| Author | Message | ||
     Brian Vogel Grand Master Username: guyslp Post Number: 395 Registered: 6-2009 |
Virtually every set of instructions I've ever seen for bleeding the brakes states that the end of the vinyl tubing must be submerged in a bit of brake fluid in the discharge catch. My question is: Why? Since these systems have a supply of positive pressure from the accumulators throughout the bleeding process there's never an instance I can think of where there would be the possibility of sucking air back in through the bleed screws. [This is not true in conventional systems, which is what I've always been led to understand is the purpose of having the fluid in the catch bottle: to create an air block once the fluid has filled the tube between the bleed screw and the bottle.] Is this really necessary and, if so, for what reason? Brian | ||
| gordon le feuvre Experienced User Username: triumph Post Number: 14 Registered: 7-2012 |
It is the only way to see if there are air bubbles still in system. When bleeding conventional systems, it stops fluid being drawn back into cylinder, but on HP system such as Shadow/Spirit it is supposed to be guide. This does not always work out in reality because of the difficulty of trying to see the bleed screw AND the jar at same time, the practice is to crack bleed until an even flow is seen/felt! | ||
| Paul Yorke Grand Master Username: paul_yorke Post Number: 1031 Registered: 6-2006 |
Brian, if you spray any hp fluid from a hose through air into a liquid how on earth will you tell what bubbles are from the system and what is picked up from the air? Also the tube keeps draining and can refill with air adding more bubbles. You are also more likely to produce splashes and atommised brake fluid. So although you can bleed these cars without even a tube it would be a foolish, wasteful, and pointless method. | ||
| Richard Treacy Grand Master Username: richard_treacy Post Number: 2830 Registered: 4-2003 |
On top of the above imperatives, it keeps your garage floor clean. Random spillage over chassis components cannot help longevity either. Also, your garage floor paint will not be stripped by RR363, a DOT3/4 brake fluid derivative and hence a very effective paint stripper. The effort to use a tube and a jar is hardly onerous. RT. | ||
| Brian Vogel Grand Master Username: guyslp Post Number: 396 Registered: 6-2009 |
I believe you all are misunderstanding my question. I'm not proposing that one not use clear tubing and catch bottles. They'd be useful even if they weren't necessary. When I open the bleed screws to watch for no bubbles in the fluid I don't do that by looking at anything in the catch bottle, but rather what's coming out at the source - the bleed screw. What I see there is either with or without bubbles whether or not the end of the tube is submerged in fluid in the catch bottle. I never use anything as my guide other than what I can see occurring in the tubes where the fluid issues from the bleed screw. What I'm asking is why all of the instructions insist that there must be a layer of fluid already in the bottles that the tips of the bleed tubes must be under? It seems utterly unnecessary to have that layer present. Brian, who had one of the tubes on a height control ram work its way off while flushing the system, so I'm quite aware of the need for the tubes and the mess that would result without those | ||
| Richard Treacy Grand Master Username: richard_treacy Post Number: 2831 Registered: 4-2003 |
BTW on most SYs bleeding the master cylinder to the rear calipers can sometimes be tedious, and the tube/jar method saves uncertainty. On SY and SZ cars alike, component prices are presently very favourable. I have just fitted all new calipers, rotors, pads, hoses and spheres as part of the scheduled service on my SZ Continental R. I discarded the old calipers rather than bothering to overhaul the old ones as new calipers are rather inexpensive. It is no longer really worth overhauling calipers on SYs and SZs given the price of brand new ones. Machining rotors is no longer economical either when new rotors are the cheaper and far superior option. Bleeding the LHM follows the SY procedure, and was painless with the tube/jar method. RT. | ||
| Randy Roberson Prolific User Username: wascator Post Number: 129 Registered: 5-2009 |
I always understood that the tube submerged in the bottle technique allowed one to bleed brakes without a helper: you could work the pedal and the air would come out but could not take any air back in, only fluid if there were backflow at the bleeder. Problem is: seems like when I bled with a MityVac there was usually significant air leak at the bleed screw threads. | ||
| Brian Vogel Grand Master Username: guyslp Post Number: 409 Registered: 6-2009 |
Randy, That was my understanding, too, but it doesn't seem to apply in any way to how the braking/hydraulic system works on the SY and SZ cars. There is a constant supply of positive fluid pressure from the accumulators and you're cutting off an active outflow while it's running. The whole idea of "sucking air back in" on these systems doesn't seem to apply. That was the reason for my question initially. I think in the future I'll probably just start with empty catch bottles. Brian | ||
| Randy Roberson Prolific User Username: wascator Post Number: 131 Registered: 5-2009 |
I think you are right: for the Rolls-Royce, just hold the pedal down and it will keep flowing. Regards, RR | ||
| Bob Reynolds Experienced User Username: bobreynolds Post Number: 46 Registered: 8-2012 |
I always understood that the tube submerged in the bottle technique allowed one to bleed brakes without a helper: you could work the pedal and the air would come out but could not take any air back in, only fluid if there were backflow at the bleeder. In a conventional system, the tube-in-the-bottle method still requires a helper, to tighten the bleed screws on the up-stroke and prevent the contaminated fluid being sucked back into the system. Otherwise the same contaminated fluid would just keep going backwards and forwards in and out of the jar! As already agreed, this does not apply to Rolls-Royces with a positive brake pump and no backflow. | ||
| Geoff Wootton Prolific User Username: dounraey Post Number: 192 Registered: 5-2012 |
I agree. There is no need for the tube to be submerged. On the SY-I with the auxilliary master cylinder I use a hand operated vacuum pump to bleed this system. I have found it to be very effective and negates the need to stand the car on it's front bumper. | ||
| Geoff Wootton Prolific User Username: dounraey Post Number: 237 Registered: 5-2012 |
I have just bled the hydraulic system on my car and found it so much easier to use a 6" diameter tupperware tub with a hole punched in the lid to hold the bleed tube. So much easier that using the conventional small diameter, tall receptacle for the bleed tube, which would overflow if not carefully monitored and had a propensity for falling over, spilling the collected brake fluid. Although I knew there is always positive pressure at the bleed nipple, it never occured to me to take advantage of this fact, before reading this thread. Geoff | ||
| Brian Vogel Grand Master Username: guyslp Post Number: 487 Registered: 6-2009 |
Geoff, I also stopped using tall skinny containers with small openings after having one too many tip over. A very convenient (and disposable, should one wish to pitch them) and stable option is the large bottles that Minute Maid and other fresh-squeezed orange juices come in, as well as some iced tea brands such as Peak. They're also very handy to cap and take to your recycling center to dispose of the fluid. I practically filled every one of these that I used during my last massive flush and refill with LRK37110. Brian |
