Hot master cylinder=brake drag?
#3230934
05/04/24 07:39 AM
05/04/24 07:39 AM
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Joined: Jan 2003
Posts: 8,028 Tulsa OK
Bad340fish
OP
master
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OP
master
Joined: Jan 2003
Posts: 8,028
Tulsa OK
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I have had this issue on and off for awhile now. My brakes will have a pretty heavy drag after the car has been driven awhile.
This problem seems to be related to master cylinder temp vs actual temp from heavy braking. I originally thought it was a pushrod issue but that is not the case, I can lift the brake pedal some and it has zero impact. When this happens the pedal is more firm than normal.
I idled in line for 20 minutes or so getting into the track last night and the pedal was rock hard by the time I got into the gates, the car cooled for about 20 minutes and I looked over and saw the brake lights on and the pedal had returned to normal feel after a few pumps.
I have the Dr Diff master cylinder kit which is an aluminum mopar unit with the smaller of the two bore options(7/8 I think). Willwood discs front and rear.
Should I toss a new master on it and see if that fixes it or is there something else I am not considering.
The level of drag is enough that if you are rolling in neutral you don't necessarily feel it until it almost comes to a stop then you feel it grab.
68 Barracuda Formula S 340
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Re: Hot master cylinder=brake drag?
[Re: Bad340fish]
#3230944
05/04/24 08:42 AM
05/04/24 08:42 AM
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Joined: Jan 2003
Posts: 2,924 A shed in England
Tig
master
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master
Joined: Jan 2003
Posts: 2,924
A shed in England
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I had an issue with the brake fluid spitting out of the "breather" hole in the front cap, master cylinder was warm to the touch but not hot. Never worked out how, as there is a rubber seal for the caps but the fluid was getting past it when hot. I made a shield (as pic) and I put a heat resistant mat on there too to solve the problem. I don't recall the brakes dragging though ??
'74 Challenger..9.46 @ 145.9 1/4, 6.001 @ 118 1/8 so far. 4023lb !!! # N/A, Marsh performance 655ci, Indy Maxx, T/R, Indy 600-13 X's, Street legal, pump gas, full interior, Cal-Tracs, mufflers, 3:73's and real 10.5 radials. 9.51 @ 142.4 1/4, 6.003 @ 114 1/8 with our old mule KB, 572-13, 580 wedge. RHD '68 Barracuda Fastback 323ci street/strip. Best ET 13.88 @ 99.03
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Re: Hot master cylinder=brake drag?
[Re: Moparteacher]
#3230998
05/04/24 01:33 PM
05/04/24 01:33 PM
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Joined: Aug 2011
Posts: 2,864 Pattison Texas
CSK
master
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master
Joined: Aug 2011
Posts: 2,864
Pattison Texas
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gotta be a bad master or the pushrod , the test is get the master hot so the brakes are dragging & then open the lines at the master & see if the drag goes away , then isolate the problem by getting it hot again & loosen the master bolts to give it some slack, OR if you have an adjustable rod shorten the rod & see if the drag goes away
1968 Charger COLD A/C Hilborn EFI 512ci 9.7 compression, Stealth heads, 4.10 gear A518 ODtrans 4100lb,10.93 full street car trim 2020 T/A 392 Stock 11.79 @ 114.5
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Re: Hot master cylinder=brake drag?
[Re: Bad340fish]
#3231026
05/04/24 03:51 PM
05/04/24 03:51 PM
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Joined: Aug 2003
Posts: 43,223 Bend,OR USA
Cab_Burge
I Win
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I Win
Joined: Aug 2003
Posts: 43,223
Bend,OR USA
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Check both ports to make sure there is no residual valve in either port by using a small wood screw into the brass adapter (seat) and pull it out to see if the little flapper valves are in their behind the brass adapter fitting, seat, or not , If they are in their remove them
Last edited by Cab_Burge; 05/04/24 03:53 PM.
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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