A PSA on buying a new drum brake master for your classic.
cdnpont said
May 2nd
So I'll be soon converting the 69 to front discs, 69/70 single piston style. I'll need a disc/drum master so I order one. Advertised as "Front disc brakes, power brakes". I like this style as it seems to approximate what would have been under hood if the car came with discs. The price is good and I know what that means, it means it's Chinese. Fine, and its got the "popular part" heart, so people must love it, right?
The package arrives. I open it up and immediately look to the line seats on this thing, and low and behold the brake line flair seats are machined as cast.
Bad sign off the get go, if the seats are iron, the master has no residual check valves. And I'll still need one in the rear. Lightly probed with a paperclip, it's obvious there is no valve behind the seat. You can clearly see the cast iron seats below,
10 and 2 lb residual valves in a drum system originally served 3 functions. First, rectified in GM cars post 54, the mater resided under the drivers floor. The brake wheel cylinders were above the master, and as such would drain by gravity back to the reservoir. Second, the early designs of the wheel cylinder seals tended to draw or pump air back into the system when cycled too far too often, a 2 lb valve was used originally. And thirdly, as today, drum brakes tend to have a good amount of mechanical "take up" before the shoes contact the drum, this take up would be seen in excessive pedal travel. 10psi held in the line will hold the wheel cylinder pistons out at just the right spot, the same spot that you originally adjusted the brakes to. The residual valve takes care of all 3 issues. 10lb is the accepted pressure today. Discs need not have a valve, as the pistons will usually remain out at just the right spot allowing the pads to just kiss the rotor waiting for increased pressure. Some pro touring guys will say discs should have a 2lb valve for a faster pedal. But I don't think on the street we need it. I've done 2 conversions without it.
The tell tale is this, you usually will have a brass flair seat for it to have a residual valve fitted. It fits behind, then the seat gets pressed in. It can also sometimes be steel.
As cast, a valve cannot be fitted.
You can easily spot brass seats,
This is something you really need to confirm if you are installing any new master on a drum brake car. And as far as I can tell, this omission is rampant in these offshore masters. They rarely are as advertised. Sometimes you get a comprehensive info list describing the part, but I've not seen any description of "Check Valve = Yes" in them.
Now the fronts obviously will be fine, no valve required for a disc system, but I'm loath to return it seeing it's a pita. I think I might just buy a Wilwood 10lb residual valve and plumb it in along with the hold off valve. Paint it black and it might not look too out of place.
The two lessons,
Buy your new master locally, open the box and actually look at what you are buying. Confirm you have a valve or valves depending on your configuration. No valve, no thanks.
Drum brakes 100% need a 10 lb residual valve. without it, you will have poor pedal (or any pedal at all) after bleeding.
Now, this might seem a lot of hullabaloo about this valve, but I know instances where brake jobs became a lesson in frustration, all because of the lack of this tiny little valve, and the lack of knowledge about it. I'll be honest, up until a couple of years ago I'd always just take it for granted that my replacement master would be correct and ready to install. Nope, not anymore.
Wow. This is an interesting topic. I didnt really know about them but yes I have seen the pressed in valves. Now I have to go check the new spare cyls I have in inventory. They are more recent rock auto purchases. All my stuff is drum. I have nothing with disc. Thanks for the heads up!!!!!
cdnpont said
May 3rd
Let us know what you find. I'm curious. Hopefully all is good.
If you were to have brass seat inserts, and no valve behind them, it's apparently quite easy to pull the seat and add a valve.
4SPEED427 said
May 3rd
I have an NOS 67 B body drum brake master. It's an oldy but it has no valves. I assume that is because it's for drums though?
cdnpont said
May 3rd
Thats interesting Carl. Curious if it at least has brass seats. As far as I can tell, any drum system needed a valve in place. Perhaps some drum mechanism designs found away around this?
I wonder If I kept an old Drum/Drum master laying about. Now you've got me questioning my sanity.
Beaumont67 said
May 3rd
For what its worth I went through the same issue last year. After installing an aftermarket master cylinder in my Beaumont with an internal proportioning valve I couldnt get a straight answer from their tech line about whether or not it had a residual valve. I installed a Wilwood 10lb valve in the rear line and braking was much better.
cdnpont said
May 3rd
It seems like all the vendors are out to lunch on the subject Rick. Total hit and miss. Maybe it's intentional?
And like you, I did the same on my 67, as the master did not come with the valve, but that was completely expected, as it was listed as a C3 corvette part. Worked fine with the Wilwood valve..
The last conversion on the old 65, the master HAD the rear residual in place. So some do, some don't.
I've just searched around the Summit site looking at masters, pre selecting front=disc, rear=drum. The extensive part descriptions make no mention of any valves.
