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adjusting the power brake booster push rod #1833386
05/24/15 07:23 PM
05/24/15 07:23 PM
Joined: Aug 2003
Posts: 8,774
Houston, Tx
hemi68charger Offline OP
master
hemi68charger  Offline OP
master

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Posts: 8,774
Houston, Tx
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


Troy
Houston 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)
Re: adjusting the power brake booster push rod [Re: hemi68charger] #1833423
05/24/15 08:18 PM
05/24/15 08:18 PM
Joined: Feb 2003
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Andrewh Offline
master
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I didn't know factory ones were adjustible. but here is how I did it.

basically there is a hole in the master if you look down.
even with fluid in it you should be able to see in to that hole with a good light.

if you pull the master away from the booster, and adjust the rod out till you see the piston in the master move as you push the master back onto the booster.

then turn the adjuster in a little at a time till the piston in the master doesn't move as you put the master back onto the booster.

with fluid in the master, you might even see fluid movement first so be careful how forcefully you put the master back on.

Re: adjusting the power brake booster push rod [Re: hemi68charger] #1833620
05/25/15 01:12 AM
05/25/15 01:12 AM
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Mass
DAYCLONA Offline
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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

vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv.JPG
Re: adjusting the power brake booster push rod [Re: DAYCLONA] #1833645
05/25/15 01:45 AM
05/25/15 01:45 AM
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Granite Bay
Frankenduster Offline
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I have dealt with this in my 70 Charger. I have a 1975 Dart booster and master cylinder on it, 4 wheel disc. The A body boosters have an adjustable pushrod tip on the rod that presses the master cylinder. I have tried to adjust it to get as little freeplay at the pedal as possible, but it always ends up smoking the brakes. I've had to settle with a small bit of dead travel before the brakes engage. It sucks.

Re: adjusting the power brake booster push rod [Re: hemi68charger] #1833688
05/25/15 05:39 AM
05/25/15 05:39 AM
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Oregon
hooziewhatsit Offline
master
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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. shruggy

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.
Re: adjusting the power brake booster push rod [Re: DAYCLONA] #1833902
05/25/15 02:46 PM
05/25/15 02:46 PM
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Omaha Ne
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TJP Offline
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Omaha Ne
Quote:
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


iagree

Re: adjusting the power brake booster push rod [Re: hooziewhatsit] #1833905
05/25/15 02:49 PM
05/25/15 02:49 PM
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Omaha Ne
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TJP Offline
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Originally Posted By hooziewhatsit
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. shruggy

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.

Re: adjusting the power brake booster push rod [Re: hemi68charger] #1833994
05/25/15 04:48 PM
05/25/15 04:48 PM
Joined: Aug 2003
Posts: 8,774
Houston, Tx
hemi68charger Offline OP
master
hemi68charger  Offline OP
master

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Houston, Tx
thanks everyone.. I will attempt to tackle this shortly....


Troy
Houston 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)
Re: adjusting the power brake booster push rod [Re: hemi68charger] #1834052
05/25/15 06:50 PM
05/25/15 06:50 PM
Joined: Aug 2003
Posts: 8,774
Houston, Tx
hemi68charger Offline OP
master
hemi68charger  Offline OP
master

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Houston, Tx
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....

IMG_20150525_154034_041.jpg

Troy
Houston 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)
Re: adjusting the power brake booster push rod [Re: hemi68charger] #1834207
05/25/15 10:39 PM
05/25/15 10:39 PM
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Omaha Ne
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TJP Offline
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HMM one of these are handy, we made ours. Hope this helps up



http://www.classicperform.com/TechBook/pushrod_adjust_tool1.gif

Last edited by TJP; 05/25/15 10:40 PM.
Re: adjusting the power brake booster push rod [Re: hemi68charger] #1835749
05/28/15 01:43 AM
05/28/15 01:43 AM
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Freeport IL USA
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poorboy Offline
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Back when I did it, I would turn the in (shorten the rod length) for more pedal travel or out (lengthen the rod) for less pedal travel. I would do 1/4 turn at a time in the direction it needed to go, and test it. It may require puling the master off a few times, but it always worked very well. Gene

Re: adjusting the power brake booster push rod [Re: TJP] #1836307
05/28/15 11:27 PM
05/28/15 11:27 PM
Joined: Jun 2004
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Chicago Burbs
sthemi Offline
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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. purple

Re: adjusting the power brake booster push rod [Re: hemi68charger] #2539579
08/21/18 02:14 PM
08/21/18 02:14 PM
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MI
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EV271 Offline
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EV271  Offline
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MI
This thread has such great information, I had to resurrect it. Plus I am also having brake issues with my recently restored 71 Cuda(disc/drum). When car is cold front wheels spin with light drag, after a trip around the block BOTH front wheels are impossible to spin(locked up).
Do you think this is a booster arm adjustment?
Too much fluid?
Heat?
Help!
Thanks!

Re: adjusting the power brake booster push rod [Re: EV271] #2539582
08/21/18 02:18 PM
08/21/18 02:18 PM
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Posts: 22,087
Rio Linda, CA
John_Kunkel Offline
Much ado about nothing
John_Kunkel  Offline
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Rio Linda, CA
Yes, pushrod adjustment. If in doubt, loosen the MC nuts a few turns and see if the lockup stops.


I'm supposed to respect my elders, but its getting harder and harder for me to find one now.
Re: adjusting the power brake booster push rod [Re: hemi68charger] #2539602
08/21/18 02:43 PM
08/21/18 02:43 PM
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MI
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EV271 Offline
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MI
Thank you JK, I'll give that a try.

Re: adjusting the power brake booster push rod [Re: hemi68charger] #2539698
08/21/18 06:04 PM
08/21/18 06:04 PM
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3
340clone Offline
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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 10:41 PM.
Re: adjusting the power brake booster push rod [Re: hemi68charger] #2539707
08/21/18 06:18 PM
08/21/18 06:18 PM
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MI
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EV271 Offline
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MI
Wow thanks! I'll pick one up. What is clearance supposed to be? .30-.60?

Re: adjusting the power brake booster push rod [Re: EV271] #2539759
08/21/18 08:09 PM
08/21/18 08:09 PM
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Posts: 22,087
Rio Linda, CA
John_Kunkel Offline
Much ado about nothing
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Posts: 22,087
Rio Linda, CA
The ideal clearance is .020".


I'm supposed to respect my elders, but its getting harder and harder for me to find one now.
Re: adjusting the power brake booster push rod [Re: hemi68charger] #2539766
08/21/18 08:41 PM
08/21/18 08:41 PM
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Andrewh Offline
master
Andrewh  Offline
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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 08:43 PM.
Re: adjusting the power brake booster push rod [Re: hemi68charger] #2539837
08/22/18 12:19 AM
08/22/18 12:19 AM
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mopars4ever Offline
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I have replaced many master cylinders and I never had to touch the adjustment. Have I just been lucky?

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