Due to little experience and never having seen how the little “check valve” in the outlet of all MC’s works, I remain deeply suspicious of it. It is nominally designed to keep a “small” residual pressure on the tubing, stop-light switch and WC’s downstream of the MC. Unless you have deteriorated flexible brake hoses, I would guess this little device may be the culprit. The “valve: may be viewed in Figures 18 and 19 on page 14 of: http://www.jholst.net/60-
service-manual/service-brakes.This valve, or something else like the booster unit, is holding too high pressure on the system with the brake pedal up. Care should have been taken to make sure the rod that drives the booster and MC was of the precise correct length and properly installed.
I doubt if the MC check valve can be replaced or cleaned. It could have some scale or other crud in it to restrict flow. Another MC of highest quality might be your best bet unless the little valve is available by itself or in an MC overhaul kit. Been too long.
Repetition from many previous posts: The little valve is there to hold a small positive pressure on the plumbing and WC’s to minimize the inspiration of moist are past the WC pistons. This phenomenon is thought to be the root cause of corrosion in the bottoms of WC’s.
Brentwood, CA--98 @ 5PM
Welcoming your thoughts on recent braking issues my F is suffering -
Problems started last Sunday afternoon, on my 77 mile drive back home from the Belvidere, IL Mopar Happening. About halfway home, I smelled a brake shoe burning smell, and saw the engine temp gauge move up to the midway point, from its typical cool position - this while running at 70 mph with 90 degree outside temps. The brakes were clearly making contact. The brake pedal was also sitting an inch or more higher than normal, with a hard feel, but the brakes still stopped the car when applied. I backed into my garage, and noticed my brake lights stayed on, even when not touching the pedal. When I lifted up on the pedal, the brake lights would go off. I popped off the hubcaps, all 4 of which were very hot to the touch, to let the wheels cool off a little quicker. When the car cooled down, it was back to normal.
This week, I went to 3 local cruise nights, each about 15 minutes away, with no apparent braking issues. I also took the F to the local shop I've used for all my undercarriage work. They tried to replicate the issue, but couldn't. They cleaned up the front shoes and drums a bit, but said all looked fine.
Yesterday, I drove the F up to Kenosha, WI, to check out the AMC reunion show, and visit with John Begian and his freshly restored '68 AMX. No issues driving the 72 miles up, in the cool morning air. Same issue as last week, however, on the way home. When traffic bottled up on I-294 near O'Hare, the brakes started grabbing, and the engine temp headed higher. I pulled over at the O'Hare Oasis, let the car cool down for 40 minutes, and then drove home with no further issues.
John Begian suggested that I try pulling the vacuum hose off the brake booster, before shutting off the engine, to see if that released the pedal. So this afternoon, I went out cruising again to heat up the car, and got the brakes to grab again, with the smell of brake linings, and engine temp climbing. Brake lights again stayed on when I was out of the car, and the pedal was high and hard. I pulled off the vacuum hose, as John suggested, and heard a whoosh of air, but no change in the high pedal height, and the brake lights still stayed on. The front right hubcap was the hottest, with right rear and left front also pretty warm. Left rear was cool.
Some added background on this car -
- Master brake cylinder was replaced about 2 1/2 years ago.
- Hydraulic brake light switch was replaced less than a month ago, when up at the Iola, WI car show.
- Rear brake shoes were replaced this past winter, along with new used brake drums sourced from a fellow Club member.
- Front brake shoes and drums are about 3 years old.
- Still running DOT3 brake fluid.
- I've drive the F just over 5,000 miles this driving season, and have never had any brake issues of this type over the 48,000+ miles I've driven this car over the past 10 or so years.
I'm thinking it's the brake booster causing these issues, but not sure. My mechanical knowledge is weak, at best!
I welcome your thoughts!
Burr Ridge, IL
--Ray Jones. Y'all come on down an see us. Ya hear?