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Nonlinear Brakes #1476118 07/29/13 07:28 PM 07/29/13 07:28 PM
Joined: Mar 2011 Posts: 183 Charleston, SC B bronco9588 OP member
bronco9588 OP member B Joined: Mar 2011 Posts: 183 Charleston, SC	So I have changed out rear drum brake pistons, rebuilt front calipers, new flexible hoses, new stainless steel lines I ran her for a little while on that setup, and then purchased a new master cylinder and brake booster. Now I have 0 braking effort for 90% of the travel and then the brake kicks in a the last second and locks up. I have bled my brakes twice with no noticeable effort. I think I have one of two problems: 1) Push rod adustment: I don't feel like the brake pedal is loose and that the pushrod is making contact further down the travel. It wouldn't explain the brakes locking up. Are these guys compatable with brake boosters? http://chucker54.stores.yahoo.net/brakcylpuspa.html 2) Do I need to bench bleed the master cylinder? '73 Charger Petty Blue, Black Vinyl, and Gill Slits 727 torque-flight 400 BB Chrysler 8 3/4 rear

Re: Nonlinear Brakes [Re: bronco9588] #1476119 07/29/13 08:09 PM 07/29/13 08:09 PM
Joined: Sep 2007 Posts: 14,889 up yours Supercuda About to go away
Supercuda About to go away Joined: Sep 2007 Posts: 14,889 up yours	Did you properly adjust the rear shoes? 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.

Re: Nonlinear Brakes [Re: Supercuda] #1476120 07/29/13 08:18 PM 07/29/13 08:18 PM
Joined: Mar 2011 Posts: 183 Charleston, SC B bronco9588 OP member
bronco9588 OP member B Joined: Mar 2011 Posts: 183 Charleston, SC	No, but they were working before I swapped out the master and the booster. I then drove 1,000 miles. If they were off, would they not have adjusted by then? This problem showed up after the master cylinder and booster swap. '73 Charger Petty Blue, Black Vinyl, and Gill Slits 727 torque-flight 400 BB Chrysler 8 3/4 rear

Re: Nonlinear Brakes [Re: bronco9588] #1476121 07/29/13 08:33 PM 07/29/13 08:33 PM
Joined: Jan 2003 Posts: 6,608 Indiana EV2DEMON The Camaro Kid
EV2DEMON The Camaro Kid Joined: Jan 2003 Posts: 6,608 Indiana	Are you saying you did not bench bleed the master before you installed it?

Re: Nonlinear Brakes [Re: EV2DEMON] #1476122 07/29/13 08:38 PM 07/29/13 08:38 PM
Joined: Mar 2011 Posts: 183 Charleston, SC B bronco9588 OP member
bronco9588 OP member B Joined: Mar 2011 Posts: 183 Charleston, SC	That is correct. I have a pair of old brake lines that I can use to do the job. I think after my reading that this is probably the problem. Why would the brakes lock up so quickly? '73 Charger Petty Blue, Black Vinyl, and Gill Slits 727 torque-flight 400 BB Chrysler 8 3/4 rear

Re: Nonlinear Brakes [Re: bronco9588] #1476123 07/29/13 10:10 PM 07/29/13 10:10 PM
Joined: Sep 2007 Posts: 14,889 up yours Supercuda About to go away
Supercuda About to go away Joined: Sep 2007 Posts: 14,889 up yours	Quote: So I have changed out rear drum brake pistons, That statement tells me you fooled with the rear brakes. Mind you the rear brakes will only self adjust if, A. the self adjusters are properly assembled and working and B. they only self adjust when you stop while going backwards. How many of those 1000 miles were your stopping while going backwards? The self adjusters are really only there to compensate for wear, not to correct maladjustment, though it will eventually do so. And yes, you should always bench bleed your M/C, make sure you have a cover on it and do not stomp the pedal or you will squirt brake fluid all over the place. 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.

Re: Nonlinear Brakes [Re: bronco9588] #1476124 07/30/13 05:08 PM 07/30/13 05:08 PM
Joined: May 2007 Posts: 553 Sac, CA, USA N ntstlgl1970 mopar
ntstlgl1970 mopar N Joined: May 2007 Posts: 553 Sac, CA, USA	also make sure that the master cyl pushrod isn't too long (master cyl preload - there shouldn't be any) this won't allow the cylinder to fill correctly because the piston/seal covers the compensating port in the bore

Re: Nonlinear Brakes [Re: bronco9588] #1476125 07/31/13 05:27 PM 07/31/13 05:27 PM
Joined: Jan 2003 Posts: 1,037 Texas, Dallas G_T super stock
G_T super stock Joined: Jan 2003 Posts: 1,037 Texas, Dallas	did you switch from manual to power brakes? Probably not it... but some of these cars had different brake pedal lengths/pivot points/ratios for the booster rod and that can happen. We switched from manual to power on my bothers 70 Fury and it did the same thing... nothing for 90% of travel then lock up... Changed out the pedal and all fixed. didnt make sense... but... hey 1970 Charger - V10, 6spd, Alterkation, Street Lynx 4 Link, Moser Dana 60, Wilwood 14" disks, Forgeline 18" Wheels (Rear:335's), ISIS Multiplexing Wiring http://www.v10mopar.com 2012 Charger SRT8

Re: Nonlinear Brakes [Re: ntstlgl1970] #1476126 08/02/13 01:08 AM 08/02/13 01:08 AM
Joined: Mar 2011 Posts: 183 Charleston, SC B bronco9588 OP member
bronco9588 OP member B Joined: Mar 2011 Posts: 183 Charleston, SC	Quote: also make sure that the master cyl pushrod isn't too long (master cyl preload - there shouldn't be any) this won't allow the cylinder to fill correctly because the piston/seal covers the compensating port in the bore How do you go about setting this? '73 Charger Petty Blue, Black Vinyl, and Gill Slits 727 torque-flight 400 BB Chrysler 8 3/4 rear

Re: Nonlinear Brakes [Re: bronco9588] #1476127 08/02/13 02:14 AM 08/02/13 02:14 AM
Joined: May 2007 Posts: 553 Sac, CA, USA N ntstlgl1970 mopar
ntstlgl1970 mopar N Joined: May 2007 Posts: 553 Sac, CA, USA	- This is not something you run into very often - Loosen the master cylinder and see if there is any resistance when you attempt to push the master towards the firewall which would indicate preload. There should be no resistance. Or if you have a dial caliper, you can measure the depth of the pushrod bore in the master vs. the length the pushrod from the firewall to the end of the pushrod. Another possibility - if there is preload - loosen the brake lamp switch - it doesn't take much preload to mess things up.

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