Guest pipsdad Posted July 31, 2008 Share #1 Posted July 31, 2008 I cannot get any pressure for the rear master cylinder. I rebuilt it, and suspect that the problem lies in the proportioning valve. I can get one new for about 150 online. My question would be, does anyone know what years this part was the same. Our bike is an 84. Or if not, at least an OEM part number, all the sites i find only give a SKU number. Link to comment Share on other sites More sharing options...
Dano Posted July 31, 2008 Share #2 Posted July 31, 2008 Have you checked the parts finder at www.flatoutmotorcycles.com ? Great prices, good folks to do business with. Dan Link to comment Share on other sites More sharing options...
Redneck Posted July 31, 2008 Share #3 Posted July 31, 2008 More than likely you still have air in the system you may have a problem with the proportioning valve but it won't cause the problem you are describing. make sure you bleed the whole system if it still won't build pressure its probably in the master cylinder. Link to comment Share on other sites More sharing options...
rod Posted July 31, 2008 Share #4 Posted July 31, 2008 +1 on the air. Did you let the master cylender go dry? If so try cracking the fitting (banjo bolt) and see if you can get the air out. Good luck Rod Link to comment Share on other sites More sharing options...
Squidley Posted July 31, 2008 Share #5 Posted July 31, 2008 It can be a bear to get it all full of fluid again, I have done those many times. Make sure that your bleeding from the bleeder up by the steering head too as the brakes are linked. Persistance is the key to doing it, I also use the Valvoline Synthetic blend for DOT 3 & 4 Link to comment Share on other sites More sharing options...
endo Posted July 31, 2008 Share #6 Posted July 31, 2008 Don't buy the valve - it is just a real PITA to bleed. On my '84 I used a new trigger-pump oil can to fill the rear master. Bleed at the union (no bleeder) at the steering stem, the high point in the system. Cover everything and be prepared to clean up any spills right away. Once a little juice flows out of that union, apply pressure to the brake pedal and crack open the rear brake line where the valve attaches to the master cylinder. You'll get air. Keep cracking it until the spitting (air) stops. Then work your way back to the rear caliper until it is flowing out without any air. Keep pumping in the brake fluid. If it goes dry you have to start over! Go back to the steering stem and crack that open with pressure on the pedal until the air stops. Then move to the left front caliper, and bleed there. Then bleed the left anti-dive if you have it. You might do it at the steering-head union and all bleeders once more to be sure all the air is out. This takes forever, you go through a lot of fluid, so be patient and have a helper handy. Maybe beer. Keep filling the reservoir. I surround the unions and line junctions with paper towels to catch the juice, as it will destroy paint. I immediately hose and rub off any spills. I use a couple of feet of clear tubing fitting tightly over the nipples to divert the fluid into a pan. You will get the pedal back, probably better than it was before. This is my least-favorite Venture task, but when you're done, you'll be happy. Endo Link to comment Share on other sites More sharing options...
kilowatt55 Posted August 1, 2008 Share #7 Posted August 1, 2008 Don't buy the valve - it is just a real PITA to bleed. On my '84 I used a new trigger-pump oil can to fill the rear master. Bleed at the union (no bleeder) at the steering stem, the high point in the system. Cover everything and be prepared to clean up any spills right away. Once a little juice flows out of that union, apply pressure to the brake pedal and crack open the rear brake line where the valve attaches to the master cylinder. You'll get air. Keep cracking it until the spitting (air) stops. Then work your way back to the rear caliper until it is flowing out without any air. Keep pumping in the brake fluid. If it goes dry you have to start over! Go back to the steering stem and crack that open with pressure on the pedal until the air stops. Then move to the left front caliper, and bleed there. Then bleed the left anti-dive if you have it. You might do it at the steering-head union and all bleeders once more to be sure all the air is out. This takes forever, you go through a lot of fluid, so be patient and have a helper handy. Maybe beer. Keep filling the reservoir. I surround the unions and line junctions with paper towels to catch the juice, as it will destroy paint. I immediately hose and rub off any spills. I use a couple of feet of clear tubing fitting tightly over the nipples to divert the fluid into a pan. You will get the pedal back, probably better than it was before. This is my least-favorite Venture task, but when you're done, you'll be happy. Endo The reservoir he's talking about is the brake but feel free to fill the stomach reservoir with beer as well:nanner: Link to comment Share on other sites More sharing options...
Guest pipsdad Posted August 1, 2008 Share #8 Posted August 1, 2008 Thanks to all for the great info!!!!!!!!!!! I will get on this tomorrow, wish me luck!!! Link to comment Share on other sites More sharing options...
Black Owl Posted August 1, 2008 Share #9 Posted August 1, 2008 I would also strongly recommend installing speed bleeders... Link to comment Share on other sites More sharing options...
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