Even the Wilwood master descriptions on the Wilwood site have no info about this. But to their credit, I'm sure most people buying their product are adding the a separate residual in the build and are fully aware.
This is interesting. A friend of mine just replaced the master on his 58 Austin Cambridge. These cars are not fun to bleed. They have two wheel cylinder at each front wheel however no matter how many times he's bled it he can't get a decent pedal. I wonder if this is his issue? I emailed your post as he has another new master on order.
cdnpont said
May 3rd
Interesting. It certainly could be the issue Todd. I think it might be often overlooked.
Last summer I helped my friend Scotty in Gaspe' convert his single master under floor 1950 Plymouth to a dual remote reservoir system (no more open the floor to add fluid). I built the bracket and master assembly. It used two Wilwood 10lb valves, a 1/8" bore Wilwood tandem remote reservoir master and a pressure valve inline to the rears. This all in concert with the original single master shell. Custom adjustable brake pushrod now passes through the old shell and acts on the new master.
This 1950 also had the dual wheel cylinders on the front, and I can tell you that the bleeding was no real trouble at all. Gravity first, then most distant to closest, pressure and crack, twice round. Front lower cylinders first, then uppers. Fast and good pedal. Road test, best they'd ever been.
Getting fluid up to the remotes was a wee trick, but mcgiver did it and we didn't spill too much lol!
Please keep us posted as I have yet to purchase my new master cylinder
4SPEED427 said
May 3rd
cdnpont wrote:
Thats interesting Carl. Curious if it at least has brass seats. As far as I can tell, any drum system needed a valve in place. Perhaps some drum mechanism designs found away around this?
I wonder If I kept an old Drum/Drum master laying about. Now you've got me questioning my sanity.
I double checked it in case it's my sanity in question but for sure there are no valves in it.
cdnpont said
May 3rd
Strange.
cdnpont said
May 3rd
I just went and ordered a valve. Less hassle than returning and trying to find a correct unit.
It's funny, this is the third time I've ordered these. And expectedly they have gone up in price each time. They are exactly twice what they were maybe 6 years ago.
There must be more to this story. Because I have 4 new 67 68 masters for my 67 chevelle, 67 beaumont(different than the chevelle) and for my 68 c10. They are all drums. All 4 masters are new not rebuilds. All 4 are different brands. Reybestoes centric cardone and dynamic friction.
None of them have brass check valves all are cast.
I then have one known good older well used one off a driving car. Also no valves but performed fine. I also have a new one on my station wagon w no valves and works perfect.
Then I have another one. This is an original delco off a 67 beau parts car. It original date coded to the car. It is the only one I own with the brass check valves. And they seen to work still dispite the piston being totally seized.
So the valves are either not necessary or the check valve is internal somehow?? Just a guess but probably unlikely.
cdnpont said
May 3rd
Yes, it's definitely conflicting information. You read anywhere on line and most all of it points to drum brakes needing this feature. Maybe it's simply a case of internet misinformation. We know that happens, but the stories you read indicate the difficulty of achieving pedal without it, and the success with.
I guess the proof would be to actually install this master as is and see what happens? If not happy with the pedal, then fit the valve. Also the master coming off the car will be interesting to see.
I'll try this. Maybe the difference after all is internal to the master like you suggest?
I'm seeing some talk of the manufactures eliminating the RPV as the orifice sizes in the master were reduced in size in some way to eliminate the issue. But that is a rare comment.
Also, most all Disc/Drum masters appear to no longer have them, while Drum/Drum might.
I think perhaps the bottom line is if the master does not have one, it's probably safe to add it. Just don't add another on top of one already there.
So I'll be soon converting the 69 to front discs, 69/70 single piston style. I'll need a disc/drum master so I order one. Advertised as "Front disc brakes, power brakes". I like this style as it seems to approximate what would have been under hood if the car came with discs. The price is good and I know what that means, it means it's Chinese. Fine, and its got the "popular part" heart, so people must love it, right?
The package arrives. I open it up and immediately look to the line seats on this thing, and low and behold the brake line flair seats are machined as cast.
Bad sign off the get go, if the seats are iron, the master has no residual check valves. And I'll still need one in the rear. Lightly probed with a paperclip, it's obvious there is no valve behind the seat. You can clearly see the cast iron seats below,
10 and 2 lb residual valves in a drum system originally served 3 functions. First, rectified in GM cars post 54, the mater resided under the drivers floor. The brake wheel cylinders were above the master, and as such would drain by gravity back to the reservoir. Second, the early designs of the wheel cylinder seals tended to draw or pump air back into the system when cycled too far too often, a 2 lb valve was used originally. And thirdly, as today, drum brakes tend to have a good amount of mechanical "take up" before the shoes contact the drum, this take up would be seen in excessive pedal travel. 10psi held in the line will hold the wheel cylinder pistons out at just the right spot, the same spot that you originally adjusted the brakes to. The residual valve takes care of all 3 issues. 10lb is the accepted pressure today. Discs need not have a valve, as the pistons will usually remain out at just the right spot allowing the pads to just kiss the rotor waiting for increased pressure. Some pro touring guys will say discs should have a 2lb valve for a faster pedal. But I don't think on the street we need it. I've done 2 conversions without it.
