Another brake question....Master Cylinder issue?
#1737424
01/24/15 04:17 AM
01/24/15 04:17 AM
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Joined: Oct 2003
Posts: 3,698
NE Oklahoma
Von
OP
master
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OP
master
Joined: Oct 2003
Posts: 3,698
NE Oklahoma
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I noticed the other active brake thread so I thought Id ask about my braking system.
The brakes work OK, not great but OK. The car stops fine, but the brakes wont lock up (front or back).
The car is in my sig. My system consists of 10.75 front discs, 11 inch drums rear. No booster, manual. The calipers are from a 72 Challenger. The master is a MP unit from the late 90s. I do believe it is a 1.125 bore. Not 100 percent on the bore size, but I do know it was bigger of two sizes listed in the MP catalog in 1998ish. I do have a dial type prop valve in the rear brakes.
Ive had the car back together for about 5 years. I drive it on the street as well as track.
But, I feel they arent "right" as I cant make them lock up. The pedal feel is good, not overally stiff or soft.
I assume I need a smaller bore master. Something around a 7/8 inch unit?
72 RR, Pump gas 440, 452s, 3800 lbs, Corked, ET Radials,. 11.33@117.72.
Same car, bone stock 346s, 9.5 comp, baby solid. 12.24@110.
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Re: Another brake question....Master Cylinder issue?
[Re: Von]
#1737427
02/01/15 02:59 AM
02/01/15 02:59 AM
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Joined: Nov 2003
Posts: 36,040
Lincoln Nebraska
RapidRobert
Circle Track
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Circle Track
Joined: Nov 2003
Posts: 36,040
Lincoln Nebraska
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My 65 dart had 76 A body 10.87" discs (2.75" pistons same as yours). 1&1/8 truck dual alum MC. 10" later 7&1/4 brakes & it will lock em up with enough pedal (rears first). Not sure what your exact problem is but my components are similar to yours.
live every 24 hour block of time like it's your last day on earth
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Re: Another brake question....Master Cylinder issue?
[Re: Von]
#1737429
02/01/15 08:29 AM
02/01/15 08:29 AM
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Joined: Jan 2003
Posts: 3,575
The Netherlands
BigBlockMopar
master
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master
Joined: Jan 2003
Posts: 3,575
The Netherlands
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Quote:
Up. Anymore ideas?
I would find out exactly what bore-diameter you have now and go one size smaller.
Going from 1.125" to 7/8" is way too much of a step and most likely won't work if you have a proper manual brakepedal ratio in the car.
If you don't have a residual valve in the rear brake-line I would get one as well.
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Re: Another brake question....Master Cylinder issue?
[Re: Von]
#1737430
02/01/15 12:00 PM
02/01/15 12:00 PM
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Joined: Nov 2010
Posts: 105
Ontario, Canada
D149
member
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member
Joined: Nov 2010
Posts: 105
Ontario, Canada
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Have you checked the brake safety switch? If the o-rings in it are no good, the brakes won't work very well. To check it, just take out the switch. If there is fluid behind the switch, the o-rings are no good. If no fluid, it is fine. This was the problem on my Dad's Cuda. We could not get the brakes to lock up (disc/drum). We tried everything, new master, booster, fluid, rebuild calipers and wheel cylinders. Nothing worked until we rebuilt the safety switch. Brakes work great now. Here is a link on how to rebuild. Link
1968 Valiant Signet 4dr. 273 4spd
1969 Road Runner 383 4spd
1969 Barracuda 318 auto
1970 Dart Swinger 340 4spd
1975 Cordoba 400-4bbl
1988 Caravelle 318 Auto
1999 Dakota R/T
2000 Viper GTS
2001 Ram 2500 Diesel 6spd
2018 Dodge Challenger GT (Winter beater!)
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Re: Another brake question....Master Cylinder issue?
[Re: D149]
#1737431
02/01/15 12:33 PM
02/01/15 12:33 PM
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Joined: Sep 2007
Posts: 14,889
up yours
Supercuda
About to go away
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About to go away
Joined: Sep 2007
Posts: 14,889
up yours
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Quote:
Have you checked the brake safety switch? If the o-rings in it are no good, the brakes won't work very well. To check it, just take out the switch. If there is fluid behind the switch, the o-rings are no good. If no fluid, it is fine.
This was the problem on my Dad's Cuda. We could not get the brakes to lock up (disc/drum). We tried everything, new master, booster, fluid, rebuild calipers and wheel cylinders. Nothing worked until we rebuilt the safety switch. Brakes work great now.
Here is a link on how to rebuild.
Link
That is not a combination valve, which is what you want in a disc/drum combo.
They say there are no such thing as a stupid question.
They say there is always the exception that proves the rule.
Don't be the exception.
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Re: Another brake question....Master Cylinder issue?
[Re: Cab_Burge]
#1737432
02/06/15 08:05 PM
02/06/15 08:05 PM
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Joined: Oct 2003
Posts: 3,698
NE Oklahoma
Von
OP
master
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OP
master
Joined: Oct 2003
Posts: 3,698
NE Oklahoma
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Quote:
Try adjusting the proportioning valve until the back tires lock up and then set it so it just won't and see how you like that with the present parts    That is a big car  Stay safe 
No matter where I have the prop valve, neither front or rear locks.
