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:
Posted by: John Grady <jkg@xxxxxxxxxxxxxxxxx>
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