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Manual Master Cylinder bore size - Disc/Drum

Posted By: Mopar72Man

Manual Master Cylinder bore size - Disc/Drum - 10/19/14 03:48 PM

I am currently running a 1.125" bore 2-bolt master cylinder with front 11-3/4" brakes and rear 10" drums. I pretty much hate it, I've had it on there for quite a while and am not too happy with the effort required. I'd like to go down to a 1.032" master and an aftermarket proportioning valve.

I would like to run rear discs in the near future and want to make sure I won't regret making the swap.

What master are you running and is it with disc/disc or disc/drum?

Thanks!
Posted By: goldduster318

Re: Manual Master Cylinder bore size - Disc/Drum - 10/19/14 04:21 PM

I have the same setup you do in a Duster with a 15/16" master cylinder from Dr. Diff. Had a 1 1/32 before and it's a lot better. That's what I would suggest.
Posted By: dart4forte

Re: Manual Master Cylinder bore size - Disc/Drum - 10/19/14 04:36 PM

I was looking for the correct 1" bore m/c for my big block A body. The particular unit is pretty much unobtainable. Got with the Ramman. He set me up with a unit that had a 11/16" bore which is pretty close. I've since found the correct numbers correct unit which he's restoring so I won't be needing the one he setup for me.
Posted By: ntsqd

Re: Manual Master Cylinder bore size - Disc/Drum - 10/19/14 04:54 PM

What calipers do you have? If OE, what is their piston diameter?

I'm using wilwood dynapro's (way stiffer than dynalites of any flavor) with a late model Mopar 1-1/16 M/C and I find the pedal effort to be just about right. This is in a '65 A body, which sets up the next question.

What is the ratio of your pedal?

This is going somewhere, so please bear with me.
Posted By: John_Kunkel

Re: Manual Master Cylinder bore size - Disc/Drum - 10/19/14 09:39 PM


If you have the room for the additional pedal travel, go with a 15/16".
Posted By: 72Swinger

Re: Manual Master Cylinder bore size - Disc/Drum - 10/19/14 10:45 PM

15/16" here.
Posted By: Mopar72Man

Re: Manual Master Cylinder bore size - Disc/Drum - 10/20/14 12:46 AM

Thanks for the input. Does anyone have a part number for the 15/16" bore? I haven't been able to find that in the 2-bolt flavor.

Also, do all of the aluminum 2-bolt masters have a provision for the manual pushrod grommet?
Posted By: 72Swinger

Re: Manual Master Cylinder bore size - Disc/Drum - 10/20/14 01:03 AM

http://www.doctordiff.com/aluminum-master-cylinder-kit.html
Posted By: ntsqd

Re: Manual Master Cylinder bore size - Disc/Drum - 10/21/14 04:49 AM

Without knowing the caliper piston area and pedal ratio it is impossible to choose the m/c size. Or suggest one.
Posted By: YO7_A66

Re: Manual Master Cylinder bore size - Disc/Drum - 10/22/14 01:18 PM

I also use the Dr. Diff 15/16" MC with "manual" disc (OE 11-3/4") up front and 11" OE drums in the rear.
Posted By: Lefty

Re: Manual Master Cylinder bore size - Disc/Drum - 11/05/14 12:08 AM

Disk/Disk

7/8 piston

6-1 pedal
Posted By: FASTBACK340

Re: Manual Master Cylinder bore size - Disc/Drum - 12/11/14 03:18 PM

Quote:

Disk/Disk

7/8 piston

6-1 pedal



A co-worker was telling me he has a `95 (?) Dakota 7/8" master in his **** with 4 wheel disc w/o a proportioning valve. Says it stop fine (90% drag car, 10% street) Anyone have experience with this unit?

Not to hi-jack, but I'm planning on adding rear disc over the winter. I already have an aluminum Mopar M/C similar to the one advertised by Dr. Diff. Is there any way to tell bore size without pulling it all apart? I installed this M/C 10 yrs. ago and honestly don't remember the bore size. I got it from a well know supplier and it was advertised for a Diplomat.

Car is a `68 A body, stock 4 piston front disc, will be adding a Right Stuff rear conversion, which uses Ford calipers.

Thanks!
Posted By: feets

Re: Manual Master Cylinder bore size - Disc/Drum - 12/13/14 04:28 AM

It's time for the brake math spreadsheet.

http://3gduster.com/brakes.html

I've got an updated version available should anyone want it.
Posted By: GoodysGotaCuda

Re: Manual Master Cylinder bore size - Disc/Drum - 12/13/14 04:47 AM

Quote:

It's time for the brake math spreadsheet.

http://3gduster.com/brakes.html

I've got an updated version available should anyone want it.




Those will do for some pretty basic numbers, adding relative weight transfer and rate of deceleration will help provide some input on how those numbers relate to the world. Our FSAE spreadsheets were in G of deceleration with force varying force input that could be plotted.

Don't forget units on your spreadsheet Feets. You mention pounds as one of your inputs, the rest should be Imperial/US or some can end up with a wonky pounds-MM and not know it.

I wasn't the guy in charge of braking/pedal box however, so I'm not the guru in this field by any means.


[spreadsheet goes up to 2G, but I just cut the screenshot short]

Attached picture 8360338-ScreenShot2014-12-12at8.43.59PM.png
Posted By: FASTBACK340

Re: Manual Master Cylinder bore size - Disc/Drum - 12/13/14 09:24 AM

Quote:

It's time for the brake math spreadsheet.

http://3gduster.com/brakes.html

I've got an updated version available should anyone want it.



While your reply reminds me of the old saying "I asked what time is it, not how to build a watch", your spreadsheet IS the absolute definitive answer to what was asked. Thank you.
Posted By: feets

Re: Manual Master Cylinder bore size - Disc/Drum - 12/14/14 02:48 AM

Goody, it is possible to over engineer things. I sometimes have a hard time knowing when to stop "making it better."

What I posted is a very basic spreadsheet that I cobbled together late one night. As I stated above, I have an updated version available that does have units of measure listed. However, I do not have admin access to that link so I can't change it.

The spreadsheet won't win any Formula 1 races (especially with friction as 1) but it'll be more than enough for a car on the street.
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