adjusting the power brake booster push rod
#1833386
05/24/15 06:23 PM
05/24/15 06:23 PM
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Joined: Aug 2003
Posts: 8,828 Houston, Tx
hemi68charger
OP
master
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OP
master
Joined: Aug 2003
Posts: 8,828
Houston, Tx
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Hello All, I looked in my 71 Dodge FSM and couldn't find anything about adjusting the push-rod that activates the master cylinder. The brake system is a power front disc brake car. I'm looking to try and fix a situation where the brakes seem to be hanging a wee bit ( like if you were in a driveway and the car doesn't roll down the driveway as it should )..
Cheers, Troy
TroyHouston Mopar Connection Club'69 Charger Daytona 440 - auto - 4.10 Dana (now with 426 hemi) '69 Charger 500 440 - 4speed - 3.54 Dana '70 Road Runner 383 - 4speed - a/c (now with 440)
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Re: adjusting the power brake booster push rod
[Re: hemi68charger]
#1833620
05/25/15 12:12 AM
05/25/15 12:12 AM
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Joined: Dec 2007
Posts: 18,167 Mass
DAYCLONA
I Live Here
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I Live Here
Joined: Dec 2007
Posts: 18,167
Mass
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You'll need to unbolt the master from the booster, leave the cap and lines alone, pull it forward enough so that you can measure the tip of the pushrod to the mounting location of the master on the booster's surface/face, I'd recommend a set of Verniers/dial Calipers...then measure from the bottom of the inside piston bore of the master to it's mounting base/face/flange that would bolt on to the booster's surface, the do the math based on the values you have, either lengthen/shorten as needed, .030 minimum to .060 max for Mopar applications
be sure to grip the knurled/splined portion of the pushrod with pliers/vise grips, and turn the hex headed pushrod tip in/out for the desired length
Mike
FYI if your not familiar with using Calipers to measure the bore of the master, you use the section/bar that slides out of the "rear" of the Calipers and the "rear" portion of the main caliper frame to establish your measurement ( the DEPTH ROD as described in the pic below
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Re: adjusting the power brake booster push rod
[Re: hemi68charger]
#1833688
05/25/15 04:39 AM
05/25/15 04:39 AM
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Joined: Oct 2007
Posts: 3,953 Oregon
hooziewhatsit
master
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master
Joined: Oct 2007
Posts: 3,953
Oregon
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I measured to get close... then I ended up pulling the pushrod out of the booster, gently setting the MC in place (keeping it square), then seeing how much farther in I could move the pushrod. Currently have it adjusted to zero, with no apparent brake dragging. Apparently you're also supposed to be able to look in the master and see a poof of fluid when you press the brake pedal an inch or so if it's adjusted correctly (with everything bolted together).
If you ever find yourself in a fair fight, your tactics suck.
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Re: adjusting the power brake booster push rod
[Re: hooziewhatsit]
#1833905
05/25/15 01:49 PM
05/25/15 01:49 PM
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Joined: Jan 2003
Posts: 16,118 Omaha Ne
TJP
I Live Here
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I Live Here
Joined: Jan 2003
Posts: 16,118
Omaha Ne
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I measured to get close... then I ended up pulling the pushrod out of the booster, gently setting the MC in place (keeping it square), then seeing how much farther in I could move the pushrod. Currently have it adjusted to zero, with no apparent brake dragging. Apparently you're also supposed to be able to look in the master and see a poof of fluid when you press the brake pedal an inch or so if it's adjusted correctly (with everything bolted together). As previously mentioned You need to have .030 clearance between the pushrod and piston when the pedal is released.
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Re: adjusting the power brake booster push rod
[Re: hemi68charger]
#1833994
05/25/15 03:48 PM
05/25/15 03:48 PM
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Joined: Aug 2003
Posts: 8,828 Houston, Tx
hemi68charger
OP
master
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OP
master
Joined: Aug 2003
Posts: 8,828
Houston, Tx
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thanks everyone.. I will attempt to tackle this shortly....
