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Discussion Starter #1
There's two parts to this post:

1. I'm having some issues with leaking from the small chamber of my master cylinder. It tends to seep out from the seal. I replaced the seal which had no impact, and tried to increase force from the clip but haven't had any luck improving the situation with that. So, I'm planning to either refurb the one I've got or buy new to try and stop this leaking. Does anyone have any experience in attempting a refurb of a master cylinder and is it worth it or would the recommendation be to buy new. If new, then anyone got any recommendations?


2. Whilst researching master cylinders I've learned about the possible requirement for proportioning valves. My 65 Mustang has disks on the front and drums on the rear. Correct me if I'm mistaken, but this is a classic case of needing a proportioning valve right? There doesn't seem to be a proportioning valve in sight, but if you spot something in the images that makes you think otherwise, or have any thoughts then please let me know.


Thanks all
 

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That's your proportioning valve just below the distribution block, Follow the brake line from the front bowl of the MC and it should dive down into a round, cylinder "thing". This "thing" is the proportioning valve. there will be a brake line leading out of this to the rear distribution block on your axle.

I'd just go ahead and replace the MC. They are cheap, around $60.00 for a 15/16 bore dual bowl MC. You may also want to talk with someone about rebuilding the proportioning valve.
 

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MAster cylinders can be rebuilt - you just have to find seals and must make sure the bore is good. I have not done a mustang- (well ok I did take a new one apart and powder coat the exterior and then reassemble) but unless this was numbers matching/date coded for a shelby/k code/boss car- its probably not worth it. I think a new master was 22-ish dollars-

I believe the factory part is a residual valve- (holds slight pressure on the rear brakes so they engage w/o lots of pedal (which would by then lock up the front)-so you should be good if the car is factory equipped discs

IIRC a proportioning valve is the aftermarket part that is adjustable and allows for more precise control over the rear brakes whether drum or disc- so if you convert from say drum/drum- you remove the residual valve and install a proportioning valve

I am tired- and this was from memory so forgive me if I am incorrect- Chockostang might weigh in - he is THE BRAKE man- you can probably PM him for advice and he sells parts too so he can get you all hooked up- I have used him several times and will continue to do so- he is friendly, accurate, and has extremely good knowledge of mustang steering/brakes as factory equipped
 

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Replace the master with new Raybestos.
Should be the MC 36440. It has clip ring provision in piston so push rod does not fall out. the 440 does not have residuals in either port, so if rear drums are not adjusted correctly, will not function as new, the inline 10 pound residual might be needed.
 

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Ophthos is correct, it's the factory proportioning valve.
If you replace the M/C, try to get one with a residual valve already installed in the rear brake line port.
Edit...Chock beat me to it
 

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Ophthos is correct, it's the factory proportioning valve.
If you replace the M/C, try to get one with a residual valve already installed in the rear brake line port.
Edit...Chock beat me to it
The Raybestos Mc 35251 has a residual in the port for rear brakes. ONLY problem is no clip ring provision in piston. You stomp on brakes, release brakes, push rod fall out rear of master, next push on brakes you hit Semi, Tree, child.
 

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The Raybestos Mc 35251 has a residual in the port for rear brakes. ONLY problem is no clip ring provision in piston. You stomp on brakes, release brakes, push rod fall out rear of master, next push on brakes you hit Semi, Tree, child.
I think I've used that one before ... made a pedal stop to prevent that scenario ... I like kids and trees.
But yes, don't half-*** anything to do with brakes ... or steering, or, ...
 

