| Re: [GMCnet] Master Cylinder Pushrod Clearance [message #78056 is a reply to message #78052] |
Thu, 25 March 2010 21:38   |
emerystora
Messages: 4442
Registered: January 2004
Karma:
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Senior Member |
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On Mar 25, 2010, at 9:04 PM, Gary Bovee wrote:
> Everybody has done a great job straightening me out on the question
> of what
> should be the master cylinder pushrod length. It seems that there
> are too
> many variables for one size fits all (length of master cylinder
> pushrod) to
> have a specific length listed for any application. We need to make
> sure we
> have the proper length and the clay testing method works easy enough
> for me
> to check that clearance. My next question then is there consensus
> on what
> is the ideal clearance between the pushrod and master cylinder?
>
> Thanks again for everyones input.
>
> Gary Bovee
> Red Bluff, CA
> 78 Royale
>
>
Here is something that I had posted a long time back.
> Just for information:
>
> Correct pushrod length is essential to reliable braking. If the
> push rod is too long it causes the master cylinder compensating
> ports to be blocked off, eventually resulting in brake drag. If the
> rod is too short, it will give excessive pedal travel and not use
> the full stroke of the master cylinder which limits the volume of
> fluid going to the wheels.
>
> Here is how you can check it:
>
> 1. Remove the master cylinder cap.
> 2. Have an assistant depress the brake pedal (SLOWLY AND
> SLIGHTLY). Watch for fluid movement in the master cylinder when the
> pedal is depressed 3/8" to 1/2". This will indicate correct push
> rod length. On dual piston master cylinders, fluid movement may
> occur in the front reservoir only.
> 3. If the pedal travels more than 1/2" before fluid movement is
> noticed, the push rod is too short. If nothing happens no matter
> how far the pedal is depressed, the rod is too long.
> 4. To adjust the rod length, turn the adjustment (if you are using
> an adjustable rod), or replace the rod if its to short,. It its too
> long, either use shims between the booster and the master cylinder
> or grind the rod to make it shorter.
> 5. Install the master cylinder and recheck the rod
> length.>>>>>>>>>>>>
I had posted this back about 2007:
>> I actually made a wooden rod and checked the length with some
>> modeling clay on the master cylinder end. I adjusted the rod
>> length when I had about .015 clearance and then made a steel rod to
>> that length.
When I did this I ground the master cylinder end of the rod to a
"ball" radius. The end of the rod against the booster was left flat
and that is the end that I ground to adjust the length.
So, my findings were that about .015" is enough clearance.
You want to have as long as possible to have more pedal but you have
to have some clearance to allow the ports in the master cylinder to be
covered by the pistons.
1/16" is .0625". My findings indicate that would be too much
clearance. I subsequently did a bit of research on the Internet and
found other data to substantiate the .015" clearance.
Emery Stora
77 Kingsley
Santa Fe, NM
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