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Old 01-08-2019, 04:54 AM   #1
chevyman
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Default new IHPA master cylinder questions

So, I installed a new m.c. from IH parts, post bench bleeding, bled brakes, re-checked pedal height and push rod length, adjusted shoes and it normally stops great. Except twice now the push rod has slid through the push nut inside the M.C. bore and gets stuck with the pedal half way down. My push rod looks exactly like the one pictured on the main store site but not sure if perhaps the push nut (retaining clip?) was installed backwards from factory?
does anyone have a picture of what there master cyilinder looks like going down the bore without the pushrod installed? When this happens, the rod gets stuck inside the inner bore of the first piston and is a pain to remove. its acting almost as if the od on the ground down end of the pushrod is too small and is slipping inside the bore.
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Old 01-08-2019, 07:19 AM   #2
chevyman
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Default Re: new IHPA master cylinder questions

Found a 7/16 fine thread bolt and turned it down on the lathe, I'm going to try this but I think the problem may be in the master cylinder. Anyone have a picture of what the scout 800B master from IH parts america looks like as viewed down the bore?
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Old 01-08-2019, 04:12 PM   #3
Robert Kenney
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Default Re: new IHPA master cylinder questions

What master # and for what? Photo of the push nut you are referring to would be super helpful.
The actuator rod would seat hard against the piston and usually in a hemispherical seat.
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Old 01-08-2019, 05:47 PM   #4
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Default Re: new IHPA master cylinder questions

The master cylinder is # S800-BRK-MC-ASSY for a 71 800B

The part I'm referring to is either a push nut or internal tooth locking washer.

On most other master cylinders I've installed the rod seats into a tapered cone that is machined into the rear most piston/plunger. On this model it seems to use one of these washers to make up for the difference in push rod cone outer diameter vs piston hemispherical seat.
In the first attached picture (not mine) you'll notice the inner black washer with 4 tangs. The one on my m.c. has 8, more similar to the second attached picture.

The supplied pushrod pushed through those tangs and got stuck.
I believe I have remedied the problem by modifying my newest pushrod to have a larger conical seat preventing it from pushing through the washer. Very phallic looking

I welded some padding around the end of that bolt and turned it down to about .535" with a matching 45 degree taper. The factory one was .440 ish. I'll get a picture of that up tomorrow if it can help anyone in the future.
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File Type: jpg push nut.jpg (25.0 KB, 15 views)
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Old 01-09-2019, 08:51 AM   #5
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Default Re: new IHPA master cylinder questions

The pushrod needs to push thru and be up against the back of the piston of the master cylinder. The toothed washer is there to hold that push rod in there. You should not have to be modifying any of these parts, unless of course a mistake was made and a wrong part was shipped. From what I can see you need to put everything back together the way you originally had it and thread out the adjuster so the brake pedal height matches the clutch pedal height.

Hope that all makes sense, if not let us know so we can better explain or post pictures.
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Old 01-09-2019, 12:07 PM   #6
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Default Re: new IHPA master cylinder questions

Thanks for the reply. Its not in front of me now and I'll try to get some pics of it. I absolutely understand what your saying, but, what has me confuzzled is depth of the hole after the washer. When it pushes through that washer, the back of that hole is about 2" past and when its seated there the arc of the pedal swing binds hard as you can see by the slight bend in the factory push rod. I'll get at it this weekend, take pics, figure it out and post back. Thanks again for all your help.
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Old 01-09-2019, 08:50 PM   #7
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Default Re: new IHPA master cylinder questions

You have manual brakes and that master may be for a power booster. The geometry binding you are having can’t be avoided. Is there a non power master available?
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Old 01-13-2019, 05:37 PM   #8
chevyman
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Default Re: new IHPA master cylinder questions

So, spent some time this afternoon with the old scout and pedal pushrods and master cylinder. The first picture is the master that came in the box from ihpa as installed on this scout.
Gave the included pushrod another try. After it pushes through the washer, it binds the pedal in the brake applied position. There just isnt enough spring to return the pedal. Its as if it gets past center of the swing and binds. It does not matter where the rod is adjusted from tight to turnbuckle to ALL the way out.

I gave my home made push rod end a try. It sits tight against the cup in the washer and does not push through it. It is the second and fourth pictures. I adjusted it so the pedal sits near the height of the clutch pedal and the pushrod cant back out because the pedal hits the brake light switch solid.

It currently stops good and the brake light switch works.

Thanks for all the replies.
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File Type: jpg 20190113_145413 (1).jpg (65.8 KB, 13 views)
File Type: jpg 20190113_151234.jpg (65.0 KB, 13 views)
File Type: jpg 20190113_150308 (1).jpg (49.4 KB, 13 views)
File Type: jpg 20190113_151237.jpg (60.7 KB, 12 views)

Last edited by chevyman; 01-13-2019 at 05:47 PM..
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