Re: Car brakes too sensitive....
[Re: Andrewh]
#2687779
08/14/19 06:40 PM
08/14/19 06:40 PM
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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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What Andrewh said, this will isolate the problem
live every 24 hour block of time like it's your last day on earth
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Re: Car brakes too sensitive....
[Re: robertop]
#2687859
08/14/19 10:29 PM
08/14/19 10:29 PM
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Joined: Jan 2003
Posts: 10,525 Freeport IL USA
poorboy
I Live Here
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I Live Here
Joined: Jan 2003
Posts: 10,525
Freeport IL USA
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I might suggest you pull the master cylinder off the booster, and add one flat washer per stud, then replace the master and tighten the bolts. Test drive the car someplace very open, very slowly, and check the brakes to see if they are better. You will need to push the pedal farther down then before, and the brakes won't grab as quickly, so be prepared. If the brakes function better, then remove the master cylinder, and remove the washers. You will need to adjust the length of the rod between the master and the booster.
The little rod between the booster and the master cylinder is suppose to have an adjustment on it. That adjustment is to adjust for slightly different depths of the master cylinder piston. If the brakes grab too fast, the rod length is probably too long. If the pedal seems to travel a long way before the brakes begin to apply, the rod length is probably too short. The threads on the end are fine thread, and a very little movement makes a huge difference. A full revolution to shorten the length of that end could result in no brake application at all!
The rod has a small threaded end with a lock nut on it. Loosen the lock nut, and turn the end in one 1/4 turn, then tighten the lock nut. Do not go more than a 1/4 turn at a time (you don't have to turn the end a 1/4 turn, but its a good starting point). A 1/4 turn makes a pretty big difference. Turning the end in gives you more pedal movement before the brakes are applied, if you turn the end out, it applies the brakes quicker.
Once the adjustment has been made, reinstall the master (without the extra washers) and test the brakes. If farther adjustments are required, its only a matter of removing the nuts that hold the master to the booster and adjusting the rod length as needed, then reinstall the master. If you want to play with the adjustment a bit, you can get the brakes to apply when you want them to. Gene
Last edited by poorboy; 08/14/19 10:42 PM.
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Re: Car brakes too sensitive....
[Re: robertop]
#2687983
08/15/19 11:18 AM
08/15/19 11:18 AM
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Joined: Mar 2007
Posts: 3,277 West Coast, USA
jbc426
master
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master
Joined: Mar 2007
Posts: 3,277
West Coast, USA
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I'm guessing it is your rear brakes that lock up first. That's normal for a factory Mopar brake system. If it is your front discs, you have something else going on at he booster/master cylinder as mentioned above. A larger bore master cylinder will reduce the rate or slope of the initial brake pressure, a smaller bore will steepen the rate of pressure increase.
As mentioned above, the master cylinder rod adjustment is critical. Its a bit of a pain to take it out and adjust it, but the time doing so is well spent. This era of Mopars tend to lock up the rear brakes way to early, especially on a panic stop. Drum brakes are "self-energizing" by design when applied. The brake shoes on them essentially wedge towards the brake drum once they start touching it and that wedging effect increases the total force of the braking at a given wheel.. Adjusting them does help significantly, but there are other "tricks" to reduce the overall braking power the provide once applied such as changing the wheel cylinder bore size, removing a portion of the brake pad(not too much though) and using either a proportioning valve or pressure surge flattening device.
On the surface, It sounds to me like you need a larger bore master cylinder. You can contact Dr Diff to find out which one you can swap out to reduce the rate of braking for a given pedal pressure. .
1970 Plymouth 'Cuda #'s 440-6(block in storage)currently 493" 6 pack, Shaker, 5 speed Passon, 4.10's 1968 Plymouth Barracuda Convertible 408 Magnum EFI with 4 speed automatic overdrive, 3800 stall lock-up converter and 4.30's (closest thing to an automatic 5 speed going)
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Re: Car brakes too sensitive....
[Re: jbc426]
#2688577
08/16/19 10:13 PM
08/16/19 10:13 PM
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Joined: Jan 2003
Posts: 5,788 Hamilton, Ontario Canada
Magnum
master
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master
Joined: Jan 2003
Posts: 5,788
Hamilton, Ontario Canada
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I replaced a power brake booster in an 87 Ram. The new one had a symptom you are describing. Try to tickle the stop pedal as lightly as possible and all 4 wheels LOCK like someone threw a stick through the spokes. No members, this is not touchy brakes because I'm not used to it.
I brought the booster to a local brake rebuilder. He installed what he called a reaction valve inside the booster. It worked perfectly after this.
69 Super Bee, 93 Mustang LX, 04 Allure Super
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