Trying to figure out my brakes

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kowality

kowality

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Hi all,
I have a question about a 72 Dart. My car came with power disc brakes according to the paperwork on the car that came with it new. My problem is the car locks up the rear brakes upon of any kind of stop that requries more pedal than a light push.
The pedal is also very hard and seems to sit up higher than normal.
My question is did these car come with a brake booster? The car doesn't have one on it and I would think it would.
I picked up the Dart from a person who was not really mechanically apt. Anyway while talking about the car he said that they tried to put the new style brake system on the car at one time but it didn't work out very well so they put the brakes back the way they came. I am thinking I may have some mismatched parts and would like to see what the car should have came with.
Thanks,
Kowality
 
dirty shoes or they had greese on them. or try a new hard wear kit. i,v had both do that on hard brakeing
 
There were both power and manual disc brakes available.
The first thing that comes to mind is brakes assembled wrong the longer shoe libbing goes to the rear. Backward will cause them to grab.
Next usual suspect is the perportion valve. Same symptom but not so simple fix. The valve is not servicable. Replace it with same correct or adjustable alternative.
 
A couple great suggestions guys, but first thing I checked for. I also did find a funny little bracked sticking up from the firewall under the master cylinder.
Sometimes it can be fun dealing with 38 year old vehicles, you never know where they've been or who messed with them.
 
kowality said:
A couple great suggestions guys, but first thing I checked for. I also did find a funny little bracked sticking up from the firewall under the master cylinder.
Sometimes it can be fun dealing with 38 year old vehicles, you never know where they've been or who messed with them.
Click to expand...

OK . Vacuum boosters do have added support brackets. One underneath and one to the left inner fender. Installing a booster might be the cure.
I would first find out if there were different master cylinders for power disc and manual disc. You may get by with just a different master cylinder. Good luck
 
1972 was the final year of the great-in-theory-but-failure-prone-in-application Kelsey-Hayes 4 piston calipre disc brakes .

As mentioned , these could be had with or without vacuum assist ; 340 Swingers had the disc brakes sans booster as standard fare .
Look for codes "B41" ( disc brakes ) and "B51" ( power boosted disc brakes ) on your car's fender tag and/or build sheet .

My first car was a 1972 Swinger , and it had the power disc brakes ( 318 / 904 combo driver train ) .
I constantly had problems with those brakes !!!
The pistons would come-out unevenly , thereby causing a pulsating brake pedal and premature pad wear .
Naturally , the rear drums would overcompensate for the lack of braking power on the front , and would lock-up easily ( ever try to find those odd ball 10x1.75" drums ? Expensive as hell ; these actually had a core charge on them !! Guess they'd reline them with a new friction surface ) .

If you wish to keep those factory brakes ( e.g. , if your car's a resto ) , do yourself a solid and have the calipres rebilt with stainless piston sleeves , and use D.O.T. 5 silicone brake fluid ONLY .
I did that temporarily on my '72 until I was able to convert the car to the superior '73 & up setup .

Parts are much easier to find for these brakes these days ; but back when I had my '72
( 20 + years ago !! ) , parts were nearly impossible to find !!
 
The car has B51 on the fender tag and I am starting to think that it should probably have a booster on it, however I think that would make the problem worse. Does B51 come with booster?

The original owner said they at one time tried to switch the brakes over, but put it back because they were too gabby. I dismissed what he was saying because he really wasn't mechanically inclined. When I test drove the car they seemed touchy, but I didn't really try hard braking at the time (you know, beating up somewone elses stuff), but now I know I have to definetly sort something out

I am not against changing the system over and in the long run I know it would be the best way to go, but the car has really cool Cragers on it that are in really good shape and I want to keep those on the car. The car has the exact look I wanted (other than sagging in the back a little) and don't want to alter it too much anyway.

Thanks for all the advice and keep it coming!!
 
I'm going to vote with Redfish on this one. Prop valve and reversed rear shoes.

I checked the parts manual and found that the factory fitted the same power brake booster to disk cars as it did drum cars. There is a second part number that was designated for field conversion of manual to power assist cars.

There are three potential master cylinders for 1972. 1 each for disk brake cars, 9" drums, and 10" drums. The power brake cars will have a longer pushrod to the master cylinder. The disk brake master cylinder has a smaller forward well, than the rear. The drum brake M/C will have equal size fluid wells front and rear.

There was also a running change made to the master cylinder pushrod on 1 March 72. Hope this helps.
 
LH23H2R said:
My first car was a 1972 Swinger , and it had the power disc brakes ( 318 / 904 combo driver train ) .
I constantly had problems with those brakes !!!
The pistons would come-out unevenly , thereby causing a pulsating brake pedal and premature pad wear .
Naturally , the rear drums would overcompensate for the lack of braking power on the front , and would lock-up easily

Good point. If the front rotors were turned to minimum or below and the linnings are worn, the added fluid cavities in those calipers would make a difference in front to rear responce. Only a larger bore master cylinder could overcome that condition. The perportion valve does what it does but has its limits.
Click to expand...
 
Well, I am pretty sure the car came with a brake booster, but if I put one of those on, I am sure the problem would only be worse.
Now I am starting to wonder if the master cylinder lines are backwords.
Who knows....
 
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