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Master cylinder bore size question #2542964
08/29/18 11:53 AM
08/29/18 11:53 AM
Joined: Jan 2003
Posts: 20,356
Eagle, Idaho
Neil Offline OP
The Doctor is in.
Neil  Offline OP
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Eagle, Idaho
In the market for a new master cylinder. Looks like the factory bore size for a disc brake 1970 a-body is 1". Most of the ones I see are larger than that by a small amount. Mancini has one that is 15/16", and that is the smallest I have run across.

Just guessing here so...

Smaller bore = higher and firmer pedal?

Larger bore = a softer pedal and more pedal travel?

No power brakes if that matters....

Re: Master cylinder bore size question [Re: Neil] #2542990
08/29/18 01:05 PM
08/29/18 01:05 PM
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backwards


They say there are no such thing as a stupid question.
They say there is always the exception that proves the rule.
Don't be the exception.
Re: Master cylinder bore size question [Re: Supercuda] #2543288
08/30/18 12:37 AM
08/30/18 12:37 AM
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Eagle, Idaho
Neil Offline OP
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Ok, that's what I wanted to know. Thanks!

I had a near original 71 Dart with the 73 and up disc conversion done to it by the previous owner and that car stopped very well. Trying to get the same results out of the 70 I have now.

Re: Master cylinder bore size question [Re: Neil] #2543294
08/30/18 12:57 AM
08/30/18 12:57 AM
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Granite Bay CA
Kern Dog Offline
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The 70 may have needed that bigger bore since they had a 4 piston caliper as opposed to the single piston design from 1973 and later.

Re: Master cylinder bore size question [Re: Neil] #2543544
08/30/18 06:17 PM
08/30/18 06:17 PM
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Supercuda Offline
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If you have a 70 style front disc setup, it used a 1" bore master

The 73 style discs used a 15/16" bore manual or a 1 1/32" bore power M/C.

If you were putting a 73 style disc setup in the 70, just use the complete 73 setup in front.


They say there are no such thing as a stupid question.
They say there is always the exception that proves the rule.
Don't be the exception.
Re: Master cylinder bore size question [Re: Neil] #2543685
08/31/18 01:56 AM
08/31/18 01:56 AM
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Polson, MT
DoctorDiff Offline
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Actually, the 73 style discs used a 15/16" bore POWER or a 1 1/32" bore MANUAL master cylinder.

This is bass-ackward from what seems logical.

Re: Master cylinder bore size question [Re: DoctorDiff] #2543789
08/31/18 11:40 AM
08/31/18 11:40 AM
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Eagle, Idaho
Neil Offline OP
The Doctor is in.
Neil  Offline OP
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71 car I owned had the full 73 setup on it. That car was parted and I still have the spindles, calipers, control arms, etc. My 70 had drum brakes so I need a disc brake master cylinder to complete the setup.


I have access to an original kelsey hayes SBP setup and was thinking of doing the early mustang rotor swap just to keep the track width narrow.

Re: Master cylinder bore size question [Re: Neil] #2543909
08/31/18 04:23 PM
08/31/18 04:23 PM
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East Coast
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A/MP Offline
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Try the aluminum MC that are in the mini vans. most are specified as 7/8". Rock Auto has them cheap.

Re: Master cylinder bore size question [Re: A/MP] #2544280
09/01/18 02:48 PM
09/01/18 02:48 PM
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north of coder
moparx Offline
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what year minivan ? my wagner master catalog states 99 and earlier as 15/16" [.937] for 99-97 or so , then 24.0mm [.944] down to the early 90's. i haven't looked at my newer master catalog to check specs for new ones.
beer

Re: Master cylinder bore size question [Re: Neil] #2544310
09/01/18 04:10 PM
09/01/18 04:10 PM
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South San Francisco, Ca
70sixpkrt Offline
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I was using a 1 1/32" master cylinder and the pedal was high and very hard. Switched to a 15/16" and now the pedal goes down more and feels a little spongy. I like this better.

Last edited by 70sixpkRT; 09/01/18 04:11 PM.

[img]http://www.imgur.com/hxlGUJt.gif[/img]
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Re: Master cylinder bore size question [Re: DoctorDiff] #2544374
09/01/18 07:34 PM
09/01/18 07:34 PM
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The Netherlands
BigBlockMopar Offline
master
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Spongy brakes are solved by installing residual valves.
I have a modern 15/16" MC on my '73 Dart on which I installed res.valves in both front and rear line (2 lbs valve in front / 10 lbs to rear).
This helped and firmed up brakepedal-feel.
But it also caused the fronts to grab the disc to hard at rest. Difficult to rotate the wheels when jacked up.
It cost me a full mpg in economy too.
Removed the front res.valve helped release thme again and get my lost mpg back.
But the calipers got a bit more spongy again.



Originally Posted By DoctorDiff
Actually, the 73 style discs used a 15/16" bore POWER or a 1 1/32" bore MANUAL master cylinder.

