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Residual Pressure Valve Removal?

Posted By: 392charger

Residual Pressure Valve Removal? - 02/22/12 04:29 AM

Hey all. The front rotor's on my sons 69 GTX have a ton of drag on them and my research says to make sure the residual pressure valve is removed (since it is power disc, not drum). I know he changed the m/c recently and I suspect the valve is in place. Where is it and how to remove it? Thanks for any and all help
Posted By: RapidRobert

Re: Residual Pressure Valve Removal? - 02/22/12 04:43 AM

take off the line from the M/C half next to the firewall & stick a drill bit deep into the brass cone seat. The RPV is just a piece of neoprene on a spring and you'll feel it if it's there. Screw a screw of the right thread pitch into the brass seat and lever it up/out w a pair of screwdrivers then remove/toss the rpv then reinstall the brass seat carefully. Be carefull not to mar it. The brake line fitting will help (re)seat the brass cone. EDIT 1st I'd (it'd be easier) crack the front brake line & see if it's a pressure prob or if one or both of the front calipers ain't retracting right/enough either from a piston/square seal problem or mechanically hanging up on the adapter that supports the caliper. One or both calipers may be the culprit. Most (& I'd think all) M/C's w the large/small bowls which are designed for disc/drums which you're GTX has would not have a RPV in the disc half which is next to the firewall. I've replaced calipers that had way too much drag w a $15 rebuilt caliper & prob solved. Holler w any news
Posted By: Cab_Burge

Re: Residual Pressure Valve Removal? - 02/22/12 04:50 AM

Quote:

Hey all. The front rotor's on my sons 69 GTX have a ton of drag on them and my research says to make sure the residual pressure valve is removed (since it is power disc, not drum). I know he changed the m/c recently and I suspect the valve is in place. Where is it and how to remove it? Thanks for any and all help

It is under the brass retaining adapter plug on the reservior that the front brakes (the line to the front brakes, not usually the front line on the M.C., verify that line ) are hooked into It is a very small brass adatpter for the flared steel line to seal against in the M.C., use a small self tapping sheet metal screw, #6 or #8, to insert into the brass plug and pull it out, they are removeable and resuable The residual valve is usually a small rubber one way flapper valve with a small coil spring in it If it is in there remove and discard it and reuse the brass adapter flare to reseal the brake line to the M.C. Let us know if it has one or not, did he buy a front disc brake M.C.? if not it will have the residual valve in it, usually
Posted By: 392charger

Re: Residual Pressure Valve Removal? - 02/23/12 12:50 AM

Sorry for the delay guys, just now got a chance to work on it and can't get the brass cone seat out . Appears to really be stuck in there good! Tried threading a small sheet metal screw into it which slipped and pulled out with out grabbing enough threads. Then tried the next size screw, got a pretty good bite but still won't come out! Any other tricks? Oh, and I am pretty sure it's got a residual valve because I stuck a small drill bit in there and I can feel a spring inside. I made sure it was the right brake line I was messing with btw. It's the rear bowl, which also is the larger one and it's closest to the fire wall. One last thing I need to confirm, do I discard both the flapper and the spring when I finally get it apart? Thanks again for the help
Posted By: RapidRobert

Re: Residual Pressure Valve Removal? - 02/23/12 02:05 AM

Quote:

One last thing I need to confirm, do I discard both the flapper and the spring when I finally get it apart?

Correct, & if the brass seat gets too mangled may have to get a new M/C as that's where it seals is on the cone/inverted flare interface
Posted By: Cab_Burge

Re: Residual Pressure Valve Removal? - 02/23/12 03:36 AM

Quote:

Sorry for the delay guys, just now got a chance to work on it and can't get the brass cone seat out . Appears to really be stuck in there good! Tried threading a small sheet metal screw into it which slipped and pulled out with out grabbing enough threads. Then tried the next size screw, got a pretty good bite but still won't come out! Any other tricks? Oh, and I am pretty sure it's got a residual valve because I stuck a small drill bit in there and I can feel a spring inside. I made sure it was the right brake line I was messing with btw. It's the rear bowl, which also is the larger one and it's closest to the fire wall. One last thing I need to confirm, do I discard both the flapper and the spring when I finally get it apart? Thanks again for the help

Thye do not slide out easily, get the screw in ther firmly and use pry bar to remove it. Don't worry about it resealing, I've never had one not reseal The brake line seals agianst the middle of the tapered seat on the adapter the out side is held into the master cylider and sealed by how tight you tighten the brake line into the master cylinder Pry that rascal out
Posted By: Rick_Ehrenberg

Re: Residual Pressure Valve Removal? - 02/23/12 04:40 AM

Just a cautionary note: If he inadvertently installed a drum m/cyl, the reservoirs are much smaller, you can run out of fluid as the pads wear!

Rick E.
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