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Old 04-29-2019, 07:06 PM   #21
Talkwrench
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Default Re: Dual master cylinder update

Yes Tommy, the wheel cylinders are proportionally different front and rear and in some cases the cylinders themselves can have one side a different bore size also.
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Old 04-29-2019, 08:18 PM   #22
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Default Re: Dual master cylinder update

I knew about the different bore sizes in a cylinder but not front to rear differences.
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Old 04-29-2019, 08:40 PM   #23
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Default Re: Dual master cylinder update

Not knowing what I have can you identify this master cylinder?

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Old 04-29-2019, 08:49 PM   #24
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Default Re: Dual master cylinder update

https://www.speedwaymotors.com/1939-...Bore,1982.html
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Old 04-30-2019, 03:11 AM   #25
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Default Re: Dual master cylinder update

That's the standard fitment ford master cylinder. 1-1/16 bore.

I bought one from rockauto recently.

That is assuming it is the car/pickup application. Bigger trucks use a bigger bore master. You can fit a brake light switch in the end of the banjo bolt if you want to. Someone has plugged the hole.

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Old 04-30-2019, 12:09 PM   #26
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Default Re: Dual master cylinder update

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Bigger trucks use a bigger bore master.
Mart.
I see that the F2 has a 1 1/8 bore. Does this mean more braking power if used on a car?
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Old 04-30-2019, 12:23 PM   #27
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Default Re: Dual master cylinder update

No. A larger bore would give you less braking with the same amount of pressure on the pedal. You would probably not have the same stopping ability on an emergency situation.
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Old 04-30-2019, 01:04 PM   #28
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Default Re: Dual master cylinder update

My guess is they can use the larger diameter master cylinder because the brake pedal is designed with more mechanical leverage. The larger the MC dia the lower the line pressure for a given pedal force (leg force). This can be overcome with a larger pedal ratio. This is somewhat difficult to do in a car because of space constraints, easier in a truck (more room). The only real advantage to a larger dia MC is it moves more fluid volume for a given amount of pedal travel.
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Old 04-30-2019, 05:50 PM   #29
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Default Re: Dual master cylinder update

According to Macs website the trucks used a larger diameter wheel cylinder so the master cylinder would have a larger bore as well.
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Old 04-30-2019, 05:52 PM   #30
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Default Re: Dual master cylinder update

The brakes are generally bigger all round on the size of truck that takes the bigger master. I only mentioned it because from the image showing the master cylinder, I could not identify what it was in.

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Old 04-30-2019, 05:55 PM   #31
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Default Re: Dual master cylinder update

We need a "like" icon...
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Old 05-07-2019, 04:09 PM   #32
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Default Re: Dual master cylinder update

put the mc out of a gremlin on my 40 coupe project. lots of pedal and stops good, so hopefully cured the problem
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Old 05-14-2019, 03:48 PM   #33
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I just had a member PM me saying he ordered the 36456 master cylinder from Rock Auto. It arrived and has a 1 inch bore. I checked and sure enough, it is now listed as a 1 inch bore. Thinking I made a mistake I went out and measured mine. It is 1 1/16. Couldn`t get a real good picture but it does measure 1 1/16. Also during my search I found several references to this being a 1 1/16 bore cylinder. Something changed?? (I ordered mine last fall) I have no idea.
thumbnail_image1[1] (2).jpg

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Old 05-14-2019, 04:27 PM   #34
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Default Re: Dual master cylinder update

jeep cj5 has the same style mc but with a 1" bore, may that is the one he got. I have one in my collection, will measure to night
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Old 05-14-2019, 06:52 PM   #35
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Default Re: Dual master cylinder update

I did have an ASE Master Mechanic license and an ASE Heavy Truck Master Mechanic license until I retired. Both of those master licensees required separate brake licensing tests. One of the questions on those tests is what is the purpose of a residual pressure valve on drum brakes? Its something you would almost never need to know. They are built into a drum brake master cylinder where you never see them. Most people do not know they are there. If your replacing a master cylinder with another replacement master cylinder everything would work just fine. If you start swapping master cylinders you can create problems.

Something to think about with drum brakes is there is usually a built-in residual check valve in the master cylinder to hold a little pressure in the brake system. This prevents the wheel cylinder's seals from leaking when not being driven. The pressure held in the system forces the wheel cylinder cup lip out against the bore which makes the seal. It also eliminates some of the pedal travel because there is already some pressure in the system. Its just enough pressure to make the cups seal but not enough to overcome the pressure from the brake return springs. If you look at how the cups are made you will see that the outer edges taper and the back of them are recessed. The pressure pushes on that recess in back of the lip forcing the lip against the bore in the cylinder. If there was no pressure in the system when not in use the lip might not seal and fluid could seep out though there. If your ever rebuilding one and your not sure which way the cups go in just look at how they are designed. One direction would cause the seal to expand and seal. The other direction would push the edge of the lip away from the bore and it would leak (see photos)

A dual master cylinder for a vehicle with front disc brakes would not have the built-in residual check valve on the disc brake side. The larger of the two reservoirs is for the disc brakes. Because the disc brake pistons are so large they take a larger volume of fluid to move them, that is why the disc brake reservoirs are larger. You do not want a residual pressure valve on the disc brake side because that would cause the pads to always be dragging on the brake rotors. You want to find a dual master cylinder from a vehicle with four wheel drum brakes or install a residual pressure valve on the outlet port on the disc brake side of the master cylinders.

Scroll down through Wilwood valves and read what it says about residual brake valves. The correct valve will give you a better pedal with less travel on drum brakes.

https://www.wilwood.com/MasterCylind...CylinderValves

Also,here is a H.A.M.B. post on residual brake valves.

https://www.jalopyjournal.com/forum/...-valves.74978/
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Old 05-14-2019, 07:16 PM   #36
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Default Re: Dual master cylinder update

the disk brake reservoirs are larger because as the pads wear the piston moves out. they don,t return all the way back like the rear cylinders. so as the pads wear more fluid is reqired to fill them . both front & read master cyl have the same dia you just need more fluid reserve on the disk chamber to fill the disk cylinders as the pads wear .
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Old 05-14-2019, 08:06 PM   #37
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Default Re: Dual master cylinder update

In line residual valves have been around for a long time for applications like this. A 10lb valve is recommended for drum brakes, and for disc brakes a 2lb valve is available for applications where the master cylinder is lower than the calipers.
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Old 05-14-2019, 08:11 PM   #38
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37 cab has it right
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