| Author | Message | ||
     Carl Jensen New User Username: carl_jensen Post Number: 8 Registered: 2-2005 |
This is embarassing, but the simple G Valve (aka Deceleration Conscious Pressure Limiting Valve) is giving me problems. I recently did a lot of rebuilding on the hydraulic system on my 1975 Shadow, and this included rebuilding/cleaning the G Valve, but now the valve has no fluid coming out of the output pipe when I apply the brakes. My valve has the inlet on one end of the valve and the output pipe and a bleed tube near the other end. I get fluid coming out of the bleed tube when I activate the brakes, but nothing comes out of the output pipe that goes to the rear brakes. This doesn't make sense to me, but I can't see in the service manual how the bleed outlet v.s. output pipe fitting is configured internally. I also made sure that the output pipe to the rear brakes is not blocked (per Bill Coburn's recommendation in Tee One Topics), and it is fine. So my questions are: 1. Why does fluid come out of the bleed tube but not the output pipe? Did I somehow mess up this simple rebuild? 2. Do I need to remove the whole G Valve to rebuild it (a big pain), or can I just remove the master cylinder that is below the G Valve and then unscrew the big end of the G Valve into which the input pipe goes? Thanks very much for your help. I feel like a dummy and am getting a little discouraged after all of the work I have done, but most of the pain is self-inflicted. | ||
| Bill Coburn Moderator Username: bill_coburn Post Number: 561 Registered: 4-2003 |
Carl too many pipes I am confused. The only thing I can think of is that you are bleeding too fast. That is the function of the valve. It picks up that big ball and hurls it onto the rubber cushion sealing off the flow to the rear\. Simply open the bleed valve on the rear caliper a little bit and the fluid should dribble. Usually you can open the valve slowly and let a good flow flow. But if it locks off then back off releast the pedal and start again. | ||
| David Gore Moderator Username: david_gore Post Number: 526 Registered: 4-2003 |
Hi Carl, Further to Bill's advice, the rubber seat for the steel ball that functions as the pressure restricting device is prone to being dislodged if the ball hits it too hard due to no back pressure to cushion the impact if the brakes are bleed too fast with the system pressurised {Been there; done that!!!}. The seat will turn sideways in the bore thus blocking the rear brake line and no fluid gets through. | ||
| Patrick Lockyer. Grand Master Username: pat_lockyer Post Number: 479 Registered: 9-2004 |
Rather bemused at all this,please clarify the how you can bleed the hydraulic to fast with the standard workshop procedure for this type of system. Bill David as you have indeed had this type of experience what incorrect procedure method was performed to cause this strange event. Always willing to learn a new one. | ||
| David Gore Moderator Username: david_gore Post Number: 527 Registered: 4-2003 |
Hi Pat, In my case, the problem occurred when my trusty apprentice took his foot off the brake pedal with the engine running and yours truly at the back of the car with the calliper bleed valve open - realising what he had done my apprentice {son] then put his foot back on the pedal without telling me and applied full system pressure through the G valve with no downstream back pressure. There was a resounding clunk as the ball hit the seal then the end of the casing when the seal was dislodged and turned sideways in its bore thus blocking fluid from the rear brake lines. I managed a repeat performance by fixing the valve seat then opening the calliper bleed screws too fast with the pedal applied [yes both at once to get the job finished - my patience had run out by then as I needed the car for an event next day]. The valve seat was damaged after the first effort but I had a spare and fortunately it was not damaged the second time and just had to be repositioned. More patience and a controlled gentle bleed then fixed the problem. One of my Self-Help advisors hearing of my exploits later offered the advice that the ball can be held away from the seat with a strong magnet while bleeding the brakes to expedite the process. My thoughts were not fit for publication!! | ||
| Patrick Lockyer. Grand Master Username: pat_lockyer Post Number: 480 Registered: 9-2004 |
Thank you David for your account,now all we need to know is if Karl can confirm that he carried out the bleeding as stated above. There may be another solution to this. In my early years my mentor showed me how to do all the bleeding of this type of system by himself. Now theres a clue David. | ||
| Bill Coburn Moderator Username: bill_coburn Post Number: 562 Registered: 4-2003 |
I do hope my sensor for patronising remarks is incorrectly winking. A bit of history. You will remember the late Bruce Ross at Pennant Hills. He owned the earliest Shadow brought to Australia ten something as I recall. Quite near his establishment there was an apocalyptic accident which prompted the the placement of the brake pedal about four inches below the floor boards. The car had to be lifted to move as the brakes were jammed on tight. End result was that he discovered probably the first blocked rat trap to rear caliper line blockage. Nothing would clear it. He finished up making a new line! Years later me (as in I) still trying to learn how to spell Shadow sorted out brakes on Ian Dunn's '75 car. Now came the rear caliper bleed and nix as in nil or no brake fluid exited. I located the blockage between the deceleration valve and the rear subframe junction. Replaced the line., Opening the decel valve - no cushion. It is the sort of occurrence that reduces grown men to tears. As to bleeding David sack your assistant, get a length of 2 X 1" with a bit of cloth both ends and jam it between the brake pedal and the front of the seat. If necessary winch the seat forward!!! You then have a permanent assistant that won't get bored etc!!! | ||
| Patrick Lockyer. Grand Master Username: pat_lockyer Post Number: 481 Registered: 9-2004 |
Bill spot on but remember to exhaust the system till the warning lights come on first,open the bleeder in the correct order then start the engine and bleed to your hearts content with the length of wood. Topping up with RR363 of course. Carl you must get back to us all with your procedure and findings,do register and have all the benefits of help within the forum. | ||
| David Gore Moderator Username: david_gore Post Number: 528 Registered: 4-2003 |
Thanks Pat, As you can see, I failed to observe the old adage "More Haste; Less Speed" coupled with a considerable amount of frustration from spending more time than I wanted under the car working in a space that was too small for my size 20 hands. When I am reincarnated, I am insisting on size 8 hands to allow me to work on my favourite Shadows  . | ||
| Carl Jensen New User Username: carl_jensen Post Number: 9 Registered: 2-2005 |
I believe that I have found the problem. The good news is that I did not have to completely remove the "G" valve to do the work, but instead was able to lower the master cylinder (it sits right below the "G" valve in my rat trap). I then unscrewed the end of the valve and everything came out. It turned out that the ball bearing was stuck tight in the valve, so no fluid was able to get to the rear brakes regardless of how I tried to bleed the system. Apparently the problem was the little metal insert that fits in the small seal that the ball bearing pushes against. I had not pushed this insert in far enough, so the insert/seal was always pushed tight against the ball bearing. It looks as if the machining of my replacement insert was off since I had to use a center punch to drive it in. In fact, I had bang on it so hard that my punch messed up the end of the insert somewhat. I then put the small seal over the insert and checked for movement of the ball bearing. The bearing now has about 1/8" play back and forth. I hope this is enough. I am just surprised that the insert had such a tight fit, since I really had to bang on it to get it in. I am also reluctant to admit that I was ready to just take the ball bearing out completely and leave it out. However, I was afraid that I would never hear the end of it from you guys so I did the right thing. Thanks again for everyone's advice. I will use your recommendations to bleed the rear brakes and hopefully everything will work fine. Thanks again! |