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Discussion Starter #8
MAster cylinders can be rebuilt - you just have to find seals and must make sure the bore is good. I have not done a mustang- (well ok I did take a new one apart and powder coat the exterior and then reassemble) but unless this was numbers matching/date coded for a shelby/k code/boss car- its probably not worth it. I think a new master was 22-ish dollars-

I believe the factory part is a residual valve- (holds slight pressure on the rear brakes so they engage w/o lots of pedal (which would by then lock up the front)-so you should be good if the car is factory equipped discs

IIRC a proportioning valve is the aftermarket part that is adjustable and allows for more precise control over the rear brakes whether drum or disc- so if you convert from say drum/drum- you remove the residual valve and install a proportioning valve

I am tired- and this was from memory so forgive me if I am incorrect- Chockostang might weigh in - he is THE BRAKE man- you can probably PM him for advice and he sells parts too so he can get you all hooked up- I have used him several times and will continue to do so- he is friendly, accurate, and has extremely good knowledge of mustang steering/brakes as factory equipped
Thanks for the explanation. Need to check if it was factory fit, no idea from memory.
 

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Discussion Starter #9
Replace the master with new Raybestos.
Should be the MC 36440. It has clip ring provision in piston so push rod does not fall out. the 440 does not have residuals in either port, so if rear drums are not adjusted correctly, will not function as new, the inline 10 pound residual might be needed.
Ophthos is correct, it's the factory proportioning valve.
If you replace the M/C, try to get one with a residual valve already installed in the rear brake line port.
Edit...Chock beat me to it
Thanks, perfect recommendation. Wouldn't have known about the clip ring.
 

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Discussion Starter #10
I think I've used that one before ... made a pedal stop to prevent that scenario ... I like kids and trees.
But yes, don't half-*** anything to do with brakes ... or steering, or, ...
Noted want to keep it away from those kid, trees, …., Not in a rush so I can try and work it all out with some guidance. Got to wait a few weeks for postage of parts anyway.
 

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The Raybestos Mc 35251 has a residual in the port for rear brakes. ONLY problem is no clip ring provision in piston. You stomp on brakes, release brakes, push rod fall out rear of master, next push on brakes you hit Semi, Tree, child.
Not to hijack this thread but can you expand on this? My MC is a 1" bore. My push rod has the clip on the end but it didn't "clip" into the bore. I get what your saying about the push rod coming out but how does this happen when everything is installed?

Can the brake pedal pull the pushrod out of the MC before the back pressure pushes the piston against it????? This seems very concerning to me! Can this happen very easily?
 

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If you can lift the pedal far enough for the rod to become disengaged, you need some sort of stop mechanism.
 

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how does this happen when everything is installed?

Can the brake pedal pull the pushrod out of the MC before the back pressure pushes the piston against it????? This seems very concerning to me! Can this happen very easily?

If the pushrod is not clipped into the piston it can be possible to hook your foot under the brake pedal and pull the pedal toward you and have the pushrod fall out of the MC piston. It all depends upon the length of the pushrod and whether or not you have a brake pedal stop attached.

The piston pushing back against the pushrod is not the problem. The problem is a pushrod that's too short or a missing brake pedal stop. I don't have a clip on my pushrod but I have confirmed that if I pull the brake pedal all the way back until it hits the stop the pushrod does not fall out of the piston. I made an adjustable pushrod so that I can adjust the height of the brake pedal at rest to be even with the clutch pedal.
 

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If you slide your foot of the pedal from fully engaged, M/C piston snaps back to the circlip, pedal keeps moving cos its not connected to the piston. It's possible for it to move far enough to become disconnected. Kinetic energy.
How likely it is to happen is anyones guess ... but why risk it?
Edit beaten again
 

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My 1970 doesn't have a pushrod clip. The pushrod does stay within the bore of the piston under all conditions. I checked it with the master cylinder drained and the piston forward. There is a slight looseness to it and the pedal can make a noise if it pops up, but it doesn't go far.

Master cylinders that don't have a groove machined into the piston to accept a pushrod are probably meant to be mounted on a power booster. The master cylinder on my car is too big for manual brakes. I hope to switch to the Raybestos MC36440.

I hope it comes with the pushrod loose just in case it's not the right size.