This is bass-ackward from what seems logical.



Probably the brake pedal/MC strut is in a different hole which changed its ratio.

Re: Master cylinder bore size question [Re: Neil] #2544496
09/02/18 03:45 AM
09/02/18 03:45 AM
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Granite Bay CA
Kern Dog Offline
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The power setup on a 73-76 A body uses a bell crank and pivot linkage between the firewall and the booster. The manual is a solid pushrod from the pedal to the manual master cylinder. They use the same brake pedal for manual and power and there is only one hole.

Re: Master cylinder bore size question [Re: Kern Dog] #2546271
09/05/18 04:32 PM
09/05/18 04:32 PM
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Posts: 20,356
Eagle, Idaho
Neil Offline OP
The Doctor is in.
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Found a place that has a couple NOS master cylinders for the small bolt pattern cars. Not cheap.

Also, not sure if buying a close to 50 year old master cylinder would be a great idea. Any rubber parts inside them may be too dried out to be trustworthy????

Re: Master cylinder bore size question [Re: Neil] #2546340
09/05/18 07:17 PM
09/05/18 07:17 PM
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The Netherlands
BigBlockMopar Offline
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Some NOS items and parts are better left in their boxes for nostalgia reasons. Or at least get a rebuild-kit for it right away.

I think I would trust a NOS M/C as much as a PRC-made POS.
Although the China-piece will probably deteriorate at 5 years, while the NOS one took 50 years to become questionable.

Re: Master cylinder bore size question [Re: BigBlockMopar] #2583175
11/26/18 12:48 PM
11/26/18 12:48 PM
Joined: Jan 2003
Posts: 20,356
Eagle, Idaho
Neil Offline OP
The Doctor is in.
Neil  Offline OP
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Ended up picking up a nearly complete small bolt Kelsey Hayes setup off a 71 Demon yesterday. Master cylinder part number says 1-1/32" bore + fits 71-74 A body except manual applications. Could that master cylinder be used in a non-power-brake application? It needs rebuilt for sure.

Re: Master cylinder bore size question [Re: Neil] #2609923
01/21/19 03:53 PM
01/21/19 03:53 PM
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Colorado front range
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BcudaChris Offline
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Does anyone have PN's for a 7/8" or 15/16" bore 2 bolt MC that will fit four our purposes? I ordered a 15/16" listed for a minivan, and the push rod was too large for the socket. Of course, not returnable after opening the bag.

Re: Master cylinder bore size question [Re: BcudaChris] #2610190
01/22/19 12:11 AM
01/22/19 12:11 AM
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Oregon
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AndyF Offline
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Originally Posted By BcudaChris
Does anyone have PN's for a 7/8" or 15/16" bore 2 bolt MC that will fit four our purposes? I ordered a 15/16" listed for a minivan, and the push rod was too large for the socket. Of course, not returnable after opening the bag.


Doctor Diff has them.

Re: Master cylinder bore size question [Re: Neil] #2610197
01/22/19 12:19 AM
01/22/19 12:19 AM
Joined: Feb 2010
Posts: 18,493
Granite Bay CA
Kern Dog Offline
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Originally Posted By Neil
Ended up picking up a nearly complete small bolt Kelsey Hayes setup off a 71 Demon yesterday. Master cylinder part number says 1-1/32" It needs rebuilt for sure.

It needs to be rebuilt?
Who has their M/C rebuilt nowadays except for the restoration guys?

Re: Master cylinder bore size question [Re: Kern Dog] #2610317
01/22/19 10:03 AM
01/22/19 10:03 AM
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Posts: 14,889
up yours
Supercuda Offline
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Originally Posted By Frankenduster
Originally Posted By Neil
Ended up picking up a nearly complete small bolt Kelsey Hayes setup off a 71 Demon yesterday. Master cylinder part number says 1-1/32" It needs rebuilt for sure.

It needs to be rebuilt?
Who has their M/C rebuilt nowadays except for the restoration guys?


Guys who are tired of poorly made foreign junk.


They say there are no such thing as a stupid question.
They say there is always the exception that proves the rule.
Don't be the exception.
Re: Master cylinder bore size question [Re: AndyF] #2610448
01/22/19 03:16 PM
01/22/19 03:16 PM
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Posts: 403
Colorado front range
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BcudaChris Offline
mopar
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Colorado front range
Indeed he does. I got my adapter plate and other specialty items from him over the years, and my car will be wearing his Viper setup when I get to big brakes.

Unfortunately, my budget balks over the premium he is compelled to charge for such things.

I totally get the economics of the business model, and swing as much of my cash as I can to the good Doctor, you Andy and other vendors that keep the Mopar community getting faster (and properly slowed wink with their passion, dedication and engineering skills, and by bringing products to market so us weekend wrenches spend more time wrenching and driving, and less time playing engineer, fabricating and sorting things out.

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