72 MC bore size and correct pushrod

[9teen69]

So after much searching I went with a 1 1/8 bore size and an Oreilys part # NMC1423. But this one has a deep bore depth.

Does anyone know what MC part number would have the shallow bore depth?

Trying to fix my brake issue with this $35 fix isn't as easy I though. Though mine was 1 1/4 but measured wrong.
http://67-72chevytrucks.com/vboard/s...d.php?t=682026

Read I can use an adapter but Oreilys didn't know what I was talking about.

thanks

[mike16]

I am not sure of the diameter of the bore. I recall 1 inch. the way to be sure is to pull a rebuild kit off the shelf at a local parts store and see what comes in the box. Maybe the parts catologe will show some specs.

as for the short vs long.... the long push rods and the deeper holes in the back of the master cylinder piston are typical of manual powered brake master cylinders while the short push rods and shallow hole in the back of the master cylinder piston are for boosted or power brakes. the difference between short and long are considerable so you wont make a mistake there. that having been said I have made that very mistake.

this distance and length too can be confirmed when you pull a master cylinder rebuild kit of the shelf for each application and look at it. Some rebuild kits dont include the replacement piston though.

I hope I got that right.

[9teen69]

Thanks for the suggestion, I'll get by there this weekend and grab a rebuild kit and see what's in there.

I ended up slapping it back together and driving it as it. I didn't even bleed after putting the old MC back on. Actually tightened up the pedal and feels better.

I just give myself plenty of room to stop.

thanks

[MikeB]

1-1/8" bore is correct for power brakes on a 72 pickup.

AC Delco #18M1036 is the correct M/C. It's $44.79 with no core charge at RockAuto.com. Or you can probably cross the P/N at a local parts store.

If your truck's lines and tube nuts are not stock, you may need to adapt them to the M/C. Adapters are readily available, even at some parts stores. Let me know if I can help.

[9teen69]

Most excellent....Thanks Mike!

One day I'll get back to Plano...where I was born!

[9teen69]

Took a closer look at the images and looks like the pocket on AC Delco #18M1036 is too deep also.
http://www.rockauto.com/catalog/more...&jnid=4&jpid=0

After finding this thread http://67-72chevytrucks.com/vboard/s...d.php?t=668503

Looks like the 78 Corvette and other years. ACDELCO 18M91 is what I need, has a small pocket.
http://www.rockauto.com/catalog/more...id=1123&jpid=5

[MikeB]

Originally Posted by 9teen69

Took a closer look at the images and looks like the pocket on AC Delco #18M1036 is too deep also.
http://www.rockauto.com/catalog/more...&jnid=4&jpid=0

That is strange. Your picture shows an M/C (the 18M91) with a shallow hole for power brakes, as it should be. Guess it must be designed for use with a factory booster, which is apparently different than a generic aftermarket booster. Maybe I misunderstand what you're calling a "pocket".

Here is a picture of the two types of M/Cs -- one with a deep hole for a manual brake pushrod.

[9teen69]

Yep that's what I need the one with the shallow hole.

[Keith Seymore]

Originally Posted by MikeB

That is strange. Your picture shows an M/C (the 18M91) with a shallow hole for power brakes, as it should be. Guess it must be designed for use with a factory booster, which is apparently different than a generic aftermarket booster. Maybe I misunderstand what you're calling a "pocket".

Here is a picture of the two types of M/Cs -- one with a deep hole for a manual brake pushrod.

I just went through this converting from the old single pot to a dual master cylinder on my '63 Grand Prix (needed the deep hole).

It is funny that I used to be a brake development engineer for GM but these things always turn into a science fair project for me, too.

K

[Keith Seymore]

Originally Posted by 9teen69

Yep that's what I need the one with the shallow hole.

Are you disc/drum or drum/drum?

K

[9teen69]

Disk/disk. My truck didn't originally come with power brakes. PO installed aftermarket booster/MC combo.