 

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Discussion Starter #16
Replace the master with new Raybestos.
Should be the MC 36440. It has clip ring provision in piston so push rod does not fall out. the 440 does not have residuals in either port, so if rear drums are not adjusted correctly, will not function as new, the inline 10 pound residual might be needed.
The only site that I can find with specifics on the Raybestos MC36440 fitment says it only goes back to 1974 Mustangs. Could just be the site that goes back that far but wanted to be sure that you think this will fit for 1965 application? Also is the 10lb residual valve to replace the stock proportioning valve or would both be used, and where is it best placed? Straight out of the MC or inline as per the image (not sure what the image is from)?
 

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The 440 has a 15/16" bore
Will bolt on the 64-73 Firewall perfectly
Front bowl rear brakes, rear bowl front brakes
Comes with push rod---Do not clip in till you check pedal height. You will most likely use old push rod.
A residual does not replace a proportioning valve
10 pound residual goes in rear brake line CLOSE to master, not in rear of vehicle
Front disc brakes have proportioning valves for rear brakes (can go in line anywhere)

Picture above. That is a 2 pound residual valve. 10 pound is red (Rear drum brake type)
 

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Not everything stated above is true - CHOCK is always right though...



Proportioning valve = apples, residual valve = orange. Proportioning valves tend to be square when you look at them. Earliest Mustangs with a stock disc/drum break system do not get a proportioning valve but some of the later ones e.g. somewhere around 1968-1970 and on, stock disc/drum cars got them and the later ones provide some nice features that keep the rear brakes from locking when you hit the brakes hard and the weight shifts forward. You can tell these types of P valves because they have a big nut on one end that holds a spring mechanism behind it. They limit the pressure for a microsecond then let the full pressure go back. Its a noticeable improvement, I added one to my '66 from an '86 Tbird. Adjustable proportioning valves are square also but have a knob or lever. These tend to be used in racing to tune to a track or when people go to disc brakes in the rear to keep the heavier disk brakes from locking up first (dangerous) and basically detune them to function EXACTLY like the lighter drum brakes they took off - as the engineers designed the system. have a If there is no gizmo on your square brass block, its just a distribution block with no function other than send fluid from one pipe to two or three. Note that the adjustable ones do NOT have the anti-lockup feature that I have seen because they are meant for racing where the springs are stiff and the car doesn't nose dive when the brakes are slammed.



Residual valves on the other hand are either installed in the MC on the drum brake circuit only or installed in the rear brake line somewhere and look like a cylinder, one in, one out line. These just hold 10 pounds of pressure to keep the brake shoes against the drums so the pedal engages sooner. There is actually a 2 lb residual valve available for Disc circuits but I haven't seen anyone use one yet.



When your master cylinder leaks like that and the seal and surfaces are good (not rusted), you are likely to find that hitting the brakes sends a nice fountain of brake fluid upwards when you hit them with the top off the MC. One circuit is not functioning as it should and you will likely find a noticeable difference in braking when you replace it. Rebuild kits are available and its easy to rebuild one but cleanliness is everything and inspect the bore for pits from water in the brake fluid when its not changed every 2 - 5 years. Every time I break open my brake system and I have to bleed it, I buy an extra jug of fluid and bleed the system till its clear to keep the water out. It will get in, brake fluid absorbs water...



Good luck
 

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The only site that I can find with specifics on the Raybestos MC36440 fitment says it only goes back to 1974 Mustangs. Could just be the site that goes back that far but wanted to be sure that you think this will fit for 1965 application? Also is the 10lb residual valve to replace the stock proportioning valve or would both be used, and where is it best placed? Straight out of the MC or inline as per the image (not sure what the image is from)?



When I get home I'll take some pictures of my set up with an adjustable proportioning valve and 10 lb residual valve.
 

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Don't be fooled into thinking a "pedal stop" ONLY will keep the pushrod from falling out. The issue isn't that you can pull the brake pedal "up" and disengage the pushrod... it's that the pedal may "return" faster than the master cylinder piston and on the way back the pushrod can fall out.... especially if there is a lot of travel in the system.
 
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