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Brake problems in a NON B body using wrong year parts!

Kern Dog

Life is full of turns. Build your car to handle.
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I'm working on a 65 Dart. This was a 4 wheel, 9" drum car originally. I've added the 73 Dart 11"front disc brakes. Of course, this car came with the famous single reservoir "Deathpot" master cylinder. I pulled that out and mounted up a 4 wheel disc master cylinder. I figured it would work fine since I plumbed in a 73-76 disc/drum proportioning valve.
Bleeding the brakes in this turd has been a pisser. I always start at the right rear, furthest distance from the M/C. I figured this could take awhile since the front half of the system was replaced. The rear seemed to bleed out fine, no air after 3-4 pump and bleed sessions. The pedal feel was spongy but improved from how it was. It would firm up with multiple pumps.
The front though...Holy crap! I'd bleed until the fluid ran clear, then move to the drivers side. The pedal got worse. I'd bleed the left front and get all sorts of foamy fluid and bubbles. Back to the right side and the bubbles were back. It was as if the system was actually making bubbles. I saw a drip from the firewall and it turned out to be from the backside of the master cylinder. I think it was defective and sucking in air on the backstroke! I figured I'd just buy a M/C for a vehicle that is directly compatible with the calipers and prop valve. I have a few used M/Cs at home but new is better, right?
I went to three parts stores..Or COURSE nobody had what I needed in stock. I asked for a NON power, manual front disc M/C for a 73 Duster. They showed different part numbers for cars with power front disc. Why? I've measured these before. The bore size is 15/16" in both.
There is a lot of interchangeability in these cars so it isn't as if I am some cheap junkyard hack! I have a 75 Dart M/C and booster in my Charger and it works great.
I have a few used Power disc master cylinders here that came off of operational cars. I am curious about what the difference is between a power M/C and a manual M/C. Is the stroke travel different? They both have the same 15/16" bore size. The fitting size is the same. They look identical to me externally.
I'm going to bolt in one of my power M/Cs and see how it works. In the meantime, anyone have anything to add ?
Thanks.
 
I'm working on a 65 Dart. This was a 4 wheel, 9" drum car originally. I've added the 73 Dart 11"front disc brakes. Of course, this car came with the famous single reservoir "Deathpot" master cylinder. I pulled that out and mounted up a 4 wheel disc master cylinder. I figured it would work fine since I plumbed in a 73-76 disc/drum proportioning valve.
Bleeding the brakes in this turd has been a pisser. I always start at the right rear, furthest distance from the M/C. I figured this could take awhile since the front half of the system was replaced. The rear seemed to bleed out fine, no air after 3-4 pump and bleed sessions. The pedal feel was spongy but improved from how it was. It would firm up with multiple pumps.
The front though...Holy crap! I'd bleed until the fluid ran clear, then move to the drivers side. The pedal got worse. I'd bleed the left front and get all sorts of foamy fluid and bubbles. Back to the right side and the bubbles were back. It was as if the system was actually making bubbles. I saw a drip from the firewall and it turned out to be from the backside of the master cylinder. I think it was defective and sucking in air on the backstroke! I figured I'd just buy a M/C for a vehicle that is directly compatible with the calipers and prop valve. I have a few used M/Cs at home but new is better, right?
I went to three parts stores..Or COURSE nobody had what I needed in stock. I asked for a NON power, manual front disc M/C for a 73 Duster. They showed different part numbers for cars with power front disc. Why? I've measured these before. The bore size is 15/16" in both.
There is a lot of interchangeability in these cars so it isn't as if I am some cheap junkyard hack! I have a 75 Dart M/C and booster in my Charger and it works great.
I have a few used Power disc master cylinders here that came off of operational cars. I am curious about what the difference is between a power M/C and a manual M/C. Is the stroke travel different? They both have the same 15/16" bore size. The fitting size is the same. They look identical to me externally.
I'm going to bolt in one of my power M/Cs and see how it works. In the meantime, anyone have anything to add ?
Thanks.
Here's all you need to know.
http://www.mbmbrakeboosters.com/ind...cylinder-faq&catid=2:brake-boosters&Itemid=10
 
From the above link:

"What is the difference between a power brake master and a manual brake master?
A power brake master will have a larger bore diameter than a manual master."

That is the odd part. On the 73-76 A body cars, I've found that both use the same 15/16" bore size although they show different part numbers. The manual cars use a direct pushrod to the back of the M/C. The power setup uses a series of linkages that lessen the pedal ratio because the booster makes up for it.
I guess what I can "assume" here is that if the reservoirs are the same and the bore size is the same, it should work.
 
Don't quote me on this, Kern Dog.

Went through the same deal on mine, needing a manual MC. I think there are some differences internally, too. I was told there's different part #s for each, so...
 
sometimes when i get weird brake problems like that i isolate the problem
i remove lines at m/c and make some plugs and block pf master and
bleed and try it , if pedal is hard that you know is good, then i move down i clamp off all rubber lines ( lightly) and try pedal ,it says hard then un clamp one at a time.
is it cause it s soft or air coming back.
on my car when i did the power disc brake swap i took the complete system from the 82 dodge , the only thing that did not fit was the booster
so i found one that would fit in the hole. the pedal is kinda soft but thats because of the different booster to m/c and fulcrum point changed
when you drive it very little effort needed to lock up the wheels
good luck
 
Did you bench bleed the first master before installing?
 
The 4 wheel disk master requires an orifice to slow the return of fluid on the drum brake side. All manual drum masters have these orfices right behind the line connections. The orfice slows the return of fluid from the wheel cylinder.
 
I bench bleed every master cylinder before installing them. A few times, I have been so lucky that I was able to install a M/C and make one pass at each corner and be done!
 
To your original question, I'm not sure of the difference between the manual and power M/C. But, on my recently done front disc conversion I used a manual disc/drum 15/16" bore master and worked perfectly. I used the Right Stuff master from Summit.
https://www.summitracing.com/parts/RSD-DBMC15
 
So the disk/disk master cyl you have has no residual valve for the rear circuit, you didn't say if the the car has disk or drum in the rear but if you still have drums in the rear the lack of a residual valve in the rear circuit is going to cause the wheel cyls to suck air into the system.
 
So the disk/disk master cyl you have has no residual valve for the rear circuit, you didn't say if the the car has disk or drum in the rear but if you still have drums in the rear the lack of a residual valve in the rear circuit is going to cause the wheel cyls to suck air into the system.
Go back to original po. But I think we have nailed the problem down. Rear drums with no master residual.
 
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