72 RR, Pump gas 440, 452s, 3800 lbs, Corked, ET Radials,. 11.33@117.72.
Same car, bone stock 346s, 9.5 comp, baby solid. 12.24@110.
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Re: Another brake question....Master Cylinder issue?
[Re: BigBlockMopar]
#1737433
02/06/15 08:06 PM
02/06/15 08:06 PM
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Joined: Oct 2003
Posts: 3,698
NE Oklahoma
Von
OP
master
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OP
master
Joined: Oct 2003
Posts: 3,698
NE Oklahoma
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Quote:
Quote:
Up. Anymore ideas?
I would find out exactly what bore-diameter you have now and go one size smaller.
Going from 1.125" to 7/8" is way too much of a step and most likely won't work if you have a proper manual brakepedal ratio in the car.
If you don't have a residual valve in the rear brake-line I would get one as well.
So try a 1 inch master or a size between 1 and 1.125. I do have a pedal from a manual brake car.
Why the residual valve in this app?
72 RR, Pump gas 440, 452s, 3800 lbs, Corked, ET Radials,. 11.33@117.72.
Same car, bone stock 346s, 9.5 comp, baby solid. 12.24@110.
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Re: Another brake question....Master Cylinder issue?
[Re: D149]
#1737434
02/06/15 08:08 PM
02/06/15 08:08 PM
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Joined: Oct 2003
Posts: 3,698
NE Oklahoma
Von
OP
master
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OP
master
Joined: Oct 2003
Posts: 3,698
NE Oklahoma
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Quote:
Have you checked the brake safety switch?
Safety switch is gone...
72 RR, Pump gas 440, 452s, 3800 lbs, Corked, ET Radials,. 11.33@117.72.
Same car, bone stock 346s, 9.5 comp, baby solid. 12.24@110.
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Re: Another brake question....Master Cylinder issue?
[Re: ahy]
#1737436
02/07/15 02:33 PM
02/07/15 02:33 PM
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Joined: Oct 2003
Posts: 3,698
NE Oklahoma
Von
OP
master
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OP
master
Joined: Oct 2003
Posts: 3,698
NE Oklahoma
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I may be way off base...but I dont think car weight is an issue. My car weighs no more or within a few lbs of the average BB e body. I have shucked quite a bit of weight off it. Just wondering...how does a similar system work in an e body?
Also, it has been my experience that an "under braked" vehicle usually locks the brakes easily? For instance, ( I know not an exact dollar to dollar comparison) my nissan pickup will lock the brakes way too easy if you put a trailer on it.
This car had 4 wheel manual drums from the factory. It didnt stop as "good" as the current setup, but it would lock all 4 if need be. The car weighs at least 300lbs less than those days.
As far as linkage, I have a pedal from a 71 RR manual brake car. The rod is, I believe, an adjustable rod from master power.
What are the measurements to verify that I have the correct pedal?
Could an incorrect pedal height, too low for instance, be helping cause the issue?
The car does stop pretty decent. On a short 1/8 mile track without much shut down area, I have to lock her down pretty good, but it does it fine. I just dont think that not being able to lock either front or rear is "correct"?
72 RR, Pump gas 440, 452s, 3800 lbs, Corked, ET Radials,. 11.33@117.72.
Same car, bone stock 346s, 9.5 comp, baby solid. 12.24@110.
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Re: Another brake question....Master Cylinder issue?
[Re: Andrewh]
#1737438
02/07/15 03:44 PM
02/07/15 03:44 PM
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Joined: Oct 2003
Posts: 3,698
NE Oklahoma
Von
OP
master
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OP
master
Joined: Oct 2003
Posts: 3,698
NE Oklahoma
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Quote:
reading the original post, I do believe you are correct. you need a smaller bore mc.
here is why.
The amount of force you are applying does not equate to enough force at the calipers to lock up the brakes.
by using a smaller master, the math showed for me an increase of over 100 ft pounds of force applied at the calipers over the larger master that I was using.
since you don't have a booster, this is the only way to increase your brake force applied.
feets excel sheet shows that just by changing the master cylinder, no other differences, makes a huge amount of force difference.
I found that out too real world, that I could lock mine up after that.
Thanks for your input!
How much smaller did you go in MC bore size?
Is feets excel sheet available on here or should I PM him for it?
72 RR, Pump gas 440, 452s, 3800 lbs, Corked, ET Radials,. 11.33@117.72.
Same car, bone stock 346s, 9.5 comp, baby solid. 12.24@110.
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Re: Another brake question....Master Cylinder issue?
[Re: feets]
#1737440
02/07/15 08:33 PM
02/07/15 08:33 PM
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Joined: Feb 2003
Posts: 8,676
Andrewh
master
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master
Joined: Feb 2003
Posts: 8,676
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I only had one choice because of the aftermarket brakes. 1 and 1/8 down to 1 inch. that 1/8th was a huge improvement. they didn't make a smaller one for my application. there were a few people that adapted some from other cars, but I figured that was a worst case thing, trying to find a 7/8ths. and you can download it from http://3gduster.com/brakes.html
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