Touchy brakes

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deanster

deanster

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Hi all. I recently did a disc brake change over on my 75 dart Sport. The donor car was a 73 Valiant 4door. The previous owner of the Valiant said he is a mechanic and had replaced the M/C, booster, shoes, pads, calipers, and the rear rubber hose. I also replaced the front rubber hoses. The problems I have are the brakes are very touchy and if I brake hard the car keeps braking for one to two seconds after I lift my foot off the pedal. When I had the front end aligned the shop turned the drums and rotors and sanded the shoes and pads although they are very new. The brakes were touchy on the donor car also. Any ideas? TIA...Deanster
 
could really be a number of things. i would start by putting the car up on jacks and have someone hit the brakes while you turn each wheel to check for the one or more thats sticking. hopefully it will be something easy like a sticking caliper. check it running too in case there is an issue with the booster or m/c.
 
The rear drum brake adjustment is too tight. Back off the rear adjusters half a turn.

The brake booster pushrod may be adjusted too tight too. There should be some play before the master cyl plunger is pushed but I don't have the spec in front of me.
 
I'm thinking like Ramcharger about the pushrod being adjusted too tight.

The only other thing I can think of is the pad or shoe material is too aggressive. I worked for Hyster forklifts yrs. ago back when everything was switching over from asbestos shoes to the new organic compound shoes they had a terrible problem with the new organic stuff being too aggressive. I went to a customers location once to work on one that was that way and the first time I hit the brakes it about threw me over the steering wheel. I thought all that stuff was worked out but maybe you got a pair of old stock shoes and/or pads.
 
Thanks for the replies, I haven't made time to try any adjustments though. I'll post back when I do...Dean
 
The booster's plunger should be preset within a tolerance. A mis-matched booster and master cylinder will cause sensitive pedal. master cylinder can too. My parents had a fwd Cutlass sierra that would lock the right rear in a heartbeat, especially in snow. Replaced master cylinder, fixed it.
 
Sounds like a manual brake mc with a small diameter piston combined with not enough clearance between the booster pin and the mc. You need .002" clearance to prevent the brakes from dragging.There are a lot of rebuilt MC that are not always what they say!
 
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