TroyHouston Mopar Connection Club'69 Charger Daytona 440 - auto - 4.10 Dana (now with 426 hemi) '69 Charger 500 440 - 4speed - 3.54 Dana '70 Road Runner 383 - 4speed - a/c (now with 440)
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Re: adjusting the power brake booster push rod
[Re: hemi68charger]
#1834052
05/25/15 05:50 PM
05/25/15 05:50 PM
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Joined: Aug 2003
Posts: 8,828 Houston, Tx
hemi68charger
OP
master
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OP
master
Joined: Aug 2003
Posts: 8,828
Houston, Tx
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Initially, this is what I see. I am going to try and figure out how to measure the distance from the mating face of the MC to the inside part of the piston cup. But, as one can see, it is adjustable....
TroyHouston Mopar Connection Club'69 Charger Daytona 440 - auto - 4.10 Dana (now with 426 hemi) '69 Charger 500 440 - 4speed - 3.54 Dana '70 Road Runner 383 - 4speed - a/c (now with 440)
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Re: adjusting the power brake booster push rod
[Re: TJP]
#1836307
05/28/15 10:27 PM
05/28/15 10:27 PM
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Joined: Jun 2004
Posts: 3,319 Chicago Burbs
sthemi
master
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master
Joined: Jun 2004
Posts: 3,319
Chicago Burbs
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First determine if the brakes are a wee bit tight without the engine running/ vacuum to the booster... If they are still tight the booster push rod is not the problem. Still tight with the engine running, pull the master off just slightly and turn the rod in a bit 1/4 to 1/2 turn and repeat, until the problem is fixed. There is normally enough room that you do not need to remove the brake lines and re-bleed.
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Re: adjusting the power brake booster push rod
[Re: EV271]
#2539582
08/21/18 01:18 PM
08/21/18 01:18 PM
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Joined: Jan 2003
Posts: 27,096 Rio Linda, CA
John_Kunkel
Too Many Posts
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Too Many Posts
Joined: Jan 2003
Posts: 27,096
Rio Linda, CA
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Yes, pushrod adjustment. If in doubt, loosen the MC nuts a few turns and see if the lockup stops.
The INTERNET, the MISinformation superhighway
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Re: adjusting the power brake booster push rod
[Re: hemi68charger]
#2539698
08/21/18 05:04 PM
08/21/18 05:04 PM
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Joined: Nov 2004
Posts: 507
340clone
mopar
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mopar
Joined: Nov 2004
Posts: 507
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I have done this twice, and both times I used a contour gauge. They are available at Home Depot and are inexpensive.
Set the gauge in the M/C plunger, then adjust the push rod according to the opposite side of the gauge. At that point, any spacing becomes easy. You can see exactly what you're doing because your measurements are right in the gauge.
Last edited by 340clone; 08/21/18 09:41 PM.
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Re: adjusting the power brake booster push rod
[Re: EV271]
#2539759
08/21/18 07:09 PM
08/21/18 07:09 PM
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Joined: Jan 2003
Posts: 27,096 Rio Linda, CA
John_Kunkel
Too Many Posts
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Too Many Posts
Joined: Jan 2003
Posts: 27,096
Rio Linda, CA
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The ideal clearance is .020".
The INTERNET, the MISinformation superhighway
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Re: adjusting the power brake booster push rod
[Re: hemi68charger]
#2539766
08/21/18 07:41 PM
08/21/18 07:41 PM
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Joined: Feb 2003
Posts: 8,788
Andrewh
master
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master
Joined: Feb 2003
Posts: 8,788
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if your fluid is clear you can see into the hole in the bottom of the master. I can actually watch if the piston moves when I push the master onto the booster. I just adjust based off of that movement rather than any measuring device. I back it off till it doesn't move any more, then a hair more.
however if you didn't replace anything recently and this just started to happen, I might spend time checking other things. like the check valve inside the booster? I had one go bad and suck the brake pedal down.
Last edited by Andrewh; 08/21/18 07:43 PM.
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Re: adjusting the power brake booster push rod
[Re: hemi68charger]
#2539837
08/21/18 11:19 PM
08/21/18 11:19 PM
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Joined: Jan 2003
Posts: 13,758 md
mopars4ever
I Live Here
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I Live Here
Joined: Jan 2003
Posts: 13,758
md
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I have replaced many master cylinders and I never had to touch the adjustment. Have I just been lucky?
Time just gets away from us I`m here until I`m not
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