| Master Cylinder Pushrod [message #219767] |
Sat, 24 August 2013 14:37  |
Who_dun_it
Messages: 176
Registered: April 2007
Location: Thousand Oaks, CA
Karma: 1
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Senior Member |
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Hi - the folks that have added rear discs, 80MM front calipers,sensitized booster and P-30 master cyclinder, what did you end up with for a length for the new pushrod between the booster and master cylinder?
Les
T.O. CA
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| Re: [GMCnet] Master Cylinder Pushrod [message #219785 is a reply to message #219767] |
Sat, 24 August 2013 17:27  |
emerystora
Messages: 4442
Registered: January 2004
Karma: 13
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Senior Member |
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Les
The length of the pushrod depends whether you put the brace for the master cylinder between the booster and the master cylinder or whether you have a brace that will mount on the outside of the master cylinder.
In my case my bracket (brace) is between the booster and the master cylinder.My push rod has to be longer than the Harrison rod because he has a brace made for the front of the master cylinder.
Here is something that I posted about 5 or 6 years ago:
-------------------------------------------------------------------------------------------------
On Oct. 22 I had posted the below message and indicated that I would report my final push rod length later.
I made the push rod to 2.63" and checked to make sure that I still had some clearance. I have just returned from a 3000 mile round trip and found that my braking was much better and that I had more peal (clearance to the floor when pressed all the way) and I had no problem with the rod being of excessive length. 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.
So, the use of the Carquest master cylinder 20-2234 (which corresponds to a Delco 174-834 and a GM 14009146) is working very well for me while using the original brace placed between the master cylinder and the master cylinder. It give plenty of clearance between the end of the master cylinder and the front door. It also has the metal reservoir instead of plastic ones that I have also seen.
Gene Fisher, you might want to add that length of push rod to your listing of them on your site.
Emery Stora
<<<<<<<<I have now received information from Peter Walker that the Harrison rod is 2.475" in length.
I have an old email in my files from Denny Allen that the original is 2.469" in length.
I had once been told that the Harrison rod was about .01" longer than the stock rod.
If the above numbers are correct then the rod is .006" longer. (very close to the .01")
The GM 14009146 master cylinder corresponds to an AC/Delco 174-834.
This also crosses to Wagner F103239, Bendix 11641, EIS E150063 and a CarQuest 20-2234. I don't have the NAPA cross.
This is a 34 mm piston bore (approx. 1-21/64").
This fits a 1977-96 P35/P3500 Van (with 4 wheel disk brakes) and a P-30 Van. It also fits a 1991 C3500 Pickup.
It will give sufficient volume for the use of 80mm front calipers added to the front wheels of the GMC and for 4 calipers added to the rear wheels.
It will fit behind the front cover (below the windshield) without any modifications to the cover or the necessity to shim the hinges.
This master cylinder has a 1/2x20 threaded port for the front chamber and a 9/16x18 threaded port for the back chamber.
NOTE: the original GMC master cylinder had the 1/2 in the back and the 9/16 in the front. So it is necessary to move the 9/16" (rear brake line) to the rear chamber and the 1/2" (front brake line) to the front chamber. This is not a problem as this master cylinder has two chambers that are of equal size - unlike the original one that has a smaller front chamber that went to the rear brakes.
On Gene Fisher's site there is a write up from me that details my use of a P-30 master cylinder with a 1-5/16" bore. I have now replaced it with this 34mm master cylinder.
I have found that my original master cylinder brace fits just fine BEHIND the master cylinder (between the booster and the master cylinder) so it was not al all necessary for me to fabricate a new brace. To release the rear clip on the cover of the master cylinder just push it with a screwdriver and it will move off the cover to the rear. It can be tightened back on by using a screwdriver to one side to pull it back on.
Peter Walker has told me that when he got a new style booster from Jim Bounds he found it necessary to modify the Harrison brace to mount it to the front of the master cylinder so he went back to the original GMC stock push rod. My calculations show that the result was an effective length of 2.594" rather than the 2.475 of the Harrison rod.
If that works without causing the master compensating port to be blocked off (which can cause brake drag) then it should actually give more pedal stroke.
I will experiment with the rod length and report my findings soon. I may end up with the 2.475" or longer.
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.>>>>>>>>>>>>
Emery Stora
On Aug 24, 2013, at 1:37 PM, Les Leach wrote:
>
>
> Hi - the folks that have added rear discs, 80MM front calipers,sensitized booster and P-30 master cyclinder, what did you end up with for a length for the new pushrod between the booster and master cylinder?
>
> Les
> T.O. CA
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| Re: [GMCnet] Master Cylinder Pushrod [message #219869 is a reply to message #219785] |
Sun, 25 August 2013 11:14 |
Who_dun_it
Messages: 176
Registered: April 2007
Location: Thousand Oaks, CA
Karma: 1
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Senior Member |
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My bracket is between the booster and master cylinder. I made an 'adjustable' pushrod to be able to check for length. The front of the pushrod slips into a tube. I checked twice and came up with about 69MM. I will have the assistant push on the pedal and check for bubbles.
Thank you for the input.
Les
T.O. CA
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.>>>>>>>>>>>>
Emery Stora
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| Re: [GMCnet] Master Cylinder Pushrod [message #219878 is a reply to message #219869] |
Sun, 25 August 2013 12:42 |
emerystora
Messages: 4442
Registered: January 2004
Karma: 13
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Senior Member |
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Your 69mm (2.72") is close to the 2.63 inches that I and others have used. It is only 2.2mm more. However, make sure that you have enough clearance. If the piston doesn't return all the way you can get some residual pressure on the master cylinder and the brakes. I recommend 0.015 inches (3.8mm) clearance between the end of the push rod and the piston.
Emery Stora
On Aug 25, 2013, at 10:14 AM, Les Leach wrote:
>
>
> My bracket is between the booster and master cylinder. I made an 'adjustable' pushrod to be able to check for length. The front of the pushrod slips into a tube. I checked twice and came up with about 69MM. I will have the assistant push on the pedal and check for bubbles.
>
> Thank you for the input.
>
> Les
> T.O. CA
>
> 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.>>>>>>>>>>>>
>
>
> Emery Stora
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
_______________________________________________
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Unsubscribe or Change List Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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| Re: Master Cylinder Pushrod [message #220141 is a reply to message #219767] |
Tue, 27 August 2013 19:54 |
kerry pinkerton
Messages: 2565
Registered: July 2012
Location: Harvest, Al
Karma: 15
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Senior Member |
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When Ken Henderson and I installed the Manny Brakes on my coach. I went with a P30 MC and we used Ken's handy tool to determine the length. I'm not sure that there is a SINGLE number that will be the same for everyone.
Kerry Pinkerton - North Alabama
Had 5 over the years. Currently have a '06 Fleetwood Discovery 39L
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