Master Cylinder Slotting Holes

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   That's a disc booster all right. Have 2 here that look just like. Dual diaphragm. Drum brake single diaphragm booster is much thinner.

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Heavy 488 Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Addicted Joined: Apr/27/2019 Location: In the Status: Offline Points: 3557	Post Options Post Reply Quote Heavy 488 Report Post Thanks(0) Quote Reply Posted: Jan/18/2021 at 7:32pm
	That's a disc booster all right. Have 2 here that look just like. Dual diaphragm. Drum brake single diaphragm booster is much thinner.

ramblinrev Members Profile Send Private Message Find Members Posts Add to Buddy List Moderator Group Joined: Dec/28/2008 Location: Wisconsin Status: Offline Points: 11543	Post Options Post Reply Quote ramblinrev Report Post Thanks(0) Quote Reply Posted: Jan/18/2021 at 8:52pm
	What you have is either a Matador/Ambo disc booster and AMX/Javelin master or vice versa. The Matador/Ambo booster appears identical to the AMX/Javelin one, but the bolt spacing is a bit wider, because the larger cars used a master with a larger piston (1 1/8? I'd have to look.) I can't imagine that the booster itself is calibrated much differently. But it was AMC's way of making sure that someone wouldn't put a smaller replacement master cylinder onto a power disc brake Matador or Ambo. I think you can widen your slots on your master and you'll be set. If you measure your studs (that the master bolts to) center to center on your booster, I can tell you for sure what you have.
	74 Hornet Hatchback X twins (since 1977) 62 American Convertible (still worth the $50 I spent in 1973!) AMCRC #513, AMO #384 70 AMX 360 4-speed (since 1981)

Calcommon Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Apprentice Joined: Sep/21/2019 Location: Salinas, CA Status: Offline Points: 74	Post Options Post Reply Quote Calcommon Report Post Thanks(0) Quote Reply Posted: Jan/18/2021 at 9:22pm
	Thanks ramblinrev, center to center on the booster bolts = 3.25" using a tape measure and a mark one eyeball, I might be off a couple hundredths. The master cylinders I have are closer to 3.4"

ramblinrev Members Profile Send Private Message Find Members Posts Add to Buddy List Moderator Group Joined: Dec/28/2008 Location: Wisconsin Status: Offline Points: 11543	Post Options Post Reply Quote ramblinrev Report Post Thanks(0) Quote Reply Posted: Jan/18/2021 at 9:40pm
	The AMX/Javelin disc brake booster and master have about a 3 1/8" stud spacing. The Ambo/Matador ones with the larger bore master cylinder have about a 3 3/8" stud spacing. If the booster is from an AMX or Javelin, I wonder if you have the wrong master? (Or if suppliers are using the larger casting?) I still think you're ok with widening the slots.
	74 Hornet Hatchback X twins (since 1977) 62 American Convertible (still worth the $50 I spent in 1973!) AMCRC #513, AMO #384 70 AMX 360 4-speed (since 1981)

tomj Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Addicted Joined: Jan/27/2010 Location: earth Status: Offline Points: 7553	Post Options Post Reply Quote tomj Report Post Thanks(0) Quote Reply Posted: Jan/18/2021 at 11:44pm
	I too see no issue widening the holes. I think OP said they checked pushrod length, that's critical. Having gone through a lot of OEM type master cyls looking for various fitments in weird (foolish) circumstances, it's surprising how small the variations are between very many of them. You'd think OEMs would have used a narrower range of a part with multiple close-tolerance machined surfaces (master cyl) and change things that vary with model and installation, so easily (brake lines, pushrod). The majority of AMC master cyls, and most of the Other Brands too, are 1" bore. They all have a similar stroke, fluid capacity, two-bolt flange, pushrod style, outlets one one side or the other, fore/aft ports, ... all slightly, annoyingly different.
	1960 Rambler Super two-door wagon, OHV auto 1961 Roadster American, 195.6 OHV, T5 http://www.ramblerLore.com

hffej Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Apprentice Joined: Sep/19/2007 Location: Massachusetts Status: Offline Points: 147	Post Options Post Reply Quote hffej Report Post Thanks(0) Quote Reply Posted: Feb/11/2021 at 3:29pm
	Went through this last year on my 69 Javelin. The new booster I installed had the slightly wider spacing which I found out was a booster for a Matador/Ambo. I slotted the master and set the pushrod length. Everything now works fine. Feels the same as my AMX. What ever the difference is with the booster, I can’t discern a difference with the brake performance.
	69 BBB AMX 69 BBO Javelin