The tell tale is this, you usually will have a brass flair seat for it to have a residual valve fitted. It fits behind, then the seat gets pressed in. It can also sometimes be steel.
As cast, a valve cannot be fitted.
You can easily spot brass seats,
This is something you really need to confirm if you are installing any new master on a drum brake car. And as far as I can tell, this omission is rampant in these offshore masters. They rarely are as advertised. Sometimes you get a comprehensive info list describing the part, but I've not seen any description of "Check Valve = Yes" in them.
Now the fronts obviously will be fine, no valve required for a disc system, but I'm loath to return it seeing it's a pita. I think I might just buy a Wilwood 10lb residual valve and plumb it in along with the hold off valve. Paint it black and it might not look too out of place.
The two lessons,
Now, this might seem a lot of hullabaloo about this valve, but I know instances where brake jobs became a lesson in frustration, all because of the lack of this tiny little valve, and the lack of knowledge about it. I'll be honest, up until a couple of years ago I'd always just take it for granted that my replacement master would be correct and ready to install. Nope, not anymore.
Let us know what you find. I'm curious. Hopefully all is good.
If you were to have brass seat inserts, and no valve behind them, it's apparently quite easy to pull the seat and add a valve.
I have an NOS 67 B body drum brake master. It's an oldy but it has no valves. I assume that is because it's for drums though?
Thats interesting Carl. Curious if it at least has brass seats. As far as I can tell, any drum system needed a valve in place. Perhaps some drum mechanism designs found away around this?
I wonder If I kept an old Drum/Drum master laying about. Now you've got me questioning my sanity.
It seems like all the vendors are out to lunch on the subject Rick. Total hit and miss. Maybe it's intentional?
And like you, I did the same on my 67, as the master did not come with the valve, but that was completely expected, as it was listed as a C3 corvette part. Worked fine with the Wilwood valve..
The last conversion on the old 65, the master HAD the rear residual in place. So some do, some don't.
I've just searched around the Summit site looking at masters, pre selecting front=disc, rear=drum. The extensive part descriptions make no mention of any valves.
Even the Wilwood master descriptions on the Wilwood site have no info about this. But to their credit, I'm sure most people buying their product are adding the a separate residual in the build and are fully aware.
Interesting. It certainly could be the issue Todd. I think it might be often overlooked.
Last summer I helped my friend Scotty in Gaspe' convert his single master under floor 1950 Plymouth to a dual remote reservoir system (no more open the floor to add fluid). I built the bracket and master assembly. It used two Wilwood 10lb valves, a 1/8" bore Wilwood tandem remote reservoir master and a pressure valve inline to the rears. This all in concert with the original single master shell. Custom adjustable brake pushrod now passes through the old shell and acts on the new master.
This 1950 also had the dual wheel cylinders on the front, and I can tell you that the bleeding was no real trouble at all. Gravity first, then most distant to closest, pressure and crack, twice round. Front lower cylinders first, then uppers. Fast and good pedal. Road test, best they'd ever been.
Getting fluid up to the remotes was a wee trick, but mcgiver did it and we didn't spill too much lol!
I double checked it in case it's my sanity in question but for sure there are no valves in it.
Strange.
I just went and ordered a valve. Less hassle than returning and trying to find a correct unit.
It's funny, this is the third time I've ordered these. And expectedly they have gone up in price each time. They are exactly twice what they were maybe 6 years ago.
https://www.amazon.ca/gp/product/B01H7RO6IU/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1
Yes, it's definitely conflicting information. You read anywhere on line and most all of it points to drum brakes needing this feature. Maybe it's simply a case of internet misinformation. We know that happens, but the stories you read indicate the difficulty of achieving pedal without it, and the success with.
I guess the proof would be to actually install this master as is and see what happens? If not happy with the pedal, then fit the valve. Also the master coming off the car will be interesting to see.
I'll try this. Maybe the difference after all is internal to the master like you suggest?
I'm seeing some talk of the manufactures eliminating the RPV as the orifice sizes in the master were reduced in size in some way to eliminate the issue. But that is a rare comment.
Also, most all Disc/Drum masters appear to no longer have them, while Drum/Drum might.
I think perhaps the bottom line is if the master does not have one, it's probably safe to add it. Just don't add another on top of one already there.