Re: [Chrysler300] 300-F brake problems -
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Re: [Chrysler300] 300-F brake problems -

Hi Noel -- sounds like the brake fluid is unable to return fully to get back into the master cylinder when hot .. This is the 
 First thought . If brake switch is good, it is clearly telling you exactly that. What was wrong with first one? Great test to pull off booster hose , eliminates a lot of complicated stuff with power brakes . You pulled it right at booster right , not manifold ( there is a vacuum check valve) . 
Two things come to mind , there is not enough gap at master actuating rod when pedal is up or return spring is somehow not pushing pedal up enough ? Or mechanically stopped somehow . ( wires under dash ?)  Master piston  should come ALL the way back toward the driver against a stop in the master when just sitting there , nothing to do with pedal, that position uncovers a port that lets fluid from retracting shoes back into the reservoir . You can see that piston action against its stop if you can get rubber boot out of way . There should be a small amount of play there between push rod  and master, pedal up ,  master out all the way , if you wiggle pedal in and out  , see FSM , but guess ..030 ? Misadjusted gap? Fairly critical thing . That play must be there with pedal at rest, and master piston all the way out. 
What else ? Piston sticking in master bore, not coming all the way back ( foreign material got in ? Changing switch ? ) 
Second , There is a small check valve in outlet of master to hold a residual pressure . Various kinds , metal ball and brass best, but some have a rubber thing like a duck bill . Slight chance that is stuck or if rubber , deceased , blocking line on return . On application , psi is 100x more it gets by easily Blocked lines in general ,??  but if all 4 wheels doubt it .
Hope this helps. Great they survived that , well bedded now! You know my story of towed off Dan Ryan at 6 pm. Brakes. Human error. At rear axle . 
Hopefully just adjustment of rod gap .. 

Ps rise in engine temp probably (?) unrelated, more that the drag on engine  caused by brakes , so you step on gas a bit more to maintain highway speed it works harder . However that much drag I would expect would really burn up brakes pretty fast . 
Any satisfaction , or better empathy -- maybe it is (!) ---I was in 67 Dart coming  down mt equinox (vt) 6 miles all drop last weekend 727 would not go into first . ( wha??? why me) Brakes smoking on descent in one mile in 2nd . Toy 9" drums. Almost three hours to come down a mile at a time . Wait 25 minutes , thick mags on car  helped but could not touch them . The cause ? Transmission cooling line bent  wrong , it blocked the shift lever at trans attachment arrgh . Happens to all of us.. 🚗
Sent from my iPhone

On Jul 30, 2017, at 4:44 PM, Noel Hastalis cpaviper@xxxxxxxxxxx [Chrysler300] <Chrysler300-noreply@xxxxxxxxxxxxxxx> wrote:

Hello Group,

Hi Everyone,

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!

Noel Hastalis

Burr Ridge, IL

F coupe


Posted by: John Grady <jkg@xxxxxxxxxxxxxxxxx>

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