Technical 53 Chevy - Brakes Dragging - New Residual Valves and Master Cylinder

Hi All,

I just installed a new replacement master cylinder from a 68-72 Mustang on my 53 Chevy. I replaced the old one that was already in there (it is underfloor mounted with an adaptor to mount on the k-member). I also added a 2 psi residual valve for the front disc (9" rotors) and a 10 psi residual valve for the rear drums.

I installed and bled the system and tested for leaks. I stepped on the pedal a bit hard to see if it would hold. I didn't see any leaks but the problem is that the front wheels are a bit hard to turn by hand. Is this normal for a system with a 2 PSI residual? I'm afraid the rotors will smoke up if I drive it that way.

I also have the master cylinder quite full so I don't know if that is partly the issue? I haven't driven it yet.

My other thought is maybe the pushrod is engaging the new master cylinder a littler earlier than the one I replaced. They should be pretty much the same though.

Does anyone have suggestions on what I need to check?
Thanks.

 

With the push rod disconnected from the pedal ***embly there is still pressure in the lines making it hard to turn the wheels so at least I know the pedal and push rod ***embly is fine.

 

crack the front bleeders for a second on each front.

then see if they are still tight, but don't use the brake pedal yet.

report back with what happens

 

Thanks. I did just that. They freed up nicely.. Then I go and pump on the pedal moderately and they hang up again but I can still move them by hand just with a bit of force.

I also drained a little more fluid from the M/C so its closer to 3/4 full for front and rear

 

Does the master cylinder have check valves in them? I believe some mc have them in the ports in which case you would have an additive amount of back pressure. Whether that would be too much I don't know but if that is the case remove the inline ones and try it. Just a thought

 

How much play in the push rod? Does the return spring return the pedal all the way back?

 

Thanks, not that I know of. I was told also by ECI a while ago to get a mustang 68-72 m/c and put a 2 psi residual.

With the old M/C they would always spin freely however there was no residual and it appears the calipers are a little higher than the m/c so i decided to put one in.

 

Not much play at all. When I took the push rod off, i tried spinning the front wheels and they would not spin super freely. This makes me think the pedal ***embly is fine and is not engaging the brakes too early.

 

I had a similar problem on a 66 Corvette, pushrod was a tad too long, put washers behind the MC and it worked fine.

 

Thanks but when I took the pushrod off I still felt the wheels tight. Doesn't this mean the pedal ***embly is fine?

 

Does anyone else have any ideas? I'm not sure if this is normal or ok?

 

are you sure the master you are using doesn't have residual valves build in? If they do and they are for a drum brake set up that might cause the calipers to drag.
Just an idea, sounds like youve checked everything else. Cesar

 

Thanks, I'm pretty sure, I got one that is compatible with a 68-72 Mustang.

Here is a photo, if it was drum/drum the front and back reservoir would be the same size right?

 

If you push the pedal down with lid off, do you get a little surge of fluid back into the bowls when you let off the pedal?

 

I've double checked. The line going to the front is connected to the front port next to the larger reservoir. The line going to the rear is connected to the rear port closest to the smallest reservoir.

I have 10 psi connected to the rear line facing the correct way. I have the 2 psi connected to the front line also facing the correct way.

When I disconnected the push rod the wheels were both still just as tight. When I had cracked the bleeder open on one caliper, both wheels freed up.

This is a Dorman master cylinder, is it possible they put a residual in the front instead of the rear?

Yep, when I was bleeding the brakes I had seen that. Should I check for that again after having bled the brakes?

It could also be I'm an idiot. I bought an M/C that looks like it should work for front disc/rear drum.
This is the one I bought:

Dorman M83579
http://www.dormanproducts.com/p-31316-m83579.aspx?origin=keyword

It says 67-75 Ford and it appeared to be an M/C similar to the one I had.. looks identical in dimensions. Dorman is useless when I tried to ask them what set up it's for. they just say they can only look up cars by part numbers or car make/model/year.

Did I mess this one up?

When I look up the applications on the Dorman website for the M83579, I see some cars such as a Ford E300 econoline and various others. When I look these ones up on Autozone I see they sell front rotors/calipers so it seems it's set up for front disc/rear drum.

 

Crack the line between the front residual valve and the master cylinder and check this should tell you if the master cylinder also has a residual too.

 

next step, take the residual valve out and try it.

 

Thanks. What should I look for as I crack the fitting open on the "IN" side of the residual?

 

That will be a pain, I would have to make a new line from the front T to the M/C to test this, or find a union with the same length as the residual.

Hmmm.. anything else I should try first, maybe cracking the "IN" side of the residual as suggested by sunbeam?

 

See if the rotor will turn easyer If it does the master also has a residual valve in it. More than likely a 10 lb unit for drum brakes sense the valves are differential with your 2 lb valve you could be seeing 12 lb of residual.

 

Thanks, so a master cylinder that has different sized reservoirs doesn't necessarily mean its for a drum/disc setup?

 

not a pain, just get a short line and a union. put an arch in the line. it is just temporary to test it.

 

oh thanks i need two unions and i have a short extra piece leftover.

 

I just saw an article about someone removing their residual valve on their M/C.

I actually remember seeing the two br*** pieces on each port and didn't make anything of it. Should I remove the one going to the front? I thought since the two reservoirs were different sized that it was for a disc/drum setup.

Any thoughts?

This is a photo of the one I bought:




Here is a photo from the article I had seen.

 

You need the reverse flair for the fitting to seal against. It has to remain in there.

Having an extra residual valve of the same pounds in line with the same size valve in the master is not gonna be a problem. They don't add too much pressure. The problem is if you actually have a 10 pounder in there (if you bought a drum/drum master) and you only need 2 pounds for the disks.

 

I'm using special banjo fittings with crush washers to get a 90 turn.. that being said i don't need the reverse flair fitting inside. I should be able to pull the residual in the front port out right?

 

So basically just because a M/C has a larger front reservoir, that doesn't mean it's set up for disc/drum?

 

I just got a master cylinder from NAPA for my 67 Ford F350 with drum brakes it has big and little reservoirs

 

Thanks. I removed the 10 psi residual that was in the front port on the M/C. What a pain. Now when I press on the pedal and let go and spin the wheels they spin a little more freely for sure though I still need to use a little bit of force to get them to spin. I'm guessing that's the 2 psi residual only now.

 

just to let ya know, i just jacked up my model A and checked it for ya, same exact stuff you have, and it's got some resistance, not sure easy to turn,, it has about a zillion trouble free miles on it.
don't sweat it man. drive that **** !!