful not to push the brake pedal more than halfway to the floor when you are bleeding the system to keep from tripping the new valve and winding up with the same problem. Hope this helps.
 
Thanks fellas. Please keep all of the suggestions coming. I'll let you know how it ends (hopefully)!
Bill
 
Are the bleeders of the calipers at 12 oclock? Is all the air out of the system? Are the pads glazed?
 
Yes, they are plumbed correctly and the M/C was bench bled. Still no or little front brakes. Do I need a residual valve on the master for the rear shoes?
Bill


Aaron said:
Are you sure the lines are plumbed properly? The front disc brakes will use the larger cavity of the MC (the rear most one) and the rear drum brakes use the smaller cavity (usually the farthest forward one).
Click to expand...
 
Yes, the bleeders are at 12 o'clock. Systems has been bled. New M/C was bench bled. Took off the distribution/safety switch and all looks well. Took apart the new M/C and it looks ok however, it measures 1 1/8" not 1 1/32" as advertised. Would that make any difference for not having front brakes?
Also, am changing rear wheel cylinders to 7/8" to see if that makes a difference.
Any more suggestions?
Help....
Bill


redfastback said:
Are the bleeders of the calipers at 12 oclock? Is all the air out of the system? Are the pads glazed?
Click to expand...
 
Took off the distribution/safety switch. looks OK. As soon as you take pressure off, it recenters itself.
Question: it is the stock 1968 unit. The parts book for 1968 says that ALL Mopars used this unit in 1968 for both discs/drums. I now have a 1972 B/E brake system. So...does the distribution block/safety switch need to be changed? I never read about this needing to be swapped in any tech article(just add the rear prop valve-which I've done).
Still no front brakes(well maybe 10-20%).
Bill

grumpuscreature said:
Your '68 combination valve will work fine with the 4 piston KH calipers, but won't pass enough fluid for the single piston calipers. Sounds like your valve has tried to fill an open line and needs to be reset to boot. Just switched my '66 Valiant to '75 Duster upper A arms, spindles, brakes, and valve block. Using a '74 Charger manual disc brake master cylinder it will stop on a dime and give you 7 cents change. There is no delay valve or check valve in the rear line. I'm thinking that if you would change your combination valve for the one from a '73-'76 disc brake A body you should be OK. Be careful not to push the brake pedal more than halfway to the floor when you are bleeding the system to keep from tripping the new valve and winding up with the same problem. Hope this helps.
Click to expand...
 
Changed the rear wheel cylinders to 7/8" very little improvement. I'm using the stock Dart power disc booster with the B body 1 1/32 " master. Can that be a problem?
Do I need to change the stock Dart safety switch/distribution block?
Bill



billkrz said:
Yes, the bleeders are at 12 o'clock. Systems has been bled. New M/C was bench bled. Took off the distribution/safety switch and all looks well. Took apart the new M/C and it looks ok however, it measures 1 1/8" not 1 1/32" as advertised. Would that make any difference for not having front brakes?
Also, am changing rear wheel cylinders to 7/8" to see if that makes a difference.
Any more suggestions?
Help....
Bill
Click to expand...
 
Is there a filter and filter retainer between the booster and master? The filter is plastic and the retainer is metal, either look in a fsm or a member might be so kind as to post a pic. Take the master off the booster and adjust the little acorn nut out about .910-.920 from base of filter where master mounts to. this controls the depth into the back of the master.
 
Are you getting a soft or hard pedal?
How did you bleed the brakes?
Did you check all front brake lines for a kink in the line?
 
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