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MG MGB GT V8 Factory Originals Technical - Brake residual valve
|As I run new brake lines, I'm wondering if I should install a 10# residual valve in the line to the rear. Has anybody used one of these to any benefit, or experienced a downside after installing one? Now is the time, before fluid is added, so I thought I'd ask. Best, Joe|
I think it depends on what master cyl you are runing. I used one as I have a 7/8" GM MC that did not have a risidual valve built in. If stock I dont think you need one.
|Thanks, Mike. Yes, it's stock. I'm not sure what part of that serves as a residual valve, but guess I'll not worry about it for now. Joe|
|Typically, you use residual valves if the master cylinder is lower than the wheel cylinders/calipers.|
|Ah, thanks, Wayne|
|Master cylinders designed for use with drum brakes usually had a check valve built in for that side of the system. I believe the reason was to limit the retraction of the shoes by the springs in order to help reduce pedal travel. Most of these 'factory' check valves were located inside the exit port of the master cylinder. Most can be removed if changing to rear disc brakes. Unless your rear brake retracting springs are especially strong, I'd think that a 10psi valve would be a bit much, but then I don't remember ever seeing pressure specs on most system valves. The only down side you might have is that the shoes don't retract away from the drums and cause excessive drag and heat build up. It's pretty easy to check after the system is filled, just apply the brakes and then release. If the rear drums don't release well then the pressure is too high. Most disc brake systems don't use check valves. This is to prevent pad drag as there are no retracting springs for most discs.|
|My comment was a bit too general, which, of course, made it half wrong. After reading Bill's post, a light bulb dimly flickered. See these two links: |
http://www.wilwood.com/Products/006-MasterCylinders/010-RPV/index.asp and http://www.classictruckshop.com/t3_page2.asp .
|Does anyone know if the Lockeed MC used on the later model B's had such a check or residual pressure valve built into it. I know they have the pressure differential switch but this serves a completely different function.|
|I haven't looked closely at my B cylinder, but my '73 midget cylinder has check valves located in each outlet. Access is by removal of the adaptor (item 20 in the drawing) http://www.mossmotors.com/Shop/ViewProducts.aspx?PlateIndexID=29029|
The valve is shown as item 21. This is for the early dual cylinder, but I'm pretty sure the later cylinder is the same in this area.
|Oh, I thought that those little plastic pieces served a proportioning function, since they have the different sized little holes in the center. Well, the diagram says 'trap valve'; sounds like a check valve to me.|
|Correct my last statement. Wondering if I was seeing it right, I took the trap valves out of my dry brake master cylinder to have a look and see if the little holes in them were indeed different sizes, the way I saw them the first time. Musta been a trick of my eyes, cause to set the record straight, they're the same size. I guess that answers my question on the fitting of a residual pressure valve to the rear drums, in order to keep the pedal up. Seems to be built in to the mc, and shouldn't be necessary to double up. Although one website supplier of aftermarket brake parts says it won't hurt, and recommends doing so anyway; I think they just want to sell more of 'em. Thanks for the input, guys. You led me to the answer of what I needed to know. Joe|
This thread was discussed between 03/06/2006 and 10/06/2006
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