Master Cylinder
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Champion
Joined: May 2008
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From: Apex, NC
Master Cylinder
So it was brought to my attention by a friend of mine that when I get the rear disc brakes on my truck I'll have to get a new master cylinder because ours have a check valve for the drum brakes?
First, is this true? Second, does anybody know of a master cylinder that will fit our brake booster that doesn't have the check valve? (one designed for 4 wheel disc brakes)
First, is this true? Second, does anybody know of a master cylinder that will fit our brake booster that doesn't have the check valve? (one designed for 4 wheel disc brakes)
I can't remember which year but you can get one off a ford explorer. I think it has the right proportioning valve.
Don't quote me on that. But I think thats what I was told by a friend that worked for a Chrysler dealer. Ask one of their brake techs at a dealer to make sure.
Don't quote me on that. But I think thats what I was told by a friend that worked for a Chrysler dealer. Ask one of their brake techs at a dealer to make sure.
Champion
Joined: Dec 2003
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From: Sycamore, Illinois (displaced to Arkansas)
I don't know about a check valve.
I know we've got the combination valve for that purpose, to hold off front brake pressure until the rear brakes are applied.
I'd assume you could bypass that and/or use an aftermarket product, when you use the new axle.
I know we've got the combination valve for that purpose, to hold off front brake pressure until the rear brakes are applied.
I'd assume you could bypass that and/or use an aftermarket product, when you use the new axle.
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Joined: Aug 2007
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From: NM
As far as I know there is no check valve. Just the rear proportioning valve. Which you could remove. And install an adjustable one. Bad did a write up on it.
My guess the stock MC can handle the rear disks. But the stock PV has to go. But with the dual pistons up front you will need a stronger MC.
I believe a Rams MC will fit the lines but not the booster. The Rams booster is not a direct bolt on. I checked on it one time at the junkyard.
My guess the stock MC can handle the rear disks. But the stock PV has to go. But with the dual pistons up front you will need a stronger MC.
I believe a Rams MC will fit the lines but not the booster. The Rams booster is not a direct bolt on. I checked on it one time at the junkyard.
Last edited by Crazy4x4RT; Mar 7, 2010 at 02:23 AM.
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Champion
Joined: May 2008
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From: Apex, NC
I'm already counting on re-plumbing the brakes! The ABS valve and computer both have to go! The 14 bolt doesn't have the sensor setup. And I figure with the same size front and rear disc brakes, I'll have to get an aftermarket proportioning valve to hold off the rear brakes some, but I really wasn't counting on replacing the master cylinder!
Can someone confirm if there is a check valve in the master cylinder? I can't find anything about it in the FSM.
Can someone confirm if there is a check valve in the master cylinder? I can't find anything about it in the FSM.
Thread Starter
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Champion
Joined: May 2008
Posts: 4,839
Likes: 5
From: Apex, NC
As far as I know there is no check valve. Just the rear porportioning valve. Which you could remove. And install an adjustable one. Bad did a write up on it.
My guess the stock MC can handle the rear disks. But the stock PV has to go. But with the dual pistons up front you will need a stronger MC.
I believe a Rams MC will fit the lines but not the booster. The Rams booster is not a direct bolt on. I checked on it one time at the junkyard.
My guess the stock MC can handle the rear disks. But the stock PV has to go. But with the dual pistons up front you will need a stronger MC.
I believe a Rams MC will fit the lines but not the booster. The Rams booster is not a direct bolt on. I checked on it one time at the junkyard.
Champion
Joined: Dec 2003
Posts: 4,119
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From: Sycamore, Illinois (displaced to Arkansas)
If you compare page 5-3 (of the 1996 service manual) or 5-12 (1995 service manual), to Figure 5-405 (page 104/105 of the 1994-1996 parts manual)... I ain't seeing anything.
Can you ask your friend what this check valve is supposed to do?
Can you ask your friend what this check valve is supposed to do?
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Champion
Joined: Dec 2003
Posts: 4,119
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From: Sycamore, Illinois (displaced to Arkansas)
I know what a check valve is.
I've just never heard of one in a brake system, or what the theory would be for having one in a master cylinder. (Having one past the master cylinder piston would be useless, since that wouldn't allow pressure to be relieved)
Since the front/rear brakes fluid supply are separated within the master cylinder.
I've just never heard of one in a brake system, or what the theory would be for having one in a master cylinder. (Having one past the master cylinder piston would be useless, since that wouldn't allow pressure to be relieved)
Since the front/rear brakes fluid supply are separated within the master cylinder.
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Champion
Joined: May 2008
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From: Apex, NC
The Residual Check Valve is located in the master cylinder outlet to the rear drum brakes. Its purpose is to maintain about 6 to 8 psi in the hydraulic circuit. When the brakes are released the brake shoe return springs force the wheel cylinder pistons back into the bore. Without the Residual Valve the inertia of fluid returning the master cylinder may cause a vacuum and allow air to enter the system. In addition to preventing a vacuum, the residual pressure pushes the wheel cylinder cup into contact with the cylinder wall.
This is pretty much exactly what my friend told me about it. He said he has seen many people swap in rear discs without losing this check valve the pressure it holds on the system will burn up the pads.